Rear edge stiffeners ?

[Kitfox Pilot]

Did most you add these 3/8 pipes to the trailing edges ? I read they keep the rear edge from deforming when covering? Is this a problem when covering? I just read this on another build and had not heard of it.

[Shadowrider]

What type of covering are you doing? Not needed with Oratex but recommended with poly.

[efwd]

I used them. I used Oratex. The last thing I wanted to see was a trailing edge resembling the Batman logo.

[jrevens]

I used them with Oratex too, Harlan. As an aside, the first time I was folding my wings in the 3-point attitude (before the first flight) I stupidly let a wing rotate back & slam into a cabinet with the trailing edge. The result was a relatively minor repair. I believe that if I hadn’t had the stiffening tubes I would’ve probably had to replace a section of the trailing edge.

[jiott]

In my opinion the stiffeners are a must; the 350F final fabric shrink pulls on that edge with a LOT of force. Some folks, I have heard, stop at 250F or so, but I have seen several in-flight videos of the top surface of the wing bulging up; so I personally want maximum fabric shrink and tightness on the wings. Even with the stiffeners I put a straight edge on the trailing edges after 350F shrink (I used Polyfiber) and found them slightly bowed inward about 1/8" at midspan, which was not visually noticeable.

[jiott]

One other idea I saw on this forum was instead of the 3/8" tubes he used carbon fiber arrow shafts at midspan hysoled between the trailing edge and the rear spar; an interesting lightweight solution he claimed did the job. Maybe the member/s who posted this quite a while ago will chime in and verify.

[Kitfox Pilot]

Thanks guys I will get some ordered. I am using oratex.

[Shadowrider]

I will play devils advocate.......unnecessary weight in my opinion but do what makes you most comfortable. Both of our planes we did not use them. We shrunk both wings to 450F and trailing edges are both straight. Wings are tight as a fiddle! When you shrink your wings you go longitudinally and start at the front of the wing so there is not much pulling on trailing edge verus pulling against the ribs. Of course we did a lot of things different than others on here like no rib stitching and minimal finishing tape. On another note this is what drove me crazy about kitfox. Where is the secret menu to order these "must" items? If something is required then include it with the kit!

[Kitfox Pilot]

I will play devils advocate.......unnecessary weight in my opinion but do what makes you most comfortable. Both of our planes we did not use them. We shrunk both wings to 450F and trailing edges are both straight. Wings are tight as a fiddle! When you shrink your wings you go longitudinally and start at the front of the wing so there is not much pulling on trailing edge verus pulling against the ribs. Of course we did a lot of things different than others on here like no rib stitching and minimal finishing tape. On another note this is what drove me crazy about kitfox. Where is the secret menu to order these "must" items? If something is required then include it with the kit!

I had no idea about the little pipes, just ran across them looking at the builders logs. I thought oratex might pull harder since its a tougher material but I guess not if you've done two you should know.

[Dave S]

Harlan,

I believe the instructions to include the aluminum tubes as an option was mentioned in my build manual (early S7); and, at the time I ordered them from aircraft spruce following the demise of skystar.

I see the addition as a way to increase the ruggedness of the trailing edge as well as dealing with the fabric shrinking stress as mentioned in the manual. I have seen way too many OOPS! happen in various hangars with visitors and I would rather see a dent in the perpetrator than the wing if at all possible.:rolleyes:

Overall I think it is well worth the trouble but everyone's mileage certainly varies. Regarding weight - I just try to avoid eating too much stuff I shouldn't.

[kitfoxrk]

The tubes came with my kit. I believe I saw a reference to them in the wing covering section of the manual.

Bob

[Kitfox Pilot]

I will look again but I don't remember seeing any with my kit, I haven't studied much about the wing section yet but getting closer.

[efwd]

The material is not included in the kit. It is not required and is merely a suggested technique many builders use to ensure the fabric doesn't warp the trailing edge.

[Shadowrider]

Was not included and no mention in our manual. Maybe the STI wing is different.🤷*♂️

[109JB]

They weren't installed on the Kitfox IV I am working on that was covered with polyfiber, and they weren't installed on my friends Kitfox IV also covered with polyfiber. Here are a couple pictures of the wings on my project airplane that have since had the covering removed. Trailing edge looks pretty darn straight to me. I'm sticking with the motto that everything you add adds to the empty weight. When I recover my IV it will not be getting any of these tubes.

