Hello everyone. I've lurked for years, but this is my first post. Unfortunately I've run into a big setback on my project (Osprey GP-4) that I feel is beyond my knowledge and skill level to repair.
Project background: I bought this project partially complete from another builder who decided he was too old to fly a plane like the GP-4 and also was worried he wouldn't be able to get insurance due to a lack of retract time. He has built and flown other wooden aircraft, and all the work he did is very high quality. All gluing was done with T88 and FPL-16A. The project sat for about 20 years before I bought it from him. During that time he moved overseas and back, and the GP-4 went with him. Perhaps it took some bumps and vibration along the way, as I've run into a few popped joints and cracks which were fortunately fairly straight-forward to repair due to their location on the plane, state of construction, and the simplicity of the joint.
As far as the fuselage goes, when I bought the project the only work that had been done was the fuselage sides had been built. So all the glue joints on the vertical faces on each side of the fuselage are ~20 years old. I did the inner skins, bent and joined the two halves with crossmembers/formers/gussets, and installed the stringers.
On to the current problem... I just returned from 3 months away, and while looking over the plane to reacquaint myself before resuming construction I discovered the splice in one of the longerons had broken. The specific joint is pictured below:
This is where the break is, but it's not broken in this picture. The plane is currently upside-down on the work table and I don't have anyone to help me turn it over at the moment. I should be able to flip it over this evening, and then I can take some better pictures.
And here is the actual break:
This part of the fuselage is where most of the bending takes place, and as you can see the joint sheared and the two pieces have "scissored" apart, and delaminated from the inner skin. The area where the break is has pushed out about 1/16 of an inch from centerline. The rest of the fuselage is still straight.
I have been discussing the problem with the previous owner, and have been doing some brainstorming of my own and these are the repair options I've come up with.
1. Make a custom curved clamp, using the curve of the other side of the fuselage as a template. Use a router or skill-saw to cut out the bad joint (just the seam itself, maybe 1/8" wide cut), and then glue in a splice using the curved clamp to hold the correct shape while the glue cures. Cut out the delaminated portion of the inner skin, and scarf in a new section.
questions/problems for this method:
- Probably need 2 clamps - one that covers both sides completely for glueing, and a second one that has a gap in the center to allow access for cutting out the bad joint and shaping the splice.
- Does the splice need to be a straight piece that is bent into place along with the longeron, or can it be a curved piece that fits without a bending force on it? A straight piece will be under the same load as the longeron when the clamps are removed, but it seems a curved piece will be loaded in the opposite direction. I don't know if this matters or not.
2. Curved clamp as in method 1, except instead of just cutting out the glue seam remove the whole section of longeron and the upright, then scarf in a new piece.
questions/uncertainty for this method:
- Back wall of the cockpit/baggage area is connected and will get in the way requiring at least partial removal, which means more cutting and splicing. A lot more.
3. Seek professional help. Load up the fuselage and take it to a repair service that specializes in wood aircraft repair/restoration. I'm also trying to track down some local EAA support, but my local chapter (Durango, CO) seems to be nonexistent. The website hasn't had any activity in years.
questions/uncertainty for this method: Professional help is probably expensive. Transporting the fuselage without damaging it further will be a PITA.
4. It's not worth repairing. Build a new fuselage.
I'm open to any and all ideas. Thank you in advance for any advice. Will post better pictures once I'm able to get the fuselage turned over.
Project background: I bought this project partially complete from another builder who decided he was too old to fly a plane like the GP-4 and also was worried he wouldn't be able to get insurance due to a lack of retract time. He has built and flown other wooden aircraft, and all the work he did is very high quality. All gluing was done with T88 and FPL-16A. The project sat for about 20 years before I bought it from him. During that time he moved overseas and back, and the GP-4 went with him. Perhaps it took some bumps and vibration along the way, as I've run into a few popped joints and cracks which were fortunately fairly straight-forward to repair due to their location on the plane, state of construction, and the simplicity of the joint.
As far as the fuselage goes, when I bought the project the only work that had been done was the fuselage sides had been built. So all the glue joints on the vertical faces on each side of the fuselage are ~20 years old. I did the inner skins, bent and joined the two halves with crossmembers/formers/gussets, and installed the stringers.
On to the current problem... I just returned from 3 months away, and while looking over the plane to reacquaint myself before resuming construction I discovered the splice in one of the longerons had broken. The specific joint is pictured below:
This is where the break is, but it's not broken in this picture. The plane is currently upside-down on the work table and I don't have anyone to help me turn it over at the moment. I should be able to flip it over this evening, and then I can take some better pictures.
And here is the actual break:
This part of the fuselage is where most of the bending takes place, and as you can see the joint sheared and the two pieces have "scissored" apart, and delaminated from the inner skin. The area where the break is has pushed out about 1/16 of an inch from centerline. The rest of the fuselage is still straight.
I have been discussing the problem with the previous owner, and have been doing some brainstorming of my own and these are the repair options I've come up with.
1. Make a custom curved clamp, using the curve of the other side of the fuselage as a template. Use a router or skill-saw to cut out the bad joint (just the seam itself, maybe 1/8" wide cut), and then glue in a splice using the curved clamp to hold the correct shape while the glue cures. Cut out the delaminated portion of the inner skin, and scarf in a new section.
questions/problems for this method:
- Probably need 2 clamps - one that covers both sides completely for glueing, and a second one that has a gap in the center to allow access for cutting out the bad joint and shaping the splice.
- Does the splice need to be a straight piece that is bent into place along with the longeron, or can it be a curved piece that fits without a bending force on it? A straight piece will be under the same load as the longeron when the clamps are removed, but it seems a curved piece will be loaded in the opposite direction. I don't know if this matters or not.
2. Curved clamp as in method 1, except instead of just cutting out the glue seam remove the whole section of longeron and the upright, then scarf in a new piece.
questions/uncertainty for this method:
- Back wall of the cockpit/baggage area is connected and will get in the way requiring at least partial removal, which means more cutting and splicing. A lot more.
3. Seek professional help. Load up the fuselage and take it to a repair service that specializes in wood aircraft repair/restoration. I'm also trying to track down some local EAA support, but my local chapter (Durango, CO) seems to be nonexistent. The website hasn't had any activity in years.
questions/uncertainty for this method: Professional help is probably expensive. Transporting the fuselage without damaging it further will be a PITA.
4. It's not worth repairing. Build a new fuselage.
I'm open to any and all ideas. Thank you in advance for any advice. Will post better pictures once I'm able to get the fuselage turned over.
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