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Old 14th Dec 2006, 05:09
  #2105 (permalink)  
robsrich
 
Join Date: Aug 2003
Location: Australia
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Kirt - good thinking!

About 20 years ago there was an incorrect version of the Bell 206 manual that said LTE was caused by a stalled tail rotor. It was the cause, we believe, of a film crew coming to grief over the 1984 City to Surf Fun Run in Sydney. About 10,000 mad keen runners watched the Bell 206 enter LTE and plunge into a school yard. The pilot did what he was taught and in accordance with the handbook. It took about nine seconds to come down 1,000 feet. (Saturday - kids were at home).

Manual (later withdrawn) stated the way you unstall any aerofoil is to is reduce the pitch, or angle of attack.

Now the only way to reduce pitch on the tail rotor is to use right pedal. Problem is you already have an uncommanded right yaw, and now the manual suggests you correct the situation by adding right pedal? This increases the spin even further, and loss of control may occur.

Later research showed that when you are spun around the mast (to the right) your loose shoulder harness allows you to be thrown forward in your seat. Your bum is anchored by the lap seat belt, and your upper body will lean forward. Net result is your bum slides a little under the lap belt as your shoulders move forward; just enough to pull your thigh/leg/foot aft sufficiently to reduce left pedal, and the spin is slower to recover – or not at all.

You need “metal to metal” to stop the spin in about 90 degrees in the Bell 206 family.

Lesson is to always to move your pedals towards you as your strap in, then lean forward and ensure you actually get full left pedal travel.

To reassure the Robbie drivers, Frank was a tail rotor specialist before he made the Robbies, and he took care to design this trait out of the design. However it can happen in any helicopter!

Want to try and get it – just fly into wind, then do a steep descending right hand turn to a downwind quickstop! A Bell no no, and a Robbie also.

So ends the sermon……….
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