----- Original Message -----
Sent: Thursday, November 11, 2004 8:45
AM
Subject: [FlyRotary] Re: Belts- nobody's
perfect
Thomas Jakits
(I have abour 5000 hrs flying time in
front of belts double-v-typ as the only means of powertransfer from the engine
to the rotor....)
Sorry, but this showed up in my Avweb email,
and I couldn't resist.
Rusty
The
Canadian Transportation Safety Board is trying to figure out why the drive
belt came off a Robinson R-22 helicopter, resulting in a crash that killed its
pilot in August. The chopper suffered the "sudden loss of power" over a lake
on Vancouver Island. Spokesman Bill Yearwood said that although the pilot
initiated autorotation, he apparently flared too high and the aircraft plunged
vertically into McGyver Lake, near Campbell River. Yearwood said safety board
technicians have spent the last couple of months going through the
helicopter's drive system to see if the problem is a design fault or a
maintenance error. He did say the belt appears to be the wrong size for the
helicopter. Technicians are also examining the electrically operated
belt-tensioning system.
No sorrys here Rusty!
I am glad you pointed this one out! We have 2 R22s in the hangar,
and didn't hear about this one yet!
Now lets wait to find out if the belt WAS the wrong
size.
a) As far as I understand there is only 1 size of belt for this
application. They always come in matched pairs too.
b) If the tensioning system was wrong the pilot should notice (time
needed to engage, clutch operating warning light)
c) If the clutch (belt) engaged correctly and then fails to retension,
it still would not lead to slippage at a power level needed to fly straight
and level.
d) We had one case where on a customer helicopter the pilot failed to
observe that the engage process was about twice as long as normal, and that
since the aircraft was new. It was a defect (new) microswitch that didn't
stop the tensioning system at the right tension, but alway ran to the very end
where another (safety)switch stopped the electricmotor. It took more than 200
hrs of running time in over-tensioned condition for the belts to
fail.........perfect reaction by the pilot this time - successful autorotation
- changed belts and tensioner microswitch - the bird flies perfect since
then...
Now IF they had a wrong belt,
someone messed up big time.
Also, if the sheaves are not
correctly aligned it might eat up the belt in a hurry, although in this case
the belt will also mess up the sheaves and in any case this will not happen
fast enough to get wrong in the first flights after the incorrect
maintenance. Latest at the next preflight (you preflight your flying machine,
do you?), the frayed condition of the belts and the worn edges on the sheaves
should alert the pilot and then the maintenance personal.
But it is always easy to
suspect, lets wait what the CTSB finds out........
Thomas
J.