A aviation & planes forum. AviationBanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » AviationBanter forum » rec.aviation newsgroups » Soaring
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

K8b restoration



 
 
Thread Tools Display Modes
  #21  
Old February 22nd 19, 05:59 AM posted to rec.aviation.soaring
John Foster
external usenet poster
 
Posts: 354
Default 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.
  #22  
Old February 22nd 19, 06:12 AM posted to rec.aviation.soaring
Charles Longley
external usenet poster
 
Posts: 290
Default K8b restoration

It was probably a fabric width or budget issue. You can glue a piece around the leading edge easily enough.
  #23  
Old February 22nd 19, 07:44 AM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 41
Default K8b restoration

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
  #24  
Old February 22nd 19, 05:47 PM posted to rec.aviation.soaring
Eric Munk
external usenet poster
 
Posts: 179
Default K8b restoration

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.

  #25  
Old March 18th 19, 07:41 PM posted to rec.aviation.soaring
John Foster
external usenet poster
 
Posts: 354
Default K8b restoration

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.
  #26  
Old March 18th 19, 08:05 PM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 41
Default K8b restoration



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
  #27  
Old March 19th 19, 02:05 AM posted to rec.aviation.soaring
John Foster
external usenet poster
 
Posts: 354
Default K8b restoration

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?
  #28  
Old March 19th 19, 02:07 AM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 394
Default K8b restoration

Hi John,
I have repaired and recovered a K-6 and a K-13, both were licensed in Standard Category. Simply stated, the rules are you must do what the manufacturer did and use the same materials originally used, or get written permission from Schleicher or the FAA to deviate. I had to get FSDO permission to use epoxy glue to rework the ribs and check with Stits Fabric to see they had aTSO for each ship in order to use their Poly Fiber covering materials. All this can lead to problems with the IA who will be asked to sign off your form 337 and the Feds who must accept the work done, methods and materials used, as stated on the 337.
If I were you I would ask my local FSDO to change the ship over to Experimental, exhibition & racing. I’d tell them you wish to do this in order to use modern glues, materials and coverings. I have done this a couple of times with no problems at all. Once your licensed Experimental, an A&P can sign off all the work with a log book entry, no form 337, no IA, no TSO’s needed!
JJ Sinclair
BTW, covering the D tube with fabric is not allowed on your type certificated ship (you must do what the manufacturer did)........bad idea anyway because after shrinking, the fabric will bridge over all low spots and the dope will form a ring at the edge of these low areas and show up as very ugly rings in your final paint Job!
  #29  
Old March 19th 19, 04:36 AM posted to rec.aviation.soaring
John Foster
external usenet poster
 
Posts: 354
Default K8b restoration

On Monday, March 18, 2019 at 7:07:16 PM UTC-6, wrote:
Hi John,
I have repaired and recovered a K-6 and a K-13, both were licensed in Standard Category. Simply stated, the rules are you must do what the manufacturer did and use the same materials originally used, or get written permission from Schleicher or the FAA to deviate. I had to get FSDO permission to use epoxy glue to rework the ribs and check with Stits Fabric to see they had aTSO for each ship in order to use their Poly Fiber covering materials. All this can lead to problems with the IA who will be asked to sign off your form 337 and the Feds who must accept the work done, methods and materials used, as stated on the 337.
If I were you I would ask my local FSDO to change the ship over to Experimental, exhibition & racing. I’d tell them you wish to do this in order to use modern glues, materials and coverings. I have done this a couple of times with no problems at all. Once your licensed Experimental, an A&P can sign off all the work with a log book entry, no form 337, no IA, no TSO’s needed!
JJ Sinclair
BTW, covering the D tube with fabric is not allowed on your type certificated ship (you must do what the manufacturer did)........bad idea anyway because after shrinking, the fabric will bridge over all low spots and the dope will form a ring at the edge of these low areas and show up as very ugly rings in your final paint Job!


I would prefer to keep this standard certification if possible. I hope that once the glider is restored, it will be a club glider, that can be rented out to club members. Possibly even in a commercial setting. Thus the desire to kept standard certification.
  #30  
Old March 19th 19, 04:57 AM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 41
Default K8b restoration

Mr Foster (John),

The articles are not posted online. If you contact me by email, I can see about getting them to you. You should consider becoming a VSA member, since there are members across the country that have experience and can help.

In short, FAA guidance material states that epoxy may be used for some repairs, but must be approved. Unfortunately, there is no uniformity to that approval between FAA offices. Since wood aircraft have not been built commercially here in the US since the 50's at the latest, thee was no incentive to qualify epoxy as a wood adhesive. Homebuilts have used epoxy for years. Properly used, it provides good joints while not requiring tight joints or high pressure. In fact, with cotton flox or other fiber material, it can actually bridge small gaps. This makes it ideal for repair without factory fixtures.

You also received comments from JJ, who has a lot of experience with glider repair, wood and otherwise. Taking it experimental fixes some issues, but I would suggest that keeping it Standard category would be worthwhile, especially for selling it down the line. However, if you want to use epoxy, it will require finding an inspector that is willing to allow you to use that adhesive for your repairs, and willing to take it to his or her FAA office to get the Form 337 approved. I have been able to find IA's to do that for me. I have typically used T-88 for smaller repairs like ribs. It will provide a better joint than the original Kaurit. One IA also did some more major repairs for me using Aeropoxy. It comes in different viscosities, so it is easier to use for some repairs.

You could also use a resorcinol adhesive. Schleicher used Aerodux (resorcinol) to attach plywood skins (but generally Kaurit (a plastic resin glue) to do much of the structure.) Cascophen or similar resorcinol adhesives have a general approval from the FAA, but you need to have tight fitting joints and be able to provide uniform, tight clamping. That can be difficult with some repairs.

There is coverage for the Schleicher gliders in the Polyfiber (Stits) STC. But if one reads the details of the STC, it says to overlap all fabric joints, which would infer that fabric should cover the leading edge D-tube. This can be done with lightweight fabric, since it does not carry air loads, and it is glued tightly to the leading edge. The Stewart Systems covering system allows the fabric to be applied just over the open bays, like the original factory installation. Ceconite using dope also allows this. Aerotech and Superflight may also do the same. I have moved from Polyfiber to Stewart Systems to make my wife happier. If does not use the MEK and other volitiles in the the other systems. Also all bu the last paint coat can be cleaned up with water.

Again, send me an email if you want more info, and please consider checking out the Vintage Sailplane Association website (http://www.vintagesailplane..org/).

...... Neal


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
TG-2 and TG-3 restoration ken bash Soaring 4 August 9th 16 02:49 AM
P-26 restoration Byker Aviation Photos 1 August 3rd 15 11:56 AM
P-26 restoration Byker Aviation Photos 0 August 3rd 15 06:05 AM
P-26 restoration Byker Aviation Photos 0 August 3rd 15 06:05 AM
P-26 restoration Byker Aviation Photos 0 August 3rd 15 06:05 AM


All times are GMT +1. The time now is 09:25 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 AviationBanter.
The comments are property of their posters.