Printable View
I need to attach a forged aluminum part (landing gear mounting bracket) to a bulkhead made of 4130 steel, probably with bolts, but I may decide to rivet it.
What are the standard practices used in the aviation industry to prevent corrosion in this situation? Any type of non conductive material put between the 2 parts would be subject to some fatigue, and there will still be conductivity at the bolt/rivet holes.
If you look under the inspection covers in the floor of a Cessna, you will see steel landing gear bolted to what look like aluminum forgings that transfer the loads into the fuselage structure. All I see are AN bolts and painted spring steel.
I know that stainless steel and aluminum create dissimilar metals corrosion, but based on my observations of the construction of Piper/Cessna/Mooney aircraft, I do not see lots of concern about more common steels being in contact with aluminum, held together with cad plated bolts.
A good 2-part (epoxy) primer on the forging will probably be a good thing.
I will suggest that bolting is preferable to riveting so that if you ever see a hint of corrosion you can jack the airplane and take it apart to check.
Best of luck,
Wes
N78PS
RV's have quite a few aluminum to steel joints. A good dose of primer seems to prevent problems - I haven't seen any corrosion in those areas on 11+ years. Like the previous poster said, I'd bolt, rather than rivet, just because landing gear get bent occasionally and it is nice to remove them with a few bolts rather than tens of rivets.
I was considering some sort pf primer - I wonder if POR-15 makes something that sticks as well to aluminum as it does to steel? Of course if I spray the fuselage frame with POR-15 primer & Chassis Black I probably don't have to worry about anything else, that stuff is pretty much indestructible.
BTW, I am using Cessna gear, so Cessna aluminum forgings. I have had some bad experiences with corrosion in race & street cars where aluminum & steel came together so I wanted to be sure I was thinking this thru properly. And I do think bolting is best.
At the airlines we used A 1/2 but even B sealant will work. http://www.aircraftspruce.com/menus/...ksealants.html .. I just spent the afternoon removing super glue some einstein used to secure a bagage door seal on a C-182. I should have been a half hour job.. I find amatures use alot of stuff from home depot that was not clearly made for use on aircraft.. I even found liquid nailes to hold the carpet in a PA-140. That was a two day job removing that with a plastic scraper... I even found self expanding house insulation. Do yourself a favor and stick to materials in the aircraft spruce catalog.
I will lobby for the use of white primer in enclosed spaces and on parts that will need inspection. Black blends in the dirt and hides cracks, corrosion, and other issues.
Best of luck,
Wes
N78PS
That is a good thought. I wonder why all our motor mounts are black? A lighter color would be easier to inspect.Quote:
Originally Posted by WLIU
The POR-15 primer is silver & they did used to have a white topcoat.
Everything on that page appears to be for sealing fuel tanks???Quote:
Originally Posted by RV8505
I've installed trailer hitches made of steel that are powder coated that mate with aluminum structure on the towing vehicle, the hitch manufacturer provided what they called "galvanic isolators" to go in between the dissimilar mating parts. The isolators were a clear material with adhesive on one side, like packing tape but roughly 2-3 times thicker.
We used to use something like that in industrial applications ~20 years ago. It worked fairly well, at least in the short term. I didn't usually stick around in a job long enough to know about the long term. :DQuote:
Originally Posted by DaveH
It isn't just for fuel tanks.. We used it matting steel to aluminum, pressurized areas, Lap seams, and on repairs. Use (fuel resistant ) FR primer if you have it and some of that sealant. It will last longer than you.Quote:
Originally Posted by Mike Switzer
OK, thanks. Learn something new every day.Quote:
Originally Posted by RV8505
The plus is your not married to it like POR 15. You can remove sealant with a little elbow grease and a plastic scraper. Unlike P0R-15 you would have to sandblast or strip to remove it
Back in 94 I sandblasted a pickup frame & painted it with POR-15 - then I had to take a job out of town & never got back to the project. It has been sitting in Dad's side yard ever since & still looks like it did the day I painted it.
JC5a is a non-hardening chromate corrosion inhibiting paste that can be smeared on critical bolts, rivets and mating surfaces prior to assembly.
Almost anything that physically separates the metals with a non-conducting layer will be effective, but you need to consider deterioration and inspectability if it's in a critical area.
A conversion coating like alodine will further help prior to priming etc.
In the composites business with carbon structures in contact with aluminum, the alum is sacrificial galvanically. In the presence of moisture, a galvanic cell between the materials will force the alum to corrode away. That's why you never place alum rivets into a carbon structure.
To prevent this cell from starting, a simple layer of fiberglass between the carbon and alum will act as an insulator and prevent contact and corrosion. The glass is usually placed into the carbon laminate if you know where the alum will contact. if you have to do a field setup, then a wet layer of glass, maybe .005" thick, placed at the junction will work well. There are many coatings available which also act as electrical isolators but the glass works best.
Good one Mark! Another fine PRC product!Quote:
Originally Posted by Mark
PRC-Desoto 6 OZ Sealant
JC5A is a one-part, non-curing, corrosion inhibitive compound. It can be applied to removable fasteners and assemblies to prevent the ingress of moisture and to provide protection from galvanic corrosion. JC5A is paste-like in consistency, allowing for easy application by brush, roller or spatula. It will remain permanently fluid and is resistant to aviation fuels (jet fuel and aviation gasoline) over a wide temperature range.
Gee, if you are using Cessna parts, why waste time trying to be smarter than them? Bolt the things together like Cessna do and use your "thinking cap" time on something that needs that time.
Cheers from Oz
Cessna rivets them into an aluminum bulkhead assembly, my structure is steel.
Do you have any pictures?
See figure 30 in the parts manual:Quote:
Originally Posted by RV8505
What item ? Are you talking about items 5 and 8?
Yep - also 6 & 8, they are aluminum forgings everything else you see is sheet aluminumQuote:
Originally Posted by RV8505
Mike Pm me your number I'll give you a call.. Sorry for the tardy reply I am strung out between the east and west coasts.