XP-39 II - The Groundhog Day Thread (1 Viewer)

[P-39 Expert]

You just described setting the mixture control to Auto Rich which is what we have been trying to tell you was the correct approach all this time.
In case you forgot, you were advocating using manual mixture controls to tune for best power in combat.....

The mixture control could be varied between the pre determined settings. How else did the pilot get a "best power" setting?

Because it was not in the same condition as ones in service or operated the same way.
.....
Listing just ONE test report for PROOF would be good. Without the proof, this is just Hearsay and not deemed to be not even as reliable as a "Hangar Story".

Do your own research, it's all in wwiiaircraftperformance.

Did he give the conditions?
Context is important.

Just a verbal interview I saw many years ago.

For Boyd Wagner to ask for a piece of armour to be installed in the P-39 when it ALREADY came as STANDARD would have been interesting. You do know that the Oil Tank armour came as standard on every production Airacobra after the P-39C, right?

Right.

The Russian philosophy was simply different, and no, many of their engines did not allow a gun firing through the propeller. All the Yaks and Laggs that had inline engines had a cannon firing through the propeller hub.
Radial engines have a bunch of things in the middle which get in the way of a gun. No radial ever had a gun firing through the propeller hub.
Jets are a whole different story. You can start a different discussion if you want to go there.



You have yet to prove the aerodynamics are EXACTLY the same. Many knowledgeable people have been trying to convince you of that.

Same airframe. Wouldn't two P-39Ds have the same aerodynamics? Only difference between the C and D were internal.

Many highly proficient pilots did indeed over boost their engines staying below the limits for detonation. This was documented with the P-40 models using the V-1710-39 which was similar to the -35 engine in the P-39D-1 and when using V-1710-73 engines similar to the P-39's -63 engines.
Have you ever seen the Allison memo on the subject? The pilot in the test caused his engine to detonate, was he highly proficient?

- Ivan.

 

[P-39 Expert]

And "less effective" is not the same as "ineffective". You're inserting your own interpretation and passing it off as fact.

YET AGAIN you keep banging on about Wagner's report being after 2 weeks of combat. However, the P-39s remained in combat for MONTHS. Did they remove the "useless" 30 cals at any time? NO. Other than "I don't know", you don't have an answer for why that might be.

I'd really appreciate it if you'd stop hitting the reset button and acknowledge that the operational crews maybe...just maybe...had a clue about what they were doing and kept the 30 cals because, despite being "less effective" they were still deemed mission critical for the sorties flown over PNG and Guadalcanal.

I was using Wagner's exact words, not my interpretation. The .30s were clearly less effective and less reliable. I guess the Russians were crazy to get rid of them and increase the performance of their planes.

 

[P-39 Expert]

Do you know why the radio is way back in the tailcone? It's to get it as far as possible away from the vibration, heat, and ignition interference from the engine. You're proposing to put it "right in the lion's den". Same reason they didn't put it in the only other logical place, up in the nose by the guns. I've never been up close and personal with an Oldsmobile 37MM cannon, but I have with 20MM and .50 cal, and I can tell you it's an earth shaking experience. Have you ever disassembled an old fashioned vacuum tube radio? Even "ruggedized" for airborne use their tolerance for vibration and heat is pretty limited. One of the failures of the Zero was the inability of its voice radio to cope with the (supposedly shielded) electronic noise from the engine.
Look in any P-39 pilots manual and radios are clearly shown exactly where I advocate locating them.

Did it ever occur to you that that boost limit could be an arbitrary number with considerable safety margin built in, set by conservative engineers wary of the exuberance of testosterone driven young pilots? And that the pilot selected for the test might be proficient enough and knowledgeable enough to realize he could shave those margins a bit without too much risk, considering he may have been under pressure not to let the Zero show him up too badly? Your faith in the incorruptibility of pilots is touching. The pilot in the test caused his engine to detonate by using excessive manifold pressure way beyond any safety margin.

 

[buffnut453]

I was using Wagner's exact words, not my interpretation. The .30s were clearly less effective and less reliable. I guess the Russians were crazy to get rid of them and increase the performance of their planes.

You have repeatedly said in prior posts that the 30 cals were "ineffective". That's YOUR word, not Wagner's.

Why is it so hard for you to accept that Russia wasn't PNG or Guadalcanal, and that the U.S. pilots flying in the Pacific clearly wanted the 30 cals?

 

[P-39 Expert]

You have repeatedly said in prior posts that the 30 cals were "ineffective". That's YOUR word, not Wagner's.

