K8b restoration

On Friday, February 1, 2019 at 6:29:38 PM UTC-7, John Foster wrote:
I was given a junked K8b due to water damage to the wood at the wing root and multiple tears in the original fabric and chipped/peeling paint. However, it looks like it may be restorable (worth it, that's another story). Anyway, I'm interested to know if there is an online repair manual that lays out the specific techniques of repairing or replacing wood in the wings, and specifications on what type of wood to be used, etc. I looked around and found the list of ADs, but nothing that laid out what I am looking for. I've contacted Schleicher as well, but they simply directed me to a link on their website, that didn't really give the information I needed. This is a certified glider, and I'd like to keep it that way, as I'm hoping to use it as a club glider.

Is it common for the fabric to not go all the way to the leading edge? This one has the fabric to just forward of the spar, and the rest of the leading edge is covered by painted plywood. Would there be any harm to have the fabric cover the whole wing? I don't imagine it would add any significant weight, but it would protect the underlying plywood better.

It was probably a fabric width or budget issue. You can glue a piece around the leading edge easily enough.

On Thursday, February 21, 2019 at 10:59:13 PM UTC-6, John Foster wrote:
On Friday, February 1, 2019 at 6:29:38 PM UTC-7, John Foster wrote:
I was given a junked K8b due to water damage to the wood at the wing root and multiple tears in the original fabric and chipped/peeling paint. However, it looks like it may be restorable (worth it, that's another story). Anyway, I'm interested to know if there is an online repair manual that lays out the specific techniques of repairing or replacing wood in the wings, and specifications on what type of wood to be used, etc. I looked around and found the list of ADs, but nothing that laid out what I am looking for.. I've contacted Schleicher as well, but they simply directed me to a link on their website, that didn't really give the information I needed. This is a certified glider, and I'd like to keep it that way, as I'm hoping to use it as a club glider.

Is it common for the fabric to not go all the way to the leading edge? This one has the fabric to just forward of the spar, and the rest of the leading edge is covered by painted plywood. Would there be any harm to have the fabric cover the whole wing? I don't imagine it would add any significant weight, but it would protect the underlying plywood better.

It depends.... From the factory, it would have had fabric that extended about 50mm ahead of the rear side of the main spar. That is considered an adequate coverage with cotton, glider cloth, or even Dacron when using traditional dope (Ceconite process). The Polyfiber process (formerly known as Stits, since it was developed by Ray Stits) includes a requirement in its STC that many A&Ps & IAs would interpret to require putting all edges in double shear. This would require require covering the leading edge with fabric and overlapping the fabric on the open bays. The Stewart System STC allows the fabric to be installed in the same fashion as defined originally by the factory. I believe that SuperFlight and AirTech also allow that.

I would suggest carefully sealing the plywood on the leading edge with epoxy. Often people use Polyfiber EV400 epoxy varnish, but using a squeegee with WEST System epoxy will provide a more effecting sealing. Then you can either paint the scuffed leading-edge surface or decide to cover it with cloth. If you decide on cloth, you can use lightweight, uncertified fabric on the leading edge, since it is not carrying an air load.

Send me a private email if you would like to discuss more. I have direct experience with replacing fabric on Schleicher gliders with Stits & Stewart. I can give you some hints on what order to do the covering and handle the stitching.

...... Neal

I think you will find that all wooden Schleicher gliders have been finished
from the factory with fabric up to 50 mm forward of the rear face of the
main spar, and with paint on the D-box. Sometimes the D-box has been
reworked (especially on Ka6s) with a thin layer of filler to reduce drag.
In fact, reducing drag by creating a smooth painted surface opposed to a
more rough fabric'ed D-nose is probably the main reason it was finished
this way. Fabric width was no problem.

On Friday, February 22, 2019 at 10:00:06 AM UTC-7, Eric Munk wrote:
I think you will find that all wooden Schleicher gliders have been finished
from the factory with fabric up to 50 mm forward of the rear face of the
main spar, and with paint on the D-box. Sometimes the D-box has been
reworked (especially on Ka6s) with a thin layer of filler to reduce drag.
In fact, reducing drag by creating a smooth painted surface opposed to a
more rough fabric'ed D-nose is probably the main reason it was finished
this way. Fabric width was no problem.

What glue is recommended for fixing broken glue joints? I understand that the original glue was not the best--very brittle.

What glue is recommended for fixing broken glue joints? I understand that the original glue was not the best--very brittle.

This topic was covered in Bungee Cord articles published by the Vintage Sailplane Association (also VGC News). There is not a simple answer, since all IA's and FAA personnel are not the same. I've sent you a separate, private email on this topic. ..... Neal

On Monday, March 18, 2019 at 1:05:49 PM UTC-6, wrote:

What glue is recommended for fixing broken glue joints? I understand that the original glue was not the best--very brittle.

This topic was covered in Bungee Cord articles published by the Vintage Sailplane Association (also VGC News). There is not a simple answer, since all IA's and FAA personnel are not the same. I've sent you a separate, private email on this topic. ..... Neal

Are these articles available online?