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

[GregP]

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.

 

[GregP]

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

 

[Koopernic]

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.

 

[GregP]

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!

 

[Koopernic]

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,

 

[Juha]

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

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.

 

[GregP]

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.

 

[grampi]

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...

 

[GregP]

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.

 

[tomo pauk]

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.

 

[GregP]

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!

 

[grampi]

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

I find that extremely difficult to believe...

 

[GregP]

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.

 

[razor1uk]

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?

 

[grampi]

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....

 

[GregP]

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.

 

[tomo pauk]

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

 

[Koopernic]

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.

 

[davparlr]

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.

 

[GregP]

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.