Strut ad

[blakecarl]

Re: Strut ad

Don’t worry Hank, I’m not going to trash the struts. I’m planning to keep any part that is replaced. Never know when I or someone else might need them even if they require repaire before reuse.

Bill, I had the same thoughts about the struts primarily being in tension. IMO our dents would not affect the tension capability of the struts significantly. The real question is how much compression force are the struts required to have for planned or unplanned negative g situations. Sounds like I have to discuss this further with our A&P.

Blake

[fearofpavement]

Re: Strut ad

Bill, please don't use bad words in your posts! I had sorta forgotten about that dark period of T-craft history...

[Pearson]

Re: Strut ad

AC43.13 is full of illustrations showing how to repair a dented strut. I am wondering why your IA hasn't mentioned this to you.

[blakecarl]

Re: Strut ad

He did say that it could be repaired but suggested this would be nearly as much as replacing with new. I did look at AC43.13, Para. 4-101 which show how to repair with a splice. Are there other sections that address strut repairs or if any denting is acceptable in a strut?

[Hank Jarrett]

Re: Strut ad

See if you can get one of the "Paint-less dent repair" guys to take a look at it. Maybe he will look at it as a real challenge. The places that do that kind of dent repair are actually plastic deforming the skin in the area of the dent and that process would take out the dent with no real loss of strength. Problem for him would be to get his spooning tool into the strut to press the dent out.
If I was still at the Navy overhaul facility I would machine out a sleeve for the strut that prevented the strut from expanding beyond the original shape and then slip a bladder into the strut to the dent. Inflate the bladder with oil and allow the strut to be pressed out against the sleeve.
Of course it would help if the Navy was using strut braced monoplanes, but I am pretty sure a process could be designed to fix dents in streamlined tubes. I KNOW it can be done on round tubes.
Hank

[Pearson]

Re: Strut ad

Probably not going to be able to use the paintless dent repair technique due to lack of accessability as Hank mentioned. However, there is a method where you remove the paint and weld a small rod, or thick wire, to which a slide hammer is then attached and the dent pulled out using the slide hammer. Automotive paint and body shops have these. The rod is attached using a MIG type spot welder, which as you probably know induces stress cracks. So you would want to normalize the area with a torch before you repainted it.

I personally feel that, unless the dent is really deep, you could just live with it, or fill it with Bondonium as Bill suggested. In tension, the dents aren't going to affect the strength unless they are really large. My plane flew with dented and patch lift struts for many years until I replaced them due to the AD.

[Larry Lyons]

Re: Strut ad

I guess I should take a pic of my repaired strut. The repair is atrociously rippled and dimpled. (;f
Larry

[Hank Jarrett]

Re: Strut ad

Rippled and dimpled!!?!?!?
That is a LOT different than a simple "dent". A smooth discontinuity in the surface isn't a real problem (like a shallow, smooth dent). Any sudden discontinuity will create a stress riser that could be very serious!
Before anyone panics, no one has defined what smooth or sudden is yet. I think some pictures would be a very good idea. Just be careful how you take them. Shadows can almost completely hide damage in a photo or make minor problems look like the Grand Canyon! If you can wax the damage and fill the "dent" with plaster that has been smoothed flush with the surrounding area the splash mold of the damage will give you a much better idea of how bad it really is. That's how we used to evaluate damage on curved surfaces on the A-6 to keep the curves from confusing the eye.
Hank

Airplanes are like women. The curves can confuse the eye. (;f

[VictorBravo]

Re: Strut ad

OK, here's another idea that our resident Engineer Emeritus can apply his considerable brain function to:

Cut out a piece of 4130 sheet that exactly fits into the outer perimeter of the dent.Size and shape it so that when you put it into the dent "crater" it forms a "roof" over the dent... and the roof happens to be flush with the rest of the strut. This will require a curve or camber to be bent into the sheet steel "patch". I'm not talking about an overlap repair, I'm talking about a flush repair made by shaping the patch to fit flush against the "slope" of the dent.

Once it is made to be completely flush, "reverse chamfer" the edge of the patch so there is a small groove or depression around the perimeter. Now weld the patch all around the perimeter, using the groove as your filler rod puddle the same way as the 43.13 textbook shows you to chamfer two steel plates into a V to make a butt weld. The V groove I believe allows you to insure full weld penetration.

Now file the puddle flush with the rest of the strut, fill any voids with spot putty, prime and paint.

