Why the La7 is so Uber(important)

[Spritle]

J_A_B,

You don't get something for nothing.  I don't know what kind of HP the La-7 engine has, but I believe this statement would hold true.  

Assuming equivalant efficiency if both engines produce approximately the same HP at WEP they will both use approximately the same amount of fuel regardless of the differences in MAP.  

It's a mass flow rate equation I believe.  You put fuel and air in and get power and heat out.  Both sides of the equation HAVE to equal.  

I believe 1 gallon of gas is 125,000 Btu.  4 stroke engines have pretty crappy efficiency ~20+/-%.  Higher compression ratio engines TEND to have better efficiency.

F4UDOA,

What you might be missing is this.  The La-7 often didn't have far to travel to the fight in real life as you stated.  In the MA this isn't true, but if the La-7 can utilize a lower power setting to get to the fight (due to less drag) then he will have burned less fuel.  But in regards to this:

The Hellcat has almost the same exact fuel duration as the La7 in the MA. According to the posted chart the F6F has 30minutes of flight time at full throttle mil power and the La7 has 28 minutes.

Internal fuel loads

La7 122 gallons

F6F 250 gallons

That doesn't seem right.  Assuming that full throttle mil power means that both engines are making their full rated HP for that altitude I would say that the fuel burn rates would be some how proportional to their HP outputs.  

Spritle

[214thCavalier]

JAB

Regarding the F6F-5 and fuel consumption rates at Mil and cruise settings.

Arena fuel burn at 1.5

12,000ft with 2x 1k eggs, rockets and 100% internal fuel, from a worst of 38 minutes and 160 miles, using the correct cruise settings you can get the F6F-5 to fly for 125 minutes and cover 360 miles.

[F4UDOA]

Spritle,

For some reason your the only one who is getting my point.

In fact you hit the nail on the head.

How does an engine in the La7 develope 1850HP and only burn a fraction of the fuel of an engine that generates 2000HP?

JAB,

I don't know that the fuel burn in cruise is proportional to fuel burn in military. If it was I would do that. In fact it is not the same from the F6F to the F4U with an identical engine. The F4U has a more economical cruise by about 10GPH.

And even if the La7 had a fuel burn of approx. 140GPH and the F6F has a fuel burn of 280 GPH then the La7 is much more efficient than the Pratt&Whitney R2800. Last time I checked the Russians had to capture a B-29 to copy a Pratt&Whitney.

F6F
2000HP Mil.
280 GPH

7.14 HP per Gallon of fuel per hour

La-7
1850
140 GPH???

13.21 HP per Gallon of fuel per hour

Meaning the La7 would be almost TWICE as efficient as the F6F!! Actually the number is 1.85 times more efficient.

Wow, I had no idea the Soviets were so advanced in 1944


Seriously I doubt this is true.

In fact if both engines were equally as efficient in producing HP then you could take the 30 minute fuel duration number for the F6F and multiply it  by 1.85 to even the playing field then the F6F flight time at mil power would be

55.22Minutes in the MA on full internal fuel at mil power!!

Meaning that the long range F6F would only have to fly with half of the internal fuel percentage (albeit still more volume than the La-7) to accomplish the same mission as the short range La-7. IE La-7 100% fuel 122 Gallons to the F6F 50% fuel 125 Gallons.

Hmm, sounds like reality to me:D

Cav,

I am comparing apples to apples. Mil power to Mil power. The F6F should have twice the range of the La-7 no DT's on either in cruise or mil power all things being equal.

[214thCavalier]

Yes F4UDOA i understand thats why my post was aimed at JAB just as information he had asked about.
Some of the difference could easily be explained by engine efficiency however what your describing is pushing it a bit.
I have no idea of the specifics of these 2 engines but for example compression ratios, combustion chamber shape, spark plug positioning and even the amount per cylinder, metal the bores and cylinder heads are manufactured from can all have significant effects on an engines efficiency. Also what fuel grade where they using in each plane ?

Spritle your post does not really hold water as you are making some huge assumptions that the efficiency of the engines is the same, if it was and they produced the same HP  (which they dont) then yes i would agree.

[J_A_B]

"Arena fuel burn at 1.5 "

I thought it was 2.0 in the MA.  



Anyway......

