N83002 Fuselage Repair

bsafran · Post by **bsafran** » Sat Dec 31, 2011 11:29

This topic is dedicated to a man who devoted his life to helping the Aeronca community. He has received the Charles Taylor Master Mechanic award for over 50 years of continuous high quality aircraft maintenance along with the Wright Brothers Master Pilot award for a matching 50 years of being a safe pilot. Along the way, he also got inducted into the EAA Hall of Fame. Who else could I be talking about other than Bill Pancake. Beside being a walking, talking encyclopedia of Aeronca facts, he also built a jig to help him with his countless repairs to 7AC Champ fuselages. That jig passed through several hands until it landed in our welding shop in northern Ohio. Since so many Champs out there are needing to be rebuilt, I thought I would take the opportunity of using the website to take everyone through a typical Champ fuselage repair. This badly damage fuselage arrived this last week. It came in two pieces, the front part in a small trailer and the rear in the back of a pickup truck. Not only do we need to splice these two halves together, we also have to correct several previous repairs that have knocked the alignment out of whack.

bsafran · Post by **bsafran** » Sat Dec 31, 2011 11:37

The first thing we do is to attempt to set the fuselage on the bottom frame of Bill's jig. (The FAA says I should call it a reference fixture!) I say "attempt" because so few fuselages have remained trued out over their lifetime. A ground loop here, a rusted tube there and each fuselage starts taking on their own personality. What might look like a perfectly sound frame starts showing all its warts when compared to the blueprint outline that Bill copied with his jig. It becomes easy to see what tubes are in line and which ones have wandered.

bsafran · Post by **bsafran** » Sat Dec 31, 2011 11:49

Even planes that have no damage history can be out of alignment. One area we always look at is the door side of the fuselage. The easiest way to check is to measure the distance between the front spar fitting on top to the strut attach fitting on the bottom of the fuselage. The distance on the left side should match the one on the right because that's how they rolled out of the factory. Over time (and a few hard bounces) the structurally weaker right side compresses slightly and you might find that your door doesn't seal as well as it should. We made a fixture that bolts into the strut attach fitting and should fit into the front spar fitting as well. You can see by this picture that the right side is quite a bit off. Since Aeronca made a fixed length strut with no adjustment possible, this small difference between the right side and left will tend to make the plane fly just a little out of whack.

bsafran · Post by **bsafran** » Sat Dec 31, 2011 17:22

One of the parts that have worn out with use over the decades is the bushings that make up the hinge points. During a rebuild is the best time to check them. They are easy to replace and will eliminate any slop between the control surfaces (horizontal stabilizers and elevators) and the fuselage and rudder. Take a new hinge pin (Bill Pancake could probably recite the part number!) and see if there is any wear in the bushing. If it is tight and you can't wobble the pin, no problem. If the bushing interior looks egg shaped or the pin can rock back and forth, it's time to replace them. Please don't look at the picture and comment that the pin is too short. It's what I had in my pocket when it was time to take the picture!

bsafran · Post by **bsafran** » Sat Dec 31, 2011 17:38

There are several ways to repair rusted or damaged tubing. One way is an external casing of the damaged tube with a larger tube and the other way is to slide another tube inside the original. (Or you could just cut out the entire tube and replace it with new material) The external fix is the easiest and probably most common type of tube repair. This is fine just about anywhere in the fuselage except along the bottom tubing that makes up the longerons and gear area. Those tubes are where the fabric directly contacts the fuselage and the external repair interferes with a smooth line. If you put your fabric on overtop one of these repairs, you have to be extra careful with the cover process. You have to be VERY cautious when sanding the tapes because it is so easy to scuff up the fabric right at the edges of the repairs. Even if you do an outstanding job, the tubing repair will be obvious to everyone who looks down the sides of your airplane. The repair in the picture will be cut out and redone so that the owner will have an easier time with his recovering job.

bsafran · Post by **bsafran** » Sat Dec 31, 2011 18:00

The guys on the Aeronca assembly line along with the engineers never in their wildest dreams figured we would be still be flying their airplanes in the 21st century. They assembled the planes in the best way they knew how and then moved on to the next plane on the line. Priming and painting the basic fuselage just was not a long term concern. However, Bill Pancake has discovered an area in the intitial construction that needs addressed any time you are rebuilding a Champ. The door sill frame which makes the shape of the door was welded on before any primer was sprayed. It has laid unprotected since the 1940's and unfortunately rust and corrosion have moved in. He suggests that everyone remove the door sill plate and look underneath for problems. We do that for every fuselage that comes through the shop and guess what? Mr. Pancake was right! Every single plane has had serious corrosion, many of which required replacement of the tubes hidden by the door sills. The first picture show a typical area where the sill is tack welded. The next pictures shows how to cut the weld to remove the sill. We are using a pretty hefty cutting disc in the picture, but the best final cut should be done with a smaller dremmel cutting tool.

bsafran · Post by **bsafran** » Sat Dec 31, 2011 18:15

This fuselage has seen better days. Not only was it torn into two pieces, it's easy to imagine that some tubes were bent as well. Some twists are pretty obvious to see, some are more subtle. However, one thing to keep in mind is the design of the bridge type structure of the 7AC frame. A strong shock in one area travels the entire length of the fuselage which is made up of different strength tubing. Don't assume that the visual damage to one part of the fuselage is contained to just that part. You just might find a weaker tube bent downstream of the impact point where you might never have thought to look. A straight edge works wonders to show off a problem that the naked eye might not notice. It is obvious in this picture that the overhead tube where the trim knob fastens has a sway to it. Tubes like this can be straightened without welding, but please inspect the weld at either end of the tube. One of the welds just might have a small, difficult to see crack which could ruin that flight around the pattern several years later.

