Another LS4 gear probem.
Derek Robson
collapsed on my LS4. The operating handle remained firmly in the
down position. A BGA Bulletin describes loose lock nuts in the
drive system but mine seem ok. Has anyone experienced a similar
problem.
Derek Robson
Northumbria Gliding Club.
or
Wodside Green Cottage,
Woodside,
Ryton,
Tyne & Wear
ENGLAND
Rich Carr
: During a recent landing (a real greaser on a good field) the gear
: down position. A BGA Bulletin describes loose lock nuts in the
: drive system but mine seem ok. Has anyone experienced a similar
: problem.
Here's what I posted a few months ago in response to previous LS4 gear
collapse queries. Hope it helps, although your incident sounds
different from those described here.
- Rich Carr
First pilot
-----------
JK experienced 2 gear collapses in his LS4 (not LS4A). One was on an
off-field landing, and one was at the gliderport, but both were on
prairie. Prairie landings are fairly rough, with clumps of grass 1-3"
above intervening depressions spaced about a foot apart. Both of these
incidents occurred around 1985, before the problems with LS4
"uncommanded retractions" were well known. At the time, JK had about
1200 hours in gliders, with all but 200 in fiberglass and all but about
50 in taildraggers. (I mention this because I received mail suggesting
inexperience or poor low-energy technique on the part of the pilots.)
He remembers that in each case, the landing was not unusually hard, with
the tail touching first, followed by the main gear, followed 2-5 seconds
later by a sinking feeling as the gear collapsed. So there was a
substantial amount of weight on the gear, but not the entire weight of
the glider.
JK spent quite a bit of time poring over the LS4 gear mechanism, which
is one of the strangest around. In order to provide some compliance in
the landing gear, rubber donuts flex in torsion to support the glider's
weight. Because of this compliance, the normal method of using the
actuating arm to keep the gear over center doesn't work, and the gas
strut is supposed to do this job instead. However, under conditions of
vibration such as landing on a rough surface, the gas strut isn't up to
the job. JK thinks the shock absorber was an after-thought to the keep
the short-term shocks of landing on a rough surface from affecting the
gas strut. He also believes that the vibration cycles have to be just
right to cause the gear to go over center and collapse, because he had
many other landings on prairie without incident.
An interesting feature of this design is that there is no direct
connection between the gear-extension handle in the cockpit and the
landing gear itself. Consequently, LS4 pilots suffering gear
collapses are confused to find themselves coming to a stop on the
belly with the handle still in the extended position.
JK speculates that the LS4A may be less susceptible to the problem than
the LS4 because, in order to keep the extra water ballast of the LS4A
from compressing the gear too much, a third donut was installed in the
suspension. The added resistance to deflection may reduce the amount of
movement in the gear and keep it from going over center.
Second Pilot
-----------
About four years ago, SH landed his LS4A on prairie at the gliderport
and had a gear collapse about halfway between his touchdown and where he
expected to stop. He recalls hitting a substantial bump which
precipitated the collapse, but he felt it wasn't so big a bump that any
adverse result could be expected. At the time, he had 20-30 flights in
the glider. He pointed out the following:
- In the section of the manual describing the test of the gas strut,
there is a units conversion error. The pounds figure is about
three times smaller than the value correctly converted from metric
units.
- Our field elevation is 5500' MSL, and the higher TAS at touchdown
causes more energetic jouncing of the gear on our rough ground
than at lower-altitude, smoother fields.
- He'd been flying at 14,000' MSL shortly before landing, and the
gas strut may have been cold, which, as anyone with gas lift struts
in their car knows, reduces the gas pressure in the strut.
Third Pilot
-----------
BP landed his LS4A off-field on prairie and had his gear collapse within
a few seconds of touchdown. He noted that it was a fairly cold day,
which may have inhibited the functioning of the strut. He took the
glider to George Applebay for cosmetic repairs, and George felt that
another factor causing problems was that one end of the gas strut is
attached to the bulkhead behind the seat. This bulkhead flexes, which
allows excessive movement in the over-center mechanism. George
installed a steel stiffening plate in the bulkhead. In the 6+ years
since then, BP has never replaced the strut or conducted a strut test,
and he has had no more gear-collapse incidents.
Guy Byars
>During a recent landing (a real greaser on a good field) the gear
>collapsed on my LS4. The operating handle remained firmly in the
>down position. A BGA Bulletin describes loose lock nuts in the
>drive system but mine seem ok. Has anyone experienced a similar
>problem.
The first thing to check on the LS-4 gear is the gas strut. If
it has lost pressure due to age or other problem, it would be
the reason your gear collapsed. My A/P at a recent annual said
that those struts need to be replaced every few years. Please
call LS to find out for certain how many years that should be.
Guy Byars
Steve Deadman
10052...@CompuServe.COM says...
>
>During a recent landing (a real greaser on a good field) the gear
>collapsed on my LS4. The operating handle remained firmly in the
Happened to two of us in OZ within three days of each other, Mine was a
rough landing, my mates was a greaser. All we can put it down to is the
gas strut in the U/C. We now replace these with a new one every two years
and make sure that the U/C is 100% to Spec each and every annual.
regards
Steved