Str^m-Tejsen and Chislett 



Side forces and turning moments can be obtained from the gauge-forces accord- 

 ing to Eqs, (15), the cubic terms having been multiplied by 3/2 as described above. 



Integration and Interpretation of Crosscoupling 

 Terms in Yaw and Drift-Angle Tests 



Crosscoupling effects due to simultaneous yaw velocity and drift angle are 

 expressed in the mathematical model by the terms Y^,.^, N^^^, Y^^^, and N^^^. 

 Similarly the crosscoupling due to yaw velocity and rudder angle is expressed 

 t>y Ygrr> ^stt) YrS85 ^jid N ^ ;, - . Thcse two sets of coefficients can be obtained 

 from the "yaw and drift-angle" and the "yaw and rudder-angle" tests respec- 

 tively, outlined in Fig. 4. As the same principles are used for measurement of 

 both sets of terms, only the derivation of the crosscoupling between yaw velocity 

 and drift angle is described in the following. 



The terms vrr and iw, shown diagrammatic ally in Fig. 20, constitute a 

 flexible means of expressing the experimental data, while conforming to the 

 port and starboard symmetry condition f(r,v) = - f(-r. ■ v). The two terms 

 have essentially the same character, as can be seen by replotting on a base of v 

 instead of r. 



Fig. 20 - Crosscoupling terms Y^^^, 



The side force acting on a model in a "yaw and drift-angle" test can be ex- 

 pressed on a time basis by 



Y(t) = Y.f(t) + Y^r(t) + Y^v + Y^^^r(t)v2 ^ Y^,^^vr(t)2 . 



(16) 



where v corresponds to drift angle, held constant during each measuring run, 

 and r(t) and f(t) are the sinusoidally varying yaw velocity and acceleration. 

 Again, the corresponding expression for N( t ) is exactly analogous. 



The first three terms in Eq. (16) are known from the "pure yaw" and "static 

 drift angle" tests. The manner in which the last two terms can be derived from 

 the "yaw and drift-angle" test is shown schematically in Fig. 21. 



346 



