Capt. Eric M. Brown at the Norwegian National Aviation Museum 25 April 2007

[Nashwan]

From an old post by Hohun:

"About the beginning of 1944 reports begang reaching the RAE of Thunderbolts diving out of control from high-altitude combat, and eventually in March of that year a P-47D was seconded to RAE Farnsborough from the US Eight Air Force for investigation, since it was suspected that the cause was compressibility induced, and the RAE was at that time heavily involved in researach in the transonic flight range.

[...]

Before the next flight, a Machmeter was fitted to the aircraft, and as instructed I climbed to 35,000 ft, carried out a 2 min level run at full power and trimmed the aircraft before pushing over into a 30 degree dive. At Mach=0.72, the aircraft begang to buffet slightly and pitch nose down, requiring a strong pull force to maintain the dive angle. At Mach=0,73 the buffetting increased severely and the nose-down pitch was so strong that it needed a full-blooded both-handed pull to keep the dive angle constant. I had to hang on grimly in this situation, unable to throttle back until Mach number decreased as altitude was lost. The pull-out was not effected until 8,000 ft. Analysis showed that a dive to M=0.74 would almost certainly be a 'graveyard dive'.

I have only subsequently experienced such severe compressiblity nose-down pitch effects in two other aircraft, the Messerschmitt 163B and the Gurmman F-8F [sic!] Bearcat."

(From "Testing for Combat".)

http://forums.hitechcreations.com/forums/showthread.php?s=&postid=2180107&highlight=P47D+seconded#post2180107

Judging by the "I", Brown did indeed dive test the P-47.

[Knegel]

Originally posted by Viking
The early models literally shook apart in the heavy buffeting. Completely out of control. Also the P-38 had a tendency to lose its tail section in compression dives.



The P-47D model got modified with each production batch to improve dive handling, the D-30 also getting the dive flaps. While the dive flaps did increase drag they were not dive-brakes. They increased lift to avoid the plane’s tendency to “tuck under” into a vertical “graveyard” dive and also helped pilots in pulling out of dives. When approaching compression the wings would lose lift due to the shockwaves forming at the leading edge thus nosing the plane down out of control. They would literally fall out of the sky.

Hi,

the question for me is, at what speed and which P47 felt appart??

Afaik the combat P47C/D dont had this problems, at least not more than a FW190 or Bf109. The problems of the P38 are well known, but thats something absolut different.

Since the bomberescort dont had the absolut need to destroy the interceptor, but to drag him away from the bombers, i realy cant see why a limitation of mach0.72 make the P47 not combat worthy in high alt. Mach0,72 is good above the normal attacking speed of a FW190 or 109G. Actually the P47 did proof that it was a very good escort plane vs the 190A and 109G, its only real limitaion was the rather short range(in 1943).  It simply wasnt a air superiority fighter, but still a very good escort fighter.  In high alt it could outaccelerate/climb its oponents.
Of course the pilots had to get used to the dive limits, but same problem the 109 pilots had as well and the 262 wasnt able to dive more than 30° without to end very fast in a death trap, but its advanced horizontal speed made it more than combat worthy, same imho count for the P47.
The P38 is a other story, but even this plane did suffer more by the engine problems in high alt, than by its dive problems.

Some of the RAE war time statements got prooven as wrong by history. The Hurri also wasnt even to the 109E, although this was their conclusion after making testfights. I think the statements regarding the P47 as escort fighter in high alt are in the same class.

hogenbor,

i dont wrote Brown is biased and i absolutly respect his knowledge, i only particular dislike the way he offer HIS knowledge as truth. This reminds me to Mr. Rall and Galland, who, imho, also made to many, fast , not exact, but good sounding statements,  without a proof or clarification.

Greetings,

Knegel

[Knegel]

Originally posted by Knegel
Hi,

the question for me is, at what speed and which P47 felt appart??

Afaik the combat P47C/D dont had this problems, at least not more than a FW190 or Bf109. The problems of the P38 are well known, but thats something absolut different.

Since the bomberescort dont had the absolut need to destroy the interceptor, but to drag him away from the bombers, i realy cant see why a limitation of mach0.72 make the P47 not combat worthy in high alt. Mach0,72 is good above the normal attacking speed of a FW190 or 109G. Actually the P47 did proof that it was a very good escort plane vs the 190A and 109G, its only real limitaion was the rather short range(in 1943).  It simply wasnt a air superiority fighter, but still a very good escort fighter.  In high alt it could outaccelerate/climb its oponents.
Of course the pilots had to get used to the dive limits, but same problem the 109 pilots had as well and the 262 wasnt able to dive more than 30° without to end very fast in a death trap, but its advanced horizontal speed made it more than combat worthy, same imho count for the P47.
The P38 is a other story, but even this plane did suffer more by the engine problems in high alt, than by its dive problems.

