# 1950: Lavochkin La-9 v.s Grumman F8F-1B Bearcat



## ShVAK (Sep 22, 2012)

Two of the last piston engine fighters from two families of aircraft with successful WWII combat histories, and on opposing sides at the onset of the Korean War not long before MiGs and Sabres usurped the fighter throne. Both very impressive performers, the Grumman setting a number of records and later a Reno favorite. 

I can't find any evidence of KPAF La-9's and Bearcats (cannon armed -1B models or otherwise) shooting it out but from looking at the numbers, they seem like a pretty close match. From Wiki: 

*Lavochkin La-9*







General characteristics

Crew: 1
Length: 8.63 m (28 ft 4 in)
Wingspan: 9.80 m (32 ft 2 in)
Height: 3.56 m (11 ft 8 in)
Wing area: 17.6 m² (189 ft²)
Empty weight: 2,638 kg (5,816 lb)
Loaded weight: 3,425 kg (7,551 lb)
Max. takeoff weight: 3,676 kg (8,104 lb)
Powerplant: 1 × Shvetsov ASh-82FN air-cooled radial engine with a two-stage supercharger and fuel injection, 1,380 kW (1,850 hp)

Performance

Maximum speed: 690 km/h (428 mph) at altitude
Range: 1,735 km (1,077 mi)
Service ceiling: 10,800 m (35,433 ft)
Rate of climb: 17.7 m/s (3,484 ft/min)
Wing loading: 195 kg/m² (40 lb/ft²)
Power/mass: 0.40 kW/kg (0.25 hp/lb)

Armament

4 × 23 mm Nudelman-Suranov NS-23 cannons, 75 rpg

*Grumman F8F-1B Bearcat*






General characteristics

Crew: 1 pilot
Length: 28 ft 3 in (8.61 m)
Wingspan: 35 ft 10 in (10.92 m)
Height: 13 ft 9 in (4.21 m)
Wing area: 244 ft²[38] (22.67 m²)
Empty weight: 7,070 lb (3,207 kg)
Loaded weight: 9,600 lb (4,354 kg)
Max. takeoff weight: 12,947 lb (5,873 kg)
Powerplant: 1 × Pratt Whitney R-2800-34W "Double Wasp" two-row radial engine, 2,100 hp (1,567 kW)

Performance

Maximum speed: 421 mph (366 kn, 678 km/h)
Range: 1,105 mi (1,778 km)
Service ceiling: 38,700 ft (11,796 m)
Rate of climb: 4,570 ft/min (23.2 m/s)
Wing loading: 66.7 lb/ft² (192.1 kg/m²)
Power/mass: 0.22 hp/lb (360 W/kg)

Armament

Guns: 4 × 20mm M3 cannon
Rockets: 4 × 5 in (127 mm) unguided rockets
Bombs: 1,000 lb (454 kg) bombs


Given pilots of equal skill in our hypothetical over Korea, which fighter would've won the day? Discuss.


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## Juha (Sep 23, 2012)

Even if I'm Bearcat abd Sea Fury fan I must admit that according to Ray Hanna La-9 was even better than those 2 carrier fighters. Oh, at least Bearcat climbed better.

Juha


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## ShVAK (Sep 23, 2012)

La-9 did seem more aerodynamically advanced than the Bearcat. Laminar flow wing and all that. That doesn't necessarily make it a better dogfighter, even Griffon Spitfires could always outturn a P-51. 

The Bearcat made up for a lot in brute P&W power. Would've probably been the fastest-climbing fighter on Earth in '46.


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## spicmart (Sep 23, 2012)

Off topic, the La-9 is much more pleasing to the eye imo.

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## ShVAK (Sep 23, 2012)

spicmart said:


> Off topic, the La-9 is much more pleasing to the eye imo.



I agree though the Bearcat has its own appeal. Kind of like a 60's muscle car with wings.


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## Gogler (May 10, 2015)

From what I have heard the F8F has a excellently designed airfoil which has exceptional low-speed performance while also having fairly low drag at high speed. Unfortuanatly I have not heard anything about the La-9. Hope that helps.


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## Shortround6 (May 11, 2015)

A few notes, The ASh-82FN engine used a two _speed_, supercharger, not a two _stage_ one. 

Either plane has enough firepower to destroy the other given even a second or more with a good firing position/solution. _However_ the MV of the Russian guns are are almost 150m/sec slower than the 20mm guns on the Bearcat meaning it needs more lead at a given distance/firing angle. The Russian plane has about 9-10 seconds of firing time, give or take. The Bearcat has about 14 seconds on the outer guns and 17 seconds on the inner guns. Bearcat carried 188rpg for the outer guns and 225rpg on the inner guns and the Bearcats guns had a higher cycle rate. 

The R-2800 engine on the Bearcat is a bit under-rated. It had water injection and the 2100hp rating is for 100/130 fuel and no water. It was good for 2300hp dry using 115/145 fuel for take-off/military power and 2100hp at about 3200ft. It also had 1700hp at 17,000ft. I can't find figures for the water injection. 

The ASh-82FN _may_ have had 1850hp for take-off and 1650hp at 5400ft military rating and 1450hp at 15,200ft in high gear. 

ranges given for both planes seem to require drop tanks. 

In air to air combat both planes would be operating at "normal" loaded weight or _below_ so the given wing loading for the Bearcat is nonsense. Both planes would have a wing loading within 2-3% of each other.


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## Koopernic (May 12, 2015)

Gogler said:


> From what I have heard the F8F has a excellently designed airfoil which has exceptional low-speed performance while also having fairly low drag at high speed. Unfortuanatly I have not heard anything about the La-9. Hope that helps.



Bearcat has NACA 5 digit: same as every other USN fighter and the Fw 190. The deft choice of wing platform, wing twist of course make a big difference as does other aspects such as tail moment arm, decollage. Bearcat canted its engine down and to the side by 2 degrees to neatly overcome engine torque issues. It was refined.

See:
The Incomplete Guide to Airfoil Usage

I see the La 9 as belonging to the same era as the P-80.

La 9 did have a laminar airfoil, Russians took a lot of time getting this right as the La 7 needed slats to tame the stall/spin.

One poster mentioned the Griffon Spitfire v the P-51. I believe the appropriate comparison would be between the P-51H and the Spitfire and I suspect the P51 might come out on top.

One aspect that I believe will be absolutely decisive assuming the aircraft are matched in other areas is the bubble canopy of the Bearcat. When the Soviets captured a F-86 Sabre during the Korean war they were stunned at how much a difference the bubble canopy made: the Satbre pilot could not only seen behind himself but slightly below both by turning or by using his mirror. This is a big factor in situational awareness and the decision making loop of the pilot.


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## GregP (May 12, 2015)

This is a tough call and I like both airplanes.

I'll have to waffle and say the better pilot would likely prevail ... though I've never seen a roll-rate comparison or a turn-rate comparison between the two. Seeing one or the other might sway the argument, but all I have seen is a one-man general statement from Ray Hanna, who well might have been drumming up business for the La-9 ... I don't know. 

I have no trouble believing the La-9 was a very good airplane, and really have no basis for choosing either one as a winner except for a climb-rate advantage for the F8F. That is important, but so are roll and turn.

One definite advantage for the La-9 is centerline armament. I understand the NS-23 cannons are VERY hard-hitting, MUCH more so than our cannons. The Germans always said one in the nose is worth two in the wings. If that is the case the La-9 outguns the F8F, even with synchronizing. 

Though I love the Bearcat, the La-9 is a more pleasing look to me, sacrilege though it might be to say.

I'd really like to see performance graphs (not just speed) for the La-7 before engaging mouth here any farther.

Good subject! Maybe some real performance numbers will show up!

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## tyrodtom (May 12, 2015)

Koopernic said:


> One aspect that I believe will be absolutely decisive assuming the aircraft are matched in other areas is the bubble canopy of the Bearcat. When the Soviets captured a F-86 Sabre during the Korean war they were stunned at how much a difference the bubble canopy made: the Satbre pilot could not only seen behind himself but slightly below both by turning or by using his mirror. This is a big factor in situational awareness and the decision making loop of the pilot.



Why would the Russians be " stunned" by the view from a bubble canopy ? The Mig 15 had a full 360 degree view also, just one small reinforcing rib to the rear, as did the Mig 9, even the piston engine Yak 9 had a full vision canopy, and several other Russian aircraft.

