XP-39 II - The Groundhog Day Thread

[GrauGeist]

How many P-39s were lost to spinning/tumbling?

A quick glance at Joe Baugher's site shows that six P-39s out of the production batch 41-6722/41-7115 (P-39D-BE) crashed due to spin.
There's many more out of the batch that indicate wrecking with no specifics - those could be crossed with the USAAF MACR reports for details.

There's more, but I don't have all day to look the rest up.

 

[GregP]

With reference to post #527 above and the P-39 doing a "snap and spin" at anything below 250 mph:

1) You take off and land well below 250 mph.
2) You climb at 158 - 162 knots, well below 250 mph.
3) Approach speed is 130 mph.
4) The airplane cruises around 250 mph in high-speed cruise.

In general, go look at a pilot's handbook. Almost ALL speeds given are below 250 mph except the very high speed stuff. I doubt they'd have bought something that was a coffin in most of its operating envelope. It would "snap" only if you stall it.

So, I'm not too sure what is being said. Stall speed is about 105 mph flaps up and about 90 mph flaps down, and the stall is relatively benign unless you are aft of the aft CG limit.

 

[P-39 Expert]

Not at all! Just pointing out the potential for an inexperienced or negligent pilot!


Many from dives, agree! Now your comment "Either engine, since both turned the wrong way" makes totally no sense! Do you know what a critical engine is? Do you know why there were many engine out facilities on the P-38? It definitely wasn't from "Either engine, since both turned the wrong way."

The props both turned outward so if one engine was lost the torque of the good engine wanted to bank the plane toward the heavier side of the dead engine.

Agree - to include the P-39

 

[P-39 Expert]

Hello P-39 Expert,

It seems like most of these points have already been addressed by other forum members but here goes anyway.



Even with existing engines, the P-39 had a serious tendency to overheat on the ground. It also tended to exceed temperature limits in high power operation such as sustained climbs. Putting in a more powerful engine and running at higher altitude makes the problem worse. There is a reason why modern operators of P-39s tend to have spray bars installed to cool the radiators.

Would overheat if kept on the ground too long. Not normally a problem since the P-39 had excellent visibility forward while taxiing, while a tail dragger was blind to the front and had to s-turn while taxiing. P-39 just drove to the end of the runway while the pilot performed the pre-flight checks and then took off.

The P-51 85 Gallon Fuselage tank certainly created a CoG problem for the aircraft that did not exist before.
To state that, "P-39 didn't have any real CG problems." means you either don't understand the evidence that has been presented or are in complete denial. I don't know how to correct either situation.

You could just stop this heresay that the P-39 was out of balance. It certainly was not. After the nose ammunition was expended one normally returned to base instead of doing acrobatics.

Let's say it is possible to add another 30 Gallons in fuel cells to the outer wing of the P-39 in place of the wing guns.
That would make a total of 150 Gallons.
Please note that the P-51 already had 184 Gallons of internal fuel BEFORE it was determined to be necessary to add a 85 Gallon fuselage tank that caused some CoG problems without drop tanks.
Note also that the P-51 could carry two drop tanks on the wings.
The P-39 could carry at most one drop tank on the centerline.
What makes you think this is sufficient fuel?

Sufficient because 150gal was the internal tankage of the contemporary P-38F/G and P-40E/F/K. Actually the P-38 didn't see combat on a large scale until late 1942. The Mustang I didn't see combat until April 1943 with the Brits. It already weighed 8600lbs clean. With two 75gal drop tanks it would have weighed 9600lbs and likely couldn't leave the ground with its 1150hp engine.

