The Story of the Photographic Reconnaissance Spitfire

[the lancaster kicks ass]

i can't qualify this statement as it was a while back but i once saw a documentary that said it was thought the spit's airframe could withstand the stresses of mach 1.3, if she could be propelled to such a speed...........

 

[helmitsmit]

i can't qualify this statement as it was a while back but i once saw a documentary that said it was thought the spit's airframe could withstand the stresses of mach 1.3, if she could be propelled to such a speed...........

The "they" mentioned above ws the R.A.F aircraft development unit. They tried the prolonged dives in 1954 with a MkXIX and in 1944 with a MkXI. However, there isn't anything on the Internet to prove it but I've got in a book. There were reports at a local police station that residents heard a loud bang high above them and a greenhouse actually shattered. Moments later they saw a lone spit heading back to base.

 

[Hop]

I read somewhere many years ago, that the RAF (maybe the French participated too?) in a high altitude aerial survey of Germany in the months leading up to the start of the war.

Supposedly it was done in secret and the recon aircraft was skillfully camoflaged as to remain unobserved during its transits.

Anyone know of this? Was it true?

Yes. Google for Sidney Cotton. He used a Lockheed Electra outfitted with cameras. He worked for MI6 though, not the RAF.

The highest speed ever "officially" accomplished in a dive by a propeller driven aircraft was by Flt Lt. Ted Powles, RAF, in a Spitfire Mk.XIX at 690 mph or .94 mach. in an emergency power dive from a true altitude of 51,550 feet.

There's nothing official about that. It's a calculated figure, using some dubious assumptions.

The highest speed by a prop fighter officially recorded, and probably the highest reached with a successfull pullout (ie not including aircraft which broke up in the air) was mach 0.891 by a Spitfire XI piloted by Sqd ldr Tobin in 1944. That was 609 mph IAS.

If that's such a big deal how come Hub Zemke's group's Thunderbolts pegged their 700 MPH airspeed indicators in dives?

Normal air speed indicators were not accurate in very high speed dives. P-38 pilots frequently reported exceeding the speed of sound in dives, they didn't come close either.

How the hell could the light-weight Spit with its Dumbo sized wings dive with a 14,000-lb. P-47 or 18,000-lb. P-38

Because it had a higher critical mach, thanks to it's thinner wings. That means it experienced mach divergent drag at higher speeds than the P-47 or P-38 (the P-38 was in fact one of the worst fighters at high mach numbers, and had a very low limit)

This is from an RAE report about their dive tests:

Note the later onset of MDD, which quickly dwarfs all other forms of drag. In other words, above about mach 0.75 the Spitfire has less drag, despite it's large wings. That's the beauty of thin wings.

The record if it can be substantiated is a P-38 flown by Col. Cass Hough. Hough was in P-47s before his group switched to P-38s at Bovington. Allegedly he began a dive at 43,000 feet and leveled off at 25,000 after an indicated 780MPH.

That's why it's no use relying on an ASI at very high speeds.

The P-38 had the lowest mach limit of the big 3 US fighters. The P-47 was next, the P-51 best. Both the P-38 and P-47 had to be fitted with dive recovery flaps because of their low critical mach.

The placarded limits were mach 0.68 for the P-38, 0.8 for the P-51B, somewhat lower for the P-51D, about 0.72 for the P-47 (iirc) and 0.85 for the Spitfire.

When did "they" measure it and how and where

The Spitfire high speed dive trials were carried out by the Royal Aircraft Establishment at Farnborough. The various service limits I listed above were found by various test pilots, for both the USAAF and RAF.

 

[helmitsmit]

Yes. Google for Sidney Cotton. He used a Lockheed Electra outfitted with cameras. He worked for MI6 though, not the RAF.



There's nothing official about that. It's a calculated figure, using some dubious assumptions.

The highest speed by a prop fighter officially recorded, and probably the highest reached with a successfull pullout (ie not including aircraft which broke up in the air) was mach 0.891 by a Spitfire XI piloted by Sqd ldr Tobin in 1944. That was 609 mph IAS.



Normal air speed indicators were not accurate in very high speed dives. P-38 pilots frequently reported exceeding the speed of sound in dives, they didn't come close either.



Because it had a higher critical mach, thanks to it's thinner wings. That means it experienced mach divergent drag at higher speeds than the P-47 or P-38 (the P-38 was in fact one of the worst fighters at high mach numbers, and had a very low limit)

This is from an RAE report about their dive tests:

Note the later onset of MDD, which quickly dwarfs all other forms of drag. In other words, above about mach 0.75 the Spitfire has less drag, despite it's large wings. That's the beauty of thin wings.



That's why it's no use relying on an ASI at very high speeds.

The P-38 had the lowest mach limit of the big 3 US fighters. The P-47 was next, the P-51 best. Both the P-38 and P-47 had to be fitted with dive recovery flaps because of their low critical mach.

