Rosette welds

[Marty57]

I have a couple question regarding rosette welds. I am laying out the
lower longerons of my 2+2/PA-14 project and the plans show rosette welds at station 2 and 3 where the longerons bend up toward the front of the fuselage (gear attach location). Each station has an inner sleeve 6" long. The plans only show one rosette on each side of the junction of the two tubes. I have two questions. First, is the inner sleeve bent at an angle to match the angled joint to be welded at the station and are two rosette welds enough as shown on the plans? One of my EAA welding books shows about 6 rosettes in a spiral pattern on either side of a longeron repair. AC 43-13B doesn't give a particular number and only shows one on each side of the joint. Any ideas?
Thanks
Marty

 

[Dan2+2]

Marty, yes prebend the innerliner. I did not and now I have a curved area from the front gear mount about 6in forward. I don't think it affects function but the floorboards don't lay flat against the tube as they should. That may be why most 2+2's have a speed fairing, to hide the curve from knowing eyes. I put two rosettes on either side, four total. Call Tom at wagaero. He is easy to talk to. Also recall this is my first homebuilt so not an expert opinion.

 

[Marty57]

Dan,
Thanks for the info. That’s what I plan on doing, pre-bend the inner tube. I wonder how Piper did it in original production of the Cub series. Did they use a full length longeron, firewall to tail post and bend at each station or did they build it up like our plans show and weld in a sleeve?

Marty

 

[Crash]

3/4" longerons require 11/16 .063 tube turned down on a lathe about .010 to .014 to fit snugly inside the longeron. A straight piece of 5/8 tube will be too loose to be used as a proper inner liner. Crash

 

[Marty57]

Crash,
You are right, the 5/8 seems a bit loose, I cut a piece tonight for a test fit. AC 43-13B says that a snug fit doesn't need rosettes, you can leave a gap of 1/8" between the tubes to join them to the sleeve. Right now, I am leaning toward the 11/16 idea with the rosettes. I know this is a very critical area and a failure here could be very dangerous. Do you know what Piper did during manufacturing? Did they use the 11/16 .063 turned down to fit? As always, the info from this site is very valuable in presenting many great options and ways to look at a problem.
Thanks,
Marty

 

[Crash]

Marty

11/16" 4130 .063 is a hard size to find. The only place I have ever found it was Earl Edgar of Northland Manufacturing and he passed away about two years ago. A great guy.

As you know, Super Cub longerons (3/4" .035 4130) have an inside diameter of .680. If you can't find 11/16" 4130 you can get 3/4" 4130 thick wall tubing in .095, .120, .156 and .188 wall thickness.

I know it will take a little lathe time but you can turn down 3/4" .120 wall by .070 (.035 cut) and you will have a .680 tube with a wall thickness of .050 or a piece of .156 and give you a wall thickness of .086. I think the .120>.050 wall will be plenty for an inner liner.

Aircraft Spruce has 3/4" .120 4130 for $3.17 per foot. A good reason to go out and but that metal lathe you always wanted. Take care! Crash

P.S. I would slant the tube ends 30 degrees and butt weld them. Then rosette weld the inner liner about 1 1/2" back from the splice.

 

[Marty57]

Crash,
I think I will go your rout with the 3/4 unless I can find the 11/16. As far as the lath, I am an industrial arts teacher at a junior high and our high school has a couple of laths. It's been a few years since I have used one, but I think I can get up to speed. I had a similar problem at the front of the fuselage. The wag-aero plans called for a 1/2" tube to be welded inside the 3/4" tube at the top of the firewall. The other tubes that make up the front "square" were all 5/8. Needless to say, I used 5/8 inplace of the 1/2. The fit was a bit loose, but with the cluster that is welded on later, I feel ok. I think I might add a couple of gussets at that location just to be sure. Thanks again for the help. I remember a thread a while back concerning the 11/16 inside a 3/4. Maybe you gave the same advice then. Sounds good to me.

Marty

 

[Frank T]

Have you tried Dillsburg for 11/16? They have had it in the past.

Frank

 

[Marty57]

Yes, I emailed them today and will call tomorrow. They seem to have all sizes of tube. I will post what I find. I know this has come up for other builders. Thanks.
Marty

 

[Crash]

I would be great if they had 11/16" .063 tubing. With all the 4130 manufacturing going to China I think some of these odd sizes will start to dissappear. The 11/16" will come in around .690 O.D. and as I mentioned before, it will still need to be turned down .010 to .014 to get it to slip inside the .680 I.D. longerons. It's best to trial fit the inner liner as some of the tolerences are not 100% perfect. Take care. Crash

 

[6 short]

Wicks has 11/16 X .120. Here is the site: www.wicksaircraft.com

Pat

 

[Marty57]

Thanks Pat for the heads up with Wicks. I am checking with Dillsburg to see what they have otherwise I will order from Wicks. Crash, what do you think of the thicker .120 that Wicks has for the inner sleeve?

