Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: joeblogs on January 22, 2003, 12:43:31 PM
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Some time ago there was an extensive debate on the historical vs. modeled endurance of U.S. heavy iron and European fighters (Look for the thread "Why the LA-7 is so Uber," started by F4UDOA ). At the time, I used the information contained in the post to compare the the F6f-5 Grumman Hellcat, using a P&W R2800 Double Wasp against the Soviet LA-7 using the ASH-82FN engine. I didn't have quite all the information I needed to make a direct argument, so instead I showed that the endurance of the LA-7 in Aces High implied an absurdly low specific fuel consumption (SFC), in lbs of avgas per horsepower per hour, for the ASh-82FN.
Well I have found a source of data on this engine. It is Paul Wilkinson's Aircraft Engines of the World, published in 1949.
Bore 6.12 in
Stroke 6.10 in
Displacement 2514 cu in
Compression Ratio 7:1
Weight 1984 lb
Weight/horsepower 1.07 lb/hp
Fuel consumption 0.46/lb/hp/hr
Gasoline grade 95 octane
Output/displacement 0.74 hp/cu in
BMEP 234 lb/sq in
Rating (take-off) 1850 HP/2500 RPM/47.9 in + 9.0 lbs boost
Rating (military, low) 1650 HP/2400 RPM/5400 ft
Rating (military, high) 1450 HP/2400 RPM/15200ft
Rating (normal, low) 1500 HP/2300 RPM/6600 ft
Rating (normal, high) 1350 HP/2300 RPM/16400 ft
This engine used direct fuel injection and a two speed, single stage supercharger. It's performance is comparable to the Wright R2600 and inferior to the P&W R2180 Twin Wasp, both rated on 100 octane avgas.
Prior to my seeing these numbers, my best guess for the SFC of this engine was about 0.45, assuming the La-7 cruised in a manner similar to the F6f. Turns out I was pretty close. With an SFC of 0.46, the endurance of the La-7 should never exceed one-half that of an F6f on internal fuel.
-Blogs
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Yes, lots of aircraft have screwy fuel consumption in AH.
The Spitfire has more endurance than the Mosquito as modeled in AH, whereas in reality the Mosquito had more than twice the endurance.
The F4F has far less endurance than it should when compared to the short legged European fighters such as the Bf109, Hurricane and Spitfire.
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Joe Blogs.
I will begin beating the wardrums ASAP!!
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Beating war drums about what? Anybody bother comparing AH lb/hp/hr to the real figures?
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If you read the thread I refer to above, my posts there are all about figuring out what AH is assuming about the performance of these engines and comparing them to historical data.
AH doesn't come out and tell you what they have modelled, but you can back it out from flying the planes as long as possible before the tank goes dry...
-Blogs
Originally posted by funkedup
Beating war drums about what? Anybody bother comparing AH lb/hp/hr to the real figures?
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Good.
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Funked,
Yes I have. In a huge post a while ago.
Fact is the La-7 (and I suspect many others 109,Spit, Yak) have a huge advantage over A/C with larger fuel capacities ala the F6F, P-47,P-51 and F4U.
Why? Because they have equal duration running at mil power with A/C that in reality with similar power setting would have had twice or even 4 times the duration of the La-7.
The thread was entitled "Why the LA-7 is so Uber"
Karnak and JoeBlogs were knee deep in it and Joe Blogs just confirmed some VVS data that was posted in that thread.
The center of the post was the fact that the F6F and La-7 have nearly identical fuel durations in the MA. In reality the La-7 with similar fuel settings should not have half the duration of the F6F.
The same applies to the Spit and Mossie in AH to possible a larger extent. Joe Blogs numbers relate to how many HP an A/C produces per hour and how much fuel is required per HP.
Believe me when I say this has been hashed through and through again.
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Can you direct me to that? What SFC have you measured for the La-7 in Aces High?
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Funked,
Here is the link to the previous thread.
http://www.hitechcreations.com/forums/showthread.php?s=&threadid=68462
I'm a little tired right now so I might not be as thorough as could be.
What is SFC?? Not thinking clearly right now. Long day.
Anyway the root of the problem is that if both A/C have the same duration then you are forcing the larger A/C to carry more fuel into combat than would be necessary creating an unfair advantage.
Must stop typing, to tired, fading, the light, arrrrggghhhh............
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Look for my second post near the very end of the thread. The SFC implied by AH is in the low 0.3 using American measurements. No high-output piston engine of that era attained such an efficiency.
-blogs
Originally posted by funkedup
Can you direct me to that? What SFC have you measured for the La-7 in Aces High?
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Thanks.
Here's my rough analysis:
From Gordon & Khazanov's "Soviet Combat Aircraft - Volume One" we get 1470 hp as normal power for the Ash-82FN engine.
We know (from Snefens' chart) that endurance at this power setting in AH is 28 minutes. Fuel multiplier is 2.0, so in "real life" terms it would be 56 minutes or 0.93 hours.
Fuel capacity (from the AH aircraft info page) is 122 gallons. At 6 lb / gallon that's 732 lb of fuel.
So the specific fuel consumption is 732 lb / 1470 hp / .93 hr = 0.54 lb/hp-hr.
Compare this to the real world figure posted above, of 0.46 lb/hp-hr.
Looks like the La-5FN and La-7 use about 16 percent more fuel than they should.
So if the basis for your "banging of war drums" is Wilkinson's 0.46 lb/hp-hr figure, then you might want to reconsider.
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S!
La5FN could fly less than one hour in combat including take-off and landing. One figure I saw was about 45-50min with take-off, climb, cruise, combat, return and landing. La7 had LESS endurance than La5FN because of less fuel. Same figure for BF109G was about the same. Re-collecting from Finnish aces stories the La's and 109G had pretty similar endurance.
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>>The Spitfire has more endurance than the Mosquito as modeled in AH, whereas in reality the Mosquito had more than twice the endurance. <<
I keep seeing this, yawn. The Mosquito is a bomber. If you fly it at its rated 'maximum continuous' of +7lb/sq.in at 2,650 rpm, it'll fly you to hell and back on half a tank. If you fly it at its '5 min limit' power, +18lb boost and 3,000 rpm, you won't get very far.
Mosquito fuel consumption charts only range from 2,000-2,600rpm at +7lb boost because that's how pilots flew them. They show a variation from 70-110+ gallons per hour. You can bet it's a hell of a lot more at emergency power.
>>Fact is the La-7 (and I suspect many others 109,Spit, Yak) have a huge advantage over A/C with larger fuel capacities ala the F6F, P-47,P-51 and F4U. <<
Yawn. Has anybody compared the weights of these aircraft? F6f-5 'combat' weight 12,740lbs. La7 weight ranges from 2,638kg empty to 3,400kg absolute maximum. That's 5,800 to 7,500lbs!
This could be why the ASH-82 is listed for 1,330hp cruising at alt (probably optimistic), where the R2800 in the F6f-5 makes 1,625. Hardly comparable.
As for fuel consumption at different settings. Combat range chart for the F6f-5 shows a variation from 960 miles at 180mph down to 480 miles at 280mph (both at 15,000 feet). You can bet it gets even worse if you go faster than that.
I don't have an FOIC chart for the F6f-5, but i'm willing to bet it's fuel consumption ranges from a minumum of below 50gph up to more than 200gph at Max power.
People will have to learn to ease off on the throttle.
>>La5FN could fly less than one hour in combat including take-off and landing.La7 had LESS endurance than La5FN because of less fuel<<
La5 range - 1000 kilometres.
La5FN range - 775 kilometres.
La7 range - 990 kilometres.
must have flown bloody fast in that hour - perk it!!!
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Originaly posted by Crowbaby:
keep seeing this, yawn. The Mosquito is a bomber. If you fly it at its rated 'maximum continuous' of +7lb/sq.in at 2,650 rpm, it'll fly you to hell and back on half a tank. If you fly it at its '5 min limit' power, +18lb boost and 3,000 rpm, you won't get very far.
Mosquito fuel consumption charts only range from 2,000-2,600rpm at +7lb boost because that's how pilots flew them. They show a variation from 70-110+ gallons per hour. You can bet it's a hell of a lot more at emergency power.
Do you think I'm an idiot or something?
I tested the Mossie at cruise settings as defined by the Mosquito FB.Mk VI's Pilot Notes.
It drained it's tanks twice as fast as it should have.
Here is my test described exactly as I performed it:
Some time ago I stated that I felt the Mosquito consumed fuel too rapidly. As evidence I gave the fact that the Spitfire Mk IX has greater endurance than does the Mosquito in AH.
Spit_9 -- 35/+21=56
Mossie -- 34/+16=50
The original thread can be read here: The Mossie's flight endurance still seems too short (http://www.hitechcreations.com/forums/showthread.php?s=&threadid=64339)
Acting on advice from that thread I obtained a PDF file of the Pilot's Notes for the Mosquito FB 6 from snafu's website.
On page 11 of the pilot's notes it lists the fuel capacity of the Mosquito FB 6's various fuel tanks:
MAIN SUPPLY
Centre tanks....................50 gallons
Inner tanks....................286 gallons
OUTER TANKS................116 gallons
_____________________________
Total........................ .....452 gallons
Long-range tank...............63 gallons
Wing drop tanks..............200 gallons
(2 x 100 gallons)
_____________________________
Total fuel capacity...........715 gallons
On pages 30-33 of the pilot's notes there are flight planning charts that give the fuel consumption for various speeds, weights and altitudes.
For the ease of calculations I selected settings that would consume fuel at a rate of 100 gallons per hour so that I could simply use the 50 gallon Centre tank. If the fuel consumption was correct, then the fuel should last half an hour.
The settings were:
AUW: 17,000lbs
Altitude: 10,000ft
RPM: 2,400
TAS-KNOTS: 275
TEST SETUP
Using the AKDesert map in offline mode I set the fuel consumption to 1.0000. I selected A56 as my take off field, planning a southwest flight along the channel.
To get roughly an All Up Weight of 17,000lbs I set the Mosquito to full fuel, no external or internal stores, 150 rounds per 20mm gun and 500 rounds per .303 gun.
TEST
Once on the runway I selected the right inner (RI) fuel tank before starting the engines so as to keep the centre tank (AUX) full.
I then took off, climbed to 10,000ft and set a southwest heading.
I then reduced my RPM settings from 3,000 to 2,400 and reduced my boost setting from 14lbs./sq.in. to 8lb./sq.in.
The Mosquito's airspeed declined until it settled at about 265mph. (This was 265mph true airspeed, not indicated airspeed)
I then switched to the AUX tank and started a timer simultaneously.
RESULTS
The AUX tank was drained in 13 minutes and 52 seconds which indicates a fuel consuption rate with those settings of approximately 200-225 gallons per hour, or more than twice the fuel consumption listed for those settings in the Flight Planner Charts of the Pilot's Notes for the Mosquito FB 6.
CONCLUSION
The Mosquito FB.Mk VI in AH is consuming fuel at more than twice the rate it should be.
As you can clearly see I tested the fuel consumption in a proper fashion, and no, it doesn't fly forever on half a tank.
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Oops. Just read through that other thread. How vain of me to think i could stop the madness..........
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Read my test and tell me where I made the mistake.:rolleyes:
It is very vain of you to assume that such elementry errors were made and that everything is just fine without ever running any tests of your own.
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o.k.
off i go to test the FB6 endurance as per the manual. and i'm ready to eat my words if need be...
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Thanks.
Please post your test method when you are done. I am curious what results you get.
One thing I did notice is that the Mosquito would not reach the speed indicated in the Pilot's Notes when I used the described settings. It was 10-15mph slower than the listed speed.
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Before i go.
Going from the endurance charts. At 10,000 feet alt, 200 T.A.S. it recommends setting +7lb boost and 2,000 rpm for a consumption of 70 gallons per hour.
I don't expect to hit all these on the button, so i'll be looking to maintain 200 at 10k alt with the most economical settings it'll take.
With an internal fuel capacity of 452 gallons, this equals 6 and half hours. To cut this down a little, i'll use 25% fuel (assuming that this works as avertised).
I'll take off on AKdesert with no wind, (and fuel multiplier at 1)climb to 10k on drop tanks and see how i go. See you in an hour or so (hopefully).
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In the previous thread (http://www.hitechcreations.com/forums/showthread.php?s=&threadid=68462) a number of people argued the obvious disparity between historical endurance and what we observed in AH was due to different power settings. My calculations showed that power settings did not matter, AH seemed to penalize fighters with large gas tanks across the power spectrum. Others raised the question of the weight of the plane, so I used actual performance under cruise settings to show that disparities in weight or other characterisitcs of these planes could not explain the disparity.
But the definitive test is to compare the engines best efficiency at any power setting and that is why I went looking for actual numbers on specific fuel consumption for these engines.
Specific fuel consumption is reported for the most fuel efficient settings of the engine, not for the rated power of the engine. That means auto-lean fuel mixture at something well below an engine's rated power, typically 65 percent of normal or 50 percent of military power.
