P-47 Actions 29 Mar 44 near Berlin

[drgondog]

All of the fighters mentioned had compressibility issues which led to structural failures when pilots tried to pull out of dive before reaching dense enough altitude to use trim to start the pull out. This resulted in either control reversals or 'concrete stick' as back pressure was attempted to pull the aircraft out pre-maturely.

The P51D had several mods applied to correct the wing root/spar failures of the B/C which killed several pilots... while 'directional stability' at very high speeds manifested itself, it was actually better served in that respect than the D which required the fin 'strake' modification to assist after removing the 'turtledeck' of the B/C.

The also D had a greater root chord than the B and improved the gear and door design - which was identified as one of the root causes (i.e 'popping open in compressibility dive)... which makes a D so easy to identify from above (from a B/C) with a more pronounced angle from the leading edge inboard of the .50 Cal machine guns.

The P-38 had a different aerodynamic issue due to the interaction if center section airflow over the horizontal stab - causing flutter in a high speed dive.

I candidly do not know what issues the Spit or FW or 109 had re; Compressibility. I'm pretty sure that Mach Critical was in same range for all ----> .79 to .82 range

None of the pilots I talked to growing up ever mentioned that the P-47 was difficult to control in a dive and these included Gabreski and Mahurin and Billy Hovde (who flew in the 355th FG with my father in WWII - first P-47's, then Mustangs). They were very unequivocal in their praise of the 47 in pursuit of both the Fw 190 and Bf 109 in dives.

These are interesting debates which I have had in different formats with Wing Commander Brown in his assessments of 'Best WWII fighter..' Thank you Franek!

Regards,

Bill

[Franek Grabowski]

Bill
Yes, indeed, every 'modern' piston fighter was able to reach tremendous speeds, though I think control reversal (aeroelasticity) was more an issue of early jets rather than pistons. More an issue was propeller overspeeding and all the issues related to speed of prop tip.
Problems with Mustang were more related to trouble with identifying weak points rather than rectifying them. Early P-51B/C suffered several high speed dive crashes but I think it was suspected a structural weakness rather than unstability.
Measured Spitfire CrM was 0,89, this based on tests by 'Fuehrer' Martindale. I think it was a highest value for any piston fighter. I recall reading about German high speed dives but I cannot recall where.
The main issue with Thunderbolt was that due to superior engine power it was better suited to high speed manouvers, also it never accelerated that fast to reach dangerous speeds. The one must have been very careful in Spitfire, but I think the main problem was that it was not realised that Spitfire could have outdived any German aircraft. Pilots were not awared and not believed that.
Best wishes
Franek
PS I am droping you a PM.

[Graham Boak]

The critical mach number (and hence maximum dive speed) of the Spitfire was higher than its contemporaries because of the thinner wing. Mcrit is a function of the thickness of the wing and how far aft is the point of maximum thickness. Hoerner's classic work on aircraft drag has a figure showing the curve produced from the experimental data on many aircraft. The Spitfire is, if I remember correctly, around 0.91, the Mustang around 0.84. Other aircraft, such as the Me 262, cluster around 0.78-0.82. Which is sufficient in itself to prove that no, the Me262 did not go supersonic. Some aircraft e.g the P-38 encounter compressibility problems at speeds lower than Mcrit because of local interferences, in this case between the fuselage and the nacelles.

A postwar Spitfire PR XIX was timed at a greater rate of descent (than Martindale) in a thunderstorm over the South China Sea: however, I suspect that the air mass itself was descending and thus the local Mach Number no greater.

[Six Nifty .50s]

Originally Posted by Franek Grabowski

Actually, T-bolt had pretty poor dive performance, both Mustang and Spitfire outdiving it. This was a surprising result of supersonic dive tests performed in Britain.

Your comment is misleading. The Spitfire, except for the wing shape, was not a particularly clean aircraft and its dive acceleration was not very impressive. And, the British did not use a fighter version of the Spitfire for those high speed tests. It was an unarmed, Mk XI high-altitude photo plane that was dived from the thin air at about 40,000 feet. The Mustang Mk I was a low-altitude photo plane dived from 28,000 feet, with guns and radio removed. I'm not sure about modifications to the Thunderbolt, if any, but the pilot was not very experienced at diving this type. During the tests he lost control of the aircraft and had problems with the engine.

Under combat conditions most if not all Axis and Allied fighters could escape from a Spitfire by diving away from it. It was a standard disengagement tactic used by German pilots.

[Franek Grabowski]

Originally Posted by Six Nifty .50s

Your comment is misleading. The Spitfire, except for the wing shape, was not a particularly clean aircraft and its dive acceleration was not very impressive.

Acceleration is one thing, maximum speed attainable - another. Airfoil and wing shape are decisive in regard of aircraft performance.

