Gavagai:
I understand your logic. However you and others have made too many aerodynamic assumptions.
For starters are you sure you removed the effect of yaw or sideslip from your roll tests between the Spit V and Spit IX? Because yaw and sideslip will change your roll performance.
For grins let's say that you have and assume we can simplify the analysis just to one degree of freedom. The following is the general equation for estimating roll rate in the one degree of freedom case:
It covers both the roll accleration and steady state roll. It's already been mentioned that the Spit IX has two radiators vs. the Spit V's one. Why does a small thing like that matter? Because the roll transient time constant 1/T, which determines roll accleration is impacted by the rolling moment of inertia (Ixx). Here's the equation for 1/T:
where:
Q = dynamic pressure (.5*air_density*velocity^2)
S = wing surface area
b = wing span
Clp = coefficient of rolling moment due to rolling
Ixx = rolling moment of inertia
V = velocity
The 2 radiators under each wing increases the rolling moment of inertia. Increase the moment of inertia reduces 1/T which reduces roll acceleration.
And that's just one variable. There are others. Roll performance is complicated and there are more details to be considered that can affect it than the factors folks have brought up in this thread.
Why do the WB roll rates differ from AH for the Spit V and IX? Beats the heck outta me
.
Should HTC look the AH Spit V and Spit IX numbers? Sure thing.
Is there something wrong? Maybe / Maybe Not, but I sure the heck can't tell from speculating from your data points and the simple factors that people have thrown out so far for why it is wrong because we're totally ignoring other key aerodynamic factors as well.
Tango, XO
412th FS Braunco Mustangs