If you can get an SFC of 0.54 on auto rich, you have an amazing engine. SFC on auto-rich for high output US radials is on the order of 0.8 to 0.9 for normal and military (non wep) power settings. Given that the ASH-82FN is no more efficient (in fact it's less efficient) than a comparable American engine in auto lean, it is extremely unlikely to be more efficient in auto-rich.
My estimate of the implied SFC for the ASH-82FN in AH is on the order of the low 0.30s, which is simply implausible.
-Blogs
Originally posted by funkedup
Thanks.
Here's my rough analysis:
We know (from Snefens' chart) that endurance at this power setting in AH is 28 minutes. Fuel multiplier is 2.0, so in "real life" terms it would be 56 minutes or 0.93 hours.
...So the specific fuel consumption is 732 lb / 1470 hp / .93 hr = 0.54 lb/hp-hr.
Compare this to the real world figure posted above, of 0.46 lb/hp-hr.
Looks like the La-5FN and La-7 use about 16 percent more fuel than they should.
So if the basis for your "banging of war drums" is Wilkinson's 0.46 lb/hp-hr figure, then you might want to reconsider.
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Karnak - I stand corrected. All i can say in my defense is that i hadn't seen your initial test when i posted.
Results of my test were the same, each individual tank lasted half as long as expected. Total flying time was roughly 45mins on 1/4 fuel load, again, half of expected. All the other numbers i hit with no problem, 10k alt, 200 TAS at 2000rpm, +7lb boost. Tested again with a fuel multiplier of 2, just in case there was a problem there, and got the same kind of results. As you have pointed out, there definitely seems to be a problem with the Mosquito.
I'm still not convinced by the La7 vs. F6f argument though. I'd like to see test flights for them against handbook data rather than a lot of maths mixed with guesswork.
The La7 test chart shows fuel consumption rangeing from 55-166 gallons per hour. 42-290 has been quoted for the F6f, preumably based on the P47 and F4u charts with the R2800 engine.
HTC list La7 fuel capacity as 122 gallons, F6f as 250 gallons.
La7 weighs roughly half of F6f.
Snefens endurance chart shows 28mins for both La5 and La7, 30mins for F6f. To me this chart is pretty meaningless, as efficiency varies hugely across speed ranges. Could we not either get or agree on, some cruise settings and test them in game? Has anyone done this?
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Right, i'll try it then.
From the La7 information posted,
altitude 3,000m (9842 feet)
1,500rpm
545mm mercury (no use with AH instrumentation)
400kmph TAS (249mph)
gives fuel consumption of
220 litres ph (58 us gal)
therefore 1/2 tank (61us gal/230 litres) should give just over an hours flying time.
I'll take off with 3/4 tank, reach alt and start the timer when the tank is 1/2 full. Again, no wind, fuelburnmult at 1.
Obviously this is only one of a range of listed tests, and the original document could be wrong for a myriad of reasons, but, what the hell....
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I have to apologize for making those posts more complicated than they needed to be.
I did exactly as you suggested. I went through the manuals, engine charts, and flight test information we had and computed the endurance of these two planes. My conclusions follow from comparing that data to the endurance calculations reported for these planes in AH.
The algebra only came in because I did not have a number on the best efficiency of the russian engine and I had to address all these questions about different power settings, weights etc. Using the algebra I could show that none of that mattered.
Now we know the historical efficiency of the ASh-82FN and we know it does not jibe with fuel consumption in AH.
If any additional flight testing in AH is required, I would suggest the following:
1) Do two tests, one on the deck and the other that requires a climb to 5k at the best climb rate.
2) Use two speed settings - the first at about 50 percent horsepower and the second at just above stall speed.
-Blogs
Originally posted by crowbaby
Karnak - I stand corrected. All i can say in my defense is that i hadn't seen your initial test when i posted.
...I'm still not convinced by the La7 vs. F6f argument though. I'd like to see test flights for them against handbook data rather than a lot of maths mixed with guesswork.
The La7 test chart shows fuel consumption rangeing from 55-166 gallons per hour. 42-290 has been quoted for the F6f, preumably based on the P47 and F4u charts with the R2800 engine.
HTC list La7 fuel capacity as 122 gallons, F6f as 250 gallons.
La7 weighs roughly half of F6f.
Snefens endurance chart shows 28mins for both La5 and La7, 30mins for F6f. To me this chart is pretty meaningless, as efficiency varies hugely across speed ranges. Could we not either get or agree on, some cruise settings and test them in game? Has anyone done this?
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My results on the La7 at the above settings.
I used roughly 26" Manifold on the gauge to get speed and rpm right.
1/8 tank 13mins
1/4 tank 26mins
1/2 tank 50mins
Which would equate to 276 litres per hour, or 73 us Gals.
more than would be expected from the data posted. However, i probably didn't get the optimal settings, and those tests appear to be VVS, so may be optimistic.
I'd prefer to stick to simply testing endurance, so has anyone got any decent figures for the F6f-5? The best i can find is Combat range of 600miles at an av. speed of 260kts at 15,000 feet. It's a lot simpler to test than the combat radius equations, but it's not very precise.
I'll test the La7 again first. This time:
altitude 3,000m (9842 feet)
2,200rpm
830mm mercury (no use with AH instrumentation)
588kmph TAS (365mph)
should give fuel consumption of
438 litres ph (115 us gal)
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"Snefens endurance chart shows 28mins for both La5 and La7, 30mins for F6f. To me this chart is pretty meaningless, as efficiency varies hugely across speed ranges.
First, those charts are not meant to compare to any historic values, they are simply there to let the player know how much fuel he have on 100% power. Second, the AH engine model is rather simplistic. I choose to list the endurance for 100% power, because that's simply what the majority of players use all the time with the occasionally WEP, but there is no difference in the consumption. I just tested it again to be sure:
La7, SL, 100% power, Max speed: 56 min
La7, SL, WEP power, Max speed: 56 min
La7, SL, 100% power, 175mph: 56 min
La7, 30K, 100% power, Max speed: 56 min
Fast/slow, WEP On/off, high/low. At the moment it makes no difference in AH.
__________________
Ylil. Snefens
Lentolaivue 34 (http://www.muodos.fi/LLv34)
My AH homepage (http://home14.inet.tele.dk/snefens/index2.htm)
(http://home14.inet.tele.dk/snefens/209.gif)
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Try this for starters. - Blogs
Originally posted by crowbaby
My results on the La7 at the above settings.
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I'd prefer to stick to simply testing endurance, so has anyone got any decent figures for the F6f-5? The best i can find is Combat range of 600miles at an av. speed of 260kts at 15,000 feet. It's a lot simpler to test than the combat radius equations, but it's not very precise.
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First, my apologies to Snefens if my wording caused offense. Your charts are great for Newbies and useful for furballers, indeed, useful for anyone. But, as you say yourself, they are ahistorical, and i don't see how they can be made relevant to a debate about engine simulation and fuel consumption.
Next, results of second test on La7
I used roughly 38" Manifold on the gauge to get speed and rpm right.
1/8 tank 7mins
1/4 tank 14mins
1/2 tank 29mins
Which would equate to 450 litres per hour, or 118 us Gals. This is pretty damn close to the VVS tests posted in the other thread.(download here) (http://www.tilt.clara.net/pics/AKT_LA7.rtf) but not as good as I'd expect from looking at the data posted on Tilt's site here (http://www.btinternet.com/~fulltilt/Engine.html). This may be to do with performance at altitude, so to finish the La7, i'll test against Tilt's data.
1,650metres (5,413 feet)
2,400rpm
1,000mm merc. (from looking at his charts i'm guessing this is max without WEP)
600kmph TAS (372mph) from this page (http://www.btinternet.com/~fulltilt/Perform.html)
should give 310-355 litre per hour.
Then i'll try the F6f against three or four lines on Joeblogs chart (may have to wait until tomorrow). If i'm doing anything wrong, let me know.
(edit, re-read Tilt's charts and it seems the entries for 1,650m are below, not above, where it says @1,650, so i'll start again.)
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That page from Tilt is a tranlation from Russian and I have to wonder if range and fuel consumption numbers were not transposed. Those are plausible numbers for range, but not for fuel consumption. I am inclined to rely on the VVS data.
-Blogs
Originally posted by crowbaby
... Next, results of second test on La7
I used roughly 38" Manifold on the gauge to get speed and rpm right.
1/8 tank 7mins
1/4 tank 14mins
1/2 tank 29mins
Which would equate to 450 litres per hour, or 118 us Gals. This is pretty damn close to the VVS tests posted in the other thread.(download here) (http://www.tilt.clara.net/pics/AKT_LA7.rtf) but not as good as I'd expect from looking at the data posted on Tilt's site here (http://www.btinternet.com/~fulltilt/Engine.html).
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Results of third test on La7 - sorry took so long, my other half came home from work :)
I got 375mph at 5,400 feet with 2,400rpm and 40in MAN.
1/8 tank 7mins
1/4 tank 14mins
1/2 tank 28mins
Which would equate to 472 litres per hour, or 124 us Gals.
Way more than I'd estimated from the data on Tilt's page, but again it tallies pretty well with the VVS data.
So, from three quick tests, our La7 seems a close match for the best data i've seen. This may not mean much, but if i can fly in AH as they did historically and get the same results, then that's good enough for me. For me, this also bypasses various engine arguments based on hp output, etc. Which is great, 'cos i haven't a clue how the various countries measured these.
Tomorrow, the F6f, which now seems to be the real worry anyway.
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I think thats the same conclusion they came to crow. The la-7 seems right, just the others are wrong in comparison. They both can't be right, least from what I understand.
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>>Try this for starters. - Blogs <<
Unfortunately, this is just the SEFC for the F4u. I can't test the F6f from this. They may have the same engine, but they're obviously not comparable:
Combat Weight-
F6f5 - 12,740
F4u-1 - 12,405
Fuel
F6f5 - 250 Gallons
F4u-1 - 234 Gallons
Range
F6f5 - 1,130 miles
F4u-1 - 1,515 miles
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Joeblogs sez:
Specific fuel consumption is reported for the most fuel efficient settings of the engine, not for the rated power of the engine. That means auto-lean fuel mixture at something well below an engine's rated power, typically 65 percent of normal or 50 percent of military power.
If you can get an SFC of 0.54 on auto rich, you have an amazing engine. SFC on auto-rich for high output US radials is on the order of 0.8 to 0.9 for normal and military (non wep) power settings. Given that the ASH-82FN is no more efficient (in fact it's less efficient) than a comparable American engine in auto lean, it is extremely unlikely to be more efficient in auto-rich.
My estimate of the implied SFC for the ASH-82FN in AH is on the order of the low 0.30s, which is simply implausible.
OK I understand what you are saying.
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Thanks for taking an honest look at this stuff crowbaby.
I also noted that the Spitfire on full power guzzles fuel as well. There is no way that a fully fulled Mosquito should run out of fuel before a fully fueled Spitfire if similar power settings are used. The furball friendly endurance chart that snefen created should still favor the Mosquito over the Spitfire by about twice because the single Merlin on the Spitfire consumes fuel as fast as a single Merlin on the Mosquito, and the Mosquito carries five times the fuel load.
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Download the standard aircraft characteristics for the hellcat from:
http://www.history.navy.mil/branches/hist-ac/fighter.htm
It has all the data you need to work out the endurance of the f6f-5. I use that data in one of my orginal posts.
-Blogs
Originally posted by crowbaby
>>Try this for starters. - Blogs <<
Unfortunately, this is just the SEFC for the F4u. I can't test the F6f from this. They may have the same engine, but they're obviously not comparable:
Combat Weight-
F6f5 - 12,740
F4u-1 - 12,405
Fuel
F6f5 - 250 Gallons
F4u-1 - 234 Gallons
Range
F6f5 - 1,130 miles
F4u-1 - 1,515 miles
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Just got home from a long day to find this.
1. JoeBlogs- Don't apologize for being too compicated. If I understand it's not complicated. What your saying makes pefect sence.
2. Crowbaby- You keep comparing apples and oranges and your making this much more comlicated than it is really.
A. Don't use any power condition other than full Mil power for testing. Nobody flies anything other than full mil power in AH anyway and it skews the results when you change to normal or max continious. For the purpose of testing use the La-7 vrs F6F or F4U-1D(The -1D had 237gallons of fuel internal).
B. You have referred several times to the extra weight of the F4U and F6F compared to the La-7. Also you have mentioned range. None of this is relavent when you are testing endurance at a given power setting.
Pretend the R-2800 and ASH-82FN are sitting in jack stands in a garage IE there is no airplane. I set them both to run at mil power. How long does it take the ASH-82FN to burn 122 gallons of fuel? How long does the R-2800 take to burn 237gallons and then 250Gallons. That's all I need to know to prove my point.
La-7 122 US gallons internal
ASH-82FN
Rating (military, low) 1650 HP/2400 RPM/5400 ft
F4U-1D 237 US Gallons internal
R-2800-8W
Rating Mil Low 2000HP/2700RPM/2500FT
F6F-5 250 US Gallons Internal
R-2800-10W
Rating Mil Low 2000HP/2700RPM/2500FT
Meaning that
1. Fact- The ASH-82FN put out 82.5 percent of the power of the F4U/F6F at equivilent power settings.
2. Fact- The F4U had 49% more internal fuel.
3. Fact- The F6F had 52% more internal fuel.
4. Fact- In AH the La-7 has equal flight time duration at mil power as the F4U-1D and 2 minutes less than the F6F-5
My point of contention.
