Wing play

I have noticed several older sailplanes with some play in the wings.
They don't seem to pull into the fuselage and have a few thousandths
play so that the wings move fore and aft, slightly. Can this be
shimmed? I know from working on L-33's that they come from the factory
with shims. Is this an acceptable fix for older glass ships?

Jack

The ASW 20 has instructions to nock the fuselage pins
out and put shims behind them to remove slack, apparently
to prevent the fuselage fishtailing. The Hornet and
Club Libelle i fly both have external shims on the
fuselage pins, they would have a lot of slack otherwise.
manufacturer maintenace manual should advise

Pete

At 16:54 02 July 2007, Jack wrote:
I have noticed several older sailplanes with some play
in the wings.
They don't seem to pull into the fuselage and have
a few thousandths
play so that the wings move fore and aft, slightly.
Can this be
shimmed? I know from working on L-33's that they come
from the factory
with shims. Is this an acceptable fix for older glass
ships?

Jack

In article ,
Peter Thomas wrote:

The ASW 20 has instructions to nock the fuselage pins
out and put shims behind them to remove slack, apparently
to prevent the fuselage fishtailing. The Hornet and
Club Libelle i fly both have external shims on the
fuselage pins, they would have a lot of slack otherwise.
manufacturer maintenace manual should advise

Pete

I think external shims on Libelles are common. Both my 301 Libelles had
shims on the pins.

Berry wrote:
In article ,
Peter Thomas wrote:

The ASW 20 has instructions to nock the fuselage pins
out and put shims behind them to remove slack, apparently
to prevent the fuselage fishtailing. The Hornet and
Club Libelle i fly both have external shims on the
fuselage pins, they would have a lot of slack otherwise.
manufacturer maintenace manual should advise

Pete

I think external shims on Libelles are common. Both my 301 Libelles had
shims on the pins.
So does my 201.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

On Jul 2, 12:50 pm, Jack wrote:
I have noticed several older sailplanes with some play in the wings.
They don't seem to pull into the fuselage and have a few thousandths
play so that the wings move fore and aft, slightly. Can this be
shimmed? I know from working on L-33's that they come from the factory
with shims. Is this an acceptable fix for older glass ships?

Jack

Jack,

I suppose there's no one answer, as a lot depends on the ship. For
example, I've owned gliders from both Grob and LS, and the approach to
adjusting out this play was very different. For example, the bushings
for the drag spars on the fuselage of the LS8 are threaded and allow
some of this play to be removed without additional shims. The Grob
Astir had a similar arrangement.

P3

If you consult the maintenance manuals, you will probably find the maximum
allowable fore-aft and up-down free motion (play). For many gliders these
are amazingly large figures.

If my Nimbus 2C were at the max tolerance (which it isn't), flight could
then be fairly described as a "loose formation of glider parts".

Form my point of view, there are two types of 'play'. One is true free
motion due to clearances in the fittings. The other involves some
stick-slip action that occurs with alarming violence - this is very
worrying.

Grob 103's are prone to this. The 103's leading edge pins (spigots)
actually protrude through the sides of the rear cockpit into the side
pockets where the rear seat occupant is likely to be resting elbows. These
pins can shift inward with a loud bang numbing the rear pilots arms. Given
the complexity of Grob wing fittings, I think very little play should be
tolerated.

Bill Daniels

"Jack" wrote in message
oups.com...
I have noticed several older sailplanes with some play in the wings.
They don't seem to pull into the fuselage and have a few thousandths
play so that the wings move fore and aft, slightly. Can this be
shimmed? I know from working on L-33's that they come from the factory
with shims. Is this an acceptable fix for older glass ships?

Jack

Bill Daniels wrote:
If you consult the maintenance manuals, you will probably find the maximum
allowable fore-aft and up-down free motion (play). For many gliders these
are amazingly large figures.

If my Nimbus 2C were at the max tolerance (which it isn't), flight could
then be fairly described as a "loose formation of glider parts".

Form my point of view, there are two types of 'play'. One is true free
motion due to clearances in the fittings. The other involves some
stick-slip action that occurs with alarming violence - this is very
worrying.

Grob 103's are prone to this. The 103's leading edge pins (spigots)
actually protrude through the sides of the rear cockpit into the side
pockets where the rear seat occupant is likely to be resting elbows. These
pins can shift inward with a loud bang numbing the rear pilots arms. Given
the complexity of Grob wing fittings, I think very little play should be
tolerated.

Bill Daniels

"Jack" wrote in message
oups.com...
I have noticed several older sailplanes with some play in the wings.
They don't seem to pull into the fuselage and have a few thousandths
play so that the wings move fore and aft, slightly. Can this be
shimmed? I know from working on L-33's that they come from the factory
with shims. Is this an acceptable fix for older glass ships?

Jack



My personal general considerations on tolerances and play.

There are designed in gaps on most moving assemblies. One that is easy to see is
the little bit of vertical freedom in most gliders rudder.

This tolerance is generally designed in - although sometimes it is simply
production quality or wear.

Thing to know is which applies to whatever you are wiggling.

So - consider the aircraft gattling gun - it has lots of precision machined
parts that rattle around as if they were unable to machine accurately. Take out
the gaps, and it would seize solid as pieces expand when it fires.

Same principle applies to gliders.
If there is excessive free movement in something (i.e.that is not designed to
have it) - ground the thing and fix it.
If you are not sure if it is excessive, find out - the manuals should have the
limits, and if they don't JAR22 or its successors have blanket limits.

Consider - the all moving elevator on my Std Cirrus has around 4mm tramline
movement. This is considered "good" by the agents given the design of the
fitting. Much less and there would be risk of binding at low temperature.
If the Kestrel had the same play it would be grounded.

From my limited experience I would expect there to be procedures for shimming
or replacing the bearing pins on the wings at the leading edge and at the drag
spar. This is a critical connection - it should be right.

One reason for developing the play on long wings is when misguided or moronic
"helpers" manhandle glass ships by the wingtips. This puts very high loads into
the pins and they will get loose.

Bruce wrote:


From my limited experience I would expect there to be procedures for
shimming or replacing the bearing pins on the wings at the leading edge
and at the drag spar. This is a critical connection - it should be right.

One reason for developing the play on long wings is when misguided or
moronic "helpers" manhandle glass ships by the wingtips. This puts very
high loads into the pins and they will get loose.

Does anyone know if there are certification standards for this kind of
ground handling force? I see people manhandling the wingtips, but I've
never heard of damage as a result, so I suspect the designers expect it
and design accordingly.

I've carefully avoided that kind of stress, but my Libelle 301 and ASW
20 C still developed audible wing play. My ASH 26 E, with more time than
the 301 and 20 combined, has not developed wing play. Go figure.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Does anyone know if there are certification standards for this kind of
ground handling force? I see people manhandling the wingtips, but I've
never heard of damage as a result, so I suspect the designers expect
it and design accordingly.

I believe that FAR23 and JAR22 call for resistance to something like
100 lbs or the equivalent kN applied fore and aft at the wingtip.
However, those standards also allow for less resistance if the lower
loads can be justified. My guess is that lighter ships like the PW5
are so certified.

Thanks, Bob K.