The Mig-15 pilot might have been more down in the fuselage than a F-86 pilot, so no matter if his canopy was a true bubble canopy or not he still wouldn't have been able to see below him to the rear.

They might have been a little surprised by the clarity of the Plexiglas, because their clear plastics of that era tended to be a little less clear than ours.


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## GregP (May 12, 2015)

I think the ASh-82FN was rated at 1,650 HP for [email protected]" HG, 1,430HP @ 40.7" HG @16,404 feet, and 800HP @ 32,808 feet. 

The 1,850 HP was the ASh-82FNU. Now some later La-9's might well have had the FNU, but all the specifications I can find say FN, not FNU.

It might be interesting to compare an La-9 with the FNU engine to an F8F-2 as both has slightly more HP.

For those of us who followed the great fighter gun debate, the Q-factor for the cannons was 10.1 for the AN/M3 and 11.8 for the NS-23. The NS-23 had a muzzle velocity of 680 m/s and the M3 had a muzzle velocity of 840 m/s, but the close Q factors tell us the NS-23 hit about 10% harder. The F8F firee from the wings without synchronization and the NS-23 fired through the prop with synchronization. I do NOT know the rate if fire reduction to allow for synchronizing, but the four NS-23's were mounted centerline while the four M3's were in the wings. I'f think that if the F8F got a bead on the La-9 and got hits, it would surely have maybe 25 - 30% more hits in any given timeframe. With the Q-factors being close, I'd give the hitting power advantage to the F8F but would give the liklihood of getting hits to the centerline mounted La-9's 4 guns.

Using the 1,650 HP for the FN model ASh engine, I have the power to weight ratios as almost identical. I think the rate of climb difference might indicate propeller efficiency or maybe airfoil differences or evena combination of both since the wing loading at normal weighs are 39.3 lbs/ sq ft for the Bearcat and 40 lbs/sq ft for the La-9.

I can say from personal experience that clear Plexi was an advantage for the F8F. I have yet to sit in a WWII/post-war through Korea Soviet aircraft that had a CLEAR windscreen and canopy. All I have been in (at least 10) have been slightly brownish in tint except for one that had a new canopy fitted here in the USA. I have one friend who had a Yak-52. He retrofitted a US plexi front canopy and left the rear canopy stock. The difference is quite noticeable between the seats.

A winner would be a tough call, again!


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## Koopernic (May 12, 2015)

tyrodtom said:


> Why would the Russians be " stunned" by the view from a bubble canopy ? The Mig 15 had a full 360 degree view also, just one small reinforcing rib to the rear, as did the Mig 9, even the piston engine Yak 9 had a full vision canopy, and several other Russian aircraft.
> 
> The Mig-15 pilot might have been more down in the fuselage than a F-86 pilot, so no matter if his canopy was a true bubble canopy or not he still wouldn't have been able to see below him to the rear.
> 
> They might have been a little surprised by the clarity of the Plexiglas, because their clear plastics of that era tended to be a little less clear than ours.



The pilot sat higher in the F-86 and the F-86 had a somehat lower tail than the MiG 15. The superior view over the rear was quite noticeable and it was considered harder to sneak up on an F-86.

But I digress:

The La 9 does not have a bubble canopy, the Bearcat does and I suspect a rather good one. Hence I would give it to the Bearcat just on this. The view over the nose on the Bearcat might be better too given the apparently higher seating arrangement. Navy aviators tend to be fussy about this due to the need of a good view when landing. It might help in combat as well.


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## tomo pauk (May 12, 2015)

FWIW: I recall a comment made on the Sabre vs. MiG-15 seating: the Sabre's pilot was sitting on the aircraft, while the MiG's pilot was seating in the aircraft.

The ASh-82FN was doing 1850 CV in low gear, using overboost, for take off and at 500 m (~1500 ft). In second gear the over-boost was not allowed, max power was 1430 CV at 4650 m (~1410 HP at ~15260 ft).

The R-2800-34W in the Tigercat:






The SAC for the Bearcat gives 2750 HP (!, S/C in 1st speed ) on SL; 2450 HP at 9500 ft (S/C in 2nd speed probably), but the speed graph suggests like the RPM was restricted for engine with S/C in second gear and using WER?


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## Shortround6 (May 12, 2015)

View over the nose helps a _lot_ when defection shooting.

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## razor1uk (May 12, 2015)

I would say that a bubble canopy has to 'bubble out' i.e; the lower edges of it relative to the pilots P.O.V positions must give at least some more downwards 'over the side' visibility when they move their head and neck to one side - in the 86 (not the Toyota 'Hachiroku' but the Sabre..) and certaily the F-14 from memory the lower edge of the canopy where it is mounted in the canopy frame rails, is inside the widest portion of the canopy which 'bubble out'-wards. You could say the original Zero-sen had a 1st operationally in service bubble top (in looks) /or a Malcolm hooded Spit. 
Or Mustang D (E, F, etc) where it was a single piece blown canopy affectively called a bubble canopy by pilots, grunts, erks and civies in general - without the downwards view boosting of the canopy mid draftage/wide-ness overhanging its frame - something the 'Stangs share with the both Lavochkins earlier Yakolevs.

But like the usage of the term 'bike' by both bicycle, motorbike motorcycle users to be 'their' understanding of the word, so to does bubble canopy have such a wide mixture of peoples intpretations of meanings - I'd say the original descriptive one was the naval or bombers transparency that had a 'blown/bubbled out' aspect to to give improved downwards viewing ability.


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## GregP (May 12, 2015)

I can find more references that say 1,650 hp than I can find that say 1,850 hp. I also found one that says 1,700 HP max. At least one give 2 numbers, but does not say whether the numbers are takeoff/maximum or dry/wet (WER).

My opinion is still out on the HP rating of the ASh-82FN's real power capabilities. Since it is Soviet, what is a definitive source? I have wrestled with this for 25 years when looking up specifications for USSR technical items.

Either way, the La-9 is formidable. I am now wrestling with why the power-to-weight should be so similar but the rates of climb should be 30%+ different. Rate of climb is almost but not completely tied to power-to-weight. Wtih a 30%+ difference, maybe the real power is being revealed. Or maybe the quoted rate of climb is wrong?


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## razor1uk (May 12, 2015)

GregP said:


> I can find more references that say 1,650 hp than I can find that say 1,850 hp. I also found one that says 1,700 HP max. At least one give 2 numbers, but does not say whether the numbers are takeoff/maximum or dry/wet (WER).
> My opinion is still out on the HP rating of the ASh-82FN's real power capabilities. Since it is Soviet, what is a definitive source? I have wrestled with this for 25 years when looking up specifications for USSR technical items.
> Either way, the La-9 is formidable. I am now wrestling with why the power-to-weight should be so similar but the rates of climb should be 30%+ different. Rate of climb is almost but not completely tied to power-to-weight. Wtih a 30%+ difference, maybe the real power is being revealed. Of maybe the quoted rate of climb is wrong?



Between the two aircraft, how do their differences or similarities relate towards that roughly 30%-ish, by that I mean weights, wing, tail and control surfaces areas, clean drag co-efficients, power loading ranges etc, if they are all say well within 10% of the other ones, and ignoring air temperature pressures at tests, then it could be some organisation has certainly fudged the facts, or at least, given the fact at lowest flight loadings of fuel and empty ammo for the mission/record attempt to get such a climb figure - perhaps to keep Stalns NKVD from executing them or their staffs.


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## GregP (May 12, 2015)

I can probably locate all those data for the F8F. I seriously doubt I can find those data for the La-9. And it's not a task I'd take on unless I was really interested to the point of investing the time. I'm curious, but the La-9 and F8F didn't figure into much combat, so I'm not interested enough to invest the time. It isn't really related to any piston-on-piston air combat war.

Now if I owned one, that would be different. I'd reseach my plane to the end, out of nothing but interest in my trusty steed.


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## tyrodtom (May 12, 2015)

razor1uk said:


> Between the two aircraft, how do their differences or similarities relate towards that roughly 30%-ish, by that I mean weights, wing, tail and control surfaces areas, clean drag co-efficients, power loading ranges etc, if they are all say well within 10% of the other ones, and ignoring air temperature pressures at tests, then it could be some organisation has certainly fudged the facts, or at least, given the fact at lowest flight loadings of fuel and empty ammo for the mission/record attempt to get such a climb figure - perhaps to keep Stalns NKVD from executing them or their staffs.