Question How does the ASH-82FN produce 82.5% of the HP of the R-2800 and only burn 50% of the fuel during the same time period :rolleyes: . I do not believe this is possible.
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Proof
This is part of a VVS doc posted in the last thread. Note the highlighted area that specifically list a mil power duration of 33minutes at 460Litres or 122gallons.
Fund of NII VVS, inv. 485716, file 273
Approved. Chief Engineer of VVS A.Repin, 11 Oct 1944
THE STATEMENT
on results of verification trials of a serial La-7 with ASh-82FN engine and
VISh-105V-4 propeller, D=3.1m
/ac.No 45210203, prod. in July 1944 by factory No 21/
Air combat with Me-109G-4
In horizontal manoeuvring up to 5000m the La-7 gets on the tail of
the Me-109 for an aimed shot after 3-4 turns. Above 5000 m the advantage of
La-7 in horizontal manoeuvre decreases. At an altitude of 7000m horizontal
manoeuverability of both planes is equal.
In vertical manoeuvring the La-7 has an obvious advantage over the Me-109
up to 3500m and can keep an altitude dominance of 150m during combat. When
it reaches an altitude of 3500m the La-7 slightly loses its superiority over
the Me-109 in vertical manoeuverability, but even at 7000m the La-7 can
maintain a dominance of about 40-50m. At 6500-7000m the vertical
manoeuverability of both planes is equal.
The La-7 accelerates into the dive faster than the Me-109 and therefore can
reduce the distance to an escaping target. However, in continuous dive the
Me-109 increases its speed faster after initial acceleration and departs from
the La-7.
------------------------------------------------------------------------
========================page02.gif======================================
Approved. 1st Deputy Chief of GK NII VVS Losyukov. 6 Jan 1945.
REPORT No 2
on results of flight trials for fuel consumption and range measurements
of La-7 No38103254 with ASh-82FN engine and VISh-105V-4 propeller.
The object of research
La-7 No 38103254 produced by plant No 381... Total weight 3265 kg, fuel tanks
capacity - 460 litres. The landing-gear and the tail wheel were up,
the canopy was closed, the cap of oil-cooler and the skirt of engine cowl
were set "along the flood" (feathered).
The results of the tests.
The measurements of fuel consumption with working engine had been carried
out on the ground and during a climb at max climb rate. As a result it has
been established that fuel consumption of a working engine is 2.35 l/min
on the ground (during warm-up and engine test, taxiing to and from the
starting position).
Fuel consumption at climb to H at maximum climb rate mode, in litres
n=2400RPM
H,m 1000 2000 3000 4000 5000 6000 7000
Q,litres 15 25 35 45 55 65 80
IAS, km/h 270 270 270 265 260 255 250
Chart of range and level flight duration of a/c La-7 No38103254 at different
flight modes at V/n=const (constant speed and RPM), G tot=3265kg (total
weight) and V fuel=460 l (fuel volume)
n, Supercharg. Speed, km/h q, Qf, Till the dry tank:
RPM pressure, IAS TAS lit./km lit./h Range of Level flight
mm of merc. level flight, duration,
pile km h-min
H=1000m (1st speed of supercharger), fuel supply for level flight - 365 l
2400 1020 575 608 1.020 620 355 0-35
2200 875 530 560 0.800 448 455 0-49
2000 745 480 508 0.655 333 555 1-06
1800 665 430 455 0.585 266 625 1-22
1600 610 385 407 0.560 228 650 1-36
1500 580 360 380 0.550 209 665 1-45
H=3000m (1st speed of supercharger), fuel supply for level flight - 345 l
2400 990 554 644 0.975 628 355 0-33
2200 830 510 588 0.745 438 460 0-47
2000 705 460 532 0.620 330 555 1-03
1800 615 415 480 0.575 276 600 1-15
1600 560 370 428 0.555 238 620 1-27
1500 545 345 400 0.550 220 625 1-34
H=5000m (2nd speed of supercharger), fuel supply for level flight - 325 l
2400 1020 513 658 0.910 600 355 0-32
2200 840 470 604 0.700 423 465 0-46
2000 720 430 554 0.600 333 540 0-58
1800 630 385 496 0.560 278 580 1-10
1600 590 340 440 0.550 242 590 1-20
H=7000m (2nd speed of supercharger), fuel supply for level flight - 300 l
2400 870 454 647 0.735 476 405 0-38
2200 685 415 593 0.570 338 525 0-53
2000 590 380 544 0.500 272 600 1-06
1800 515 340 490 0.460 225 650 1-20
1600 465 300 433 0.450 195 665 1-32
Notes:
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
========================page03.gif======================================
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
2. To obtain the values of technical range and flight duration add the
following range and time figures to the table values respectively:
1000m - 5km, 1 min
3000m - 15km, 3 min
5000m - 25km, 5 min
7000m - 40km, 8 min
The table of range and flight duration for La-7 No 38103254 with
G full=3265kg, full tank fuel supply - 460 l.
Mode Mode values Level flight
up to dry tanks:
Range, km duration,
h-min
Max. H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl. 355 0-35
speed 3000 1 2400 990 355 0-33
5000 2 2400 1020 355 0-32
7000 2 2400 870 405 0-38
Fast H=1000m(1st sup.sp.),n=2160, IAS=518 km/h 485 0-53
range 3000 1 2160 498 490 0-51
(0.9 5000 2 2160 462 485 0-49
Vmax) 7000 2 2160 408 545 0-56
Near H=5000m(2nd sup.sp.),n=1810, IAS=388 km/h 580 1-10
fast range TAS=500 km/h
Optim. H=1000m(1st sup.sp.),n=1500, IAS=360 km/h 665 1-45
mode 3000 1 1500 345 625 1-34
5000 2 1600 340 590 1-20
7000 2 1600 300 665 1-32
------------------------------------------------------------------------
========================page04.gif======================================
Approved. Chief engineer of VVS A.Repin, 21 Jun 45
The statement No 112
on results of verification trials of La-7 serial plane with ASh-82FN engine
and VISh-105V-4 propeller D=3.1m, equipped with hydraulically controlled
dust filter and new ventilation of cockpit
/ a/c No 45213276, plant No 21, prod. of April 1945 /
Table of max. horizontal speeds
H standard, TAS, km/h
m nominmal, n=2400 RPM WEP, n=2500 RPM
0 580 616
1000 604 639
2000 626 661
2200 1) - 666
3000 649 657
3250 2) 654 654
4000 645 -
5000 651 -
6000 672 -
6250 3) 677 -
7000 666 -
8000 651 -
1) - 1st altitude boundary with WEP
2) - 1st altitude boundary without WEP
3) - 2nd altitude boundary without WEP
Table of max. climb rates
H st., m Vy (vert. speed), m/s Time, min IAS, km/h
nominal WEP nominal WEP
0 20 24.2 0 0 264
1000 20 24.2 0.85 0.65 259
1600 1) - 24.2 - 1 -
2000 20 - 1.7 1.3 253
2650 2) 20 - - - -
3000 18.6 - 2.6 2.2 246
4000 15 - 3.55 3.2 239
5000 15 - 4.65 4.3 232
5100 3) 15 - 4.75 4.4 -
6000 12.7 - 5.9 5.45 224
7000 10.2 - 7.4 - 214
8000 7.6 - 9.3 - 204
9000 5 - 12.0 - 189
10000 2.4 - 16.6 - 166
10750 4) 0.5 - 26.0 - -
-
Funked,
You said
We know (from Snefens' chart) that endurance at this power setting in AH is 28 minutes. Fuel multiplier is 2.0, so in "real life" terms it would be 56 minutes or 0.93 hours.
Fuel capacity (from the AH aircraft info page) is 122 gallons. At 6 lb / gallon that's 732 lb of fuel.
So the specific fuel consumption is 732 lb / 1470 hp / .93 hr = 0.54 lb/hp-hr.
Compare this to the real world figure posted above, of 0.46 lb/hp-hr.
Looks like the La-5FN and La-7 use about 16 percent more fuel than they should.
That SFC of .46 is measured at cruise power for the La-7. The equivelent setting for the F4U/F6F would be .442 at 5K.
That gives the F4U-1D a duration of 338 minutes (5.63 hours) and the F6F-5 a duration of 357 minutes (5.95 Hours).
Compare that with the La-7's duration at equal SFC (assuming both engines are equally efficient) of .93hours.
That gives the La-7 a almost a 500% increase in duration compared two it's two rivals. Not 16%.
So bang the Drum loudly!! :D
-
Ah, so we're still unhappy with the La7.
What you have highlighted is the summary of the report i tested AH against. You forgot to highlight this bit:
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
========================page03.gif======================
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
2. To obtain the values of technical range and flight duration add the
following range and time figures to the table values respectively:
1000m - 5km, 1 min
3000m - 15km, 3 min
5000m - 25km, 5 min
7000m - 40km, 8 min
this was the reason i climbed to alt and tested against their fuel consumption figures. It made for a much simpler test.
I think it's the whole SFC/horsepower/comparing engines debate that's apples and oranges. You're looking at engines' consumption at a maximum continuous allowed by AH, for which we have no historical data. Unfortunately AH doesn't simulate jackstands in a garage. If this is your thing, then fine, but it leaves me cold. I don't know much about how the engines differ. Intuitively, it seems o.k. to me that (at its must uneconomical settings) one of the biggest fattest fighters of WW2 uses fuel twice as fast as one half its weight. Or:
Question How does the ASH-82FN produce 82.5% of the HP of the R-2800 and only burn 50% of the fuel during the same time period . I do not believe this is possible.
It doesn't seem completely unreasonable to me that one engine should consume nearly twice as much fuel as a completely different one to produce 21% more power.
All i'm doing is testing the planes against the best information we have on how they were actually flown. As i've said, if they match that, then i'm happy, it's a flight sim after all. So maybe we're after different things, it's fine to disagree. I'm off to bed. I'd still be grateful if anyone could find an SEC or FOIC for the F6f-5. Failing that i'll test the F4u tomorrow.
-
For the people who do not know what it looks like lol...
-
Crowbaby,
Test the F4U. There is more inforamtion available there anyway.
But you are way overcomplicating things.
The whole point is this.
The F4U and F6F were both long range fighters by comparison to the La-7 which was a point interceptor.
Based on that historic premise I asked the question why then is the AH flight duration (not range since the purpose in AH is not to fly far) the same between long and short range fighters since this surely puts the long range fighter at a large disadvantage.
Testing, all testing should be at mil power since that it what is used primarily in AH.
SFC- the available SFC data puts both engines at approximately the same level of efficiencywith a slight advantafe to the R-2800. Remember the R-2800 was a high tech engine and was the successor to the R-2600 and prior P&W power plants. The ASH-82FN was in fact a copy of the R-2600.
If the SFC's are equal then the duration of the A/C with the larger fuel load will ALWAYS have a longer duration.
Things like weight and range are characteristics of aircraft not engines and have nothing to do with duration.
Point being if I'm in my F4U-1D I should be carrying 25% fuel to engage a La-7 with 75% fuel and that would give me historically accurate equal duration for both A/C. Otherwise it's just arcade mode.
Of course this affects the Mossie, P-47, P-38, P-51, F6F and F4U the most. If you fly a 109, LA-7, Spit or Yak this probably is not great news.
-
too bad you had to slip to..
"my plane needs more range or its just arcade mode"
Goes along with
"My plane needs to be the most robust or its just arcade mode"
You make a huge point of these being long range fighters..But they accomplished alot of that range with a massive external fuel capability
Both the corsair and the hellcat can engage an la7 with 25% fuel if they take any external fuel at all..
That simple point makes all this whineing about the La7 kind of silly.
-
Pongo,
Please don't miss the point.
It's not my plane or his plane or anyone elses. It's either right or it's wrong. It's not subjective.
I'm not whining about the La-7. I really don't have trouble with them in the MA. In fact I think they are overrated. However I think somethings take a back seat to game play and arena parity because having a fuel multiplier that would limit the la-7 15minutes with a full tank would give a P-51 a full hour. So the answer is to bend reality in favor of better game play.
Well thats great if you are a big fan of tiny airplanes but it's one step closer to arcade more as far as I'm concerned.
BTW I have no idea if it is intentional, an oversight or otherwise becuase HTC hasn't said a word in about three threads full of this stuff.
But if you think I wrong feel free to correct me ;)
-
Originally posted by joeblogs
Yes upping w 25% internal fuel and a drop tank is the right reponse. But that is not really sufficient to cap a CV when you don't know when you can land next.
Besides you have to lose that drop tank as soon as you engage, or you can't turn worth %$$$(**& and then the heavy iron fuel penalty dictates you have about one dogfight before you are out of gas. This does not strike me as sensible game play.
-blogs
Your worried about an La7 attaking your CV?
Good response F4DOA
I still think that damage to a base should limit your fuel in gallons..not %..then we will see how much of a range advantage those big planes get.
