PVC lift strut fairing installation and painting

[N14ND]

Flipping through my task cards and looking at installing the PVC fairings to the lift struts. I like the look of the large struts with the fairing material on the round struts. I have seen bare sanded and painted and also fabric covered struts. Wondering advantages/disadvantages to either. Primarily wanting the paint to stay on the fairings, second is less time. Also, if the external channels/grooves that are visible can be sanded out or if a filler material needs to be added so as to not remove too much material and weaken the PVC. Easiest would be to get out the oscillating sander and smooth the outside, wet sand to 400 and paint. Thanks.

[JayHenry]

The factory sands and paints when they use the PVC. John said that it usually takes him about 30 hours to do a pair but being my first pair its taken quite a bit longer. Time consuming but very worth the time, most have seen 10+ MPH increase so likely the best bang for the buck on getting better performance and substantially cheeper than the other option.

[N14ND]

If anyone has the builders manual portion for the assembly of the PVC to strut directions I would greatly appreciate it. The online builders manual doesn't have that portion of the assembly. Thanks.

[Maverick]

I just reviewed my KF5 manual and could find no instructions for installing strut fairings. Since they were not there I just put them on, took them off, put them on, took them off until I was ready to put them one and leave them. . . Also, and I don't know the current thinking on this but, I was told by SkyStar years ago that the ridges on the struts were there for a reason. It had to do with laminar flow and I was advised not to remove them. I guess it depends on how much time you want to spend on them.

[N14ND]

The instructions are in the Speed Fairing Kit for the Series 5. It was a separate section.

Laminar flow? Usually span wise ridges and valleys aren't too good for flow. Even a paint line running length wise of a wing can cause separation. Anyway at 100mph I am not that worried about the laminar effects. I have a note in my builders manual that has the streamlined tube lift struts at $316 each...that was a while ago.

[DesertFox4]

I too left the ridges as was told the same story as Maverick. Not sure if it worked but I did have a fast model 4.

[4Hummer]

I have some pics of how I did mine starting around post 42:

https://teamkitfox.com/Forums/threads/10277-Mike-s-Kitfox-IV-rebuild/page2

[jiott]

As I recall, for the SS7, the PVC struts have 3 grooves (not ridges); 2 are fairly shallow and easily sanded out; the 3rd is quite deep and can be sanded out, but requires removal of a lot of material. Many folks have sanded out all 3 grooves and have not had any problems with weakening that I have heard. I took a middle-of -the-road approach and sanded out the 2 shallow groves and maybe half the depth of the deep groove. Time spent was reasonable and I think the one remaining groove actually looks fine since it is not very deep.

[bumsteer]

Are you still looking for the assembly instructions? Only 2 pages are for the lift struts the others are for the landing gear.

Rick

[n85ae]

I've spent so much time playing with Sailplane airfoils, and cutting my own foam cores, I look
at the PVC struts, and I'm pretty convinced that the only designing that went into them is
"Yup, that looks about right ..."

There are much better airfoils available for the struts than what we use, if you are willing
to cut your own cores, and do some research into "which" airfoil might be best.

Here's some links, the second can be used to plot various airfoils, at different size, and scale
into pdf's. These can then be cut/glued to template material for hotwiring foam cores. Which
is what I did, and then I glassed them with West Systems Epoxy system.

https://m-selig.ae.illinois.edu/ads/coord_database.html
http://airfoiltools.com/plotter/index?airfoil=ag36-il

Jeff


Here's a couple pics from when I did mine, the pictures are not high quality

25948

25949

[atosrider]

I just purchased new factory made lift struts this summer, the original model III struts had wood fairings which brought about their demise. The evidence was water enters at the jury strut connection, then it's trapped and rots out the wood at the lower end of the strut. The connector between the lift strut and the jury strut was aluminium, so it was corroded even worse than the steel lift struts.
But onto the fairing topic. Having canadian dollars, the factory PVC option seemed ... hard to justify. The old wood fairings could not be salvaged 100%. The local building supply that specializes in interior finishing had some oak trim that almost replicated the fairings, just some table saw, router and scarfing the joints required. In that process now, and too bad I didn't contact my RC model friend for assistance in hot wiring foam .. but then you need to protect the surface ... not impossible, just more work and more products and more weight.
For the connection between the lift and jury struts, the plan is to build an exterior fitting that will not require penetrating the fairing - some steel (same material as the jury strut !) custom bent it should spread out the load path quite nicely ..