Thanks,
Marty

 

[Crash]

They would be plenty stout but a little on the heavy side. If you can find it, some thinner wall stuff (.063, .095) would be more like the factory used but .120 will work just fine for the intended use, just a little over kill.

Tell you the truth, I've never understood why Piper made this splice to begin with. I can see the one for the long section, but the slight change in longeron angle from the gear cluster to the firewall / engine mount should not have needed a break and splice.

The next time I do a PA-18 I am going to step up to .049 for this tube and "X" brace the diagonal tube (maybe make them .049 as well) to give better crash worthiness in this area. A lot of guys have died in Cub wrecks with two broken legs when the lower firewall buckled in on their legs.

A PA-12 and 14 have the diagonal tub running from the upper longeron at the door post down to the lower firewall tube, just opposite of the PA-18 fuselage. The PA-14 also steps up to a 7/8" .049 diagonal which makes it even stronger. Take care. Crash

 

[Marty57]

Ok, here is what I was able to do. I got the 11/16 .120 from Wicks. I was able to turn it down to fit into the 3/4 longeron by sliding a smaller tube inside and clamping the smaller tube in a vice. I then used my grinder ip and down the 11/16 splice tube. The grinder set up a nice slow spin on the tube allowing me to reduce the O.D. until it fit snug in the 3/4. I polished it on my belt sander the same way. Next, I heated it and bent it in a vice. Checked fit after it cooled and the joint is ready to drill for rosette welds. The fit is much better then the 3/4. I posted some pictures in my album. The link or the picture is below if I posted it right. Thanks for all the help on this one.

Marty

 

[Bugs66]

Looks damn good to me Marty! What are you using to fishmouth the tubes? Fit up looks great.

 

[Gordon Misch]

Ditto what Buggs said! Beautiful prep, how'd you do it?

 

[Dan2+2]

Yeah how did you do that perfect fishmouth? Inquiring minds want to know.

 

[Marty57]

Thanks for the encouragement. Fitting the tubes in place has turned out to be fun. Each tube is a little milestone in the project. The process begins with the use a program on the internet to generate a paper pattern. The site is: http://www.geek.casaforge.com/code/cope.pcgi
Next, I draw a centerline on the tube from end to end. The paper pattern is cut out and taped so it will slide over the tube. Then I slip the pattern off the tube and check for fit on the tube I am attaching it to. The program calls this the “parent tube”. If the fit is good, I slip the pattern back onto the tube to be cut and trace with a silver marker, lining up the reference mark on the pattern with the center line on the tube. I use my cut off grinder to trim the larger parts of metal off the tube and then simply trim the remainder with my bench grinder. The edge of the grinder has been dressed to have a nice radius of about 3/8” on each edge. Doing it this way usually gives me a nice fit with little re-grinding. I then slip the needed pattern on the other end of the tube, mark the correct length and cut to fit. I use a rat tail or flat file to remove any burs from the tube. It usually takes me about 20 minutes to do both ends of a tube using this method. I have other pictures and pictures of the patterns at www.xanga.com/martyfeehan

 

[Bugs66]

Very interesting Marty. I knew of the program WinMiter but this web based tool seems to be a nice improvement over that. Thanks for the tip!

 

[Gordon Misch]

Thank you, Marty. I'll check it out!

 

[T.J.]

delete

 

[gander]

there is also another program . if you google "tube mitering program Giles Puckett" . it will give you a second line wich is to allow for wall thickness , you simply file between the lines and your angle is correct with the mothering tube. not real critical for thin wall but on gear legs you get a better fit. also the blue handle wiss snips for stainless cut .035 like butter just get a left and right pair and in most cases you will not need to file. its real quick.

 

[Marty57]

Thanks for the additional tube program, I will check it out. Regarding the need for the rosette welds, Ac 43-13 can be confusing. The online version from the Faa says rosettes are not needed if the sleeve is a tight fit. Your reference says they are needed. When confused, I go for overkill unless it is a big time pain. I did drill the rosettes before I did the tack welding and will finish welding when it is out of the jig, more accessible. This way, I will be covered regardless of what version is consulted when I go for my air worthiness certificate. Thanks for the heads up on the change.

Marty

www.xanga.com/martyfeehan

 

[Cub junkie]

Another thing rosettes will do for you is give equal heat through the tube if you have to bend right at or near a splice, that is if they are welded ahead of time. When possible in a splice situation such as new construction I like to weld splices up completely as it helps out wit the shrink gremlins. This goes out the window if you are doing mid longeron repair splice(s) and are pulling inner sleeves. I just did two of these on a PA12. Kevin