LS-4 landing-gear problems
Sander Holthaus
** To reply in e-mail, remove ".nubqih" from address **
Last week (monday, 1st of June), after a flight lasting over 3 hours,
I landed in our club (WBAC) ls-4a (PH-901). Just a normal landing, not
hard or anything like that. However, shortly after landing (ca 1-2 sec.)
the mail wheel collapsed back onto the fuselage. The problem is that
the wheel-handle was still in the lock. First was thought, that the gas
-strut which keeps the landing-gear locked, was broken. After measurments
, it was found that it was still in operating limits.
So, does anybody have a clue what could be the problem?
Sander Holthaus
Roosendaal, The Netherlands
email: san...@roosendaal.demon.nl
ICQ: 13577569, Sander
--
Larry Goddard
Sander Holthaus wrote:
> Last week (monday, 1st of June), after a flight lasting over 3 hours,
> I landed in our club (WBAC) ls-4a (PH-901). Just a normal landing, not
> hard or anything like that. However, shortly after landing (ca 1-2 sec.)
> the mail wheel collapsed back onto the fuselage. The problem is that
> the wheel-handle was still in the lock. First was thought, that the gas
> -strut which keeps the landing-gear locked, was broken. After measurments
> , it was found that it was still in operating limits.
>
> So, does anybody have a clue what could be the problem?
Yep. I had a similar problem with my LS-3a. Take all of the gear mechanism
out, clean and lubricate everything well. I found that there was just enough
collective friction, etc. throughout all of the mechanism that if there was
the slightest restriction, or I didn't extend the gear 'sharply' enough, it
would not "go past dead center" and lock. The result was that a bump or
something would cause it to collapse... sometimes as I slid it off the dolly
when assembling and once on a grass strip landing.
Pay particular attention to the bolts/joint where the main struts "fold" in
the middle and go over 'dead center' to lock. I found that these joints were
the most problematic on my ship. Plenty of cleaning, burnishing, etc. with a
wire brush and emery cloth brought these bolts/pivot pins back to life. A
good coat of grease and they worked like a champ.
So... give it all a good going over. Minimize all the areas of friction and
I think you will have your problem solved.
You can probably check it by placing the glider on the trailer dolly, extend
the gear sloooooowwwwly, then from the rear of the left wing, reach into the
wheel well to the left rear of the wheel and CAREFULLY pull against the
middle of the folding fork assembly (watch out not to get your fingers caught
in anything!) to be sure that it is completely past 'dead center' and
locked. On mine prior to cleaning and lubricating it would not always be
completely locked or feel a little tenuous. After the cleaning, there is not
the least tendency for it not to be locked.
--
Larry Goddard
"01" LS-3a USA
JNBearden
In article <897476865.16794...@news.demon.nl>,
sander...@roosendaal.demon.nl (Sander Holthaus) writes:
>However, shortly after landing (ca 1-2 sec.)
>the mail wheel collapsed back onto the fuselage. The problem is that
>the wheel-handle was still in the lock. First was thought, that the gas
>-strut which keeps the landing-gear locked, was broken. After measurments
>, it was found that it was still in operating limits.
I expect this will generate a huge number of responses as this is not an
uncommon problem. Perhaps the experience in Europe is different; everyone in
the US seems to have his or her own theory for this.
Besides a weak gas spring, another factor (based entirely on experience with
the LS-3 but applies at least partially to the LS-1F and LS-4, I believe) is
the stiffness of the damping strut which looks exactly like a gas spring but is
actually a hydraulic shock absorber, similar to an automobile. It is mounted
between the main vertical link and horizontal link in the landing gear close to
the main wheel. Especially when it is cold, the damping strut can get stiffer
while the gas spring presumably loses some force, an unhappy combination.
Another factor is bearings and linkages in the landing gear that do not have
enough lubrication and/or have dirt or sand in them, causing friction.
The combination of all of these can cause a problem: when you lower the wheel
with the cockpit handle, the "knee" (the hinged vertical main strut in the
landing gear) is not quite locked/over center. In that case, only a small
amount of force or a bump--as during landing--can cause the knee to become
unlocked which, with weight on the wheel, causes it to retract. Since the gas
spring strut connects the cockpit handle linkage to the landing gear actuating
arm, the gas spring merely compresses when the wheel retracts, leaving the
handle in the down-and-locked position. :>(
To check for this, put the fuselage in the trailer cradle with the wheel off
the ground and lower the wheel with the cockpit handle. Now reach up into the
wheel box and push back at the "knee" joint; if there is any movement or a
"click" as it goes over center, it means the "knee" was not fully locked/over
center.
The remedy for this depends on what causes the problem: weak gas spring, stiff
damper, dirt and/or inadequate lubrication. Of course one should also inspect
for a bent or damaged piece in the landing gear but your problem is so typical
that it is probably caused by one or more of the above factors.
A temporary solution employed by some is to remove the damper, making the
system less stiff which allows the "knee" to snap into the over center position
more easily. I have never seen any communication from Rolladen Schneider to
know what adverse consequences there might be from doing this; e.g., slamming
the landing gear down against the stop, or in a hard landing. It also ignores
the legal/airworthiness issues.