And, the British did not use a fighter version of the Spitfire for those high speed tests. It was an unarmed, Mk XI high-altitude photo plane that was dived from the thin air at about 40,000 feet.

Ridiculous comment, because it was essentially a modified Mk IX airframe with enlarged oil tank, wing leading edge tanks, unarmoured windscreen and retractable tailwheel. Not the changes making a substantial difference.

The Mustang Mk I was a low-altitude photo plane dived from 28,000 feet, with guns and radio removed.

Wing did not differ from later variants and it was the only variant then available. Actually, it was found it is quite fast aircraft but Spitfire was faster. There was no dissapointment.

I'm not sure about modifications to the Thunderbolt, if any, but the pilot was not very experienced at diving this type. During the tests he lost control of the aircraft and had problems with the engine.

Those were not ordinary pilots flying those dives. Several flights had been done and it was found that the aircraft is surprisingly bad and dissapointing in dive.

Under combat conditions most if not all Axis and Allied fighters could escape from a Spitfire by diving away from it. It was a standard disengagement tactic used by German pilots.

They did so, because nobody believed it is possible to catch a diving German, Helmut Wick believed this and it costed him life. It was quite a different story with tropicalised variants but for another reason.

[Six Nifty .50s]

Originally Posted by Franek Grabowski

Acceleration is one thing, maximum speed attainable - another. Airfoil and wing shape are decisive in regard of aircraft performance. Ridiculous comment, because it was essentially a modified Mk IX airframe with enlarged oil tank, wing leading edge tanks, unarmoured windscreen and retractable tailwheel. Not the changes making a substantial difference.

Air resistance varies according to height and which greatly affects speed and acceleration. Different results were obtained when diving planes from 28,000 feet as opposed to 40,000 feet. There is nothing ridiculous about it.

Originally Posted by Franek Grabowski

Those were not ordinary pilots flying those dives. Several flights had been done and it was found that the aircraft is surprisingly bad and dissapointing in dive.

Yet in actual combat the Spitfire's dive acceleration and ability to overtake a German fighter was much inferior to the Thunderbolt. I've yet to find a single German pilot who said otherwise.

Originally Posted by Franek Grabowski

nobody believed it is possible to catch a diving German, Helmut Wick believed this and it costed him life. It was quite a different story with tropicalised variants but for another reason.

Again this is misleading. Any fighter, including jets, could be caught from behind in a dive if the attacker's speed was higher before the victim tried to escape.

Many RAF and Luftwaffe aces who commented on escape tactics said that diving was the most common and successful means of escape from a pursuing Spitfire. I've yet to find any pilots who disagreed with their consensus, which was backed up after the British tested captured German fighters.

[Franek Grabowski]

Originally Posted by Six Nifty .50s

Air resistance varies according to height and which greatly affects speed and acceleration. Different results were obtained when diving planes from 28,000 feet as opposed to 40,000 feet. There is nothing ridiculous about it.

Speed of sound is constant and always Mach=1. It is a proportion of speed of desired object to speed of sound at given parameters - u/a.
Aim of tests was to find an aircraft with highest speed it could achieve in relation to speed of sound , ie. Mcr. So if aircraft achieved its Mcr at dive from 28,000 ft, putting it on 40,000 ft would not change anything.

Yet in actual combat the Spitfire's dive acceleration and ability to overtake a German fighter was much inferior to the Thunderbolt. I've yet to find a single German pilot who said otherwise.

Perhaps, but analysis of known records concerning 1943 combats does not support thesis of Thunderbolt's superiority.

Again this is misleading. Any fighter, including jets, could be caught from behind in a dive if the attacker's speed was higher before the victim tried to escape.

Nope, I am not talking about surprising attack but prolonged chase.

Many RAF and Luftwaffe aces who commented on escape tactics said that diving was the most common and successful means of escape from a pursuing Spitfire. I've yet to find any pilots who disagreed with their consensus, which was backed up after the British tested captured German fighters.

It was occassionally reported by pilots that the German aircraft are not that fasr in dive, eg. during Circus 138, Sgt(?) Karol Sumara of 316 Sqn noted that F.W.190 cannot outdive Spitfire - it was him, who was bounced.
A very interesting is analysis of pilots' opinions after test flying of clipped wing Spitfire. It shows, what is the value of accounts and opinions in general.

[Six Nifty .50s]

Originally Posted by Franek Grabowski

Speed of sound is constant and always Mach=1. It is a proportion of speed of desired object to speed of sound at given parameters - u/a. Aim of tests was to find an aircraft with highest speed it could achieve in relation to speed of sound , ie. Mcr. So if aircraft achieved its Mcr at dive from 28,000 ft, putting it on 40,000 ft would not change anything.

