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New spars, and different.

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occom

Joined: 26 Aug 2006
Posts: 404

Posted: Wed Sep 06, 2006 2:30 pm Post subject: New spars, and different.

My new spars arrived this morning, and they are  much stronger than the old ones. The new ones are marked .065 wall thickness, I  guess the old ones were .048. The insert web is also much thicker and the insert  is 6" longer. I'm guessing this is all the result of developments that resulted  in the heavier later series like the series seven , Vixen and such.  

  

 The spars are replacing my rear spars, the fronts  are undamaged. I expect they will result in a larger safety margin for integrity  as I'm told the rear spars bear a larger portion of the load. I had previously  noted the new lift struts are beefier than the ones original to my Model  IV-1050. 

  

 So, I've now got a Franken-fox with some stronger  newer parts. Does anyone think the mismatch front-to-back would be an issue? I  will have symmetrey side to side with most ribs original and original spars on  the front. I will be re-using one flaperon and have one from a series six that  appears to match the old one. 

  

 I've attached a photo with the difference in the  inserts showing.

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lcfitt(at)sbcglobal.net
Guest

Posted: Wed Sep 06, 2006 4:02 pm Post subject: New spars, and different.

Dave,



It is my understanding that the "beefier" lift struts are the major portion 

of the conversion from the 1050 GW to the 1200 lb. gross wt.  You might want 

to check into that if you think you might need the extra payload.



Lowell

---

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Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Wed Sep 06, 2006 5:01 pm Post subject: New spars, and different.

At 03:30 PM 9/6/2006, you wrote:

 	  Quote: 	
		  Does anyone think the mismatch front-to-back would be an issue?


	


Very possibly. Your front spars actually carry more load, since the CP is 

only about 30% of the chord from the LE. (Obviously just behind the CG.) 

Now I've noticed that my wings are very flexible. (I don't know what size 

spars I have, but will measure them when I get the chance.) What will 

happen with a softer LE is that when the wings load and deform the local 

angle of attack will increase, which will cause them to deform more, which 

will increase the local angle of attack... You get the idea. Now it's 

possible nothing will happen beyond a certain snappishness to the response. 

It's also possible you'll fail prematurely under load, or will have a 

flutter problem, or will snap roll with a vicious gust. Your's would be 

what we engineers call an "unstable" response. You'll definitely be in test 

pilot mode.



If you have to use these spars, reverse them so the softer spars are in 

back. Better yet, get the right ones. The tubes should be trivial to 

procure. (6061 tubing is ubiquitous.) The inserts a little harder, but 

worst case is you have them welded from scratch. (Cut up a tube that fits 

the ID closely, then weld on a web, then heat treat.) I'll bet John at 

Kitfox LLC has some still, or can tell you the source.

Guy Buchanan

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

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_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

smokey_bear_40220(at)yaho
Guest

Posted: Wed Sep 06, 2006 8:39 pm Post subject: New spars, and different.

I agree.  Stiffer rear spars will make the front spars

seem weaker in comparison causing some divergence and

maybe increasing a chance of flutter.



Test carefully, or change them both.



Kurt S.



--- "Dave G." <occom(at)ns.sympatico.ca> wrote:



 	  Quote: 	
		   My new spars arrived this morning, and they are much

 stronger than the old ones. The new ones are marked

 .065 wall thickness, I guess the old ones were .048.

 The insert web is also much thicker and the insert

 is 6" longer. I'm guessing this is all the result of

 developments that resulted in the heavier later

 series like the series seven , Vixen and such. 

 

 The spars are replacing my rear spars, the fronts

 are undamaged. I expect they will result in a larger

 safety margin for integrity as I'm told the rear

 spars bear a larger portion of the load. I had

 previously noted the new lift struts are beefier

 than the ones original to my Model IV-1050. 

 

 So, I've now got a Franken-fox with some stronger

 newer parts. Does anyone think the mismatch

 front-to-back would be an issue? I will have

 symmetrey side to side with most ribs original and

 original spars on the front. I will be re-using one

 flaperon and have one from a series six that appears

 to match the old one.


	


__________________________________________________

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