rigging Cub wings

Unexpected upset and resulting spins were a mystery yet common when CG Taylor started in the aviation industry. Rudders on some were often an afterthought both in design and use in initial training. Later flight testing identified various parameters for early aircraft: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082385.pdf Plane #3 is a J-3 and #5 a Taylorcraft. Read the results.

VG's can modify the behavior, especially for a Taylorcraft with the potential for an aft LE flow discontinuity and asymmetric wing stall. Fortunately the rudders on both are effective.

Gary

BC12D-4-85 said:

Unexpected upset and resulting spins were a mystery yet common when CG Taylor started in the aviation industry. Rudders on some were often an afterthought both in design and use in initial training. Later flight testing identified various parameters for early aircraft: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930082385.pdf Plane #3 is a J-3 and #5 a Taylorcraft. Read the results.

VG's can modify the behavior, especially for a Taylorcraft with the potential for an aft LE flow discontinuity and asymmetric wing stall. Fortunately the rudders on both are effective.

Gary

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Gary, you read way too much dry crap...Dr. Tim

I suggest one test after rigging. In addition to the normal post-build flight involving stalls and other maneuvers, try several extended takeoffs at minimum power. I've found that if one wing is prone to more lift than the other it'll be the first to leave Earth. Quick high power acceleration and prop flow can mask that differential lift effect. It can sometimes be revisited during coordinated stalls with the light wing letting go first with the ailerons neutral. Adjust the wing rigging for uniform lift and stall if possible, and ensure the T&B ball is centered in hands off flight during cruise. Vertical stabilizer offset is our friend.

Gary

Hello. I have a question on rigging a PA-18, too. I place it here to not open a new thread so everything is in one place. If I may.
Here is the question: I know SB 910A (Service Memo 19). I would first hang the wings on the leveled fuselage. Then mount the front struts and adjust dihedral. Having done that I would mount the rear struts and adjust wash out. Last step would be mounting the jury struts. Is that correct so far?
I think the main struts might bow slightly without jury struts. So I would mount the jury struts taking care not to alter the bowing of the main struts. Is that correct, too?
Thank you so much! Bjorn

Altmuehltaler said:

Hello. I have a question on rigging a PA-18, too. I place it here to not open a new thread so everything is in one place. If I may.
Here is the question: I know SB 910A (Service Memo 19). I would first hang the wings on the leveled fuselage. Then mount the front struts and adjust dihedral. Having done that I would mount the rear struts and adjust wash out. Last step would be mounting the jury struts. Is that correct so far? YES
I think the main struts might bow slightly without jury struts. So I would mount the jury struts taking care not to alter the bowing of the main struts. Is that correct, too? NO
Thank you so much! Bjorn

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The main struts must be straight. The jury struts are there just to stabilize and prevent the main struts from bowing. They carry no wing loads.

skywagon8a said:

The main struts must be straight. The jury struts are there just to stabilize and prevent the main struts from bowing. They carry no wing loads.

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I wouldn’t say no load. They are very important


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mike mcs repair said:

I wouldn’t say no load. They are very important

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Yes they are important. Their job is to keep the main struts stiff and straight. They do not carry flight or landing loads.

skywagon8a said:

Yes they are important. Their job is to keep the main struts stiff and straight. They do not carry flight or landing loads.

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they keep the wings from flexing.... using strut in flight as support

go to an uncovered wing hanging on plane with and without rear jury strut and flex at wing tip... huge difference....

Thank you for the answers.
Today I removed the jury struts and I have the feeling that the main struts bow slightly without them. I had nothing at the hangar to check it so I might be wrong.
If I my impression doesn't fool me I think I need a gadget to prevent bowing of the main struts while rigging... Or is the bowing without jury struts neglectable?

Altmuehltaler said:

Thank you for the answers.
Today I removed the jury struts and I have the feeling that the main struts bow slightly without them. I had nothing at the hangar to check it so I might be wrong.
If I my impression doesn't fool me I think I need a gadget to prevent bowing of the main struts while rigging... Or is the bowing without jury struts neglectable?

