Wing Strut Wood

[birddog486 21]

I see theres a conversation on the Yahoo site about the wood wing strut fairing being a required structural component and, Avid sent out an AD on it in the early days.

 

I'm pretty sure I've seen both Avid and Kitfox without these installed.  Thoughts??

[C5Engineer 1170]

I've seen them without and Kitfox sells a retrofit kit just for those. This is strictly my opinion but if that wood glued on there makes the difference of my wings folding or not I am really scared to go flying again!! It does add some rigidity but I don't think it's that much.

[Av8r3400 1179]

The Yahoo group is almost a non issue any more.  Any relevant data is nearly gone.

 

I have seen that conversation, too.  I wanted to join, but decided against.

 

As Joey said, if the wood is really structural, than my Mangy Fox should have folded in the first 200 hours of it's life without them.  They add 8-10 mph in cruise.  To me that makes them pretty useful, but I don't think mandatory.

[thebriman 69]

I know of a Kitfox 4-1200 without them.  The wings are still there.

[EDMO 1078]

Someone said that Dean Wilson flew the early (3/4?) struts at 1500 TOW (without spar inserts?) and they held - then they went to 7/8 and now at 1 inch with spar inserts - I can't see a piece of wood that probably only stiffens them fore and aft, with most of the stress being up and down, doing much good.  Good engineering has a safety factor of 150% - Don't you think that Dean is a good engineer - and look at how much stronger we make struts now.

I think all the wood or fiberglas fairings (and Joey's Lexan) are good for, is drag reduction.

The strut tests on the 7/8 was posted on here - may be in "files and forms" - and they held to about 15,000 lbs - and the rod end failed.

Yes, that was 15 Thousand - Not a misprint!

EDMO

Edited 4 Apr 2014 by Ed In Missouri

[Trackwelder 12]

I believe after lookingat steve wittmans Buttercup and Tailwind Plans, that the Jury struts are taking the need for the wood fairings extra buckling strength out of the picture, I remember the amount of load that an unsupported Avid A model wing could take and believe that you could get away without the fairings. That said, the aerodynamics mean that some sort of fairing needs to be on there.

[SuberAvid 617]

There was a KF at Birchwood with 2X4's for lift struts (wish I had a picture of it now).  Of course that was after the heavy snow we had that year collapsed the struts.      Obviously the lift struts will take a lot more in tension (pos. G's) than in compression ( neg. G's).  The question is, that is the weakest link?  I had heard the same thing about the wood fairings being a required structural necessity and I am sure they add some strength but one would have to see the calculations to see if they are the weakest element in the system of the wing.  The rod end apears to be a weak link and I need to try to find some information of the alllowable working load for them in tension and compression.  Does anyone have that?  I would like to read the strut test information Ed mentions also if anyone knows where that is located.  It may save me the effort and expense of cutting up my 7/8 lift struts and welding in 1" tube.  The 1/4 " lift strut attach bolt have been mentioned as possible weak links as well but they are in double shear loading verses single tension/compression loading so I don't think they are the weakest link but need to check them. 

 

Ed, your right, it only needs to be as strong as needed with a reasonable SF (1.5).  Anything else is just extra weight.

[akflyer 1427]

There was a KF at Birchwood with 2X4's for lift struts (wish I had a picture of it now).  Of course that was after the heavy snow we had that year collapsed the struts.      Obviously the lift struts will take a lot more in tension (pos. G's) than in compression ( neg. G's).  The question is, that is the weakest link?  I had heard the same thing about the wood fairings being a required structural necessity and I am sure they add some strength but one would have to see the calculations to see if they are the weakest element in the system of the wing.  The rod end apears to be a weak link and I need to try to find some information of the alllowable working load for them in tension and compression.  Does anyone have that?  I would like to read the strut test information Ed mentions also if anyone knows where that is located.  It may save me the effort and expense of cutting up my 7/8 lift struts and welding in 1" tube.  The 1/4 " lift strut attach bolt have been mentioned as possible weak links as well but they are in double shear loading verses single tension/compression loading so I don't think they are the weakest link but need to check them. 

 

Ed, your right, it only needs to be as strong as needed with a reasonable SF (1.5).  Anything else is just extra weight.

 

The AD (Avid Directory) states that the wood fairings add strength under compression loads.  I upped my struts to 1" X.058" so I could use the Kitfox PVC fairings.  They added a lot of weight, but also helped a bunch in cruise and climb.  My original struts had the wood fairings, but they were not bonded well nor sealed well and they rusted out BAD under the wood.  As I use the plane on floats the last thing I wanted was wood fairings that hold moisture!

 

Here are the AD's that I have and AD 007 is the one that talks about the counterweights and the wood fairings.

Avid AD's.pdf

[EDMO 1078]

Randy,

      I was the one who posted the strut tests - could have been Kitfox tests - anyway, I cant find it in files and forms, or other places - Cant remember what title I put on it - I think that Doug wanted to copy it

- I will look in my books and if I can find it, I will post it again and let you know.

      If the standard rod end lasted up to 15 Thousand pounds, then I presume it is safe to use it - I would be gone by 15 g's anyway!

The rod end is for a 1/4 inch bolt.   The same size is used on the 1700 gw Magnum......so, figure?

One thing I might add:  When the strut end was changed to a rod end, they narrowed the space on the Spar fittings to match the rod ends.   Would a spacer or two work for that with the old Spar fittings?

EDMO

Edited 4 Apr 2014 by Ed In Missouri

[akflyer 1427]

Randy,

      I was the one who posted the strut tests - could have been Kitfox tests - anyway, I cant find it in files and forms, or other places - Cant remember what title I put on it - I think that Doug wanted to copy it

- I will look in my books and if I can find it, I will post it again and let you know.

      If the standard rod end lasted up to 15 Thousand pounds, then I presume it is safe to use it - I would be gone by 15 g's anyway!

The rod end is for a 1/4 inch bolt.   The same size is used on the 1700 gw Magnum......so, figure?

One thing I might add:  When the strut end was changed to a rod end, they narrowed the space on the Spar fittings to match the rod ends.   Would a spacer or two work for that with the old Spar fittings?

EDMO

 

The one rod end I have just had a stack of washers in there to take up the space.  It has held up just fine for 600 hrs that I know of

 

[akflyer 1427]

http://www.avidfoxflyers.com/index.php?/topic/264-m-t-o-w-modifications/?p=1010

 

This is a previous discussion that Doug posted up.  It goes deep into the max weights and the reported testing.  I know I have seen pictures and write ups of the load tests someplace on the web and I will see if I can dredge them up.