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KITFOX STRUT TUBE SIZES?

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Posted

Anyone have info on Wing Strut tube sizes and wall thickness for Kitfox 4 and later?

I have a copy of an article about Kitfox testing the 7/8" KF3(?) struts to 15G of 1050 GW before rod end failed. But no wall given.

Seems to me that these should be plenty strong for 1320 GW.

Avid sizes, wall & GW also appreciated.

ED in MO

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Posted

Can you post that article Ed? Not sure I've seen it, thanks.

Your lift strut answers are here >>> http://www.avidfoxfl...ctural-changes/

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Posted (edited)

Can you post that article Ed? Not sure I've seen it, thanks.

Your lift strut answers are here >>> http://www.avidfoxfl...ctural-changes/

Thanks Doug,

I see that the struts on the 3 were 7/8" x .035 wall, and the 4 was one inch diameter - but didnt get a wall thickness - Am guessing it was .049 ? I was considering going to 7/8 x .058 wall, or by using that size as a shim between the old 3/4 and a one inch x .058 wall. I have a good set of the old Piper J3 struts, but really think they are a lot heavier - got to weigh them.

Will pull the test page out of my book and see if daughter can copy it an post on here. The photos are bad quality. It is from the old Denny newsletter, I think.

ED in MO

Edited by Ed In Missouri

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Posted

Actually the newsletter does say KF4-1200 lift struts = 1.0" dia. x .049" wall.

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Posted (edited)

Actually the newsletter does say KF4-1200 lift struts = 1.0" dia. x .049" wall.

Tried 4 times now to attach strut test page, and failed each time - something wrong - did it OK on last server. ED in MO

Trying one more time. Now got it on here - and I cant open it - BS !!!!

strut test.pdf

Edited by Ed In Missouri

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Posted (edited)

Thanks Doug,

I see that the struts on the 3 were 7/8" x .035 wall, and the 4 was one inch diameter - but didnt get a wall thickness - Am guessing it was .049 ? I was considering going to 7/8 x .058 wall, or by using that size as a shim between the old 3/4 and a one inch x .058 wall. I have a good set of the old Piper J3 struts, but really think they are a lot heavier - got to weigh them.

Will pull the test page out of my book and see if daughter can copy it an post on here. The photos are bad quality. It is from the old Denny newsletter, I think.

ED in MO

OK - If the 7/8 x .035 wall will support 1050 to 15 Gs, Then where will I be with 1320 and .058 wall struts, without the rod ends?

or possibly heavier rod ends?

A little correction here - the 3 has 7/8 - but the strut used in the test was a 2, which I believe, has 3/4 struts. Got to check mine.

Where are the experimental structural engineers with an answer? Please.......

ED in MO

Edited by Ed In Missouri

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Posted (edited)

OK - If the 7/8 x .035 wall will support 1050 to 15 Gs, Then where will I be with 1320 and .058 wall struts, without the rod ends?

or possibly heavier rod ends?

A little correction here - the 3 has 7/8 - but the strut used in the test was a 2, which I believe, has 3/4 struts. Got to check mine.

Where are the experimental structural engineers with an answer? Please.......

ED in MO

I checked the KF2 struts, and they are 3/4", and THAT was what was used in the test. Cant tell what wall unless I cut them, but bet that it was .035, like the KF3.

Ed in MO

Edited by Ed In Missouri

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Posted

Anyone know what size and wall struts and bolts/rod ends are on the Magnum?

If anyone talks to Brett, will you please ask him?

ED in MO

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Posted (edited)

Here are some numbers for you engineering types to chew on:

If the skinny 3/4" x .035 Kitfox 2 struts will pull 15Gs at 1050 pounds before failing (actually, a rod-end failed - not strut),

Then that would amount to 15,750 lbs of force.

