Alternative covering method?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
Hello, i am currently working on my 50% P-51 Mustang. The original builder sheeted the original wooden airframe in aluminum. He used several 1'x2' squares of aluminum sheeting and attatched them to the stringers and bulkheads with hundreds of brads that are approximately 3/4" long. This is ok, i guess, except for that many of the brads are coming loose, i assume due to the wood drying out? Although none of the panels seem to be loose. Also, when they hammered the brads in, it appears they used a regular claw style hammer and around each brad there is a circle where the hammer head struck the aluminum. Thus now the airplane looks like is has gone through a heavy hail storm, on all the sides. The plane has suffered damage to the right hand side wing spar where it attatches to the fusealage for an unknown reason. I am going to completely unskin the plane and check the entire airframe for any further damage as well as repair the current damage. So now this brings me to my problem, how and what do i recover the airframe in/with? I really like the fact thats it covered in aluminum, except for that it looks like hell. Any other ways to affix alumium to the airframe? Possibly covering it in fiberglass? carbon-fiber? Cloth? Any help will be greatly appreciated! Thanks!
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,268
Location
Port Townsend WA
How thick is the aluminum skin?

I did some experiments with bonding .006" aluminum foil to heat shrunk dacron fabric (using contact cement). It seemed to work well but would be even better if the edges are fastened with small screws or pop rivets (or maybe thumb tacks in your case). Not flight tested yet.

The aircraft is covered with fabric, so the foil is not structural.
 
Last edited:

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
I'm not entirely sure how thick it is just yet. I'm guessing its similar to the type of aluminum used for flashing on a house? The brads heavily resemble rivet heads, which I really like because it looks so scale. However I don't like how dented and rippled the whole thing looks. I was really thinking of covering the whole thing with fiberglass. I am concerned about weight issues with fiberglass.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
10,082
Location
CT, USA
Regardless of anything else, aluminum flashing would be a poor choice as it's very soft, weak material. 2024-T3 Alclad in the same thickness would be much stronger and more durable.

-Dana

We are born naked, wet, and hungry. Then things get worse.
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
6,228
Regardless of anything else, aluminum flashing would be a poor choice as it's very soft, weak material. 2024-T3 Alclad in the same thickness would be much stronger and more durable.
The flashing we get around here is actually pretty stiff and tough stuff. No idea what alloy it is but it's not soft at all.

But in any case, the covering method outlined by the OP is a poor one. The sheeting won't accommodate compound curves, the metal will be far heavier than fabric and paint, the brads will work loose, and corrosion and rot between the wood and the sheet and brads can be expected. Better to toss all the metal and use fabric only.

Dan
 

NorthwestJack

Well-Known Member
Joined
Feb 8, 2008
Messages
73
Location
Monroe ,Wa ( close to Seattle)
Many wood replicas of ww2 airplanes are covered with 1/16 aircraft grade birch plywood. It actually works quite well, and If glued on properly will give the aircraft a fair amount of rigidity. typically the compound curves are changed slightly to conical sections. I have found that in my own construction, I have been able to do slight compound curves with plywood by steaming the plywood with an iron and applying water , then temporarely stapling/clamping the plywood until it dries and then fastening it permanently. It takes a lot of staples to hold it in place until it dries.
Jacq
 

Attachments

Last edited:

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
The real question here though is whether the original designer had intended for the aluminum to have a structural role or not. If it was to act as a form of shear web then replacing it with something else will have an element of risk unless of course it is properly analyzed. In general though, you will be hard pressed to find anything lighter than the thin sheets of aluminum (I'm assuming the sheets were either .016" or .020"). In a shear role, the brads would most likely have been sufficient but yes, you would benefit from something a bit more dependable. Assuming you don't want to analyze the airframe, I'd recommend sticking with the aluminum but instead of depending on the brads, I might recommend bonding it to the wood with a Methacrylate adhesive (Extreme Adhesives, Inc. - www.extremeadhesives.com - do a test panel first because I'm not sure how the material bonds to wood) and then after it fully cures, going back over the seams with brads or equivalent. To keep the brads from working out you might want to coat them with adhesive also - either the Methacrylate or something simpler like 3M's 5200.

