XP-39 II - The Groundhog Day Thread

[XBe02Drvr]

When the P-39 prop pitch control went, the blades went into fine pitch which meant they produced less forward thrust whilst being easier for the engine to spin. If you did nothing, the aircraft speed gradually drops whilst the engine quickly over-revs. Whilst the engine screams, the aircraft loses speed

Mad Dog, what's your information source for these statements? The Curtiss Electric prop we had at mech school was not at all like this. If the governor or the slip rings failed (rare), yes, it would go to full increase, but since it came off a single engine plane (Curtiss SC21? I think), it wasn't featherable. Full increase would be roughly equivalent to a "TO & climb optimized" fixed pitch prop. A modest throttle reduction would get RPM back in the normal range and cruise would be slower than normal, but stalling out of the sky sounds pretty extreme to me.
A much more common failure would be for the electric pitch motor to fail, freezing the pitch at whatever value it's at. Unlike a hydraulic prop, which allows aerodynamic loads on the blades to drive it to the stops when hydraulic pressure is lost to the dome, blade loading on an electric can't drive the motor due to the mechanical advantage of the reduction gear. About like jacking one wheel on a car and trying to turn the engine over by rotating the raised wheel by hand. This changes your constant speed prop into a fixed pitch one, and returns RPM control to the throttle.
If you could feather the prop, the P39 looks like it would be a good glider, with its sleek profile, EXCEPT for that dang symmetrical airfoil. Now with a nice NACA high lift airfoil, I bet it would sport a pretty decent L/D, albeit at an alarmingly high speed and sink rate.

 

[MiTasol]

1. Maintain Aircraft Control
2. Analyze the Situation
3. Take Appropriate Action
4. Land as soon as conditions permit

1 means fly the plane. If you are about to stall get the nose down and add power (if that's an option). 2. Using aircraft systems knowledge assess. 3 means coming up with a plan. 4 means get it to a safe conclusion.

Freezing up indicates task saturation / sensory overload.

Cheers,
Biff

The three priorities in order in three words - Aviate, Navigate and Communicate.

 

[MiTasol]

Mad Dog, what's your information source for these statements? The Curtiss Electric prop we had at mech school was not at all like this. If the governor or the slip rings failed (rare), yes, it would go to full increase, but since it came off a single engine plane (Curtiss SC21? I think), it wasn't featherable. Full increase would be roughly equivalent to a "TO & climb optimized" fixed pitch prop. A modest throttle reduction would get RPM back in the normal range and cruise would be slower than normal, but stalling out of the sky sounds pretty extreme to me.
A much more common failure would be for the electric pitch motor to fail, freezing the pitch at whatever value it's at. Unlike a hydraulic prop, which allows aerodynamic loads on the blades to drive it to the stops when hydraulic pressure is lost to the dome, blade loading on an electric can't drive the motor due to the mechanical advantage of the reduction gear. About like jacking one wheel on a car and trying to turn the engine over by rotating the raised wheel by hand. This changes your constant speed prop into a fixed pitch one, and returns RPM control to the throttle.
If you could feather the prop, the P39 looks like it would be a good glider, with its sleek profile, EXCEPT for that dang symmetrical airfoil. Now with a nice NACA high lift airfoil, I bet it would sport a pretty decent L/D, albeit at an alarmingly high speed and sink rate.

A welded relay was also a failure mode and depending on which relay that would drive the prop to one end or the other of its pitch range. Anecdotally this tended to fail in the full fine pitch which, as you say, is the TO and climb pitch.

The hydromatic and counterweight props go to opposite ends of the range though when there is an oil pressure failure - counterweight goes to cruise pitch and hydromatic to fine pitch if the rusty memory is correct.

 

[Peter Gunn]

1. Maintain Aircraft Control
2. Analyze the Situation
3. Take Appropriate Action
4. Land as soon as conditions permit

1 means fly the plane. If you are about to stall get the nose down and add power (if that's an option). 2. Using aircraft systems knowledge assess. 3 means coming up with a plan. 4 means get it to a safe conclusion.

Freezing up indicates task saturation / sensory overload.

Cheers,
Biff

I always get the strangest feeling that you've studied some of these issues before, I can't put my finger why though.

I also just noticed there are three "f"s in your screen name.

 

[fubar57]

I also just noticed there are three "f"s in your screen name.

Jaysus H. "Tap Dancing" Christ. Now that you've mentioned it.........

 

[pinsog]

I've never read "Nanette" and I may be mistaken, but was Nenette the P39 book that was all fiction? Someone wrote an all fiction P39 novel but I can't remember the name.

 

[DerAdlerIstGelandet]

The three priorities in order in three words - Aviate, Navigate and Communicate.

I can still hear my instructor...

Fly the plane, fly the plane, fly the plane!

 

[P-39 Expert]

I've never read "Nanette" and I may be mistaken, but was Nenette the P39 book that was all fiction? Someone wrote an all fiction P39 novel but I can't remember the name.

Nanette was fiction, based on fact. Author was Edwards Park who was actually there as a pilot. His companion book "Angels Twenty" was a factual account of the same period January 1943 through the rest of his tour at Port Moresby, NG.

 

[Juha3]

I believe the Russians pulled the .30s from the very first P-400s that the Brits gave them. And the IFF radio in the tail cone. Saved about 330lbs. Made them competitive with German planes...

I began to read this thread late and it seems that I cannot catch up because this is so active. But I have become so irritate to your posts that I answer to this message now.
1st: Russians did not pulled out the .30s from all their P-400s or P-39Ds - Ns. They pulled them out from some and kept them in some, that can easily be checked from photos. E.g. the first famous Soviet Airacobra ace Ivan Bochkov's P-400 had wing guns but e.g. Pavel Klimov's P-39D is photographed without wing guns. There also photos of P-39Ns with wing guns serving with active units.
2nd: Why would .30s be ineffective against unarmoured Japanese planes? Hit into pilot or into a metal fuel tank could be fatal, was it by .30 or .50. Most of men hit by .30 into back of the head were killed, weren't they?

 

[P-39 Expert]

There's no need to expand further, you either get it, or you don't. By now, if you don't get it, you ain't gonna get it. Quit trolling.

When I said "Please expand above" I was instructing the sender to expand that condensed box so he could see my replies to his statements directed to me. Not trolling.

 

[P-39 Expert]

I began to read this thread late and it seems that I cannot catch up because this is so active. But I have become so irritate to your posts that I answer to this message now.
1st: Russians did not pulled out the .30s from all their P-400s or P-39Ds - Ns. They pulled them out from some and kept them in some, that can easily be checked from photos. E.g. the first famous Soviet Airacobra ace Ivan Bochkov's P-400 had wing guns but e.g. Pavel Klimov's P-39D is photographed without wing guns. There also photos of P-39Ns with wing guns serving with active units.
2nd: Why would .30s be ineffective against unarmoured Japanese planes? Hit into pilot or into a metal fuel tank could be fatal, was it by .30 or .50. Most of men hit by .30 into back of the head were killed, weren't they?

Sorry to irritate you. The primary reasons the .30s were deleted by the Russians were to 1. Save weight to improve climb rate/ceiling and 2. The .30s were not effective against armored German planes as compared to the 37mm cannon and the .50cal MGs.

I believe the .30s were deleted for these reasons on the vast majority of Russian P-39s. Of course with almost 5000 P-39s delivered to the Russians some would retain the .30s.

Regarding the effect on the Japanese planes, yes the .30s would be more effective than against armored German planes, but the need for better climb/ceiling was even more urgent since their G4M bombers operated at 18000'-22000'. Sure, more guns are better, but weight is also a primary concern and the P-39 still retained the 37mm cannon and two .50cal MGs.

 

[fubar57]

You believe....That's your rebuttal?

 

[P-39 Expert]

No you don't.


