stick free airspeed divergent

just curious if the experts here would consider flying hands off and having the airspeed go divergent with respect to airspeed and throttle changes dynamically unstable. cb, doug?

Baron, not sure what you mean by "consider." I used to do it all the time, because that was the only kind of gyro that was available. Didn't know any better. I tried to do aerial photography hands-off in rough air. I could usually get off a shot or two before the nose departed and the gyro headed into a dive. Then drop the camera (yes, it had a strap) and get things back under control and make another pass. Things went fine in smooth air.

Today, if I test-flew a new gyro for possible purchase and it did stuff like that, I'd worry that the "designer" didn't have a clue. What else didn't he/she know that would bite me? Like, how to calculate the strength of a beam? Or a column? Why pay for a gyro and then have to check every bit of homework that the "designer" may or may not have done?

It is not impossible to fly an unstable machine, there's just no point to it. It's harder and riskier for a newbie to master. If a designer rejects those thoughts, then I simply don't care to place my life in his/her hands.

Redbaron said:

just curious if the experts here would consider flying hands off and having the airspeed go divergent with respect to airspeed and throttle changes dynamically unstable. cb, doug?

Click to expand...

It's unstable alright but not dynamically but statically. It may still be dynamically unstable but the behavior you describe is about static stability.

-- Chris.

Chris: Maybe I read more into Baron's post than I should have. I thought what he was describing was static airspeed instability AND dynamic (oscillatory) power instability in pitch.

IOW, the machine speeds up or slows down hands-off (at constant throttle) as I described AND it tends to porpoise when throttle setting is changed.

Either condition could happen because of HTL and a lack of H-stab. The second also could conceivably happen even with LTL, if there is no H-stab and, perhaps, a rotor with very little damping (i.e a high-RPM, lightweight one such as a Bensen rotor).

maybe I should have worded things better, doug. I gave the issue more thought and believe its just a trim spring problem, I was trimmed for nearly full power. she's solid as a rock stick locked and always has been.

I haven't played around with differnt trim springs, a longer spring would probally help compared to my short and stiff spring. it responds more like a fw floatin the stick now!

Doug Riley said:

Chris: Maybe I read more into Baron's post than I should have. I thought what he was describing was static airspeed instability AND dynamic (oscillatory) power instability in pitch.

IOW, the machine speeds up or slows down hands-off (at constant throttle) as I described AND it tends to porpoise when throttle setting is changed.

Either condition could happen because of HTL and a lack of H-stab. The second also could conceivably happen even with LTL, if there is no H-stab and, perhaps, a rotor with very little damping (i.e a high-RPM, lightweight one such as a Bensen rotor).

Click to expand...

Hi Doug, if you read it like you do then it really is a static as well as dynamic instability. But stability testing should be made with fixed stick to be really meaningful, anyway.

-- Chris.

Yes, I thought there were two different stability scenarios under discussion.

Dynamic INstability pre-supposes static stability. In fact, static stability CAUSES dynamic instability, in the absence of sufficient damping.

You never get to dynamic instability if you have no static stability. The system just keeps diverging in the same direction; there's no oscillation. I think Red was actually experiencing static hands-off instability.