Another temporary fix: I have seen quite a few pilots lose contest days because
this occurs and they do not have a new gas spring available. One problem is
that these springs lose gas pressure (and force) gradually over time **whether
or not they are installed in the glider** so carrying a spare with you for
years does not necessarily insure it will work properly when it is needed. The
same applies to any gas spring, e.g., the one which holds the canopy in the up
position and the struts for the Komet/Cobra trailers. The life of these springs
is enhanced when they are stored with the smaller (i.e., piston) end down so
that the oil inside the cylinder remains around the piston seal.
Ignoring the airworthiness issues, I know that there is adequate room in the
LS-3 fuselage to install two gas landing gear springs in parallel (i.e., on
either side of the usual position) using longer bolts and washers. Since the
force of the old springs typically seems to decline, then stabilize at about
half the force of a new spring, two old springs roughly equal the force of one
new spring. It might make sense to keep one or two of the old springs in your
toolbox, along with two longer bolts, just in case. Warning: as before, this
technique is not, to my knowledge, authorized by the factory and there may be
other consequences.
I can tell you that an LS-3 equipped with two old (i.e., weak) gas springs and
the damping strut removed flew an entire contest in the US some years ago,
including several off-field landings, and performed just fine, although not
without causing the pilot some anxiety whenever he landed back on the
hard-surface runway after finishing. :>)
I'm interested to hear from other pilots and technical experts who have had
experience with the LS landing gear system.
Chip Bearden
ASW-24 "JB"
(formerly LS-3)
LS484
The LS-4a has both a gas strut and a gas damper in the landing gear system. Is
the damper weak or non-functional?
Peter Wilson
IT may appear that the gas strut is functioning within limits but the
only way to really tell is to take it out and actually measure the
spring force it excerts, there are specs for thius in one of the manuals
we have for oour LS4, if the spring is slightly weak it is enough to
allow just enough slop in the mechanism for the over-centre lock to flip
out and the undercarriange to collapse.
It puzzled us for a long time, but replacing the gas strut seems to have
fixed the problem.
--
------------------------------------------------------------------------
Peter Wilson peter....@uk.sun.com
Hardware Engineer Tel: +44 (0) 1207 585568 Fax: +44 (0) 1207 585592
Sun Microsystems Ltd. TPG BU, Medomsley Road, Consett, Co. Durham, UK
------------------------------------------------------------------------
DBrotto
I suffered a gear collapse in my LS-1f on a slightly bumpy landing a few years
back. No damage except some minor scrapes on the belly since I landed in grass.
Chip Bearden helped me pull the gas strut out and test it (thanks Chip!) It
seemed within spec; 90 lbs to compress. So we reinstalled it and I chalked the
failure up to maybe dirt preventing an overcenter or maybe a funny harmonic in
a landing bounce.
A few months later the gear again collapsed during landing while a friend was
landing the ship. This time the damage was more extensive requiring a trip to
Paul Weiden at Keystone G-port. The failed gas strut was now down to about 50
lbs to compress. Paul installed a new strut, cleaned up the glass damage, and I
was back in buisness. Since then I have had no problem w/ gear collapse.
I did follow-up with some research on strut failures for other LS ships. It
seems that the gas strut starts to fail after about 6 to 8 years of use. My
thoughts are to just replace the strut with a new one every 3 years. They are
inexpensive enough and available (thanks Mike Adams!) This fall will be 3 years
from the last replacement so Paul, I'll be calling you to get on your schedule!
BTW, the strut is stowed and spends the vast majority of its life in the worst
possible position; upside down (no oil on the seal) and compressed.
Danny Brotto
T.W. de Boer
Ha Sander, hier Jeppe de Boer van de Friese.
Ik weet niet de oplossing op jouw probleem, dus meel ik gewoon maar even.
Groeten,
JEPPE
boe...@gironet.nl
Sander Holthaus schreef:
> ** To reply in e-mail, remove ".nubqih" from address **
>
> Last week (monday, 1st of June), after a flight lasting over 3 hours,
> I landed in our club (WBAC) ls-4a (PH-901). Just a normal landing, not
> hard or anything like that. However, shortly after landing (ca 1-2 sec.)
> the mail wheel collapsed back onto the fuselage. The problem is that
> the wheel-handle was still in the lock. First was thought, that the gas
> -strut which keeps the landing-gear locked, was broken. After measurments
> , it was found that it was still in operating limits.
>
> So, does anybody have a clue what could be the problem?
>
DBrotto
Someone mentioned the possibility to mount the gas strut in the LS gliders
"upside down" to keep the seal/gasket lubricated. (In the -1f, at least the
stowed gear keeps the strut compressed and at an attitude such that the seal is
dry.) We tried to reinstall it in a "lubed" position but it would not fit or
clear in that position. Good thought though! Might work with other LS ships.
Danny Brotto
BTW, if you EVER get a chance to fly a -1f, do yourself the favor.. It's a
really sweet flying machine. A bit tight in the cockpit but wow, do they ever
handle well!