24890

24891

[bbs428]

Someone else came up with this idea. I just plagiarized and tweaked it.
I priced out some carbon tube. Was more economical to buy these practice carbon arrows and you can get two braces per arrow. I will be
covering the wing soon so I'll let you know how it goes. Lighter than the aluminum tubes? Yes. Stronger? Yes, since it is in compression. :)

[Kahle76]

One other idea I saw on this forum was instead of the 3/8" tubes he used carbon fiber arrow shafts at midspan hysoled between the trailing edge and the rear spar; an interesting lightweight solution he claimed did the job. Maybe the member/s who posted this quite a while ago will chime in and verify.

I used the carbon fiber arrows. You can buy used ones at you local archery shop for next to nothing.

[HighWing]

I remember - back in the old days - early 1990s of the talk on the early email lists about the scalloped trailing edges guys found after heat shrinking the fabric. I used the carbon fiber arrow blanks on my two Model IV builds. I don't recall hearing or reading of the factory recommending stiffiners, but those who commented on the scalloping were enough to prompt me to do the trick. 900 hours on the first build and almost.200 on #2 with no changes or issues appearing as eye catchers. Would I do it again? Simple - yes.

[Kitfox Pilot]

Lowell,
What do the scalloped trailing edges do for the build? I have saw a few but didn't know why it was done.

[kitfoxrk]

I just looked at the assembly manual on the Kitfox website. Page 8 of the fabric covering section has a note about adding the stiffeners. Says they are optional.

Bob

[HighWing]

The scalloping was not intentionally done, but was a result of the thin aluminum trailing edge structures inability to restrain the shrinking forces of the fabric. Standing at the wingtip and sighting down the trailing edge, you could see a slight inset between each wing rib tip.

[efwd]

Harlan, are you speaking of the scalloped trailing edges of the Laker Leading Edge fiberglass?

[Kitfox Pilot]

Yes that's what I was referring . I misunderstood the previous poster.

[Delta Whisky]

Harlan - the opening (for the reinforcing aluminum tube) in my trailing edge was not large enough to manage the size of tubing the manual recommends. I bought a smaller size of 6061 T6 and used it.

[Kitfox Pilot]

Thanks for that heads up.

[jrevens]

Mine might have been a little different than Delta Whisky, but I originally thought the tubing wouldn’t fit properly also. However, I found that with the proper “rolling” technique it would pop into place nice and tightly, although I still used Hysol to really secure it.

[DesertFox4]

I used the aluminum tubes bonded into the trailing edges in my 7SS. No "scalloping" when shrinking the PolyFiber. Slightly heavier than the carbon rods some use but less chance of galvanic corrosion issues than between the aluminum tailing edge pieces and the carbon fiber. Those near the coasts might consider this type of corrosion with regards to sea water and the reaction between these two materials.
Not an "expert" on corrosion issues but read enough to decide to pass on the carbon fiber rods buried in the trailing edges with no way to inspect for corrosion issues.
Not a quick or simple fix if corrosion does get a foothold in the trailing edges. Anyway, food for thought. I do love carbon fiber but where I can see and inspect it.

[bbs428]

Interesting. I did a search and found in a salt water environment the corrosion can be significant.


"When Eurocopter started to mix carbon composite and aluminum in their helicopters structure and these machines were flown in the North Sea for the oil rig... Within a few weeks they had holes (you read right: holes) starting to develop. If I recall correctly it was less than 2 months!

If you do an Internet search you will find all of this well documented and some people involved with fixing these problems are still today very negative regarding aluminum and carbon.

Nevertheless, it is possible to mix the two with some good design, engineering and care."

Food for thought...

[Jerrytex]

Anyone know the size of this tubing 3/8" OD? What about wall thickness?

Thanks.

[Dave S]

Jerry,

The length can be measured between the ribs. The instruction, which are buried as a Note under the wing covering section say tubing wall thickness of 0.028" to 0.035". I used the 0.035" as the difference in weight is almost irrelevant (like eating 1/2 a bagel less for breakfast); and, once the tubes are bonded in, nobody is going to take them out and replace them after covering if they change their mind. No problem with bending with max shrink on the 0.035" wall thickness tubes.

[Jerrytex]

Thanks Dave.

I looked for this info in the manual and must have looked right at it 5 times.......

[Dave S]

Thanks Dave.

I looked for this info in the manual and must have looked right at it 5 times.......



Hi Jerry,

Well, it takes some sleuthing in the manual - they reference the stiffeners in the wing build section but do not include the wall thickness there. Then, cleverly hidden in the note section within the covering portion they have the dimensions - it's a trick!

Take care, Dave