-
O.k. I can see how the figures look funny:
F4u-1
2000hp - from SEFC
for
43mins - from Snefens
with
361 gals - from HTC
=
238hp*min/gal
La7
1650hp - quoted by joeblogs from Aircraft Engines of the
for World, published in 1949.
28mins - from Snefens
with
1650 - from HTC
=
378hp*min/gal
which would mean that the F4u engine is working only at 63% of the efficiency of the La7 engine. However:
-We don't know that any of these HP figures are accurate.
-We have no historical data to compare to Snefens tests because its an arcade-y way to fly the planes.
-We really can't assume any equivalence of engine performance. If engine performance was as simple as fuel in equals HP out across a range of power outputs. If engines were that staightforward, then people wouldn't write head-breaking reports like these:
1943 study on fuel economy and' crank angle' (http://naca.larc.nasa.gov/reports/1943/naca-tn-915/)
similar report on 'inlet valve design' and power output efficiency (http://naca.larc.nasa.gov/reports/1943/naca-tn-915/)
In addition, i understand that the ASH-82 engine was fuel injected? and that the R-2800 was not? I can't find corroboration on this, but it would also explain a difference in efficiency at high output settings. 1939 NACA report on injection v. carburetor here (http://naca.larc.nasa.gov/reports/1939/naca-tn-688/)
Thus, i still maintain the only sensible thing to do if you have concerns is to test the planes against reliable performance figures. I now plan to do this for the F4u-1. Offline, i'll test with no wind, fuelburnmult at 1, against a range of settings from this chart. Again, i'm only interested in endurance, not climbrate or anything else, just level flight at alt and settings as listed.
-
Wouldn't it be easy enough to test the endurance of the F4U, F6F, P-51 and any other long ranged aircraft against their historical endurance and verify that they consume too much fuel?
I suspect that aircraft like the La-7, Spitfire and 109 are fine and it is simply that the long range aircraft are consuming fuel too rapidly.
-
This thread is perhaps a tad more complicated than it needs to be.
Karnak found out that the Mossie's endurance is a lot less than it was in real life. We will have to accept Real life figures as true, and there is no way to calculate ones way out of there. In WW2 the mossie was running missions as far as Berlin you know, while the Spitfire mission wouldn't even go deep into France!
Now regarding fuel burn rate pr/hp/time of course engines can be compared, but then the weight and aerodynamic factors such as frontal area, wingloading, or in other words, Drag, start playing with the equation, and as you can see on the comparison between the F6F and the F4U-1 these do quite a bit!
Anyway, if you guys prove your points nicely like Karnak did, I am sure those little things will be corrected by HTC in the future:D
-
alt-tabbed, got bored of reading a book.
About this SFC stuff people keep bringing up (F4UDOA and joeblogs) and i keep trying to shoot down. Look at the SEFC above.
At take off power, the R2800 in the F4u produces 2000hp for a fuel flow of 290 gallons ph.
At max cruise, 570hp for 42 gallons per hour.
This is without even bringing alt into the equation.
There just is no magic formula for fuel consumption over time equals output (hp).
-
And here are the results of the tests on the F4u-1. These are not 100% accurate because i kept getting distracted, but they're pretty close. Some of them don't take long anyway, feel fry to try yourself...
Max Cruise
10,000ft alt - 2150rpm - 34"Man
i got 150IAS/285TAS and 59mins from 1/4 tank = 90 gallons.
chart says 83gph, my result is 91.5gph - 10% over
Normal Rated
7,000ft alt - 2550rpm - 44"Man
i got 275IAS/300TAS and 24:30 from 1/4 tank
chart says 220gph, my result is 220.4gph - spot on.
Military
16,000ft alt - 2700rpm - 53"Man
i got 305IAS/380TAS and 23mins from 1/4 tank
chart says 275gph, my result is 234gph - 14% under
Military
2,000ft alt - 2700rpm - 52.5"Man
i forgot to record speed:) 22:00mins from 1/4 tank
chart says 290gph, my result is 245gph - 15.5% under.
This doesn't surprise me. The F4u-1 Specific Engine Flight Chart as used by pilots in WW2 says 290gph if you fly at full military power, which people seem to be doing in the MA (full rpm and Manifold pressure, no WEP). The F4u-1 carries 361 gallons. This would equate to 74 minutes of flight, or 37 minutes with fuel multiplier set to 2. Snefens chart, which people are so upset by, shows 43 minutes endurance. This is 16.2% better than the plane performed historically.
If i were you i'd back sheepishly away from those drums you wanted to bang.
As for the F6f-5 - we know that with the same engine and more fuel than the F4u, it had a significantly lower range historically. I don't see any point pursuing this further.
The Mosquito, however, does definitely seem to be off. to Karnak for finding and testing that.
again, i'm prepared to eat my words if someone can prove my logic, or my math, wrong.
edit for P-38 and P-47D-11
Snefens chart suggests 332gph for the P-38, it should consume 334gph.FOIC here (http://www.zenoswarbirdvideos.com/Images/P-38/38FOIC.gif)
Snefens chart suggests 242gph for the P-47D-11. As it consumes 205gph at a max continuous of 36" and 2550rpm, this figure seems reasonable to me for Military Power. FOIC here (http://www.zenoswarbirdvideos.com/Images/P-47/47FOIC.gif)
Snefens chart suggests 152gph for the P-51D, it should consume 180gph.
FOIC here (http://www.zenoswarbirdvideos.com/Images/P-51/51FOIC.gif)
-
Originally posted by crowbaby
Has anybody compared the weights of these aircraft? F6f-5 'combat' weight 12,740lbs. La7 weight ranges from 2,638kg empty to 3,400kg absolute maximum. That's 5,800 to 7,500lbs!
This could be why the ASH-82 is listed for 1,330hp cruising at alt (probably optimistic), where the R2800 in the F6f-5 makes 1,625. Hardly comparable.
Pls explain me why weight should influence engine ouput...
Originally posted by crowbaby
Snefens endurance chart shows 28mins for both La5 and La7, 30mins for F6f. To me this chart is pretty meaningless, as efficiency varies hugely across speed ranges
Pls explain me why speed should influence the engine consumption when those engines run with constant RPM. We donīt talk about range, we talk about endurance. We donīt even talk about aircraft or prop efficiency, we talk about results that could also be measured on ground in the caves of a testing institute.
Originally posted by crowbaby
Which would equate to 276 litres per hour, or 73 us Gals.
We talk about l/Ps/h, not l/h
Originally posted by crowbaby
-We don't know that any of these HP figures are accurate.
-We have no historical data to compare to Snefens tests because its an arcade-y way to fly the planes.
-We really can't assume any equivalence of engine performance. If engine performance was as simple as fuel in equals HP out across a range of power outputs. If engines were that staightforward, then people wouldn't write head-breaking reports like these:
A) Not true, we know very well the correct engine outputs
B) Not true, because flight endurances were measured systematically, and for flight endureance you just need a clock. Again, we donīt talk about range. All what it needs is a pilot that takes the aircraft in the air and cruises around for a given TIME with constant power setting. If you think this would be to complex for a test pilot, ok believe it, i for myself think that such a test was probably the simpliest, most boring test for a test pilot.
C) American radial engines were probably the best radials in the world, due to the concurrence pressure of Wright and P&W some very fine engines were available. Nearly all other foreign radial engine manufactors (russians, germans) copied or were influenced by the american engines.
Check the link to the rtf file from tilt in the other thread once more, and compare those numbers to AH. This is all you need to do.
niklas
-
Nope. i'm sick of jumping through hoops. Did anyone even read the test results, do the sums based on Snefens chart?
I've tested AH against the best historical data and the fuel consumption seems o.k. across a wide range of settings. The P-51 and F4u seem to do better than historical figures dictate, but then in reality they only flew at these setting for 5-15 minutes, whereas in AH people want to use them constantly. Who knows how HTC have decided to address this? The Mosquito, however, seems to be way out. This may be a simple mistake.
Other than Karnak's test of the Mossie, all i've seen is bald headed conjecture, faulty logic and whines. I'm sorry, but that's how it looks to me.
Pls explain me why speed should influence the engine consumption when those engines run with constant RPM. We donīt talk about range, we talk about endurance. We donīt even talk about aircraft or prop efficiency, we talk about results that could also be measured on ground in the caves of a testing institute.
You're suggesting that increasing speed won't decrease range? that altitude is irrelevant? These arguments still seem to come back to this notion of an 'SFC'. Engine fuel consumption for power output is radically different for different engines. It will also change differently for each engine depending on rpm, Manifold pressure, altitude, fuel injection, superchargeing and temperature. The richer your mixture, or the higher your manifold pressure - the more inefficient the engine is likely to be. Where do you think the energy comes from when an engine overheats?
Look at the charts, the hp for gph listed for the F4u changes its ratio hugely. Show how an SFC makes sense of this chart!
Why do you want to stick your head in the caves when we can flight test the planes and see that they match historical data?
As modeled, the endurance numbers in AH imply the American engines (about which we know the most) are half as efficient as shown in the historical data.
i refer you to my previous post. Snefens chart, at full AH power (2700rpm and 54"Man at sea level) shows 43 minutes endurance for the F4u-1. Double this to allow for the fuel multiplier and we get 86 minutes. With 361 gallons in the tank this is 251gph. The F4u-1 historical data says it should consume 290gph at these settings. please answer this.
as for,
About the only test that remains to be tried is for a good heavy iron pilot to fly one of these plane to an intermediate altitude (where there is less drag), say 15k, and fly at the lowest power setting that will maintain altitude and look at the watch until the engine quits. If you really want to be rigorous, do this for 1/4, 1/2, 3/4, and full internal fuel.
i've done this, but by the book, and i'm happy that the results match the historical documents. Tell me where my tests are wrong or do your own.
-
Originally posted by LLv34_Snefens
"Snefens endurance chart shows 28mins for both La5 and La7, 30mins for F6f. To me this chart is pretty meaningless, as efficiency varies hugely across speed ranges.
First, those charts are not meant to compare to any historic values, they are simply there to let the player know how much fuel he have on 100% power. Second, the AH engine model is rather simplistic. I choose to list the endurance for 100% power, because that's simply what the majority of players use all the time with the occasionally WEP, but there is no difference in the consumption. I just tested it again to be sure:
La7, SL, 100% power, Max speed: 56 min
La7, SL, WEP power, Max speed: 56 min
La7, SL, 100% power, 175mph: 56 min
La7, 30K, 100% power, Max speed: 56 min
Fast/slow, WEP On/off, high/low. At the moment it makes no difference in AH.
__________________
Ylil. Snefens
Lentolaivue 34 (http://www.muodos.fi/LLv34)
My AH homepage (http://home14.inet.tele.dk/snefens/index2.htm)
(http://home14.inet.tele.dk/snefens/209.gif)
I'm not sure if this factors into your findings or not, but
Originally posted by hitech
If wig = Ground Effect, then yes. Yes planes gain mpg effiecentcy with alt.
HiTech
I noted he says mpg and not time.
-
Crowbaby,
Please use the the F4U-1D for comparison. It carried 237 gallons of fuel and for the prupose of arguement it compares more easily with the F6F-5.
This is why you are wrong or mistaken in either your math or logic.
Math the F4U-1D uses 290 gallons per hour of fuel at full mil power with a 237 gallons tank. 237 is 81.7% of 290. That gives it a durantion (forget about range) of 81.7% of an hour or 49minutes. I'm not sure were you got 43minutes.
Mistaken-The table of range and flight duration for La-7 No 38103254 with
G full=3265kg, full tank fuel supply - 460 l.
Mode Mode values Level flight
up to dry tanks:
Range, km duration,
h-min
Max. H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl. 355 0-35
speed 3000 1 2400 990 355 0-33
5000 2 2400 1020 355 0-32
7000 2 2400 870 405 0-38
The duration here from the VVS test data clearly shows a duration of either 33 or 35 minutes at low alt.
Logic- the SFC for the La-7 of .46 is for max cruise power setting. A comparable SFC for the F4U-1D is also at max cruise and shows an SFC of of .465 and a GPH of 83 or a duration of 2.85 hours for the F4U-1.
Here is the La-7 at max cruise and economical cruise.
Near H=5000m(2nd sup.sp.),n=1810, IAS=388 km/h 580 1-10
fast range TAS=500 km/h
Optim. H=1000m(1st sup.sp.),n=1500, IAS=360 km/h 665 1-45
mode 3000 1 1500 345 625 1-34
5000 2 1600 340 590 1-20
7000 2 1600 300 665 1-32
This shows a fast cruise duration of 1 hour 10 minutes and a optimum cruise duration of 1.45 minutes. This is not even comparable to the F4U, F6F or P-47 all using the same engine. In fact it's not even in the ballpark. It is less than half.
Here is what I have calculated based on a duration of 35 minutes at mil power for the La-7
122 gallons burned in 35minutes= 193 gallons burned for 60minutes.
193 GPH for the La-7 at mil power = 1158lbs of fuel per hour giving it a SFC of .70!!! that is still a rediculously low number for what it should be and that only gives it 35 minutes of flight time.
The Comparable SFC for the F4U is .87 with a far superior engine.
