Russell McMahon wrote:

> >Note - I have seen photos of model helicopters being flown inverted by
> >suitably expert pilots.
> >The cyclic has to be capable of suitable range to allow blade pitch to
> apply
> >vertical "lift" in the opposite direction to normal.
>
>         And this is very common! But they say that's impossible in a real
> heli, why?!?
>
> 1,    A model can easily be modified to have increased control range needed
> to do this.
> Doing the same thing in a full sized machine would require major design
> changes which would need to go through the horrendously expensive and
> complex certification processes for man rated flying. Unless there was a
> good economic reason to do this it won't get done.

A few years back you used to see one or two different helicopters
do loops at air shows although not the same as inverted flying it has
some of the same problems.

The biggest problem on full sized helicopters is tail strike from a flexing
rotor
when inverted the rotor cones towards the tail. Although not that complicated
inverted flight needs a inverted fuel and oil system. Unlike an airplane an
engine
failure on an inverted helicopter would eat up a lot of energy getting upright
before an auto-rotation.

Many years ago I worked at company that built a prototype(s) of a
battlefield stabilized camera platform on an inverted helicopter base.
(Counter rotating blades on the bottom) It was electric powered by a cable
running down to the ground. (600 volts 400 hertz) We used to sign out
test flight films at lunch hour for our amusement. It did a great figure 9 .

A helicopter is unstable in a hover and tends to have positive feedback.
Flying forward it is more like an airplane with an aft Cof G.

w..

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