Lift strut dent

[jimboflying]

I had a jack slip and wound up with a dent in the rear lift strut. Is it possible to remove the dent and if so what is the best technique or does a dent require a new strut? The picture is a little dark but the dent is below the 3 white dots.

 

[mike mcs repair]

Before they were sealed, you would put air fitting in fork hole, air it up and soften dent with a torch, common... Be creative. Not going to finish the steps, but you get the idea.


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[skywagon8a]

Before they were sealed, you would put air fitting in fork hole, air it up and soften dent with a torch, common... Be creative. Not going to finish the steps, but you get the idea.

mike, does just heating the strut with a torch harm the sealed struts? A welding rod could be welded to the center of the dent, then heat around the dent's edges while pulling on the welding rod. After the dent is out, cut off the rod and smooth the spot.

 

[Steve Pierce]

They are mild steel.

 

[Crash Jr.]

mike, does just heating the strut with a torch harm the sealed struts? A welding rod could be welded to the center of the dent, then heat around the dent's edges while pulling on the welding rod. After the dent is out, cut off the rod and smooth the spot.

Definitely not a good idea to heat a sealed strut. Being sealed there is a fixed amount of air in there and if you heat it that air will expand and possibly bulge the strut tube.

Plus I don't think you can pop a dent in tubing out like you would pop a dent out of a car door.

I don't have the data in front of me but allowable tolerance for strut dent depth is somewhere in the range of 1/2 the wall thickness of the strut tube which is about .035 for front struts and .049 for rear struts. Don't quote me on it though, that's from memory.

Best bet is to replace the strut if it's out of tolerance. After all it's the thing holding your wings on....

 

[bob turner]

Agree - although I flew for years with a slightly dented strut, probably not a great idea if you fly in heavy turbulence. A dent, or even a repaired dent, impairs the compressive strength. They are designed for limited compression anyway, and are really strong in tension.

The only time you see real compression (other than flying inverted) is in heavy turbulence, or landing, or tied down in heavy wind.

 

[skywagon8a]

Definitely not a good idea to heat a sealed strut. Being sealed there is a fixed amount of air in there and if you heat it that air will expand and possibly bulge the strut tube.

That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.

 

[mike mcs repair]

you guys realize the strut started out as a ROUND TUBE, and was rolled through a series of dies to make it into the streamlined shape...... fixing a dent is NOTHING compared to how they are made.....

 

[Webfoot]

I Once saw a cub with a belly tank which caught fire and burned. The heat made the lift struts round.

 

[mike mcs repair]

That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.

oil or air expands more????

heat strut away from dent to pressurize, then heat dent perimeter to soften and remove dent...... carefully ....

might want a hammer handy incase you over do it....

 

[badmdcnman]

In the auto body world we use PDR (Paintless Dent Repair) techs to push hail and small dents out of damaged vehicles. In areas they cannot get behind such as the outer roof rails on your pickup or SUV they use a glue gun procedure. I have been amazed at how perfect the repairs have turned out. Each dent is unique and not all lend themselves to this procedure. Only an experienced tech would be able to determine if the repair has a chance to succeed. They typically approach the procedure from the standpoint they will make the dent disappear completely. They can sometimes be convinced to simply make it better which in my experience is amazingly good. And when they are done the paint is unscathed. No don’t go out and buy a glue gun. Ask around car dealers or autobody shops for a name of an experienced PDR tech. Hope this helps Good Luck. Rod

 

[flynlow]

Is removing the dent for structural integrity or cosmetic
If cosmetic...bondo
I make a living sitting on tractors and horses


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[behindpropellers]

That makes it sound like a viable solution for a small dent. It's unlikely that the expansion would cause a bulge unless you go overboard with the heat.

I have read on this website about powdercoating and the oven caused the strut to look like a banana.

 

[mike mcs repair]

I have read on this website about powdercoating and the oven caused the strut to look like a banana.

No it makes them kinda round.

Boodie (original airframes, they bought out) made bannnana shaped struts as they were originally getting rollers adjusted


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[astjp2]

They are mild steel.

I thought some of the suppliers were using 4130 for the streamlined tubing and once it was roll formed it had to be NDI'd for micro cracks, am I way wrong here?

 

[mike mcs repair]

I thought some of the suppliers were using 4130 for the streamlined tubing and once it was roll formed it had to be NDI'd for micro cracks, am I way wrong here?

pretty sure boodie(Airframes) was 4130, at least heavy duty rear one....

https://www.airframesalaska.com/PA-18-Super-Cub-Rear-Lift-Strut-p/af89498-02.htm

 

[Crash Jr.]

Can confirm: Front struts are 1010 mild steel and rear struts (heavy duty) are 4130

 

[mvivion]

It seems to me the question is: Is strength compromised by this dent? Since struts are stressed in extension, it seems to me that a small dent probably wouldn't effect strength.

IF (note the big IF) that's the case, a little body putty and a rattle can spray job would seem to be the safest approach, rather than trying to re-form the strut.