The 37 mm cannon certainly is a big hammer, but it has a ridiculously low firing rate, low ammunition capacity and a low duration of fire and of course has a pretty loopy trajectory because of its low muzzle velocity. Google 37mm M4 cannon and you will see how rapid it's rate of fire was. Trajectory was flat out to 400yards, about the outer limit of accurate air to air gunnery. P-47s wing mounted guns were set to converge at 300-350yds. After that they were diverging instead of converging.
This is not an ideal weapon to track maneuvering targets. 12 seconds of fire isn't much at all. 60-80% of planes shot down never saw their assailant, so they weren't maneuvering. 12 seconds is exactly what Spitfires had with 120rds. P-38 had 15 seconds. Three whole seconds more.
There are many better ideas for motor cannon and neither of the guns that were normally installed in the P-39 qualify as such. Fine, then use the 20mm cannon with a larger ammunition tray. Save 80lbs over the 37mm.
The remaining two synchronized .50 cals even as you pointed out really do not deliver a great weight of fire. They were centerfire weapons and a .50calMG was certainly capable of shooting down another fighter. The 37mm and twin .50s offered more weight of fire than four .50cal MGs on the P-51A/B/C. You have posed these same statements and gotten the same answers from me before in this thread.

- Ivan.

Please expand above.

 

[fubar57]

The Bell P-39 Airacobra & P-63 Kingcobra

Another reason was that the Red Air Force thoroughly evaluated the Airacobra before putting it into service, finding out the hard way about its vicious spin characteristics, with several test pilots killed. The faults were documented, however, with rules for flying the aircraft written up for operational pilots -- they were warned to never perform aerobatics if they had expended their ammunition -- and training implemented to make sure P-39 pilots knew how to avoid spins and, when possible, head them off before the point of no return. Procedures had to be devised for maintenance in extreme cold conditions. Bell engineers went to the USSR to assist the Soviets in qualifying the P-39, obtaining feedback for refinements to the design
Sources include:

• US AIRCRAFT IN THE SOVIET UNION & RUSSIA by Yefim Gordon, Sergey Komissarov, and Dmitriy Komissarov, Midland Publishing, 2008.
  
  
• "Bell P-39 / P-63 Variant Briefing" by Robert F. Dorr, WINGS OF FAME, Volume 10, 1998.

EDIT: added sources for above

 

[DerAdlerIstGelandet]

"One normally returned to base instead of doing acrobatics".



Sorry, I have been trying hard to give you the benefit of the doubt, but with that comment you have lost me.

No one is saying the P-39 was un-flyable, and no one is talking extremes here but you. It is clear you don't actually understand what you are talking about. You have great "book" knowledge, but you don't know how to put the pieces together.

You don't have to be flying acrobatics to be in a deadly situation with a tail heavy rear CG aircraft. Any aircraft may have issues, especially when landing, or recovering from a stall. Any aircraft type can get into a stall, at any speed, and at any mode of flight just by exceeding the angle of attack. If your CG is out of balance or even very close to it, the risk is higher.

The aircraft I fly is not permitted to perform spins or acrobatics, and is a slow little single engine monoplane. Guess what? If I get out of CG, or really close to my limit, I am going to possibly experience problems with control and stability. That includes your beloved P-39.

So please stop, just stop...

Stop with the heresay, and listen to the people trying to help you.

 

[Ivan1GFP]

Hello GregP,

Consider the context of those comments by the pilot.
The P-39 certainly has a CoG either close or behind its aft limits to be able to be tumbled.
It is NOT stable and its ability to weathervane is somewhat lacking.
Its tendency to enter a flat spin is much higher than if the CoG is in a reasonable range.
The recovery from the tumble is a vertical dive which needs some control input to avoid becoming a lawn dart.
It may be quite reasonable to carry a bit extra speed to be able to pull out safely under those conditions without entering an accelerated stall.

- Ivan.

 

[Ivan1GFP]

Hello P-39 Expert,

Would overheat if kept on the ground too long. Not normally a problem since the P-39 had excellent visibility forward while taxiing, while a tail dragger was blind to the front and had to s-turn while taxiing. P-39 just drove to the end of the runway while the pilot performed the pre-flight checks and then took off.

You MIGHT be correct if your squadron operated a single aircraft with nothing else competing for the same runways.
That is not how fighters are used operationally. They are typically flown in groups. Having an aircraft idle a bit longer than expected and then suffering an engine failure on take-off is not an acceptable outcome. Pilots who flew the P-39 comment on its tendency to overheat. What makes you so much more knowledgeable than the men who flew the actual aircraft that you can declare this not to be a problem when it has been extensively documented to be a problem with the type?

