Restoring a 1946 Aeronca Champ

This is my Champ that I bought in 1985 and have kept based at Anoka Co., just north of the Twin Cities in MN. Over those years I’ve had a lot of fun flying it around. Cruising at 75 mph it burns 4.2 gallons per hour so it’s affordable. It’s the perfect little plane for summer evenings and grass strips. But for some time now I’ve been thinking about doing a complete restoration on it and the time was right. I had a number of reasons for doing this rebuild. Although it looks good from a distance it has numerous patches and small dents in the cowling area. Nothing unusual for an airplane that’s nearly 60 years old. The fabric was still in good shape but some of it was getting to be over 30 years old. I’d gotten tired of the paint scheme and a rebuild would allow me to bring it back to original colors and condition. Since I’m keeping this airplane, my choices were to rebuild it now or rebuild it later. And heck, I just wasn’t getting any younger.

Just after it’s last flight, March 26 2004.

For those of you unfamiliar with this plane, it was Aeronca’s answer to the famous Piper Cub. It’s fuselage is steel tube with wood formers and stringers The wings have wood spars and aluminum ribs, all fabric covered. In the early 90’s my IA and I majored and converted the engine from a Continental A65-8F to a A75-8F, other than some parts changes it’s mostly just a RPM increase. About that same time I had the main oleo gear rebuilt by Safe Air Repair in Albert Lea, MN with all new internal parts. Other than those improvements and some other minor ones over the years it’s basically the same as when I bought it.

My first step was to rent scales to weigh it so I could find out what the actual empty weight was and compare it to afterward. One of my goals was to keep everything as light as possible throughout the process. With a gross weight of only 1220lbs weight is very critical. I’m not planning on adding any extra instruments or equipment that wasn‘t installed from the factory. Only an intercom to go with my handheld is planned.

Stripping the fabric off the wings while they were still on the fuselage was relatively easy. After removing the wings I completely disassembled the left wing, leaving the right side intact for a pattern. What I found in the left wing were some small repairs on the spars and numerous ribs that were bent and or had patches. Every aileron rib had a factory nose rib grafted on with scrap aluminum angle. This aluminum angle was just cut to fit with no sharp corners or rough edges removed with a file at all. Apparently whatever happened to be laying on the workbench was used for repairs, with a combination of AN and pop rivets. Some AN rivets were driven to the point of being smashed flat or just barely driven at all. The workmanship was very disappointing! There was no way I was going to put those parts back in my plane. Through the years when it was recovered they just re-varnished the spars and zinc-chromated the steel parts with a brush. Probably very little if any disassembly was ever done. I’m sure this was not uncommon for an inexpensive airplane in its day.

Looking at a aileron rib at the front spar opening. Assorted rivets and scrap aluminum angle were used to attach a factory nose rib. All 5 of the aileron ribs in the left wing looked similar to this.

From the leading edge looking aft at the right main spar fitting and butt rib, notice the different layers of zinc-chromate. This is the same spar in the last picture at the end of this article.

I made a list and ordered the spars, ribs and other parts from Safe Air Repair. The spars were then epoxy varnished. The ribs that were too bent or patched were replaced. Two ribs that had small cracks were re-patched with the proper material and rivets, and were saved. Then they were cleaned of varnish with lacquer thinner and prepped with Alumi-prep and epoxy primed. In all, 9 out of the 15 ribs in the left wing were replaced.. All new trailing edge was ordered to go with the new leading edge I’m making. New steel wing tip bows will also have to be replaced because of rust at the trailing edge. All the metal brackets and fittings were bead blasted and epoxy primed or Zinc-chromated. I wanted everything in the control system to be new so cables, rod end bearings, bushings and aileron bearings were installed. Every bolt, nut and washer in the wing was replaced. Only the clevis tie rod terminals for the internal tie rods were cleaned, primed and reused. I assembled the left wing using the right side and the service manual as a guide. I’m making a fixture to hold the wing spars in alignment while I “trammel” or square the tie rods in the 4 wing bays. After the bays are trammeled the rest of the bolts will be tightened. Then the .016 aluminum leading edge will be attached to the ribs with ¼” PK screws and the ribs will be nailed to the spars.

