Subject: Re: Blade Strikes on Tail Boom
Date: Sat, 26 Feb 2000 04:06:41 GMT
From: Norm Melick

Unbeknownst to us, we had an instructor who taught his students to slow the blades down after shutdown by "pulling pitch" with the collective. After a few tailboom strikes, the boss found out what was going on, and after re-entering the atmosphere, explained it this way.

As the blades are slowing down, the blades will droop. Pulling collective to slow the rotor blades exacerbates this by causing the advancing blade to climb very high, and the retreating blade to descend very low. "Bam" blade strike.

When I was going for my CFI rotorcraft rating, and during recurrent training at Bell, I was cautioned to make sure I, and my students, lowered the collective after touchdown to complete the autorotation process/demonstration. As I remember, most autorotations ended with the collective up in your armpits in the Bell 47, Hiller and the R-22. Therefore it was drilled in me to lower the collective to complete the autorotation.

Subject: Re: Blade Strikes on Tail Boom
Date: 26 Feb 2000 21:15:16 -0600
From: Rick Troxell

...the transmission and rotor system on a helicopter allow for a surprising amount of movement given the right circumstances. With low rotor rpm and excessive blade flapping, the transmission can rock enough to contribute to a tailboom strike. A poorly executed autorotational touchdown sets you up for this.

Most of my experience is in Bell products and the issue of reducing collective or leaving it alone after touching down depends on the specific aircraft. In the UH-1 and AH-1, you would touch down in a slight nose-high attitude, and you would not lower the collective to flat pitch until the aircraft came to a complete stop. In the Bell 206 / OH-58, you level the aircraft just prior to pulling cushion pitch, and you lower the collective immediately after touching down.

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