Sustained turn performance is a tricky animal. For what it's worth Urchin, here are my educated guesses.
First some math:Radius(turn) =
V^2
-------------------------------------
g x sqrt [ ((Cl / Cd) x (T / W))^2 - 1]
From other relationships we can replace V^2 with 2x(W/S) where S= wing area. This gives us the following:
Radius(turn) =
2 x (W/S)
---------------------------------------
g x sqrt [ ((Cl / Cd) x (T / W))^2 - 1]
So now we have turn radius as a function of the following aircraft variables:
a) weight
b) wing area (S)
c) lift (Cl)
d) drag (Cd)
e) thrust
(1) Spit 14 vs. 8/9/16 sustained turn radiusOthers have pointed out already that the Spit 14 is significantly heavier than the other variants. The AH website does list the Spit 16 as the same normal weight as the 14 but as pointed out by others this is probably incorrect and that the 16 is about the same weight at as the 8.
Looking at the equation we can see that turn radius increases with increasing weight. So my guess is that though the 14 has probably a larger wing area and greater thrust, the greater weight more than offsets these other things and is the primary factor for the larger sustained turn radius.
(2) Spit 9 vs. Spit 16 sustaine turn radiusIn AH if you look at the current climb charts the Spit16 has a much greater excess power margin compared to the Spit9 meaning the Spit16 having greater excess thrust. In our friendly equation we can see that as thrust increases, turn radius decreases. I surmise the additional thrust is the primary factor that gives the Spit16 a better sustained turn radius compared to the Spit9.
Tangent for sgtpappy - wingloading will give you an indication of instantaneous turn performance. For sustained turn performance you have to evaluate it considering the variables above.
(3) Flaps flaps flapsWhere flaps come into play in is how the Cl/Cd values differ between the variants at the specific airspeeds that these sustained turns were flown at for each plane.
I Don't know anything about the spitfire flaps and don't have the time to spend researching the alphabet soup spit wings
to try and figure what the lift-to-drag ratios with flaps are for the Spit variants. What the tests suggest IMHO is that the spit 8 with flaps out has a good Cl/Cd ratio.
Cheers!
Tango, XO
412th FS Braunco Mustangs
