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The following letter was received on the 22 of May 2004 from an English Gyro PilotHello Martin,
I have been reading your website about pitch stability problems in gyroplanes and have just ordered your book - hopefully it will answer some questions that are in my mind.
About 20 years ago, I built and flew a Bensen B8V giro which I found at the time to be over weight and/or under powered. I could get it airborne but it's climb rate was very marginal (150 ft/ min max). However, it did fly and I managed to complete my training on it with no problems - in fact it seemed an easy enough machine to fly and turbulence and cross-wind didn't effect it much at all.
However, I stopped flying it and sold it to a lighter pilot within a few months, as it lack of performance worried me. Now, 20 years later (well, last summer) I thought it time to get another one, so I bought a 'Cricket Mk4' which is like a Benson with a pod and a Rotax engine.
Boy, this was as far as I can remember, a different animal to fly. Oodles of power. much lighter and needing a delicate touch on the controls to get it down in one piece. Anyway I think I have got the hang of flying it down the runway now!
A couple of weeks ago, one murky Saturday afternoon, I decided to do a circuit. I took off ok, climbed to 500' down the runway and continued a climbing turn to downwind. On rolling out of the turn I was astonished to see the ASI at around the 70 kts and dropping fast. I could not perceive that I had put any control inputs in to cause this and although there was no real horizon to see, my attitude did not look or feel out of place. I left full throttle on and then watched as the airspeed bottomed out at around 40 kts and then climbed up through 70 kts . I then just closed the throttle and the machine came back under control - it was then time to turn finals and land. The point is, I never realized what was happening until it was nearly too late. You think I would have learned from this. I certainly did some research on the 'net' about PIO and now I though I understood what was happening, I would recognize earlier and not get into such a situation again. That's a joke - last weekend I went to the airfield. Perfect day 5 kts down the runway and 10 kts. Time to try another circuit. And guess what, this time, I have climbed up over the runway, turned cross-wind and i am lining myself to come out of the climbing turn parallel to the runway. I am keeping one eye out on the clear horizon as a pitch reference. I guess I must have let the nose drop a little while rolling out of the turn and I was still on full throttle with the airspeed rising.
I put a little back pressure on the stick and was about to reduce power when the whole aircraft rotated forward. I think both the fuselage and the rotor disk must have pitched forward together as I felt no feedback through the controls. I was pointing about 45 degrees nose down when the action of knocking off the power completely stopped the forward pitching. It had taken less than 1 second to get into this position. Fortunately, I had just caught it in time and the rotors must have still had enough inertia for me to use them as a flying surface. With the power off, the gyro became a little pussy again and it ended with a good landing. Now the point of all this is - I never expected the machine to bite so hard and so fast with such little warning. I am surprised that more people aren't killed in this situation - though I here a lot are and I am lucky to be able to send you this e-mail.
Of cause, the Cricket has no horizontal stab. and a low body and C of G compared to the thrust line.
A chap at the airfield has designed and fitted a horizontal stabilizer to his cricket.
He has applied to the PFA for a formal permit to test but with our regulations, no one wants to know. So his machine is grounded and we all have to perhaps take unnecessary risks flying.
Of course none of the designers or manufactures will admit that their machines should be retrofitted with stabilizer I guess it would be admitting a design weakness, and with it costing peoples lives, could end up very messy in court.
Anyway, I feel I have got this off my chest a little - not sure where I go from here - except keep the speed down and be ready to close the throttle at any time!. I shall read your gyro design book and play with the software with great interest.
Best regards, Steve Kirkby