How good is the LA-7's Engine?

[Karnak]

Read my test and tell me where I made the mistake.

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.

[crowbaby]

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...

[Karnak]

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.

[crowbaby]

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).

[joeblogs]

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.

[crowbaby]

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?

[crowbaby]

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....

[joeblogs]

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?

[crowbaby]

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)

[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
My AH homepage

[joeblogs]

Try this for starters. - Blogs

Originally posted by crowbaby
My results on the La7 at the above settings.

...

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.

[crowbaby]

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) but not as good as I'd expect from looking at the data posted on Tilt's site here. 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
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.)

[joeblogs]

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) but not as good as I'd expect from looking at the data posted on Tilt's site here.

[crowbaby]

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.

[Dnil]

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.