05 February 2010

Dynamic Rollover in a Rotorway Exec.

What happened here? I can only guess-
This is a "Homebuilt" helicopter. You buy it in kit form and put it together from thousands of parts. Then as the builder, you are also the "Test Pilot". I believe this machine has a tail rotor that is driven by several long V-belts inside the tailcone. That tone of descending pitch you hear in the video? I think it's likely the sound of those belts beginning to slip, allowing the tail rotor rpm to slow. Obviously as the tailrotor rpm slows it becomes less and less effective, requiring the pilot to apply more and more anti-torque input to compensate.
At some point the tailrotor would reach a critical angle of attack and would stall. I think that may be what's happening here just as the helicopter is touching down. Once the tailrotor is stalled the pilot cannot stop the fuselage from turning in reaction to the torque the main rotor is applying to the fuselage, so the pilot loses control of the helicopter and gets into the phenomenon known in the helicopter realm as "dynamic rollover".

(Remember, the rotor on this thing turns opposite from most helicopters.)
Anyone got a better explanation?

Interesting video on the subject here.


Cissy Apple said...

The rubberband broke?

Greybeard said...

Stretched Cissy.

Bloviating Zeppelin said...

It's GOT to be the tail rotor. You can hear the clear AUDIO difference between the two systems. You can hear the lower-pitched and rhythmic chuffing of the main, and the higher-pitched buzzing of the tail -- which, then, lowers in RPM.

It's all about what you can hear, I submit.

Do you have any idea if this was the experimental aircraft's "maiden" flight? And if so, how/why would the rotor bands have stretched?


Greybeard said...

That's what I hear too, BZ.
I was interested in these kits long ago, but from my viewpoint there were several engineering flaws in it that precluded me from buying one. Many of those flaws have been re-engineered in the newest kits, and I think the belt-driven tailrotor drive system is one of them.
I have taught several students who have built them, and the finished product is a beautiful thing to look at, but when finished, none of them trust the aircraft enough to actually use it like a real helicopter.
Considering the $$$$, that's a shame.

Steve at the Pub said...

The CFI of the rotor wing school I got my CPL at was an agent for these things.

He was a fully licenced engineer, and had built one. He used to zip around the airfield & environs in it.

Neither of the other two instructors were prepared to go up in the thing, and despite offers of "free hours & an endorsement" all of the students, if asked, always happend to have pressing prior engagements.

Anonymous said...

He almost saved it. If he had just powered down at the end. I agree about the tail rotor but at the same time the main rotor is acting funky aswell.

Anonymous said...

Sorry guys... I disagree with all of you. In my experience, particularly at the Rotorway flight school, the 162F is grossly underpowered... If you know these helicopters, you would be able to identify this immediately. The Rotorway 162F needs more reserve power available to it...as you can hear by listening to this video... It did not have. This helicopter, in my opinion, quickly ran out of any reserve power and began to lose rpm in both the main rotor and tail rotor systems. Simply, there was little, if not any reserve power left, causing the ship to start settling, coercing the pilot to add more and more collective, causing him to apply more right pedal or counter torque. This caused the ship to settle further due to the engine being fully taxed out for power, making the ship unstable and unresponsive for recovery.

If the pilot would have just put it down, instead of trying to leave the ground once touched down, he wouldn't have rolled the aircraft in the first place.

The tail rotor failure as a cause of the crash, I cannot buy it! Running this helicopter at 100% simply isn't sufficient. 102% to 104% would be a better torque to run this ship at, except I don't believe the RI162 engine would hold up for long at those settings. The 162F simply is too underpowered. As a reference, the Robinson R22 is always ran at 104%, but the R22 has twice the engine...and the Lycoming 0-320 or 0-360 engines are derated and are operated below their maximum outputs, making that engine safer, having more available, reserve power.

As I believe most Rotorway pilots already know, the 162F helicopter is really, only good for cold to moderate temperature flying. Really hot days, you are limited at best, if you can fly at all. Does anyone know what the flight conditions were when this happened?

Absolute altitude + barometric pressure + temperature = density altitude. It very well could be that this particular helicopter was attempting to operate out of its range.

Also, speaking of range, what was the weight of the pilot, fuel on board, and last but not least... What was the weight of his storage pod on the skids? All of this has to be taken into consideration.

Additionally, if in fact, this was a new helicopter being flown for the first time, the engine may not have been operating at its peak. I think we all know, until an engine is broken in, it cannot perform at its best.

At any rate, I have watched this particular video many times. I hope that the pilot was able to walk away without injury.

John Garabedian said...

if you guys actually flew these thing you would understand that this was a pilot error probably due to lack of training or very few hours in it. I have over 400 hrs in these and still fly regularly and if you want to come fly with me i'll prove their reliability !

Greybeard said...

Thanks for your comment, John.
With 17,400 hours in helicopters, I was just expressing my opinion.
Thanks for yours.