XP-39 II - The Groundhog Day Thread

[windhund116]

What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?

Thanks!

 

[wuzak]

The follow-on Bell XP-83 flew in Feb 1945 and did 522 mph (840 km/h) at 15,660 ft (4,773 m).

The top speed of the Me 262 A-1 was 560 mph, so the XP83 wasn't far off when Bell had more information. The Me 262 had a service ceiling of 37,000 feet and XP-83's service ceiling was 45,000 feet. The XP-83's rate of climb was 5,650 fpm versus 3,900 fpm for the Me 262. The XP-83's range was 1,730 miles versus 650 miles for the Me 262.

So, again, when Bell had more information, they didn't exactly do badly. The XP-83 beat the Me 262 in all specs except top speed, and the top speeds were very close.

Having twice the thrust of the Me 262 helped (2 x 4,000lbf vs 2 x 1,980lbf).

The XP-83 was about 30mph faster than the Meteor F.III, which was in service by late 1944, first flying in April 1943. Again the thrust of the F.III's engines were well down on the XP-83's (2 x 2,400lbf).

When the XP-83 was making its first flight the Meteor F.IV was entering production. The F.IV had more powerful engines (3,500lbf) and was about 50mph faster (best speed was at sea level and 60mph faster than XP-83's best speed).

And the XP-83 didn't match the P-80A, which was in production at the time, and also had about half the thrust of the XP-83.

So Bell wasn't doing that well.

 

[GregP]

Actually, I didn't mean the XP-83 was a real winner. I meant that, for the time, after they got the information needed for a successful design, their design was right there in the ballpark.

Wasn't the best of the lot, but also wasn't bad. I don't think it should have been bought over what WAS bought, but it wasn't a P-59, either.

 

[P-39 Expert]

And for the umpteenth time, we showed you what will happen if you remove nose armor and any weight forward of the CG. Unless you calculate exactly where you think you can put this radio, you're delusional!

I have always said that removing the nose armor would require moving the radio (approx. 50lbs) from the tail cone (arm approx. 278) up to just aft of the aft cabin armor plate (arm approx. 154). This would move the CG from arm 134.32 to arm 134.56, a difference of .24 of one inch, still within CG limits. By the way, your excel weight and balance chart is great.

Even though Bell (the manufacturer) said that the nose armor plate was not necessary for balance.

 

[FLYBOYJ]

I have always said that removing the nose armor would require moving the radio (approx. 50lbs) from the tail cone (arm approx. 278) up to just aft of the aft cabin armor plate (arm approx. 154). This would move the CG from arm 134.32 to arm 134.56, a difference of .24 of one inch, still within CG limits. By the way, your excel weight and balance chart is great.

Now you're getting it, and thanks, but that chart was Greg's invention.

Even though Bell (the manufacturer) said that the nose armor plate was not necessary for balance.

And I guess we showed, based on Bell's own data, they were wrong.

 

[P-39 Expert]

I think this point has been made before. The P-39 had a very high accident rate in the training programs in the US.
View attachment 599408

Again, training flights would probably result in more accidents than operational flights by experienced pilots who have completed training.

 

[P-39 Expert]

Now you're getting it, and thanks, but that chart was Greg's invention.

And I guess we showed, based on Bell's own data, they were wrong.

The manufacturer was wrong and we guys on a message board are right?

 

[fubar57]

Again, training flights would probably result in more accidents than operational flights by experienced pilots who have completed training.

...and these were quite possibly due to the tumbling that an inexperienced pilot could not get out of

 

[ThomasP]

Don't know how much this applies, but the P-40 was also used for advanced flight training (don't know if that is the correct term), which is part of the reason there were so many lost stateside. If the number of P-40 crashes per flight hour is significantly lower than for the P-39, that may imply the P-39 was not as safe to fly (at least during the learning period).

 

[FLYBOYJ]

The manufacturer was wrong and we guys on a message board are right?

It hasn't been the first time!!!

 

[P-39 Expert]

What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?

Thanks!

Early P-39D/F/K/L with the -35 or -63 engines (8.8 supercharger gears) couldn't get much above 18000' with a drop tank. As with any contemporary fighter most aerobatic maneuvers were prohibited, the drop tank had to be jettisoned before combat. Without the drop tank about 22500' could be gained at normal power (2600rpm) and about 27500' at combat power (3000rpm). But the drop tanks were almost always used. The Russians hardly ever used drop tanks and lightened their planes by removing the .30cal MGs, some armor and the IFF radio so their performance was much better.

A bomb could be accurately delivered with little practice by dive bombing, really more glide bombing. Normally high altitude wasn't needed on a bombing mission as the only way to accurately deliver the bomb was by diving.

Later N/Q models would cruise at 25000' with a drop tank and the N would cruise at 30000' in clean condition per the pilot's manual.

 

[GregP]

But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.

 

[Stig1207]

But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.

The most important thing about high altitude is getting up there first; over New Guinea the P-39's usually gained altitude advantage over the Zero's due to the early warning provided by the Coast Watchers.

 

[P-39 Expert]

But at any altitude above mid-teens in feet, it didn't have fighter performance. So, cruising at 30,000 feet ina P-39 was not going to happen in a war zone. Might see that in training in the U.S.A., but that didn't help win the war.

I don't know about that. With the early P-39D/K/L in 1942 you are still looking at 360mph at 22500', very competitive in the Pacific. 40mph faster than a Zero. Would climb that high easily without a drop tank.

A P-39N speed graph is attached. There are more graphs of the Q that show even faster speeds.

In 1943 there aren't going to be any FW190As at 30000'. No F4Fs. Not many Zeros or Oscars. I agree that there were not many P-39Ns cruising at 30000' but the capability was there.

I cringe whenever I hear 30000' mentioned. I just don't see it. Highest need for a fighter to go is maybe 27000' in Europe with the B-17s and B-24s at 25000'. Getting to 30000' was such a chore at wide open throttle crawling up at less than 1000fpm. Hard enough in test situations, much less actual combat. Certainly not by any Japanese bombers.

 

[jmcalli2]

At 11,040 lbs, the P-51B's wing loading ws 28.6 lbs.sq in. and 11,040 was takeoff weight for the aircraft. Oh, and they did a lot of gliding because they ran out of fuel semi-often, according to the pilots who flew them. At the Planes of Fame, we've had 3 or 4 guys who flew OUR tail number come and give a talk. Many P-59 pilots ran out of fuel and glided to the nearest airport and called for jet fuel from the nearest bar, which usually had a telephone. Jet fuel wasn't very widely available , even in 1949.

According to the book "Flame Powered" as well as former Bell employees, the huge wings were because they didn't give Larry Bell much information except a big block of wood and told him the engines would not be any bigger than the block of wood. So, Bell designed an engine bay around it, and even had to add engine mounts later when the exact location of them was passed along. They put the big wing on because they didn't have any information and erred on the "more area" side.

Also, they didn't tell Bell how much air the engines used, so the intakes are WAY oversize, and create a lot of drag when air goes in, circulates around in the intake, and leaks back out the front because there isn't enough air used to take it all. I can tell you from personal experience that the build quality is pretty good. But, Bell Aircraft simply didn't have much information about the engines and built what is basically a test bed for the engines.

The follow-on Bell XP-83 flew in Feb 1945 and did 522 mph (840 km/h) at 15,660 ft (4,773 m).

The top speed of the Me 262 A-1 was 560 mph, so the XP83 wasn't far off when Bell had more information. The Me 262 had a service ceiling of 37,000 feet and XP-83's service ceiling was 45,000 feet. The XP-83's rate of climb was 5,650 fpm versus 3,900 fpm for the Me 262. The XP-83's range was 1,730 miles versus 650 miles for the Me 262.

So, again, when Bell had more information, they didn't exactly do badly. The XP-83 beat the Me 262 in all specs except top speed, and the top speeds were very close.

Great info! Thanks.

 

[jmcalli2]

What were the flight characteristics of the P-39, with a drop tank or under-slung bomb?

Thanks!

http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf

Hope that helps.

 

[Ivan1GFP]

Hello P-39 Expert,

The manufacturer was wrong and we guys on a message board are right?

Bell made a lot of unsubstantiated claims to sell his aircraft.

It is quite astonishing to see this statement from YOU. You want us to believe your performance and handling claims when the trained test pilots, and combat pilots who actually flew the aircraft report something quite different.

I don't know about that. With the early P-39D/K/L in 1942 you are still looking at 360mph at 22500', very competitive in the Pacific. 40mph faster than a Zero. Would climb that high easily without a drop tank.

Here you go again with the "40 mph faster than a Zero". The facts simply don't agree with you.
When a captured and beat to crap and rebuilt aircraft can hit 335 MPH in testing without emergency power, what do you think one that HASN'T been wrecked and rebuilt can do when its pilot chooses to use emergency power?
Your numbers don't add up.
These early P-39s also were equipped with engines that had a critical altitude at around 12,000 feet. They made their maximum speeds around 13,000 feet.

They also weren't carrying drop tanks for decoration. They were not going to have the range to do anything useful without drop tanks.

In 1943 there aren't going to be any FW190As at 30000'. No F4Fs. Not many Zeros or Oscars. I agree that there were not many P-39Ns cruising at 30000' but the capability was there.

