Couple questions on tail feathers

[ddeaton66]

Good evening,
I am brand new on here, just got my plans today but have been in research mode for months. I have a couple quick questions about the aluminum tubing on the tail feathers. (1) It seems that there is always some variation in at least one bend radius to accomplish the overall dimension. So is the bend radius important or just the overall dimensions? If a tubing bender was used (like a JD Squared) so long as the outside dimensions were accurate could the same bend radii be used? (2) Has anyone bent, coped, and welded the 6061 tubing rather than use the sheet metal gussets and pop rivets?

Additional on the fuselage, likewise has anyone bent the longeron tubes cold with a good bender, then jigged and welded up the fuselage post-bend?

TIA,
David

[ArcticDave]

Hi David, 
Welcome to the show!
I'm sure you can get more qualified answers than mine, but this is what I know...
Welding the aluminum: the general consensus being....don't.  The leverage applied to the welded joints could cause cracking of the host tubing in the HAZ. In my experience, welded aluminum would need thicker/larger tubing to survive. The Backyard Flyer from the folks over at Valley Engineering uses welded aluminum throughout, but if you look...it's much bigger OD tubing. 
Radius of the tail bends, go for it! As long as the amount of surface area of the tail isn't altered that much. 
Cold bending the longerons? I bent mine in place with heat. I read another builders log awhile back and he bent them cold and I believe he regretted it. It was easy enough to lift into position when red hot and the bend radius is small enough it is captured and secured by the landing gear/wing strut fittings welded at station #2 & #3. 
Hopefully someone else will chime in that can explain it better than I. 
Have fun building and post up a build thread. 

~Dave~

[Tom XL-7]

Welcome, David.
The best advice anyone should give you is to build to the plans. So there is your best answer.
You just got your plans. You need to spend a lot of time with them. Learn them. If you want to change things, those have to be your choices.
For your reasons.  The result must be your responsibility.
 Next advice is if you have not seen a flying example find one. Spend a day traveling if required, or two. 
 I will answer your questions from my point of view but I do have a few for you. How do you intend to weld? Are you a tig welder? Do you own a welder?
I can guess you may live in California based on our 3 hour time difference. If so the good news is there are very good builders and examples out there. The bad news, that is a very large state. 
 So here we go.
I have asked the radius question myself. Leonard bends tube by hand, with the tweak a little move a little and repeat until you get it method. So he can get anything he wants. He can even change things up as he goes. I want some help. But will probably jig something up out of scrap on hand. It can be as simple as screwing a drywall bucket to your table and bend around it. That will generate something around a 6-inch radius. As to whether you need various radiuses draw one of the corners to scale or full size and see for yourself what the overall difference is between a 5 and a 6 in the big picture.
 I know of no builders who welded the alum tubing together. I am not sure if you would gain anything for the effort. The wimpy little gussets may be stronger.
You are going to use the gussets at the ribs anyway unless you can weld that very thin rib to the tubing. Again the only way to know would be to mock up test pieces and destroy them. I think the gussets would win a strength test. The tail is covered and can't be thoroughly inspected. What you do must pass the test of time.
 The idea of bending the 4130 has been done. You will have a challenge figuring out the indexing and the total bend. The front bend and the rear bend or any others you add will not be the same. These are not flat bends like the tail. The go up and in. that's why I asked about welding are you trying to avoid a heated bend. Aircraft structures are designed with straight pieces, point to point in clusters. The curvey stuff adds eccentric loading. As such you are changing the structural design. I thought about doing the pre-bending myself but have decided it easier and more accurate done with the torch.
 Please do not read any of this as negative. Your questions are good and normal. If you don't have questions you're not thinking about it. Keep any questions coming.
 Good building
Tom XL-7

[ddeaton66]

Thanks to everyone for your responses. To answer a couple questions from you - yes I have a TIG welder and can weld aluminum but just because you can do something, doesn't mean you should. Just trying to glean from others experience and it seems that the plans method is not only acceptable but probably the best method. I don't intend to stray from the plans much but was just curious about a few things. The cold bending of the 4130 seemed a natural thing for me, I have fabricated tubing and rarely heat it to bend, just use a quality bender. The means to determine the bends is certainly a learned operation, I have some software to assist

I have used the sand and scrap cut radii method on several projects in the past, just not on structural items and I have a bender available but with limited radii dies so I thought it might be easier to perform repeatable bends with it.

I am excited and will pour over the plans many times, I hadn't thought of finding a flying example close but I will try to do so as I am sure it will offer many insights. I am in KY though, I must not have my settings set properly for my timezone.

Has anyone else moved the fuselage bend aft of the gear/strut attach points like "LegalEagleAirplane" it seems like potentially a better approach than bending the attach fittings after - thoughts?

Looking forward to being an Eagle owner - much great information on here, thanks to all for sharing!

David

[Tom XL-7]

The time thing is just the way it is. I am in Pacific time zone as well. Right here in Ohio. So I saw something that wasn't actually our reality. We were set up in Ca and the program uses that time to operate. Makes sense now. 
 regardless of which model one is building the longeron bends should be as close to station 3 as possible and should be of a minimum radius.  
While you want to avoid collapsing the inner wall of the bend it should be as tight as you think you can get.  
  I believe the method on the legal eagle was set station 3 bottom tube to the longerons, heat and bend your tubing in. Fabricate the bottom on the table and heat both tubes at the same time and raise the tail into position.
 That trick may require two torches and two people.  On the XL one heat and a single bend was utilized per tube. In many respects, I like building on a table but the three longeron design puts a lot of this build in 3D regardless.
 The gear strut attach plates will be one of the last things on your fuselage. Those longerons must be bent to complete the upper portions of the aircraft. The bending of the plates is just trying to conform a flat sheet to a tube section with the goal of better welding. The idea of moving the bends behind station 3 on purpose should be avoided. Remember the ideal is straight into the cluster. Our bends are sort of a forced error. 
 Tom XL-7

[scottiniowa]

Mr. DD  
    I think you will find the Eagles falling into the category of “ many ways to build-most work well “  Simply being, you can’t go to far wrong if you stick with the basics.

These have been covered pretty well. But I will touch just a few things once again.

On welding the 6061,  in general, welding alum weakens the base material by 50%, thus the reason for large fill volume in the joint to make up for it.  Of course on the inside of the joint will never be seen, but the top and bottom of it, where the fabric goes, to be “as strong” you should have pretty good weld bead, thus a lump under the fabric. And like what was pointed out, you can never view this again when fabric covered.  Just something to consider.

As far as bending and I think  you were striving for the most consistent bends on the 4130, this has been done by many methods and am guessing your thoughts are amongst them. It is harder to index each piece in the tail boom area “after the main  bends” but can be done.  This might fall out of the category of SIMPLE, but certainly a long ways from HARD.  Mostly this would fall into what works best for you.  NO really right or wrong methods of bending unless kinks or cracks are formed.

Wishing you great success.

Scott