Avid A wings on a KF 3???

[6320012s 12]

Looking for informed opinions on the prospect of using my Avid A wings that have been hanging in the garage for 25 yrs on my KF3.   As far as I can see, the dimensions all match although I haven't tried to actually fit them up.  

The spars are .070 and the KF 3 are .060.

The spar stiffener is plywood instead of the KF I beam

The struts are .75 instead of .875 on the KF.

The Avid A is rated at 950 gross and the KF is rated at 1050.

The Avid A has rounded wing tips and the KF has droop tips.

The Avid A has trailing edge cable and KF has formed TE.

 

My thoughts:

The main difference is the struts (which I suppose I could have a .875 or 1.0 set made,)  I would guess the shear on the bolts is less than the yeild on the .75 tubing, although I gues if would fair even worse than the .875 if I ever flip it again.  (the .875 didn't want to support the Fuselage in the inverted position without bending)

My guess is that the primary gross weight limit on the Avid A is with the  Fuselage and landing gear not the wing.  Is there something I am missing?

The flaperons and airfoil seem to be identical.  Is that correct? 

Since I have the extra fuel tanks, I am thinking of adding at least one if not two to the avid wings.  This will require removal of a drag tube, but the tanks are rivited in so should take the drag load.

Any opinions on the droop tips vs rounded or the cable vs formed T.E.

Also considering inserting a strip of 1/8 plywood in the center thirtd of the spars and filling each side with foam to increase rigidity.  Any thoughts?

 

Thanks for your help, I'm dying to get back in the air, but can't afford the 200 hrs to build a whole new set of wings.  My other option is to buy a complete set of KF 3 wings I found for sale and ship them to AK.  Still no struts though.

 

 

[EDMO 1078]

There are probably minor variations in the wall thickness of all spars - probably enough for you to get .005 difference in both of your readings.

IMO, if you stay at your Avid GW of 950, you are the same weight as the Kitfox 2 with the 3/4 struts - If you plan on the increase of GW to 1050, then you might want to splice some 7/8 tubing to the cut-off ends of your 3/4 struts - that is the increase they made for the Kitfox 3 at 1050.

I don't think that you would notice any flight difference in the tips, except that the Kitfox tips are a lot heavier than the Avid tips.

The only Avid fuselage strut attachment I have seen is different than the Kitfoxes I have - and I don't think they will interchange without modifications somewhere. I forgot which you have - If you have (xxxxAvidxxxx Correct this to read Kitfox) struts, then they should fit with no problem.

The biggest thing is getting your spar to fuselage bolts in - you might have to enlarge the holes to make them match.

There's my 2 cents worth - for what it is worth - why put off flying when you have wings!

EDMO

Well - I sure screwed this up - got it bassackwards - You are going the other way - blah - blah - blah! The Avid wings are about 3 feet shorter span than the Kitfox, but unless you are trying to set some STOL records, it probably wont matter.

P.S. I am TOTALLY OPPOSED to riveting the tank to the spars - I would not drill all those holes in my spars - Kitfox didn't drill theirs - Just used GE Silicone II. That's my 5 cents worth!

ED

Edited 2 Sep 2013 by Ed In Missouri

[1avidflyer 1983]

Just a heads up, the gross weight of an Avid A was around 760 lbs. The B was listed at 911 lb.   Not sure if the wings were the limiting factor on that though.  The strut attachments are different from the Kitfox to the Avid as well.  Jim

[EDMO 1078]

Just a heads up, the gross weight of an Avid A was around 760 lbs. The B was listed at 911 lb.   Not sure if the wings were the limiting factor on that though.  The strut attachments are different from the Kitfox to the Avid as well.  Jim

That's a big difference Jim - As best that I know, there is a difference in the crossover tubes that affects Gross Weight, along with struts and longerons - Just look at the Kitfox 1,2,3, and early 4, with the different gross weights and the same spars.

Since he has the Kitfox 3 fuselage and the 1050 weight was for that with the 7/8 struts, then the Avid wings would probably be OK, but he would have a slightly higher wing loading - I could figure that out, but it would not be too much difference. This would actually give him MORE safety factor in rough air.

I cant verify this, but someone posted that Dean Wilson flew the Avid at 1500 GW, but didn't say which model. I know the KF 3 struts were tested to 15 G's before a rod end failed - that would be about 15 THOUSAND POUNDS, more or less. I would think that the 3/4 struts would be OK for the 1050 GW - They would probably test out at 10,000 lbs, or so?

Most everything built is designed with a 150% safety factor - just something to consider.

EDMO

P.S. Just for curiosity, I did the wing loadings:

Kitfox wings = 32 ft. span x 4.25 chord = 136 sq.ft at 1050 lbs. = 7.7 lbs/sq.ft.

Avid wings = 29 ft. span x 4.25 chord = 123.25 sf at 1050 lbs. = 8.5 lbs/sf

of course these loadings are not constant across the wing - about 3/4 of the total lift is between the fuselage and the strut attachments.

ED

Edited 2 Sep 2013 by Ed In Missouri