Aeronca didn’t use rib stitching to attach the fabric, they used a system of ¼” PK screws to attach the fabric to the ribs and tail surfaces. That’s what gives Champs and Chiefs the characteristic bumps on their wings. The new ribs came pre-punched with 1/8” holes for the pop rivets that attach the fabric to the wings like the Citabria. The older original ribs have smaller #44 holes for the ¼” PK screws. It’s my understanding that pop rivets are not approved on the old ribs because of the edge distance with the bigger holes on the rib flange. I didn’t want to use a mixture of pop rivets and PK screws because even under the fabric the bumps look slightly different I know I’m fussy, just ask my wife. I solved the problem by moving all the holes aft about 3/8” and drilled new #44 holes to stay with the original type screws. Altogether, there are about 900 holes in both wings.

Picture shows the right wing. Ribs were lined up straight, masking tape was used to mark lines where holes needed to be drilled. Old ribs were primed and new ribs were left bare.

Most of the leading edge sections had some small dents, probably from hail damage and wear and tear. Those years of being tied down outside take their toll. Since it will always be hangared and to keep weight down I’m making new leading edges out of .016 2024 aluminum, as were the originals. These airplanes are too valuable to be left outside anymore so I’m not to worried about that kind of damage. The tip bows are made out of ½” steel tubing with small brackets, and screwed to the last full rib. I haven’t decided if I want to find a way to make my own or buy them new.

Fall 2005, left wing, needs leading and trailing edge and tip bows. Old ribs are primed and new ribs were left bare.

I know most of this sounds like the wings were a complete mess concerning the previous repairs, and to a certain extent they were. I knew that I needed to replace some parts but just not quite as many as I thought. Like I said before these planes were sometimes kept on the farm and fixed on a budget with whatever they had around That’s just the way things were many years ago.

In the 40’s and 50’s this plane was in the Rockford IL area, it moved to the Dubuque IA area in the early 60’s and moved to MN in the mid 60’s. Besides being owned privately, this plane was used as a trainer for a number of years in the 40’s and late 50’s. On some of those days they flew it up to 6 hours per day, even in January. All that wear and tear adds up over the years. So some of what I found wasn’t to surprising, considering the age of the airframe. It’s all part of a restoration on a 60 year old plane.

Since this plane is all that I can afford I plan on keeping it. With the price of fuel and since it only burns 4.2 gallons an hour it’s worth holding on to. I want this plane to last, so that’s why I’m trying to do the best job that I can with my skills and resources. I know my work won’t be perfect and I won’t win any awards but I want to be proud of what I’ve done. Also years from now I don’t want anyone to open the airframe and be disappointed with my workmanship.

Another view of the left wing looking outboard at the aileron. About 70% of this wing is new material.

Because the hangar I’m in is unheated, work out there slows down dramatically each fall. You try working out there in the cold in January. So assembly of the left wing started in the spring of 2005. Once the spars are varnished and everything is primed the actual assembly goes quickly. It’s the trammeling, aligning and fitting of the leading edge that takes time.

In the summer of 2005 I started the disassembly of the right wing. Overall this wing looked to be in better shape. It had less repairs and was covered at a later date by someone else. But when I removed the front wing root fitting the spar under it looked unusual The wood on the end was dished in and I saw a crack. The more I sanded the old dope off the blacker the wood got. There was evidence that someone had welded on the steel fitting while it was bolted on the wood spar. Part of the wood was burned away with scorch marks left behind. Whether the crack was the result of welding or happened at a later date is impossible for me to determine. I was hoping that I would only need to replace the two spars in the left side until I saw the crack All I could do was bite the bullet and spend whatever it took to make things airworthy. Spars are “somewhat” important to the integrity of the structure. This wing only needed 4 ribs to be replaced and the leading and trailing edges Of course all the hardware just like the left side was replaced.

So two new spars were ordered from a different supplier at Oshkosh 2005. When they arrived at the end of the month, I looked them over and found a major problem right away with one. The front spar already had a crack about 6” long on the top face, inboard about 18” from the butt end. Somehow it slipped through inspection Sometimes these things happen, you just deal with it and move on. I called the company and they immediately agreed to replace it. The only problem was they had a hard time getting another supply of aircraft spruce. A 1”x6”x16’ piece of aircraft spruce is expensive and rare. It took them a few months to get the spruce from their supplier. By the time the replacement spar arrived in December, it was to late to varnish it until warmer weather. I know it’s frustrating but what are you going to do.

Front face of original right main spar, note wood that appears to be burned away. There was a crack from the damaged area to the nearest bolt hole. Outline of the spar fitting is visible.

Well that’s the latest as of March 2006, another update later in the year.

Restoring a 1946 Aeronca Champ

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Updated April 2006