Trailing edge questions

[HighWing]

My system simply used lengths of the carbon fiber tubes glued between the spar and trailing edge between each rib. It required a third less tubing and much less glue. They are straight running fore and aft (parallel to the ribs). I made up some aluminum fittings by punching holes in some thin aluminum (.016). then cutting them out to about a half inch by three quarter inch. By punching the holes it created a star shaped burr that fit into the end of the tube to stabilize it while the Hysol was setting and to separate the carbon fiber from the spar. One was placed on each end of the tube after cutting to a snug length. Hysol was placed between all surfaces. Again, my supports were not span wise, but were essentially a standoff between the ribs halving the distance between the trailing edge supports. I have no progress shots of that part of the build, but made up an aluminum part and attached a picture of that. The tube is slightly undersized as that is all I have right now. The trailing edge is straight as a string after shrinking.
Lowell

[MotReklaw]

Many thanks for the photos Tom and Lowell.
Now I see and will check out my aluminum stock and/or order some of the carbon fiber blanks.... found lots of them on EBay....

Thanks again,

[rogerh12]

Tom;

That aluminum tubing in the trailing edge, what type and wall thickness did you end up using (6061 @ .035)???

Thanks in advance

Roger

[Tom Waid]

My invoice says 6061T6 5/16 X .058

I bought it here

Happy Homebuilding!!

[jtpitkin06]

6061T6 .0375 x .035

Nice fit, good strength with minimum weight.

The 3/8 size tube is a tight fit but you will need to work it a bit to get it in the trailing edge slot. Cut each piece about 2 inches shorter than the distance between the ribs so you don't pop the trailing edge bond loose from the ribs. Once inserted the 3/8 tube nicely fills the void for maximum strength with the greatest available cross section. There is just enough slop to allow the tube to rotate and smear the Hysol for a good bond. I found it easiest to rotate the tubes with an awl inside the end of each tube section at about a 45 degree angle.

John Pitkin

[rogerh12]

WOW, .058 ??

Well that auta do it all right.

Fortunately, AirParts in Kansas City is only 45 minutes from me, so I will just jot on over and pick up a few feet on the cheap (.035 has the best pricing). Plus, they have loads of surplus AN hardware too. You just can't ever have enought extra AN, can you?

Thanks for info!!!


Roger

[HighWing]

Reading John's most recent post suggests that the challenge of fitting the aluminum tubing into the trailing edge might just be a sequencing issue. If the trailing edge was fitted and trimmed, then the tubing inserted and the trailing edge glued in with the same glue batch, it doesn't seem that there would be near the difficulty.

Maybe the manual is what needs the touch up. If the tube suggestion is made at the finishing stage, maybe it should be made at the wing build stage. Then again, with the optional quick build wings, maybe it should be included from the factory rather than challenging the builder with an out of sequence step.

[dginok]

I bought a set of pre-cut tubes from the factory for my quick-build wings. At first, I thought there must be some mistake -- I did not see how they could possibly fit in the trailing edge slot. I made it over that mental hurdle and got them to slide in with a little care and coaxing.

[jtpitkin06]

I suppose I should give a bit more background...

I built my wings last summer before going to Oshkosh without the reinforcement. At the end of the chapter in the build manual it refered to the reinforcement as optional and there was no material in the kit. When I visited the Kitfox Booth I asked J McB about the tubing and he gave some tips about inserting the reinforcement after my trailing edge was already installed. Evidently it is done all the time.

The 3/8 size fills the trailing edge nicely but the opening (slot) in the edge metal is less than 3/8 inch. The slot must be flexed open a bit to get the tube inserted. Trying to force the tube in all at once is far too difficult. It's best to start at the midpoint between the ribs where the trailing edge will flex the most. Once you get a tube started use a twisting motion while pushing at the same time. The tube it will slide into the training edge and toward the a rib at the same time. When you have it about two thirds inserted just roll it in with your thumbs.

It's really not a difficult procedure. Brush some Hysol into the trailing edge, start the rib, twist and push. It pops right in. I did have one of my trailing edge-to-rib joints pop loose requiring a rebond. Not a big deal.

If I were starting from scratch I would insert the reinforcement tubes before the trailing edge is riveted or bonded to the ribs.

Two things improved after installing the tubes. I noticed an immediate improvement in the trailing edge stiffness in both fore/aft and up/down.

The negative is the tubes and Hysol add yet a bit more weight. Every little thing you install in the airplane adds up. A few ounces become pounds and pounds breed like rats in an airplane.

However, I really think this added weight is worth the penalty. The additional strength is a real plus. Where I see the real payoff is a reduction in hangar rash. The non-reinforced trailing edge can be bent or kinked very easily. Just a bit of rough handling or a bump can lead to some wing repair. With the added tubes, I think the trailing edge can take a lot more bumps and bangs without bending the flimsy metal trailing edge.

The thing I like about Lowell's use of arrow shafts is the yield point on metal tubes is far lower than the shafts. If a trailing edge reinforced with the carbon fiber shafts were to take a blow it would have to bend much further before the trailing edge would have a permanent kink.

Lowell installed the reinforcement differently but he achieves a lot of resistance to scalloping when the fabric is shrunk. Because the distance to the spar is less than the distance between ribs, he gets additional stiffness with less weight. There is more than one way to beef up the edge.

John Pitkin

[rogerh12]

Speaking of adding aluminum;

I purchased 12 foot aluminum tubes to be used instead of the wood lateral stringers, the ones the fabric wraps around. They might add a bit more weight, but won't break when someone knee's the side of my plane like the wood ones can. Replaced my wood floor boards with aluminum too.

I guess I am on an alumunim kick, but wood is so, well.... wooden !!!

I think I will just glue/roll some exra aluminum tubes into the trailing edge, sounds easy enough. I figure I will just knock off 50 lbs to make up the extra wieght before I go fly (I will just stop eating for a while).
Roger