Even with the SFC of .70 the F4U and F6F should still have a significant advantage in duration and I still doubt the La-7 was anyware near that good.
Joe Blog please check my numbers. .70 sounds rediculous at mil power.
-
Crowbaby,
Please use the the F4U-1D for comparison. It carried 237 gallons of fuel and for the prupose of arguement it compares more easily with the F6F-5.
No. I have a chart for the F4u-1. I used it. It worked.
As regards the VVs La7 data, it clearly says this:
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
The 35 minutes is not for a full tank, it is real flight duration after warm up, etc. That is why I compared to the fuel consumption data only. Which I found to be reasonably accurate in three separate tests. I have pointed this out previously.
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Here is what I have calculated based on a duration of 35 minutes at mil power for the La-7
122 gallons burned in 35minutes= 193 gallons burned for 60minutes.
193 GPH for the La-7 at mil power = 1158lbs of fuel per hour giving it a SFC of .70!!! that is still a rediculously low number for what it should be and that only gives it 35 minutes of flight time.
The Comparable SFC for the F4U is .87 with a far superior engine.
Even with the SFC of .70 the F4U and F6F should still have a significant advantage in duration and I still doubt the La-7 was anyware near that good.
Joe Blog please check my numbers. .70 sounds rediculous at mil power.
__________________
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CrowBaby,
Warm up is done at idle with barely any fuel consumption.
Read my calculation above.
SFC varies with power setting.
At full mil power the La-7 should have the fuel duration of an Estes Rocket.;)
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For high output US radials on 100/130 PN avgas the SFC at military power (no WEP) ranges from 0.9 to above 1. At normal rated power SFC is about 0.8 to 0.9 depending on altitude in the flight test data I have seen.
With lower rated fuels the SFC numbers would be significantly higher.
-Blogs
Originally posted by F4UDOA
Crowbaby,
Please use the the F4U-1D for comparison. It carried 237 gallons of fuel and for the prupose of arguement it compares more easily with the F6F-5.
This is why you are wrong or mistaken in either your math or logic.
Math the F4U-1D uses 290 gallons per hour of fuel at full mil power with a 237 gallons tank. 237 is 81.7% of 290. That gives it a durantion (forget about range) of 81.7% of an hour or 49minutes. I'm not sure were you got 43minutes.
Mistaken-The table of range and flight duration for La-7 No 38103254 with
G full=3265kg, full tank fuel supply - 460 l.
Mode Mode values Level flight
up to dry tanks:
Range, km duration,
h-min
Max. H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl. 355 0-35
speed 3000 1 2400 990 355 0-33
5000 2 2400 1020 355 0-32
7000 2 2400 870 405 0-38
The duration here from the VVS test data clearly shows a duration of either 33 or 35 minutes at low alt.
Logic- the SFC for the La-7 of .46 is for max cruise power setting. A comparable SFC for the F4U-1D is also at max cruise and shows an SFC of of .465 and a GPH of 83 or a duration of 2.85 hours for the F4U-1.
Here is the La-7 at max cruise and economical cruise.
This shows a fast cruise duration of 1 hour 10 minutes and a optimum cruise duration of 1.45 minutes. This is not even comparable to the F4U, F6F or P-47 all using the same engine. In fact it's not even in the ballpark. It is less than half.
Here is what I have calculated based on a duration of 35 minutes at mil power for the La-7
122 gallons burned in 35minutes= 193 gallons burned for 60minutes.
193 GPH for the La-7 at mil power = 1158lbs of fuel per hour giving it a SFC of .70!!! that is still a rediculously low number for what it should be and that only gives it 35 minutes of flight time.
The Comparable SFC for the F4U is .87 with a far superior engine.
Even with the SFC of .70 the F4U and F6F should still have a significant advantage in duration and I still doubt the La-7 was anyware near that good.
Joe Blog please check my numbers. .70 sounds rediculous at mil power.
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CrowBaby,
Warm up is done at idle with barely any fuel consumption.
try again,
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
that's a possible 95 litres depending on their methods and the translation. Which is why i tested against their listed data for fuel consumption at various altitudes and power settings. Flight testing in AH against historical data works - why do you not want to do this?
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CrowBaby,
Thanks.
Thats 95 total Litres = 25US gallons
Like I said that's not much fuel especially in the world of AVGAS.
You realize that just makes the La-7 fuel endurance that much worse?
The SFC of .70 which is already to low is based on 122gallons of fuel at mil power. If you base it on 97 gallons and the fact that it used 95octane fuel then the SFC becomes even more outragous.
I'm not sure this Aircraft should have been able to make it to the end of the runway. It keeps getting worse!
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I show that you've been making the same wrong assertion over and over and you thank me? This mad scientist stuff is going to your head.
I'm not sure this Aircraft should have been able to make it to the end of the runway. It keeps getting worse!
Well, lots of people seem to think it flew. They took note of its flight characteristics and performance. Years later HTC came along and used those numbers to model a simulator.
You can now compare the performance of the plane in the simulator with those 50 year old numbers. I did this and saw that HTC did a great job.
If your engine theories, unrelated to real life or the game, disagree, then it might be you who is wrong.......
crowbaby over and out.
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These are not my theories.
Bernoulli, Newton and Venturri maybe but definitely not mine.
Test this based on numbers that you showed me.
According to YOU. The La-7 burns 95 litres or 25 gallons warming up and climbing to 1,000Meters. Or exactly 20% of it's fuel.
Jump in your AH La-7 sit at idle then climb to 1,000Meters and see if you have burned 20% of your fuel. If you have then you might have a point but I doubt it.
Drum Roll Please!!!
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Based on Crowbaby's results I made a mistake in some earlier posts-I've corrected them.
It appears that crowbaby's endurance numbers for the corsair are quite close to the numbers you will find in the historical data for this plane. The one exception according to crowbaby's numbers is at full military power (no WEP) where endurance in AH seems to be about 10 percent too high.
The mistake I made was in reading crowbaby's test results for the La-7. These do not compare at all with the VVS flight test data. They generally show the endurance in AH is twice that expected based on historical information.
So I was wrong, the US heavy iron seems to be modeled ok, its the La-7 that seems clearly off.
Lets go through the tests in detail. This is what crowbaby found:
(1) Low power settings
"I used roughly 26" Manifold on the gauge to get speed and rpm right.
1/8 tank 13mins
1/4 tank 26mins
1/2 tank 50mins
Which would equate to 276 litres per hour, or 73 us Gals.
more than would be expected from the data posted. However, i probably didn't get the optimal settings, and those tests appear to be VVS, so may be optimistic. "
This is quite close to VVS data for flight at low power settings for the La-7. My table gave fuel consumption of 70gph.
(2) Next crowbaby checks performance at full military power:
"La7, SL, 100% power, Max speed: 56 min
La7, SL, WEP power, Max speed: 56 min
La7, SL, 100% power, 175mph: 56 min
La7, 30K, 100% power, Max speed: 56 min
Fast/slow, WEP On/off, high/low. At the moment it makes no difference in AH."
Here's the problem. the VVS data says this plane should fly only 35 minutes, just a little over half what crowbaby found.
If we just calculate endurance as the ratio of gallons in the tank to gph, the most time you would get is 122/164*60 = 44 minutes. That is 30 percent less than what crowbaby found.
What's more, the implied SFC from crowbaby's data is = (732/1850)*(60/56) = 0.42. If we assume mil horsepower is only 1700, we get an SFC of 0.46, the number Wilkinson reports as the engine's best efficiency.
That is more than 50 percent too low. US engines run at military power have an SFC of 0.9 to 1.0. I've already shown the Ash-82FN was no more efficient than an American radial.
He reports two more tests, but the conclusion is the same.
IT APPEARS THE PROBLEM WITH THE LA-7 IS THAT EVEN AT FULL OUTPUT THE ENGINE HAS THE FUEL EFFICIENCY OF AN ENGINE ON AUTO LEAN.
If you were to try a lean fuel mixture with that manifold pressure on 95 octane gas you would blow the cylinders right off the engine.
-Blogs
Originally posted by crowbaby
Nope. i'm sick of jumping through hoops. Did anyone even read the test results, do the sums based on Snefens chart?
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Agh - it's a quagmire - it's sucking me in - i can't get out - Help! Help! Hel m mmmm .....
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
1. In line with a lot of these documents these are allowances, not fixed in stone. i'msimply pointing out that the 35mins you qouted is not for a full fuel load.
2. If we spent 15minutes warming up, testing our engine and taxiing. Then allowed 45 litres for landing. Then, yes, that might account for 20% of our fuel in AH. If you want to play realistically, you'll get realistic results, this is a microcosm of the whole fuel consumption debate.
3. This debate is a many headed hydra. First fuel consumption. From La7 to F6f and back again. Now including things like warm up, etc. just makes it impossible to answer all the unsupported criticisms of AH.
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As modeled, the endurance numbers in AH imply the American engines (about which we know the most) are half as efficient as shown in the historical data.
i refer you to my previous post. Snefens chart, at full AH power (2700rpm and 54"Man at sea level) shows 43 minutes endurance for the F4u-1. Double this to allow for the fuel multiplier and we get 86 minutes. With 361 gallons in the tank this is 251gph. The F4u-1 historical data says it should consume 290gph at these settings. please answer this.
I didn't really address this fully earlier so I will now.
First the Mil power 2700RPM 54" setting shows 290GPH. The F4U-1D has 237Gallons of of fuel.
237/290=81.7%
81.7% of 1 hour = 49minutes Where did you get 43?
290GPH= 1740LBS of fuel per hour/2000HP
=SFC.87 for the Pratt&Whitney R-2800-8W
La-7 2400RPM 1650HP
122Gallons of fuel lasted 35Minutes of flight duration.
35minutes is 58.3% of 60minutes meaning that in 1 hour at mil power it would burn 172.83gallons (my math was wrong earlier and this is worse for the la-7) in 1 hour
173gallons= 1038lbs of fuel/1650HP=.62
So the La-7 had an SFC of .62 at mil power huh? And that is with 122Gallons not the 97 gallons after warm up.
Congradulations you've inveted the perpetual motion machine and won the Nobel Prize. Soon we will all be driving SUV's that get 50miles to the gallon.
:rolleyes:
Note: I noticed that you multipied the duration time by two for the MA. The fuel mutiplier means you devide by two. So the F4U-1D would have a duration of 24.5 minutes in the MA if things were calibrated according to the chart. But the La-7 would have about 15minutes and that is being optimistic.
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Joe Blogs,
Just read your last post.
You are EXACTLY right.
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As both those sets of data are supplied via myself............
I have the original Russian for both and the numbers are not transposed........... although they do contradict each other.
I would place more faith in the VVS test data......... it is a record of actual trials signed off by a respected test pilot and transposed into the chart you see.
The engine data is from the La 7 pilots handbook (pages 228 / 229)........ I tend to think of it as a test bed data........ also it is therefore not data of record more data of promice.........
For example it gives the power out put for 2600 rpm which can be held for 30 secs........... I find this in no other text pertaining to the aircraft. Yet I can well imagine that Shetsov had conducted the bench test and decided to add to the engine data sheet.
Bearing this in mind we can easily see that the fuel consumption figures would be ones extrapolated from the test bed.
We do not really have to look too hard to see the VVS test data repeated in many "generic" sources elsewhere in terms of range and durability.
Taking the VVS data to AH one thing shouts out to me that makes much of the detailed work above a little redundant........ this is the variation in range against the engine setting. Perhaps someone can do the trials but i would proffer in ignorance that whilst MIL power range in AH is too long we would find that reduced power range is too low.
It brings up two stages of arguement.......
1) its clear that near combat power settings do not factor fuel consumption properly and that this discrepancy is to the disadvantage of AC that have to carry incorrect increased fuel weight to compensate for the error.
2)conversely if (as I proffer) low power fuel consumption is too high then this inhibits range of smaller tanked AC that should be achievable thru sensible engine management.
The question is then asked "has a compromise been made here?"
What were the RL ratio's of range per AC at the best and worst settings (for range)? Is this ratio achievable (regardless of actual range) in AH? If this ratio is not the same (indeed smaller) where is it placed in the AH model.
eg Given the La7 has an endurance of 35/40 mins at near full power and 100 mins at low power cruise. (often repeated figures for the La7) this puts its endurance ratio to 1:2.5 ( range extrapolated via fuel consumption/km @ the test speed)
So if the La7can be modelled to get 100 mins endurance at 1500/1600 rpm and 50 minutes at 90% v max at 2160 rpm then it should certainly be limited to 32 minutes at 2400 rpm.
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I was going to post this back when i tested the La7, but i hoped the La7 bashers would do their own tests, and thought they'd get more pleasure out of posting this than i do.
Seriously, though, I did not withold these results to skew the argument, but because i wanted to present them clearly and with tests on the F4u-1 for comparison.
