Stability
Firstly, Thanks to the gentleman who e-mailed me the details. Took a load off my mind. However, I remain sad and angry in equal measure.
Thanks indeed to Bladewashout for the detailed description of low-G as applies
to helicopters.
There are some differences where gyros are concerned, however.
The primary difference is that the forward propulsive force( the pusher propeller)
remains active during the Low-G event.
The result is that the propulsive force is active, but the control, and drag of the
rotor are temporarily lost.
Given that in most current gyros, and almost ALL UK-operated gyros, there
is a vertical offset between the propellor thrustline and the vertical location
of the CG, the resultant combination of forces during the low-G event serve
to tumble the machine rapidly forward.
This rotation can be very rapid, in the order of 100+ degrees/second.
The rotor could not follow such a rate of change even if it were properly
loaded.
The result is a massive destructive mast-bump, which destroys the rotors,
usually resulting in the rotor hitting the propellor and tail fin/rudder.
The machine then tumbles vertically to the ground.
The normal eye-witness description is of a loud bang, followed by pieces
departing the aircraft, as it falls. The rotors are frequently described as
stopped and folded back on themselves.
The likelihood of this type of event occurring is dependent on the degree
of vertical offset between the thrustline and the centre of mass.
Whatever the offset, the undesirable effects can be reduced by a large amount, by the use of a horizontal stabiliser.
This (a) stabilises the pitch attitude in normal flight, reducing the potential
for PIO, and (b) slows the rate of rotation in the event of PPO, which may give the pilot some time to throttle back and save the situation.
The dynamics of PIO/PPO are fairly well understood at this stage.
These accidents SHOULD NOT be happening.
I am not aware of any accident or problem caused by the use of the currently
available crop of stabilisers.
If the above is not as clear as it should be, its because I'm knackered tired
just now. Sorry.
I have no technical qualifications, but I read any and all available accident
reports, and I also avail of the expertise available from the Rotary Forum in
the U.S. and elsewhere.
I have built, and am learning to fly, my own gyro, which now has a generous
horizontal stabiliser, and even I can see the difference.
On a positive note, I believe the CAA now has someone on board who has
actually had a flight in a gyro, so maybe things will improve in time.
Hope this helps, Nr Fairy.
I appreciate the verdict is brief and premature, but I've come across too many of these reports not to see the signs.
There will be assertions re weather decisions, pilot experience etc., but the
underlying issue is stability in pitch.