Bending the Fuselage sides

[dougm]

OK Folks, I have all the various cross members in place from the rear 'pit (Sta. 84.00) forward and I'm ready to bend the aft portion towards the tail. The more I look at it the more I grow unsure of just where to bend it... The plans are not entirely clear. From what I can see on the plans it looks like the top longeron bends at approx. 85" (1" aft of Sta. 84) and the bottom longeron bends right behind Sta. 82.5. However, this would mean those points are not directly above/below each other which means the bend would not be in the vertical plane... wouldn't that result in the side not staying flat on the table?

Exactly where have you folks made the bends? On a side note, I heated and test bent a piece and it kinked, so what's the trick to not getting it kinked? I really don't feel like packing sand in the tube.

[Dave]

Hi Doug

Will have to review my notes to determine bend points but will do so tonight and post info. For me, the secret to the bend was to heat a small area and bend it a little, then heat an adjacent area and bend it, etc. It really was not too severe a bend as I recall and it came out OK. I will try to take a couple of photos of the bends in my fuselage and post later tonight. More to follow.

Dave

[dougm]

Thanks Dave... That will be a big help.

[Dave]

Hi Doug

Sorry to be so late but got a call from FSDO and they want my DAR renewal paperwork, like yesterday, so I had to drop everything build the package.

Looked and do not have any pics of the bending process and wife tells me the batteries in camera are dead. Will try to get some photos tomorrow.

I remember bending the sides and although it appeared to be daunting, it turned out to be no big deal. I bent the top longeron right at station 84 (aft of the cluster) and the bottom longeron at station 82.5. As best I can tell, each longeron is bent in two places, the above referenced stations and again at station 151. Neither bend is very severe (only a few degrees). You can scale the print to determine the angle, etc if you want.

I securly clamped the fuselage side to my work table back as far as station 151, heated the longerons (both top and bottom at same time) with O/A torch, and gently bent longerons up. It really helps to have two people here, one to keep the joints hot, and one to bend the longerons. I calculated the distance off the table beforehand and bent slightly past to account for springback. I also had a piece of wood cut to the right dimension to use as a gage and to put between the longerons (at the tailpost position) and the table to let the bend cool. I also slipped a thin piece of steel between the longerons and my table before heating the longerons to avoid burning the table. I am too damned old for all the excitement a burning building generates. By keeping both the top and bottom longerons the same distance above the table You can be sure the tailpost will be vertical when you weld it in.

I then unclamped the sides as far foreward as station 84 and 82.5 and repeated the procedure for the bends that occur at station 84 and 82.5. Again, if you raise both longerons the same height above the table, you will keep the tailpost square. Another plywood gage is helpfull here to get the right distance above the table and to keep both longerons the same height above the table. Because of the slight bends required, I did not have any problems with tubes kinking and did not use any sand or other filler.

Don't worry if everything is not exactly perfect. You can make adjustments when you clamp the fuselage sides in their final position and weld in the tail post and all the horizontal braces. You will want to jig up and true up everything at this stage because after the tailpost is welded in things start to get rigid.

My advise is just do it. I think it takes longer to describe the procedure than to actually bend the tubes. Go slow and carefull but I think you will find it is no big deal and you will be pleased with the results. As an old guy once told me, "strive for perfection but be willing to accept just a little less". Obviously you want a good looking bend but remember it is all inside the fabric when you are done, so you are the only one who will ever know if you have a slight ripple.

Hope this makes sense. If not, maybe some of the other builders who are past this stage can offer better advice.

Good luck and don't forget to have fun. Thats what this is all about.

Dave

[JBMoore]

I didn't build a classic but here is what I remember about my LB-1....
I built each side up through tack weld and then placed them on my table top longeron down. I drilled a hole in the table for the tail post and fixed its position square and plumb. I laid out the fire wall distance from the tail post and then started at that end installing all of the cross tubes until I got to the stations behind the pilot's seat, making sure the sides stayed square. CB-1 plans had both of those stations pretty close to the same dimension but I moved the top one back 4" so the bends aren't in the same vertical plane. Next I laid out the tube centerline for the top longeron from that station to the tail post and put small wood blocks along the way for reference. Mistake on my part... I laid out the center line of the longeron to go through the center of the tail post diameter and should have made it tangent to the tail post. This made the distance inside the "VEE" extremely tight and I almost didn't have enough clearance for the hardware. From this point, I applied heat to station and gently pushed the the tube over to the reference blocks and held it there until it cooled with other small blocks. I did both top longerons first and then did the bottom ones last; cutting and fitting the tube ends to the tail post as I went along.
A hint about bending. Heat the tube to a cherry red color and heat from the inside of the bend. If you heat only the outside of the bend, the metal will stretch and become thinner in that area.

Good Luck!

Jeff Moore

[dougm]

Dave, Thanks for the feedback... sounds like you bent your sides prior to assembling the rest of the fuse???

Jeff, Thanks... so to clarify, the bend that is immediately behind the rear 'pit, where did you make the bend? Immediately behind the cross tube top & bottom? Which, as you said, meant the bends are not in the vertical plane? This didn't cause any issues?

[JBMoore]

As close to the clusters as I could get, with a generous radius, and I didn't have any issues.
Attached is a picture of me at Blakesburg a couple of years ago. You can see a line behind my head where the cockpit aluminum meets the fabric. The top cross tube/cluster is right there and the bottom is where the plans have you locate it... remembering the LB/CB-1's have a more flat side than the Classics.

Jeff

[dougm]

Thanks Jeff. that helps. I've emailed a couple folks of line as well... I'm starting to feel more comfortable with moving ahead on this.

[dougm]

Success! Thanks to all for the advice and a special thanks to Scott Plischke for the phone call and detailed info!

[splischke]

Doug,

Looks great. You had it all figured out before you called but I'm glad to help.

-Scott