spar question

[TJay 1041]

Hey guys I have 4 spars here 2.5" 2024-t3 .083  and I see the book says 6061-t6 .065 for my kitfox 1 would you use the heavy ones or order new ones from spruce. also I have the stiffeners shaped like a Z, 48" long would you use those or get the updated I beam. thanks

[High Country 69]

if the z stiffeners that you have fit the .083 tubing than I would just use it. this setup will be plenty strong for you KF 1. I'm running .083 tubing with just flat plywood stiffeners as per the original Avid manual and have no concerns with it for the gross weights that these early planes are for (I'm set at 1050) FWIW the setup you have with those stiffeners is probably stronger than mine and I have no worries at gross or even ahem... above. 

[akflyer 1427]

I am not so sure about the 2024 T3.  All the other avid / kitfox that I know of use 6061 T6 for the spars.  Mine are .083 as per the HH specs.

 

[EDMO 1078]

I believe the 2024 may be slightly stronger and cost more than 6061 - either one in .083 is a lot stronger than the .065 originally used, and still in use, for the Kitfox 1, and all Kitfoxes - the original GW for the Kitfox 1 is only 850 lbs.

EDMO

[akflyer 1427]

the 2024 is stronger yes.. but as much as these wings flex, will that be an issue over time

 

[EDMO 1078]

I would think that the .083 2024 would flex less? ?  Maybe put more stress on the cross tubes?

EdMO

Edited 26 Dec 2014 by Ed In Missouri

[FoxDB 17]

Just a side light with no bearing on the spar issue but the flex (or deflection) of the material does not have to do strength but modulas of elasticity. For aluminum that is 10 x 10 to the 6th.

Dave

[EDMO 1078]

Not being an engineer or metallurgist, I cant compare the copper/aluminum 2024T3 with the silica?/aluminum 6061T6 for elasticity, but it would be hard for me to imagine that they would both have the same as pure aluminum.

I think the 2024T3 is stronger, maybe harder - read that as stiffer - and I know that the .083 is stronger/stiffer than .o65 wall used in the original Kitfoxes.

I leave the engineering specs to the engineers - I just know what seems logical. 

If there was no differences in different types of aluminum alloy, then why do aircraft companies use different types in the same plane?

My lifetime work has been with the differences in steel alloys which vary greatly in strength and other properties. 

I have some papers from an FAA engineer on the modulas of bending (?) of some 6061T6 aluminum tubes, but I get a headache when I try to read them!  

EDMO

Edited 27 Dec 2014 by Ed In Missouri

[FoxDB 17]

Not trying to oneup just educate. Elasticity is prior to failure of the material in yield strength. This is why we see such wing defection in an airliner in turbulence, but it does not fail due to the yield strength of the aluminum alloy. Hardness is not stiffness.

Edited 27 Dec 2014 by FoxDB

[EDMO 1078]

I graduated back when everything was paper and pencil - Maybe too old to educate now?

EdMO

[akflyer 1427]

I was hinting at that when I made my statement. Some aluminums will bend and flex all day long and return to shape with millions of cycles needed to fail. Others, while "harder" or higher strength will only bend once and stay there, or will flex a few times and break. Hence my question of whether or not 2024 or 7075 would make a better spar material than 6061. For some reason, the faa loves 6061 t6 for load bearing structures and fittings. When we were machining float rigging, they would only let us use 6061 t6.

[EDMO 1078]

I think 2024 has more tendency to corrode than 6061 - might be wise to get some paint on those spars?

Would anyone have a clue as to how the .065 spars with the insert compare with the strength of the earlier Kitfox spars with the full-length extruded I-beam? I am of the opinion that that early spars may be stiffer/stronger, but maybe a little weaker at the strut attachment because there is no doubler inside the spar.

I have never heard of any wing/strut failures without some kind of ground accident.

I bought mine way back when these were still available when I was going to build the Kitfox 1 clone.

EDmo

Edited 28 Dec 2014 by Ed In Missouri

[TJay 1041]

Hey guys back from the cabin here and catching up, I spoke with John mb at kitfox a while back and he said use the 2024 t3 if you have them. So I will, and Im not to worried about the flexing,  Im going to keep my wings short at 12 foot instead of the 13 foot 6 inches the books call for. should be a strong little airplane hope so at least, like always it will be flying over gross ha. Now hopefully I can hammer down at nights and weekends again and get her done.