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**crispy critter** · 12-18-2010, 12:52

Re: Hole in Airframe

There shouldn't be a hole there unless it's something they put on the factory sea planes that I know very little about but they wouldn't leave an unsealed hole in that location. If it's not rusted then I suspect it's a hole someone has drilled for some reason like to put in some kind of tube seal and forgot to plug it off,maybe it was to mount something to the wood and went through the tube by mistake. Who knows the reason but I would certinly plug it with something. You can used a drive rivit with some sealer on it for a easy quick fix but I would recommend welding it closed.

**TonyL** · 12-19-2010, 00:38

Re: Hole in Airframe

have to be careful. The location of the hole is the point where the greatest loads are imposed on your bird. The usual repair for tubular primary structure is welding. AC 4313 Repairs show you the approved method for US certified Aircraft. If this member is primary structure it could be compromisef. At the least, I suggest you make it a point of inspection every hundred hours. Just in case it migrates into a fracture crack. I know the repair is complicated due to fabric, possible fuel tank, and wood components. If you need an actual repair reference, I need to confirm exact location and match the repair to the 4313 section. Good Luck, Happy Holidays

**Pearson** · 12-19-2010, 13:24

Re: Hole in Airframe

Tony I am fortunate in that there is no fabric on the airframe. I understand your concern about welding the hole shut, as I am quite sure this would be considered a high stress area. It is literally about 1" inward from the forward wing attach point. Do you think it would be better to just put a scew in the hole to seal it, and forget about welding? Or would it be best to weld it shut being careful not to overheat the surrounding area? If needed, I could post a picture of the location of the hole.

**Pearson** · 12-19-2010, 14:48

Re: Hole in Airframe

Here is a photo of the hole. Forward is to the left.

Attached Files

**TonyL** · 12-19-2010, 14:54

Re: Hole in Airframe

No sir. That would not bring back the strength to the tubing. In the past I usef two halves with the inside diameter being the same as the outside diameter of the existing tube, same thickness or one size thicker. Welded to the area. Tonight, I'll research it and recommend an FAA approved fix. This tubing is very thin need a goos weld job, - regards - TonyL

**Hank Jarrett** · 12-19-2010, 14:56

Re: Hole in Airframe

Do NOT put a screw in it!!! The threads will put stress risers in the hole and initiate a crack. NEVER fill a hole in a high stress path with a threaded plug.

Sorry I can't tell you the BEST way to repair it without seeing the stress report but I expect Forrest will chime in here pretty soon and he probably knows if there was ever a hole there for a legitimate reason. My "feeling" is (note NOT WHAT I THINK, what I FEEL. What I feel isn't worth a hoot in H**L for you to take any action) that this is a welded steel structure and there is a good chance the hole was put there by someone drilling into the wood who screwed up. It has probably been there for years and not cracked. If the member is in compression it probably won't ever crack.

I would show it to my IA (who I trust with my life) and get his opinion. HE is the one who will have to sign off the paperwork. I also like my IA enough to make sure he gets the best possible input (Forrest) to make his decision.

If I had to guess, I am betting you will end up welding it shut (probably TIG to keep from heating the area too much) but that will take someone who can look at the loads in the area. Everything everyone says till then (including me) is just smoke.

Get real data on the loads and someone who can interpret them and can sign off the repair. All of us are just talking and our opinions are only worth what you are paying us.

Hank

**Hank Jarrett** · 12-19-2010, 15:04

Re: Hole in Airframe

OK, several folks replied between what I read and when my post showed up. I am pretty sure a couple of them are IAs so their comments have some weight. I will stand by the NO THREADED SCREW PLUGS statement AND the statement that you and YOUR IA have the ultimate decision.
Get a read from your IA and hopefully Forrest has some solid data for guidance.
Hank

**Guest** · 12-19-2010, 19:07

Re: Hole in Airframe

Originally posted by Pearson View Post

Here is a photo of the hole. Forward is to the left.

Hi Richard

My first guess is that somebody in the past had to drill out a windsheild attach screw and went too far by accident and went thru the tube.