Sufficient because 150gal was the internal tankage of the contemporary P-38F/G and P-40E/F/K. Actually the P-38 didn't see combat on a large scale until late 1942. The Mustang I didn't see combat until April 1943 with the Brits. It already weighed 8600lbs clean. With two 75gal drop tanks it would have weighed 9600lbs and likely couldn't leave the ground with its 1150hp engine.

The P-38 actually carried twice that amount of internal fuel, but since it had two engines, that is reasonably comparable.
The difference though is that it could also carry two drop tanks of either 150 or 300 Gallons each.
There is no argument that the P-40 carried a pretty comparable fuel load to your hypothetical P-39.
As for the P-51, what you are forgetting is that even with an engine comparable to the P-39D, it was hitting speeds that were about the same as a P-39Q with a much later engine. The Mustang Mk.II still with the single stage Allison was also able to achieve over 400 MPH at 10,000 -12,000 feet which is well beyond what any P-39 could do.

Although you can argue that the fuel loads are comparable, the P-39 has to sacrifice a substantial portion of its armament to get this increased fuel load which was already standard in the other fighters.

Google 37mm M4 cannon and you will see how rapid it's rate of fire was. Trajectory was flat out to 400yards, about the outer limit of accurate air to air gunnery. P-47s wing mounted guns were set to converge at 300-350yds. After that they were diverging instead of converging.

37 mm T9 / M4 cannon. Rate of Fire: 140-150 rounds per minute
Muzzle Velocity: 610 Meters / second -- 2000 feet per second.

The problem isn't that you can't get all the guns on the P-39 to converge on a point at a distance.
That part is easy.
The problem is that as soon as you start pulling any G while firing, the trajectories don't line up any more.
A uniform battery or at least guns that have similar ballistics avoid that situation. The Hispano 20 mm cannon on some Airacobra is very similar in velocity to the .50 cals but the problem is the lack of duration of fire.

You also might want to keep in mind that bullets don't just disappear past their point of convergence.

60-80% of planes shot down never saw their assailant, so they weren't maneuvering. 12 seconds is exactly what Spitfires had with 120rds. P-38 had 15 seconds. Three whole seconds more.
.....
Fine, then use the 20mm cannon with a larger ammunition tray. Save 80lbs over the 37mm.

The question here is what else do these other fighters have remaining when their cannon ammunition runs out?
These other cannon also have a much higher rate of fire that the 37 mm does not.
Switching to the 20 mm Hispano Mk.I / HS-404 option on the Airacobra only makes things worse.
The duration of fire drops to 6 seconds instead of 12.....

They were centerfire weapons and a .50calMG was certainly capable of shooting down another fighter. The 37mm and twin .50s offered more weight of fire than four .50cal MGs on the P-51A/B/C. You have posed these same statements and gotten the same answers from me before in this thread.

Your opinion and mine differ. The US Army who was paying for the weapon systems didn't seem to agree with your opinion.
The Soviets seemed to be in pretty good agreement with you but they were not the ones buying the aeroplanes.

ANYTHING can shoot down an aeroplane. That is the principle of the "Golden BB".
I just would not want to depend on it on a large scale.

- Ivan.

 

[FLYBOYJ]

The props both turned outward so if one engine was lost the torque of the good engine wanted to bank the plane toward the heavier side of the dead engine.

And that doesn't make a difference! Apparently you never heard of a "critical engine."

Critical engine - Wikipedia

Depending who you talk to the P-38 didn't have a critical engine or both were critical. In either case the P-38 had great engine out characteristics once you were trained on how to fly a twin!

 

[glennasher]

Ivan1GFP, I think you're typing to a brick wall.

He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.

I have learned a lot from this place, but I certainly don't claim to be an "Expert" at anydangedthing. I've often thought that self-declared "experts" are anything but that. I kinda think that he's just trolling you all. I'm moving on to other things.

 

[GregP]

Hi Ivan!

I fully realize the possibilities for the P-39 and agree there was an issue there, but saying it would snap out of control if the controls were moved below 250 mph is ... a bit of an exaggeration.

