Wing Contour?

What technique do you use to make templates ("pull a set") for the leading edge as Hank states? Do you guys know if there are existing coordinates or templates for ASK21 and ASW24?

Doug

On Thursday, August 1, 2019 at 12:03:56 PM UTC-4, wrote:
What technique do you use to make templates ("pull a set") for the leading edge as Hank states? Do you guys know if there are existing coordinates or templates for ASK21 and ASW24?

Doug

I make templates out of 1/4 inch plywood cut to a very close profile to the leading edge.
I wax the wing well, then put a thick coating of aerodynamic fairing compound(body filler) on the inner surface of the wood template and squish into place.
When cured remove a clean up. Label immediately.
'21 has published airfoils. No idea why anyone would want to profile one.
Have '24 templates for B mod.
UH

Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?

Doug

On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?

Doug

You understood correctly.
First 10% or so. About 3 inches inboard and 2-1/2 outboard.
Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
UH

Originally Posted by

On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?

Doug

You understood correctly.
First 10% or so. About 3 inches inboard and 2-1/2 outboard.
Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
UH

Next step ? So you then wax the female end of the template and fill the wing stations and place the template into the filler . Remove and that becomes a screed point between stations?

I've seen a recently refinished wing that had lots of small cracks every few inches on the leading edge . Bad filler product? Does the filler shrink ?

Somewhere buried on www.jimphoenix.com are pictures of how he reprofiled the wings on a Nimbus 3. It’s worth taking a look.

On Thursday, August 1, 2019 at 1:12:02 PM UTC-4, wrote:
On Thursday, August 1, 2019 at 12:50:22 PM UTC-4, wrote:
Just to clarify, the 1/4 inch ply is "rough cut" as closely as possible and the filler adheres to the wood and gives the smooth surface needed to re-profile? How far back above, and below the wing do you go for a glider you want to perform well?

Doug

You understood correctly.
First 10% or so. About 3 inches inboard and 2-1/2 outboard.
Purpose of the templates is to have finished wing with same profile it started with. "Normal" sanding will usually make the leading edge too blunt.
UH

I am interested in doing a resurfacing on a Libelle 201b. I have been loaned templates which appear to be well made, possibly water jet cut, about the size you describe. My wings, in the very leading edge portion are off(differently at different stations and on opposite wings) by as much as 1/4 to 5/16. I too have the spare bump. My plane thermals better to the left but shows no fall off in stall. I was expecting to sand and contour maybe 1/10 of an inch but what product is useful for 1/4 of and inch? I know, and have used Bondo to that depth on other things, but aircraft?
Thank you for the insight and expertise you have shown in the answers you have give.

I had MDF templates made on a CNC laser cutter, they cost $30 Australian each.
In my case, the templates were for measuring control deflections, so were one piece.
Particularly with the FX67 series airfoils, accuracy is critical.
Do not believe getting rid of waves will be all you need to do, despite some other posters.
Two local reprofiled a Mosquito and A mini Nimbus.
Mike Borgelt reprofiled the mini, and beat all the ASW20 to win an Oz nationals.

Several years ago (1970 time frame) Wil Schumann did a re-contour of the H301 Libelle leading edge. It required a bit of build-up with balsa to the extent you're talking about. My father glued the balsa directly to the existing surface and roughed it to shape, slightly undersized on the templates.

The Bondo was then added to create the actual contour and was followed by a thin fiberglass layer, filler and paint.

It lasted until I bought the glider in 2015(!) and it's still there with no damage, other than a few chips that needed to be refilled.

I think if you check back in the archives you can find an article describing Wil's process.

Mike B.

One last point, most of the gliders that use the FX 67 series start with 67k170 17% thick, then at some point,
either from the root or the taper change at the aileron, transition to 67k150 15% thick at the tip.
This means that special care in needed to calculate the templates for intermediate stations.
My DG200 is 67k170 all the way. The 40 year old wing is very accurate still, something that cannot be said of
the PIK20 (one locally is 19% thick) the Mosquioto, and the Mini Nimbus, all of which seen to have suffered moulding errors.
As I recall, the reprofiled mentioned previously required special calculations for each individual aircraft.