XP-39 II - The Groundhog Day Thread (2 Viewers)

[DerAdlerIstGelandet]

He needs a little actual hands-on stick time. Betcha he's never flown in anything but an airliner. Any volunteers? I would if I could still pass a physical. Except it's nigh impossible to find a rental plane or small airport flight school or instructor any more. Insurance costs and the university affiliated "pilot factories" have put them out of business.

Someday I will have my CFI, and then can let Karma come back and bite me in my ass for always trying to kill my instructor.

 

[XBe02Drvr]

and then can let Karma come back and bite me in my ass for always trying to kill my instructor.

DITTO! I was even worse than "Ex-spurt" here when I first started flying. Couldn't pack anything new in on top of all the "mis-info" and Caidinisms my head was stuffed with. I KNEW IT ALL and was in need of some humble meter adjustments by my instructors. These were accomplished with glee upon my fragile E3 ego by the various Chief Petty Officers and Lieutenant JGs who instructed at the flying club. I was eating a lot of crow with humble pie for dessert. It's a wonder they put up with me. I wouldn't have. I've taught pilots who were "naturals", and many more that weren't. I definitely wasn't.

 

[GrauGeist]

I certainly wouldn't qualify, as I was just rated VFR.
The upside to that, is I was taught by WWII combat pilots and it was interesting to note that the former Army pilots had a much different approach to things than the one, who was a former VMF-212 Corsair driver.
Army: good job, nice handling!
Marine: WTF was that? Are you trying to kill my machine? Do NOT kill my machine!

 

[P-39 Expert]

You have not been absolutely right. Especially when it comes to WB, CG, how moving weight in an aircraft is affected, critical engines, etc. You regurgitate knowledge and data without understanding it. That is what people are correcting you on. People who actually work and do these things. You have a guy in here who has actually worked on one, and you argue with him. You have a twin engine commercial pilot telling you that your understanding of critical engines is wrong. Do you know how ridiculous that sounds when you do that? It sounds like a War Thunder video gamer telling a pilot how his aircraft works. That is why people get snarky with you. You invite it. Go back and look at your exchange with X XBe02Drvr. He is a commercially licensed twin engined pilot. He used to fly 1900D's a notoriously tail heavy aft CG twin engine turboprop aircraft. He has reached out to you on multiple occasions to correct you, and you blow him off. Of course he got snarky!

It's obvious you have read a ton of books, and have a lot of knowledge from those books, now let people help you put it all together.

Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery. Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.

I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.

I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.

 

[Juha3]

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.

Have you any proof that the .30s were deleted on the vast majority of Russian P-39s? I can only say that from the photos I have seen of Soviet P-400s/P-39Ds - Ns serving with combat units from which one can see at least one wing leading edge I would say about a half had wing guns and another half had not. The problem is that from most of photos one cannot see the critical part of a leading edge because of that the photo is taken from an angle that does not show a leading edge, it shows only the cockpit area or the nose, or there are men front of the wing.

E.g. many if not most/all of the P-39s of 103 GIAP/2 GIAK PVO in autumn 1943 had their .30s in place. The fighters of the PVO were used as interceptors because the PVO was the air defence arm of the Soviet armed forces and still at least some of its units seem to have thought that the .30s were more useful against German planes than the weight of them and their ammunition was detrimental to their climbing ability. And after all we are talking on P-400s/P-39s of the USAAF in PNG in 1942 facing unprotected Japanese planes and the usefulness of .30s in that situation when after all the 37 mm cannon was suffering badly from unreliability.

Ps: but after all you had kept this very interesting thread alive 34 pages. Thumps up for that!

 

[XBe02Drvr]

My guess is that an experienced pilot probably would have put the propeller into manual control and tried to adjust the RPM to something reasonable for the power setting.

Most constant speed prop failures result from failure of the pitch change mechanism itself, leaving no control of prop pitch at all. There are some modes in which a governor can fail and pitch can be controlled manually, but these are pretty rare.

 

[XBe02Drvr]

]

I understand WB and CG as well as the next person on here. It's not brain surgery.

If you do truly understand W&B, you certainly have a problem communicating it to professionals here who work with it regularly and have for a long time.

I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it.

Nobody's saying pilots and mechanics are the sole authorities, just that their training and experience gives them the context to better distill raw data derived from books and publications into credible information. They've walked the walk which gives them an edge at talking the talk. Researchers who aren't aviation professionals, but have done rigorous broad based research, carefully vetting sources and examining and comparing their credibility, are also respected here, and we have some onboard that you've tried to correct. Not trying to be a snark, just trying to point out some truths we hold to be self-evident.

