Posted: 4/14/2006 4:11:08 PM EDT
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What went wrong here? Tail rotor problem? media.putfile.com/helicrash1 |
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You screwed up the link. media.putfile.com/helicrash1 ETA: Yes, he lost the tail rotor. Might have damaged the connecting shaft or gearbox with the rather hard initial impact. |
The TR was definitely damaged, which is why it started to spin in the first place (torque reaction). If you watch closely you see the TR spinning down as the video progresses, and before he hits the ground it has completely stopped rotating. If he had pushed on of the tail rotor pedals full deflection all he had to do to stop the rotation is reverse the motion. Plus the other pilot would have backed him up and fixed the problem, thats why there are two. 
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1) The landing isn't anywhere near "hard" for a helicopter. On the Puma, you'd have to land hard enough to shear off the landing gear before you caused any tail rotor component failure. During crash investigations, we could easily tell the approx G forces of landing from what components failed. It's unfortunate that we can't see the T/R at touchdown, as he may have struck it on the ground, or a piece of FOD could have struck it. The T/R system may have been assembled incorrectly or there could have been a material failure. Either way, his T/R wasn't doing what it was supposed to. 2) The pilot never looses cyclic control. He maintians the aircraft upright, even during some hard spinning. The slight roll towards the outside of the spin is from the G forces acting on his arm and the cyclic. It isn't until the wheel plants in the ground that the aircraft, which now has a pivot point to act against, rolls over. 3) If you haven't recovered from this in the first two times around the block, you probably aren't going to. You can put opposite pedal in until your blue in the face, but by the second revolution there isn't really any saving it. I'll tell you from personal experience, that by the first revolution you're pretty much running out of time. 4) Odds are high that no one died, or was even seriously injured. The guy that got thrown out was probably in the greatest danger due to all the shrapnel flying around one the blades struck. 5) My take is something happened to the tail rotor during the approach. During the descent, the pilot probably isn't making any power changes. I think he notices that something's wrong just a split second before the touchdown. Right before the wheels touch, there seems to be something wrong, at least to my eye. I think he pulled in power to arrest the rate of descent and naturally added right pedal to keep the nose straight for the touchdown (right pedal because in the Puma you add right when you add power. The main rotor rotates opposite to US mil helos, and that's why the left yaw when he adds power) and when it touches down and the nose won't respond, he adds power to get off the ground and keep from rolling over. As he adds power, the lack of response from the T/R results in the spin. The wheel plants and the aircraft pivots around that and rolls over. I lost T/R effectiveness in a UH-1H during a maintenance test flight (for work on the T/R  , but that's why we test fly them before release). It wasn't rigged correctly and when I got the wind in a certain direction I started to spin. The performance planning charts give you great info, but are based on a working T/R. Needless to say when it's not working right, new numbers get invented. By the first time around in the spin, it was apparent that it wasn't going to weathervane (what usually happens with the Huey when you ran out of pedal) and to this day I'm not sure why it didn't other than the mis-rigging must have caused it. By the start of the second revolution it was also apparent that time was running out alot faster than I wanted it to. I figured if I didn't get control of it by the start of the third go around I'd roll the throttle off and auto, which would probably have resulted in a banged up aircraft because it's just not an easy thing to do at night, in the dark, at a field site (yeah, well that's the Army) with no control of your heading. So I reached into my test pilot bag of tricks and nosed the aricraft over and rolled it into the spin at the same time. This got the aircraft basically chasing the spin and the tail rotor cutting into clean air, with some forward motion to help things along. Sure enough it worked and I returned to the LZ, had the T/R re-rigged, and flew it again a hour later to complete the test flight and insure the aircraft was indeed airworthy. Such was a day in the life of an Army Maintenance Test Pilot. Then there was the time the main rotor was rigged wrong and we couldn't come down..... |
Because tail rotors are evil. Landing didn't look hard, but the pilot did put in some extra flare on short final. Maybe a tail rotor strike when he did that Ross? |
Great post, thanks! |
They are indeed the Devil's spawn I'm thinking that a tail strike is highly possible. It's unfortunate that we don't get to see the tail rotor on touchdown.
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TR strike is my guess as to what happened. In a 46 you would have to have 24 degrees nose high on level ground for the rotor tips to touch. Maybe a couple degrees less if you hit really hard and flexed the blades, especially at low rpm. For the non helo drivers, 24 degrees might not sound like much, but it feels like you are in the space shuttle to pull it, especially close to the ground. |