Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

wuzak · May 23, 2021

P-39 Expert said:
RAF did have a pretty solid idea for armament: the 20mm cannon, which they went to right after the BoB.

Biggest drawback with the 30calMG was effective range was only 200yds (AHT).

What about the British 0.303"? wasn't that used for the Airacobra I?

There was only 60 rounds for the 20mm in the Airacobra I, compared to 30 rounds of the 37mm.

Glider · May 23, 2021

P-39 Expert said:
So the better performance had to wait until 1944? I'm talking about 1942 and 1943.

However Also on the web site you mention

August 1942.
Cleaning up Typhoon 1.
Level speeds of production aircraft.
Level speeds done at Gloster Aircraft on a Typhoon 1B (R.8705) with short exhaust pipes, gave the following maximum level speeds.

F.S. (M.P.A.) 403.5 m.p.h. at 20,650 ft. M.S. (M.P.A.) 392.5 m.p.h. at 8,750 ft.

These still compare well to the P39N
389mph at 16,100 ft and 398mph at 9,700ft I would suggest both are still pretty equal

I haven't mentioned before the caveat to the P39 figures that you don't mention Airplane does not meet Air Corps cooling requirements at any of these powers which begs a few questions over how safe the aircraft was when delivering these figures.

Previous comments re the advantages to the Typhoon of its considerably greater firepower, payload and armoured protection still apply.

The other question which hasn't yet been asked. If the P39N was so good, why did the USA produce the P39Q which was so much slower maxing out at about 385mph?

A final point is the handling for the P39Q which presumably applies to the N which you never seem to mention

Conclusions
1. The P-39 should not be spun intentionally under any circumstances.
2. The P-39 should not be snap rolled as the roll usually ends in a spin.
3. The best spin recovery is to simultaneously apply opposite rudder and neutralize the stick.
4. Power should be cut immediately if a power on spin is entered.
5. Care must be excercised during the recovery to prevent an accelerated stall and re-enty into the spin.
6. The wing tip spin chute does not aid recovery of the P-39Q from a flat spin.

A fighter that operates best at low to medium altitude, that cannot snap roll when attacked as there is a significant chance of a spin (at low altitude), isn't a healthy place to be.

Edit Range
I don't have much information about the range of the P39 but if I remember correctly the P39N which you always quote for performance figures only had about 90 gallons of fuel which is on the low side. The P39Q had an increased capacity of 110 gallons which may impact its performance.
I do know that Typhoons were often used to escort Mosquito's on bombing missions as they were one of the few aircraft with the cruise performance to keep up with the Mosquito and had a range of approx 1000 miles using drop tanks

GregP · May 23, 2021

Radial engine fighters have a very low cruise speed in general. The F4U-4 cruised at 215 mph, and that is a later, faster version of the original F4U. The main reason was fuel burn. I can believe your calculation if you cruise the F4U at 300+ mph! Try a more realistic 200 mph for the F4U and you will get much more real-world results.

Just FYI, an F8F Bearcat that could make 455 mph top speed cruised at 185 mph most of the time for more economical operation. Now, if the F8F was coming up on an areas where combat was likely, then they would speed up so that the energy state was better if combat happened.

Cheers.

FLYBOYJ · May 23, 2021

P-39 Expert said:
Gladly. P-39N with 120gal internal less 16gal res. for T/O&Climb, 24gal for combat at 25000', and 10gal reserve for landing nets 70gal x 344mph cruising speed = 378mi. range.
F4U calculated the AAF way 237gal internal less 45gal for T/O&Climb, 93gal for 20min combat at 25000', and 20gal reserve for landing nets 79gal x 344mph cruising = 292mi range. F4U cruising speed was estimated, not in the pilot's manual.

That's for an AAF interception or escort mission at 25000ft. Both straight from the pilot's manuals. Range includes distance covered in climb but not descent. That R-2800 was a gas hog.

Several things - The P-39N manual I have shows best fuel consumption climb to 25K at 31.2 GPH at 30 minutes

Then there is no data for a 25K cruising altitude if that was your intention?? And nowhere do show GPH.

And you didn't include the 20 gallons for warm up, you use 16 gallons reserve for the P-39 and 20 for the F4U, so I'm not going any further with the P-39

F4U

Way high cruising speed and fuel consumption. Greg beat me to the punch. Try around 200 MPH indicated at around 42 GHP at 5000' for the F4U's best cruise fuel consumption.

Sticking with your initial numbers (which are very wrong)

79 gal @ 42 GPH = 1.88 hrs in the air at 200 mph = 376 miles.

pbehn · May 23, 2021

Glider said:
I haven't mentioned before the caveat to the P39 figures that you don't mention Airplane does not meet Air Corps cooling requirements at any of these powers which begs a few questions over how safe the aircraft was when delivering these figures.
s

As far as I remember this was the issue that caused 601 squadron so many problems, the engines overheated. Many of the losses were put down as pilot error, and overheating the engine was seen as evidence of a pilot error.

ThomasP · May 23, 2021

Hey P-39 Expert,

1. You forgot to subtract fuel for 20 min Combat at 15,000 ft from the fuel available for range of the P-39. If we use 5 min WEP and 15 min Military, you have to subtract ~48 USgal from the fuel available for range.

