Jinx,

Regarding Aircraft Cruise control....

In most aircraft, when you trim things up a the required height and speed
and then sit back, you can watch the aircraft slowly oscillate around your
set points. The nose drops slightly and the speed slowly builds up, which
causes the nose to rise, which causes the speed to slowly drop....

With much fiddling, you can usually get it stable for a while, and then as
you burn fuel and the weight distribution changes it starts all over again..

In a sedate training aircraft the effect is quite minor, but in a high
performance aircraft the effect is a best annoying and at worst dangerous...

By nailing one of the primary variables (e.g. RPM) the effect can be
entirely eliminated...   hence Cruise Control.

Be careful that controlling one of the secondary variables (e.g. pitch
rather than RPM), you don't actually make things worse...
(The nose drops slighty, the speed builds up, the revs increase, the pich
increases, the speed increases further ......)

................ Zim

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