Thanx for the site ad. Very interesting. The quoted 'do not exceed' speeds and dive angle limitations were clearly set before the dive recovery flaps were introduce as the text states clearly that a/c with the flaps can increase permitted dive angle from 15 deg. to 45 deg. and add 15-20 mph to listed speeds. The document is not dated that I could find, but as it refers to the P38L-1 I assume it was published about the time that model began production, very shortly after the dive flaps went into use. I think that the Powers That Be were being cautious about the effectiveness of the flaps. From what I have read elsewhere, 8thAF Lightning pilots with the flaps felt free to pursue any '109 or '190 that tried to dive away from them. This was one of the reasons that the last couple of months of service by the '38s in the 8th were so successful. The Germans were used to escaping Lightnings by diving as they hadn't followed previously. Result was a number of cheap kills while the Luft. pilots learned that the rules had changed. Best to be very careful about reported airspeeds above about 440-450 mph as the airspeed indicators used at that time also suffered from Mach effects and became very inaccurate. There were claims of prop. a/c reaching speeds above 600 mph in dives, and even claims of exceeding the speed of sound. All crap, of course, but that was what the indicator said. Hence the use of Mach meters. I don't know how much higher the compressibiltiy vel. of the Spit was compared to the '38, but it couldn't have been too much. With all that wing area, the Spit just didn't accelerate nearly as quicly as the Lightning when the nose went down. I know that the MkXIV could get into compressibility (buffeting, control freeze and nose tuck), but had to be dived long and hard. Don't know about the MkIX or VIII, but I can't believe anything earlier would get into that range.

By the way, the actual onset of compressibility effects for the P-38 at 36K was 445 mph tas. It wouldn't have been much higher than that for the Spitfire.

Just convert from IAS to TAS to find out, 340 MPH IAS limit for the spit at 35,000' results in TAS of 578 MPH. The spit had a much thinner wing so compressibility occurred at higher speeds. The fastests verified dive in a spit was a bit over 600 MPH, then there was the post war one which apparently reached 690 MPH.

I didn't think that a second chain of radars was in operation during the BoB. Then once they are over the coast there would undoubtedly be more problems with IFF and in accurate reports. But even a small loss in accuracy would result in a much increased search volume. For example if the new bearings were only accurate to +/-4 degrees instead of +/-2 and the range was +/-2 miles instead of +/-1 the search volume has gone up 4 times.

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Instead of building a Merlin hawk, you could simply put a pair of fuel tanks in the wing of spit, albeit small tanks and a rear fuselage tank to increase range and endurance. You then retain the handle qualities and performance qualities of the spit while gaining the range of the P-40.

I thought the spitfire had a thicker wing.

no, the wing on the spitfire was very much thinner.

Testing at Boscome Down gave: Spitfire: Mach Limit in tests 0.89, advised maximum in operational use 0.85. Mustang (which had a thicker wing) was 0.8. It gave a good warning as it tended to porpoise when getting close to the limit. P-47 was 0.75 from recollection (might have been a little lower than this).

The speed correction for altitude (IAS vs TAS) is not adequate as you approach Mach. At high subsonic M numbers, the AirSpeedIndicator will give increasing high side errors, showing IAS well above TAS. No prop a/c could get much above 600 in any situation due to the propellor. The fastest moving part of a prop a/c are the propellor blades which are airfoils. Somewhere in the range 0.8-0.9 M, the blades will reach their compressibility range and (one) cease to produce thrust, (two) suffer extremely sever buffetting as each blade hits the shock wave of the preceeding blade. As M decreases with altitude (and reduced air pressure), and is only a few mph above 700 even at low altitude, a speed of 690 would seem to be completely out of the question. In fact a TAS above 600 would be pretty doubtful without a lot of confirmation. So how was the speed verified?? The usual system for the 1940s was just to record insturment readings with a movie camera in the pit.

Real problem is the time (and altitude) needed by the Spit to reach this kind of dive speed. The greater drag effect of the long cord wing was the reason that all the US a/c (and especially the P-38) accelerated so much faster. To add to my last post, ref the propeller problem, the MkXIV with its 5-blade prop would have a much harder time of it than a Lightning with its 3-blade units.

The tips of the propeller were actually going supersonic in most aircraft. That is the tearing sound you hear when a WW2 fighter flys past at an airshow. I doubt that the drag from the skin friction of the wing was that great. The P-47 has an eliptical wing and it was the best diver of the war. The Spit XIV could actually outdive the Fw-190 and Bf-109.