Good theory, except it's the La-9 that has the 30% shortfall in climb performance.


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## tomo pauk (May 13, 2015)

The graph and table for ASh-82FN, with 3 engine sub-types that have different prop reduction gearing. Take off rating is again specified at the bottom part of the table (1850 CV at 2500 rpm and 1200 (-20 tolerance) mm Hg, 5 min). (open the pic separately for hi-res)

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## GregP (May 13, 2015)

First Tomo,

Thank you for the pic-post!

Can't read it but I see the FN in Greek. Exactly what book is this from and why should it be believed over other references? I have several that say diffferently for the FN.

Not arguing, just asking as I can't read most of it, but the Greek letters are easy. 1,850 cv is about 1,824.7 HP in the U.S.A. (550 ft-lbs/min type HP).

As long as I'm asking, do you know the airfoil section for the root and tip chords?


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## Koopernic (May 13, 2015)

That a Soviet engine in 1946 would be producing less power than a BMW801 in late 1943 is somewhat hard to believe.


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## Juha (May 13, 2015)

Hello Greg
most documets/WWII publications on engines I have seen agree the 1850cv WEP, 1630cv or 1650cv military max power at 1650m, but claimed either 1430cv or 1450cv as max 2nd gear sc power at around 4700m, but some a/c books give for La-5FN/La-7 1470cv as max 2nd gear sc power at around 4700m, the low level power being same as in the WWII sources.


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## tomo pauk (May 13, 2015)

GregP said:


> First Tomo,
> 
> Thank you for the pic-post!
> 
> ...



The La-9 and -11 were supposed to be outfitted with laminar-flow wing, I dont know the exact profile used. The LaGG-3, La-5 and -7 was using the NACA 230 series.
The graph is from the manual for the ASh-82FN. The name "АШ-82ФН" is in cyrilic, the type of letters that emanated from Greek wrting. The monks (later sainted) Cyril and Method brought it from Byzantium to the many Slavic people in the early Medieval. It is in use in Serbia and Bulgaria today, for example, the last known writtings in Croatian cyrilic were dated circa 1500-1600s.



Koopernic said:


> That a Soviet engine in 1946 would be producing less power than a BMW801 in late 1943 is somewhat hard to believe.



I don't see a reason why it would produce more than BMW 801 - both were using the same technology and were roughly of same size. The 801D turned greater RPM and was using better fuel from mid-war on.


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## Shortround6 (May 13, 2015)

Koopernic said:


> That a Soviet engine in 1946 would be producing less power than a BMW801 in late 1943 is somewhat hard to believe.



Not really, the Soviets never really progressed beyond 95 octane fuel. At least for service engines. Add in the fact that the ASh-82 was never rated for more than 2500rpm for take-off and the other ratings were at 2400rpm and the lower power rating seems inline. A Wright R-2600 which was slightly bigger, used 100/130 fuel and ran at 2800rpm for take-off made 1900hp.

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## tomo pauk (May 13, 2015)

Another thing that might be observed is that ratings for the ASh-82FN, other the 5-min overboosting in low gear, were called 'nominal'. So we might be better off comparing the 30 min power of the BMW 801D with that nominal power - 1320 CV at 2400 rpm at 5300m equals the nominal power of the ASh-82FN at that altitude. Granted, the 801D was rated for greater powers for short term ratings.


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## grampi (May 13, 2015)

spicmart said:


> Off topic, the La-9 is much more pleasing to the eye imo.



I was thinking just the opposite...the La-9 looks like a Russian version of the P-36 to me...the Bearcat on the other hand looks like a mad hornet ready to take on anything in the sky....


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## GregP (May 13, 2015)

For those of you who wish to pursue this, I found the airfoils at *The Incomplete Guide to Airfoil Usage*: The Incomplete Guide to Airfoil Usage

The Grumman G-58 F8F Bearcat, both the F8F-1 and F8F-2, had an NACA 23018 airfoil at the root and an NACA 23009 airfoil at the tip.

The Lavochkin La-9 was a different animal. The LaGG-1 through La-7 all had an NACA 23016 airfoil at the root and an NACA 23010 at the tip. The La-9 changed to a "TsAGI Laminar Airfoil" at the root and tip ... and that’s all the explanation I can find, so coming up with a coherent analysis might be tough. At this time, I do not know how a TsAGI laminar arfoil would different from another laminar airfoil.

Thank you Tomo and Juha. I am assuming the 1,850 cv is wet War Emergeny Power (limited boost liquid ADI) and 1,630 - 1,650 cv is dry military power. Max without ADI. That makes sense. Most of the sources I have seen did not have the wet power, they only had one number. If two powers had been present, I would have suspected ADI for the upper number.

I must say I am impressed with the La-9. I have seen many Bearcats but never a "real live" La-9 ... only pics of the one Ray Hanna used to fly. It is a good-looking aircraft indeed.

I still need some hard performance charts for the La-9 to want to open my mouth about a winner, but the La-9 makes a really interesting opponent for the Bearcat. Had jets not come along, the fifties might have been a very interesting time for aviators.


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## Koopernic (May 13, 2015)

Shortround6 said:


> Not really, the Soviets never really progressed beyond 95 octane fuel. At least for service engines. Add in the fact that the ASh-82 was never rated for more than 2500rpm for take-off and the other ratings were at 2400rpm and the lower power rating seems inline. A Wright R-2600 which was slightly bigger, used 100/130 fuel and ran at 2800rpm for take-off made 1900hp.



Shvetsov ASh-73 that was used on the Tu-4 (B-29 clone) wasn't quite as much a laggard compared to the R-3350. I would imagine they knew the direction was going to be jets (apart from long range aviation) and chose not to invest in catching up.


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## dedalos (May 13, 2015)

Once again , for a soviet fighter of the era, we must note its very low weight
And once again i ask
1) What Navigation and radio equipmentit had? What flying instumentation it had?Hoe effective its gunsight was?The pilots work load?
2) What strength limits ithad? What was its mach limit?What armor it carried?
3) While F8F was also a dedicated low level fighter,the La s altitude performance was terrible for its day.In korea could barely reach the speed of b29s
4) What was its exterior load capability?
5)The f8f could reliably deliver 2300hp, and even up to 2800hp if nessecary. The La s 1850 hp ,was for very short duration at very low level, and its questionable its RELIABILITY at this power setting

Judging 2 aircrafts is more than just throwing numbers.
In my opinion the F8F is FAR superior

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## tomo pauk (May 13, 2015)

> In my opinion the F8F is FAR superior



It probably is.



GregP said:


> ...
> Thank you Tomo and Juha. I am assuming the 1,850 cv is wet War Emergeny Power (limited boost liquid ADI) and 1,630 - 1,650 cv is dry military power. Max without ADI. That makes sense. Most of the sources I have seen did not have the wet power, they only had one number. If two powers had been present, I would have suspected ADI for the upper number.
> ...



The ASh-82FN (or other -82 radial) never featured the ADI. The over-boost was of the 'dry' variety, boost of 1200 mm Hg means about 47.25 in Hg (+8.5 psig, ~1.63 ata). Rather a modest value, for example the R-2800 'B' was at ~52 in Hg for military power, on better fuel though (100/130 grade).


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## GregP (May 13, 2015)

If I am not mistaken, 1200 mm HG converts to 77.2 inches HG (USA), 23.2 psi (British), and 2.665 ata (German). Most of our radials were not boosted that high.

For refrence, 55 inches HG is 637 mm HG.

1 ata = 28.958" HG = -0.326 Bar = -3.258 kPa = -0.473 psi

I posted a spreadsheet that does the conversions some time back but can do it again if anyone wants it.

Gut feel, I think the F8F is far superior in general, too, but I have almost NO documentation on the La-9 and was attempting to not claim what I don't know. I'd like to confirm it before claiming it. Been bitten by that before ... in here.


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## Juha (May 13, 2015)

one in=25,4mm; 4.7in=120mm (a RN naval gun) so 1200mm ~47in
And as Tomo wrote in the ASh-82FN case forsage means "dry" overboost


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## GregP (May 13, 2015)

These are not linear units of equivalence, they are national standard units of manifold atmospheric pressure. Some are absolute pressure and some are gauge pressure, notably British Boost. 1 ata is NOT 1 standard atmosphere, it is 1 technical atomsphere.

1) The U.S.A. uses inches of Mercury (in Hg) absolute pressure.

2) British psi of boost (lbs Boost) = [(14.696/29.92) * in Hg] – 14.696 ... gauge pressure of boost. Hence you subtract the 14.696.

3) German Technical Atmospheres (ata) = (in Hg) / 28.958 ... not a stndard atmosphere.

4) Japanese / Russian mm Mercury (mm Hg) = (in Hg – 29.92) * (760 / 29.92)

If you look below on the figure , you will notice 47.25 inches of Mercury (U.S.A. units) is right at 440 mm HG (Japanese units), right where my spreadhseet says it is (really it converts to 440.2 mm HG) ... and it is also right at +8.5 psi Boost (British units) and 1.632 ata (German units). I didn't make this stuff up, but it isn't all that hard to come up with it, either. 

I can post an "extended" chart if anyone is interested, that covers idle to Reno racing levels. The chart below covers from near cruise to upper levels usually attained by radials.

The Russians typically used mm H2O, not mm HG ... but they DID use mm HG every once in awhile. When they did, it matched the Japanese units exactly, not surprisingly.


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## Juha (May 13, 2015)

Hello Greg
thanks for explanation, I also have that scale, but were the Japanese and Soviet scales identical? I can understand that Japanese used the same 0 level than Brits but somehow I'd expect that the Russians would use a system with similar 0 level than that used by French (whatever it was) or Germans? After all they used cv/ps not hp.

Edit: German wwii book on Soviet engines gives for M-82FNW (must mean 82FNV) 1850 ps at 1.60 ata 2500rpm


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## GregP (May 13, 2015)

If anyone is interested, attached is a spreadhseet that converts among the popular WWII aviation engine boost units and has a table from zero inches of Mercury up through 150 inches of Mercury.

That's the most boost that anyone I know of runs in an aircraft piston engine, and that happens at the US Reno National Championship Air Races every year.

The engines that run that boost are not Merlins. They start with a Merlin block, add Allison G-series rods, custom pistons and valves and springs, modern mags or electronic ignition, spray bars, run ADI, and run very low compression ratios. One even has Dwight Thorne custom racing cams and all the others WANT them. Most are running transport heads because that's mostly what is left to run AND they are strong. Reduction gear ratios vary from stock and props are almost all shorter than legal for Limited Category aircraft.

- Greg

View attachment Boost.zip


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## GregP (May 13, 2015)

Hi Juha,

cv or ps is power. The U.S.A. uses 550 ft-lbs/sec HP while others use boiler or metric HP. Other units are available. Some use kW. Power-to-weight can be in lbs/HP, lbs/cv or ps, cv/kg, kW/kg, or even the inverse of these. Converting isn't difficult.

The manifold pressure scale is just manifold pressure and is unrelated to power units. It really only matters whether the manifold pressure is absolute or gauge pressure. The Germans are the only nation who used something related to technical atmospheres rather than internation standard atmospheres ... and, as long as you know that, conversion isn't all that difficult.

If you use gauge pressure, you get boost pressure, not MAP absolute.

It surely would be nice to standardize, wouldn't it?

I would not care which unit we standardized on, but I tend to use the unit associated with the nation in WWII since that is what is generally quoted in any specifications from the time period. As long as you can convert, it doesn't matter.


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## Juha (May 13, 2015)

Hello Greg, thanks for the zip!

Juha

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## GregP (May 13, 2015)

You are welcome. Might come in useful in a bizarre set of circumstances.

If you own one, you usually just follow the book!


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## kool kitty89 (May 13, 2015)

razor1uk said:


> I would say that a bubble canopy has to 'bubble out' i.e; the lower edges of it relative to the pilots P.O.V positions must give at least some more downwards 'over the side' visibility when they move their head and neck to one side - in the 86 (not the Toyota 'Hachiroku' but the Sabre..) and certaily the F-14 from memory the lower edge of the canopy where it is mounted in the canopy frame rails, is inside the widest portion of the canopy which 'bubble out'-wards. You could say the original Zero-sen had a 1st operationally in service bubble top (in looks) /or a Malcolm hooded Spit.


The F2A was flying and in service before the A6M, and while not as aesthetically similar to the typical 'bubble' configuration as the Zero, the Buffalo may have had better all-around visibility. (even ignoring the belly glazing on the F2A) Without the telescopic sight, the F2A also has some of the better forward visibility of WWII fighters as well. (very broad canopy, heavily ribbed but not 'caged' ) Part of that was, of course, due to the bulky fuselage on the Buffalo, such that even if the canopy was no wider than the fuselage sides, it was still wider than the canopy of the slimmer A6M.

The Gladiator's canopy also very much resembles the 'bubble' configuration and has little framing at that, but in practical terms the biplane wing configuration restricts vision a good deal more. (the same canopy applied to the F.5/34 is a more compelling example, but then so would some He 112 variants) 

And on a slightly more relevant note, I'd imagine the B.239's cockpit visibility was one of the more notable advantages the aircraft gave experienced Finnish pilots during the continuation war.



> But like the usage of the term 'bike' by both bicycle, motorbike motorcycle users to be 'their' understanding of the word, so to does bubble canopy have such a wide mixture of peoples intpretations of meanings - I'd say the original descriptive one was the naval or bombers transparency that had a 'blown/bubbled out' aspect to to give improved downwards viewing ability.


There's the 'teardrop' canopy term used at times as well, and the lesser bulging on the P-51D's canopy that put it at a visibility disadvantage to the bulged Malcolm hood configuration.


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## GregP (May 13, 2015)

The original "bubble canopy" described a canopy that eliminated the turtledeck.

How the canopy terms grew from there would be a guess on my part, but most of the fighter pilots I have spoken with were not concerned with looking down. You can always roll over to do that. 

They were concerned with looking back at their six o'clock position to see if anyone was getting into position to shoot them down. It WOULD be good to have some bulge, but not at the expense of much speed ... depending on how much speed advantage or disadvantage you have. If you were 40 mph faster then giving up 10 mph for better visibility might be OK. If you were slower, don't give up ANY speed.


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## GregP (May 14, 2015)

I have a question about manifold pressure. I KNOW my calculations for inches of Mercury, psi of boost, German ata, and Japanese mm of Mercury are correct.

However, I have never seen anything in Russian that tells me whether the Soviet-era mm of Mercury were absolute or gauge pressure (MAP or boost: MAP is manifold absolute pressure). Japanese mm HG is boost since 29.92 inches of Mercury is 0.000 mm HG. Since both of the units were in mm of Mercury, I assumed they had the same calculation. Howver, it is entirely possible that one is absolute and the other is gauge.

Are there any readers of Russian out there who can say for sure?

If so, I would be very glad to hear what you have to say.

I'm keeping in mind that the Soviets used to run Allison V-1710's that were approved for 58" HG by the USA at 75" HG, so running a Soviet radial at these pressures is NOT a stretch in my book. The stretch would be it holding up for long under that MAP. A few minutes is one thing, 15 minutes is another.

Thanks in advance -Greg

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## Koopernic (May 14, 2015)

Isn't a US standard atmosphere for engine purpose 30 inches of Hg even though it's actually 28.5?

The German system is the one that is most sensible.


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## GregP (May 14, 2015)

The US standard is 29.92 inches of Mercury (one international standard atmosphere). The Germans are the only nation that used a a technical atmosphere (28.958 inches of Mercury) during the war, so it hardly makes the most sense. It is certainly usable. The Germans don't use a technical atmosphere today for aviation travel, at least internationally.

Most German airline pilots are very familiar with feet since a large percentage learned to fly in the U.S.A. . Training is one thing we do a LOT of and our airspace assignments are in feet. Probably in meters at home and that makes perfect sense to me. If we ever go over to the metric system officially I am comfortable with it, no problem. The main issue would be ensuring prices don't change for what you get! People tend to take advantage of basic changes financially and that would have to be avioded for anything like public acceptance. That is another post ... sorry to even bring it up in here.

