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Hail damage question

Maxrate

Well Known Member
So trying to help a friend with a spam can that took some pea sized hail that left several small dents in the thinner skins like elevators and such. I had a few dents taken out of my wife’s car a while back with a paintless dent removal company. They did an amazing job with a heat gun and some tools. I don’t know if that process would be approved for a certified plane though and they are not big enough to replace skins. The paint on his plane is still in good condition so it seems like a candidate. Anyone with this kind of an issue before? Thanks
 
I know that the aluminum is not the same as a car body. I have heard that heat can change the strength if over done.
 
So trying to help a friend with a spam can that took some pea sized hail that left several small dents in the thinner skins like elevators and such. I had a few dents taken out of my wife’s car a while back with a paintless dent removal company. They did an amazing job with a heat gun and some tools. I don’t know if that process would be approved for a certified plane though and they are not big enough to replace skins. The paint on his plane is still in good condition so it seems like a candidate. Anyone with this kind of an issue before? Thanks

I am aware of one airplane that has had dent removal after experiencing some hail damage. No idea how much it costs, so it may be cost prohibitive.

https://www.aviationpros.com/home/a...ic-dent-removal-a-look-at-this-unique-process
 
A couple things..

I have been doing heavy aircraft structural work for 43 years at my day job, and also GA aircraft damage repairs. Hail dents in thin skin 2024-T3 are seldom successful to the level of them being fully worked out, simply because the material is stretched and will not return to its original shape(inny becomes outy). Curved surfaces are a little easier, but access to the back side is required for "spooning", a form of massaging the smooth dents out. The heat gun the car guys use if often to make the paint mailable and not crack rather than soften the metal. 2024-T3 takes 940F to start back to annealed condition, and we don't even need to go into all that. I am very familiar of the Boeing process , and have some experience with that on airliner bonded honeycomb surfaces. In those instances, there is no access to the back side, and the unique tool supercharges the skin and collapses the field generating a very loud bang ..sounds like a shotgun going off when it does. Perhaps someone has a better idea, and if so, Id like to know it!. Most often, lightweight filler and paint are the best option.
 
Just to see what happened, I took a piece of scrap .040 2024-T3 and heated it with a torch. After it cooled it was brittle and cracked. I don’t think the heat gun process is a good idea. They are small enough that a paint shop should be able to possibly use a very lightweight filler when the plane gets painted. Thanks for the input.
 
Aluminum is very different from steel. The latter tends to bounce back from light stretching where alum does not, allowing a skilled operator to push back small dents in steel sheet, but not so much with Alum. Heat has no real affect on shrinking the Alum unless taken far enough to eliminate the temper and you don't want to do that. Alum is shrunk by hammering and need a dolly on the back side.

I speculate that more than a small amount of filler on a certified control surface is a no go with the FAA, but not sure. These surfaces are prone to flutter and weight must be considered for balance purposes.

Even if a dent guy can work with Al, they typically use a series of tools that push from the back side of the panel and guess that access is very limited on a control surface.

Larry
 
Last edited:
Arthur Dent

I have been doing heavy aircraft structural work for 43 years at my day job, and also GA aircraft damage repairs. Hail dents in thin skin 2024-T3 are seldom successful to the level of them being fully worked out, simply because the material is stretched and will not return to its original shape(inny becomes outy). Curved surfaces are a little easier, but access to the back side is required for "spooning", a form of massaging the smooth dents out. The heat gun the car guys use if often to make the paint mailable and not crack rather than soften the metal. 2024-T3 takes 940F to start back to annealed condition, and we don't even need to go into all that. I am very familiar of the Boeing process , and have some experience with that on airliner bonded honeycomb surfaces. In those instances, there is no access to the back side, and the unique tool supercharges the skin and collapses the field generating a very loud bang ..sounds like a shotgun going off when it does. Perhaps someone has a better idea, and if so, Id like to know it!. Most often, lightweight filler and paint are the best option.

Rule of thumb taught at my A&P school was that if aluminum is heated enough to boil water it will change temper. While hand-forming parts, I’ve torch annealed aluminum with an oxyactelene torch by adjusting the flame to a long yellow feather and playing it over the surface to deposit a thin coating of black soot and then using a soft welding flame to carefully burn off the soot. But I would never anneal skins on a monocoque surface anyway. Getting hail dents out of the tailfeathers on a spam can (.020, .025, O Too Thin?) is going to be pretty tough. Even filler will be very finicky to get right and if it’s on a movable control surface it should be rebalanced. Replacing the part or at least just the skin is the only reliable way to make it look like it never happened. God help your bank balance if you have to buy parts from Cessna.
 
Rule of thumb taught at my A&P school was that if aluminum is heated enough to boil water it will change temper. While hand-forming parts, I’ve torch annealed aluminum with an oxyactelene torch by adjusting the flame to a long yellow feather and playing it over the surface to deposit a thin coating of black soot and then using a soft welding flame to carefully burn off the soot. But I would never anneal skins on a monocoque surface anyway. Getting hail dents out of the tailfeathers on a spam can (.020, .025, O Too Thin?) is going to be pretty tough. Even filler will be very finicky to get right and if it’s on a movable control surface it should be rebalanced. Replacing the part or at least just the skin is the only reliable way to make it look like it never happened. God help your bank balance if you have to buy parts from Cessna.

hardening temp of alum is in the neighborhood of 800-1000* before quench. Some alloys need precip hardening around 300-400* after that, similar to tempering in steel. It takes 600-800 degrees to anneal most aluminum, which is substantially hotter than boiling water. Given that they raise the temp to 300-400 after hardening to develop that extra bit of strength, it would stand to reason that you bringing it back to that temp will not take it away. Not a metallurgist, so not certain.

Larry

Larry
 
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