Covering my 2+2 wings ......... finally!

[Marty57]

It's been a long road but I'm finally covering my 2+2 wings! Scratch building is not for the faint of heart. I bought my wood at a mill in Forks, Washington back in 2007. I stored the wood and started working on the wings in 20010 or so. Moved twice, retired, finished the fuselage (uncovered) and all and all the other normal life stuff in between. The ailerons and flaps are covered and stored in EkoFill waiting on paint. I had many false starts; there were so many little things I had to finish on these wings that simply weren't in the plans or in my concept of the process. Anyway, yesterday I finished up all the anti-chafe tape and today I started with some glue and the first fabric will go on this evening. I'll post progress; I hope to get through this in a fairly timely manner. Wings take about 80 hours to cover and paint so it will be a few months as I work through both wings side-by-side. I hope I haven't forgotten anything ........
Marty 57

 

[flybynite]

Kind of a shame to cover up all of that beautiful woodwork. Might want to just buy a pair of aluminum wings and put the wood ones on display.

 

[Sarpy]

It's been a long road but I'm finally covering my 2+2 wings! Scratch building is not for the faint of heart. I bought my wood at a mill in Forks, Washington back in 2007. I stored the wood and started working on the wings in 20010 or so. Moved twice, retired, finished the fuselage (uncovered) and all and all the other normal life stuff in between. The ailerons and flaps are covered and stored in EkoFill waiting on paint. I had many false starts; there were so many little things I had to finish on these wings that simply weren't in the plans or in my concept of the process. Anyway, yesterday I finished up all the anti-chafe tape and today I started with some glue and the first fabric will go on this evening. I'll post progress; I hope to get through this in a fairly timely manner. Wings take about 80 hours to cover and paint so it will be a few months as I work through both wings side-by-side. I hope I haven't forgotten anything ........
Marty 57

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Marty…A quick question hoping not to show my ignorance. I’ve built a couple sets of wood wings and always trussed and faced rib #3 just like the butt rib. Is there a reason that you elected not to?? Just curious.
Sarpy Sam

 

[Marty57]

Marty…A quick question hoping not to show my ignorance. I’ve built a couple sets of wood wings and always trussed and faced rib #3 just like the butt rib. Is there a reason that you elected not to?? Just curious.
Sarpy Sam

I think you may be looking at my tank bay? Those are the two tank straps and not ribs. The tank bay had a shear plate on the bottom and the tank lid is structural so no cross brace through the tank. Sheeted ribs on both sides of tank fully enclose the tank with ample drain holes should fuel or water enter the bay. Maybe that is what you are seeing. Here's a better look at the tank bay area.
Marty57

 

[Sarpy]

I think you may be looking at my tank bay? Those are the two tank straps and not ribs. The tank bay had a shear plate on the bottom and the tank lid is structural so no cross brace through the tank. Sheeted ribs on both sides of tank fully enclose the tank with ample drain holes should fuel or water enter the bay. Maybe that is what you are seeing. Here's a better look at the tank bay area.
Marty57
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I’m seeing it now Marty. Those four vertical elements are not the rib but rather create a support for the tank lid. I had considered your solid floor in the tank bay but had PA-18 tanks so just fabricated the drag tube through the tank. Nice work. That mahogany’s sure pretty. I had built a center section for a Hatz early in the project. My buddy said we could use it for a coffee table until we assembled the airplane.

 

[skywagon8a]

I think you may be looking at my tank bay? Those are the two tank straps and not ribs. The tank bay had a shear plate on the bottom and the tank lid is structural so no cross brace through the tank. Sheeted ribs on both sides of tank fully enclose the tank with ample drain holes should fuel or water enter the bay. Maybe that is what you are seeing. Here's a better look at the tank bay area.
Marty57
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Marty, when you shrink the top fabric, it will bow the outboard tank bay rib outward. Then the tank cover holes will no longer match the rib holes. That rib needs bracing. Two or more compression braces to the spars is generally the way it's done. You would be surprised how little the fabric has to shrink to move those holes to where you wish they weren't.

I can't see the tip rib at the outboard end of the aileron. That also needs bracing from the spar angled aft about 45 degrees to the tip bow as the fabric pulling the tip will bow the rib trailing edge towards and sometimes hitting the aileron.

 

[Marty57]

Marty, when you shrink the top fabric, it will bow the outboard tank bay rib outward. Then the tank cover holes will no longer match the rib holes. That rib needs bracing. Two or more compression braces to the spars is generally the way it's done. You would be surprised how little the fabric has to shrink to move those holes to where you wish they weren't.

I can't see the tip rib at the outboard end of the aileron. That also needs bracing from the spar angled aft about 45 degrees to the tip bow as the fabric pulling the tip will bow the rib trailing edge towards and sometimes hitting the aileron.