To get the skin panel stability that you get with the aluminum you'll have to use so much glass that the weight penalty will be prohibitive and despite its lighter weight, by the time you're done with the graphite you'll have very similar penalties. Wood ply might work but again you're dealing with panel stability so by the time you make it thick enough to get a good look you might again pay a penalty in extra weight.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,268
Location
Port Townsend WA
Like Dan said, I found the flashing sold at Home Depot to be very hard. It looked like .012". It would be hard to find .012" 2024-T3 anymore, I think. When it comes to very thin sheet and foil, normally the commercial industry uses only work hardened alloys such as 1100 or 5052. These alloys are probably comparable with 2024 in such thin gauges where buckling is about the same for any alloy.
 

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
The flashing at Home Depot however is most likely some form of coated steel. Aluminum flashing, even in 2024-T3 (which I seriously doubt it is) in that thickness would be easily damaged. I did some work with .016" 2024-T3 and even carefully shifting it on the palette resulted in minor creases. To the best of my knowledge the only airplane that used .016" aluminum material was the Bonanza (wing skins) but it was supported by a relatively narrow framework of ribs and stringers. Replacing a section of it is a major pain.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
10,082
Location
CT, USA
I've done a fair amount of home projects using aluminum flashing from Home Depot or whatever and I've done the same with left over 2024 Alclad from an airplane project. There is a big difference between the workability; the 2024 is a lot harder.

-Dana

Can a Cessna 150 truly "slip the surly bonds of Earth"?
 

Dan Thomas

Well-Known Member
Joined
Sep 17, 2008
Messages
6,228
I think the aluminum flashing is likely 5052-H32 or something like that. It comes rolled, and in a range of widths.

When I suggested fabric only I was making the assumption that the aircraft was likely designed for fabric, not requiring metal (or plywood) for stiffness. Even if the metal was supposed to be structural I sure wouldn't trust the brads to keep it tight. Adhesive, at a minimum, would be necessary.

Dan
 

rheuschele

Well-Known Member
Joined
Jan 12, 2010
Messages
533
Location
Chicago Il. USA.
One thing that seems to stand out it the use of brads in the original build. I would be very fearful of re-attaching with brads and aluminum again, doubling the amount of holes in the structure. How much weaker are you making these parts? If your setting these brads in a straight line with the original brad holes, are you spiting the wood? I would consider taking an original peice of aluminum and getting either a sq. inch or sq. foot weight and finding a plywood match. At least with ply you will be gluing all parts and the brad holes won't matter. I'd even think about finding the structural strength of the aluminum, compared with the ply and see if you could go the next size smaller so you could cover the entire structure with a coat of composite. This way you could also make those hard curves (wing attach to fuse.) that seem out of reach.
Ron
 

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
This is all really great information! From everything i have been learning, the aluminum is very difficult to work with. Which is probably why my plane looks the way it does. I think im liking the idea of finding a light plywood and using adhesives to hold it together, and maybe screws or brads at some key points? What kind of composite are you referring to rheuschele? My concern is how curvy the P-51 is, and i would hate to take away from those curves. Where does a guy find such plywood? What is it called? Thank you all very much for the help!
 

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Well, a couple of points to consider: First, you still don't know if the aluminum had any structural purpose in the build. As such, substituting material is a risk without knowing the details or running at least a cursory analysis.

Second, applying ply and covering it with a laminate skin means that you are essentially building two structural shells. Since the laminate will be significantly stiffer than the wood, even if you use glass, all the load is going to go into the composite, which means that the wood is just extra weight. Also, since the loads are going into the composite, you now have to make sure that it is strong/stable enough to handle what it needs to.

