Interesting old gyro accident I'm confused

[gyroplanes]

I was researching Sycamore stuff and I found this well investigated accident. The sequence of failure and the gyro pitching down puzzles me. I'd like to see a discussion of this accident.

 

[WaspAir]

I wonder how much of the deformation was caused by hitting the trees.

 

[Vance]

I am unfamiliar with a Sycamore gyroplane.

I have flown gyroplanes that require a lot of trim spring pressure and if the trim spring fails in flight the gyroplane immediately pitches nose down and it takes a lot of force to manage the cyclic.

A trim spring failure might produce a loud bang.

I did not see much in the report about the control system pre and post accident.

 

[Brent Smith]

I wonder how much of the deformation was caused by hitting the trees.

I agree. Both the agency report and the lab report seem to conclude that the bracket failed over time because of inadequate design and/or materials and was the precipitous cause of the accident. Yet neither addresses the loud bang that preceded the pilot's challenges, and there was no mention of a/the trim system. The bending of the bracket was consistent with the CCW turning rotor hitting an obstacle (like a tree) on the right side of the aircraft, and a tree impact as the aircraft was still moving forward could also explain the brackets being jerked to the rear and the mast bending. Inadequate bracket mount hole distance appeared to have been a factor in the brackets' mounting failure. Like Vance, I have no experience with a Sycamore, but I think more info about the trim system would be helpful.

 

[Brent Smith]

I was researching Sycamore stuff and I found this well investigated accident. The sequence of failure and the gyro pitching down puzzles me. I'd like to see a discussion of this accident.

Can you describe the trim system in your Sycamore? Thanks.

 

[gyroplanes]

Well Brent, I saved the rotorhead until last in my restoration of my Sycamore I have looked everything over, at least once. I tried to find reference to the trim system in all of the manuals and it is non-existent.
The Sycamore appeared to be a "work-in-progress" as some of the manuals are labelled "first draft".
My Sycamore has an electric trim system, operated by a non-PC "Coolie" hat. The hat trim button roll control, controls cables pulling on springs, attached to the push rods about mid way up the mast. Pitch trim appears to be a cylinder located at the rotorhead, (see last picture) The photo below, shows what happens when the bolts pop through the leading edge of what we call cheek plates. My cheek plates are not at all looking like the accident plates. The design, I believe, would, if the bottom two bolts pulled through, cause the rear (2) 1x2 mast tubes to allow the top bolt to act as a pivot and allow the forward (1) 1x2 tube to carry the load and bend back. I cannot understand how the gyro would be at all controllable (especially in pitch) with a bent mast as pictured. I'll bet there is a lot more to this story. I would appreciate any South African gyro people that may be familiar with this accident to shed some light on the subject. If anyone is in contact with the Sycamore designer, Norman Shelly, I would love to talk to him. At Wunderlich prerotators, we manufactured parts of the Sycamore system and I spoke to Norm in the past. I only had the factory phone number. The factory is now appears to be in Lithuania, but dormant.

WOOS! These backwards rotorheads make you have to stop and think a minute. If the plates pivot as pictured, there might be a loud pop as the cheek plates failed (or that action could have made a noise elsewhere, such as the prop strike. There probably was an angular battle of degrees as the rotorhead tilted forward and the mast components separated and bent aft. Either way, the two occupants were saved with no injuries reported.