David Johnson · Post by **David Johnson** » Sun Jan 01, 2012 08:00

Brian, Excellent information! Thanks for posting. David J.

williamc · Post by **williamc** » Sun Jan 01, 2012 09:43

Brian,
Do you have a price list or hourly rate for different parts of the process? For example, what would it cost for putting in a champ fuselage in the jig and checking the alignment with no repairs. I know it would be impossible to know exact cost but it would be nice to know some ballpark numbers. It could make the difference between repairing and parting out a project. When someone has to come 600 + miles, it would be nice to have some idea of cost. Thanks and Happy New Year.
Bill

rkittine · Post by **rkittine** » Sun Jan 01, 2012 19:19

Thanks Brian,

This is great information. I doubt that I would ever take on a project like this, but I love watching you go through the process.

Ciao - Robert

kyleb · Post by **kyleb** » Sun Jan 01, 2012 20:43

williamc wrote:Brian,
Do you have a price list or hourly rate for different parts of the process? For example, what would it cost for putting in a champ fuselage in the jig and checking the alignment with no repairs. I know it would be impossible to know exact cost but it would be nice to know some ballpark numbers. It could make the difference between repairing and parting out a project. When someone has to come 600 + miles, it would be nice to have some idea of cost. Thanks and Happy New Year.
Bill

One thought: There are quite a few Aeronca fuselages spread around the SE. Rather than everyone driving a thousand miles carrying one fuselage apiece, why not get a big trailer and carry 5-6 fuselages in one trip? That would make it cheaper, less time consuming, etc.

If anyone is up for that kind of thing, let's talk...

rkittine · Post by **rkittine** » Mon Jan 02, 2012 12:45

What kind of cost would be incurred (Cost to owner, not your cost only) for a repair of this magnitude? Does anyone make a new fuselage assembly like there are ones available for a Cub? Would it make more financial sense to make a new one from scratch with all new material?

bsafran · Post by **bsafran** » Mon Jan 02, 2012 16:52

Bill Pancake suggests that everyone undergoing a Champ restoration remove the door sill frame to see the material underneath. The tubing covered by the door sill was never primed or painted at the factory and it is inevitable that rust will creep in over time. The first picture shows why Mr. Pancake is right. Every single fuselage we have worked on has had some level of corrosion and N83002 is no exception. You can see the rust on every tube hidden by the door sill. This plane is one of those "good news, bad news" stories. The good news is that the surface rust doesn't penetrate deep enough to require replacement. The bad news is shown in the second picture. The tube that holds the door hinges is cracked in two places where it meets the square tube making the bottom of the door frame. That tube will have to be replaced.

bsafran · Post by **bsafran** » Mon Jan 02, 2012 17:04

The tube that supports the door hinges in this plane is cracked and needs to be replaced. The two cracks are too close to the surrounding cluster of tubing to be repaired, so out it comes and a new tube goes in. If you look at one of the first pictures I posted on this thread, you can see where the distance between the main spar attach point on the fuselage to the strut attach point is almost a whole bolt hole off. Usually, when we cut the tube with the door hinges, there is a loud "TWANG" and the fuselage springs back to where it was originally formed and the spar / strut measurement is almost back to normal. That didn't happen with this fuselage. When the tube was cut, everything stayed pretty much where it was so we knew there were other issues with this airframe.

bsafran · Post by **bsafran** » Mon Jan 02, 2012 17:21

The step for climbing in the cabin has been a real pain for us on almost all of the fuselages we have worked on. If it is original and untouched, it is most likely rusted, weak and usually needs replaced. If it has been repaired in the past, it has proven to be harder to correct than a rusted original. The step on this plane looked a little odd to me when I first looked at it. I knew at first glance that it would have to be replaced. It was too short, had the wrong diameter aerodynamic tube and was cocked at the wrong angle to even fit into Bill Pancake's jig. To help settle the fuselage down into the jig, I took a hacksaw and cut off the step. The first picture shows how far off the step was from being the right length and alignment. The second picture show why I laughed when I sawed off the step. I knew the support tubing looked odd, but most repaired steps have unique repairs. I've seen the streamlined tube of the wrong size or replaced by round tubing. This was the first time I had seen one tube completely surrounded by another larger tube. We had a good laugh and then ordered the right material to be installed later.