The placarded limits were mach 0.68 for the P-38, 0.8 for the P-51B, somewhat lower for the P-51D, about 0.72 for the P-47 (iirc) and 0.85 for the Spitfire.



The Spitfire high speed dive trials were carried out by the Royal Aircraft Establishment at Farnborough. The various service limits I listed above were found by various test pilots, for both the USAAF and RAF.

Thanks mate. That was what I was failing to explain. You put it much betterthen me!

Didn't the Spit MkXI lose it's propellor after the dive but managed to glide back to base?

 

[Hop]

Didn't the Spit MkXI lose it's propellor after the dive but managed to glide back to base?

Not after this series of dives.

The RAE report I have is dated Jan 1944. The Spitfire involved was EN409. The report notes that all the flights were carried out by squadron leader Tobin.

In February, piloted by squadron leader Martindale, the same Spitfire, EN409 suffered damage in a high speed dive. In late April, with Martindale flying again, EN409 lost it's prop and part of the engine in another dive. I have no idea what speed was reached on these subsequent dives. It might have been faster than mach 0.891, it might not.

The US was carrying out similar research. In July 1944 they tested a Mustang at Wright Field. They carried out a series of dives, the fastest being mach 0.83. The buffeting was so strong they felt it was unsafe to try any higher speeds. The Mustang had suffered considerable structural damage and was written off.

 

[helmitsmit]

Not after this series of dives.

The RAE report I have is dated Jan 1944. The Spitfire involved was EN409. The report notes that all the flights were carried out by squadron leader Tobin.

In February, piloted by squadron leader Martindale, the same Spitfire, EN409 suffered damage in a high speed dive. In late April, with Martindale flying again, EN409 lost it's prop and part of the engine in another dive. I have no idea what speed was reached on these subsequent dives. It might have been faster than mach 0.891, it might not.

The US was carrying out similar research. In July 1944 they tested a Mustang at Wright Field. They carried out a series of dives, the fastest being mach 0.83. The buffeting was so strong they felt it was unsafe to try any higher speeds. The Mustang had suffered considerable structural damage and was written off.

Good stuff! Is there any info of planes like the Tempest doing these test?

 

[Twitch]

These Spitfires or Mustangs that MAY have hit 600 MPH in dives were popping rivets and more when they pulled out. Certainly they were in no condition to safely fly in combat again.

I used the P-38 dive tale to show how silly stories can be believed, like 690MPH in a Spit. But now that figure has become 609 MPH?!

I can categorically tell you that 5 Thunderbolt aces personally described to me pegging the 700 MPH airspeed indicator as common. One was Hub Zemke and the other was Fred Christensen who did post war testing for Republic. He was an aero engineer as well. Gabby Gabreski described it. Bob "Shorty" Rankin did too.

I really doesn't matter what calculated drag factors are and the Mustang's laminar flow wings should have made it superior to all, in theory, but it wasn't. The proof was in the deed and the P-47s in practice had it all over P-51s or Spitfires in the ability to dive. Its tremendous weight, double a Spitfire's, coupled with it powerful 2,300 HP engine engaging the 4-blade paddleblade prop gave it initial inertia to accelerate to 700 easily. They did this ALL THE TIME.

As Bob Johnson also confirmed the Jug would not pull out under any circumstances until thicker air was hit at 8-12,000 feet. The Thunderbolts pulled out and almost never popped a rivet and had no structural damage. They were on the roster for combat the next day.

I don't believe for one second that any Spitfire, Mustang or P-38 outdived the Thunderbolts. The men of the 56th dived at 700+ indicated on a regular basis and made no big deal out of it. These are guys I'll believe when it comes down to it.

 

[Hop]

Is there any info of planes like the Tempest doing these test?

Not high speed research flights, afaik, but I'm sure the RAE got their hands on one to try (they certainly tried Mustangs and P-47s as well). However, in 1946 the RAE wrote to Supermarine saying the Spitfire was the most suitable of all the aircraft they'd tried.

I do have the AFDU mach limit reccomendations for the Tempest V:

I.A.S. Height
370 30,000
410 25,000
450 20,000
490 15,000
540 10,000

The lower 540 mph figure should be treated with caution, as it might not be the effective limit of the plane. The AFDU are giving only mach limits, lower limits were often enforced at low level.

The AFDU limits for the P-51B:

I.A.S HEIGHT
298mph 35,000ft
336mph 30,000ft
376mph 25,000ft
422mph 20,000ft
468mph 15,000ft
520mph 10,000ft
574mph 5,000ft

 

[Jabberwocky]

Depends what you mean by 'out dove'.

The P-51, P-38, P-47, FW-190 et al, had better INITIAL dive than the Spitfire, either through heavier weight, better aerodynamics or more power.

However, the very thin wings and small frontal area of the Spitfire meant that once it got up into the high subsonic region, the Spitfire was actually a better diver than most of us have been lead to believe.


I have a post-war dive chart for a P-47D-30-RE: