------Sloping windshields, tilted horizontal stabilizers and whatever may affect the angle by which it dangles but as long as the cyclic controls aren’t up against a stop, there will never be a runaway situation with a stable rotor. I suspect “dragover” is a hypothetical that exists only in our minds. It’s a new ball game if drag or whatever forces cyclic controls against a stop.
Chuck, "Fixed Stick", or even pilot restricted stick movements are the worst case for all stability issues. If the stick is allowed to float completely free, the gyro is truly a "glob of stuff hanging from a rotor" - the "glob" is no longer "dangling". But, a "fixed" or restricted stick is essentially the situation where the cyclic controls are "against a stop" and any airframe pitch change is coupled to the rotor through cyclic action of the spindle - no matter how airspeed stable the rotor is. Also, the trim spring does not fully allow the rotor to float relative to airframe pitch actions anyway - not truly dangling.
To account for both the trim spring coupling from airframe to rotor, and a novice restricting the stick, aircraft stability criteria generally require stability - including static Airspeed - with
fixed stick as well as free stick. The worst condition where the sloping windscreen, shaded HS, draggy LG, etc. can be a source of airspeed runaway is with a fixed stick - not with a stick that can freely float, if any could really float (without a trim spring?)
Just saying the worst case is with a fixed stick - I'm not sure Stan was even describing a "fixed" stick. The pilot experienced in flying a gyro that does not have a stabilized airframe (HS), will allow the stick to float - to minimize coupling unstable airframe pitch action to the rotor and forcing the rotor to also pitch in that divergent direction. (This may be one reason why pilots experienced in their unstable gyro are probably safely flying that gyro - they have learned to allow the stick to float and apply only pressures to the moving stick.) But, a novice pilot will likely restrict or freeze or over-react on the cyclic to a sudden nose-down pitch. And the trim spring coupling to the rotor may essentially "fix" the stick anyway.
For instance, if the controls in Terry's SH broke or locked, the rotor may not be free to float, or may respond stangely to airframe motions - essentially the fixed stick scenario - and a continued "drag over" of the airframe due to a HS that does not compensate for a windscreen or enclosure (for instance), would force the rotor to follow the airframe's continuing nose-down attitude.
If Terry had become incapacitated, as some scenarios of the accident suggest, the very novice Bill Finnegan, upon increasing airspeed and nosing down, would likely have had the intuitive presence of mind to reduce the throttle - unexpected by him, that would have made any "drag over" effect worse. As Stan and Bill's other SH friend have reported, if you don't do anything upon reducing power, the gyro tended to nose over and pick up speed until, when the airspeed exceeded around 80 mph, the stick forces to raise the nose become formidable - especially for a novic pilot who would be afraid to pull that hard on the stick.
Another point. If the loss of LTL thrust is not the cause of this reported characteristic, but ROTOR instability is, why would the gyro not tend to also diverge to increasing airspeed with power applied. I have heard no reports that the SH had this diving tendency at normal power levels. I suggest this is because both the LTL is helping to hold the airframe nose up, and the extra prop blast on the HS is enhancing the HS effectiveness to balance the enclosure and windscreen and LG.
It is a simple matter to test this - if someone flying a SH would do - just repeat Stan's description of cruising S&L at 60 mph, and then reduce power without moving the stick - or with letting the stick float free - to see if the gyro remains at the trimmed airspeed or starts to accelerate in an increasing dive. That's Static Airspeed stability or instability. If the speed and slope of dive increase beyond where you feel comfortable pulling on the stick, add power to force the LTL nose up and recover the airspeed. Start at high enough altitude, because recovery with power from over 80 mph is reported to take as much as 500 ft.! It would be helpful if someone with RAF blades would also do this test - the reports of this phenomena, I believe were with Sport Copter blades. As Chuck explains, there are other rotor characteristics that could also present airspeed instability or divergence from trimmed airspeed - such as "blade runaway" due to torsional flexibility of the blades.
- Thanks, Greg