Wing Bending Oscillation

Reminds me of two situations where natural oscillation
of a glider component has surely saved me from potential
harm.

A few years ago I was a staff instructor at a club
here in the UK with a couple of K13s as the main school
fleet.
One day after a good few flights we were walking back
up the field to the take off point with the student
walking the wing, he commented that the wing 'felt
strange'. A good visual inspection showed nothing out
of order. However a gentle shake at the wingtip revealed
a broken spar about 4 ft in from the tip - result of
a poor repair several years previously.

Note *gentle* shake - we're not trying to snap off
the tip...just feeling the natural resonance, maybe
a degree of mechanical empathy is needed. But I think
if you are shown what 'feels right' for a particular
glider then anyone would notice if things were amiss.

The other somewhat scarey situation was visiting another
club and being given an Astir to fly. Ok that's scarey
enough, but seriously...
I had been shown a long time before how to check for
tailboom damage using the same method - a gentle push
back and forth at the top of the fin.
In this case the oscillation check revealed serious
internal damage from an unreported ground loop - again
there was no external visual clue!

I now always check both, after rigging my Std Cirrus
and everytime I fly anything else.

Rowan
Cirrus C2




At 11:48 19 February 2006, Jcarlyle wrote:
Yikes! I guess the moral to that story is, if you're
going to shake
them then do it before flight!

-John