BF 109 Dive Rate

[Juha]

Hello Drgondog
thanks for the clarification. IIRC when just before WWII British planned to try to get the speed record from Germany they modified one Spit for the try and one of the modification was much shallower angled windscreen.

Juha

 

[drgondog]

Hello Drgondog
thanks for the clarification. IIRC when just before WWII British planned to try to get the speed record from Germany they modified one Spit for the try and one of the modification was much shallower angled windscreen.

Juha

Juha - I would point out that drag is freqently reduced to 'flat plate' drag for comparison purposes and the 'normal' area of the spit windscreen is not insignificant - just not as important as the wing

 

[NZTyphoon]

Apparently the precautions laid down in the Spitfire II manual about the dangers of excessive accelerations during pullout were to be taken seriously.

Due to size restrictions, I will only post the summary here, but I don't think many are familiar with report in its full, so it would be probably a good idea to create a PDF from it, and upload to the flight tests.

In his book "Spitfire: a Test Pilot's Story" Jeffrey Quill wrote a chapter on the Spitfire's "Longitudinal stability and Increased Range" ; Amazon.com: Spitfire - A Test Pilot's Story (Crecy Soft Cover Range) (9780947554729): Jeffrey Quill, Jeffrey Quill: Books In this chapter he explains that Supermarine went to great lengths to ensure that the Spitfire was longitudinally stable; he defined instability as potentially dangerous and a trait to be avoided. I doubt whether he would have allowed the Spitfire to go into service with such a problem.

He went on to describe how several Spitfire Vs broke up during a dive. Tests showed that some squadrons were not complying with cg requirements when fitting new equipment - in many cases the Spitfires were dangerously unstable, with the cg too far back in the fuselage (pages 248-256). Once bob-weights had been installed on the elevator controls and proper loading procedures put into practice the problem disappeared.

The dates on the extract of the report presented by Kurfurst indicate that this report was one of those enacted by the RAF in response to the break-up of Spitfires, in which case it is not representative of all Spitfires.

 

[NZTyphoon]

I think you would find interesting the findings of A&AEE at Boscombe down a fully armed Spitfire Mk IX, ie. the fighter variant tested in dive trials.

As you probably know the often referenced Mach 0,89 dives with were performed with an unarmed photo-recce Mk XI variant. As I recall however this report does not describe the behaviour of the aircraft during the dive, only records the speeds measured with a pitot (which as you noted was not a particularly accurate device at those speeds).

This variant had no cannon stubs or gun ports in the wings, neither it did have the armored windscreen of the fighter variants, ie. it was considerably different aerdynamically than the normal fighter variants. Personally it strikes me as illogical to compare a fully armed fighter such as the P-51 with the additional burden of armament with an unarmed photo recce.

Below you will find the details of the dive with the said Spitfire Mk IX fighter variant. It strikes me that the general behaviour was not at all different from the results with the Mustang in the test you quoted - normal in operation up to Mach 0.70, clear danger signs at around Mach .75, and begun to loose control at anywhere above Mach 0.80+.

If the Spitfire manual said Mach .85 as a limit, it was certainly a very bold suggestion for the pilots.

Interesting that the actual mach no quoted in the last sentence "At mach numbers above about ?? the aircraft developed..." The difference between mach .83 and mach .85? As everyone knows mach numbers differed according to altitude - no altitudes are specified in this extract.