WRONG! You've been corrected on this at least twice, and yet you persist in this erroneous explanation. Critical engine is the engine most dangerous to lose, in this case, left engine. I earned my multi engine rating and multi instructor rating in planes of this sort, then instructed in them. The differences between critical and non-critical engines are due to P factor, and torque has next to nothing to do with it. The real killer here is asymmetric thrust and the yaw and roll it induces, and that happens with EITHER engine out, it's just a little bit worse with the critical engine out.
Don't come to me with your shiny new Whizbang 260 looking for a multi engine rating! From what I've seen of your willingness to absorb new information if it conflicts with your preconceived notions, I wouldn't get in an airplane with you and put both our lives on the line for all the tea in China. Engine-out training is risky enough with a student who's got his/her head screwed on straight. You never know what creative new stunt they'll pull, out of confusion, misunderstanding, or nervousness. In your case it could easily be a suicide mission.

Apparently you don't understand "critical engine" either, see posts #603 and #605. And you don't need to be so snarky.

 

[fubar57]

A twin engine pilot that doesn't understand "critical engine"?

 

[GrauGeist]

The .30s were not effective against armored German planes

So that's why the RAF lost the battle of Britain.

Oh, wait...

 

[P-39 Expert]

Hello P-39 Expert,



I have that book as well. It has a lot of nice photographs and references but the author is a "fan boy" for the Airacobra.
His opinions which are asserted as fact often do not stand up to scrutiny so I would be very wary of quoting him. So, my source is no good?
Regardless of who made that statement of a "Flat trajectory out to 400 yards", you should have the sense to know it can't possibly be true. NOTHING flies flat (mostly true). It is just a matter of HOW curved the trajectory is.

When I say "flat trajectory" it is in comparison to the trajectory of the accompanying .50cal MGs. so that they can be used together. Trajectory drop is only 22" greater than the .50s at 400yds. Relatively flat. His source is Operational Suitability Tests at Eglin Field. By the way he quotes muzzle velocity as 2600-3000fps, a little better than the 2000fps you use.

If the 37 mm were such a great weapon, why was Bell the only company that chose to use it? Specified by the AAF.
Everyone else seemed to go with multiple .50 cal or 20 mm instead even when the aircraft clearly could carry the 37 mm if it needed to.



Perhaps because increasing the ammunition capacity wasn't that easy.
As for reducing weight, the operators of the aircraft were of the opinion that more armour and not less was needed.

So why was 240lbs of armor plate/glass needed on a P-39 when only 111lbs were needed on a contemporary P-40E?

Hello Mad Dog,

From what I have read about the King Cobra, it seemed to have very good maneuverability as compared to the types already in service. The problem though was that it was also significantly slower than types already in service and those in power seemed to prefer speed over other qualities.

- Ivan.

Please expand above.

 

[P-39 Expert]

So that's why the RAF lost the battle of Britain.

Oh, wait...

And that's why the RAF developed the 20mm cannon as fast as they could.

 

[buffnut453]

Given the inability of some people to accept that others might actually know better than they do, it's time to break out the obligatory General Sir Anthony Cecil Hogmanay Melchett quote:

 

[GrauGeist]

And that's why the RAF developed the 20mm cannon as fast as they could.

It's a shame the Yanks had to struggle against those flying tanks with their piddly .50MGs

 

[DerAdlerIstGelandet]

Apparently you don't understand "critical engine" either, see posts #603 and #605. And you don't need to be so snarky.

He is a dual engine commercial pilot. I think he understands critical engine very well.

People might be less snarky with you if you would stop pretending that you are a know it all, and listen to what people are telling. Your inaccuracies have been pointed out by many people here, and you clearly continue to blow them off. At first it was humorous, but now its a lil insulting really.

As I said you can regurgitate book knowledge all day long, but you clearly are incapable of putting it together.

The first step is to admit you are wrong. It's ok, we all are from time to time. Besides it might humble you a lil.

My intent here is to not insult you, but damn man... Admit when you are wrong, listen to people with experience and knowledge in the matter and learn something.

I get the feeling you would argue with BiffF15 about Eagle tactics just to be "right".