Third, replacing the aluminum with an equivalent ply may be a significant weight penalty since the wood in the ply may have a strength of about 1/10 that of the aluminum. Also keep in mind that the ply has only half the plies going in the principal strength direction so if you look at it in the simplistic terms, you will have to use twice as much wood as you calculated. But the relationship is not all that simple since you also need to consider panel stiffness and skin stability.

In order for these answers to be a bit more complete at this point, it might be best if you post some pictures and also let us know which plane you are building. Is it a one-off design or is it a known plan set? Regardless of which one, do you have access to the original design information and structural analysis?
 

rheuschele

Well-Known Member
Joined
Jan 12, 2010
Messages
533
Location
Chicago Il. USA.
Orion is right, you need to learn more about your plane and if and to what extent that aluminum was structural. I'm also curious to see pictures, before and after. As for doubling plywood to get more grain in specific directions, this shouldn't be problem nor necessary. You really need to contact the original builder and designer to answer most of your questions. I'm also curious as to the performance specifications of the plane. If your looking to do 200mph, then your asking the wrong people. If your doing under 100mph, most everything shouldn't be a problem.
ron
 

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
I posted some pictures, the pictures that show damage are on the right side. Have yet to figure out exactly what has happened. There is absolutely no damage to any of the underbelly, so that rules out crash landing. No damage to the gear either. This plane is a one off design that a guy built. The story i got was that the guy was a Mustang pilot in WWII. After the war he got back and started working in aviation industry and from what i understand he built several experimental airplanes, this being the only P-51. I recieved a few big binders of information, but nothing saying anything about the design of the airframe. The certification papers state that it has a vNE of 140 knots, that is all that is said. The gentleman that built it passed away last year and i bought it off of a guy who bought it from the estate sale. I have a receipt for just about every single nut, bolt, and piece that it took to build it. As well as having many detailed drawings of some of the systems such as the retractable landing gear,and the gear reduction/prop drive.
 

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
Also, it may go without saying, there are wing extensions that bolt onto the ends of the pieces that are made into the fuse. They are approximately 6 feet long each and there is no damage whatsoever to either one. It has a wingspan of 18' and the overall length from tip of the spinner to the nav light on the rudder is 16'. Its has hydraulic, retractable landing gear, and flaps.
 

orion

R.I.P.
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Wow, that was quite an ambitious project. Well, off the top of my head I would estimate that yes, the aluminum structure did have load carrying capability, primarily in shear. As such, replacing it will necessitate that you keep that in mind. Assuming you want to keep things simple, I really have only two solutions. The first you already mentioned: Cover the plane with a light, nonstructural ply and bond in place. Okume ply is softer than aircraft structural ply and can form somewhat more complex surfaces without being steamed. For complex surfaces fill region with foam and carve and sand into shape. Then, cover the whole plane with a structural laminate and be willing to live with the weight penalty.

The second option would be to make up your own flat composite panels (preferably graphite) and then cut and bond said panels into place. As before, for complex surfaces, fill with foam and sand to shape, then laminate material over foam, attaching the laminate to the surrounding prefabricated sheets with a sufficient overlap. The overlap will be then covered with a filler that will blend it in.
 

halfscalemustang

Well-Known Member
Joined
Dec 11, 2010
Messages
52
Location
Osawatomie, KS United States
Yea, i under estimated this project when i took it on, but thats ok, Im young and ambitious. I have been playing with radio controlled airplanes for years and decided to build a half scale P-51 mustang to which i could fly myself. I accidently found this on craigslist, in Phoenix,AZ, and i live near Kansas City, KS. Decided i had to have it and made the 3000 mile round trip to bring it home. Now i have the task of fixing it, and i am going to fix it. Fortunately i have found this forum with so many knowledgeable people that are willing to help out. How much of a weight penalty do you think there may be? The plane was designed around a 6', 250lb individual, i myself is close to 190lbs, so i have a little room to play with. Is the okume ply available at local lumber yards? Is the graphite hard to come up with? Thank you all very much for all the help, i greatly appreciate everybody's time! Sorry for so many questions, im really excited about this project!
 
Top