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Why not bond lines?

Mconner7

Well Known Member
As a 10 year owner of a Tiger (50 years of bonding vs riveting), I marvel at the thousands of rivets it took to stick my -10 together. I have wondered how many hours of construction might be saved if we added bond lines and reduced the number of rivets by a factor of three or four?

I was going to make a crack about adopting newer and simpler construction techniques but Jim Bedee was gluing planes together in the 60’s and they are flying still.
 
Bonding aluminum is a fairly tedious procedure. Not really practical for the homebuilder. John Monnett tried it with the Moni wings and ended up changing to rivets.
 
Your Tiger was bonded together in a factory under carefully controlled conditions. The same thing CAN be accomplished in a Homebuilder’s workshop, but can also be done incorrectly, and no one will be able to inspect for the difference…
 
I can't speak for Grumman back in the day, but in the modern era, all the metal bond that is done on the jet side of the house in the Cessna and Beech factories is done with some crazy expensive equipment, like autoclaves big enough to drive a truck into, CNC ultrasonic inspection after the fact to look for voids, stuff like that.

It's out of scope for the average home builder, and just not that practical for most certified prop singles. It's cheaper and easier to build with rivets, not to mention easier to repair in the field, which is why they're still building Bonanzas and 172's with a good old 3x rivet gun.
 
I'm building an RV-3B and am now hanging the horizontal stabilizer and elevators on the fuselage.

I bonded and riveted the entire fuselage, using structural bonding. First, I'd bond a joint. Then when the glue was fully cured, I'd clean the joints up and rivet - the riveting wasn't concurrent. Here are the main take-aways from that experience:

1. It's a great way to triple the build time, because the prep is all labor-intensive. I had to do all the prep for riveting plus all the prep for bonding. The cost goes up too, but not as much. I'm not exaggerating the time factor here, either.

2. Almost every skin joint required one or more helper. I could not do these myself - and this was separate from the riveting.

3. I had to be careful and consistent with the process.

4. Once bonded, the joint was permanent - there were no options to unrivet something and do over. It had to be done right the first time.

5. When done perfectly, the finished joints look great. When done with less than perfection at every step, the joints reflect that, visibly.

So would I do it again?

Maybe, maybe not. Frankly, I don't see any reason to do that, but then again, I'm now too old to do it again anyway, so it's moot.

What were the main advantages?

When done very well, the joint appearance is excellent.

I didn't need clecos once the bond line had cured.

You can take a look in my VAF build blog for more information if you want. I think around post 300 or so is when I began, not sure.

Dave
 
It Was a Homebuilt at First

Worked for a Grumman dealer for a couple of years. The story I got was that Jim Bede planned the airplanes as a bonded homebuilts but decided that gluing aluminum properly was beyond the skills and resources of homebuilders so they ended up being built in a factory. I was fortunate enough to be sent to the Savannah Georgia Grumman factory to pick up a new AA-1C Lynx and got a tour of the facility. I’d had visions of people with paper cups and popsicle sticks gluing these things together and that’s exactly what I found. Of course, all those bondlines had already gone thru several steps of sanding, etching, cleaning and prepping before they actually got glued with the odd anti-peel rivet here and there, and then they were clamped together and placed in an oven for final cure. Having been told that aluminum is hard to bond along with extra shear loads resulting from widely different coefficients of expansion between epoxy resins and aluminum, I am amazed and respectful of how well these airplanes have aged. I saw a couple of debonded trailing edges on early AA-1 airplanes. Grumman cured that with tight-fitting, bonded channels over those trailing edges. I don’t recall seeing any other problems, even in areas that showed up in Grumman’s Service Letters. I flew all the single engine Grummans and never had a thought about the glue. In fact, I really like the Grummans. The Tiger is a great airplane even after getting past the exaggerated performance numbers.
 
I don't think the BD-1 was planned as a homebuilt. When I was a kid, Dad worked for Douglas Aircraft around the corner, and brought home a copy of something that might have been called "Aviation Daily" almost every day. Once there was a paragraph about the BD-1. It was essentially a Jim Bede press release - he was good at publicity even then.

It said that the BD-1 would cost $2,500, be powered by a Continental 65 hp engine, and cruise (I think) at 125 mph.

Subsequently I'd read about his difficulty getting financing. Finally he lost control of the project and when it came to market it had a larger engine and a larger price. But that took years. By then I'd given up waiting for it.

Dave
 
Nooooo!

After 42 years in the heavy jet industry, I have seen about every type of construction..Fokker and Airbus are notorious of bonded structure, but Fokker in particular did a ton of metal skin /stringer joint bonding. It was a process not replicable "in service" when doing repairs and modification, as the environment for bonding is extremely critical. At my day job, we do as significant amount of metal bonding, but it is usually sheet-to-sheet stack-ups rather than structural joints. I'm a fan of rivets for both build simplicity and reparability.
 
My first thought is, how would I know I did it right? Even as a hobbyist I can look at a rivet and see that it's right with a good degree of confidence. OTOH I've done plenty of epoxy work that looked terrific right up until it failed.
 
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