Why is it so hard for you to accept that Russia wasn't PNG or Guadalcanal, and that the U.S. pilots flying in the Pacific clearly wanted the 30 cals?

show me a quote where any AAf pilot wanted the .30s.

 

[Ivan1GFP]

The mixture control could be varied between the pre determined settings. How else did the pilot get a "best power" setting?

So HOW did the pilot determine which way to adjust the mixture?

Do your own research, it's all in wwiiaircraftperformance.

Actually there are aren't any test reports of a A6M2 in good operational condition that were operated correctly on wwiiaircraftperformance.
I am no expert, but I am certain that I have done considerably more research on Japanese aircraft than you have.

Same airframe. Wouldn't two P-39Ds have the same aerodynamics? Only difference between the C and D were internal.

Same airframe, different propeller part number. Different arrangement of equipment and balance may cause some very different aerodynamic consequences. This has been explained to you.

The pilot in the test caused his engine to detonate, was he highly proficient?

This pilot probably was fairly certain he could over boost that particular engine. Problem is that he guessed wrong about the actual limit before detonation. Even highly proficient pilots make mistakes and guess wrong. Being proficient and being perfect are different things.

- Ivan.

 

[buffnut453]

show me a quote where any AAf pilot wanted the .30s.

Two can play at that game. Show me a quote where any AAF pilot said they wanted the 30 cals taken out? Better yet, show me any instance where any AAF P-39 had the 30 cals removed for performance reasons.

C'mon...I want to see the evidence to contradict my points. Are you at least willing to accept that the USAAF P-39s flew with the 30 cals and that, given the simplicity of removing them, that does at least indicate that the pilots thought it was better to have the 30 cals than not to have them?

 

[pbehn]

Two can play at that game. Show me a quote where any AAF pilot said they wanted the 30 cals taken out? Better yet, show me any instance where any AAF P-39 had the 30 cals removed for performance reasons.

C'mon...I want to see the evidence to contradict my points. Are you at least willing to accept that the USAAF P-39s flew with the 30 cals and that, given the simplicity of removing them, that does at least indicate that the pilots thought it was better to have the 30 cals than not to have them?

What was an ineffective gun against a Japanese aircraft? In aviation history planes were continually loaded with more stuff, fuel guns ammunition armour radios mirrors radars, the cases of "stuff" being taken out are rare and for special reason, generally pilots wanted guns and armour.

 

[wuzak]

Lots of photos of radios in that exact spot.

In aircraft that kept the nose armour?

 

[P-39 Expert]

So HOW did the pilot determine which way to adjust the mixture?

Either way by feel and sound. We're talking about 3mph.

Actually there are aren't any test reports of a A6M2 in good operational condition that were operated correctly on wwiiaircraftperformance. Not a single one? All were wrong? What about the one that showed the 335mph top speed?
I am no expert, but I am certain that I have done considerably more research on Japanese aircraft than you have.

Okay, show me all the reports that said the A6N2 was faster then 330mph.

Same airframe, different propeller part number. Different arrangement of equipment and balance may cause some very different aerodynamic consequences. Nothing that would account for a 1000fpm difference in climb rate. This has been explained to you. It certainly hasn't been explained to me adequately.

Same airplane. Same everything except internal weight. Both planes were in balance. None of these factors would account for a 1000fpm difference in climb rate except the 836lbs of weight. Weight affects climb.

This pilot probably was fairly certain he could over boost that particular engine. Problem is that he guessed wrong about the actual limit before detonation. Even highly proficient pilots make mistakes and guess wrong. Being proficient and being perfect are different things. Now you know what that pilot was thinking? I don't think so. He overboosted the engine past the point of detonation. In a test. Not a contest. The whole point of the test was to see how both planes performed when operated properly. If he had known how to properly operate the plane he wouldn't have risked engine damage or failure.

- Ivan.

 

[GregP]

By feel? Here's from an Allison user's manual:

Of course, the Allison was behind the pilot, so he may have had some difficulty with this procedure. Alternately, if you have climbed, you are likely lean. If you have descended you are likely rich. Both assume you haven't touched the mixture before changing altitude. Generally speaking, you either lean or rich to get peak exhaust gas temperature and then adjust from there. In WWII, they always ran rich of peak temperature, maybe 100° rich of peak. Today, we generally run lean of peak.

But is isn't a quick thing. Usually, setting the mixture correctly in a Cessna takes maybe 1-1.5 minutes. 1 minute of straight and level inattention in a combat zone may mean you are dead. The rule of thumb is never fly straight and level in a combat zone for more than 30 seconds.