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I don't worry about it. Seems like not a big deal for initial rigging. I have not run into a problem and I rig dihedral first with just the front struts pinned. Good luck.

T-craft wash out is made by adjusting jury strut length, hence bowing main liftstruts/wing spars...


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T-craft rear strut has adjustable threaded insert at top end- never heard of adjusting jury struts to change washout...

My 1941 Taylorcraft has adjustable length jury struts both front and rear. Threaded adjustable fittings at spar bottom/upper jury strut connection. Use them to straighten main struts after rigging. If the mains bend some and are bothered then temporarily tie a piece of tubing, angle, or wood lengthwise to offer support. The potential change in length slightly bowed versus supported and straight is inconsequential for me. Cub jury fittings can be slid up or down the main struts slightly to correct for bowing.

Gary

ak49flyer said:

T-craft rear strut has adjustable threaded insert at top end- never heard of adjusting jury struts to change washout...

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Yeah, I've never heard of washout being adjusted with jury struts. The rear lift strut has an adjustable barrel for washout.

I can definitely believe they were to adjust for straightening main struts. I though Maule's tolerances on welded parts was bad until I started selling Tcrate struts. Anywhere from 0 to 8 degrees of angle on the rear strut wing attachment. Struts have to be fitted to the individual wing and how it's built. Wouldn't surprise me if the same was true for jury struts.

mike mcs repair said:

they keep the wings from flexing.... using strut in flight as support

go to an uncovered wing hanging on plane with and without rear jury strut and flex at wing tip... huge difference....

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They are for flutter prevention of both the wing and the long strut. The main struts need to be straight for structural purposes. Granted a small bow may not make much difference, but it is not correct.

Successfully rigged. Thank you!

Interesting point on rigging Cubs ...... Everyone seams to think "by the book" rigging is the final answer. And in a perfect world it is. However: probably 80% of the Cubs floating around have not been in a jig, in 50/60 years! So when you level the fuselage perfectly level, ( some form of shimming) and set the wings precisely, from that. Don't be shocked when you set it back down on the level floor on its gear, that a quick measurement from outta wing strut bolts to the floor, will now show you how "crooked" your airframe is, with perfectly rigged wings to an absolutely level airframe?
Another quick check: is to just set both fork ends: To say 6/7 turns out; ( with standard 122" struts that will be close to the 1 degree of dihederal) Then slap the struts on, and see how far off the altitudes are: on the outta strut attach bolts. ???[emoji848]
Lots of folks flying around with same amount of threads showing on both sides.
But when observed on the ramp it is certainly NOT level at all.........[emoji2955] Unless the airframe is absolutely perfect, not likely on most of the Cubs out there.[emoji36]
E

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TurboBeaver said:

Interesting point on rigging Cubs ...... Everyone seams to think "by the book" rigging is the final answer. And in a perfect world it is. However: probably 80% of the Cubs floating around have not been in a jig, in 50/60 years! So when you level the fuselage perfectly level, ( some form of shimming) and set the wings precisely, from that. Don't be shocked when you set it back down on the level floor on its gear, that a quick measurement from outta wing strut bolts to the floor, will now show you how "crooked" your airframe is, with perfectly rigged wings to an absolutely level airframe?
Another quick check: is to just set both fork ends: To say 6/7 turns out; then slap the struts on, and see how far off the altitudes are: on the outta strut attach bolts.
Lots of folks flying around with same amount of threads showing on both sides.
But when observed on the ramp it is certainly NOT level at all.........[emoji2955] Unless the airframe is absolutely perfect, not likely on most of the Cubs out there.
E

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I put struts off a cub that was in a jig on one that wasn’t. Fly’s beautiful, but it sure does sit lopsided


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I am swapping a set of sealed for aluminum struts, I am planning on a measure and make them the same, then swap them out one at a time, test fly to verify that they are the same as when Atlee put it together 30 years ago. Tim