Qestion about installing my spar Inserts

[TJay 1041]

Hey guys Winter is getting closer and Im excited to work on my Kitfox again. So I have these beautiful 60n inch long spar Inserts here that I will be installing in my spars, Now my question is, the inserts are meant to be as vertical as possible but since I already have installed the Z bar inserts earlier and have them strait up and down that means I have the holes real close center in the spars and I plan to re-use the holes that I already have drilled, Now would you guys set the new inserts a few degrees off  from strait up and down to avoid drilling in to the web of the i-beam or would you set the i-beams strait up and down and drill the rivet holes slightly into the web. My guess is the rivets only stabilize  the i-beams, really don't do much for strength what do you guys think.

[EDMO 1078]

TJay,

       If I was doing it, I would set the beams just enough off of vertical to NOT drill into the web.  Maybe one very slightly to rear and the other slightly to front.  Avid has a method of drilling into their owner-made insert that has you drilling exactly into the web, and I can copy that for you, but don't recommend doing that with your inserts.

       If you make some very visible marks on the outside of your inserts for the top and bottom center of web, you can make sure that your holes are not on the mark before drilling them.  A slotted pipe, board, or broomstick is very handy to positioning the inserts.  Kitfox even shows putting several wood clamps on the sides of the spars to make them a little bit of an oval temporarily to ease positioning of inserts.

Hope this helps.  EDMO

Edited 8 Oct 2015 by EDMO

[tcj 150]

If the inserts are not vertical it will be a bastard wing.  The strut attach brackets are designed for a rivet pattern to capture the insert at very specific locations with the insert vertical.  Kitfox warns to be very careful to not even nick that insert web.  To keep from hitting the web with a rivet hole the rivets will be located so that forces on the rivets will not be as designed in relation to shear or tinsel strength.

I would use the parts supplied with the Kit.

Edited 8 Oct 2015 by tcj

[dholly 718]

I've never built a KF wing with either inserts, so I can't offer much. Trying to get a mental picture of the situation, you are considering replacing the already installed 'Z-bar' style inserts with the long 'I-beam' inserts, right? How many holes would have to be abandoned and how close would they be to the new holes if the long insert were installed according to manual? I'm not saying the holes are inconsequential, but the Avid and early KF spars had a lot of holes for spar stiffeners, drag tubes, airspeed tubing etc. I think I read somewhere that holes with a properly smoothed edge result in less opportunity for stress risers vs. scratches in a spar? I wonder if cleaning up the old hole edges and Hysoling in a rivet would make any sense? I do know the Avid manual warns of any scratch deep enough to catch a fingernail within 12" (IIRC) to the root end pin holes or spar attach brackets.

[EDMO 1078]

As far as I know, the Kitfox later model spar inserts were not actually riveted, but the strut attach fittings rivets also held the insert in place.

I don't see where 1/8" or 1/4" off of vertical would be hazardous, and he does not have Kitfox spars or inserts, he has .083 thick spar tubes.

Since he is making a change to an earlier assembly, he just has to figure out what will work best, or leave it as built.

Avid used a row of rivets in the Magnum 24" long builder-made insert drilled into the center of the web for clearance of the rivet ends to expand. 

I did not care for Avid's Magnum insert plans when I read the manual, and believe Kitfox and Just have a better insert.

EdMO

[tcj 150]

TJay, do you have the instructions for fish mouthing and installing the I beams?  Are your strut attach brackets already drilled?  My concerns are that if you don't install the I beams vertical you will not have the correct edge distance to drill holes in the strut attach brackets and the flanges on top and bottom of the I beams.

 

Besides 4 of the the 40 rivets that attach the rear strut bracket and 10 of the 40 on the front bracket that capture the I beam flanges, there are 4 or five rivets that attach the spar to each flange ( thats 8 or ten on top and 8 or 10 on bottom (16 to 20) additional rivets attaching the I beams to the spars.

Does this help any with your decision?

Edited 9 Oct 2015 by tcj

[TJay 1041]

Maybe I would be better off abandoning all the center holes and re drilling new holes like your print shows or maybe fill the old holes with a rivet that is just sticks through the spar and into the i beam a tiny bit. but in all honestly I really think if the inserts are a 1/8 inch from vertical it would really be no big deal. When I installed the Z bar inserts I put the center of the Z vertical which places the rivet off center by an 1/8 inch top and 1/8 inch bottom, guess I'm not sure what I will do yet.

[EDMO 1078]

TJay, and every one interested,

I am attaching 3 pages from the 1700 gw Avid Magnum manual on building and installing the spar inserts.

I DONT LIKE THIS DESIGN, and would substitute either Kitfox or Just Aircraft inserts if I were building a Magnum, but guess it works!   But, IMO, the Magnum wings don't look as strong as the Kitfox 1 wings with integral web, and certainly not as strong as the later Kitfoxes, or Just with inserts, even tho they are a little heavier wall spars...

EDMO

Edited 9 Oct 2015 by EDMO