This has nothing to do with measuring the greater air resistance against the plane and propeller at lower heights. There is simply no way that a Spitfire or any other aircraft could attain the same Mach Number or accelerate as quickly if the pilot began his dive in denser air; in this case 12,000 feet below the original starting point.

Originally Posted by Franek Grabowski

Perhaps, but analysis of known records concerning 1943 combats does not support thesis of Thunderbolt's superiority.

Whose analysis? It's always reckless to draw general conclusions based on the results of one pilot and one plane. But if you insist, anyone can play that game ...

Boscombe Down January 1941. Spitfire P7525. Complaints by No. 66 Squadron over handling qualities included a diving speed restricted to 320 mph in spite of full forward trim. Flew left wing low and had airflow problems with the tailplane. Modifications made to improve handling.

Farnborough June 1942. Spitfire P7251. Failures of tailplanes had occurred in high speed dives, usually breaking off at Frame 19, and tests were started to locate the cause. Out of 36 accidents under investigation at the time, the tail unit broke off in mid-air 24 times and 15 pilots were thrown out of the aircraft. A new mainplane was fitted to P7251 together with recording instruments used to measure tail plane deflections. Two pull outs were made at 300 mph and one at 400 mph and there was some twisting of the fuselage near the tail. The terminal velocity of the Spitifire was quoted at "560 mph True Air Speed, corresponding to about Mach .79".

Farnborough April 1944. Spitfire EN409. This aircraft was dived from a height of 40,000 feet and reputedly reached a True Air Speed of 600 mph, which destroyed the engine and propeller.

Farnborough August 1944. Spitfire PL827. This aircraft was dived from a lesser height of 36,000 feet, but the pilot was unable to complete his high speed run because the supercharger exploded and the aircraft was set on fire.

Farnborough November 1944. Spitfires NL345, NH476, PT357. These aircraft were fitted with recording instruments to assess structural damage caused by dive-bombing, although the pilots did not dive at particularly high speeds, nor at excessively steep angles (usually 45 to 60 degrees). The test was prompted by complaints from No. 125 Wing which experienced a large number of buckled mainplanes within a few weeks.

I really don't think that anyone is interested in reading responses such as: "This cannot be true because I seem to remember talking to a Polish pilot who never mentioned this to me".

Originally Posted by Franek Grabowski

It was occassionally reported by pilots that the German aircraft are not that fasr in dive, eg. during Circus 138, Sgt(?) Karol Sumara of 316 Sqn noted that F.W.190 cannot outdive Spitfire

I doubt it, unless the Focke-Wulf had an engine failure. And you're the one who implied that we should not question the findings from RAF tactical trials.

RAE Farnborough and AFDU Duxford tested Oberleutnant Arnim Faber's FW 190 A-3 against the Spitfire V and the Spitfire IX. The Focke-Wulf ran away from both in dive performance, even though Faber's plane was not exactly tip-top. It had a derated engine which did not deliver maximum potential power and level speed, and the BMW also ran rough because of bad spark plugs.

I don't know if the RAF tested a Griffon-engined Spitfire against a Jumo-engined FW 190D, but former Luftwaffe pilots have said that the Dora 9 accelerated faster in a dive than the FW 190A.

[Franek Grabowski]

Originally Posted by Six Nifty .50s

This has nothing to do with measuring the greater air resistance against the plane and propeller at lower heights. There is simply no way that a Spitfire or any other aircraft could attain the same Mach Number or accelerate as quickly if the pilot began his dive in denser air; in this case 12,000 feet below the original starting point.

I am afraid you cannot understand simple laws of physics. If an aircraft reaches Mcr at low level, increasing it will not change anything! Mcr is constant non-dimensional value non dependant on AS.

Whose analysis? It's always reckless to draw general conclusions based on the results of one pilot and one plane. But if you insist, anyone can play that game ...

Yup, let's go. Please, prove me that M=0,83 that Herb Fisher was unable to exceed is more than M=0,89 achieved by Martindale.

Boscombe Down January 1941. Spitfire P7525. Complaints by No. 66 Squadron over handling qualities included a diving speed restricted to 320 mph in spite of full forward trim. Flew left wing low and had airflow problems with the tailplane. Modifications made to improve handling.

Every aircraft that was reported to have poor handling qualities or performances was tested at Boscombe Down. In most cases this was caused by poor servicing - apparently this was the case of this Spitfire, which was damaged at 66 Sqn, then rpaired and sent to BD.

Farnborough June 1942. Spitfire P7251. Failures of tailplanes had occurred in high speed dives, usually breaking off at Frame 19, and tests were started to locate the cause. Out of 36 accidents under investigation at the time, the tail unit broke off in mid-air 24 times and 15 pilots were thrown out of the aircraft. A new mainplane was fitted to P7251 together with recording instruments used to measure tail plane deflections. Two pull outs were made at 300 mph and one at 400 mph and there was some twisting of the fuselage near the tail. The terminal velocity of the Spitifire was quoted at "560 mph True Air Speed, corresponding to about Mach .79".

