Gyro Accident Tasmania

[Des Garvin]

Allan,
..........

[Greg Mitchell]

G"Day Des and all,The MLS unit is bolted to the torque tube via 4, 1/4" AN bolts with thick nuts. These bolts go thru two 6061-T6 plates and thru the torque tube. The Crossover bar is 4130 heat treated to a Rockwell hardness of 38-40. The rod ends are aircraft grade.Allan"s setup may have been different, ie: rod ends,

[Greg Mitchell]

More MLS pics

[Greg Mitchell]

Last two MLS pics

[Des Garvin]

Hi Mitch & All,

[asra]

Hello Mitch, from Allans description it sounds like the controls and trim spring disconnected from the torque tube. I"m with Des on the point where the crossover bolts pass through the torque tube as being the weakest point. With all that gear out the back any vibration from the rotors would cause stress on this area. Hope you get to the bottom of it.

[Ken Watson]

These are my personal views and

[asra]

Allan and Mitch, one question - will the rotor brake always engage at full forward stick. If controls and trim spring were disconected trim should have been regained at some airspeed causing the angle of the dive to be self govening, possibly 110-120knt"s. The reason I say that is I shortened the gimbal offset on mine at one stage and trim without spring pressure was 60knt. If the rotor brake could engage at full forward stick in flight this may explain why the machine was vertical or slightly inverted at the end of the dive. Also the description of a mechanical thump or clunk near the rotor head is not the description anyone would give of a prop strike. If the torque tube were to break across the control cross bar, possibly hanging for a bit before letting go completely the pre rotater would then hang by the belts and trim spring and allow free movement of the controls. If this happened, in a steep dive the pre rotator could come forward possibly under the torque tube also accounting for the vertical or inverted position.

[Greg Mitchell]

Peter,Yes the brake will engage at full forward stick.The torque tube is specially designed to give 6 degrees of forward movement past the horizontal, this then allows for brake engagement past this horizontal position.We have been told, It is unlikely the stick and torque tube would be situated forward of horizontal at any point in flight.If by self governing you mean, that at some stage it would have settled out into a fixed nose down position, then NO! The angle of the dive was not self governing.......the Monarch kept nosing over to the point of impact which by all accounts was at 90 degrees or slightly inverted. Ken,The torque tube is specially designed to work with the slider head and MLS system, allowing for the use of the brake system also. So yes it was a new torque tube, that to my knowledge had not been flapped or had any other damage etc.My rod ends are aircraft grade. Allan"s had been changed out to what the QLD fellas use as std. This was done (along with other mods, Cross over bar, Tail stops at about the 30 degree position etc) so as to allow single place type certification (dont hold me to the phrasing of that). Gents,One eyewitness report suggested that Allan"s rotors were slowing and the body of the aircraft was rotating. Also another reported the "clatter" was being heard all the way to impact.We have been told that if the blades were slowing then they would indeed nose over.Also if the trim spring had moved from the right hand 2 O"clock position back to the 12 O"clock position this may have accounted for the lack of control feeling, as the trim was ground adjustable only.There is a lot of discussion going backward and forwards between, big hours pilots and other manufacturers, including Larry.Several theroies abound and all are speculation only. Whilst it may never be known for certain a very good understanding of what may have happened is beginning to develope.I certainly appreciate peoples views and insight as I fly a similarly configured craft.Thankyou.Mitch.

[Waddles]

Giddday Again Everyone,Having mulled further over the possible failures and having taken numerous measurements on the 2 remaining Monarchs in OZ and had discussions with Larry, I provide the following for further speculation:Witness report 1: From about 1 - 1 1/2 km away, saw the steep descent of the gyro which appeared to be rotating in a direction that he could not determine.Witness report 2: From about 400m from the impact site, saw and heard the whole event. He states there was a distinctive rapid "pop, pop" followed by a clattering that continued until impact. He didn"t notice the gyro turning or spinning.Theory 1: The upper left rod end failed allowing the control rod to rotate backwards contacting the propeller, the "pops" being consecutive prop blades (Brolga 4 blade) hitting and cutting off the end of the control rod at a position such that the end of the remaining control rod contacted each prop blade as it passed (the clattering).Against: The trim spring should have had some effect in precluding the abrupt nose down flight path. It didn"t. This would however, explain the "lightness" of the controls and the apparent no effect that their use had.Theory 2: The Revolution rotors had been assembled such that the strap bolts were inserted with the heads of the bolts on the top side and the nylock nuts on the lower side. I completed the assembly personally immediately before this flight. As these blades were my "travelling set", I had not used them for at least 2 years. The usual blades were manufactured by Peter Barsden and were the ones fitted when the MLS system was fitted and signed off by another TA. When the bolts on Mitch"s rotors were inserted in this manner, at near full teeter, the nuts struck the MLS housing!!!!!!! In discussion with Mitch, I explained that by convention, bolts are fitted down from the top. In this case however, the blade manufacturer states that the bolts should be fitted from the bottom up to allow for greater clearance from other head components!!!!!With the above in mind, I speculate that due to very gusty conditions even in straight and level flight, it may be possible to go "negative" unintentionally for suffucient period of time to allow the rotor speed to decay enough such that near full teeter of the blades occurred. The "pops" were the inner strap nuts of successive blades striking the MLS bendix housing causing it to bend clockwise when viewed from the rear. The second strike caused the housing to contact the ring gear on the upper right and lower left edges (the clattering). Once this occurred, the blades immediately started slowing and the gyro would have rotated to the left. As the rotors slowed, lift was lost and the nose dropped irrespective of the trim spring which may have been displaced anyway. Similarly, the loss of rotor speed would have caused the rotor blade to lose it"s gyroscopic rigidity thus rendering any control inputs ineffective and causing the controls to feel "loose".Against: It is not possible during straight and level flight for the rotors to teeter anywhere near the teeter limits.That"s as far as we"ve got to date. Mitch is going to do some more angular measurements to determine on his gyro, exactly how much teeter is required before the nuts contact the MLS housing. I expect it will be less than the 6 degrees we normally see.Regards,Waddles.