Over the world's oceans, all airliners operating in the flight levels have their altimeters set at 29.92 inches of Mercury (760 mm HG, 101.325 kPa. 1.01325 Bar, 406.8 inches of water, 1 atmosphere or 1.03323 technical atmospheres). That way, they don't run into each other due to local atmospheric pressure gradients.

To me the one that makes the most sense for manifold pressure is boost pressure, not absolute pressure ... but I am stuck in a system that uses absolute pressure, so I am comfortable with it. I expect to see about 29.92 inches (or whatever local presure is at sea level) of MAP when the engine is not operating. 

Boost would read zero when the engine is not operating, indicating to me operation (or non-operation) at normal atmospheric pressure. Anything above that is boost and I don't care at all if it is psi, inches of Mercury, mm of Mercury or watever. Above atmospheric is boost, which is what makes high altitude flight possible with piston engines. If they fought with normally-aspirated aircraft engines, the combat would likely be at 10 - 12,000 feet (3,048 m - 3,658 m) and below so as to retain fighter-like performance. Without boost over and above normal atmospheric pressure, I doubt if we'd ever climb much above 12,000 feet except maybe for reconaissance flights.

Of course, flak will cause people to go higher and that is probably why we flew with supercharged and tubocharged engines ... to get above accurate flak altitudes.

At least we're not still measuring in rods, cubits, fathoms, furlongs, and leagues ... nevermind the poppyseeds, barleycorns and shaftments!


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## Koopernic (May 14, 2015)

The advantage of using an atmosphere, similar to but not quite the same as a bar, is it allows rapid conversion to other units and one had a good idea of pressure ratio. The atm was also completely sensible being 101,300 newtons a meter(pascals), exactly sea level, whereas the bar was rounded to 100,000 newtons per meter.(pascals)

The temperature increase experienced after compression in a supercharger is a function of the *ratio* of the pressure change multiplied by the starting temperature not the absolute manifold pressure.

It's elevated manifold temperature rather than pressure that causes pre ignition. It is not absolute pressure that causes high temperature but rather high pressure ratios.

Hence an engine that has generated 2 ATA (60 inches Hg) manifold at just over 30,000 feet has a compression ratio of 6:1 as opposed to 2:1 for the same manifold pressure at sea level. Unless an intercooler or water injection is added the engine manifold air at 30,000ft will be hotter. Of course at 30,000ft the air is about 1/3rd as dense and 60C cooler. The ratio is important in more ways than one.

I suspect that modern airliners calibrating their altimeters don't have a 1m column of mercury in an evacuated tube but a certified reference. Still, it gets rid of mistakes and in between instruments. I doubt P51 pilots who claimed to be pulling(really pushing) 85 inches actually had a column of glass about 3 yards high handy. It all went through a Bourdon gauge I suspect.

Maybe we should have been defining engine figures of merit by maximum manifold temperature, in kelvin please,


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## Juha (May 14, 2015)

GregP said:


> I have a question about manifold pressure. I KNOW my calculations for inches of Mercury, psi of boost, German ata, and Japanese mm of Mercury are correct.
> 
> However, I have never seen anything in Russian that tells me whether the Soviet-era mm of Mercury were absolute or gauge pressure (MAP or boost: MAP is manifold absolute pressure). Japanese mm HG is boost since 29.92 inches of Mercury is 0.000 mm HG. Since both of the units were in mm of Mercury, I assumed they had the same calculation. Howver, it is entirely possible that one is absolute and the other is gauge.
> 
> ...



Hello Greg
that waswhat I tried to say, British influence in Japan was substantial but in Russia the contacts were more to Continental Europe and the SU put much way to"scientific" nature of their state. So probably they used absolute pressure. The info I gave that according to WWII German book M-82FNV, the initial designation of the ASh-82FN, was capable of the short-time overboost of 1.60 ata seems to confirm that. French also seems to have used absolute mmHg, the H-S 12Y 31 V-12 engine of M-S 406 had max boost of 960 mmHg, which as absolute converts to 37.8 ins of Hg, +3.8 Lbs per SqIn and 1.3 ata, which seem reasonable for late 30s engine.

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## GregP (May 14, 2015)

Hi Juha,

Thanks for the reply. That's what I asked. Japanese mm HG is gauge. From your answer, it appears Russian mm HG is absolute. I can go from there.

Thanks, I'll make up an absolute column for Russian absolute pressure in the next day or so.


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## grampi (May 15, 2015)

I doubt the La-9 would stand much of a chance against a Bearcat...the Cat was designed to outfight anything in the sky, and I believe it would have done just that at the time...with the exception of maybe a few of the later model Spitfires and the P-51H at high altitudes...


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## GregP (May 15, 2015)

The power loading and wing loading of the F8F and La-9 were almost identical. Again, I'd want to see some roll graphs and turning circle times before I picked a winner. And the La-9 had centerline armament to boot. Ray Hanna said the La-9 would out-accelerate a Bearcat in an article on the La-9 when they were trying to book the La-9 for arishows, but I have no idea if he ever used WER in a Bearcat or not.

The Bearcat was designed to defend carrier groups, conduct low-to-medium altitude fighter sweeps over ocean/coastal areas, and out-fight anything it encountered there. It was never intended for high-altitude escort missions.

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## tomo pauk (May 15, 2015)

When you've mentioned racing - I've had a costumer today, the man of 50-ish years who had the 'Critical mass' cap on his head. So I went to do some talking, he said that the aircraft was a modification of the Hawker Sea Fury, owned by his brother. Further, he said that aircraft is now under modification to appear as a stock bird, more or less. The man and his wife (my guess) then proceeded on their own business.


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## GregP (May 15, 2015)

Some of the less-drastically modified racers can be returned to stock configfuration without too much difficulty. Many of the less-modified racers still have all the stock parts.

The heavily-modified racers from the 60's through 70's usually were done when warbirs were plentiful and cheap, and would be VERY difficult to return to stock. The really fast Mustangs have had their vertical fins moved to straight and their horzontal stabilizers changed to be good at top speed, not 230 knots, and have had their engine mounts changed to straight. They don't fly well at low speeds, but handle just fine at racing speeds.

I thought Critical Mass was decently far from stock, but the parts might be easily interchangeable ... or it might be major surgery. Changing the fin might be just remove the tail and rivet back on the stock tail. If they are going to stop racing, then changing back to stock form would allow them to go back into the Limited category from Experimental Exhibition category and be able to fly the plane around wherever they want instead of just to a public events.

Thanks for the update!

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## grampi (May 19, 2015)

GregP said:


> Ray Hanna said the La-9 would out-accelerate a Bearcat



I find that extremely difficult to believe...


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## GregP (May 19, 2015)

Since the power-to-weight is so close, I find it easy to believe the two accelerated closely with one another, but I can't defend Ray's statement as he said it ... I didn't.

Grumman had a reputation as "the iron works" and they "overbuilt" their planes. Perhaps the Soviet Union didn't and the La-9 could out-accelerate the F8F. But I can't ever prove it one way or the other. When I look inside a Bearcat (about every weekend) I don't see a lot of "extra" beef ... but I have also never looked inside an La-9. The only Soviet-era planes I get to look closely into are a Yak-52 and a Yak-3. The Yak-52 is bulit stout and strong. The Yak-3 seems sort of like a Hawker hurricane built from metal inside. Steel tube framing in a lot of areas similar to the Hurricane's wood ansd steel, with hinged netal covers rather than fabric. I have NOT looked inside of the Yak-3's wings since it is airworthy and I have other projects than removing inspection plates to look into the wing.

I am still wondering why a plane with the power-to-weight of the La-9 doesn't climb at least 1,000 feet per minute better than it does.


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## razor1uk (May 19, 2015)

Propeller size, prop aerofoil, what the pitch adjustment range/travel is and how that is incremented in control, and also what hieghts/speeds the prop and engine are designed to be 'averagely' at, also the drag from oil cooling inlets vs. outlet ducts flaps/vents etc ..sorry if I'm sounding insensative.

It could be the Yak/Lav have higher parasitic drag co-efficients when opperating in certain modes/ranges, where as the Bearcat, being radial engined and having the Hellcat as a development father/grandfather had a cleaner overal co-efficient across its ranges, perhaps?


