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Old 03-14-2011, 06:38 PM   #1
jtpitkin06
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Default Rigging jury struts

I'm installing the jury struts and have a question on alignment.

My question is: Are the jury struts supposed to be longitudinally aligned with the slip stream?

I understand the struts should be vertical and perpendicular to the cabin floor. I also get it that the lift struts should be straight and the jury strut brackets should be in line with the strut tubing and centered on the spars.

When I get all the points lined up, the jury struts are angled outward by maybe one inch. If I align the jury struts fore and aft, the front bracket is short of reaching the forward spar by 3/8 inch.

I plan on making longer brackets, I just want to know if I'm missing something. Is this typical of the Kitfox?

John Pitkin
Greenville, TX
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Old 03-14-2011, 08:11 PM   #2
Dave S
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Default Re: Rigging jury struts

Hi John,

I do not know if the situation you describe is typical or not. I can tell you my experience - very similar to what you have observed.

For the record - my kit was built by the previous company.

1) When everything is secured - the lift strut tubes have to be absolutely straight - running a tight fishline or string down the lift strut will provide a reference.

2) The Jury struts are intended to be perpendicular to the spar tubes. What I don't know is if it makes any difference if they are angled a bit to be sure the lift strut tubes are straight.

This may be the Norwegian way of doing this (I can say that since my name ends in ...son); but, I elected to cut off the upper 1 1/2 " off the ends of the jury struts - weld on 4130 tubes of the same dimensions that were a little longer - trim the length, flatten the ends and drill new holes. This way the jury struts were perpendicular to the spar tubes and the lift strut tubes were absolutely straight.

Sincerely,

Dave S.

KF 7 Trigear
912ULS Warp
St Paul, MN
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Old 03-14-2011, 11:42 PM   #3
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Default Re: Rigging jury struts

As I understand it, jury struts' purpose is to prevent bending/buckling of the main strut during negative G conditions. Thus the jury strut should be perpendicular to the spar or it's tendency would be to buckle too under high negative G loads. When all was said/done with my Model 2 kit, I also had a little angle to the jury struts when installed per the manual. The angle was < 1.5 deg though and the simple clamp style fittings that attach the jury to the main were easily adjusted. This puts the jury maybe an inch or so further out the span of the main but preserves it's perpendicular orientation.

Chris
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Old 03-15-2011, 07:11 AM   #4
jtpitkin06
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Default Re: Rigging jury struts

It sounds like this is a minor alignment problem. Iíll just make a longer set of brackets at the front where the jury strut connects to the forward spar.


This will accomplish two things:


Iíll get the jury strut alignment into the slipstream which probably wonít make a bit of difference in drag but makes me think I did a better job; and,
The forward attach bolt will not be buried halfway in the fabric covering.


One thing I have to say is how impressed I am with the kit. I got this far without a major snag in construction and this is only a minor detail. Sure, I had a couple of oops along the way like cutting a trailing edge piece on the wrong side of the line. But, so far, I havenít run into anything that couldnít be corrected. Great kit!
JP
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Old 03-15-2011, 09:20 PM   #5
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Default Re: Rigging jury struts

Well, it turns out I donít need longer jury strut brackets.



I made a short phone call to John McBean at Kitfox LLC to ask about fitting the jury struts. He was very helpful in telling me my situation was not normal. We agreed I needed to look for the cause. While not able to diagnose over the phone he did give me some tips on where to look. I have to say the Kitfox customer support is terrific.


Per the assembly manual, I used a taut string to ensure the forward lift strut was not sagging; but the jury strut was still low by 1/4 inch. Shifting the front of the jury strut outboard to raise it up put the fore and aft alignment off by one inch. Not ideal in my book.


With some clues from my conversation with John, I checked the rear lift strut and found it had a warp in the upward direction. That was totally unexpected. I had assumed it would be sagging from gravity.
I gave a quick tweak to the rear lift strut to remove the upward warp and everything came into place.


While some may find this episode a bit boring, I pass this information on as a reminder. When you get stuck, keep asking questions. Try different sources. Keep searching. And feedback, no matter how small, is a big help.


And lastlyÖ if something doesnít seem quite right, it probably isnít.
Net result here is: The problem is resolved and I get to move forward.

John Pitkin
Greenville, TX
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Old 03-16-2011, 04:12 PM   #6
carlisle
 
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Default Re: Rigging jury struts

Good job John. An engineer's perspective for sure and while I can't always claim I'm as persistent about such problems and sometimes compromise where I shouldn't, reading someone elses success stories helps to keep me motivated.

Chris
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Old 03-17-2011, 08:09 PM   #7
Paul Z
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Default Re: Rigging jury struts

Quote:
Originally Posted by jtpitkin06 View Post
I'm installing the jury struts and have a question on alignment.

My question is: Are the jury struts supposed to be longitudinally aligned with the slip stream?

I understand the struts should be vertical and perpendicular to the cabin floor. I also get it that the lift struts should be straight and the jury strut brackets should be in line with the strut tubing and centered on the spars.

When I get all the points lined up, the jury struts are angled outward by maybe one inch. If I align the jury struts fore and aft, the front bracket is short of reaching the forward spar by 3/8 inch.

I plan on making longer brackets, I just want to know if I'm missing something. Is this typical of the Kitfox?

John Pitkin
Greenville, TX

John

If you want to drive to Mesquite you could look at my Plane, to get your answer about the jury struts.
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Old 03-17-2011, 09:01 PM   #8
jtpitkin06
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Default Re: Rigging jury struts

Thanks for the offer Paul,

John McBean answered my questions on how the jury strut it is supposed to align and I found the error was with the rear strut having a slight upward warp. It was easily corrected. All is well and the construction continues at a rapid pace.

The fun meter is pegged.

JP
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Old 03-18-2011, 02:33 PM   #9
SkyPirate
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Default Re: Rigging jury struts

just a thought ,..but are the struts backwards? meaning left is on the right and visa versa?
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Old 03-18-2011, 07:49 PM   #10
jtpitkin06
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Default Re: Rigging jury struts

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Originally Posted by SkyPirate View Post
just a thought ,..but are the struts backwards? meaning left is on the right and visa versa?
Not possible on the SS Model 7. The struts have an upward angled fish mouth on the fuselage end. They are left and right specific and only go on one way.

As I stated, the problem was an upward warp of the strut.

The warp was probably caused by welding heat when fabricated. It was easily corrected once it was discovered.

John Pitkn
Greenville, TX
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