You can see if that is correct guess by checking to see if this hole is aligned with the windsheild attach holes for the t-nuts in the piece of wood.

I would be concerned that the hole allowed water to get into that tube (1" dia tube maybe?) and has rusted the bottom of that tube. Please check for rust by tapping it with an awl. Also look for signs of cracks formed by expansion of ice in case the tube ever was filled with water.

The concern about stress in that particular tube should be more about buckling failure from the large compressive load applied by the front spars. That is one reason that you need to check for a weakened rusted wall in the tube.

Repairing the hole will be simple.

I agree with Hank that you must not put a screw in this hole, or a plug. I say this for a different reason though. This hole is on the top of the tube. The tube is compression/buckling critical. The stress around the hole is not an issue but the integrity of the cross section at the tube middle is. The hole needs to be welded shut to keep the water out.

I would have no problem welding it shut OR MAYBE applying a small patch per ac43.13-1b para. 4-94 IF it did not end up making a bigger mess.

Dave

A/P, IA, mech. engineer, elec. engineer - if that means anything

**Pearson** · 12-19-2010, 19:38

Re: Hole in Airframe

I did a closer examination of the hole in the tube. It is within 3/16" of the hole in the wood that goes on top of the tube. I bought this plane as a project that had already had the airframe blasted and primed. The wood was already temporarily screwed on. I didn't discover the hole until I removed the wood to prep the airframe for a top coat. I could not detect any sign of rust inside the tube. If the hole was drilled by the guy I bought the project from, it has not been outside to get any water in it since it was drilled. I have not checked with my copy of AC 43.13, but I suspect that a small diamond patch might be the way to go. I don't have access to TIG. But I can either gas weld it, or MIG weld it and then relieve the stresses with the gas.

**crispy critter** · 12-19-2010, 19:56

Re: Hole in Airframe

Originally posted by Pearson View Post

I did a closer examination of the hole in the tube. It is within 3/16" of the hole in the wood that goes on top of the tube. I bought this plane as a project that had already had the airframe blasted and primed. The wood was already temporarily screwed on. I didn't discover the hole until I removed the wood to prep the airframe for a top coat. I could not detect any sign of rust inside the tube. If the hole was drilled by the guy I bought the project from, it has not been outside to get any water in it since it was drilled. I have not checked with my copy of AC 43.13, but I suspect that a small diamond patch might be the way to go. I don't have access to TIG. But I can either gas weld it, or MIG weld it and then relieve the stresses with the gas.

Remember if you put a dimond patch here it will be hard to get your wood to fit properly without some careful carving. I would just gas weld the hole taking extreme care not to burn it out. It's an easy hole to fill but if you get carried away and have a burn out in this location it could cost some major problems trying to fix it.

**Hank Jarrett** · 12-19-2010, 20:25

Re: Hole in Airframe

Since there are so few steel tube and fabric spacecraft out there I really don't have the experience to say which method should be used but can one of the welders who DOES know about tube repairs explain how putting a rosette on the hole could cause more loss of integrity or damage to the tube than a diamond over the hole?
Hank

I learn things here I never learned at NASA!

**TonyL** · 12-19-2010, 21:51

Re: Hole in Airframe

Hi, I'm back. AC 4313-1BPage4-69 Figure 4-38 Splicing by outer sleeve method or figure 4-35. reinforcing sleeve to be of same material and at least the same gauge as tube being repaired Page 4-66. Ypu can proceed any way you wish, that is the approved repair. the wood you can always reome enough to fit. The wood is not primary structure, Iy's an aerodinamic contour to fit windshield wing and fuselage contour. Good luck on your decision. Merry Christmas. We are now on countdown . Incidentally, you don't have to buy the 4313-1B manual. Go to FAA Home. - Advisory Circulars and you can view it online. Maybe even download it.

**crispy critter** · 12-20-2010, 10:55

Re: Hole in Airframe

I hope I don't show my stupidity here but your talking about a very small hole....why can't it simply be spot filled with 4130 rod using a gas welder?

**flyguy** · 12-20-2010, 11:10

Re: Hole in Airframe

Ditto.
DC

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