A few years ago I had cause to have a close look at the trim mechanism
of a Libelle. I noticed on the "quadrant plates" (either side of the
toothed trim wheel) signs of old welds or some such. I checked a couple
more Libelles. In fact of 4 I checked, three had indications of welds on
the quadrant plates and the remaining one had a robust wire stop. The
stop prevents the trim toothed wheel from going further than 45 degrees
_rearward_ .
Why so many of these Libelles had no apparent stop, I don't know. The
wire one was quite robust, the others were just small spots of weld. It
would be conceiveable that the Libelles came out of the factory like
that, but also possible that they had a very light stop which was broken
off un-noticed.
But that's not all. I was able to check the "rack" the toothed trim
lever wheel fits into on two of these Libelles. Both of the racks had 21
grooves, but one had the rear most 10 grooves especially deep while the
other one had the rear most 15 grooves deep. I believe the deep slots
are for the toothed trim wheel to engage in while the shallower grooves
are for the trim locking mechanism to fit into. (Some deep grooves might
serve dual purpose).
Anyway I think that the rack with the 10 deep grooves allows the trim
wheel to move between 45 degrees forward and backward while the 15 deep
groove rack allows the trim wheel to move 45 degrees rearward to 90
degrees forward. IE I think all Libelles should have a rear stop for the
trim wheel at 45 deg rearwards and some use the horizontal control
column tube as the 90 degree forward stop. Interestingly I checked a
Hornet and that particular one seemed to use the stick tube as a stop
both 90 deg. forward and back.
Info for consideration.
SWK
Terry Neumann wrote:
Mal Bruce wrote:
<schnipp> ----------------------------------------
What happened early in the climb the trim popped out from the teeth
of the trim ratchet and the load was removed from the stick and I was
near vertical the winch driver gave the winch full power and saved my
life other than that like death at Gulgong a few years ago and the
more resent accident I believe that they were in the same predicament
as me in my case the winch driver saved my life.
I have stated this each time a pilot has died in a Glasflugel
aircraft launching that has been killed in fact when I have been
described the incident over the phone I have said the pilot was
flying a Hornet or Mosquito and they have stated yes that's correct.
Mal
It's an interesting observation Mal, and one that has worrying
overtones. It's been a long time since I flew a Club Libelle, but
I've a feeling that they also had the parallelogram control column
setup with a similar trim mechanism. If that's the case, I can think
of at least one other accident which happened in similar circumstances
and which defied reasonable explanation - at least at the limited
level of information which filtered back to the ordinary GFA members.
Does anyone know if there was ever a A/D (or an ops advice of some
sort) on these aircraft to address the issue you've described above?
Terry
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