I also got pissed off with everyone wilfully misreading this chart:
(edited only for clarity)
Chart of range and level flight duration of a/c La-7 No38103254
at different flight modes
at V/n=const (constant speed and RPM),
G tot=3265kg (total weight)
and V fuel=460 l (fuel volume)
H=1000m (1st speed of supercharger),
fuel supply for level flight - 365 l
RPM - 2400
Supercharg. pressure,
mm of merc. pile - 1020
Speed, km/h - IAS575
----------------- TAS 608
lit./km - 1.020
lit./h - 620
Till the dry tank:
Range of Level flight km - 355
level flight, duration, h-min - 0-35
The chart clearly says that 35 mins is for 365 litres. If we do the maths, we find 365/35*60 = 625 litres per hour, close enough to the 620 litres per hour stated for these settings (highlighted in blue).
So, does the AH La7 consume 620 litres per hour at these settings? I tested it (novel idea!).
H=1000m = 3,280 feet
RPM - 2400 = max for La7 (2600 in AH)
pressure, - 1020 = max for La7 (41.5" in AH)
Speed, - IAS575 = 357mph, i got 351mph
--------- TAS 608 = 377mph, i got 376mph
Half a tank (fuelburnmult at 1) gave me 28minutes flight (this also tallies with Snefens chart - 28mins full tank with fuelburnmult@2).
The tank is 460litres, therefore 230/28*60 = 492 litres per hour in AH. So that's 20.6% less than real life.
Compare this to the F4u-1, which consumes 251gph at full power, when it should be 290gph, which is 13.5% less than real life (it's worst result in testing was 15.5% less consumption than RL).
At the other extreme - tests at economy cruise setting showed the La7 consuming 25% more fuel than it should have, and the F4u-1 10% more.
So, from testing two planes each at four different power settings, it seems that while AH is accurate at normal and max continuous power settings, we could assert that AH:-
1) allows planes more endurance than they should have if they're flown in an arcadey fashion.
2) allows less than it should at very lean, econmical settings.
-But even these would be foolish, gross generalisations, and only two planes were tested.
This all assumes my tests are correct Worse, it also
1) assumes HTC used the same documents as us (which i seriously doubt).
2) assumes that mixture controls are modelled as they are used on these charts, a huge consideration.
3) disregards any decisions HTC may have made with regard to the completely unrealistic/ahistorical use of the engines which produced some of these figures.
I, for one, am still happy with AH's modelling of the planes fuel consumption.
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Clueless
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Can you guys test against another small fueled aircraft so Crowbaby doesn't cry-baby anymore?
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LLv34_Snefens, I couldnt help noticing you've got a pic under your name, could you tell me how to do that please?
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Originally posted by frank3
LLv34_Snefens, I couldnt help noticing you've got a pic under your name, could you tell me how to do that please?
They are called avatar I believe.
They are in the settings.
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Originally posted by crowbaby
You're suggesting that increasing speed won't decrease range? that altitude is irrelevant?
I wrote 2 times that we donīt talk about range, and you say i suggest speed wonīt decrease range? Hopeless case...
niklas
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Guys, crowbaby is on the mark when he says that the crux of the debate is comparing apples and oranges.
Firstly, there seems to be some confusion here as to the term "fuel consumption". GPH, LPH are units of FuelFlow, not fuel consumption.
FuelFlow (FF) = SFC * Drag * Velocity / 550
[velocity in units of fps]
I hope it's clear as to the other variables that determine fuel flow. It's more than just SFC values for the engine.
Hopefully it's also clear from this equation just how a/c weight factors into fuelflow as well since induced drag varies with weight.
2ndly, there seems to be some confusion regarding aircraft endurance as well.
Specific Endurance = 1 / FF. SE is in units of time/unit of fuel.
To find flight endurance you multiply SE by amount of fuel you are interested in.
Hopefully it's clear that if you're going to compare endurance of aircraft you can't just compare SFC values.
Tango, XO
412th FS Braunco Mustangs
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Some of you guys can't see the forest because of all the trees. It's a uniquely human ability to take something so simple, and make it so needlessly complicated.
Fact: The AH F4U/F6F can stay aloft about as long as their historical counterparts could at MIL power.
Fact: The AH LA7 can stay aloft longer than its historical counterpart could at MIL power.
Conclusion: Something is amiss with the AH LA7's fuel usage at MIL power.
It's pretty simple and pretty obvious, no?
Trying to manipulate the math to "prove" your point, or trying to confuse the argument by bringing up red herrings won't change that.
The LA7 isn't the only one; there are other planes which seem to have odd fuel usage. This isn't a crusade against the LA7 or anything, it just happened to be the plane that was brought up.
That said, I think this particular issue is most likely DOA since IIRC HTC has said in the past that they don't feel it's worth their time to look at it and/or fix it. Considering what they've said with regards to the task of making "AH2", they've probably got bigger fish to fry.
J_A_B
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<
Fact: The AH LA7 can stay aloft longer than its historical counterpart could at MIL power. >>
-J_A_B
Testing in AH shows that both the F4u-1 and La7 stay aloft longer at full power settings than they would have historically.
-The F4u-1 Specific Engine Flight Chart as used by pilots in WW2 says 290gph if you fly at full military power(full rpm and Manifold pressure, no WEP).
-The F4u-1 carries 361 gallons (HTC figure tallies with historical). This would equate to 74 minutes of flight, or 37 minutes with fuel multiplier set to 2.
-Snefens chart shows 43 minutes endurance for the F4u-1. This is 16.2% better than the plane performed historically.
(edit to ad F4u-1D)
Please use the the F4U-1D for comparison. It carried 237 gallons of fuel and for the prupose of arguement it compares more easily with the F6F-5.
This is why you are wrong or mistaken in either your math or logic.
- F4UDOA
The F4u-1D also uses 290gph at full military (according to HTC, and tallies with F4u-1 chart)
-The F4u-1D carries 237 gallons (HTC figure). This would equate to 48 mins flight time, or 24 mins with fuel mult at 2.
-Snefens chart shows 28 mins endurance for the F4u-1D. This is again 16.6% longer than it should.
To keep everyone happy, none of these figures above are from my tests. If there's any problem here it's that the F4u-1 would historically only have been used at this power for a maximum of 5 minutes anyway, not it's entire flight.
I take my hat off to the guys who complain that if we fly our planes in an unrealistic, ahistorical manner, then we get unrealistic, ahistorical results.
<>
- Puke
- You got a problem with my posts? you do the test yourself instead of chipping in with a pointless insult.
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J_A_B:
On the contrary. I have not seen conclusive proof that the La7 has greater endurance than historically possible.
The argument has been this. The La7's most economic SFC is about the same as the F6F-5 or the F4U-1. If the SFC's are similar then fuel flow rate between the a/c shouldn't be that different. Therefore the La7's fuel flow must be wrong because it's flow rate is lower than that of the F6F-5 of the F4U.
Unfortunately the flaw in this logic is that you can't just compare SFC's to tell you fuel flow rates.
FF = SFC * D * V / 325 (equation for units of d=lbs and v=fps)
You also have to factor in total drag and velocity which are significant variables to examine fuel flow rates.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
J_A_B:
On the contrary. I have not seen conclusive proof that the La7 has greater endurance than historically possible.
365l/460l = 0.79 = 79%
Flight time in AH with 100% fuel 56min (Mil)
Flight time in AH with 79% fuel 44.3min
Flight time Real life (Mil) 35Min
Advantage in AH = 44.3/35 ~26.5%
So difficult to see?
niklas
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- You got a problem with my posts? you do the test yourself instead of chipping in with a pointless insult.
You come across to me as though you are whining the poor little LA7 is being persecuted. No matter who is right or wrong, it's an interesting discussion but your tone sounds like you take this personally and are near tears. Maybe I'm wrong, and I'll apologize now. Want me to edit out my comments?
but i hoped the La7 bashers would do their own tests
Just one of your quotes. This isn't bashing of the LA7, but rather is the aircraft which happened to be used as an example. This isn't a witch hunt and the Spit and 109 has been mentioned too. So I just figured the discussion should utilize another small-fueled aircraft so that you don't take this personally. I really do not want to go through your posts to pick out those statements that make it sound like you take this personally, but in my readings of your posts, that's how it sounds to me.
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Niklas:
I'm assuming you're saying the real life data is from the data aforementioned way above- specifically:
2400 1020 575 608 1.020 620 355 0-35
I haven't seen anyone posting AH La7 endurance tests yet for 79% fuel, 1000m alt, the said rpm, manifold pressure, etc.
I assume you got your 44.3 min by using the simple ratio of:
55 min / 100% = x / 79%. You can't use this ratio because it doesn't accurately reflect variables involved since fuel flow isn't linear.
Endurance = Specific Endurance (SE) * amount of fuel of interest
SE = 1/FF (units of time / unit of fuel)
FF = SFC * D * V / 325 (units of d=lbs, v=fps)
D is a pretty complex variable that varies with alt, velocity, and weight.
Tango, XO
412th FS Braunco Mustangs
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Puke - no offense, but it seems odd that you use your perception of my tone to justify your insult? Besides, i thought i'd made it clear that what you quoted me on was in jest by starting the next paragraph with "Seriously, though..."
So far, I thought this thread was mostly doing pretty well. I mean, it's clear that we have some major disagreements here, and some very different ways of looking at the problem, but it hadn't degenerated into name calling.
Joeblogs - sorry didn't respond to your e-mail, only just saw it now, it's an occasional account.
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I'd like to do this, but I've got to assemble some numbers on the exact models flown in AH. Had hoped to finalize the numbers on the La-7 first...
-blogs
Originally posted by Puke
...
Just one of your quotes. This isn't bashing of the LA7, but rather is the aircraft which happened to be used as an example. This isn't a witch hunt and the Spit and 109 has been mentioned too. So I just figured the discussion should utilize another small-fueled aircraft so that you don't take this personally. I really do not want to go through your posts to pick out those statements that make it sound like you take this personally, but in my readings of your posts, that's how it sounds to me. [/B]
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The reason why using the best efficiency of an engine may be an inappropriate proxy for the endurance of a given plane is that you can't be sure the engine is generating enough horsepower at that setting to actually keep the plane in the air.
The fact that you are carrying more fuel, or have more drag, etc on a plane influences the amount of miles you can fly. It only influences the amount of time you can run an engine if you have to run it at higher settings to keep the plane in the air when the tanks are near full. Otherwise there is no effect.
Assuming no bombload and a 1940s fighter, there is so much excess power on these planes I don't see this as an issue in the flight tests. The fact that actual flight test data on US heavy iron gives you an SFC very close to the best SFC of the R2800 suggests the minimum horsepower required to keep these planes flying is not far above the horsepower associated with best efficiency of the engine.
-Blogs
Originally posted by dtango
Guys, crowbaby is on the mark when he says that the crux of the debate is comparing apples and oranges.
Firstly, there seems to be some confusion here as to the term "fuel consumption". GPH, LPH are units of FuelFlow, not fuel consumption.
FuelFlow (FF) = SFC * Drag * Velocity / 550
[velocity in units of fps]
I hope it's clear as to the other variables that determine fuel flow. It's more than just SFC values for the engine.
Hopefully it's also clear from this equation just how a/c weight factors into fuelflow as well since induced drag varies with weight.
2ndly, there seems to be some confusion regarding aircraft endurance as well.
Specific Endurance = 1 / FF. SE is in units of time/unit of fuel.
To find flight endurance you multiply SE by amount of fuel you are interested in.
Hopefully it's clear that if you're going to compare endurance of aircraft you can't just compare SFC values.
Tango, XO
412th FS Braunco Mustangs
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Joe Blogs:
Specific Endurance determines how long an a/c flies not how far and is a function of fuel flow:
SE = 1/FF
Fuel flow once again is:
FF = SFC * D * V / 325
This equation shows all the aerodynamic effects on fuel flow which includes total drag. To say that drag has little impact assumes that drag (really power required = D*V) between aircraft in comparison is near the same. For a/c like F6F-5, F4U-1 vs. the La7, drag is clearly a factor. This is the same problem people run into when they look only at engine horsepower as a measure of linear acceleration / climb performance.
If we're interested in range then we use the Breguet Range Equation where we can the variables involved:
R = (V/SFC) * (L/D) * ln(Winitial/Wfinal)
Tango, XO
412th FS Braunco Mustangs
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... they affect the minumum horsepower required to keep the plane flying. Forget about speed, distance traveled, rate of climb, etc. All that matters for endurance is the least no. of horses that keep the plane flying.
So long as that requirement does not vastly exceed the horses supplied by an engine at its most efficient power rating, SFC is all you need to know.
But if you are thinking of comparing fuel consumption subject to some minimum speed at a given altitude, you are correct that drag, and other things matter. Fix a required speed, back out the required horsepower, which depends on weight, drag and some other things to a power. Then figure out the fuel economy of the engine at that required horsepower.
I've been working off flight test numbers where I can back out the required fuel from the data without having an equation that captures the drag and other components for a given plane...
-blogs
Originally posted by dtango
Joe Blogs:
Specific Endurance determines how long an a/c flies not how far and is a function of fuel flow:
SE = 1/FF
Fuel flow once again is:
FF = SFC * D * V / 325
This equation shows all the aerodynamic effects on fuel flow which includes total drag. To say that drag has little impact assumes that drag (really power required = D*V) between aircraft in comparison is near the same. For a/c like F6F-5, F4U-1 vs. the La7, drag is clearly a factor. This is the same problem people run into when they look only at engine horsepower as a measure of linear acceleration / climb performance.
