LS-4 Trim Lock coming loose with stick deflection?

[gs03jsa]

Hi Folks -

Quick question - does anyone have experience with the LS-4 Trim Lock
coming loose with large control deflection?

I'm not quite sure what's causing the mechanism to slip - whether it
is a cable adjustment issue, weak spring issue, or whether the
brackets that lock the tube are just worn out of round.

Thanks for your help!

John Andrew
Atlanta, Georgia

[JJ Sinclair[_2_]]

On Jan 30, 6:58*pm, gs03jsa > wrote:
> Hi Folks -
>
> Quick question - does anyone have experience with the LS-4 Trim Lock
> coming loose with large control deflection?
>
> I'm not quite sure what's causing the mechanism to slip - whether it
> is a cable adjustment issue, weak spring issue, or whether the
> brackets that lock the tube are just worn out of round.
>
> Thanks for your help!
>
> John Andrew
> Atlanta, Georgia

I believe they are all that way, John. Trim is a fine adjustment not
meant to hold with full throw movements. After wild movements, re-set
the trim at the desired speed. You might look at the friction plate to
see if it needs to be repositioned a bit in order to give more holding
power.
JJ

[Papa3]

On Jan 31, 10:02*am, JJ Sinclair > wrote:
> On Jan 30, 6:58*pm, gs03jsa > wrote:
>
> > Hi Folks -
>
> > Quick question - does anyone have experience with the LS-4 Trim Lock
> > coming loose with large control deflection?
>
> > I'm not quite sure what's causing the mechanism to slip - whether it
> > is a cable adjustment issue, weak spring issue, or whether the
> > brackets that lock the tube are just worn out of round.
>
> > Thanks for your help!
>
> > John Andrew
> > Atlanta, Georgia
>
> I believe they are all that way, John. Trim is a fine adjustment not
> meant to hold with full throw movements. After wild movements, re-set
> the trim at the desired speed. You might look at the friction plate to
> see if it needs to be repositioned a bit in order to give more holding
> power.
> JJ

Hi John,

Been a while since I worked on an LS4 (I used to own one), but IIRC,
the green trim lever on the left side of the cockpit sidewall was
mounted via a rubber bushing that provided the friction lock. There
was a machine screw that you could tighten (with the seatpan out) to
provide a little bit more friction.

As JJ mentions though, full/abrubt deflection of the controls will
tend to move the trim. And of course, you have to watch out that you
aren't accidentally squeezing the green trim lever on the control
stick which is easy to do either with your hand or with a boot that is
too narrow or stiff.

As I said, I'm trying to remember the trim mechanism mechanicals from
memory, as there is no diagram in the old copy of the maintenance
manual I have handy. There may be one in the repair manual...

P3

[gs03jsa]

JJ and P3 - thanks for your help!!! It is esp. helpful to know that
it is a *known* issue that doesn't warrant replacement of parts.

John

On Jan 31, 10:02*am, JJ Sinclair > wrote:
> On Jan 30, 6:58*pm, gs03jsa > wrote:
>
> > Hi Folks -
>
> > Quick question - does anyone have experience with the LS-4 Trim Lock
> > coming loose with large control deflection?
>
> > I'm not quite sure what's causing the mechanism to slip - whether it
> > is a cable adjustment issue, weak spring issue, or whether the
> > brackets that lock the tube are just worn out of round.
>
> > Thanks for your help!
>
> > John Andrew
> > Atlanta, Georgia
>
> I believe they are all that way, John. Trim is a fine adjustment not
> meant to hold with full throw movements. After wild movements, re-set
> the trim at the desired speed. You might look at the friction plate to
> see if it needs to be repositioned a bit in order to give more holding
> power.
> JJ

[Westbender]

It's not an "known issue". It's the design. I have an LS1f and it has
a similar if not identical trim control. It just applies friction, so
it will let go a little when you apply enough forward or aft movement
on the stick. The slipping prevents the spring pressure from fighting
against you for larger fore/aft movements while still keeping the
stick neutral for the small ones. This friction control especially
comes into play each time you transition from thermalling to glide or
vice-versa. It will move when you push or pull harder during those
transitions instead of trying to resist your stick movement. It still
takes a slight adjustment on the trim to neutralize completely after a
transition, but it gets the trim going in the right direction by
slipping and following the stick somewhat. Locking it down would cause
considerable spring tension and will fatigue your arm. I've tried that
and it's way nicer to fly if you adjust it correctly so it moves. It's
an adjustable friction, not a "lock".


