How good is the LA-7's Engine?

[joeblogs]

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?

[crowbaby]

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.

[F4UDOA]

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.


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.

[F4UDOA]

Joe Blogs,

Just read your last post.

You are EXACTLY right.

[Tilt]

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.

[crowbaby]

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.

[F4UDOA]

Clueless

[Puke]

Can you guys test against another small fueled aircraft so Crowbaby doesn't cry-baby anymore?

[frank3]

LLv34_Snefens, I couldnt help noticing you've got a pic under your name, could you tell me how to do that please?

[Imp]

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.

[niklas]

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

[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

[J_A_B]

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

[crowbaby]

<
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.

[dtango]

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