Forwarded from the bounce bin. Message is from
Dave Simpson twex1160@londonweb.net
**********************************************************
Tom & Cathy,
Hate to be picky but I don't think the offset thrust line is normally
designed in to compensate for P or precession factor. It's normally there
for assymmetric slipstream reasons ie. prop wash applied to the fuselage
side and fin.
Gyroscopic precession is the torque applied from the power plant as a result
of input rates of turn about an axis at right angles to the prop axis.
(Normally we're oncerned with pitch on take off so this is about a
horizontal, lateral aligned axis). The precession torque is only present
during the applied input rate and disappears when the input rate stops. The
resulting torque is generated about an axis at right angles to both the prop
axis and the input rate axis, ie. about a vertical or yaw axis.
So the precession torque manifests itself as a yaw torque during the period
that input pitch rate is applied, ie. mostly during rotation on take off. It
is proportional to rotating mass speed, rotating mass moment of inertia
(very sensitive to radius) and input rate of pitch and nothing else.
I've just re-read this and it sounds a bit pompous - sorry about that.
Humbly yours
Dave Simpson
|