Discus Aileron Seals

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

Hi Peter,

I think you have done very well if you still have the original mylar seals.
I have also replaced the seals with tape, and yes, it is better. It is also quite a bit of work though.
The tape goes on the aileron and then in an S to the wing. It needs to be glued in place, and is easiest if you can remove the aileron to do this. It simply gives you easier access to it.
You can happily put mylar seals on over it, and depending on how your Discus was done in the past will determine what needs to be done. Some have a groove milled in only the top surface, and some also on the bottom. I personally reccommend you put mylar on both surfaces.

Next tip is to put deviders between aileron and wing to stop any airflow between them. Adds to the effectiveness of the aileron too. I did it both inboard and outboard. A piece of 1.2mm carbon worked well for me.

Don't know how to test the rubber seals.

Hope this was helpful.
Cheers
Ross

On Monday, August 19, 2013 10:32:38 AM UTC-4, 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

you can do something which works just as well, and is a lot easier. its something schempp-hirth is doing now i think. you stick this thin, slippery (almost like teflon or something) tape onto the wing and the control surface, which creates a perfect seal, and then go over it with the regular external mylar seals.

if your seals are as old as you say, its been time to change them for a long time.

MandH is doing it that (I think).

Here is a very nice article on applying control seals that I have come
across, hope it helps.

http://crazyslovenian.wordpress.com/...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

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/...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!

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/...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

Good info. 2 more things can be done to help ensure a good result. First roughen the underside of the seal where the transfer tape will contact it. 220 grit sandpaper is about right. Then clean roughened surface with acetone to make sure it is really clean
It also helps to tape the seal in the right place so it is good and straight. About every foot or so seems to work. Fold the "hinge" back to roughen the seal, wipe nice and clean, peel release film, and press into place. Leave surface deflected away from the seal while adhesive bond cures.
Good luck
UH

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!

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!

On Tuesday, August 20, 2013 8:02:47 AM UTC-4, Peter F wrote:
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!

I use a hypodermic syringe to oil hinges through a needle sized hole. Not much air leaks though that hole.
UH