Covering struts kf5

[gizmos]

Any pictures on using the foam board with fiberglass to make the airfoils on struts? Or is everyone going with plastic covers? Any other options?

[Jerrytex]

Here is what I used. I am betting a sheet metal shop could make these. I used a piece of wood moulding to contour the lead edge

http://www.teamkitfox.com/Forums/showthread.php?t=3550

Here are a couple pics:

[Geowitz]

I'm still waiting to try them out... weather has been crappy, but I had a friend with a brake bend up some trailing edges out of regular aluminum flashing material. He took a 5 foot by 5 inch strip and bent it lengthwise in the middle to about 22.5 degrees. So basically you have a 2.5 inch "V". I then taped them to the trailing edge of the strut every few feet and got them lined up and then permanently used this tape...

http://www.amazon.com/dp/B00006IF5S/ref=pe_175190_21431760_3p_M3T1_ST1_dp_1

It is quite strong once you get all the tape on and doesn't look all that bad. You could make foam ribs for reinforcement if you like, but I didn't yet and it's plenty strong for flight forces at least. My main goal for this go around was for proof of concept. Total cost was the tape from amazon and about $24 in 2 - 10" x 10' flashing rolls from the local hardware store..

I'll throw up some pics tonight.

[Geowitz]

Here are some pics. Can't wait to try them out and I'll report back once I have some data.

[Av8r3400]

Geowitz - Those are the Kitfox plastic farings?

[Geowitz]

No,sorry, the explanation is in my previous post. I guess the white makes it tricky too. The white "V" is prepainted .016 aluminum flashing bent to about 22.5 degrees with 2.5 inch legs. Then I just taped them on the trailing edge of the strut for a cheap and extremely light fairing. If this weather ever breaks I can get out and test them.

[Av8r3400]

Okay. That's what I thought, but the first photo looks like thicker material...

[HighWing]

My approach to the fairings was similar to Geowitz. I also used roof flashing but manipulated a bit differently. Watching the roofers run coiled sheet aluminum into their machine and having rain gutter come out of the other end gave me an idea - bad thinking. The other idea I had been thinking about for years was based on Dan Denneys Kitfox which had aluminum lift strut fairings. His had the aluminum with the forward bend and then a very small strip of aluminum with the tight aft bend glued on to hold everything together. After much trial and error, I was able to make a rolling mill that did the first bend I thought I needed - the aft tight bend. I guess someday I might finish the project. The first photo is of the device as it stands today. The second photo shows the functional part of the rolling mill and the third photo shows the tight bend with the sheet metal brake bend that is the leading edge. The overall length of the mill is necessary as experience showed there has to be sufficient length to resist the tendency of the thin sheet aluminum to deviate from the necessary straight path through the rollers.
Lowell

[Geowitz]

Depending on how my temporary fairings fair I would like to eventually do what Lowell did. I like the idea of a complete aluminum wrap with poly foam securing it in place. Although I may elect to just bend it in the middle for the leading edge and go with a hysoled flat seam like the flaperons use at the trailing edge. Minimum weight and you can choose a shape supposedly more efficient than the extruded plastic ones.

Lowell - What thickness flashing did you use? I guess it's really no a big deal if you are supporting it with the foam. I remember seeing it. Felt really tough.

[HighWing]

I just checked the thickness and it measures to .0095. I got it at Lowes as theirs is a bit thinner than Home Depot. I wanted light weight. Originally I was planning on lots of "NO PUSH" stickers but found that with the 2 Part Urethane foam inside, they are quite tough. For the first two or three sections, I Hysoled the trailing edge wrap, but found eventually that if the inside of the aluminum skin is prepped, by sanding lightly with 400 grit and wiping with Acetone, the foam adheres very well and none of the other sections are Hysoled. It saved a bunch of time as the foam cures much faster than the hysol and I could un-mold more quickly.

Another note, My sections are only 30" long and they will twist into a corkscrew very easily so I had to make up a curing jig for the foam insertion to keep them straight. Some sort of jig would be necessary in any event as the pressure from the expanding foam will create some distortion of the thin aluminum skin.

One more thought on the skin lengths. A friend came by recently and he has a very large fabrication shop with some full sized sheet metal tools. We talked about five foot sections - joining at the jury strut location. Then thinking about the two part foam inside, I still haven't figured out just how to pour in the foam. I used one oz. increments for my application - it filled roughly 20 inches of fairing so the subsequent pour overlapped my joints. Where the unexpanded foam touches as it runs to the bottom of the fairing, it will expand there and progressive pours may eventually seal off the fairing well above the solid foam level if a full length pour is attempted. Mix time is critical as you only have seconds before the stuff begins to swell.

Two merged photos of the jig below.
Lowell

[Dave S]

Lowell,

Any idea what the weight reduction is for your method on the lift strut fairings compared to the plastic coverings? I have the kit supplied plastic fairings on our plane and they do have a certain amount of heft to them.

THX

Dave S

KF7 Trigear
912ULS Warp
St PAul, Minnesota

[HighWing]

I just weighed a section of aluminum and the total weight is about 4.5 lbs. for the aluminum and My best estimate is that it takes about ten ounces of foam.

I also have several sections of the PVC material and also just weighed a section of that and it came in at 3 lbs. 6 oz. That would be times 4 plus the aluminum skins at the V.

Then from there, the micro or Bondo to close out the ends, primer and paint is likely a wash.
Lowell

[n85ae]

I consulted with Michael Selig at UIUC, got an airfoil from their database there.
Hotwired my own foam cores, bonded them to the struts, layed up a couple
layers of glasscloth, and spent eons sanding and filling, and they look great!

My plane goes exactly the same speed as all the other IO-240B engined
kitfoxes ... So I guess they work well enough ...

Would I do it again ...? Probably not. I hate sanding and filling glass. :)

Regards,
Jeff

[Geowitz]

My first thought was to do hot wire foam cutting and fiberglass, but I too HATE sanding. Would be nice and light, but probably no lighter than aluminum.

[HighWing]

Would I do it again ...? Probably not. I hate sanding and filling glass. :)

Regards,
Jeff

Had to laugh. My first introduction to amateur building was a business neighbor who was building a VeriEze. Lots of hotwire but tons more filling and sanding. Then when I moved my first project to Livermore (LVK) I would see some hangars with white stains on the apron in front of their hangars - the Glasair guys. I decided to never get involved with a plastic airplane for the exact reasons mentioned. Then the neighbor who asked for some help in his Lancair. It was a lot better knowing it was not mine to look at for ever more. I am on a current glass project with a total surface of less than 3 square feet and it has taken at least a month to see any progress. I am putting on the first color coat today. It is fun to look at when done, but wow!
Lowell