Pam Sutton
Sander Holthaus wrote:
>
> ** To reply in e-mail, remove ".nubqih" from address **
>
> Last week (monday, 1st of June), after a flight lasting over 3 hours,
> I landed in our club (WBAC) ls-4a (PH-901). Just a normal landing, not
> hard or anything like that. However, shortly after landing (ca 1-2 sec.)
> the mail wheel collapsed back onto the fuselage. The problem is that
> the wheel-handle was still in the lock. First was thought, that the gas
> -strut which keeps the landing-gear locked, was broken. After measurments
> , it was found that it was still in operating limits.
>
> So, does anybody have a clue what could be the problem?
>
> Sander Holthaus
> Roosendaal, The Netherlands
>
> email: san...@roosendaal.demon.nl
> ICQ: 13577569, Sander
>
> --
Same thing happened to me in my LS3a landing in a grass field. As you
can see from the numerous posts, it's a common problem. I keep spares
in my trailer for the gas strut, gear door hinges and gear doors for
quick repair.
Pam Sutton
John Giddy
DBrotto wrote:
> BTW, the strut is stowed and spends the vast majority of its life in the worst
> possible position; upside down (no oil on the seal) and compressed.
I am not familiar with the details of the LS4 U/C, but many gas struts I
have seen can be installed either way around. If possible in this case,
it would avoid the problem listed above, No ?
John G.
--
John Giddy Mangalore Gliding Club
5/287 Barkers Rd http://www.gfa.org.au/vic/mgc/
Kew, Victoria, 3101
Australia
Jon Stallman
> I suffered a gear collapse in my LS-1f on a slightly bumpy landing a few years
> back. No damage except some minor scrapes on the belly since I landed in grass.
> Chip Bearden helped me pull the gas strut out and test it (thanks Chip!) It
> seemed within spec; 90 lbs to compress. So we reinstalled it and I chalked the
> failure up to maybe dirt preventing an overcenter or maybe a funny harmonic in
> a landing bounce.
> A few months later the gear again collapsed during landing while a friend was
> landing the ship. This time the damage was more extensive requiring a trip to
> Paul Weiden at Keystone G-port. The failed gas strut was now down to about 50
> lbs to compress. Paul installed a new strut, cleaned up the glass damage, and I
> was back in buisness. Since then I have had no problem w/ gear collapse.
> I did follow-up with some research on strut failures for other LS ships. It
> seems that the gas strut starts to fail after about 6 to 8 years of use. My
> thoughts are to just replace the strut with a new one every 3 years. They are
> inexpensive enough and available (thanks Mike Adams!) This fall will be 3 years
> from the last replacement so Paul, I'll be calling you to get on your schedule!
> possible position; upside down (no oil on the seal) and compressed.
Can you put me in touch with Mike Adams?
John Sinclair
> On Thursday, June 11, 1998 at 12:00:00 AM UTC-7, DBrotto wrote:
> > I suffered a gear collapse in my LS-1f on a slightly bumpy landing a few years
> > back. No damage except some minor scrapes on the belly since I landed in grass.
> > Chip Bearden helped me pull the gas strut out and test it (thanks Chip!) It
> > seemed within spec; 90 lbs to compress. So we reinstalled it and I chalked the
> > failure up to maybe dirt preventing an overcenter or maybe a funny harmonic in
> > a landing bounce.
> > A few months later the gear again collapsed during landing while a friend was
> > landing the ship. This time the damage was more extensive requiring a trip to
> > Paul Weiden at Keystone G-port. The failed gas strut was now down to about 50
> > lbs to compress. Paul installed a new strut, cleaned up the glass damage, and I
> > was back in buisness. Since then I have had no problem w/ gear collapse.
> > I did follow-up with some research on strut failures for other LS ships. It
> > seems that the gas strut starts to fail after about 6 to 8 years of use. My
> > thoughts are to just replace the strut with a new one every 3 years. They are
> > inexpensive enough and available (thanks Mike Adams!) This fall will be 3 years
> > from the last replacement so Paul, I'll be calling you to get on your schedule!
> > BTW, the strut is stowed and spends the vast majority of its life in the worst
> > possible position; upside down (no oil on the seal) and compressed.
> > Danny Brotto
>
> Can you put me in touch with Mike Adams?
Nicholas Kennedy
I could use one of these struts for a LS3a; any ideas?
Nick
T
Art Mahoney
Christoph Barniske
Piet Barber
> The gas strut on LS3/LS4 and retrofitted LS1-f is a Stabilus Lift-o-Mat, 400N, Part no. 044708. In Europe, they are available at a few online shops. Despite the service contract, DG charges their customers a premium for spare parts over here.
What a story for the bar with the glider buddies: "You did a gear up landing? Well that's nothing! Mario over here did a gear up *takeoff* !"
Moshe Braner
flat. Very short rollout, completely unexpected, stranded in the middle
of the runway. Must have hit a sharp object in the air, eh?
John Sinclair
Recommend this check be done every 6 months!
JJ
Papa3
P3