If we're interested in range then we use the Breguet Range Equation where we can the variables involved:
R = (V/SFC) * (L/D) * ln(Winitial/Wfinal)
Tango, XO
412th FS Braunco Mustangs
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But if you are thinking of comparing fuel consumption subject to some minimum speed at a given altitude, you are correct that drag, and other things matter. Fix a required speed, back out the required horsepower, which depends on weight, drag and some other things to a power. Then figure out the fuel economy of the engine at that required horsepower.
Yes exactly. Since all the tests results that have been hashed so far mainly deal with the aircraft at constant velocity at a fixed altitude then D*V becomes important. In these cases certainly there is some portion of the flight that fuel flow is mainly a function of SFC*THP(avail) since there's excess power to accelerate the a/c but this is only true until the velocity stabilizes. (Yes, there's also the case where it doesn't matter which you use since power avail = power required which occurs at max level speed.)
Off the top of my head the only time I can think of where you'd be looking at fuel flow = SFC*THP(avail) where you have constant excess power is in a constant speed climb.
The point is FF=SFC*Power(avail or required) which means you can only compare SFC's as indicators of fuel flow if power avail / power required for a given flight condition are equal between a/c which is again clearly not the case between the F6F-5 / F4U-1 vs. the La7.
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
Joe Blogs:
Specific Endurance determines how long an a/c flies not how far and is a function of fuel flow:
SE = 1/FF
Fuel flow once again is:
FF = SFC * D * V / 325
This equation shows all the aerodynamic effects on fuel flow which includes total drag. To say that drag has little impact assumes that drag (really power required = D*V) between aircraft in comparison is near the same. For a/c like F6F-5, F4U-1 vs. the La7, drag is clearly a factor. This is the same problem people run into when they look only at engine horsepower as a measure of linear acceleration / climb performance.
If we're interested in range then we use the Breguet Range Equation where we can the variables involved:
R = (V/SFC) * (L/D) * ln(Winitial/Wfinal)
Tango, XO
412th FS Braunco Mustangs
Ok Tango, thx for showing all of us that you successfully managed to read through the book "Flight Mechanics I". What you should learn now is to apply correctly what you read.
Youīre wrong in several aspects.
First: It doesnīt make sense at all to talk about specific endurance. How do you determine such values? You measure fuel consumption, time. Together with speed you can build up specific numbers. Then you want to use speed again to come back to values like time. Completly wasted effort, because we already know time. But it probably makes good impression on this board to throw around with forumlas.
Second: Your formula applies to jet engines. Actually you still have to distinguish single circuit jets and 2 circuit jets. You forgot for example the engine specific exponent Nv for speed, which is zero for single circuit jets (making v^Nv = v^0 = 1), or for props -1. A jet consumes more fuel when flying faster, because the airflow changes. A piston engine consumes at a given power setting and rpm setting a constant volume flow, thus fuel rate, independent of speed (We donīt change altitude so massflow is also almost constant).
Third: Because its for jets D is a Force, but for props the specific fuel cunsumption refer to a Power.
And again, range is completly unimportant for me. A piston engine doesnīt care about high or low cruise speeds (slow climb speeds with high power settings may be the exception), nor does it care about propeller settings and so on.
You did understand my example correctly, and my very simple calculations are correct in this case.
Personally i suppose that the La-5FN and La-7 are modelled with the unhistorical larger fuel tanks. This is the only explanation i have for the higher endurance. If so then I hope that the weight is modelled too.
niklas
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First if you know gallons of fuel consumed over a period of time at a specific engine setting you can back out the fuel economy of the engine without knowing velocity or drag.
If you don't know enough about the engine settings (RPM and manifold pressure compared to an engine chart) to infer the horsepower, you may need your equation to back it out from the speed and drag of the plane. But that has to be an even rougher calculation than the ones made in this thread.
Second, at max power you should know the horsepower being used and again the equation is not necessary.
Third, there is no requirement that in order to compare two different planes we have to use conditions where they require the same amount of power. We are normalizing by horsepower to get away from this. But to do that you need to know the horsepower required for each plane to attain a certain speed at a certain altitude. You could use an equation to figure that out, but I prefer using the flight test data.
-blogs
Originally posted by dtango
Yes exactly. Since all the tests results that have been hashed so far mainly deal with the aircraft at constant velocity at a fixed altitude then D*V becomes important. In these cases certainly there is some portion of the flight that fuel flow is mainly a function of SFC*THP(avail) since there's excess power to accelerate the a/c but this is only true until the velocity stabilizes. (Yes, there's also the case where it doesn't matter which you use since power avail = power required which occurs at max level speed.)
Off the top of my head the only time I can think of where you'd be looking at fuel flow = SFC*THP(avail) where you have constant excess power is in a constant speed climb.
The point is FF=SFC*Power(avail or required) which means you can only compare SFC's as indicators of fuel flow if power avail / power required for a given flight condition are equal between a/c which is again clearly not the case between the F6F-5 / F4U-1 vs. the La7.
Tango, XO
412th FS Braunco Mustangs
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Niklas:
REGARDING SPECIFIC ENDURANCE...
To find endurance of an a/c you multiply Specific Endurance (SE) (time/units of fuel) by the amount of fuel you are interested in.
To derive SE you need to know FF since SE = 1/FF. Fuel flow is what is being discussed here (e.g. GPH...etc.).
To find fuel flow we need to know SFC and the power(avail or required) since FF = SFC*Power.
I'm trying to show the relationships that determine fuel flow in an attempt to shed some light on how the different things being hashed fit together with regards to a/c endurance.
Joeblogs- this is the equation for fuel flow rate. At max level-speed yes we know what power roughly is but you can't just drop power from the equation above. You still plug in the known power in the equation above.
The crux of this thread was based around the argument that SFC values at the most economic engine settings between the F6F-5, F4U-1, and La7 were about the same ~.4 lb/HP/hr. I'm pointing out why comparing SFC values doesn't tell the whole story.
REGARDING EQUATIONS FOR JETS OR PROP A/C...
The above equations are for prop a/c. They agree with you exactly when you say for "fuel consumption" for prop a/c refer to power. That is exactly what I'm trying to point out. D*V = power required. At max level-speed power available = power required.
Yes there are multiple forms of the breguet range equation. The reason I listed the equation was to point out that I have been talking about endurance of an a/c and not range.
CORRECTIONS ON MY PART...
I did make an error in logic regarding your ratio. You can use the ratio you stated there for specific parameters of flight you were comparing. So the difference between 35 min vs. 44 min is an interesting anomaly but crowbaby points out some of the issues with this.
Do we know that the La7 in AH at MIL power is at the same engine RPM and manifold settings resulting in the same velocities listed at the stated alt?
2400 1020 575 608 1.020 620 355 0-35
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
... since FF = SFC*Power.
...and SFC is constant for a constant RPM and throttle setting for a prop AC in a given altitude. So is Power. So is FF finally. And this way you can easily determine your flying time. Itīs so simple.
Originally posted by dtango
REGARDING EQUATIONS FOR JETS OR PROP A/C...
The above equations are for prop a/c.
No! First of all your Range formula is the solution of a "differential formula" (?) that is only valid for constant speed and constant cl. As a result rho has to change when the ac gets lighter. This formula describes the fact that you have to fly higher and higher when you get lighter to fly always at the most economic point - FOR JETS.
Because v has a exponent in this formula, this is not valid for props.
The exponent for the range solution is v^(Nv +1). Because Nv = -1 for props the exponent becomes zero, and v^0 = 1. V disappears.
For jets Nv = 0 so v^1 = v.
La-5FN and -7 have same high endurance, it really looks like La-7 enjoys a larger fueltank in AH than in reality (Just an assumption)
btw., german engine performance chart list SFC values for rpm/throttle settings quite often. Those are the g/Ps/h values...
FF for fuelflow is misleading btw. Thereīs either massflow or volumeflow. I assume itīs massflow. g/PS/h * PS = g/h is a massflow.
niklas
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Power is constant for a given constant velocity. Comparing different constant velocities power is different between the velocities. Otherwise you would be able to fly at max level speed at cruise engine settings for instance.
EDIT: Just wanted to clarify- I think I'm discussing things in tangent with you :). As I mentioned earlier, your use of the ratio to get 43 min endurance for the La7 was correct. I made an error in my logic (won't go into it). You are right that fuel flow rate, fuel consumption rate, whatever we want to call is constant for a given constant power. (Actually this thread was so long that I didn't glean the 35min vs. 43min. issue. My bad.)
Regarding the range equations - I used that in reference to point out I was not talking about range. Yes I know the limitations of the equation.
The FF, SE equations are for prop a/c.
Tango, XO
412th FS Braunco Mustangs
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I know it's late, and maybe that's part of the problem, but now I'm starting to get lost. I'm seeing terms such as velocity, range, weight and drag and stuff like that being introduced. I didn't think any of that mattered because the comparison being made is that which how the typical AH pilot flies...100% throttle 100% of the time. Velocity doesn't matter...range doesn't matter...drag doesn't matter, only time matters and is the benchmark. If you could in real life, the comparison would be run by: air-start an LA7 (or Spit) and an F6F at the same exact moment both with their 100% allotment of internal fuel and have them run at 100% throttle and compare how *long* they run. Of course the LA7 will outrun the F6F-5, but we don't care about that (though that is probably due to drag/weight.) At max power drag doesn't matter though. In fact, give both aircraft 100% drag (put them up on chalks or something so they cannot move) and run the test. Start them at the same time and slam the throttles to 100% and time how long they last. They are both probably running at their most inefficient power setting when at 100%, just like how aircraft are flown in AH. Do this at different altitudes if you can. So now the point is to determine if fuel burn rates are as they should be. I bet you an aircraft on chalks running 100% throttle burns the same exact fuel per minute as it does at 100% throttle when in the air. So I'm lost with talk of drag, or range equations and the like. With what little knowledge I have on the subject, I do think something smells fishy here. This thread is a good one and it seems there are some really smart minds who have differing opinions. I do find it very odd that those who create the flight tables for AH which strives and promotes "high fidelity" haven't made a single peep on the matter and only leads me to conclude that a few of you are on to something. But I guess an LA7 at 100% throttle is running that much more efficiently than an F6F-5 at 100% throttle to come up with these numbers AH produces. If drag and velocity and all that mattered for the 100% throttle test, then I'd expect a difference in the resultant time flown between "up on chalks" tests at various altitudes compared to actually flying tests.
Anyway, so far this has been a great topic and I've actually learned a little bit...I think.
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Puke:
So long as you don't add some other performace requirement, like minimum speed or range, your intuition is exactly correct.
When you add those other requirements your are then asking a different question - what is the HP required to deliver that performance? That can be backed out from a formula (crudely) or from flight test data (a little less crudely). Weight, drag and other variables come into play in a problem like that.
One wrinkle we have is that we can only make comparisons with historical documents at certain settings. Crowbaby is to be complemented for doing all those flight tests to compare with the documents we have. I am still trying to sort out all the results myself.
I think the AH guys have to be cautious when they see a thread like this. When we can make sense of all these numbers and present them in a cogent way, then AH should really listen.
BTW I have learned that at least Pratt and Whitney, and probably other firms, developed pages and pages of power and fuel curves for their engines that would be ideal for the questions we are wrestling with. Now if I can just find some...
-Blogs
Originally posted by Puke
I know it's late, and maybe that's part of the problem, but now I'm starting to get lost. I'm seeing terms such as velocity, range, weight and drag and stuff like that being introduced. I didn't think any of that mattered because the comparison being made is that which how the typical AH pilot flies...100% throttle 100% of the time. Velocity doesn't matter...range doesn't matter...drag doesn't matter, only time matters and is the benchmark. If you could in real life, the comparison would be run by: air-start an LA7 (or Spit) and an F6F at the same exact moment both with their 100% allotment of internal fuel and have them run at 100% throttle and compare how *long* they run. Of course the LA7 will outrun the F6F-5, but we don't care about that (though that is probably due to drag/weight.) At max power drag doesn't matter though. In fact, give both aircraft 100% drag (put them up on chalks or something so they cannot move) and run the test. Start them at the same time and slam the throttles to 100% and time how long they last. They are both probably running at their most inefficient power setting when at 100%, just like how aircraft are flown in AH. Do this at different altitudes if you can. So now the point is to determine if fuel burn rates are as they should be. I bet you an aircraft on chalks running 100% throttle burns the same exact fuel per minute as it does at 100% throttle when in the air. So I'm lost with talk of drag, or range equations and the like. With what little knowledge I have on the subject, I do think something smells fishy here. This thread is a good one and it seems there are some really smart minds who have differing opinions. I do find it very odd that those who create the flight tables for AH which strives and promotes "high fidelity" haven't made a single peep on the matter and only leads me to conclude that a few of you are on to something. But I guess an LA7 at 100% throttle is running that much more efficiently than an F6F-5 at 100% throttle to come up with these numbers AH produces. If drag and velocity and all that mattered for the 100% throttle test, then I'd expect a difference in the resultant time flown between "up on chalks" tests at various altitudes compared to actually flying tests.