I’m not worried about the tank bay. Root end is a regular rib faced with Mahogany ply on both sides with 1/4”x 1-1/4” ply as a cap strip; same for the other end of the tank bay. Fabric will not pull that out of alignment; also has a 1/8” thick birch ply shear plate. On the tip rib at the aileron; I have bracing at the corner top and bottom along with inter rib bracing tape. The important thing also is how you shrink. I shrink very slowly in small increments and alternate bays and direction. I don’t think there will be much movement at all, none at the aileron bay corner. Here’s some pictures of how over built this thing is.
Marty57

 

[jprax]

Kind of a shame to cover up all of that beautiful woodwork. Might want to just buy a pair of aluminum wings and put the wood ones on display.

Seriously. You might want to cover it in Visqueen so the work can still be seen. Awesome to see the product of a craftsman!

 

[skywagon8a]

OK, just try one thing. Pull the middle of the top of the outboard tank bay rib outboard with your hand. How much can you move it without doing any damage? The shrunk fabric can do the same.

 

[Marty57]

OK, just try one thing. Pull the middle of the top of the outboard tank bay rib outboard with your hand. How much can you move it without doing any damage? The shrunk fabric can do the same.

No movement pulling out by hand; very rigid. I’ve covered 6 wood wings so far and this one is more rigid than the others; no issues with ribs moving on any of those wings. I copied the construction of the fuel bay from the Rearwing Commonwealth 180 for my tank bay; should be ok.
Marty57

 

[Gordon Misch]

Marty as you well know, wood can creep over time. Thinking a brace certainly cannot hurt, and might help??? Looks almost as gorgeous in a photo as it did in person!

 

[Marty57]

Marty as you well know, wood can creep over time. Thinking a brace certainly cannot hurt, and might help??? Looks almost as gorgeous in a photo as it did in person!

This has been nagging me for the past week. I covered the root and the cove the past couple days and tonight decided to listen to you guys and I added a couple braces to the outside of the tank bay. If I had floating nut plates for the tank cover a little give would be ok but with my fixed nutplates, I think you guys are right and I can't afford any movement. This addation will give me peace of mind. These are epoxied in place and I usd epoxy mixed with flox for a structural fillet. I may add corner blocks after I look it over when dried and then need to seal the new braces. On to covering the bottom side over the next couple days; I'm doing both wings side-by-side. There won't be any wood visible when the wings are done.

Thanks skywagon and Gordon for looking over my shoulder.
Marty57

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[Gordon Misch]

Looks nice. The 30.5 Attlee Dodge tanks require an aluminum shear from the tank bay to the next rib outboard. Though piper ribs aren't nearly as stiff as yours.

 

[Marty57]

Looks nice. The 30.5 Attlee Dodge tanks require an aluminum shear from the tank bay to the next rib outboard. Though piper ribs aren't nearly as stiff as yours.

My tanks are about 16 gallons so I just went out just three ribs. I do like the shear plate vs having the cross brace through the tank. Getting rid of the brace was my main reason for the change. I had a friend run numbers and stress issues (aero engineer) so my tank cover is structural and needed holes screws every 3" to provide the structure to the bay. Nice thing about the shear plate is I don't have any open ribs in the slipstream so stitching the wing will be the same for all the ribs. I'm going to do a double couver of the leading edges by starting at the spar and going around top and across the bottom and up the cove; same with other side the from bottom around top and to cove. The 72" fabric isn't wide enough so I'm going to cover the corner of the bow up to my first braces at the aileron bay then seam over the brace where it will have a 2" tape over, hiding the overlapping seam. I think this will work. Without a stock bow, this would work real easy but I have to be a little creative with stock tip. I guess I'll see how it all fits as I cut fabric today.
Marty57

 

[Marty57]

The corner is covered and I got the fabric on the bottom side, From leading edge around to the bottom, the fabric is just short but ends where I covered the corner. Everything will fit up nicely.
Marty57

 

[bob turner]

What kind of tape are you using to protect the cap strips?

 

[Marty57]

What kind of tape are you using to protect the cap strips?

I use hockey tape; sticks really well. I get it from https://howieshockeytape.com
I first paint the area with 50/50 Ekobond to Distilled water and let it tack up then I apply the tape. I do the same for reinforcing tape so it doesn’t fall off the fabric when I turn it up side down during stitching.
Marty 57

 

[Marty57]

Lots of progress. Wings are covered and I just finished rib stitching. Clean leading edge came out real nice; no seams or tapes. Rib tapes are next.
Marty57

 

[Oliver]

Looks really good Marty, like the clean leading edge.
Where did you put the seam?

 

[Marty57]

Looks really good Marty, like the clean leading edge.
Where did you put the seam?

Oliver,
With 72" wide fabric I use the manufacturer edge and start at the rear of the leading edge skin and go over the leading edge and around to the trailing edge. Second piece goes on the same. The seam, with manufacturer edge, is over the edge of the skin again goes around to trailing edge and into the cove. I establish a 2" overlap in the cove. The overlapping edge will be along the straight edge if the leading edge skin so it won't be noticed under the tape. With a stock wing tip bow, 72" isn't enough so I cover the corner of the wing at the aileron bay first than will overlap that and tape. Here's the diagram I made for my seminars that shows the covering plan. If you have a square wingtip this will work a lot easier. You have to get a little creative at the corner of the leading edge but this gets covered by the second payer of fabric and blends in nicely with glue. Last picture is the overlaping final seam.
Marty57