Thanks for all the responses.
Looks like I'll be changing the mylar over the winter, which in the UK is
due to start next Tuesday.
Will probably seal gap with teflon tape as per...
http://crazyslovenian.wordpress.com/...for-dummies-1/
Then just need to work out how to lubricate the hinges in future.
(Small gap in teflon at each hinge?)
PF
At 20:16 19 August 2013, John Galloway wrote:
I think that there are some misunderstandings here. Dick
Johnson did not fit internal fabric aileron seals in his 1986
Discus test:
http://web.archive.org/web/200506230...http://www.ssa.
org/Johnson/53-1986-02.pdf
The test aircraft, with its near-top surface aileron hingeing,
does not seem to have had the modern style of mylar gap
sealing but had "the normal tape seal bridging the spanwise
gaps between the wing and the aileron leading edges. However,
a curved piece of Mylar plastic strip was attached to the wing
portion by an adhesive layer at its leading edge."
(It is not clear from the article whether the mylar was an
original factory fit or an owner retrofit. By the time I bought a
new Discus BT in 1992 two methods of mylar-onlyseal fittings
were offered to me at different prices but neither with top
surface old fashioned gap tape.)
After intial poorer than expected performance results Johnson
speculated that a "bulge" in the curved mylar on the tested
glider might adversely affect its performance and also
speculated that"it is possible that airstream suction force over
their cambered top surfaces caused the strip trailing edges to
ride high and above the aileron, thereby adding drag".
As a result he removed the mylar seals (only), thus leaving the
aileron gaps with top surface tape seals, and then he sealed the
wing roots. To quote the article:
"For the above reasons the Mylar aileron seals were removed
and Ceconite polyester airseals were installed at the wing root
aileron control rod openings. Simpler plastic foam seals were
deemed adequate for the airbrake push-rods there. The Discus
always exhibited a quiet cockpit, but the addition of the wing
root seals quieted the cockpit even more, and roll rates also
improved. ± 450 rolls at 50 kts took about 5.0 seconds to
accomplish before the seal changes and about 4.2 seconds
afterwards, according to my stopwatch"
Fitting internal fabric seals is a lot of work - I have done it on a
Kestrel 19 a long time ago. If your wings are sealed at the
roots so that they are not positively or negatively pressurised,
and if properly fitting top and bottom mylar seals are installed
then it seems very unlikely that there will be significant airflow
between the top and bottom of the wing through the aileron
gap.
Where problems arise with mylar over time it is generally from
storage with the moving surface deflected and general ageing of
the materials.
There are various ways of fitting mylar seals. I don't know
about the US but the simplest way that of getting new Mylar
that you know will be suitable in Europe is to buy the glider
specific kit from Streifly:
http://www.streifly.de/shop%20abdichtsaetze-e.htm
John Galloway
At 18:11 19 August 2013, wrote:
On Monday, August 19, 2013 11:56:50 AM UTC-4, Luke
Szczepaniak wrote:
Here is a very nice article on applying control seals that I
have come
across, hope it helps.
http://crazyslovenian.wordpress.com/2012/03/02/pimp-my-
glider-for-dummies-1/
Cheers,
Luke Szczepaniak
On 08/19/2013 10:32 AM, Peter F wrote:
In Richard Johnson's flight test of the original Discus he
replaces the
mylar seals with internal fabric seals & gets a noticeable
improvement
in
performance.
The mylar on my Discus CS is 20years old & starting to lift
in places,
so I
will need to replace it.
Has anyone out there done the internal seal mod?
Did you think there was any advantage
Can I have both internal & mylar seals?
The pushrod holes for Aileron & Airbrake are sealed with
rubber
bellows.
These are also 20 yrs old.
Anyone know of a way to test whether these are perished,
no longer
sealing?
Many thanks
PF
this is exactly what i was proposing. thanks for the link!