Anyway, so far this has been a great topic and I've actually learned a little bit...I think.
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Yikes... change "chalks" to "chocks."
It was late when I typed that. But would make a funny image, aircraft on chalk!
:(
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DTango,
Don't want to jump on you about any calculations. The only thing I want to point out is the disparity you metnioned in your last post regarding flight duration of 49 minutes versus 35 minutes.
Consider this.
The SFC for the R2800 at 2 different power settings.
1. Normal power- 2550 44"MAP 1675HP
Fuel per hour 220gallons or 1320lbs
SFC=.78
2. Mil power- 2700 54"MAP 2000HP
Fuel per Hour= 290 Gallons or 1740LBS / 2000
SFC=.87
Now the ASh-82FN.
1. Rating (normal, low) 1500 HP/2300 RPM/6600 ft
Fuel per hour 136gallons or 816lbs / 1500HP
SFC= .54
2 Rating (military, low) 1650 HP/2400 RPM/5400 ft
Fuel per hour 173 Gallons or 1038 lbs /1650HP
SFC=.63
Using these figures provided by the VVS the ASh-82FN is more efficient at producing HP than the PW R2800 by a fair amount, this sounds optimistic considering these ratings were achieved at 93 octane with a copy of a Wright Cyclone engine. But I am not even comlaining about that. In fact I would be happy to accept these numbers.
Here are the numbers as they relate to AH.
F4U-1D
Mil power-49minutes
AH F4U-1D 56minutes (not including the fuel multiplier)
+ 12.5% This is close to real life. Duration would be 24.5minutes instead of 28minutes with multiplier.
La-7
Mil Power 35 minutes
AH La-7 56 minutes
+37.5% This is not in the ballpark. Duration would be 17.5 minutes with the fuel multiplier.
I believe the likes of the P-51, P-47, P-38 and F6F are modeled correctly however the likes of the La-7 and others ie 109, Spit etc need a good look.
Otherwise we will be running round trip raids to London, Berlin and Moscow with the La-7, 109 and Spit in AHII.
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La-7
Mil Power 35 minutes
-F4UDOA
You seem fixated on this particular piece of misinformation no matter how often it's pointed out that this is not the historical endurance time for a full tank at military power - see post above where i highlighted in red.
The figures i came out with if you choose to fly around at 100%RPM/100%MAN (and i still can't believe people do!) were along the lines of a 16% duration increase for the F4u's and 25% or so for the La7. A considerable difference, but irrelevant if you're only flying like this for 5 minutes. The fuel consumption at realistic power settings was far more in accordance with historical records.
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Crowbaby,
Engine management does not exist in AH. So everybody DOES fly around at mil power. However the LA7 is flying with a bottomless gastank in which it did not have.
As are the 109, Spit and others. I just don't have the data for those A/C.
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Originally posted by F4UDOA
Crowbaby,
Engine management does not exist in AH. So everybody DOES fly around at mil power.
Speak for yourself mate. My usual cruise home is done at 50-75% throttle and minimum revs. Lets me take less fuel and bug out later than I would otherwise have to.
ta,
aircav
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Engine management does not exist in AH.
-F4UDOA
I was under the illusion that my throttle and RPM controls worked?
If nobody can use the basic controls that we have now, i don't suppose we'll ever see a more detailed model. Sad, really for a sim....
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If your definition of engine management is a gross throttle control that includes MAP, RPM and throttle then you might as well go play space invaders. When you make such statements you out yourself as a gamer.
Actual engine management includes such things as cowl flaps, intercooler, fuel mixture and RPM controls. Also manual control over supercharger stages and the need to monitor cylinder head tempetures as well as carburator air tempeture. But since we don't do this then
WE DON"T HAVE ENGINE MANAGEMENT!!
It's really very simple.
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Fine.
I like your seond definition of engine management. But if that is how you define it, then saying this:
Engine management does not exist in AH. So everybody DOES fly around at mil power.
as a justification for people flying around at 100%RPM/100%MAN makes absolutely no logical sense whatsoever.
Oh, and by the way, do you accept yet that the 35 minutes in the La7 is not for a full tank?
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When you make such statements you out yourself as a gamer.
-F4UDOA
You are the one who won't use the two engine controls we do have.
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Crowbaby,
Why??
The table of range and flight duration for La-7 No 38103254 with
G full=3265kg, full tank fuel supply - 460 l.
Mode Mode values Level flight
up to dry tanks:
Range, km duration,
h-min
Max. H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl. 355 0-35
speed 3000 1 2400 990 355 0-33
5000 2 2400 1020 355 0-32
7000 2 2400 870 405 0-38
It looks like a full tank to me??
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Originally posted by F4UDOA
Actual engine management includes such things as cowl flaps, intercooler, fuel mixture and RPM controls. Also manual control over supercharger stages and the need to monitor cylinder head tempetures as well as carburator air tempeture. But since we don't do this then
Surely we DO have rpm control. :confused:
Would you prefer no engine controls to some (i.e. the two we have?).
Re: supercharger control, it's variable depending on aircraft. Most RAF aircraft were fitted with automatic boost control. This limited boost levels (your MAP?) to safe levels irresective of throttle position. It was there difficult if not impossible to overboost the engine below its rated altitude. AFAIK supercharger speed changes were also carried out automatically based on ambient pressure.
I believe engine/propellor managment on some German aircraft (Fw-190 and others?) was even more automated.
In contrast, the American radials grew out of many years of civil engine development, where a flight engineer was on hand to monitor and control various engine functions. I believe the majority were no fitted with anything comparable to ABC. Therefore if the pilot firewalled the throttle at low altitude, there was a real chance of damaging the engine through overboost. I don't know whether supercharger speed control was manual or not.
So the level of automation (simplification?) we have in AH is more accurate for some aircraft than others.
regards,
aircav
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Crowbaby,
I don't feel superior to anybody. But honestly you are all over the place with your arguements.
Explain your comment please:
You are the one who won't use the two engine controls we do have.
What two engine controls?
Do you have a seperate RPM and throttle control? Are you including the engine on/off switch?
Frankly I don't know what your talking about half the time.
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Originally posted by F4UDOA
Do you have a seperate RPM and throttle control?
Yes.
http://www.hitechcreations.com/htcindex.html
Have a look in Help...Key Commands.
The default keys for rpm up/down are the +/- keys on the keypad.
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It looks like a full tank to me??
-F4UDOA
You are reading the summary rather than the tests. Above what you have quoted are the actual tests.
(reformatted only for clarity)
Chart of range and level flight duration of a/c La-7 No38103254
at different flight modes
at V/n=const (constant speed and RPM),
G tot=3265kg (total weight)
and V fuel=460 l (fuel volume)
H=1000m (1st speed of supercharger),
fuel supply for level flight - 365 l
RPM - 2400
Supercharg. pressure,
mm of merc. pile - 1020
Speed, km/h - IAS575
----------------- TAS 608
lit./km - 1.020
lit./h - 620
Till the dry tank:
Range of Level flight km - 355
level flight, duration, h-min - 0-35
The drop from 460litres to the "fuel supply for level flight - 365l" is because of this :
1. For range and flight duration calculations the following fuel consumptions
are taken into account:
a) for engine work on the ground (warming-up and engine test, taxiing to and
from the start) 35 l per 15 min;
b) for climb to: 1000m - 15 l; 3000 m - 55 l; 7000 m - 80 l;
c) for circle flight before landing - 45 l.
I've cut and pasted this from the test data you didn't read properly in the previous posts you didn't bother to read.
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aircav,
Sorry, not really argueing with you.
Your point is correct about some A/C. But I assure you that the P&W R-2800 had variable supercharger controls which could be usd to the pilots advantage as far as overboosting for periods of time while watching the tempeture control. This was recorded numerous times during the war with P-47, F6f and F4U pilots overboosting there engines during emergency's. In fact these engines were proven to be durable if not reliable under stresses well beyond factory reccomendations or limits.
FYI, MAP (boost) and RPM are not tied together. They are however in AH. I know for a fact you could hold MAP and reduce RPM on the R2800. In AH it is one control for everything from fuel mixture cylinder head temp.
This is really a whole different subject.
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This is a great thread.
F4 you have to own up that crow has shown you the error in your assumptions. The tests where done with 365 litres not 460 Litres.
When I grow up I want to be able to have a reasonable debate like you two can.
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Originally posted by F4UDOA
FYI, MAP (boost) and RPM are not tied together. They are however in AH. I know for a fact you could hold MAP and reduce RPM on the R2800. In AH it is one control for everything from fuel mixture cylinder head temp.
Ok. I'm almost certain it's me that's being dense, so excuse me if that's so. But I was SURE than I can reduce revs in AH while keeping the boost needle at max. Although it does sometimes seem to be airspeed dependent. Not at home right now so can't test. Probably talking out my arse; watch this space...
[ed] The same was true of the Merlin. The most fuel efficient cruise setting was low revs, high(ish) boost, rather than vice versa; although both may have given you an identical power.
"Don't fly at night either fast or slow
With your revs too high, or your boost too low
Or you'll run out of fuel with a long way to go
And you won't get home in the morning"
- Bomber Command
:)
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Actual engine management includes such things as cowl flaps, intercooler, fuel mixture and RPM controls.
--------------------------------------------------
What two engine controls?
Do you have a seperate RPM and throttle control? Are you including the engine on/off switch?
Frankly I don't know what your talking about half the time.
-F4UDOA
I really felt for you when you said this, cos we've all been stupidly, blatantly wrong at some stage in our lives. I resisted the temptation to call you "Clueless" as you did to me.
However, I just can't read your recovery with a straight face.
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Congradulations,
You win the prize. We can manage RPM as well. I have been here since early beta and never used it. I think that actually proves my point about lack of engine control and management.
Back to the main point.
In any case I will use the reduced fuel number to calculate SFC.
Ready?
Max. H=1000m(1st sup.sp.),n=2400, Ps=1020mm Me.pl. 355 0-35
365litres=96.4 gallons burned in 35minutes or 136.5GPH for 60minutes
136.5gallons=819LBS/1650HP
SFC= .496
In other words the La-7 (ASH-82FN ) is as efficent at full military power than the R-2800 is at cruise even with 93octane fuel. In fact it is almost twice as efficient.
Does this sound right to you?
Do you realize the ASH-82FN is essentially the same engine as was in the FM-2? The FM-2 produced 1350HP with 100octane at 2700RPM.
I had no idea the Soviets were so advanced in 1943.
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Here is another way to look at it.
HP/lbs of fuel burned in one hour.
ASH-82FN
1650HP / 819LBS per hour
= 2.01HP per 1LBS of fuel burned in a hour.
P&W R2800
2000HP / 1740LBS per hour
= 1.15HP per 1LBS of fuel burned per hour
Wow those Russians were years ahead of us. How did we ever catch up?
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Hmmm, LA7 data might not be right?
Can anyone say, Stalin?
He never sent any engineers to the Gulag, did he?
Or worse, shot?
:D
Jeff
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Speak for yourself mate. My usual cruise home is done at 50-75% throttle and minimum revs. Lets me take less fuel and bug out later than I would otherwise have to. -aircav
Why does this keep coming up in this thread? I must be missing something. I'm sure both aircraft's engines can run for a while with precise engine management, but I thought this comparison was ONLY about time of flight between an LA7 and F6F running 100% full throttle/RPM. BOTH are being inefficient and are the results in Aces High close to being correct. Not sure why this other stuff keeps coming up.
The same was true of the Merlin. The most fuel efficient cruise setting was low revs, high(ish) boost, rather than vice versa; although both may have given you an identical power. -aircav
That's not what this thread is about. We aren't looking how to squeeze the most out of our engines. Just comparing 100% throttle between small fueld aircraft and the large gas tank aircraft.
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I was responding to a blanket statement that engine management does not exist in AH. It does, for those people that choose to use it. If you do not, and run out of fuel.....:rolleyes:
-aircav
I agree however, that it is straying off the original topic. See the 'Engine RPM / MAP' thread for more.
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Actually no - we are pretty sure The LA-7 is modeled so that at military power it burns fuel as if the engine is on auto-lean. The resulting discrepancy in endurance is on the order of 100 percent, when compared to a comparable American engine.
The discepancy is not quite so large when it is measured against the flight test data we have for the La-7. But even that data seems too optimistic to be correct. I have been trying to work out some way to resolve the conflicting numbers but I can't.
We've also discovered a smaller discrepancy between actual data and AH when running the r2800 at military power (crowbaby's tests). But the error here is only on the order of 15 percent.
-Blogs
Originally posted by Puke
Why does this keep coming up in this thread? I must be missing something. I'm sure both aircraft's engines can run for a while with precise engine management, but I thought this comparison was ONLY about time of flight between an LA7 and F6F running 100% full throttle/RPM. BOTH are being inefficient and are the results in Aces High close to being correct. Not sure why this other stuff keeps coming up.
That's not what this thread is about. We aren't looking how to squeeze the most out of our engines. Just comparing 100% throttle between small fueld aircraft and the large gas tank aircraft.