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## grampi (May 19, 2015)

Look at the differences in props alone...the Bearcat's got these huge diameter, wide blades, and 4 of them at that, while the La-9 has a puny (by comparison) 3 bladed prop with barely enough diameter to clear the cowling (I know, that's an exaggeration)...you can just tell by looking at these two planes the Bearcat is gonna eat the La-9's lunch in the climb department....


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## GregP (May 19, 2015)

Could be. 

The La-9 is radial-powered, too, though (I'm sure you knew that) ... and the Soviets had captured, license-built, and lend-lease-supplied propellers to look at. I find it hard to belive their props were any less efficient than ours though, operating from the strips they were, I'm sure their props were dirtier in general. If we were operating from the same strips, our props would have been dirtier, too.

The Soviets copied an entire B-29, so I'm sure they could compare their props with ours, the German props, and Japanese props, and come up with, if not the best of the three, then certianly one as good ... if they chose to do so. Since they WERE in the aircraft business, I have absolutely NO reason to doubt Soviet propellers. We light remember that the Soviet Union set more records for speed, altitude, and range than we did.

Every single Soviet aircraft I have seen shows good design and decent workmanship. Some have a lot of overlapping seams and things I wouldn't do, but that doesn't necessarily correlate with bad performance. Ask anyone who has tried to catch a MiG-25. The finish and detail on the MiG-25 isn't all that great, but the outright speed is there ... for a short time anyway.

I'd still like to see some good performance charts for the La-9, but haven't located what I'd consider to be a good set yet. I don't believe charts with no government document number, or charts generated in Excel by someone who is supposed to "know" about it ... and I also don't read cyrillic script. But I'd still like to see some performance test results for the La-9.


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## tomo pauk (May 19, 2015)

Anybody wants to correct the Wikipedia La-9 entry that states that it's engine was featuring 2-stage supercharger? Thanks


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## Koopernic (May 19, 2015)

razor1uk said:


> Propeller size, prop aerofoil, what the pitch adjustment range/travel is and how that is incremented in control, and also what hieghts/speeds the prop and engine are designed to be 'averagely' at, also the drag from oil cooling inlets vs. outlet ducts flaps/vents etc ..sorry if I'm sounding insensative.
> 
> It could be the Yak/Lav have higher parasitic drag co-efficients when opperating in certain modes/ranges, where as the Bearcat, being radial engined and having the Hellcat as a development father/grandfather had a cleaner overal co-efficient across its ranges, perhaps?



The La 9 had a laminar flow airfoil, with the Soviets having struggeled with this for a long time however they seem to have gotten it right with the La 9.

The Bearcat had an older NACA 5 digit series which was probably chosen to either minimise risk in the Bearcat development process or for low speed and landing considerations as by the time the Bearcat was designed the US had a range of laminar flow wings.

The La 9 wing almost certainly had lower parasitic or 'form drag' at high speed. The more traditional Bearcat wing might have been able to generate higher coefficients of lift and lift to drag ratio or maybe just the same, Id say better at generating lift. It's a question now as to whether the lower parasitic drag of the La 9 wing can be exploited in turning flight as during a turn the source of drag shifts to 'induced drag' and is a by-product of producing lift. Here laminar wing doesn't show any superiority thought the lower parasitic drag means there is more reserve for generating lift.

total wing drag = induced drag + parasitic drag. The Laminar flow wing only improves the parasitic drag and then mainly at high speed.


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## davparlr (May 19, 2015)

We must remember that acceleration is not only a function of power-to-weight, this only true at zero airspeed and max power, rather it is a function of excess power-to-weight. If an aircraft is using all of its power to maintain a given airspeed, it will not out accelerate a lesser powered aircraft that is not using all of its power to maintain that airspeed. This is one of the advantages of the P-51 had since it almost always used less power to maintain a given airspeed than other WW2 prop fighters. Now according to chart of spitfire performance the F8F-2 (the charts for the F8F-1B seem unbelievable showing combat power at 2750 hp at SL) generating 2500 hp at SL with a max speed of 387 mph, whereas the Russian site (believable ?) shows the La-9 generating 1850 hp at SL with a max speed of 397 mph. If these numbers are true, the La-9 is much cleaner than the F8F and therefore will need less power to operate at any given airspeed. At SL and 387 mph, the La-9 will out accelerate the F8F because it has the excess power to do so. At other envelop points, calculations would have to be run to see which aircraft would out accelerate the other, but it is possible for the La-9 to also out accelerate the F8F at other envelop points.

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## GregP (May 19, 2015)

Interesting comment, Tomo. I have seen refrences to the ASh-82FN as a 2-stage supercharged engine, but I am under the distinct impression it is a single-stage, 2-speed supercharger. I don't read Cyrillic, so I can't really tell.

Bottom Line:

My "guess" is single-stage, 2-speed; not 2-stage. However, someone who reads Russian might be able to actually tell me. I don't want to contradict on a guess, and I only have a manual for an ASh-82T, which is a sinlge-stage engine.


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## Shortround6 (May 20, 2015)

Vladimir Kotelnikov's book " Russian Piston Aero Engines" makes no mention of a a two *stage* ASh-82 of any kind except a turbo charged model called the M-82-NV(ASH-82NV) which was test flown but not put into production. 

He is just a single source and may be in error but since he lists 11 different models of the M-82/ASh-82 engine including Czechoslovakian and Chinese versions I would say that the chances of any model ASh-82 having a two *stage* supercharger are exceedingly small.


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## drgondog (May 20, 2015)

GregP said:


> I am still wondering why a plane with the power-to-weight of the La-9 doesn't climb at least 1,000 feet per minute better than it does.



I don't Know but the primary factors for ROC is excess Power = Power available versus Power Required divided by Weight. where Thrust available times Velocity - Drag times Velocity = Excess Power.

In climb, with a tangible angle of attack, one of the Drag components "Profile Drag" is significantly higher - in the order of 25-35% over zero lift Profile Drag. Also max ROC in a steady climb (versus zoom) is at a low speed in the range of 160 +/- mph or square in the middle of highest Induced Drag.

The Wing and Wing Body, including esoteric considerations of mid wing versus high/low wing are considered but the La 9 and F8F are both low wing. The tapers seem similar so Induced drag due to planform are nearly the same - I don't know about wing twist but would suspect that the la 9 didn't have near the low speed roll authority requirements as the F8F so would tend to give the bod to the La 9 given equal Aspect Ratio and Oswald efficiency.

Net - given the W and the power of La 9 engine, there is something about the Wing high angle of attack profile drag that is suspiciously high if the stated ROC is so relatively low. The La 9 as presented is about the same ROC of a fully loaded (internally) P-51D at 67", which for that gross weight says that either the Laminar flow wing is awful in higher AoA Profile drag(doubtful), the actual power delivered is much less than spec'd or the wing area is grossly overstated (and subsequent W/L).

I agree with you Greg that it is a head scratcher. The Sovs did not like fighters with high wing loading/low rate of turn attributes for the designed mission strike zone

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## Shortround6 (May 20, 2015)

I have always been a bit curious as to the effect the fuselage may (or may not) have on the overall lift of the wing. This is in regards to the size (area of wing) that the fuselage takes out (occupies). Many formulas or explanations disregard the size of the fuselage or regard it as a constant (or something.) Some say the fuselage acts a bit like an endplate or something (sorry, it's been a few years since I looked at any of this and I may not be using the right terms).

As an example of what i am trying to get at you have the P-39 with 213.2 sq ft of gross wing area and because of it's skinny fuselage it has a net wing area of 197.7 sq ft. or 92.7% 
The P-40 had 236 sq ft gross wing area and 217.6 net wing area for 92.2% so if you are comparing those two planes it doesn't make any difference if you are comparing gross or net. 
However something like the Brewster Buffalo had 208.9 sq ft gross and 178.1 sq ft net for a difference of 85.2 %. The F4F had 260sq ft gross and 222 sq ft net (?) for 85%. 
A P-47 has 300Sq ft gross and about 259.5 Sq ft net ( Wing root cord X max fuselage width taken out) for 86.5%. 

Granted the LA-9 started as a V-12 powered fuselage and may be skinnier than most radial engine planes but it also starts out with a wing that is only 189sq ft. 

It seems most fighters are going to be between 85% and 92-93% unless their wing area or fuselage size falls way out on one end of the spectrum so maybe it doesn't make much difference. 

Perhaps it does help explain why certain fighters had trouble as weight increased compared to others?


