I’m sure most of you are aware of those high speed dives in a Mark XI Spitfire dives in about 1942 where one of them reportedly reached around .92 mach?
Does anyone know if that was the true airspeed? I’m just wondering how it was calculated and is there any doubt about that speed?Thanks in anticipation!
By: dhfan - 11th February 2021 at 20:49
Look up Sqd Ldr Martindale, I think from Boscombe Down but I’m not certain. He, and a Spitfire, had a very high speed dive which resulted in the entire reduction gear and prop being torn off. Amazingly, I seem to recall he landed the battered remains.
The other one to look up is Flt Lt Ted Powles who I believe is recorded as having the highest verified speed in a Spitfire from a very high altitude over Hong Kong.
Apart from confirming Powles’ name this is all from memory so don’t believe a word until you’ve checked!
By: Oxcart - 11th February 2021 at 20:36
The reason why I’m asking is because I mentioned it on another site and somebody queried it as involving assumptions and that it could be completely wrong. And now I’m wondering what they used to calculate it and just how accurate that speed was.
By: Aeronut2019 - 11th February 2021 at 19:02
In the RAE Structures Department Note Report ACC 217 into the crash of Spitfire MK IX NH 236 during high air speed propeller trials in 1948 there are these photographs of the instrumentation modifications. The two fuselage mounted booms looked like combs as they had numerous pressure heads , after all this was a propeller trial. Similar modifications would have been carried out to aircraft conducting high speed trials with results being recorded on the aircraft and analysed by RAE Boffins post flight. Therefore, its possible to say that if the report gives a Mach number of .92 the aircraft reached .92 Mach
The maximum Mach number seen on this trial was .84 but the accident was as a result of a -6g bunt on recovery from the dive following a loss of conciseness of the pilot for some unknown reason (G Lock?)
By: Arabella-Cox - 11th February 2021 at 17:29
Oxcart. Mach is ratio of the velocity of airflow velocity to the local speed of sound in that fluid.
I have no detailed knowledge of the Spitfire events, but I would suspect the claim of 0.92 M came as a result of computation, and the ‘local’ velocity measured over an airfoil surface. It is not unusual for the velocity over an aircraft to reach Mcrit,
You may find reading-up on Mcrit and aerofoil shape of great interest to you.
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February 11, 2021 at 3:50 pm