Below is an example of a twin-engine aircraft again running out of aispeed while climbing, stalling, being unable to recover. This is the classic "out of airspeed, altitude, amd ideas" situation. The Mosquito has the highest engine out Vmc of any twin piston aircraft I know of, at 160 mph or more, depending on load. It's a "Wooden Wonder" when flown with skill and precision, but a bit of a handful when operated without said skill, as below.




Wish we' stop seeing these basic mistakes!

 

[P-39 Expert]

Hello P-39 Expert,



You MIGHT be correct if your squadron operated a single aircraft with nothing else competing for the same runways.
That is not how fighters are used operationally. They are typically flown in groups. Having an aircraft idle a bit longer than expected and then suffering an engine failure on take-off is not an acceptable outcome. Pilots who flew the P-39 comment on its tendency to overheat. What makes you so much more knowledgeable than the men who flew the actual aircraft that you can declare this not to be a problem when it has been extensively documented to be a problem with the type?

So now the P-39 can't operate in a group?

The P-38 actually carried twice that amount of internal fuel, but since it had two engines, that is reasonably comparable.
The difference though is that it could also carry two drop tanks of either 150 or 300 Gallons each.
There is no argument that the P-40 carried a pretty comparable fuel load to your hypothetical P-39.
As for the P-51, what you are forgetting is that even with an engine comparable to the P-39D, it was hitting speeds that were about the same as a P-39Q with a much later engine. The Mustang Mk.II still with the single stage Allison was also able to achieve over 400 MPH at 10,000 -12,000 feet which is well beyond what any P-39 could do.

Although you can argue that the fuel loads are comparable, the P-39 has to sacrifice a substantial portion of its armament to get this increased fuel load which was already standard in the other fighters.

Again, the P-39 was operational from the beginning of the war. Earliest Mustang I combat was April 1943. With comparable engines (-35 vs -39, -81 vs -85) the P-39 was about 10-15mph slower but outclimbed the P-51.

37 mm T9 / M4 cannon. Rate of Fire: 140-150 rounds per minute
Muzzle Velocity: 610 Meters / second -- 2000 feet per second.

The problem isn't that you can't get all the guns on the P-39 to converge on a point at a distance.
That part is easy.
The problem is that as soon as you start pulling any G while firing, the trajectories don't line up any more. They do out to 400 yards.
A uniform battery or at least guns that have similar ballistics avoid that situation. The Hispano 20 mm cannon on some Airacobra is very similar in velocity to the .50 cals but the problem is the lack of duration of fire.

You also might want to keep in mind that bullets don't just disappear past their point of convergence.

No, they just keep moving farther away from each other.

The question here is what else do these other fighters have remaining when their cannon ammunition runs out? The P-39 still had two .50s with a duration of 25 seconds.
These other cannon also have a much higher rate of fire that the 37 mm does not. The 37mm put out more pounds of projectile per second than the 20mm.
Switching to the 20 mm Hispano Mk.I / HS-404 option on the Airacobra only makes things worse.
The duration of fire drops to 6 seconds instead of 12..... I said use a bigger ammunition tray for the 20mm. 120rds instead of 60.



Your opinion and mine differ. The US Army who was paying for the weapon systems didn't seem to agree with your opinion. They only bought 9500 of them, about the same as the P-38.
The Soviets seemed to be in pretty good agreement with you but they were not the ones buying the aeroplanes. No, they were using them to win the war in the East. 4 out of their top 5 aces and scores of 20+ victory aces flew this plane against the Luftwaffe. Their favorite plane. Begged for more of them. Demanded more of them. From ground level to over 8000meters (26500').

ANYTHING can shoot down an aeroplane. That is the principle of the "Golden BB".
I just would not want to depend on it on a large scale.

- Ivan.

Expand above.

 

[GregP]

Avoiding Stalls and Spins in WWII Warbirds

 

[FLYBOYJ]

Ivan1GFP, I think you're typing to a brick wall.

He either is unwilling or unable to process the information so aptly put to him. He keeps up with a circular argument that has been refuted too many times to think it's not intentional.

