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Old 10-22-2009, 07:36 PM   #1
deedus
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Default What would you do? (Rigging)

Just for kicks, lets discuss this senario. My J5 doesn't fly straight without a little control input as follows. The tail will skid to the left without constant left rudder (just a little bit needed) and the right wing will fall off to the right if you let go of the stick. ( still only needs a little pressure). Would you fix it or fly it. Otherwise it handles great as far as stall characteristics and slow flight. We checked the rigging according to Piper rigging procedures and the right wing has no washout in it, left wing was right on. Thought we had found the problem, So we rigged it according to procedure with exact dihedral/washout on both wings and the results were very surprising. It increased the cruise speed of the airplane by at least 5-7mph but compounded the skid/heavy right wing. Wow, didn't expect that. Whats the next step. Put it back and make minor adjustments on the left wing. Thought this would be fun for discussion.



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Old 10-22-2009, 08:25 PM   #2
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Default Re: What would you do? (Rigging)

I know this sounds to simple, but check the rudder return springs and make sure they are pulling on each pedal with the same tension and that the cables are the same length. My J4 was flying more goofy than normal one day and seemed that something had gotten bent, I checked every thing and was stumped as to the problem, day's later my buddy flew it and when he get's out say's " if I didn't know any better I'd swear one rudder return spring is pulling harder then the other " end of problem.

Glenn



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Old 10-22-2009, 08:33 PM   #3
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Default Re: What would you do? (Rigging)

Maybe an aileron out of rig?

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Old 10-22-2009, 08:35 PM   #4
JimC
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Default Re: What would you do? (Rigging)

Is it skidding to the left, or yawing to the left?
I'd fix it.
With no washout on the right wing, you were prone to tipstall on the right wing and right wing drop (possibly severe) on stall, so you're better off for having fixed the washout.

The rudder return spring suggestion is really good and should be done first -- having the tailwheel cocked can cause the symptoms you describe.

Assuming the tailwheel rigging is OK, check the vertical stabilizer rigging. If it's off, correct it, and then if need be, adjust the vertical leading edge slightly to minimise the right turning tendency (that will also reduce the tendency for the right wing to fall off). After the rudder is sorted out, you can slightly adjust the washout of either or both of the wings to stop the wing drop and turn tendency. The left wing would need a bit more washout, which will reduce the right turning tendency because of reduced lift on the left, but will increase the right yaw tendency due to reduced drag on the left wing. You might then need to tweak the vertical stabilizer again.

An aileron out of rig will NOT cause the symptoms you describe unless one of the ailerons is bent along its length.

Personally, I like to keep a very slight right turning tendency at cruise so that I have to use a tiny bit of left stick -- it takes the slop out of the system. Keep in mind that the wing drop and turning tendency is going to vary with both weight and power variations -- that's normal.
JimC

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Old 10-22-2009, 09:15 PM   #5
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Default Re: What would you do? (Rigging)

You can rig them right by the book, but you need to fly them to get them perfect. If right wing heavy, then either go in on the right rear strut fork 1 1/2 to 2 turns OR go out on the left rear strut fork the same amount. Fly it and check again, maybe it might need another turn or so. I like to keep as much of the fork in the strut barrel as I can. As for the yaw, many times you can adjust it out be CAREFULLY bending the leading edge of the fin in the direction you need. Use hand pressure and apply force (a little) at the top of the fin. Clyde Smith advises a slight bend of the fin to the left if you are behind the plane so the top of the fin "aims" at a spot about 2" to the left of the center of the top of the cabin. Less for low HP ships maybe a little more for higher HP. Should fly perfectly straight with hands off and feet on the floor in cruise.

Bob

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Old 10-23-2009, 01:00 PM   #6
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Default Re: What would you do? (Rigging)

I agree with Bob. Keep in mind that going IN on the rear lift strut will increase the drag on that wing and produce a yawing moment that shifts the tail AWAY from that side. Going OUT will do just the opposite.
JimC

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Old 10-23-2009, 02:27 PM   #7
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Default Re: What would you do? (Rigging)

Ah Hah, The rudder return spring may be the culprit for the left skid as one of them on the left side is broken. Now for the right wing. Remember I checked the rigging and found no washout so we adjusted the rear strut out to get the correct reading. But that compounded the heavy wing/right turning tendency. So back to the drawing board.

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Old 10-23-2009, 03:50 PM   #8
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Default Re: What would you do? (Rigging)

Only do one thing at a time, adjust only one thing and then fly it before you change anything else, or you may end up with a boomerang.

Glenn

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Old 10-23-2009, 04:10 PM   #9
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Default Re: What would you do? (Rigging)

Well, that matches up with what I said. Keep in mind that a broken left tailwheel spring will drop the right wing if the springs have any tension on them (no effect if they are slack). After you fix the tailwheel left spring, fly it again and if the right wing is still dropping and you're still yawing left (I assume you are yawing rather than skidding), Make sure your vertical stabilizer position is correct and if so, then either increase the left washout, decrease the right washout, or both.
JimC

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Old 10-24-2009, 06:42 PM   #10
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Default Re: What would you do? (Rigging)

An aileron out of rig will NOT cause the symptoms you describe unless one of the ailerons is bent along its length

That, from Jim C above. He is of course correct. If you have not yet fixed your problem, take the aircraft up and trim for level cruise flight. Then let go of the stick, and look out both windows. The ailerons should be faired up with the wing trailing edge, or at least up or down the same amount.

By that I mean: If the left aileron trailing edge is down a bit, then the right one should be down the same amount. If one is up and the other down, go directly to Jim's quote above, and get your ailerons fixed. They too need washout, or washin, or whatever they are supposed to have. They are not supposed to be a plank.

Few aircraft will fly straight with both hands and feet off the controls. If you cannot fly a cross country using only your feet, something is not right, and should be fixed.

Opinion.


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