This should leave you with a STRONGER cross section than before, because now you have THREE thicknesses of steel in the X-section instead of two. You will add a few ounces or a half a pound of weight due to extra metal. But by all rights it shoudl be stronger than an un-dented strut.

Hank, am I on solid ground suggesting this type of repair, or is there something structural or heat/temper-related I'm missing?

[Guest]

Re: Strut ad

AC43.13 is full of illustrations showing how to repair a dented strut. I am wondering why your IA hasn't mentioned this to you.

The one that applies to wing struts is figure 4-43. I have used it a few times. ac43.131b is quoted below.


4-101. WING-BRACE STRUTS AND
TAIL-BRACE STRUTS. In general, it will
be found advantageous to replace damaged
wing-brace struts made either from rounded or
streamlined tubing with new members purchased
from the original manufacturer. However,
there is no objection, from an airworthiness
point of view, to repairing such members
in a proper manner. An acceptable method of
repair, if streamlined tubing is used, will be
found in figure 4-43. Repair similar members
made of round tubes using a standard splice, as
shown in figure 4-35, figure 4-37, or figure
4-38

[Bird]

Re: Strut ad

Just a thought here but have any of you guys thought about J B weld? This stuff can do almost anything and for something like this I think would be great, I remember a buddy of mine that used it to fix a cracked head on his boat motor (9hp) when we were kids and I know he ran it for another 3 years before he sold it.
Check out the web site, they even say it's good for aircraft. http://jbweld.net/products/uses.php

[Guest]

Re: Strut ad

Just a thought here but have any of you guys thought about J B weld? This stuff can do almost anything and for something like this I think would be great, I remember a buddy of mine that used it to fix a cracked head on his boat motor (9hp) when we were kids and I know he ran it for another 3 years before he sold it.
Check out the web site, they even say it's good for aircraft. http://jbweld.net/products/uses.php

Hi Bird,

How are suggesting that JB weld be used to repaifr a lift strut?

I am not following.

Dave

[Bird]

Re: Strut ad

Just to fill in small dents that type of things

[Hank Jarrett]

Re: Strut ad

The doubler repair welded over the damage could be stronger than the original, or the welds could reduce the strength. If it is safe or strong isn't really the question with the FAA. The question is if they will let you do it, and unfortunately it isn't the way the "book" says to do it. I doubt they would let you put a scab patch on over a dent.
In my opinion (and my opinion is worth just what you are paying for it) I would be willing to fly with any repair I could proof load to the original load requirements and feel perfectly secure. Again, unfortunately, the FAA doesn't agree with me. I suggested proof loading struts for the AD but they never even acknowledged the suggestion. The proof is in the Proof Load. If it passes, it is safe, if not, it breaks in the test fixture. If you do NDI on it (X-ray, ultrasonic or some other inspection) you never really know. You are relying on the inspector to have not missed anything. With a proof load, it is either safe or broken.
Hank

We did proof load tests of components for 25 years on the A-6. It ALWAYS worked.

J-B weld works great, but remember, it does not put back ANY strength. It is just REALLY GOOD Bondo. And yes, I use it too, but just for cosmetics, not repairs.

[Guest]

Re: Strut ad

The doubler repair welded over the damage could be stronger than the original, or the welds could reduce the strength. If it is safe or strong isn't really the question with the FAA. The question is if they will let you do it, and unfortunately it isn't the way the "book" says to do it. I doubt they would let you put a scab patch on over a dent.
In my opinion (and my opinion is worth just what you are paying for it) I would be willing to fly with any repair I could proof load to the original load requirements and feel perfectly secure. Again, unfortunately, the FAA doesn't agree with me. I suggested proof loading struts for the AD but they never even acknowledged the suggestion. The proof is in the Proof Load. If it passes, it is safe, if not, it breaks in the test fixture. If you do NDI on it (X-ray, ultrasonic or some other inspection) you never really know. You are relying on the inspector to have not missed anything. With a proof load, it is either safe or broken.
Hank

We did proof load tests of components for 25 years on the A-6. It ALWAYS worked.

J-B weld works great, but remember, it does not put back ANY strength. It is just REALLY GOOD Bondo. And yes, I use it too, but just for cosmetics, not repairs.

Hi Hank,

I am not sure what scab patch is but I can say that the sleeve in figure 4-43 has been used to cover/repair dents that had resulted when lift struts that were crumpled and then had been straightened.

Dave