RAF Accident Investigation done 12/15/06

[Chris Burgess]

I personally performed an accident investigation for the PRA IRT on Tom Monard’s RAF 12/15/06, accident of November 5th. Keep in mind the wreckage was moved and had been released by the FAA/NTSB. I have attached two "telling" photos for you to view. There was NO STRIKE on the rudder, horizontal, or winglets. NO STRIKES on the rotor. Inspecting the site showed the rotor was turning. HOWEVER, the hub is a good indication in my opinion that it slowed to the point of collapse in flight. The hub itself had been bent upward nearly symmetrically to about 17.5 degrees cone. The actual eye witness was there and I talked to him directly. He said (paraphrased) that Tom was climbing very steeply and the rotor was slowing. From there the sound changed to a whopping noise like a Bell Huey, it turned right and fell to the ground. The site indicates a near vertical impact. The head was clean indicating it landed upright but left side low as the left side main wheel hub was severely fractured. Tom was thrown out through the windscreen about 20-25 feet in front of the aircraft The windscreen separated from the aircraft intact except for a crack started from a single screw on the forward lower edge of the windscreen. The seat belt was found unbuckled by the first responder to the site. Tom’s wife and the airport manager both indicated Tom never flew without the belt. The impact was just off the left side of the 3200 foot runway in a sod area. The area was about 3/4 of the way down towards the departure end of the runway, which would be consistent with the projected distance down the runway after a steep climb. The eye witness also indicated it dropped from about 200 feet, which is consistent with the damage viewed. There was about a 6 foot arch cut in the ground from one of the turning rotors. A bend in the direction of the trailing edge in one rotor was consistent with this arch. The other rotor had only upward flexing damage (compression cracks) around the first third from the hub consistent with insufficient rotor rpm. Again, there were NO strike indications anywhere on the rotor or airframe.

This was not PPO. I believe it to be too much thrust for the load in this aircraft. The 2.2 FI produces 130 hp. The fuel load was light and flown single pilot. He had been doing touch and goes and been flying nearly an hour. I believe Tom was on full power as the eye witness indicated, slow airspeed, loading the prop and unloading the rotor. I think a word about too much power to weight is standing out here. This can cause the rotor to slow. You will also note in the hub picture that the flap stops were not severely struck. One was untouched and the other only slightly bent (perhaps -5 degrees). I do not believe precession stall is an issue here. All rod ends were intact, even the two smaller "walking beam" ¼ inch rod ends. All bolts were in place and properly safetied. All rudder cable turnbuckles were intact. Rotor head control stops were properly adjusted. Two rod end "jam" nuts were not locked but were not issues as all rod ends were intact. Most everything was of excellent construction and properly safetied and in some cases, double safetied in a way I liked to see.

There are certainly many more details I could write but I think this lets all know that I feel the rotor was allowed to slow to a point of collapse and this is what cause the subsequent accident.

Gentlemen, and ladies…., too much power can create other issues you need to know about. Power/thrust is nice to a point. You must still keep the rotor loaded and not ride on all that thrust. I hope everyone can be respectful here and not make a mess of this unfortunate accident. Tom built a “showpiece” and he loved to fly it. Tom was a good friend.

[KenSandyEggo]

Nice job, Chris.

[animal]

Still sad that another pilot is Gone. makes ya wonder how steep a climb the angle would be to unload the rotors that much, man that hub sure is bent. kind of suprised it did not break.

[dragonflyerthom]

Thanks Chris for the post. You have cleared up some and brought more in to being... I wonder how steep that climb was also. Sure not the way I have been taught. I feel for the family.

[Hognose]

Originally Posted by Chris Burgess

I personally performed an accident investigation for the PRA IRT on Tom Monard’s RAF 12/15/06,

Chris, thank you for performing this grim duty.

The hub itself had been bent upward nearly symmetrically to about 17.5 degrees cone.

Rotor slowed. Rigidity produced by centrifugal force lost. Gravity takes over.

We could calculate the forces that bent the bar to that point, but I don't know if that gains us anything. What we want to know is how to prevent a recurrence and how to incorporate what you have learned into training so that it doesn't happen again.


[Quot]The seat belt was found unbuckled by the first responder to the site. Tom’s wife and the airport manager both indicated Tom never flew without the belt. [/quote]

I saw Tom fly at Bensen Days both alone and with Romulo. I recall Tom strapping in both times and helping Romulo find the belts to do the same, on his flight. Generally belt wearing is a habit one has or one does not have. (A DE here, Bob Wade, told me of a mishap right on this field to a Navajo. One pilot lived and one died... the difference being, one man disdained his shoulder strap).