Dave

[Andy[_1_]]

On Jan 31, 9:58*pm, Westbender > wrote:
> It's not an "known issue". It's the design. I have an LS1f and it has
> a similar if not identical trim control. It just applies friction, so
> it will let go a little when you apply enough forward or aft movement
> on the stick. The slipping prevents the spring pressure from fighting
> against you for larger fore/aft movements while still keeping the
> stick neutral for the small ones. This friction control especially
> comes into play each time you transition from thermalling to glide or
> vice-versa. It will move when you push or pull harder during those
> transitions instead of trying to resist your stick movement. It still
> takes a slight adjustment on the trim to neutralize completely after a
> transition, but it gets the trim going in the right direction by
> slipping and following the stick somewhat. Locking it down would cause
> considerable spring tension and will fatigue your arm. I've tried that
> and it's way nicer to fly if you adjust it correctly so it moves. It's
> an adjustable friction, not a "lock".
>
> Dave

I find it hard to believe that a trim system that allows uncommanded
changes in the stick force gradient could ever have been
certificated. Does anyone else believe the trim system was designed
to slip in this way? Are any other gliders designed to have a trim
system that slips?

Andy

[Peter Scholz[_3_]]

Am 01.02.2011 13:57, Andy wrote:
>
> I find it hard to believe that a trim system that allows uncommanded
> changes in the stick force gradient could ever have been
> certificated. Does anyone else believe the trim system was designed
> to slip in this way? Are any other gliders designed to have a trim
> system that slips?
>
> Andy

My ASW24 also tends to 'readjust' the trim setting when moving the stick
fully back or front.

Our club LS4 has the same behaviour, I think it is working as designed.

In real flight, extreme forward/backward movements don't happen to often.
--
Peter Scholz
ASW24 JE

[John Smith]

Andy wrote:
> Does anyone else believe the trim system was designed
> to slip in this way? Are any other gliders designed to have a trim
> system that slips?

Of the three LS4s I've flown, only one has had a "self adjusting" trim.
I assume it's just worn out.

[MaD]

On 1 Feb., 13:57, Andy > wrote:
> I find it hard to believe that a trim system that allows uncommanded
> changes in the stick force gradient could ever have been
> certificated. *Does anyone else believe the trim system was designed
> to slip in this way? *Are any other gliders designed to have a trim
> system that slips?
>
> Andy- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

When new, the trim does (did) not slip on our clubs LS4s. After a few
years, they tend to do so and can be adjusted to a certain extent as
someone else described.
It can normally be adjusted so it holds with full backward stick, but
not so full forward. Luckily or coincidentally that's the safer way
round.

Marcel

[Wayne Hoover]

On 2/1/2011 7:57 AM, Andy wrote:
> On Jan 31, 9:58 pm, > wrote:
>> It's not an "known issue". It's the design. I have an LS1f and it has
>> a similar if not identical trim control. It just applies friction, so
>> it will let go a little when you apply enough forward or aft movement
>> on the stick. The slipping prevents the spring pressure from fighting
>> against you for larger fore/aft movements while still keeping the
>> stick neutral for the small ones. This friction control especially
>> comes into play each time you transition from thermalling to glide or
>> vice-versa. It will move when you push or pull harder during those
>> transitions instead of trying to resist your stick movement. It still
>> takes a slight adjustment on the trim to neutralize completely after a
>> transition, but it gets the trim going in the right direction by
>> slipping and following the stick somewhat. Locking it down would cause
>> considerable spring tension and will fatigue your arm. I've tried that
>> and it's way nicer to fly if you adjust it correctly so it moves. It's
>> an adjustable friction, not a "lock".
>>
>> Dave
>
> I find it hard to believe that a trim system that allows uncommanded
> changes in the stick force gradient could ever have been
> certificated. Does anyone else believe the trim system was designed
> to slip in this way? Are any other gliders designed to have a trim
> system that slips?
>
> Andy
The trim on my LS-4 stays put through full for and aft travel of the
stick when the trim is centered. When the trim is at it's for or aft
limit the trim will move slightly with full deflection in the oposite
dirction. However our clubs LS4's trim has significant motion in the
trim without full diflection. I find my self holding the trim knob to
keep it from moving to keep the glider trimmed. Otherwise, I am
constantly retrimming the glider while thermaling.

Wayne