 

[XBe02Drvr]

He is a commercially licensed twin engined pilot. He used to fly 1900D's

Actually ATP licensed. Never got to fly a "D", as they were just coming out when our company was driven out of business. Pilots who've flown both said they liked the "C" better. Better performance and lighter on the controls.

 

[XBe02Drvr]

it was interesting to note that the former Army pilots had a much different approach to things than the one, who was a former VMF-212 Corsair driver.
Army: good job, nice handling!
Marine: WTF was that? Are you trying to kill my machine? Do NOT kill my machine!

When your life has been defined by landing bentwings on a boat, you might be a little less tolerant of sloppy performance on landing. Gyreens had to carrier qual, too.

 

[Ivan1GFP]

Hello P-38 Expert,

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.

Do you have any information on the type of ammunition used in those Operational Suitability tests at Eglin Field?
The actual ammunition typically used in the 37 mm M4 cannon used a projectile weighing just a bit over 600 grams and with that ammunition, it was getting a muzzle velocity typically stated as 2000 fps.
Can you find a source that states otherwise?

Guns with quite differing velocities can be zeroed at the same range if the lower velocity guns are given a bit more elevation.
There is no problem if the target and gun platform are not moving. The problem comes when the gun platform is pulling G as it would be for a deflection shot. In that case, the slower projectile will drop significantly more and depending on the amount of G, will probably not hit to the same point of impact.
Shortround6 gave a pretty thorough explanation. You need to read it and understand it.

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

Glad you finally asked that question.
The basic design of the P-39 put a lot of vulnerable pieces such as the oil tank, coolant tanks, and engine in the back into the most likely path for incoming fire.
Many of these accessories in the P-40 have very limited angles of vulnerability. From the front, the engine is in the way. From the back, the armoured cockpit area is in the way.
Getting a tracking shot against these vulnerable areas on fighter with an engine in front is also a bit more difficult considering the direction of flight of attacking aircraft and target.

By the way, as a general comment, I agree with some of the others here that you are probably quite well read on this subject.
My own opinion is that it is highly unlikely this is the first time that you have seen these arguments that contradict your ideas.
My belief is that you tend to discount any ideas that disagree with yours without evaluating them for validity.

- Ivan.

 

[vikingBerserker]

Have you any proof that the .30s were deleted on the vast majority of Russian P-39s? I can only say that from the photos I have seen of Soviet P-400s/P-39Ds - Ns serving with combat units from which one can see at least one wing leading edge I would say about a half had wing guns and another half had not.

According to "Soviet Air Power in World War 2" by Yefim Gordon
Page 446: The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s so it could match the Bf 109F-4/G-2/G-4 as well as the Soviet Lagg 5 and Yak-9s
Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.
..and of course the P-63s didn't have them either.

Not sure of that covers the vast majority however.

 

[fubar57]

Went through these books, 151 page of photos....

​

.....18 of which showed wings. 15 had wing guns, from the -D to -M. The three that never had wing guns were Ms

 

[GregP]

This might be interesting ...

 

[P-39 Expert]

Hello P-38 Expert,



Do you have any information on the type of ammunition used in those Operational Suitability tests at Eglin Field?
The actual ammunition typically used in the 37 mm M4 cannon used a projectile weighing just a bit over 600 grams and with that ammunition, it was getting a muzzle velocity typically stated as 2000 fps.
Can you find a source that states otherwise? Matthews also lists a Dr. W. F. Atwater, U.S.Army Ordnance Museum, Aberdeen Proving Ground, Md.

Guns with quite differing velocities can be zeroed at the same range if the lower velocity guns are given a bit more elevation.
There is no problem if the target and gun platform are not moving. The problem comes when the gun platform is pulling G as it would be for a deflection shot. In that case, the slower projectile will drop significantly more and depending on the amount of G, will probably not hit to the same point of impact.
Shortround6 gave a pretty thorough explanation. You need to read it and understand it.

The 37mm gun didn't have to be used in conjunction with the .50s. It had a separate firing button on the stick and could be used independently.

Glad you finally asked that question.
The basic design of the P-39 put a lot of vulnerable pieces such as the oil tank, coolant tanks, and engine in the back into the most likely path for incoming fire.
Many of these accessories in the P-40 have very limited angles of vulnerability. From the front, the engine is in the way. From the back, the armoured cockpit area is in the way.
Getting a tracking shot against these vulnerable areas on fighter with an engine in front is also a bit more difficult considering the direction of flight of attacking aircraft and target. The P-40 also has a big fat fuel tank right behind the pilot.