F4UDOA, your mistake is in the assumption that these engines are equal, or anywhere close to it.   In truth, the R-2800 develops FAR more power than the M-82FN.  2200 max in the F6F compared to 1850 max for the LA7, a 350 HP difference.  NOTE:  1850 represents WEP for the LA7, NOT MIL power!

The R-2800 runs at 300 more RPM and 11'' more MAP with WEP.  At military power, the disparity is even greater--a full 13'' MAP and the same 300 RPM difference between the R-2800 and the M-82FN.

What makes you think that these engines would be anywhere close in fuel consumption at military power?   They're running at different power settings and developing different amounts of power--there is absolutely no reason NOT to expect the R-2800 to use a lot more fuel at MIL power.   More MAP, more RPM means more power, and more fuel consumption.   Heck, the R-2800 at MIL power is running more MAP and RPM than the M-82FN does with WEP!

At best cruise settings, I'd expect these engines to be a lot closer in fuel use--the R-2800 has a cruise setting of 34'' 2150 RPM, and the M-82FN cruises at 30'' 2000 RPM.  Even then the R-2800 would be making more power and using somewhat more fuel, but it'd be a lot closer.

In truth, these engines are very similar--at low to medium power settings.   The big difference is the R-2800 can develop MORE power than the M-82FN because it is rated for higher power settings.  The R-2800 is simply a better engine.   I'd bet that if you ran the R-2800 at the same settings as the M-82FN, it'd get roughly equal fuel use in AH.  

The LA7 is 7000 lbs, compared to around 12000 lbs for a loaded F6F....THAT is why the F6F needs so much power to haul itself around.

What you have to remember is "military power" is not some magical benchmark for fuel economy comparison.  It just represents the max power settings the engine was rated to run at for any length of time.  All else being equal, an engine rated for more power will use more fuel.  It's that simple.  If you want to actually compare their fuel consumption, compare them at equal RPM's and MAP, and even then it's not totally equal because of differences in compression ratio, engine valve design, etc.

Am I saying AH is definately right?  No.  I AM saying you're trying to over-simplify this issue and trying to comapre things which shouldn't really be compared.

J_A_B

[Spritle]

214thCavalier,

Actually my post holds a huge amount of water.  Otto cycle 4 stroke gas engines ALL have crappy efficiency PERIOD!  Diesels are much more efficient.  While ALL of the factors that you listed DO play a part in the overall efficiency of an engine they are NOT going to amount to a 100% difference!  Did you hear that?

Are you actually suggesting that the Russians in 1944 somehow developed an engine that was TWICE as efficient as any of its contemporaries?!?!?!?  NOT!

Now for the next lesson.  It is NOT easy to increase the efficiency of an engine.  Even today’s completely computer controlled, computer designed, advanced materials and manufacturing engines are NOT even 10% more efficient than those aircraft engines.  Do you know why?  For a hint re-read my post.

There is NO way that an engine that produces 1750 HP is only going to consume half the fuel of an engine producing 2000 HP if both engines are under full load.  

Spritle

[F4UDOA]

JAB,

I know I am over simplifying, and I expect the R2800 to burn more fuel in a larger A/C.

However I am doing it to make a point.

1. I did not find WEP rating and mil rating on the La-7. Do you know what the Mil power number is for the La-7?

2. I am comparing GPH to generate 1 HP. I was coming up with 1.85 for the La-7 compared to the F6F. This ratio is very high.

How can an aircraft that produces 1850HP and runs at Mil power with a fuel tank of 122 gallons can have the same duration as an A/C that has twice the internal fuel and produces 2250HP?

The La-7 produces 82% of the HP(1850HP) of the F6F(2250HP) but only uses 49% of the fuel in the same amount of time? Does this sound right? It doesn't to me.

One last thing. The P-51D with the Merlin V-1650-7 used 180 GPH at mil power. And It was 12 cylinders and produced 1490HP and it was liquid cooled. By comparison it is a gas guzzler compared to Honda civic of the air(La-7).

BTW. If you have gallon per hour numbers on the Spit IX, FW190A or 109G I would luv to do the same comparison. Frankly I'm surprised nobody has come up with these.

[J_A_B]

"I did not find WEP rating and mil rating on the La-7. Do you know what the Mil power number is for the La-7? "

I know the RPM and MAP values, but I do not have actual power figures MIL power for the LA7's M-82FN engine.  At WEP the LA7 reaches 1850 HP.  Of note is the fact that WEP on the LA7 adds more MAP than WEP on the F6F, so the LA7 likely has more power loss from WEP to MIL than the F6F does.  This large drop in power is supported by the plane's massive drop in performance in MIL compared to WEP.