2. You used a ridiculously high 344 mph TAS cruise speed for the F4U. The F4U-1 V for best range was 178 mph IAS/182 mph TAS at 1,500 ft.
(I can not say for sure how much more fuel would be used at 344 mph TAS as you did not specify the cruise altitude, but if it was 15,000 ft then the fuel used would be around 3x what it would be at 182 mph IAS/235 mph TAS at 15,000 ft.)

If flown at 182 mph IAS/ 235 mph TAS at 15,000 ft the range would decrease ~15% from the 1015 miles shown above, so a little under 860 miles on internal fuel with no combat or reserves.

buffnut453 · May 23, 2021

There are lies. There are damned lies. And there are P-39Expert's range calculations.

ThomasP · May 23, 2021

PS The ranges I listed in my post#1,438 upthread are from a US(?) document comparing all major models of the P-39. A copy can be found on the wwIIaircraftperformance website here:"http://www.wwiiaircraftperformance.org/P-39/P-39_Aircraft_Performance_Characteristics.jpg"

FLYBOYJ · May 23, 2021

buffnut453 said:
There are lies. There are damned lies. And there are P-39Expert's range calculations.

"Anyone who calls themselves "an expert" is a specialist who knows everything about something, and nothing about anything else."

pbehn · May 23, 2021

FLYBOYJ said:
"Anyone who calls themselves "an expert" is a specialist who knows everything about something, and nothing about anything else."

The title "expert" is normally conferred on people by others. I have only met two people who were actually legally defined "experts" they had both been called as expert witnesses in legal cases, but they never used that handle themselves.

buffnut453 · May 23, 2021

FLYBOYJ said:
"Anyone who calls themselves "an expert" is a specialist who knows everything about something, and nothing about anything else."

You mean, for example, the fact that a fighter cruising at 300+ mph wouldn't be very effective in roles that required a truly long range like, say, bomber escort?

FLYBOYJ · May 23, 2021

pbehn said:
The title "expert" is normally conferred on people by others. I have only met two people who were actually legally defined "experts" they had both been called as expert witnesses in legal cases, but they never used that handle themselves.

My dad was a mechanic for 50 years - he hated the term "master mechanic." He always said there's no such thing.

Glider · May 23, 2021

FLYBOYJ said:
Several things - The P-39N manual I have shows best fuel consumption climb to 25K at 31.2 GPH
View attachment 624415

Then there is no data for a 25K cruising altitude if that was your intention?? And nowhere do show GPH.

View attachment 624418

And you didn't include the 20 gallons for warm up, you use 16 gallons reserve for the P-39 and 20 for the F4U, so I'm not going any further with the P-39

F4U

Way high cruising speed and fuel consumption. Greg beat me to the punch. Try around 200 MPH indicated at around 42 GHP at 5000' for the F4U's best cruise fuel consumption.

Sticking with your initial numbers

79 gal @ 42 GPH = 1.88 hrs in the air at 200 mph = 376 miles.

This I find very interesting. P39 in his posts has stated that the P39N had 120 gallons of fuel internally and from the above it seems as if it only had 70 usable gallons which gives even by RAF standards a pretty miserable range.

The only range figures I can find for the Typhoon are :-
Clean - 610 miles
With 45 Gallon Drop Tanks - 1,000 miles
With 2 x 1,000lb bombs - 510 miles

Most economical cruise speed 254 mph

Thumpalumpacus · May 23, 2021

pbehn said:
The title "expert" is normally conferred on people by others. I have only met two people who were actually legally defined "experts" they had both been called as expert witnesses in legal cases, but they never used that handle themselves.

Expertise should be so apparent that there's no need to proclaim it.

fubar57 · May 23, 2021

The only thing I was an expert at during my prime

PAT303 · May 23, 2021

FLYBOYJ said:
My dad was a mechanic for 50 years - he hated the term "master mechanic." He always said there's no such thing.

I was a mechanic for 25 years, the moment you think you know everything is the moment something catches you out and makes you look like a fool.

PAT303 · May 23, 2021

P-39 Expert said:
RAF did have a pretty solid idea for armament: the 20mm cannon, which they went to right after the BoB.

Biggest drawback with the 30calMG was effective range was only 200yds (AHT).

The Browning .303 had very effective incendiary and AP rounds from start to finish, they were only replaced when the Browning .50 proved their worth, which was after '43.

GrauGeist · May 23, 2021

FLYBOYJ said:
My dad was a mechanic for 50 years - he hated the term "master mechanic." He always said there's no such thing.

At one point in my mechanic career, I was ASE rated "Master Technician" with "Advanced Level Specialist" certifications (automobile engine, drive-train, body electric, etc., etc.).
Just peices of paper on the wall, honestly. Anyone can take the courses - but what makes a difference is what you do with that knowledge.

pbehn · May 23, 2021

PAT303 said:
The Browning .303 had very effective incendiary and AP rounds from start to finish, they were only replaced when the Browning .50 proved their worth, which was after '43.

And the weight of 0.5 ammunition in UK was in danger sinking the whole island.

pbehn · May 23, 2021

fubar57 said:
The only thing I was an expert at during my prime

View attachment 624430

You may be able to drink more than me, but you will never get more drunk.

Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained) (1 Viewer)

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