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## GregP (May 20, 2015)

I have seen one viseo clip of the La-9, probably Ray Hanna but I'm not sure, doing an airshow and it looked pretty much like an F8F Bearcat show that I have seen recently as many as 8 or 10 times. Even the loops were big and round emphasizing the vertical climb.

I'm starting to wonder if the stated climb rate is anywhere close to being accurate or if the data came from Soviet disinformation.

However, I don't have any resources from the former Soviet Union except for a couple of books on jets ... no La-9 anywhere. The rest of my resources are authored in the west and the writeups on the La-9 pretty much parrot one another.

I think that I'll have to bow out of further speculation based on no data to the contrary.

I am under the strong impression that the taper on the La-9 is much greater than on the F8f but, other than that, the La-9 is somewhat sparsely covered in the part of my library that I have unpacked. A lot of it is still in boxes including a few aerodynamic texts, but I cannot recall any picked up books that detail the La-9 any better than what I have.

So I'll defer to the people who have some data here.


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## tomo pauk (May 20, 2015)

A quick look at power curves will further reinforce the information that ASh-82FN was sharing the single stage supercharger with earlier engines of the same family - above ~5,5 km, the power was in the ballpark with M-82 and M-82F (or ASh-82 and ASh-82F, so called from April 1st 1944 on). The -82FN received direct fuel injection, and greater (but still, when compared with Western engines, moderate) over-boosting was allowed under the rated heights.
At 5.4 km, all the engines of the family were doing around 950 mm Hg of boost, or 37.4 in Hg, or 1.28 ata, the -82FN was pulling 1000 mm Hg (~39.4 mm Hg, ~1.36 ata) at 4.65 km (~15260 ft) - or about the same manifold pressure like the V-1710 with 8.8:1 S/C gearing. The ancient Merlin III (1-stage S/C) was making +6.25 psig at 16250 ft, or 42.4 in Hg, or ~1078 mm Hg, a notable advantage in supercharging over M-82 family of engines.


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## GregP (May 20, 2015)

Hi Tomo,

I'm wondering if the moderate overboosting of the ASh-82 was mainly due to fuel quality in the field rather than any inherent engine characteristics. I am given to understand that Soviet fuel was a bit low on performance number rating and could mostly be covered by octane ratings, but that may not be the case from 1943 onwards. Again, somewhat a dearth of hard data. Some of what I think comes from Soviet-written, English language-translated combat reports ... but it is entirely possible they had decent fuel from sometime in 1943 onward.


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## tomo pauk (May 20, 2015)

The 'new' Soviet engines (AM 35A, AM 38, M-105, M-82 etc) were specified to use fuel of 'no less than 95 oct number' - while a bit better than 87 oct, that's barely better than Japanese 92 oct or what USA used on many engines (91 oct fuel, not for front line combat aircraft of course). So we won't see boost levels of what the fuel with 100 oct was offering (without the use of ADI), let alone he fuel with rich response at 130 grade.
The compression ratio of M-82 family of engines, 7:1, also does not allow for that great a boost. The Merlin was at 6:1, for example; plus the radials were always a bit lacking wit allowable boost. When Mikulin's team ddesigned the AM 42, they decreases the compression ratio down to 5.5:1, that allowed for manifold pressure of 1565 mm Hg, or: 61.6 in Hg, circa 2.2 ata, +16 psig - while still on 95 oct fuel, no ADI, no intercoler. They didn't made an own goal with increasing compression ratios for new versions of engines when 96-100 oct fuel was to be used, as DB and BMW did.


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## grampi (May 20, 2015)

davparlr said:


> We must remember that acceleration is not only a function of power-to-weight, this only true at zero airspeed and max power, rather it is a function of excess power-to-weight. If an aircraft is using all of its power to maintain a given airspeed, it will not out accelerate a lesser powered aircraft that is not using all of its power to maintain that airspeed. This is one of the advantages of the P-51 had since it almost always used less power to maintain a given airspeed than other WW2 prop fighters. Now according to chart of spitfire performance the F8F-2 (the charts for the F8F-1B seem unbelievable showing combat power at 2750 hp at SL) generating 2500 hp at SL with a max speed of 387 mph, whereas the Russian site (believable ?) shows the La-9 generating 1850 hp at SL with a max speed of 397 mph. If these numbers are true, the La-9 is much cleaner than the F8F and therefore will need less power to operate at any given airspeed. At SL and 387 mph, the La-9 will out accelerate the F8F because it has the excess power to do so. At other envelop points, calculations would have to be run to see which aircraft would out accelerate the other, but it is possible for the La-9 to also out accelerate the F8F at other envelop points.



One thing that makes me question the notion that the La9 will outaccelerate the F8F is the difference in climb rate...the F8F climbs at more than 1000 fpm faster than the La9...granted, lift plays into this, and the F8F has a higher lift wing than the La9, but does that wing account for all of the difference in climb rates? I would be shocked if that were the case, which leads me to believe the F8F simply makes more efficient use of it's power than does the La9, which also leads me to believe that F8F would accelerate better than the La9...you made a good point with the P-51, which has a similar laminar flow wing to that of La9, and the "D" model has a climb rate that's almost identical to that of the La9, and I highly doubt a P-51 will outaccelerate a Bearcat...


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## Shortround6 (May 20, 2015)

I think that is a major problem for the Russian engines. The temperature rise in the supercharger is much more than many people realize. For instance there is a chart in one old book that gives the temperature *rise* for an _auxiliary-stage_ supercharger (think P-38 or P-47) for air compressed from standard altitude condition to 29.92 in. Hg. abs. (sea level pressure delivered to main supercharger or carb) and assuming the a supercharger temperature coefficient of .65.

Going from the chart and using degrees Fahrenheit. 

5000=just under 50 degrees. 
10,000ft= about 80 degrees
15,000ft=about 130 degrees
20,000ft=about 175 degrees
25,000ft=about 220 degrees
30,000ft= about 260-270degrees. 

Another chart shows the HP required by a _hypothetical_ infinitely variable supercharger providing sea level air pressure to a main supercharger and shows both the out side air temperature and the temperature of the air delivered to the main supercharger. At 35,000ft or so the out side air has stopped getting colder (this is a wartime book) and is stabilizing at minus 67 Degrees F. temperature at the inlet of the main supercharger is around 240 degrees. Supercharger needs a bit over 200hp. 

At 20,000ft the temp is about minus 12 degrees F, the inlet temp is over 150 degrees and power needed is just over 100hp. 

These temperatures are for a 'standard' 59 degree F day at sea level. adding 30 degrees at sea level just adds adds 30 degrees to all temperatures until you get very high. 

If you are trying for higher than sea level pressure, say an ATA of 1.3 no matter how you measure it, the power required and the temperature will both be quite a bit higher. The higher temperature may be the reason the Russians didn't allow over boosting in high gear. The detonation limit was a combination of the pressure, the cylinder compression ratio, and the intake air temperature (or more properly, the temperature of air or mixture in the intake manifold/s) with a few other things thrown in. 

A plane at 15,000ft is trying to compress the outside air about 2.3 times in order to get 1.3 times the standard 29.92 in HG pressure. It is this _extra_ work of compression that can drive the temperature of the intake charge up so much. Please remember that the superchargers were only about 65-75% efficient so 25-35% of the power going to the supercharger went directly to heating the air and not compressing it. The cooler air at moderate altitudes (say 8-20,000ft) could in no way compensate for the higher temps caused by the superchargers.

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## Shortround6 (May 20, 2015)

Something on the acceleration and climb we may be missing is the propeller. Bearcat uses a 12' 7" diameter propeller. It has just over 122 sq ft of prop disc area and is moving a _lot_ of air. 

I have no figures for a LA-9 But a LA-5 or LA-7 prop was 3.1 meters in diameter (10.23 ft?) according to one website (open to correction) and that gives an area of about 82 sq ft. or roughly 2/3s that of the Bearcat. 

The Mustang had 97.7 sq ft of disc area. We might argue over how much the different engines/cowls masked the center of the prop disc but it seems that when it comes to moving a lot of air at low speed the big prop on the Bearcat may have an advantage. 
The big prop may have a disadvantage or two at other speeds or altitudes (and is probably heavier (much) than the prop used on the LA series of fighters.