By the way, as a general comment, I agree with some of the others here that you are probably quite well read on this subject.
My own opinion is that it is highly unlikely this is the first time that you have seen these arguments that contradict your ideas. Absolutely. The ideas you are repeating have been around since the war ended. What I am trying to show you is information that has surfaced more recently from wwiiaircraftperformance.org, recently ('90s) released information from the Russians, and other more current sources. Keep believing the older information if it makes you comfortable, but the P-39 was quite a different airplane than we all have been led to believe.
My belief is that you tend to discount any ideas that disagree with yours without evaluating them for validity.

- Ivan.

Please expand above.

 

[fubar57]

Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.

There's a photo of one of those aircraft in this book

​

 

[FLYBOYJ]

Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery.

Based on your comments, you really don't. You seem to ignore the ramifications of an aft CG (even though you're within manufacturer's limits) and some of your terminology in trying to explain yourself further revealed your understanding of , or lack of the subject.

Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.

Hmmmm. NO. Wes explained it well to you.

I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.

I'll give you the benefit of the doubt, but read on...

I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.

And understand that some of us have "been there/ done that" and it's not to toot our horn but understand that at the same time you have tied to dispel some myths and folklore about the P-39, we have seen in our experiences situations that either confirm or disqualify what was said 75 years ago and having someone with either no flight or wrench twisting experience trying to tell us about something we've done for years, well I think you should get the message. Some of us been around these machines and then some, perhaps listen more and ask questions, but I'll say in the same breath I (we) are always learning and you have enlightened me on many aspects of the P-39!

 

[windhund116]

He needs a little actual hands-on stick time. Betcha he's never flown in anything but an airliner. Any volunteers? I would if I could still pass a physical. Except it's nigh impossible to find a rental plane or small airport flight school or instructor any more. Insurance costs and the university affiliated "pilot factories" have put them out of business.

Are computer game/flight simulators pretty good at giving the user some 3D awareness? What are the best ones for PC and PlayStation?

Thanks!

 

[vikingBerserker]

According to "Soviet Air Power in World War 2" by Yefim Gordon
Page 446: The North Fleet Air Arm removed the wing guns along with some armor from their Mk 1s so it could match the Bf 109F-4/G-2/G-4 as well as the Soviet Lagg 5 and Yak-9s
Page 447 P-39Q (along with the N version were the most numerous P-39s in Soviet Service) had the wing guns removed and replaced with 2 x 0.50 in pods.
..and of course the P-63s didn't have them either.

Not sure of that covers the vast majority however.

Same book on Page 434 listing the Imported aircraft in inventory as of May 1st, 1945 shows 84% of the 2,272 P-39s still in service had no wing guns.

 

[FLYBOYJ]

Are computer game/flight simulators pretty good at giving the user some 3D awareness? What are the best ones for PC and PlayStation?

Thanks!

This has been beat to death on this forum. PC sims can provide some basic perspectives and some good "numbers" (I use one to help me when I was earning my instrument rating, but understand in the end, they are toys.

So to answer your question; "Are computer game/flight simulators pretty good at giving the user some 3D awareness?"

"Include the toxic cockpit fumes, the extreme heat or cold, sitting on a lumpy seat while restrained with belts that almost cut through your soaking wet flight suit and have a 300 pound woman sit on you every time you pull Gs - oh while breathing smelly oxygen through a face mask that smells like a prophylactic."

 

[DerAdlerIstGelandet]

Just because someone here says I don't understand something doesn't mean that is true. I understand WB and CG as well as the next person on here. It's not brain surgery. Just because you know something doesn't mean someone else doesn't know it also. Also my explanation of critical engine was perfectly acceptable as was shown be subsequent posts by other posters.

I have never once in all my posts on this board EVER told another poster that they didn't know what they were talking about. Not one time. And I have never been snarky with anyone on here that did not get snarky first. And even then they had to be pretty darn snarky for a good while.

I'm not a pilot nor a mechanic. But I can read and I do have an interest in this subject. If pilots and mechanics are the sole and final authority on planes from 75 years ago, then so be it. If quoting valid reference materials is not adequate research, then so be that also.

I never said that only pilots and mechanics can know things. I never said they are the final authority. Did I? Of course not. They don't know everything either, as we have all stated. You know much smoke I have had blown up my ass by fellow mechanics and pilots? Shit, try being around military mechanics and pilots, especially AH-64 pilots. You will hear nothing but over embellished "No Shit There I Was Stories".

But when not one, not two, not three, but four or five or more point out you are not understanding something correctly, even if your data might be ok, chances are they are on to something, right?

Anyone can read books and data, but that does not mean they get it completely. That does not mean they understand it completely.I can read a book on medicine, come in here and post the data all I want. But if a doctor comes in and says, that it is not how it works, who is probably right?

And there is nothing wrong with not knowing everything. There is nothing wrong with not understanding anything. No one thinks you are stupid either. Blowing off actual experts in the field of specific subjects, though, sure as hell comes off as snarky to me.