Not material, really. The deceleration forces (~200-ft fall into earth, stop in ~18") were not survivable.

This was not PPO. I believe it to be too much thrust for the load in this aircraft.

Interesting. Didn't roll, didn't PPO. The RRPM just decayed beyond the recovery point. The stab may have prevented PPO without preventing an accident.

The corollary to this is: this mishap could happen to any other gyro with similar power-to-weight numbers. Fins and CLT won't protect you.

You will also note in the hub picture that the flap stops were not severely struck. One was untouched and the other only slightly bent (perhaps -5 degrees).

So... the RRPM decay was so fast, such rapid onset, that there wasn't even a lot of asymmetry of lift? Is that what you're thinking here?

Most everything was of excellent construction and properly safetied and in some cases, double safetied in a way I liked to see.

Tom was fastidious about the Peasant Frog. He enjoyed playing "what if?" with its parts, and he also liked it to look good. Some parts he designed and machined or had machined because he didn't like the stock solution.

Tom built a “showpiece” and he loved to fly it. Tom was a good friend.

I still remember Romulo, who'd never flown in an enclosed gyro, wondering if Tom would give him a ride. Heck, Tom didn't need a reason to offer you a ride. A flimsy excuse was just fine. The two of them were grinning like kids as they taxied out. That's how I'll remember Tom, that and holding forth philosophically on how his gyro got its name, at Mentone 03, years ago before it and he were ready to fly.

It's just a crying shame. My heart goes out to Tom's family. Thank you again, Chris, for looking into this.

cheers

-=K=-

[Rick Whittridge]

Thank you Chris. We can all learn from this accident.

[birdy]

Thanx Chris, not the best job in the world, but someones got to do it, for the benifit of the rest.
I just hope people take note of wot you said bout power/weight ratios and maintaining rrpm.
Apparently there are people who still dont see these as an issue, maybe now they will.
I'v seen some take off and couldnt watch. If only they knew how close they are................... .

Again, thanx for the info.

[GyroRon]

Yeap, bring the nose up high with engine at full power and watch your rotor tach, it will quickly slow down. With enough power and light enough weight, if sustained, the rotor will slow too much and you end up with basically a form of in flight blade flap and in most cases there is no recovery.

The good thing is this is not a type of thing that just sneaks up on you. If you mark your airspeed indicator with a minimum speed - roughly 30 to 40 mph - and make sure that at power percentages above say 70 percent, you keep the airspeed higher than the minimum mark you made and this type of accident can not happen. In other words, just keep Airspeed in the " range " while at higher power settings, especially on very powerful gyros.

I want to let all the RAF owners know I am sorry for jumping to the conclusion of PPO a few weeks ago when news of this accident first hit the forum. I suppose that not all crashes with a RAF are certain PPO and here is one that we can say for sure did not PPO.

[StanFoster]

Chris: Thanks for your careful analysis on this. Very detailed and carefully thought out.

Stan

[barnstorm2]

Thank you Chris, good work.

[Harry_S.]

Thanks Chris. Very much appreciated.


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[Timchick]

What would be considered the minimum rotor RPMs?

[GyroRon]

Originally Posted by Timchick

What would be considered the minimum rotor RPMs?

This could be wrong, but I believe if you look at your rotor tach the absolute second the wheels leave the ground on takeoff, this is the lowest number you would want to see in flight.

[Udi]

Originally Posted by GyroRon

This could be wrong, but I believe if you look at your rotor tach the absolute second the wheels leave the ground on takeoff, this is the lowest number you would want to see in flight.

The RRPM you see the moment your wheels leave the ground, Ron, is the lowest you want to see ONLY for this airspeed, OR LOWER. At higher airspeeds, with the same RRPM you may hit the stops and have a rotor stall. Also, if you try and load the rotor with more than 1 G at that low RRPM, you may cause the rotor to hit the stops and/or stall.

Setting the flight envelope of a gyro should be done by professional test pilots. Unfortunately, most home built gyros don't have a well defined flight envelope so we, recreational pilots, must be conservative in our flying. If you want to play test pilot with your gyro and push the limits - know that you are playing with fire.

Even tough it appears that Tom's accident was not a result of PPO, it looks like it was indeed a result of departure from controlled flight. It is too bad we don't have satisfactory evidence to conclude exactly what caused this loss of control. We can come up with some plausible explanations, but none of them will be for sure.

Udi

[quadrirotor]

The AOA of the blades must be checked! may be there is a confusion between aerodynamic pitch and geometric pitch...

http://www.rotaryforum.com/forum/sho...8156#post68156