If it was loaded to 1320 pounds, then 15,750 divided by 1320 equals 11.93 Gs before rod-end failure, and our planes are only rated at 5.7 Gs, and we would probably pass out long before the strut failed, then these struts should be safe.

Of course, as a practical matter, I plan on making my struts stronger than the ones tested.

OK - that said - please give me some feedback before I start taking nerve pills and chasing them with Bud Lite before I build my new struts.....Thanks.

ED in MO

Edited by Ed In Missouri

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Posted

My buddie who just built the avid/Kitfox hybrid built his own struts too. He made them from one inch material without rod ends on the front strut, only adjusters on the rear strut. Kitfox struts have four rod ends and Avids use only one.

I will see what he used for wall thickness.

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Posted (edited)

My buddie who just built the avid/Kitfox hybrid built his own struts too. He made them from one inch material without rod ends on the front strut, only adjusters on the rear strut. Kitfox struts have four rod ends and Avids use only one.

I will see what he used for wall thickness.

Appreciate any feedback on this - for the record - KF1 and 2 only had one rod end on one wing - why not, since they were Avids with mods - think they went to more rod-ends on the 3 and later. Please ask him. Thanks.

I never saw WHAT SIZE rod-ends they were using in the test at Kitfox, but I will go to a heavier size than the one on my KF2.

You might ask your friend what size he used, both thread size and bolt size.

ED in MO

edit: Just got thru looking at the Magnum manual, and was amazed to see that they still use the same 1/4" bolt at the spar/strut attach fittings as was used on the KF 1 and early Avid models - would have thought that with the increase in GW that they would have gone to a bigger bolt there, so guess it is big enough??? Donno what size KF uses now.........

Seems to me that a more practical way to build struts would be to set up one wing and weld the struts, and then put rod ends on both struts on the other wing so you could make the wings match - doubt if I could weld both sides to match on the front strut - OR, put rod-ends on all 4 struts?

ED in MO

Edited by Ed In Missouri

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Posted (edited)

My buddie who just built the avid/Kitfox hybrid built his own struts too. He made them from one inch material without rod ends on the front strut, only adjusters on the rear strut. Kitfox struts have four rod ends and Avids use only one.

I will see what he used for wall thickness.

hate to dig up the past but did you ever find out what size wall thickness he used and possibly what size rod ends. I'm planning to make new struts soon to replace my 3/4" ones that are on there now. I want to use 1" tubing. for the rod ends is it just a bolt welded into the tubing that the rod end screws onto? I'm thinking it may be better to weld a round coupling nut into the tubing then thread a rod end with male thread into it with a lock nut. thoughts??? 

 

Edit: or would these be better http://www.aircraftspruce.com/catalog/appages/an490.php?clickkey=4183  AN490HT11P seems you would have to weld it into a 3/4" .035 tubing or perhaps 7/8" .095  then weld that into the actual 1" strut tubing. or am I over thinking this??? 

Edited by High Country

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Posted

you beat me to it!!! thanks

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Posted

Not saying this is the right way to do it, but I just had this thought. If both ends of the lift strut were strong enough from the factory, and it was just the 3/4" tube that was a bit to light, what if one were to split a 7/8" tube lengthwise and weld it over the 3/4" tube to further stiffen it up. I was first thinking half of the 7/8" tube in the front of each 3/4" tube, but maybe a thinner wall 7/8" tube and use both sides on each 3/4" tube. Probably be a bit heavier than a 1" tube, but a lot less work. I haven't thought about it for long, so feel free to shoot it down if it sounds stupid. :-) Jim Chuk

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Posted (edited)

