Oil Canning On Aft Fuse

Listers:

I got my wife out in the garage tonight and we started banging rivets on the aft fuse. Before I drilled the fuse I checked to make sure it was straight. I also checked again after I clecoed it back together. It seems like everything is straight...but I have some major oil canning going on between the 707 and 708 bulkheads, and also between the 708 and 710. Has anyone else seen this?

I've searched the matronics archives and it seems that other people have had oil canning on the bottom skins, so I'm not too surprised it's happening. It just seems that in my case the oil canning is quite severe. I've made a video to demonstrate. You can download it here:

http://rv.jpainter.org/oil_canning.mpg

What would you all recommend? Should I just continue riveting then deal w/ the oil canning later by possibly adding more j-channels, or should I stop now and take corrective action?

Any thoughts appreciated.

- Jamie

welcome to the club got similar thing going on as well.. so you're not alone...

you may want to finish riveting the tailcone and then put one or two J-channels across... I think I saw somewhere folks would just proseal it in, instead of riveting...

It looks like you haven't even riveted the entire section where you're finding oil-canning. I see clecoes all along the bottom.. And I thought I saw a moment there where it appears there's open holes on the right there...perhaps along a bulkhead bottom.

What about the sides? Are those riveted yet? The J-channels?

My gut says you don't have a real problem yet.

My, aren't we high tech. Not only pictures, but a video.

I agree with Bob that it might improve as you nail down more of the rivets. However, I've got a little oil canning in that same spot. I'm not too worried about it. During one of the flight tests, I'll leave the baggage wall off and look back there. If it's oscillating during flight, I'll just add a stiffener.

Dave

Yeah, you guys are correct. I haven't finished riveting the aft fuse yet because I wanted to see if other people saw this as well at the same stage I'm at. I also didn't want to continue if I was going to need to drill out some rivets to fix it. Looks like I'm going to just go ahead and finish riveting the aft fuse to see how it works out...then I'll take any corrective actions afterward.

Leave the baggage wall off ??

During one of the flight tests, I'll leave the baggage wall off and look back there.

Click to expand...

If I remember correctly, in my -6A manual, it specifically said not to fly the plane without the baggage compartment wall in place. I would think the -7 would have the same restriction. Might be worth checking into before flying without these pieces in place.
Just a heads up!
Bill Waters

One method of reducing oil canning is to have the skin hot while riveting. This assures that the skin is at it's most expanded state and at any cooler temp is will shrink. It won't cure your problem but it will help it considerably. I heated my wing skins while riveting and they are "drum" tight.
Mel...DAR

DAVE,
Bill is correct. The baggage bulkhead IS structural. Do not fly the airplane without this bulkhead in place.
Mel...DAR

Mel said:

DAVE,
Bill is correct. The baggage bulkhead IS structural. Do not fly the airplane without this bulkhead in place.
Mel...DAR

Click to expand...

Thanks. Didn't realize that. I haven't read the flying part of the manual yet. I'm still trying to figure out how to build it! I guess I'll just have a chase plane check on it from the outside.

Heating skins ??? for Mel

Mel said:

One method of reducing oil canning is to have the skin hot while riveting. This assures that the skin is at it's most expanded state and at any cooler temp is will shrink. It won't cure your problem but it will help it considerably. I heated my wing skins while riveting and they are "drum" tight.
Mel...DAR

Click to expand...

Mel--Never thought of that. How do you heat your skins? Before you begin riveting, while riveting? What do you use?

Steve

Maybe the sun, let it set outside in the 100 deg + afternoons in Texas

Just one I thought of... .... I wonder how hot it will be to handle

I meant that as sorta a joke, but somewhat serious.

I used a kerosene "salamander" type heater. I had the skins so hot that I had to drape a towel over my head to keep from getting "sunburned." I probably over did it, but like I say, My skins are drum tight. BTW a friend riveted his wing at the same time (winter) without heating (even his shop). His skins were so loose that he had to go back and add stiffeners between the ribs.
Mel...DAR

Just to update everyone on the status of the oil canning...I went ahead and finished riveting the aft fuse up to the upper j-stringer as per the plans. The oil canning is very minor now...and I understand that as more pieces get riveted on the less the oil canning will be present.

Long story short...with the pre-punched kits there's not really too much of a reason to be concerned about oil canning until a great deal of surrounding rivets have been set.

Thanks to everyone for the help.

Re: heating skins. Anyone read that article in the 21, 23, 27 --whatever it is -- Years of RVAtor? It warned against uneven heating of the skins.

I don't see the advantage of heating the skins with the matched hole parts. Expanding the sheet metal would move the holes away from the mating holes. Then the cooling retraction would return them to their original position. Seems you would just be inducing a loose condition and have it return to what would have been the original condition anyway. Now if you heated the skin, then drilled the holes, I could see this shrinking as being a benefit. But this is not the case with predrilled skins.

JMHO

Roberta