Some of the RAE war time statements got prooven as wrong by history. The Hurri also wasnt even to the 109E, although this was their conclusion after making testfights. I think the statements regarding the P47 as escort fighter in high alt are in the same class.

hogenbor,

i dont wrote Brown is biased and i absolutly respect his knowledge, i only particular dislike the way he offer HIS knowledge as truth. This reminds me to Mr. Rall and Galland, who, imho, also made to many, fast , not exact, but good sounding statements,  without a proof or clarification.

But i guess thats normal, cause pilots in general are not politicians.

Greetings,

Knegel

[Viking]

Originally posted by Knegel
Hi,

the question for me is, at what speed and which P47 felt appart??
 

The early P-47s (B series and perhaps the very early C series) had fabric covered control surfaces. These would often fly apart during compressibility dives dooming the plane and pilot. Also before a recovery procedure was worked out pilots would try to trim out of the dive resulting in overloading the airframe when the plane reached lower altitudes where the controls became effective again. Or in the words of Warren Bodie (a man I believe Widewing respects greatly): “Pilots were running up against compressibility and they were dying.”

Eric Brown test flew the P-47 with a Mach meter installed and found that the speed at where control was lost was Mach 0.73. This is INDISPUTABLE, and totally unacceptable in a high-speed high-altitude fighter. And I’ll take the word of an accomplished test pilot like Eric Brown who actually test flew the plane in question over some armature internet historian who’s peeved that his pet warbird got a bad rep.

[Karnak]

As I recall, from a pure air combat standpoint, he rated the F4U-4, Fw190D-9 and Spitfire Mk XIV as the best prop fighters of WWII.  I don't recall which order he put them in.

[Brooke]

Originally posted by Viking
Eric Brown test flew the P-47 with a Mach meter installed and found that the speed at where control was lost was Mach 0.73. This is INDISPUTABLE, and totally unacceptable in a high-speed high-altitude fighter.

I don't dispute the mach 0.73 number -- I'll take his word for it.  But I don't think that one statistic alone determines acceptability.  I think it is an important characteristic among other important characteristics (such as top level speed, handling at speed, ability to get to high altitude, and handling at altitude).  For example, I'd be interested to know the tactical mach number of the P-39 and P-40, which regardless of what their tactical mach numbers are would not have been as good at high-altitude escort as P-47's or even P-38's.

Also, history shows that the P-47 did very well as a high-speed, high-altitude fighter in WWII.  In the words of Major General William E. Kepner, commanding General of the 8th Fighter Command in the European Theater, ". . . it was the Thunderbolt that broke its [the Luftwaffe's] back."  The P-47 was a major high-altitude fighter from the time the Luftwaffe was still strong until the USAAF had made great strides towards achieving air superiority.  It was the fighter that most presided over the demise of the Luftwaffe.

The top-scoring fighter group in the European Theater (the 56th) flew P-47's.  The top two highest-scoring American aces in the European Theater flew P-47's, and six of the top ten in the 8th Air Force flew P-47's.  Most of the fighters in Big Week, considered a major turning point for Luftwaffe fighter opposition, were P-47's.

[Viking]

Originally posted by Brooke
I don't dispute the mach 0.73 number -- I'll take his word for it.  But I don't think that one statistic alone determines acceptability.

What you call a statistic I call a serious flaw. When reaching compressibility speed the plane literally fell out of the sky completely out of control. The 109 did not do this, the 190 did not do this, the Spitfire did not do this, the P-51 did not do this.

I do not dispute the accomplishments of those who flew the P-47 in combat. However I argue that those accomplishments were in spite of the P-47’s flawed dive characteristics and if anything makes the pilots’ accomplishments that much greater.

[Viking]

Originally posted by Angus
Very very very nice! Thanks!
 

You’re welcome

Originally posted by Angus
That museum looks great!  

If you ever find yourself in the neighborhood I’ll show you around!

Originally posted by Angus
And of course I also envy you to death for meeting mr.Brown.
 

[Brooke]

Originally posted by Viking
What you call a statistic I call a serious flaw. When reaching compressibility speed the plane literally fell out of the sky completely out of control. The 109 did not do this, the 190 did not do this, the Spitfire did not do this, the P-51 did not do this.

I do not dispute the accomplishments of those who flew the P-47 in combat. However I argue that those accomplishments were in spite of the P-47’s flawed dive characteristics and if anything makes the pilots’ accomplishments that much greater.

I don't think that the P-47 had flawed characteristics in this regard.  Every WWII aircraft has a tactical mach number, and it is not a flaw for the P-47 to have one.  Yes, the P-47's was slightly lower than the LW planes (0.71 vs. 0.75), and the P-51's was slightly higher (0.78 vs. 0.75).  But they all have finite tactical mach numbers, including the LW planes, the P-51, and the Spitfire -- they all have speeds that they can reach but beyond which they are not maneuverable.

