The Tension-Torsion (TT) straps are basically 2 bushings a certain distance
apart connected together by thousands of turns (I've heard something like
12,000 turns) of stainless steel wire (around .020" dia.), sealed in a
plastic like covering. These straps (one for each blade) are what hold the
main rotor blades to the rotor hub. The straps have to handle the huge
centrifugal loads (tension) of the blade but still allow for pitch (torsion)
control inputs from the pilot. Here is a link to Lord Corporation and a
picture of some TT straps. Lord is the present manufacture of the straps
for the BK117 and BO105. The strap that failed in Houston was made by
Bendix. http://www.lordmpd.com/aerospace/rot...ion_straps.asp

Hope this helps, I'm sure someone could describe a TT strap better but this
is the best I can do this early in the morning. JC



wrote in message
...
"Helimech" wrote:

About 2 years ago Herman Hospital in Houston, TX lost a BK117 due to a
M/R
blade loss. They were on approach, I seem to recall about 100 ft AGL,
and
broke a TT strap (badly corroded). The M/R gearbox left the aircraft and
all
3 souls were lost.

Ok another question. What is a TT strap?

Dennis.


Dennis Hawkins
n4mwd AT amsat DOT org (humans know what to do)

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