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## GregP (May 20, 2015)

You know, although I look at a Bearcat every time I go to the museum and notice the gear legs that break at the top to fold VERY strangely for ground clearance, I totally space-cased the prop disc area. 

Thanks, Shortround! It goes a long way toward some explanation that at least makes sense.


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## grampi (May 21, 2015)

GregP said:


> You know, although I look at a Bearcat every time I go to the museum and notice the gear legs that break at the top to fold VERY strangely for ground clearance, I totally space-cased the prop disc area.
> 
> Thanks, Shortround! It goes a long way toward some explanation that at least makes sense.



I think the top of the Bearcat's gear is called a trunion (spelling?) It was a very ingenious design to keep the gear length as short as possible, while providing enough ground clearance for that huge prop...


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## drgondog (May 21, 2015)

grampi said:


> One thing that makes me question the notion that the La9 will outaccelerate the F8F is the difference in climb rate...the F8F climbs at more than 1000 fpm faster than the La9...granted, lift plays into this, and the F8F has a higher lift wing than the La9, but does that wing account for all of the difference in climb rates? I would be shocked if that were the case, which leads me to believe the F8F simply makes more efficient use of it's power than does the La9, which also leads me to believe that F8F would accelerate better than the La9...you made a good point with the P-51, which has a similar laminar flow wing to that of La9, and the "D" model has a climb rate that's almost identical to that of the La9, and I highly doubt a P-51 will outaccelerate a Bearcat...



a P-51H with fully operating 1650-9 at WEP/WI 90" probably will out accelerate an F8, at least at certain initial high airspeed envelopes - maybe even a B/D at say 380mph and beyond. The F8F has a really fat wing at 18% which brings higher profile drag than the 15% NAA/NACA 45-100.

The F8F also has a higher CLmax but that is irrelevant to the climb discussion because max climg angle of attack is nowhere near max CL. Excess Power divided by Weight as noted above is the equation for ROCmax.

I just looked at Green's data for the LA-9 which I find hugely unbelievable regarding top speeds, particularly "428mph at SL and 405 at 11480 feet". 

Green states that the climb to 16,400 feet is 4.2 minutes and max ROC = 3,840 fpm which I do find believable. 

Looking at the plan views for the La-7 and -9, the -9 has a greater span, less forward sweep of the trailing edge, greater sweep of the leading edge and what appears to be a wing taper ratio of ~ .25 to clipped wing tip. All high performance fighters tended to be designed to a .25 to .6 ratio to compromise tip stall characteristics (small taper ----> lower section CL at same AR for the tip region but results in less weight of the wing due to lower bending moments - all else being equal, larger taper ---- higher section CL and better tip control at high AoA but drives to a heavier wing).

The greater taper ratio moves the lift distribution inboard while the small tip ratio the max CL trends near the tip and also results in more induced drag.

P-51 Taper Ratio = .46
F4U TR = .75
F6F TR = .52

The Mustang and F6F are right at minimum planform Delta Induced drag for non Elliptical wings.

I haven't looked at F8F dimensions but look by inspection like 51/F6f


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## davparlr (May 21, 2015)

grampi said:


> One thing that makes me question the notion that the La9 will outaccelerate the F8F is the difference in climb rate...the F8F climbs at more than 1000 fpm faster than the La9...granted, lift plays into this, and the F8F has a higher lift wing than the La9, but does that wing account for all of the difference in climb rates? I would be shocked if that were the case, which leads me to believe the F8F simply makes more efficient use of it's power than does the La9, which also leads me to believe that F8F would accelerate better than the La9...you made a good point with the P-51, which has a similar laminar flow wing to that of La9, and the "D" model has a climb rate that's almost identical to that of the La9, and I highly doubt a P-51 will outaccelerate a Bearcat...



Generally speaking, speed and hp required to maintain speed at SL is a good point of reference for comparison (also, these values are often available) of the overall aerodynamic efficiency of an airframe. However, this may not provide a reference for other performance criteria such as climb or airspeed at altitude. For example, as mentioned by SR, the propellers of the F8F and the La-9 are quite different. The F8F has a huge four bladed prop whereas the La-9 is a smaller three bladed and more slim. I don't know much about props but the F8F propellers may be great for generating the power for climbing but may not be best for top speed. The La-9 propeller may be just oposite.


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## drgondog (May 21, 2015)

Bigger disk area at same RPM will move greater mass but isn't the R2800 running at 2800rpm and 2:1 for 1400rpm - what is the actual prop rotation for the La 9 engine?


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## tomo pauk (May 21, 2015)

Engine max rpm was 2500 (ASh-82FN, only for take off), the reduction ratios were 11:16, 9:16 and 0.56. That gives prop RPM of 1718.75, 1406.25 and 1400, respectively. The fighter (smaller prop) should use higher rotation than a bomber (bigger prop).


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## Shortround6 (May 21, 2015)

Props are usually a compromise of some sort. Many books on powerplants published during the 30s, 40s and 50s often had one or two chapters on propellers but also noted that just covered the basics. A real study of propeller design needed a book (or more than one) instead of a few chapters and pretty thick book at that. And even at that Prop design was almost as much art as it was science. A small 3 blade prop could have less drag (need less power to turn) than a larger 4 blade prop and at low altitude and high speed actually "perform" better. The low altitude air is dense and the engine/prop doesn't have to move as much of it (volume) at sea level as it does at 20,000ft. At high speed the velocity of the prop stream is a better match to the aircraft speed for turning thrust into power/speed. 
An old text book has a rather simplified chart for _fixed_ pitch props showing how a lot of factors inter-relate. The Chart has power across the bottom. Diameter of 2 blade prop going up the side and five curves for different propeller speeds. The other constants were speed of 200mph and an altitude of sea level. 

Of interest are the list of corrections below the chart. 
The right sized propeller for 100mph is 33% bigger in diameter than a prop for 200mph using the same power and revolutions. A prop for 300mph can be 13% smaller in diameter and on for 400mph can be 19% smaller than than for 200mph. 
The right sized prop for 10,000ft is 7% bigger in diameter than one for sea level. For 20,000ft it needs to be 15% bigger and for 30,000ft 22% bigger. 
Going to 3 blades instead of 2 allows the prop to be 8% smaller in diameter and using 4 bales allows the prop to be 14% smaller than a 2 blade prop. 

If you goal is high speed at low altitude you can get away with a fairly small propeller. What that does to your climb rate I am not sure. But since climb speeds were usually around 200mph or less the small prop is at a disadvantage for climbing. 

I will note again this is a rather primitive chart and not only will using variable pitch or constant speed props change things (or smooth some things out) but it also assumes a constant airfoil and blade shape for it's "recommendations". Comparing real props with different airfoils and different shapes can really introduce variables (P-47s with paddle blade props? same diameter, same number of blades, not much difference in speed, big difference in climb).


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## Zipper730 (Feb 6, 2020)

GregP said:


> These are not linear units of equivalence, they are national standard units of manifold atmospheric pressure.


And these are the exact conversions the nations used at the time (I downloaded the attachment)? For example 14.696 was used for the measurement and not 14.69595 PSI, and so on...

I'm compiling a bit of a chart of my own and it's important to have accurate information.


> I can post an "extended" chart if anyone is interested, that covers idle to Reno racing levels.


Sure...


> The Russians typically used mm H2O, not mm HG


And this was gauge pressure?


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## Admiral Beez (Feb 6, 2020)

I suppose it had rubbish range, but the Lavochkin La-9 would have looked great on an aircraft carrier.


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## Clayton Magnet (Feb 12, 2020)

Koopernic said:


> One poster mentioned the Griffon Spitfire v the P-51. I believe the appropriate comparison would be between the P-51H and the Spitfire and I suspect the P51 might come out on top.



Why would the P-51H be a better comparison? Griffon Spitfires were flying operationally in late 1942, about a year after the first ALLISON Mustangs showed up. The Mk.XIV arrived about the same time as the B/C model Mustangs, late 1943, early 1944. A more appropriate comparison for the P-51H would be the Spiteful, or post war Spitfires like the Mk.22/24


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## alsaad (Feb 18, 2020)

I really like more dense armament concentration at La-9's nose.


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## BiffF15 (Feb 18, 2020)

alsaad said:


> I really like more dense armament concentration at La-9's nose.



Realize that it comes at the expense of over the nose visibility. 

Cheers,
Biff


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