Gyro Accident Tasmania

[Waddles]

Gidday Ken and All,By "contact area" I assume that you mean between the housing and the ring gear??? I"d have to go to the airport to photograph this, but Mitch might be able to provide a close up of his showing the detail you ask about.For the record as well. My crossbar was not as you see in Mitch"s pics. I had it changed early in the piece as I was not happy with the chroming process and the physical dimensions of the original. Mine was made of I think, 20 mm or 25 mm X 2 mm wall mild steel square section in the same manner as those fitted to the Predadator gyros and many others. Solid inserts were incorporated where the attach bolts go through it. Similarly, the control stick pivot assembly was modified to use a machined section of about 2 X 2 inch 6061 T6 which used bearings instead of the supplied bushings. Also, the plates used to attach this control pivot system were re-made using 5 mm 5083 plate. Again, I wasn"t happy with the 3 mm 6061 T6 original plates although no problems have been reported from the US.Can"t think of any more mods of significance that I incorporated prior to the swim event.Regards,Waddles.

[Greg Mitchell]

Contact area within the housing and flywheel.

[asra]

Hello Mitch, while what you have described may be possible several of the factors used may be incorrect.Doug Rileys post on the US forum stating that when stopped the torque tube is resting on the stops and all other times the weight is resting on the pushrods is incorrect. When flying the weight of the pushrods is supported by the torque tube because of rotor lift and offset gimbal. The torque tube also resists the pressure of the trimspring and in this case supports the weight of the pre rotator. As the rotor head, torque tube and prerotator is a rigid unit, any shake or vibration in the rotor head due to the rotors must be transmitted through the torque tube to the prerotator.Negative g or near zero g.

[Tim]

Each average push rod able to carry some 200 lbs in compression.Mitch and Allan, this spliced offset pushrod is the part that concerned me most. I sincerely doubt that it would have carried any usefull compression loads at all, and would have distorted or bent with tensile loads. I will attempt to get hold of some specifications so that I can do some accurate testing on a sample. I cannot discount the possibility that this could have played some part in the control failure.I do not believe that the inverted rotor bolts would have been a concern. Any contact here would have been most likely in the period between disengaging the prerotator and lift off (ie period of greatest teeter) - It would have also been very audible. The period of minimum teeter is during flight.

[Greg Mitchell]

G"Day Peter,I"LL ADD RESPONSES IN UPPERCASE.THANKS FOR YOUR INSIGHT.PERHAPS I SHOULD HAVE BEEN MORE SPECIFIC.Hello Mitch, while what you have described may be possible several of the factors used may be incorrect.Doug Rileys post on the US forum stating that when stopped the torque tube is resting on the stops and all other times the weight is resting on the pushrods is incorrect.MY ASSUMPTION WAS THAT DOUG WAS TALKING ABOUT WHEN NOT FLYING. IE; AT REST OR IN TANSIT ON A TRAILER ETC. IF THE STICK IS LOCKED IN ANY POSITION OFF THE BACK STOP, THEN THE CROSSOVER BAR AND PUSH RODS AND OTHER PARTS OF THE CONTROL SYSTEM NOW CARRY A GOOD DEAL OF THE WEIGHT OF THE MLS AND TENSION OF THE TRIM SPRING. When flying the weight of the pushrods is supported by the torque tube because of rotor lift and offset gimbal. The torque tube also resists the pressure of the trimspring and in this case supports the weight of the pre rotator. As the rotor head, torque tube and prerotator is a rigid unit, any shake or vibration in the rotor head due to the rotors must be transmitted through the torque tube to the prerotator.THIS ALL SOUNDS QUITE REASONABLE. MY PATRONEYS HAVE VERY LITTLE SHAKE. WHEN THEY WERE MOUNTED ON A STD HEAD, SMOOTH AS SILK. AFTER THE MAST WAS BEEFED UP (ALOT STIFFER TO COPE WITH THE ADDED TORQUE OF THE PRE-ROTATOR) A DOUBLE SLIDER HEAD WAS INTRODUCED INTO THE SYSTEM. ROB PATRONEY HAD A LOOK AT THE SLIDER HEAD AND HE SAID HE"D BE SURPRISED IF IT ACTUALLY SLID. HE BELIEVED THE HEAD WOULD SIT AT THE BACK POSITION AND POSSIBLY NOT MOVE AT ALL. THE SLIDER HAS ABOUT 1/8" FRONT TO REAR AND ABOUT 1.5MM SIDE TO SIDE. THE HEAD MOVES VERY FREELY ON THE GROUND WITH BLADES FITTED. I REALISE THAT THIS IF WORKING PROPERLY REDUCES "THE STICK SHAKE" FROM TRANSFERING THROUGH THE REST OF THE FRAME AND GYRO AND WOULD NOT HELP ANY INHERENT SHAKE IN THE HEAD, TOQUE TUBE AND MLS....AS YOU SAY THEY ARE A SINGLE UNIT. MY GYRO HAS VERY LITTLE STICK SHAKE........IT"S A SHAME NO-ONE WITH HIGH HRS WAS PREPARED TO TEST FLY MY GYRO BUT UNDERSTANDABLE GIVEN THE SITUATION.

