XP-39 and the Claims

[FLYBOYJ]

So, we're twelve pages into this topic, talking about the XP-39s top speed, the P-39's external tank capacity and range and the P-39N's performance to a point where minutia has been exhausted. After all that, so what? The P-39 had a dismal record in air combat in AMERICAN service. Woulda coulda shoulda aside, the P-39 was deemed unsuitable for AMERICAN use, which is why it was purchased by the AAF. It wasn't designed as an export fighter for the Russians.

Yup - and it may go into page 13!!

 

[P-39 Expert]

I have to say you hit the nail on the head, P-39 Expert.

Thank you Mike Williams for coming up with such a great website.

Absolutely. Do you think he will reply to my questions?

 

[GregP]

No idea. I'm pretty sure Mike Williams stays busy. At least, his website indicates he spends a lot of time there.

Good luck. I bet if he reads this, he'll answer. But whether or not he reads this thread is a bet I wouldn't care to make since I don't personally know Mike.

 

[pbehn]

Absolutely. Do you think he will reply to my questions?

How do you propose someone merely called Mike Williams would reply to someone called "P-39 Expert" on the subject of the P-39?

 

[Jugman]

NACA estimated the XP-39 would have a top speed of 340mph @ 20,000ft in its original configuration. Which strongly suggests that the top speed achieved before it went to NACA was less than 340mph.

NACA also estimated that a cleaned up turbocharged XP-39 would have a top speed of 392mph @ 20,000ft. Could this be the source of the XP-39 managing 390mph?

See XP-39 and the Claims

It's actually worse than that. The NACA full size tunnel had maximum sustained speed of 100 mph. Every NACA estimate I have seen from this time period from aircraft tested in the full size tunnel have been on the optimistic side. Based on what the XP-39B could actually do ( 375 @ 1040hp @ 15,000ft), the estimated performance ( 402 @ 1150hp @ 13,500ft) was ~15-20mph too high. The original and cleaned configurations are probably off by a similar margin

 

[drgondog]

It's actually worse than that. The NACA full size tunnel had maximum sustained speed of 100 mph. Every NACA estimate I have seen from this time period from aircraft tested in the full size tunnel have been on the optimistic side. Based on what the XP-39B could actually do ( 375 @ 1040hp @ 15,000ft), the estimated performance ( 402 @ 1150hp @ 13,500ft) was ~15-20mph too high. The original and cleaned configurations are probably off by a similar margin

FWIIW - I totally agree.

If you go back to the images including NACA renditions of original XP-39, the stated CDhs=0.0321 which REALLY high even for Sea Level (P-51B comparable was 0.0208 in Full service condition for 100mph RN of 6.19x10^6 at Langley. The comparable (much cleaner P-63 in the wind tunnel - same series of tests was 0.0221 @RN=6,41x10^6).

The calculated CDt including Mach No correction at 18,000 feet for 395mph of a P-51B at full throttle, 1480BHP/1091 THP = 0.0195 @ RE=15.31x10x^6 with CLOSED aft scoop. Compare that to the NACA CDhs = 0.0321 for 340mph. Then ask yourself, how would it ever get close to 400mph at 20K with that large Drag coefficient?

With wide open scoop the CDt for same Mach corrections,The same P-51B at full throttle, the CDt was 0.023 with WIDE Open Scoop (which caused increased Delta Cdt= 0.040)... with some Meredith Cooling drag reduction still occurring.

This CDt is the entire parasite and form drag of the Mustang x Mach No Correction (~ 1.2 for 395mph at 18000 feet) Plus Induced Drag..

Addt'l comments:
The XP-39 drag contributions of both the turbo and oil cooler intakes had to be huge relative to the Mustang.
The XP-39 had no engine exhaust thrust contribution to increase Thp - the P-51B described above yielded 256 pounds of thrust.
There is no indication one way or the other that NACA value "CDhs" included momentum recovery losses for the airframe/wing combo immersed in the prop vortex, but my calculations include such losses as well as the carburetor intake.
With Meredith contributions of closed aft scoop, the net P-51B cooling drag was estimated to be zero, although NAA claimed some net thrust at top speed. The calculated difference between the open scoop top speed and closed scoop top speed horsepower required was 230 pounds of thrust to increase top speed 25mph (393 vs 420) with open scoop.

I spent a lot of time re-creating NA Report 5534 and 8449 Performance calculations methodologies to be able to extract these values from the data gathered in the P-51B-1 Flight Test of May 1943

 

[Reluctant Poster]

In what way.

