jet pack

"John" wrote in message
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Capt. Geoffrey Thorpe wrote:
"John" wrote in message
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It's supposed to be fairly stable because the thrust reaction point is
well above the CG, so there is a strong pendulum effect. They claim
it's better than a helicopter.

An often made, completely wrong assumption - "pendulm effect" - ain't no
such thing for an object in free flight.

Early rocket experimenters often attempted use "tractor" engines
assuming that it would provide stability - Dr. Robert Goddard's first
liquid rocket is an example. It didn't take them long to figure out that
they were wrong.


So much for the roll stability advantage of high wing aircraft...

Perhaps the word should be controllability, not stability. Are you
saying the thing would have the same controllability with the thrust at
the top or bottom?

You betcha. Ain't no difference at all. Well, not exactly, there can be
differences due to the abilitly to align the thrust axis with the CG, or
the location of any control surfaces and their relation to the CG, or the
location of the CG... But pendulum's have nothing to do with it.

Take the wife's heirloom grandfather clock and throw it off the roof - you
will observe that the "heavy end" of the pendulm doesn't "hang down" or
fall any faster than the rest of the clock once you have let go of it.

Any difference between tractor and pusher aircraft controllability that
can't be explained by the change in airflow over the control surfaces?

--
Geoff
The Sea Hawk at Wow Way d0t Com
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