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THE f} DERIVATIVES (C,,f C,,f C„,, CAr)
The sideslip derivatives are all obtainable from static wind-tunnel tests on yawed models. Generally speaking, estimation methods are not very reliable, and testing is needed for accurate results.
THE DERIVATIVE C„„
“p
We shall assume that the thrust vector remains in the xz plane, so that it does not contribute to the Y force. Then in terms of Gc and CD (see Fig. 4.5) we have
 |
 |
 |
where Pe, the equilibrium value, is zero. Hence
The main contributions to Cc usually come from the body and the tail, the wing contribution being minor. That from the tail is readily estimated. From (8.1,3) we have
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(MU = |
-Gt? V2Sf Lf 2 |
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and |
(4U = |
-Gt 8-* Lf s |
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whence |
(^s^)tail |
SFdCLp _ S dp |
sF / — % 1 s |
da ~dp) |
(8.5,2) |
The CD term of (8.6,1) would often be small compared to the tail contribution
(8.5,2) , and the whole derivative Gyoften has negligible effect on the vehicle dynamics.