I have learned a lot from this place, but I certainly don't claim to be an "Expert" at anydangedthing. I've often thought that self-declared "experts" are anything but that. I kinda think that he's just trolling you all. I'm moving on to other things.

I've been in this business for over 40 years and I'm still learning, especially when I come on here!

And the same thing for "master mechanics"

 

[FLYBOYJ]

I think this video might have been posted on here. I've always enjoyed watching it. Some of our pilots, please comment when you see the attitude of the aircraft after some of the spin/ stall sequences. The last portion of the clip drives the point home!

I also think the commentator "sugar coats" this. I'd bet dollars to donuts all of these scenes were flown by seasoned Bell test pilots, to include the last portion!

 

[DerAdlerIstGelandet]

I've been in this business for over 40 years and I'm still learning, especially when I come on here!

And the same thing for "master mechanics"

I've been in the aviation industry (military and civilian) for 20 years now. Mechanic, Aircrew Member, Safety, Engineering (note: I am not an engineer), and a private pilot.

The most important thing I have learned over the last 20 years is that I know exactly enough to get myself in trouble.

Seriously, in aviation you never stop learning. Every day I learn something new. You also never know everything, or you are never an absolute expert at everything. That does not mean you can't be proficient and an expert, just that there is always room for continuous growth and improvement.

The day you stop learning in aviation is the day you need to hang it up. You are dangerous, and you're going to get someone hurt or worse.

 

[FLYBOYJ]

The day you stop learning in aviation is the day you need to hang it up. You are dangerous, and your going to get someone hurt or worse.

Amen!

 

[SaparotRob]

I think this video might have been posted on here. I've always enjoyed watching it. Some of our pilots, please comment when you see the attitude of the aircraft after some of the spin/ stall sequences. The last portion of the clip drives the point home!

I also think the commentator "sugar coats" this. I'd bet dollars to donuts all of these scenes were flown by seasoned Bell test pilots, to include the last portion!

That was neat!

 

[XBe02Drvr]

P-39 Expert said:
The props both turned outward so if one engine was lost the torque of the good engine wanted to bank the plane toward the heavier side of the dead engine.

Good god man, that's normal behavior for any twin with wing mounted engines! But it's not the torque that does it; it's the asymmetric thrust. You need to study up on this before shooting your mouth off while pointing at your foot.
"Critical engine" comes into play only in the case of twins whose engines both turn in the same direction, and then it's primarily P factor, not torque that's the culprit. I'm not going to lecture you on this; go look it up yourself.
While you're at it you might discover the meanings of things like VMCa and VMCg, VYse, Vxse, Accelerate-Stop, Balanced Field Length, and the takeoff speeds; V1, Vr, and V2.
Don't sweat it; we all get our "night in the barrel" from time to time, when every approach ends in a waveoff or a bolter and the guys in the ready room are critiquing our every clumsy move. It isn't personal, and they've all been through it too. A little ball-busting toughens the hide.

 

[Ivan1GFP]

Hi Ivan!

I fully realize the possibilities for the P-39 and agree there was an issue there, but saying it would snap out of control if the controls were moved below 250 mph is ... a bit of an exaggeration.

Below is an example of a twin-engine aircraft again running out of aispeed while climbing, stalling, being unable to recover. This is the classic "out of airspeed, altitude, amd ideas" situation. The Mosquito has the highest engine out Vmc of any twin piston aircraft I know of, at 160 mph or more, depending on load. It's a "Wooden Wonder" when flown with skill and precision, but a bit of a handful when operated without said skill, as below.




Wish we' stop seeing these basic mistakes!

Hello GregP,

The situation with the Mosquito in the accident is entirely different. It was a mechanical failure that caused the accident.
The maneuver was intended to run out of airspeed in a vertical climb.
What was NOT intended was to have an engine failure with no airspeed and while both engines were running at very high power settings. At zero airspeed, the remaining engine caused an uncontrollable yaw which the pilot was able to recover from but he could not regain enough flying speed in the altitude remaining.

- Ivan.