Hi Glider,
>Mustangs were I believe red lined at 505mph, 109G's at 466mph so 540 mph is really motoring.
Mach number is dependend on speed, so you have to add altitude information to make this information comparable. I don't believe the Me 109G had 540 mph on the clock, but it reached Mach 0.80 at an altitude where the Tempest was not cleared for 540 mph either.
(You are right that the Me 109 was really motoring ... it was modified with a reduced aileron gearing to avoid flutter, and fitted with an ejection seat just in case.)
>Planes often exceeded these figures and no one is saying that a Mustang will come apart at 506mph
Quite right. However, while the 540 mph figure probably had some safety margin, it's equivalent to less than Mach 0.80 if you'd account for the compressibility error of the airspeed indicator (which is not listed in the Pilot's Notes, so it's unknown quantitatively). Qualitatively, it causes a higher than realistic speed reading.
So all considered, and with some caution because we don't have the complete data, I don't think there is a reason to assume that the Tempest was superior to the Fw 190 in a dive. However, the gaps in our data leave room for individual speculation, so we can all safely disagree
>The Spitfire is a good example. It certainly did have the highest mach no in a dive of its time, but that was a proper test, that used a heck of a lot of hight and definately wasn't an average pilot in a combat situation.
Absolutely true - diving to that speed could save your life if all went well, and break your neck if something went wrong. And individual Spitfires would handle different in a dive, so it was hard to tell just what would happen.
One of Alfred Price' books features an interesting article by a contemporary aerodynamicist, stating that before the war, aircraft were built for smooth controllability at dogfight speeds, while dives at breakneck speeds were regarded as "of academical interest only".
RAE test pilot Eric Brown used the term "tactically useful Mach number" quite a bit, which usually was somewhat below the maximum survivable Mach number even for well-handling types.
Regards,
Henning (HoHun)