For example, I've read accounts of P-51's hitting compressibility.  In fact, a couple of months ago, I went to a talk at my local flight museum, the Museum of Flight in Seattle, and heard a talk by Clayton Kelly Gross, a P-51 ace who, among other aircraft, shot down an Me 262 piloted by Walter Schuck (who bailed out and survived and whom he met after the war).  Mr. Gross told about seeing a 262 far below him, going into a vertical dive in his P-51 to go after it, hitting full compressibility, completely losing control response in his P-51, losing all interest in and notice of the 262 while attempting to regain control, getting it back gradually as he got to lower and lower altitude, commencing a careful pullout so as not to rip his wings off, and finding himself screaming along miraculously right on the tail of the 262, which he then put a good burst into.

Now, if instead of it being a flaw to have a tactical mach number, you mean that the P-47, once exceeding its particular tactical mach number, was flawed because it was more prone to structural failure or inability to recover at lower altitudes than were the LW planes, the P-51, or the Spitfire, I don't know about that.  I haven't read or seen any statistics or even anecdotal accounts that it was more susceptible to failure in compressibility or more prone to non-recovery.  The P-38 without dive flaps, yes -- but not the P-47.

[Greebo]

I'd think the P-47 would outaccelerate anything else in a dive. Diving 109s and 190s were possibly caught and shot down before the P47 reached its critical mach number.

[Bodhi]

Impressive museum

[Widewing]

Originally posted by Brooke
I'll take his word for it.  

Don't, it's incorrect. There is a wealth of data that disproves this figure.

See the 190 Vs p-47D diving thread. P-47s had the same placarded max dive speed as the P-51.

P-47s suffered no more from compressibility than did any other modern fighter of the era. The fact that it operated at extreme altitudes made encountering compressibility more common place. The F4U and F6F were placarded with lower max speed limitations. The fact that these fighters rarely operated above 25,000 feet meant that they had much fewer opportunities to get into long, high-speed dives. Still, there were fatalities from diving these fighters too fast as well. There are documented crashes of P-40s where compressibility was ruled the cause. It was not uncommon for 109s and 190s to go straight into the ground as well. Some were captured on gun camera film.

P-47D dive data from here.



My regards,

Widewing

[Viking]

Originally posted by Widewing
P-47s suffered no more from compressibility than did any other modern fighter of the era.

This is … incorrect. The P-47 would “tuck under” when approaching critical Mach thus forcing the plane into an even steeper dive. Of all the WWII fighters Brown flew only three suffered from “Mach tuck”: The P-38, P-47 and F8F Bearcat.

[Shuckins]

Viking.....nearly every fighter capable of diving into compressibility confronted the phenomenon of "mach-tuck."  All that was required for most of these aircraft to encounter mach-tuck was sufficient altitude to build up to their critical mach number in the dive.

P-51D:  In a dive compressibility effects were indicated by instability, uncontrollable rolling or pitching, stiffness of controls, or combinations of these along with vibration.  Nose heaviness (tuck under) was noticeable, and became more severe with speed increases.  


F4U:  Vought test pilots performed many high speed dive tests.  On some early ones Mach 0.75 was reached, and considerable buffeting and tuck-under was encountered.  A limiting envelope for F4u-1D was defined based on the testing, and service pilots were instructed to stay within it.  That envelope ranged from Mach 0.63 ad 10,000 feet to mach 0.72 at 30,000 feet.

F6F:  Corky Meyer once encountered mach-tuck while test diving one of the F6F-3 dog-ships from 28,000 feet.  His instructions were to dive at a 60 degree angle and reach 485 mph IAS (580 mph true airspeed.)  At 12,000 feet the nose of the aircraft began pitching down on its own and the elevator controls felt like they were set in concrete.  He managed to pull out only after cutting the throttle and reducing his drag.  Later inspection of the velocity-G recorder revealed that he had overshot the goal of 485 mph and attained 512 mph.  While the horizontal stabilizers were permanently bent (starboard up 15 degrees;  port down by 15 degrees) by his ham-fisted, adrenalin-powered pull-out, the robustness of the Hellcat's construction was evident in the fact that not a single rivet was popped across the entire airframe.  The Hellcat's mach-limit dive speed was .78 mach at 15,000 feet altitude to keep service pilots from encounter excessive compressibility effects, including mach-tach.

Regards, Shuckins

[Squire]

There were a host of problems experienced by any of the WW2 fighters that dove to the speeds discussed in both of the current threads...

They were not intended to go Mach 1!!! they could not achieve high subsonic speeds without control issues and stability issues caused by the shockwave over the control surfaces. It was hazardous to do simply because you needed time to pull out, and you needed to know HOW to get them back under control, and not all pilots made it.

Test pilots and combat pilots therefore discussed the problems widely, and many of the reports we refer to in our posts. Some of them refer to absolute maximums attainable, others refer to sensible parameters that average pilots should adhere to where possible.

A little balance and common sense goes a long way.