[Brian]

Eye witness reports with gyros can be pretty way off as unless those witness"s have seen and heard gyros flying around, the noises associated with the rotors alone can be varied.I"m fairly certain the strap bolts weren"t the cause, specially in straight and level flight.

[Greg Mitchell]

G"Day All,Thanks Allan. I am attaching a picture of the MLS with a red graphic line indicating the line a break would likely take if it were to do so.Please note, trim spring would still be in place and so to are the pulley straps either side.I do not believe the MLS unit could make it"s way into the prop, whilst attached at three points to the mast.The prototyping of the Patroney Blades on the Monarch MLS system required the installation of 1/8" thick teeter stops, so as to give clearance to the underside strap bolt head from the top of the MLS Bendix housing.If the norm for a Bensen head is 6 degrees of teeter either side, then the new teeter stops have effectively reduced this amount. By what? I am not sure till measurements are made. It could be in the order of 1-1 1/2 degrees. Thus the amount of available teeter may now be 4 1/2 degrees. Whilst approximately +-2 degrees is required for normal flight, I find it quite conceivable that during a negative event, rotor rpm could decay enough to cause the blades to teeter more to try and equalise lift.Now the available amount of teeter may be 4 1/2 degrees, however if the strap bolts are inserted from the top, the amount of thread, fat nut and double 0.0063" washers is considerably more than the clearances allowed for during the install of the teeter stops and original prototyping. Perhaps as little as 3 degrees would have been available, before the thru bolts on each strap may have contacted the MLS housing. As each bolt thread and thick nut have impacted, the MLS Bendix housing on top of the MLS unit would have taken an almighty hit, twisting the housing to the right and impinging on the large flywheel. This may have bitten in more and more reducing blade rpm dramatically. The induced friction now causing the airframe to rotate to the LEFT.Brian I think you might agree that S & L in a blustery 30 knots of wind with those bolts swinging past the MLS housing with the bare minimum of clearance, is a little closer to the limit than even you might like.? If the blades are slowing, they are not generating the lift, the gyro is dropping rapidly.As the blades are no longer flying, the gyro noses over. Look at the angle of your gyro in a hang test.Once the blades are no longer flying, stick inputs are likely rendered useless and unresponsive.Someone recently said if you were doing a vertical decent, left spiral, the stick can feel like it is unresponsive. This is hearsay and I personally have never tried it.Anyway Fellas, I don"t think the torque tube broke off at all. I don"t believe there is any inherent problem with the Butterfly Monarch design. I also don"t believe a push rod/rod end let go. Although it is speculation, I am almost certain given Allan"s account, eye witness accounts, (both of whom have seen me flying locally on a regular basis) and several high hrs gyro pilots views, that the visual and audio recollections of all coincide quite reasonably with Allan"s account.As Doug Riley on the US forum says, there is a fair hunk of metal hanging off the rear end of the torque tube, however it is supported by the push rods when the head is off the rear stop. Each average push rod able to carry some 200 lbs in compression. The torque tube is rated and engineered to handle much more than that. Also this torque tube is not a std Bensen tube and the manufacture claims it is indeed stronger. I will be flying my Monarch with complete confidence as I did during the ASRA 2009 Tasmanian National Championships.

[Ken Watson]

Thanks Allan and Greg, this all sounds very feasible.Loosing so much money must hurt, but I know you would gladly give that amount away to keep your life. Would the contact area be very large? ken

[Greg Mitchell]

Ken See attached.I can get more accurate measurements tomorrow.Mitch.

[Greg Mitchell]

After discussions with Allan.......So as to avoid the possibility of this happening, in the future the Patroney Hub Bar will be 6 inches longer. That way it wont matter which way the bolts go.Mitch