Streamlined Strut Fairing Material

[old man emu]

I'm going to walk away from balsa. There's a lot of work in shaping it and keeping the same profile from one end to the other. I reckon it would take a couple of days to finish off the shaping. Once the shaping is done, you've got to fix the balsa to the tube, and the result I've seen are pretty yuk.

 

I can save time, effort and have a better looking end product if I do it the way I've outlined here. I'd say that I could have all my streamlining finsihed in one day.

 

OME

 

 

[sain]

OME have you considered vacuum forming the aluminium flashing to shape? I'm assuming this stuff is just thin aluminium sheet? you could use a similair method to the one a lot of sonex builders do to form their leading edge skins.

 

Essentially the method is you put a thin perforated pipe down the middle of your aluminium sheet, which you then bend up and tape the edges together. Then you wrap it in drop plastic sheets (forming an air seal around the ends of the pipe, and the ends of the sheet). Connect the pipe to your vacuum cleaner, and then switch it on. The vacuum will pull the aluminium sheet together around the pipe, forming a nice bend shape for your leading edge. After a couple of minutes you switch off and the sheet will hold its shape pretty well.

 

There is a nice video of a couple of guys forming the leading edge for a whole wing that way somewhere on the net.

 

Oh look, found the videos:

 

http://sonexproject.com/Builder Resources.html

 

The vids are kind of big, but are worth a look.

 

*edit*

 

okay, I really should have read your pdf's in your other post on fairings before I posted, vacuum forming is probably way overkill. my bad.

 

 

[facthunter]

Why did I write post 20? I thought it was/is a good idea. Not even an acknowledgement.. Nev

 

 

[old man emu]

Why did I write post 20? I thought it was/is a good idea. Not even an acknowledgement.. Nev

Sorry Nev. Your idea was one of many ways to solve the problem of streamlining. However, it does involve some engineering analytical skills which are way beyond me. I agree that your idea would result in the most aesthetically pleasing result, but when you also consider cost and time involved it is not the way to go. Also, I have to make stramlining for the undercarriage legs, so that counts wood out altogether for that bit.

 

I also priced aluminium fairing. It's about $100 per foot. Also, if the aluminium in the aluminium flashing is too pure, it would take a month od Sundays to work harden it.

 

Vacuforming looks great, but still involves a lot of extra equipment.

 

On a cost/weight basis, the method I outlined wins hands down.

 

Old Man Emu

 

 

[facthunter]

The tension is easy to calculate. (just area of section ( rod ) and material considerations). The compression aspect . Just destruct test a representative sample and use your conservative safety factor.. The safety aspect of this is it's main appeal. Resistance to hangar rash and bird impact superior to anything I can come up with. You could probably keep flying with it damaged. ( Bird impact). Nev

 

 

[djpacro]

......... The compression aspect . Just destruct test a representative sample ....

Depends what is meant by a "sample" as there are different modes of failure in compression - I suggest a complete item.

[aj_richo]

A simple method of fabricating streamlined strut fairing is to cut up some sections of 16 thou 2024 or 6061, make 2 bends and wrap the section around the strut.. a handful of rivets - viola instant streamlining. The bends are designed to hold it together under spring tension, giving the streamlined shape. The rivets stop it from springing apart.

 

Its a method I used on my own designed 95:10 machine on the 4 lift struts with great success. It made a big difference in handling with a few knots gained, and it actually glided like a winged brick instead of a standard brick.. you can just see them in the photo. pdf file shows the basic folding. Dimensions are adjusted for your diameter tubing. (Struts are 32mm)

 

streamlinestrut.pdf

 

streamlinestrut.pdf

 

streamlinestrut.pdf

[facthunter]

DJP Sample as described, means one that is representative of ALL the struts produced, not a "One -off". It's easy to use such a safety factor that safety is not an issue. Theory of compression loading of columns is an imprecise science especially for long ones ( which these aren't) Euler's formula last time I looked at it. applies. Wood interplane struts have been employed on every biplane I've had anything to do, without internal reinforcement fot the tension situation, flying and ground wires taking care of those loads, on most designs, the Fokker Triplane being an exception as it had no bracing wires. Nev

 

 

[Litespeed]

AJ richo,

 

Thanks for that mate, same idea as I had but have no way of adding a drawing.

 

OME, I think the best way is the alloy.

 

Phil

 

 

[old man emu]

Nev,

 

The Fokker Triplane actually had canter levered wings and did not require bracing or interplane struts. Any externally visible bracing and interplane struts were put on the plane by Fokker to ease the fears of teh pilots who had not experienced this type of wing design before.

 

I'm sorry, but I am going to dig my claws in. I don't want to wander too far from the design, which has proved successful. I only want to reduce Drag. Also, I don't want to add too much weight. And finally, I don't have the sheetmetal working skills required to make the fairings out of aluminium.

 

Therefore, I am going to make the fairings out of Lexan or similar, and I am going to shape them around PVC-coated foam board. I am going to use the formers to attached the fairings to the airplane.

 

I thank you all for your participation in this discussion.

 

Old Man Emu

 

 

[Litespeed]

They are your claws, so you can dig anywhere you want.

 

Thats cool, pick the method you are most comfortable with.

 

 

[djpacro]

Theory of compression loading of columns is an imprecise science especially for long ones ( which these aren't) Euler's formula last time I looked at it. applies.

Its currently a 3/4" tube of length 42" I believe so seems like a long column to me. I'm an engineer not a scientist so use methods providing for a safe design. Euler with the appropriate end-fixity certainly applies to that round tube and only one of the failure modes to consider if moving away from this tube to a different material maybe.

[facthunter]

The strut I proposed was of wood similar to a DH 82 with conical metal sheet fixtures at each end flattened to an oval which the wooden strut is shaped to fit in. I can't see the compression aspect being a problem. It's been used over and over..and I have never heard of one failing. Nev

 

 

[djpacro]

I totally agree, Nev.

 

 

[drifter45]

Have a look at this site OME http://www.carlsonaircraft.com/struts.html

 

cheers John

 

 

[drifter45]

Also if you use polyurethane foam in the same way as Gere suggests for balsa just shape it, seal with polyurethane resin and tape. It should look the same as original.

 

cheers John