saltwater landing gear

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messydeer

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Mar 17, 2010
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Bellingham, WA
Hi!

I'm planning on building an Osprey 2 and thinking about making it saltwater worthy. The plans have 4130 gear. I know of one flying boat with aluminum 6013t651 gear and would think about replacing steel with that aluminum.
Is it a simple mathematical ratio problem? If steel is twice as strong and 3 times as heavy as aluminum, could I just double the thickness to achieve an equivalent strength?

Also, what about the fasteners? I'm concerned about galvanic corrosion.

Dan
 

bmcj

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Aluminum and Steel have different fatigue life too. A properly designed steel structure can be relatively fatigue-proof, whereas aluminum is more susceptible to fatigue. Others feel free to correct me if I am wrong about this.

Also I have seen some terrible corrosion problems with aluminum aircraft that are kept anywhere near saltwater.
 

akwrencher

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Lot's of steel boats floating around in the ocean. They are not maintenance free, but a good epoxy paint will help allot.

What bmjc said on aluminum. Aluminum does not play nice with other metals in a salt environment. It likes to corrode underneath paint, powdercoating, or anything that is bolted to it. Also, there is a wide variation among alloys as to their corrosion resistance. You would need one that had the correct physical properties and corrosion resistance. (sorry, I don't know which ones those might be).

Don't get me wrong, Aluminum is wonderful stuff, but unless you really want to do a new design analysis on your landing gear, probably easier to just paint the steel very well with a suitable two part epoxy paint (ask someone in the marine world what works good on steel) and wash it off good with fresh water when you are done flying.

Hot dip galvanizing does wonders for protecting steel as well, but it tends to take the temper out of the steel. Fished with a friend once that had a whole batch of circle hooks hot dipped. We used them, and it worked, but boy where they soft!
 

Victor Bravo

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Look into a material called KG Coatings, formerly Kal-Gard. When properly applied, this stuff has passed a government salt water hot spray corrosion test, and the stuff is reportedly used in military weapons in a salt water environment. Apparently it's really good stuff and works well.

There is a product called "Salt Away" which you use to wash off metal components, engine radiators, etc. after salt water use, and this neutralizes or greatly retards the effect of salt water usage. The stuff is run through cooling systems, engine blocks, running gear, rigging, etc. in the marine world. Apparently it works well.

Between these two materials, and use of rubber bellows and "boots" wherever possible, you sould be able to live in salt water with only a moderate amount of extra maintenance. I do have some experience with the KG coating, I used it on some 4130 weldments for main landing gear attach, and it seems like it's going to perform very well.

But I do not have personal experience flying or maintaining around salt water, so you should take the advice of those who have over mine. It wouldn't hurt to look into the products though.
 

messydeer

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Thanks for the feedback, guys :)

I believe the marine alloys of aluminum today would be much better against corrosion than steel. For one, I wouldn't have to rely on a finish, like on steel, that may hide corrosion. But sticking with the original steel gear would be much much simpler, and if I could get a reliable finish on steel, I'd do it in a heartbeat.

I also found out the wheel wells of the Osprey have no shroud to keep water out. Any water, fresh or salt, gets sprayed up inside the wing. The main gear door when up leaves part of the wheel exposed, since there's only one door. So there's gotta be water sprayed all over the inside of the wing when landing. Although I'd like to have seen a shroud there, there hasn't been any problems documented about this, at least for fresh water. There are hardly any reports of people going into the salt with the plane, though. On the group, people talk about planning to do this, but that's about it.

I know wooden boats made with epoxy certainly get exposed to saltwater on a daily basis. IIRC, West System recommends 5 or 6 coats of epoxy anyplace below the waterline. Fine for boats, but that adds weight.

Dan
 

akwrencher

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I wouldn't use epoxy on metal, it is way too brittle. Epoxy paint is something different entirely. It's the standard for steel boats. You will normally only get rust where the paint has been chipped, and it is not hard to touch up. I don't know anything about the coatings VictorBravo talked about but they sound like something to check out.

Bare marine aluminum alloys do well, but they rely on a thin layer of oxidation for corrosion resistance, somewhat like stainless steel. where you will have problems is where you have something bolted to it. Corrosion will build up in any "hidden" spot, because of galvanic action and lack of oxygen, etc. Both aluminum and steel are used extensively in the marine environment successfully, however like with everything else, knowing what material to use and what it's limitations are key. I see you are in Bellingham. Shouldn't be too hard to find some boat folks that could give you some tips for what to do and not to do with metals in salt water. (disclaimer: I'm not an expert by any means, but have spent most of my life on the water. Writing this from a boat in Poulsbo)
 

TFF

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With the best coatings, you still need to wash every time with fresh water. If you plan to just keep it floating in salt, it will ruin it. You will have to have military style cleaning and constant NDI checks if you want it to float for weeks at a time in the salt water. Going for a weekend will be OK but, even the gulf oil platform helicopters wash the aircraft and the engine inside, jet, every day to keep corrosion down, and they dont touch the water.
 

Victor Bravo

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I'm really surprised Pereira didn't put a shroud of some sort in that gear well. Even R/C models have vacuformed plastic shrouds for wheel wells.

I would say that this is a really good opportunity for the Osprey group to make a mold for plastic or light glass shrouds that can keep a majority of water out of the wing.

I'm not talking about a huge aerospace production mold made out of heated concrete or steel, rolling around on a dolly in an autoclave. I'm talking about the bottom 6 or 8 inches of a plastic garbage can, modified with some sort of PVC channel sticking out on e side, and mounted in a plywood cradle, then covered in MonoKote. Two layers of light bidirectional glass cloth with West resin.

I have ZERO experience with seaplanes... am I missing something here?
 

TFF

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I think I would be varnishing that area about 4-5 times; like an old time wood boat would be. An inter liner would be good.
 

dino

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Areas like those wells you epoxy encapsulate. 3 coats of neat resin is more than enough. If the gear can be re-engineered for aluminim, there are corrosion resistant alloys that perform well in the marine environment like 5052 and 6082 especially when anodized.

Dino
 

AIRCAB

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Vancouver Island
Lot's of steel boats floating around in the ocean. They are not maintenance free, but a good epoxy paint will help allot.

What bmjc said on aluminum. Aluminum does not play nice with other metals in a salt environment. It likes to corrode underneath paint, powdercoating, or anything that is bolted to it. Also, there is a wide variation among alloys as to their corrosion resistance. You would need one that had the correct physical properties and corrosion resistance. (sorry, I don't know which ones those might be).

Don't get me wrong, Aluminum is wonderful stuff, but unless you really want to do a new design analysis on your landing gear, probably easier to just paint the steel very well with a suitable two part epoxy paint (ask someone in the marine world what works good on steel) and wash it off good with fresh water when you are done flying.

Hot dip galvanizing does wonders for protecting steel as well, but it tends to take the temper out of the steel. Fished with a friend once that had a whole batch of circle hooks hot dipped. We used them, and it worked, but boy where they soft!
Cadmium plating seems to be the prefered choice for floats planes operating in salt water,

Steve
 
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