DR-1 (Sands): Builders Group

[Fritz Kempf]

Joepolit
The method you are using to weld your fuselage is the way I have heard it explained also. I didn’t do it that way and frankly I don’t know anyone who has…..So good luck, we will eagerly await you results. Don’t think that any one is telling you not to do it this way; you have made the right choose and chose a method that you are comfortable with as did the rest of us. As for the holes, if you plan to do that, you need to drill the holes where the tubs meet so the fluid will flow in; it looks like you’re too late. Again (if it makes you feel any better) I don’t know any body that has done this. Ron actually wants you to pressure test it first then fill.


Ed

[joepilot]

Fritz Kempf & anyone else,

From what I have read, you are susposed to flush all the tubes with linseed oil to protect the inside of the tubes. We are to do this after all of the welding is complete. Yes, no, maybe?

joepilot

[Fritz Kempf]

Joepilot
Yes, that’s what Ron said, but as I said before I don’t know of anyone that has done it. And at the point you are at, you would have to cut your fuselage apart to drill holes in your longerons. You could drill straight through from the out side and then weld the outer hole closed, but that would be a lot of holes. Also, as I said Ron wanted you to pressurize the fuselage and test all the welds with soap and repair any leaks before you put in the linseed oil.

Ed

[joepilot]

Cool, thanks for the clarification

joepilot

[Jim Bruton]

I know that Dogtail2 has patiently asked a couple of times, and JoePilot is also wondering about it. How bis a deal is it to NOT flush the inside of the tubing with linseed oil? Will the plane really rust apart from the inside because you don't?

[Tim]

Recently I did the welding program offered by EAA's workshop group. In that course I discussed the linseed oil issue with him.

He specifically indicated that the tubes did NOT require the addition of any type of preserving oil. Based on his experience over decades of working with tube structures from Piper to NASA.

As a certified aircraft mechanic, I have done my share of repair work on tube structures. Corrosion requires several things to propagate, and the environment inside a closed tube structure, previously treated by machine oil seems not to be the idea location for corrosion to begin, or continue.

Tim

[worldcrusier]

My two cents. I've been involved in repairs to piper cub tail sections. Corrosion is such a big problem that replacement tail sections for the fuselage are readily available. I believe that the corrosion problems can be avoided and oil not required, by pressure testing the airframe. And pressure testing every few years. When a crack or pinhole opens in the structure, the temperature, humidity swings cause the airframe to 'breath' in humidity. That's what causes the corrosion. Older production methods probably did not catch every pinhole and even with the linseed oil, eventually corrosion develops. Problem is getting someone to pressure test every few years. If you are not going to, then the linseed oil will definitely extend the life of the airframe if a crack/pinhole develops.

[baldeagle]

Another two cents, after building 4 or 5 fuselages and numerous tail surfaces and etc., I always tack weld the entire structure together before finish welding, that's how I was taught, and that's how the EAA says to do it (it would be worth it to order one of their welding books, the product of a lot more experience than I have). I've tried finish welding piece meal on smaller structures and it definately seemed to encourage more distortion. Also, remember, you're not building the space shuttle, and you can live with some distortion, you can bet that even the factories did sometimes. As long as the wing is straight with the tail and the landing gear and engine are straight the airplane should fly OK, and a little distortion in between won't hurt things. I won't define "a little", as it depends on where it is.
Also, I've seen internal corrosion on older factory aircraft, so I always do the linseed oil thing, drilling holes at the clusters before assembly. The internal oiling that comes on the tubing burns off when you weld it, so you lose that protection at the clusters. By the way, I was told to use boiled linseed oil, not plain, supposedly the boiled stuff dries and sticks better. The book says to heat it first so it will flow better, although I don't do that as it seems to get everywhere anyway, and in fact will come through any unfinished welds or pinholes, so you'll see where they are. It can be tough to weld on a structure after it's recently been filled with linseed oil as it tends to pop back at you.
On the other hand, these are going to be pampered aircraft that spend their nights in hangars, so if you haven't oiled your fuselage it will probably be OK until long after you're gone, and it's not going to fall out of the sky from lack of oiling.
Also remember that linseed oil will spontaneously combust, I left a bag of rags with it on them outside one day after cleaning up from doing a fuselage, came in the next day and the bag was smoking and smoldering. People have burned their houses up that way.
Another interesting thing, some of the aerobatic guys build a fitting into their fuselages so that they can periodically pressure test them, to look for cracks. I've never pressure tested a fuselage though.

[joepilot]

You just got to love this forum. Thank you Jim for asking the question again, and thank you very much BaldEagle, WorldCruiser, & Tim for the answers to my questions. Thank you for making this unique path clearer. Spontaneous combustion - you know I think I may opt out of that. Sounds like I'll be 6 feet under way before my tube will rust out from the inside (being 48 years old). Yes, my fighter will be in a hanger over night. I'll be lucky to be able to get into the cockpit 20 years from now. I am hoping to finish all of the tack welding of my crate by Wednesday night. Pics to follow.

C'ya
joepilot
check 6

[Jim Bruton]

Nothing like hearing from the voices of experience- thank you all!

Jim