I estimate the LA7 makes around 1500HP on MIL power, perhaps slightly less.  That is merely an estimate though and certainly not "fact".  I also estimate that WEP on the LA7 would increase fuel usage to around 200 GPH, although this guess is too much of a "ballpark figure" to be of any real use.

While this would mean the M-82FN is still more efficient at MIL power than the R-2800, this is not unexpected since the R-2800 is developing a lot more power--as you increase power you will lose more and more efficiency.  

Basically, MIL power in the LA7 is equal to a high cruise setting in the F6F, in terms of both fuel usage AND power output.  

J_A_B

[F4UDOA]

JAB,

Like I said. I don't have the numbersfor La-7 fuel consumption.

But even if the Mil power La-7 HP rating is 1500HP that is still equal in output to the Merlin 12 cylinder at 60"+MAP at mil power sucking down 180GPH.

Speaking of which. The Spit IX uses a similar engine to the Mustang with a fuel capacity of 137 gallons. That should give it a fuel duration of .76 hours at mil power.

Compared to the F6F which has a 250 gallon tank and a 280GPH for a duration of .89 Hours.

So you might expect the F6F to have an advantage?

Well In AH the F6F has 30minutes of flight time and the Spit IX has 35minutes. I just don't think this is right.

[J_A_B]

Where are you getting your fuel consumption numbers?  They are different than what I can find.

You quote 280 GPH for the F6F at MIL power.

The info I can find all says around 250 GPH at MIL, and about 280-290 GPH at WEP.


You quote 180 GPH for the Merlin, presumably a Mustang Merlin.

The info I find generally says about 150 GPH in MIL, and 200-210 in WEP.

Generally your consumption figures are higher than mine.  It seems almost as if you're quoting WEP numbers instead of MIL numbers.

Of note, if YOUR F6F MIL comsumption figure is correct, then the F6F actually has TOO MUCH range in AH at MIL power.   Think about that for a minute.


I will re-check every source I can find, and I suggest you do the same.

J_A_B

[Blue Mako]

Why do people insist on comparing apples and oranges all the time?

Engine output is a function of Torque, RPM, fuel mixture, compression ratio, engine efficiency etc etc

Just because an engine produces less horsepower does not mean it is necessarily less fuel hungry.

From what J_A_B posted the F6F fuel consumption figures look fine.  Until someone posts some figures for the La-7, this argument is pure speculation.

[214thCavalier]

JAB MA is 2.0 those fuel tests were done for a Scenario which used a 1.5 fuel modifier.

Some of the difference could easily be explained by engine efficiency however what your describing is pushing it a bit.

Spritle you Tard you seem to have the impression i am saying the LA7 is twice as efficient as the F6F, I suggest you go and read my post again then POINT out to me where i say that.

[F4UDOA]

Blue Mako,

Your making my point for me and it's not apples and oranges.

I am comparing two radial engine fighters with comprable HP in the F6F and La-7. Then I am comparing the P-51D Mustang and Spit IX.

Frankly I'm surprised more people don't recognize this as a problem.

Why does a short range fighter like a Spit have greater range than the F6F?? Does this make sense? And it makes the F6F fight at a hugh disadvantage by carrying way to much fuel into combat reducing performance greatly. Same for the P-51, F4U, P-38 and P-47 or any other long range fighter.

JAB,

My numbers for the P-51, P-47, F4U, F6F all come from the pilots manuals. In fact the P-47, F6F and F4U numbers for consumption are all practically identical.

I have hard copies of these but you can see (almost see) most of the numbers here.

Zeno's They don't have the F6F but here are two R2800's

Here is the P-47



Here is the F4U

[F4UDOA]

BTW JAB,

Your point about WEP on the La7 is really moot.

The fuel consumption number that are always used are never sea level numbers.

The La-7 has no measurable WEP affect above very low altitudes.

And here is the P-51 fuel consumption

In low blower mil power the number is 180GPH

High blower is 140GPH. Who in AH flys at High Blower Alts?? This applies to Mustangs and especially Spits.

[ra]

I know I am over simplifying, and I expect the R2800 to burn more fuel in a larger A/C.

Any aircraft engine burns about the same amount of fuel for a given power setting/altitude regardless of the plane it is bolted to.  

ra