You have a very interesting view of history. Do you really believe those other types were not there in 1943? Some of those other types were already being replaced by aircraft with better altitude capability by 1943.

Another couple questions for you are: Would your hypothetical P-39N cruising at 30,000 feet be carrying a drop tank?
Would it be a P-39N with 120 gallons of internal fuel or only 87 gallons?
If it is NOT carrying a drop tank, then where would it be going at 30,000 feet where internal fuel would be sufficient for the mission?

Also, as GregP pointed out, just because an aircraft can get to 30,000 feet doesn't mean it can fight there. The A6M2 had a service ceiling somewhere between 35,000 feet and 38,000 feet depending on the information source but it most certainly wasn't a high altitude aircraft either.

- Ivan.

 

[P-39 Expert]

http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf

Hope that helps.

There are more P-39D tests and some graphs on the P-39K which has the same 8.8 supercharger gears also.

 

[Ivan1GFP]

http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6897_PHQ-M-19-1385-A-Addendum.pdf

Hope that helps.

Hello jmcalli2,

Actually that helps a lot.

Note that the P-39D In this particular test was only able to achieve 358 MPH @ 13,000 feet.
The aircraft was not carrying a belly tank or any of the mounting hardware in that particular test configuration.
It was making about 20 HP more than nominal and at the typical critical altitude for the early model P-39.

The only way this is 40 MPH faster than the A6M2 is if the A6M2 is puttering along at cruise power +50 mm Boost 2350 RPM (275 Knots).

- Ivan.

 

[P-39 Expert]

Hello P-39 Expert,



Bell made a lot of unsubstantiated claims to sell his aircraft. Like what?

It is quite astonishing to see this statement from YOU. You want us to believe your performance and handling claims when the trained test pilots, and combat pilots who actually flew the aircraft report something quite different.

And plenty of test pilots and combat pilots report that it handled just fine. P-39 was a perfectly good handling airplane that served the country well when there wasn't anything else except the P-40 and F4F.

Here you go again with the "40 mph faster than a Zero". The facts simply don't agree with you. My facts all come from wwiiaircraftperformance.org
When a captured and beat to crap and rebuilt aircraft can hit 335 MPH in testing without emergency power, what do you think one that HASN'T been wrecked and rebuilt can do when its pilot chooses to use emergency power? I have no idea, but there were sure a lot of captured Zeros tested. And after the war Zero pilots who were interviewed substantiated the results of those tests. The Zero was many things, but fast wasn't one of them.
Your numbers don't add up.
These early P-39s also were equipped with engines that had a critical altitude at around 12,000 feet. They made their maximum speeds around 13,000 feet. More like around 14000' with ram, and they were able to hold that speed up to around 16000'. You talk like they stopped running when they reached their critical altitude.

They also weren't carrying drop tanks for decoration. They were not going to have the range to do anything useful without drop tanks.

And those tanks were dropped for combat, weren't they.

You have a very interesting view of history. Do you really believe those other types were not there in 1943? Some of those other types were already being replaced by aircraft with better altitude capability by 1943. Initial combat dates: P-38 November 1942, Corsair Feb 1943, P-47 May 1943, Hellcat August 1943, Merlin P-51 December 1943. P-38 barely made combat in 1942 a full year after the war started. P-39, P-40 and F4F were all that was available in 1942.

Another couple questions for you are: Would your hypothetical P-39N cruising at 30,000 feet be carrying a drop tank? I already said it was in clean condition.
Would it be a P-39N with 120 gallons of internal fuel or only 87 gallons? Either way. I really don't know why the AAF reduced the fuel from 120gal to 87gal internal, unless it was at the insistence of the Russians.
If it is NOT carrying a drop tank, then where would it be going at 30,000 feet where internal fuel would be sufficient for the mission? Returning from a mission where it had to drop the tank it would have 120gal less a 20 minute landing reserve (10gal) less 15 minute combat reserve (18gal at 25000') leaving 92gal left using 48gal/hr at 30000' resulting in 1.92hr at 305mphTAS or 585mi after reserves. A radar alerted interception mission with no drop tank and 120gal internal would be reduced by the takeoff allowance of 16gal, 15min combat allowance at 30000' of 14gal and a landing reserve of 10gal resulting in 80gal useable at 48gph or 1.7hours patrol time. Plenty of time to intercept a bombing raid.

Also, as GregP pointed out, just because an aircraft can get to 30,000 feet doesn't mean it can fight there. The A6M2 had a service ceiling somewhere between 35,000 feet and 38,000 feet depending on the information source but it most certainly wasn't a high altitude aircraft either. Why couldn't it fight there? All it had to do was be above the enemy and dive on him.

- Ivan.

Please expand above.