of power induced velocities and flow dirkccion 
changes at the vertical tail are quite significant 
for the propeller driven airplane and can pro- 
duce large directional trim changes. As in 
the lontitudinal case, the indirect effects are 
negligible for the jet powered airplane. 
The contribution of the direct and indirect 
power effects to static directional stability is 
greatest for the propeller powered airplane 
and usually slight for the jet powered airplane. 
In either case, the general effect of power is 
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