strut cable adjusting?

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RonTurner
Posts: 32
Joined: Sun Nov 05, 2017 7:00 pm

strut cable adjusting?

Post by RonTurner »

Have the wings back on WR-1! Preparing to install the strut crossing cables ? I need some advise on the recommended method of adjusting those cables ? And do I tighten the strut & jury strut bolts before I adjust them? Thanks Ron
RonTurner
Posts: 32
Joined: Sun Nov 05, 2017 7:00 pm

Re: strut cable adjusting?

Post by RonTurner »

Any advice would be appreciated. I've read about the "Twang" method and measuring to the vertical stabilizer but it appears to be offset so I'm not sure about that?
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taildrags
Posts: 637
Joined: Tue Mar 07, 2017 10:39 pm

Re: strut cable adjusting?

Post by taildrags »

Ron; I'm surprised that nobody has replied to your question, because it's something that every airplane needs to have done and it's important to how the plane ends up flying and handling. I haven't had to adjust mine from scratch, only take the wings off and reinstall them a couple of times to move the airplane, so the geometry was already pretty much figured out and I only have to put everything back where it was and lightly tweak everything to get back to correct rig. I would recommend adjusting the struts first, which gets the dihedral and washout set, then check for square by measuring from the same point on both wingtips to a fixed point at the tail. It doesn't have to be the tail post, but the further aft, the easier it is to detect slight differences in the wing positioning relative to the fuselage centerline. You can use a point on the aft turtledeck right ahead of the leading edge of the vertical stabilizer, centered on the fuselage, not on the vertical stab if it's been offset to correct for yaw.

My plane has some dihedral, but the wing can be rigged perfectly level if you wish. I stretched a string tight between the wingtips and the string is about 3" above the top of the wing right at the middle of the centersection. My plane also has washout, which is good for predictability in the stall since it is set up where the stall begins at the wing roots while the tips and ailerons are at a lower angle of attack to maintain stability as the stall develops and travels outward. With no washout, the whole wing stalls at about the same time and with wash-in, the tips stall first, which can drop a wing and make stalls more abrupt. You'll want some washout. You can make a simple plywood template shaped like the upper surface of your wing, with the top edge flat, and then lay it across the wing out near the tip and back near the root, measuring the top surface with a level (or smartphone app that reads out in digital degrees) to see what you've got. The washout can be adjusted by screwing the wing strut attachment forks in or out.

Once the dihedral and washout are set, you can tighten up your jury struts to hold everything a bit tighter in position while you tighten the X-brace cables, but the whole works won't be rigid till the cables are tight so go easy. I bring the cables all up to snug first, and then tighten them to 'twang' one wing at a time and safety wire the turnbuckles. I also use a short piece of plastic tubing over one of the cables where the X crosses, with a small zip-tie to hold the tubing in place and prevent the cables from rubbing together at the crossing. After you rig the wings, clamp the control stick in the neutral position and check the trailing edges of the ailerons to make sure they are both neutral and flush with the wing. Take the airplane out and fly it in calm air to see if a wing is heavy or something doesn't feel right with the rigging, but this is something you will likely be tweaking for many future flights over many future hours, with hands-off level flight being the ultimate goal. My airplane is not there yet, but I'm still searching for the end of that rainbow ;o)
RonTurner
Posts: 32
Joined: Sun Nov 05, 2017 7:00 pm

Re: strut cable adjusting?

Post by RonTurner »

Thank you sooo much Oscar! I became worried no one would reply so I called Bill Rewey yesterday. I always really enjoy talking to him anyway. Very glad you responded with advice and instructions. Having a support group when doing something like this is very important for safety and piece of mind. Bill told me pretty much word for word what you did so I'm now confident of what to do and just as importantly why to do it and now I have them in print not just committed to memory. As they say the devil is in the details and experimental aircraft are all about the details! Planning on finishing her up this weekend as the weather is forecast to warm up here some. This has been such an enjoyable learning experience for me! Thank you again for your priceless help!
RonTurner
Posts: 32
Joined: Sun Nov 05, 2017 7:00 pm

Re: strut cable adjusting?

Post by RonTurner »

Just saw my planes twin sister ( NX17WR ) is for sale in Chico CA. on Barnstormers. Would be nice to see it come back to the Midwest!!
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