Jim,
Leni and I both used 1" x .058 wall tubes for our struts - I am fairly sure that Kitfox uses .049 wall.
I donno what Leni used for rod ends - my originals on the model 2 were 5/16 male thread x 1/4" hole - they were threaded into a solid piece welded into the tubes - I found four 7/16 male thread x 5/16 hole NOS at a bargain on the internet, and put 7/8 diameter x 3" long 4130 female threaded ends that I had made into my tubes and welded them per AC43-13, only to find out that there is not enough room for the rod ends to fit in my spar brackets, so I am making an adapter to mate them to my brackets.
You could cut 6 inches off of each end of your struts, and weld 7/8 spacers on them, and then weld the 1" tubes to them - That would be a lot easier than trying to make a split tube and weld it full length over your old tubes.
Hope this helps or gives you some ideas.
EDMO
EDMO

Edited by Ed In Missouri

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Posted

Actually the newsletter does say KF4-1200 lift struts = 1.0" dia. x .049" wall.

 

Tried 4 times now to attach strut test page, and failed each time - something wrong - did it OK on last server. ED in MO

Trying one more time. Now got it on here - and I cant open it - BS !!!!

strut test.pdf

Found this snooping around, If this test was actuality  done with 3/4 .035 struts, then I really have no reason for making my struts stronger. Makes a guy think I might be wasting my time huh. Then again Nobody has really confirmed that the kitfox 1 and 2 used the same lift struts. Is there any way of really finding that out and making sure kitfox didn't change to 7/8 .035 mid year or something. Or was the test what made them decide to bump the gross weight up to 1050 on the model 3.

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Posted (edited)

TJAY,

The strut test page should be in Files and Forms - I haven't looked at it for a while, so will check it out again.

If you have struts, just measure what the OD is - If it is 7/8, then you are as good as the test - even better if you don't have 4 rod ends.

EDMO

Yes, it is still there - along with our old conversations about it.

Edited by EDMO

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Posted (edited)

TJay,  How much GW are you going to put on this "Modified Kitfox 1 with Avid HH wing spars"?  What are you going to call it, since it is not a standard kit?

EDMO

Edited by EDMO

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Posted

they must have used the 7/8 inch .035 in that test Nevermind I only have the 3/4 .035 better make new ones I will set my gross at 1050, with the 582 not sure I would ever hit that anyway.

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Posted

I just grabbed my calculator, and ran a few numbers comparing 7/8" with 3/4"   The 3/4" is 85% of the 7/8" in circumference.  If the 7/8" tube held 15 Gs, that says the 3/4" should hold 12.85 Gs.  Maybe this is not the right way to figure something like this, I don't know for sure, but it seems to make sense to me.  But then it appears that it was not the tube that was going to fail first.  Jim Chuk

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Posted (edited)

I just grabbed my calculator, and ran a few numbers comparing 7/8" with 3/4"   The 3/4" is 85% of the 7/8" in circumference.  If the 7/8" tube held 15 Gs, that says the 3/4" should hold 12.85 Gs.  Maybe this is not the right way to figure something like this, I don't know for sure, but it seems to make sense to me.  But then it appears that it was not the tube that was going to fail first.  Jim Chuk

Jim,

Since I am not a mechanical engineer, I wonder if the failure of the smaller tube might be in bending (or compression?) instead of stretching (or tension)?  I agree with your calculations, but think that may only refer to tension, as that is how the test was performed.

I guess that 99.44% of the time, the load strain on these tubes is going to be in tension? ???  But I remember reading, that when the monowing planes were first tried, the front of the wing failed by bendind DOWN without a strut there...

EDMO

Edited by EDMO

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Posted

Ed, when I read your last post, I thought of a picture I had saved of a loaded wing.  Don't remember what the wing was for, but it gives some idea of loads anyway.  Jim Chuk

loaded wing.jpg

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Posted

I think the first wing is from a glider, here is Avid's wing test pic.  Looks like they are bending somewhat in the same way though. Jim Chuk

Avid wing stress test 001.jpg

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Posted (edited)

Great photo Jim - Wish we knew more about it.

I think the main difference between static (tension) loads like this, and aerodynamic loads is that in flight everything is not the same...I think there is some torsion loads on the wing too?

EDMO

Edited by EDMO

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