Steel Reinforced Extrusion

Yes. However, there are some issues to consider with hollow extrusions, such as whether they must be seamless or welding can be allowed. There may be further questions about dissimilar metals in contact in the final assembly.

Yes. But then you inherit other problems.

Steel is also 3 times the weight. Have you looked at extruding additional ribs to reduce the sag.

The metals have different thermal expansion rates, making a second interface problem.

You also have the problem of load transfer at the ends of the beams. You will end up with a steel structure with aluminum panels.

Thank you all

• It had been my intention to use the extrusion to support the steel on its edge
• I would guillotine galvanised strip to reduce corrosion
• It would be a slide fit, so expansion wouldn't be a problem
• I'm happy with a steel structure, I need the extrusion for attachment screw channels and accuracy where louvres nest together
• It's cheap to change an extrusion and very expensive to change a roll former
• If I can make a louvre in 1.5mm wall instead of 3mm, it's half the cost for material

Thanks Tony

Now I have a better understanding. As drawn, the aluminum shell must resist the horizontal forces and the steel resist the verticals. In that case, an "H" shape would be more efficient for the steel. The shell must provide lateral stability for the steel. The two, steel and aluminum would act independently because of the sliding fit, but must be fairly tight to avoid vertical vibration between the two.

I wonder about the connection of these structurally separate elements to whatever it is the wing is connected to.

Tonymech,

If you are up to speed on extrusion technology, then maybe you could answer an alternate approach. In plastic there was significnat advances in the '90's about foamed plastic injection moulded parts. (Gas injection)

Is it possible to extrude foamed aluminium with a thicker wall section (for sag resistance) while maintaining the low weight. I suspect that the foamed material would also provide sufficient thickness and strength for your fasteners compared to a single thickness.

The gas injection method provided solid surface conditions (no bubbles) but with significant weight reductions and good strength properties. The extrusion process is highly stable and so the gas injection outcome would be extremenly consistent.

The first wing I ever made was a canard which I whittled out of insulfoam and coated with fiberglass. It was no more than 2 inches thick, 6 to 8 inches across, and ten feet long. It supported my weight in the middle with no appreciable deformation. JaE suggested filling the centre of your structure with aluminum foam. Never used that, but my experience with the (now obsolete) handmade canard wing suggests that approach would work really well. (If you need this structure to hold fuel, well, maybe foam is not the right material. Otherwise, a first year text on moments and beams would be useful for what you want to stiffen your structure with.

Hi all

As this is a discussion, I'm hoping that a suggestion or comment may give me new direction, my understanding of beam theory is as follows:

• A beam relies on the material furthest from the neutral axis (in this case though the centre) carrying the maximum stress, either compression or tension.
• On the compression side, the material can buckle and relies on either a web ("I" beam), foam or ribs in the case of an aircraft wing to resist this.
• Foam filling only supports the outer skin and doesn't add any strength, only cost.
• Thickening or curving the material on the compression side helps resist buckling also.
• Young's modulus "E" referrers to the elasticity of the material, aluminium stretches 3 times more than steel so a system that steel clads aluminium, would be ideal, strength and cost wise.
• Also the tension side must be rigidly attached to the compression side.

As pointed out, corrosion, expansion and practicality are another issue, yet to be conquered.

Thanks for your input, Tony

Even foam has a modulus of elasticity. That changes with the foams density. The volume of foam filling the shape will give it strength.

With out knowledge of the stresses it will be under. With a slip fit there may be problems with wear as it moves in the groove.

There are a number of companies that make foamed aluminum which from my research is very strong and much lighter due to all of the cells. If I am correct it is made in a form such as a hydro forming form and the aluminum is a special alloy or mixture that upon heating foams similar to foam insulation. Depending on the weight to support it may be appropriate to try a high density urethane foam or a pourable foam as used in the fibreglass industry. This foam is used extensively in the ultra lite aircraft and home built industry. If you want to use steel you can insulate against galvanic action with plastic strips that should give a firm fit and allow for easy sliding into place compared to the galling that can be experienced with aluminum on aluminum.

Thank to all for taking on the foam idea, but there is another level to consider.

The technology that I was refering to is that during extrusion, the gas is injected into the middle of the molten material path at pressure and creates a foam sandwich with solid skins.

The outline shape that was originally proposed (including internal ribs) could be extruded in a single pass from one material (Aluminium) using a slightly thicker wall section, but foamed material to achieve a lighter weight.

Tony, if you talk to the extruder, they might be able to get an R&D grant to develop that process. Contact the S.A. technical development centre for details. (If you cannot find their details in the local directory, then contact a company trading as SMR (Used to be BRITAX Rainsfords, then Schefenacker) in Lonsdale and they will be able to give you contact details for the technology centre. With what's happening with Holden over there, the state gvt. will quickly get on side for such an opportunity.