Author Topic: How good is the LA-7's Engine?  (Read 4272 times)

Offline joeblogs

  • Nickel Member
  • ***
  • Posts: 649
How good is the LA-7's Engine?
« on: January 22, 2003, 12:43:31 PM »
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
« Last Edit: January 22, 2003, 03:08:35 PM by joeblogs »

Offline Karnak

  • Radioactive Member
  • *******
  • Posts: 23047
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #1 on: January 22, 2003, 03:13:25 PM »
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.
Petals floating by,
      Drift through my woman's hand,
             As she remembers me-

Offline F4UDOA

  • Silver Member
  • ****
  • Posts: 1731
      • http://mywebpages.comcast.net/markw4/index.html
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #2 on: January 22, 2003, 05:36:35 PM »
Joe Blogs.

I will begin beating the wardrums ASAP!!

Offline funkedup

  • Plutonium Member
  • *******
  • Posts: 9466
      • http://www.raf303.org/
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #3 on: January 22, 2003, 05:45:22 PM »
Beating war drums about what?   Anybody bother comparing AH lb/hp/hr to the real figures?

Offline joeblogs

  • Nickel Member
  • ***
  • Posts: 649
Uh yeah we did
« Reply #4 on: January 22, 2003, 08:25:03 PM »
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


Quote
Originally posted by funkedup
Beating war drums about what?   Anybody bother comparing AH lb/hp/hr to the real figures?

Offline funkedup

  • Plutonium Member
  • *******
  • Posts: 9466
      • http://www.raf303.org/
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #5 on: January 22, 2003, 08:26:33 PM »
Good.

Offline F4UDOA

  • Silver Member
  • ****
  • Posts: 1731
      • http://mywebpages.comcast.net/markw4/index.html
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #6 on: January 22, 2003, 08:27:26 PM »
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.

Offline funkedup

  • Plutonium Member
  • *******
  • Posts: 9466
      • http://www.raf303.org/
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #7 on: January 22, 2003, 09:00:48 PM »
Can you direct me to that?  What SFC have you measured for the La-7 in Aces High?

Offline F4UDOA

  • Silver Member
  • ****
  • Posts: 1731
      • http://mywebpages.comcast.net/markw4/index.html
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #8 on: January 22, 2003, 09:21:46 PM »
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............

Offline joeblogs

  • Nickel Member
  • ***
  • Posts: 649
that thread
« Reply #9 on: January 22, 2003, 09:32:28 PM »
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

Quote
Originally posted by funkedup
Can you direct me to that?  What SFC have you measured for the La-7 in Aces High?

Offline funkedup

  • Plutonium Member
  • *******
  • Posts: 9466
      • http://www.raf303.org/
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #10 on: January 22, 2003, 09:40:15 PM »
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.
« Last Edit: January 22, 2003, 10:30:58 PM by funkedup »

Offline DB603

  • Nickel Member
  • ***
  • Posts: 375
La5FN/La7
« Reply #11 on: January 23, 2003, 02:25:47 AM »
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.

Offline crowbaby

  • Copper Member
  • **
  • Posts: 223
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #12 on: January 23, 2003, 03:50:57 AM »
>>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!!!

Offline Karnak

  • Radioactive Member
  • *******
  • Posts: 23047
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #13 on: January 23, 2003, 04:16:49 AM »
Quote
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

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.
« Last Edit: January 23, 2003, 04:28:12 AM by Karnak »
Petals floating by,
      Drift through my woman's hand,
             As she remembers me-

Offline crowbaby

  • Copper Member
  • **
  • Posts: 223
Wilkinson on the ASH-82FN (on the LA-7)
« Reply #14 on: January 23, 2003, 04:21:07 AM »
Oops. Just read through that other thread. How vain of me to think i could stop the madness..........