[Greg Mitchell]

G"Day Tim,Yes that pushrod setup was of concern right from the get-go.Doug Riely says that each straight pushrod can carry an average of 200lbs in compression. Straight being the operative word. If bent it will carry far less.OK, from recollection Allan felt/heard a mechanical thump, then pop, pop, then clatter, clatter clatter all the way down. This is in line with witness recollections.Missed the camp fire chats ole Mate, maybe next year.Cheers,Mitch.

[Greg Mitchell]

Post from Doug Riley of the Rotaryforum USAGreg, that splice is the structural equivalent of putting a couple of kinks in the tube. Compression forces act along one straight line. A kinked column isn"t a column anymore -- it"s loaded in bending rather than in pure compression. The short bridge piece is trying to bend out, away from the centerline of the pushrod, when the rod is loaded in compression. It tries to bend the other way when the rod is loaded in tension.This isn"t necessarily the cause of the crash, but it is suspect.Never put bends (or lap-jointed splices) in control rods, especially near their mid-portions where they are most likely to kink anyway. If you must route around the engine or something, use scissor arms or change the mounting arrangement.

[birdy]

I"m fairly certain the strap bolts weren"t the cause, specially in straight and level flight.Im fairly certain its definatly possable to take out the prespinner setup with the strap bolts with the minimal teeter clearance mentioned.Just watch your rotor tips wen your puttn along S/L in real sh1tty air. The tips can dip n jump up to 2 and 3 feet. I dont know how many degrees this equates to at the teeter stops, but its gota be more than the clearance Allan had.Hub bar snags the bendix, bendix bends, things getn out alinement and hitn other things,.......... things get messy proper quick, and theres plenty on that head to bend and tangle to make a big mess.All that happen"n, stands to reason that sum weak link in the control systm let go and no more cyclic.BUT, we will never know till we get a look see.

[Brian]

Funny isnt it, I have always put the hub bar bolts in from the bottom and expected that it was the way to go.Even with the bolts inserted from top to bottom, there is still clearance and that hub bar would have to get a lot of pressure on it to go down even a few mm I would have thought. I wonder what Rob reckons the flex of his hub bars would be?

[asra]

One clunk, no stick shake worth mentioning, no extra strong wind gust or turbulance worth mentioning and the controls are taken out? Plus popping noise.

[Ken Watson]

I meant how much contact between the bolts and the prerotater. If they did hit would it be a slight scrape or a full on destructive strike. Was it .000mm or 12mm? Ken

[asra]

Three possibles.Left rod failure. Splice is a definite problem but left control rod failure does not explain the total lack of response to controls. Full back stick would cause a roll or climbing roll to the right.Strap bolt to prerotator clearance is a definite problem but the diffence in clearance between bolt up and bolt down means there would have to be enough turbulance for the blade to come down to the teeter stop to do significant damage.The torque tube breaking at the crossover bolts would explain the mechnical thump and the lack of response to the controls but is over engineered.Get rid of the splices, though I take it that was a one off. Ensure sufficient strap bolt to prerotator clearance. Beef up the torque tube.It would seem better to cover all the possible causes at this stage rather than trying to determine if it was an owner mod or a design problem that caused the control failure.Peter.

[Greg Mitchell]

Thought that"s what you meant the first time.It may have been in the order of 2-5mm. Will know more when I have blades hanging off the hub bar. 2mm is enough to ding/destroy the side of the flywheel slot in the MLS housing and 5mm would be definetely destructive, if indeed that happened.How about, 30 knots and blustery......rodend breaks top left (MECHANICAL THUMP), as head hits the back stop.

[asra]

The biggest problem here it is impossible to get a rock solid senario for any one of the three possibles that will match Allans account. Unless more information is found the accident seems to have been caused by one of these three, but which one.The prerotator grabbing the flywheel and slowing the blades fits a lot of Alans description but I think if one rod went first, there would have been roll involved as Allan"s first action, after what I would take to be a very quick look around, was to give corrective back pressure on the controls. With just the right hand rod attached this would pull the right side of the torque tube down causing a roll to the right. Although its possible the prerotator could slow the rotor enough to cause the dive, at the time back pressure was first applied there would be plenty of speed in the rotors to cause a reaction to control inputs. I think the sudden roll on using back pressure would be remembered. That the second pushrod could be taken out in this space of time with no hard kick or stick shake although possible, seems unlikely.If the torque tube were to break at the crossarm bolt holes, this would most likely free the bolts and the crossarm giving the feeling of looseness in the controls. With the rods linked by the crossarm the left rod may not be able to fall back into the prop, although the cross arm may still be in front of the prerotator.

[tonydenton]

gents "whats a splice".