You stated they were driving the defenses out of Northern France, Belgium and the Netherlands. I would say that was an excuse for staying within escort range and not doing what they had promised everyone they would do i.e. bombing Germany.
I would also note the USAAF wasn't really bombing the low countries: 36 tons in 1942 and 767 tons in 1943. They didn't start doing that until after D-Day: 12,312 tons in 1944.
They were bombing France: 1,624 tons in 1942 and 14,237 in 1943 but much of that was directed against the U Boat pens farther south.

 

[pbehn]

You stated they were driving the defenses out of Northern France, Belgium and the Netherlands. I would say that was an excuse for staying within escort range and not doing what they had promised everyone they would do i.e. bombing Germany.
I would also note the USAAF wasn't really bombing the low countries: 36 tons in 1942 and 767 tons in 1943. They didn't start doing that until after D-Day: 12,312 tons in 1944.
They were bombing France: 1,624 tons in 1942 and 14,237 in 1943 but much of that was directed against the U Boat pens farther south.

Some information on Luftwaffe airfields in Netherlands and Belgium. Which also details attacks on them. They were routinely attacked when in service especially during and after Big Week. It is not true that their "job" was to bomb Germany, it was to win the war, and immediately before D-Day that involved destroying as much of the LW as possible and prepare for D-Day itself. This involved bombing targets in the landing area and also distraction bombing elsewhere to draw attention away from Normandy.

http://www.ww2.dk/Airfields - Netherlands.pdf
http://www.ww2.dk/Airfields - Belgium and Luxembourg.pdf
For example Schipol my bold.
Schiphol attacked by Allied aircraft many times right from May 1940. 20 Jun 40: bombed – 1 x Ju 52 from I./KG z.b.V. 172 badly damaged on the ground. 23 Jun 40: bombed – 1 x Ju 52 from I./KG z.b.V. 172 destroyed on the ground. 10 Aug 40: bombed – 1 x He 111H from KGr. 126 damaged on the ground. 3 Oct 43: air attack by 9th AAF medium bombers – 2 x Me 410 A-1s from 14./KG 2 and 2 x He 111Hs from Wetterflugstelle Holland and a Klemm Kl 35 from Luftgaukdo. Holland bombed on the ground at Amsterdam-Schipol airfield during an Allied air attack and destroyed (1) or damaged (2). Additionally, hangars, buildings on the SE boundary and the West dispersal were all hit. 3 Nov 43: bombed – the very large hardstand apron in front of the central hangars on the SE boundary heavily cratered. 13 Dec 43: in a decisive blow against Schiphol that all but eliminated it from the war, 208 B-26 Marauders from IX Bomber Command dropped 787 1,000-lb. bombs on the airfield - 2 x Bf 109Gs from II./JG 3, 4 x Me 410 A-1s from II./KG 2 and 14./KG 2 plus 1 x He 111 H3 from Wetterflugstelle Holland destroyed (4) or damaged (3) on the ground. Hangars, repair shops, aircraft shelters, runways and taxiways received heavy damage.

 

[Aeroweanie]

After years of lurking on this site, its time for me to go public. I haven't read all 13 pages of this thread, so I apologize if I'm going over ground that has already been covered.

In 2000, several years after working with with Birch Matthews on Cobra!, I published a SAE paper on the P-39 and P-63. In this paper, which is attached, I delved into the technical side of these aircraft in deeper detail. Now, 20 years later, I have resurrected and expanded on this paper for a presentation that I'll be giving to the Phoenix chapter of the AAHS on February 17th. I'll upload slides when they are finalized. I welcome feedback.

 

[fubar57]

 

[Snautzer01]

Some information on Luftwaffe airfields in Netherlands and Belgium. Which also details attacks on them. They were routinely attacked when in service especially during and after Big Week. It is not true that their "job" was to bomb Germany, it was to win the war, and immediately before D-Day that involved destroying as much of the LW as possible and prepare for D-Day itself. This involved bombing targets in the landing area and also distraction bombing elsewhere to draw attention away from Normandy.

http://www.ww2.dk/Airfields - Netherlands.pdf
http://www.ww2.dk/Airfields - Belgium and Luxembourg.pdf
For example Schipol my bold.
Schiphol attacked by Allied aircraft many times right from May 1940. 20 Jun 40: bombed – 1 x Ju 52 from I./KG z.b.V. 172 badly damaged on the ground. 23 Jun 40: bombed – 1 x Ju 52 from I./KG z.b.V. 172 destroyed on the ground. 10 Aug 40: bombed – 1 x He 111H from KGr. 126 damaged on the ground. 3 Oct 43: air attack by 9th AAF medium bombers – 2 x Me 410 A-1s from 14./KG 2 and 2 x He 111Hs from Wetterflugstelle Holland and a Klemm Kl 35 from Luftgaukdo. Holland bombed on the ground at Amsterdam-Schipol airfield during an Allied air attack and destroyed (1) or damaged (2). Additionally, hangars, buildings on the SE boundary and the West dispersal were all hit. 3 Nov 43: bombed – the very large hardstand apron in front of the central hangars on the SE boundary heavily cratered. 13 Dec 43: in a decisive blow against Schiphol that all but eliminated it from the war, 208 B-26 Marauders from IX Bomber Command dropped 787 1,000-lb. bombs on the airfield - 2 x Bf 109Gs from II./JG 3, 4 x Me 410 A-1s from II./KG 2 and 14./KG 2 plus 1 x He 111 H3 from Wetterflugstelle Holland destroyed (4) or damaged (3) on the ground. Hangars, repair shops, aircraft shelters, runways and taxiways received heavy damage.