There was no Spitfire with such serial.

Farnborough April 1944. Spitfire EN409. This aircraft was dived from a height of 40,000 feet and reputedly reached a True Air Speed of 600 mph, which destroyed the engine and propeller.

Farnborough August 1944. Spitfire PL827. This aircraft was dived from a lesser height of 36,000 feet, but the pilot was unable to complete his high speed run because the supercharger exploded and the aircraft was set on fire.

Ridiculous. Making complaints because the aircraft reached the top speed for a propeller driven aircraft and this caused a few malfunctions? Fisher achieved TAS=560, a little bit less than Martindale, I would love to see what would have happen with Thunderbolt flying with TAS=600.

Farnborough November 1944. Spitfires NL345, NH476, PT357. These aircraft were fitted with recording instruments to assess structural damage caused by dive-bombing, although the pilots did not dive at particularly high speeds, nor at excessively steep angles (usually 45 to 60 degrees). The test was prompted by complaints from No. 125 Wing which experienced a large number of buckled mainplanes within a few weeks.

This was also reported by Polish pilots. I am not sure what it has to dive speeds but eg. Mustangs also suffered such failures. They were fatal however, so no such aircraft was ever tested.

I really don't think that anyone is interested in reading responses such as: "This cannot be true because I seem to remember talking to a Polish pilot who never mentioned this to me".

You may like it or not but PAF was the greatest foreign operator of Spitfires. Thus, I may conclude Polish stats or observations would be representative for the type.

I doubt it, unless the Focke-Wulf had an engine failure. And you're the one who implied that we should not question the findings from RAF tactical trials.

RAE Farnborough and AFDU Duxford tested Oberleutnant Arnim Faber's FW 190 A-3 against the Spitfire V and the Spitfire IX. The Focke-Wulf ran away from both in dive performance, even though Faber's plane was not exactly tip-top. It had a derated engine which did not deliver maximum potential power and level speed, and the BMW also ran rough because of bad spark plugs.

I do not know if you do that willingly or not but it was clearly noted that Fw 190 was able to escape (Split-S) due to excellent ailerons' efficiency and superrior roll rate. This was improved in later Spitfires, starting with Mk XII.

I don't know if the RAF tested a Griffon-engined Spitfire against a Jumo-engined FW 190D, but former Luftwaffe pilots have said that the Dora 9 accelerated faster in a dive than the FW 190A.

I doubt if Fw 190D had much different Mcr than Fw 190A, this means their maximum speeds must have been similar.

[Six Nifty .50s]

Originally Posted by Franek Grabowski

I am afraid you cannot understand simple laws of physics.

Then we have to wonder where you learned about 'physics' and earth science.

The 'simple laws of physics' does not suggest that the maximum speed of a Spitfire XI flying at treetop height is exactly the same as it was at 25,000 feet. The 'simple laws of physics' does not tell us that that air resistance is the same, regardless of height.

Originally Posted by Franek Grabowski

Please, prove me that M=0,83 that Herb Fisher was unable to exceed is more than M=0,89 achieved by Martindale.

These speeds were achieved at what heights?

Originally Posted by Franek Grabowski

There was no Spitfire with such serial.

You'll have to take that up with Eric Morgan.

Originally Posted by Franek Grabowski

Ridiculous. Making complaints because the aircraft reached the top speed for a propeller driven aircraft and this caused a few malfunctions? Fisher achieved TAS=560, a little bit less than Martindale, I would love to see what would have happen with Thunderbolt flying with TAS=600.

Perhaps Eric Morgan made another error when he claimed that a Spitfire reached 600 mph. And we have no way of knowing that instrument readings were always accurate.

Originally Posted by Franek Grabowski

I do not know if you do that willingly or not but it was clearly noted that Fw 190 was able to escape (Split-S) due to excellent ailerons' efficiency and superrior roll rate.

The report also clearly states that the FW 190A-3 also dived at higher speeds than the Spitfire V and the Spitfire IX. This is because the Spitfire had inferior dive acceleration. The opposite was true in USAAF tactical trials pitting the P-47 against the FW 190 where the Focke-Wulf had initial advantage but the Thunderbolt soon closed the gap.

Whatever Spitfire test pilots claimed to have achieved in very high altitude dives was certainly not borne out in combat, or in the RAF tactical trials versus German fighters.

Originally Posted by Franek Grabowski

I doubt if Fw 190D had much different Mcr than Fw 190A, this means their maximum speeds must have been similar.

When trying to escape, acceleration in the dive was far more important than maximum theoretical speed, which for the Spitfire had to be built up over a long period -- and essentially useless to the RAF pilots flying tactical trials.