Maybe.

MTV

 

[Paul Heinrich]

If the lives and safety of you and your passengers are in the slightest doubt, why would anyone ever consider not replacing the strut? Isn’t the constant worry about possible failure and the prospect of lifelong guilt and economic ruin enough motivation to spend the few dollars necessary to properly fix the issue?

Taking little shortcuts in safety now leads to a mindset of taking greater and greater risks until disaster is inevitable. Flying is dangerous enough.

Replace the strut.

 

[stewartb]

I flight wouldn't bother me but in parking? I've watched Cub wings fold under from aft strut failure. I wouldn't want a compromised strut on my airplane.

 

[jimboflying]

Followup
I tried PDR (paintless dent removal) techniques with hot glue and plastic tabs. It was an incredibly slow process but progress was made with about 10 hours of work and another 10 to go. The problem was either the tab pulled off or the glue fractured or the tab fractured because of the high strength of the 1010 steel strut. I finally tried JB weld with a metal screw bonded to the strut material. Tightening of the nut pulled up on the metal strut. Progress was slightly faster but the glue always fractured at one of the interfaces or within the glue. I tried multiple types of epoxy plus cyanoacrylates. I did not want to weld on the sealed strut.
At about 95% of the dent removal I removed the paint and found that there were actually defects in the metal associated with the previously dented area. I finally gave up and ordered a new strut.

 

[skywagon8a]

That is certainly not a "dent". I thought you were talking about that light spot at the top of your photo. That is a sharp crease from one side to the other. Altogether different from what I thought you were describing.

 

[Crash Jr.]

You should very much think twice before flying with that strut. It looks to have a decent sized crease and a bit of lost material. The previous picture did not do the level of damage justice.

 

[mike mcs repair]

That will need a weld on patch. Not that anyone bothers anymore. But you might as well do it and have it as a spare. I think it’s covered in 43.13


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[Hardtailjohn]

That will need a weld on patch. Not that anyone bothers anymore. But you might as well do it and have it as a spare. I think it’s covered in 43.13


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I did an annual on a PA-11 once, and was looking at the rear strut...something just didn't quite look right. Finally I saw it... the strut swelled a bit about 1/3 the way up. I got to digging and they'd done an exterior patch, then ran bondo, literally tapering from the patch to both ends of the strut. Very subtle, but if you looked at it, you could see, and of course once you saw it, you couldn't un-see it. We pulled the bondo and he kept it for a spare, but put a new one on.:lol:

 

[jimboflying]

The damage to the surface of the metal was not seen until the paint was removed. After seeing the damage I ordered a new strut of course. I posted the pictures for educational purposes to show that damage can be hidden. The glue pulling technique was fun to learn and would likely work well on dents to aluminum or thinner steel such as occurs in hanger rash. I have seen hail damage removed completely with lots of time and patience.

 

[mike mcs repair]

The damage to the surface of the metal was not seen until the paint was removed. After seeing the damage I ordered a new strut of course. I posted the pictures for educational purposes to show that damage can be hidden. The glue pulling technique was fun to learn and would likely work well on dents to aluminum or thinner steel such as occurs in hanger rash. I have seen hail damage removed completely with lots of time and patience.

Wouldn’t scare me to add a appropriate repair and patch over that. All well documented in I think in 43.13. Might not be pretty, but just another ”repair”.


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[Cub Builder]

Wouldn’t scare me to add a appropriate repair and patch over that. All well documented in I think in 43.13. Might not be pretty, but just another ”repair”.

That's what I was thinking. It used to be acceptable to weld on a strut. Why not TIG a formed patch over that area doing the welding in small segments so as to not cause too much of a pressure build up internally in the sealed strut? For that matter as long as the rest of the strut stays reasonably cool, I wouldn't expect much of a pressure build while welding. As Mike says, that should be covered in AC 43.13 and should be an acceptable repair.

-Cub Builder

 

[mike mcs repair]

Wouldn’t scare me to add a appropriate repair and patch over that. All well documented in I think in 43.13. Might not be pretty, but just another ”repair”.

That's what I was thinking. It used to be acceptable to weld on a strut. Why not TIG a formed patch over that area doing the welding in small segments so as to not cause too much of a pressure build up internally in the sealed strut? For that matter as long as the rest of the strut stays reasonably cool, I wouldn't expect much of a pressure build while welding. As Mike says, that should be covered in AC 43.13 and should be an acceptable repair.

-Cub Builder

You drill a 1/8” hole at top of strut. Tip to make oil not be in area of weld. Then first weld up crack. Then add patch over that area. Then weld hole shut while still warm.


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[algonquin]

I have the PDR tools and use it to pull small dents in skins etc. it’s not designed for anything as thick as a strut. Also it’s not as simple as hot glue gun and some glue. There are several glues designed for different air and skin temp.. Also the glue gun is adjustable for temp and the temp you bring the glue up to varies for conditions and type of glue. It is easy to over pull a dent also and end up with a bump. Great tool and not hard to learn how to use it.