Schiphol is the name of the airfield. Still is a mayor one in the eu.

 

[pbehn]

Schiphol is the name of the airfield. Still is a mayor one in the eu.

I know, after working in Germany for years taking the Hanover Schiphol Teesside flight every other Friday the bar staff in the upstairs bar all knew me by name lol.

 

[tomo pauk]

After years of lurking on this site, its time for me to go public. I haven't read all 13 pages of this thread, so I apologize if I'm going over ground that has already been covered.

In 2000, several years after working with with Birch Matthews on Cobra!, I published a SAE paper on the P-39 and P-63. In this paper, which is attached, I delved into the technical side of these aircraft in deeper detail. Now, 20 years later, I have resurrected and expanded on this paper for a presentation that I'll be giving to the Phoenix chapter of the AAHS on February 17th. I'll upload slides when they are finalized. I welcome feedback.

Thank you for sharing that here

 

[Glider]

Absolutely. Do you think he will reply to my questions?

You might try summarising the questions you would like responses to. Personally I admit to being totally confused as to exactly what is supposed to be outstanding.
A lot of postings are made, positions stated but questions not so much

 

[Koopernic]

After years of lurking on this site, its time for me to go public. I haven't read all 13 pages of this thread, so I apologize if I'm going over ground that has already been covered.

In 2000, several years after working with with Birch Matthews on Cobra!, I published a SAE paper on the P-39 and P-63. In this paper, which is attached, I delved into the technical side of these aircraft in deeper detail. Now, 20 years later, I have resurrected and expanded on this paper for a presentation that I'll be giving to the Phoenix chapter of the AAHS on February 17th. I'll upload slides when they are finalized. I welcome feedback.

Hope you're not vegetarian like my wife because I gave you Bacon. Has there ever been an analysis of what P-39 performance would have been like with say a Merlin XX (two stage Merlin used in the latter Hawker Hurricane to keep it competitive?) The P40F received this engine.

 

[wuzak]

Has there ever been an analysis of what P-39 performance would have been like with say a Merlin XX (two stage Merlin used in the latter Hawker Hurricane to keep it competitive?) The P40F received this engine.

Two speed.

I'm not sure where the main problem with putting the Merlin into the P-39 would be.

Some of the problems include:
Updraft carburettor would not fit - would have to be changed for an updraft carby.
The supercharger casing may be too big to fit inside the engine bay of the fuselage.
Nose case would have to be modified to suit a remote gearbox - the rear section of the nose case of the Merlin was in unit with the crankcase.
The Merlin needed more cooling than the contemporary V-1710 - the P-39 was already marginal with cooling, from what I understand.
The Merlin XX was about 100lb heavier than the single stage V-1710. May need more ballast up front.

The Merlin was shorter than the V-1710, so that is a positive.

 

[FowellBox]

Quote: Updraft carburettor would not fit - would have to be changed for an updraft carby. Endquote.
I assume a typo?
Brian

 

[Snautzer01]

I know, after working in Germany for years taking the Hanover Schiphol Teesside flight every other Friday the bar staff in the upstairs bar all knew me by name lol.

Ok you mis typed it a few times in a few post back.

 

[wuzak]

Quote: Updraft carburettor would not fit - would have to be changed for an updraft carby. Endquote.
I assume a typo?
Brian

Oops, yes. Would need a downdraft carby.

 

[P-39 Expert]

Two speed.

I'm not sure where the main problem with putting the Merlin into the P-39 would be.

Some of the problems include:
Updraft carburettor would not fit - would have to be changed for an updraft carby.
The supercharger casing may be too big to fit inside the engine bay of the fuselage.
Nose case would have to be modified to suit a remote gearbox - the rear section of the nose case of the Merlin was in unit with the crankcase.
The Merlin needed more cooling than the contemporary V-1710 - the P-39 was already marginal with cooling, from what I understand.
The Merlin XX was about 100lb heavier than the single stage V-1710. May need more ballast up front.

The Merlin was shorter than the V-1710, so that is a positive.

Also mounts were different on the Allison and Merlin.