That's why the "Auto Rich" setting was so handy in combat. You could set it there and forget it until combat was over or you had rejoined and were on the way home. "auto lean" ws a great way to cruise home, but not a good for combat when power changes were required.

 

[ThomasP]

I do not know if this helps with the radio(s) being moved, but although I have run across pictures with multiple electronics boxes on the panel above the engine, in most (all?) of the pictures of P-39Q & N when only a single box is present, the box appears to be the IFF set.

 

[FLYBOYJ]

So HOW did the pilot determine which way to adjust the mixture?

Either way by feel and sound

So this will be done when?

 

[P-39 Expert]

So this will be done when?

The performance test said the P-39D developed 368mph at a mixture setting of "Best Power" and 365mph at a mixture setting of "Auto Rich". We are talking about 3mph with a slightly different mixture setting, right? When do you think it was done? At this point I would really like to know. For 3mph.

 

[P-39 Expert]

What was an ineffective gun against a Japanese aircraft? In aviation history planes were continually loaded with more stuff, fuel guns ammunition armour radios mirrors radars, the cases of "stuff" being taken out are rare and for special reason, generally pilots wanted guns and armour.

Yes they did, but they also wanted to be able to climb above their adversaries. If deleting the .30s meant being able to get above your opponent then I think the vast majority of pilots would prefer being above their opponent. What good are .30s when your opponent has the advantage? And you still have plenty of firepower without them.

 

[FLYBOYJ]

When do you think it was done?

Well if you're manually adjusting for the best air/ fuel mixture AKA stoichiometric mixture, you're either doing it on the ground or you can try in the air in level flight at either cruise or high rpm settings.

 

[glennasher]

It's not about "3 mph". It's about getting the best out of the engine without blowing it up.

 

[Ivan1GFP]

Either way by feel and sound. We're talking about 3mph.

First of all, you are looking at the wrong detail. The important thing is NOT the 3 MPH difference in maximum speed because in a maneuvering fight with changing altitudes you will never see the difference in maximum speed.
The objective here is the extra 25 HP that gives that extra 3 MPH maximum speed.
The fuel mixture requirements of the engine will be constantly changing as the power (torque) demands and altitude are changing. In combat, the pilot has many other things demanding constant attention. Assessing the instantaneous fuel needs of the engine is not a smart distraction in that situation.

wwiiaircraftperformance. Not a single one? All were wrong? What about the one that showed the 335mph top speed?

Okay, show me all the reports that said the A6N2 was faster then 330mph.

If you are asking an honest question, I will give you an explanation because you obviously think there is more there than there actually is.
Only the first five entries for the Zero are for the A6M2.
There are five entries, but only two aircraft were tested.
One was a A6M2 that fell into the hands of the AVG in China. It was tested against a P-40K and a P-43.
Its Propeller was never in spec and it could not make more than about 2075 RPM, thus its performance is hardly indicative of a properly functioning A6M2.

The second aircraft tested was the crashed and rebuilt Aleutian A6M2 and I won't rehash what was wrong with that testing which I have covered before. Its testing and summaries for different audiences covers about 4 of the 5 reports.

As I have stated before, the only service that had good operational A6M2 and knew how to operate them properly (the only service that had the opportunity) never chose to test for maximum speed in a manner comparable to the Allies.

It certainly hasn't been explained to me adequately.

Same airplane. Same everything except internal weight. Both planes were in balance. None of these factors would account for a 1000fpm difference in climb rate except the 836lbs of weight. Weight affects climb.

We have been here before. We got here several times over the last couple days.

Now you know what that pilot was thinking? I don't think so. He overboosted the engine past the point of detonation. In a test. Not a contest. The whole point of the test was to see how both planes performed when operated properly. If he had known how to properly operate the plane he wouldn't have risked engine damage or failure.

The testing of the Aleutian A6M2 was meant to show the superiority of American fighters as much as possible.
I have already explained the evidence (I believe to the satisfaction of others here). Maybe it should not have been a contest, but the participating pilots were most likely informed of the intended results. I have seen government "tests" in other areas that were conducted that way.

- Ivan.

 

[DerAdlerIstGelandet]

The performance test said the P-39D developed 368mph at a mixture setting of "Best Power" and 365mph at a mixture setting of "Auto Rich". We are talking about 3mph with a slightly different mixture setting, right? When do you think it was done? At this point I would really like to know. For 3mph.

Lets start with do you know why you adjust mixture?

 

[XBe02Drvr]

Does anybody remember the 1970s movie: Sometimes a Great Notion? This thread reminds me of the Henry Fonda character: "DONCHA GIVE A GODDAM INCH...EVER!"