Building with Black Aluminum

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by cheapracer, Nov 29, 2019.

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  1. Nov 29, 2019 #1




    Well-Known Member

    Sep 8, 2013
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    Over the last few days I've seen a few anti-black aluminium posts that I have found rather annoying in a homebuilt forum.

    A homebuilt forum where all methods should be encouraged, merely discussing the disadvantages, as well as the advantages, rather than condescendingly dismissing it outright because that material should be used only in a manner that suits those persons, or worse, stipulating that only material 'X' can be used for "Y" genre.

    I've made plenty of fiberglass parts over the last 40 years, but far from a composites expert, and never done anything structural. I however can read, and I have read enough to see that carbon fiber sheet should not only be a direct 2 dimensional flat sheet replacement for aluminium, but also excel due to the following:

    Weight: CF can have lighter weight for the same strength

    Strength: CF can have greater strength for the same weight

    Compromise of the above: CF can have slightly less weight, while having slightly more strength.

    Speed/ease of construction: CF can be tabbed and glued together without the need for 5000 to 10,000 rivet holes and rivets. I personally have popped 1000 rivets the last few days, I wouldn't miss it.

    Aerodynamics: CF not having those exposed rivets, has less aero disturbance. Goes faster, drinks less.


    So the theory is that any plane, or any vehicle for that matter, that was created from 2 dimensional flat sheet aluminium, can be made stronger or lighter, or both, if you use CF flat panels, no 3 dimensional molds required*.

    * Where 45 degree, 90 degree, ect, bends are required, pre-fabricated lengths can be made with simple metal sheet molds, or in some cases purchased 'off the shelf'.

    The preliminary test I did today convinced me all the above theory is true.

    I happen to have a 1.6mm 0.065" piece of CF around which I believe to be of lower grade due to it being hand laid, resin heavy, and unbaked. Hmm I just realised while writing this I don't know if it was cored or all layers of CF. I'll look tomorrow.

    To match this, I riveted together 3 strips of 0.5mm 0.020" 6061T6 aluminium resulting in 1.5mm .060"


    I had no scales around, so I simply balanced a meter (yard) long pieced of wood on a drill bit.


    Now when people compare CF to Al they tend to forget that Alu to be coupled together, needs lots of rivets. A rivet is far heavier than the hole it fills, so for my test i included a guesstimate of how many rivets would affect the real world comparison.

    The result was close enough to exactly 2:1 to call it that. The 1.6mm CF weighed exactly half of the 1.5mm Alu with a few rivets.

    Carbon was clearly the winner in weight for equal thickness by aprox 2:1.

    Strength A:

    This was a little bit trickier because of the rivets in the Alu. I had too many I feel, and that made the Alu stronger than it would have been and you could see the Alu bending in segments inbetween the rivet lines, but anyway, with a box of 1000 rivets on them, they bent down more or less the same distance.

    I did notice however, that the Alu did not return to it's starting position. I must have been close to it's yield, whereas the Carbon retained it's starting shape.

    Carbon won because the Alu would have been weaker without so many rivets, and the Alu didn't return to it's original shape.

    Strength B:

    I then with my hands, bent both pieces down until a/, I felt the Alu 'give' (past yield), and b/, continued down until the CF made crackling noises.

    Upon releasing both, the Alu returned halfway, while the CF sprung back to original position.

    Carbon won that easily, but of course it's almost moot because no vehicle part should ever reach those limits. It may be important for avoiding damage while hangaring/handling the craft though.


    CF Weight strength test:

    For my last test, I doubled the CF up to 3.2mm 0.125" thick (riveted) to equal the weight of the Alu.

    It came as no surprise that the general math is correct, it easily supported the 2 boxes of rivets without breaking into a sweat.



    Now some might question the results due to the rivets factor, but that's ok, next week my 2mm 2024T3 arrives, and I will do the same test over again. That's why the header on this post reads "preliminary".

    But in the meantime I'm not moving from my position, and that is a CF "Black Aluminium" flat sheet build will out perform an Aluminium plane of the same build in every way.

    Then there's other advantages such as no oil canning, quieter, cooler and cool factor. Also a more solid feel than sitting a 'tin can'.

    After this test I would be looking at something like 2.2mm 0.090" CF to have both weight reduction and strength safety factor margin increase.

    Of course what's stopping it currently is cost of material, my recent aluminium purchases were well under half that of CF .... but it's coming down all the time.
    Last edited: Nov 29, 2019
  2. Nov 30, 2019 #2




    Super Moderator Staff Member

    Oct 19, 2003
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    Saline Michigan
    Are you going to follow up with calculations to get the true bending strength of the parts tested? If you are not comfortable with those calcs, you could send me the dimensions and I will take a shot at the forecast and actual strengths of these parts and the strength of the carbon laminate...

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