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Skidding 12

skukum12

MEMBER
The Last Frontier
Hey all, recently tore down and recovered the 12 fuselage. Wings on and flying again, wow what a lot of work. Anyway, she has always flown a half ball left of coordinated in hands/feet off the controls. All it took was to rest the left boot on the rudder to fly straight. Now the ball is pretty much pegged left and it takes a whole bunch of left boot to keep her headed in the direction I want to go.

We didn't change strut fork lengths, ailerons, actually we didn't even touch the wings. Same motor, prop. However we did get a new engine mount, could it be that the mount is not square and causing an exaggerated right yaw? It sure is tough on the ol' left leg and flying right wing up is getting old quick. Maybe vertical stab got tweaked in an overtight fabric situation?

Suggestions?
 
Take a look at how well the flaps line up with the bottom of the wings while in flight. If one flap is down at all, it will pull the ball off center.

I should have done this myself. It is clear that the right flap is adjusted to be ever so slightly down in flight. Unfortunately, I tweaked my vertical stab before I noticed the flap and will be likely tweaking the stab back after I readjust the flap.

Jeff
 
you need to"rig" it which really gets you back to squared up... then IF you even have any issues you can go from there.... crazy not to....
 
One flap does travel higher but next flight I will take a good look. Re rigging crossed mind but I sort of dismissed it because we didn't mess with attach points or wings. Thanks gentlemen.
 
.. Re rigging crossed mind but I sort of dismissed it...
it's quite mislabeled... it should really be called getting you back square and a neutral starting point... cause you have no IDEA what voodoo the last guy did..... it's WELL worth your time...(takes 20 minutes...maybe)
 
Won't make it this year either, work schedule conflict. However will be flying up to Nome at some point.
 
Hey all, recently tore down and recovered the 12 fuselage. Wings on and flying again, wow what a lot of work. Anyway, she has always flown a half ball left of coordinated in hands/feet off the controls. All it took was to rest the left boot on the rudder to fly straight. Now the ball is pretty much pegged left and it takes a whole bunch of left boot to keep her headed in the direction I want to go.

We didn't change strut fork lengths, ailerons, actually we didn't even touch the wings. Same motor, prop. However we did get a new engine mount, could it be that the mount is not square and causing an exaggerated right yaw? It sure is tough on the ol' left leg and flying right wing up is getting old quick. Maybe vertical stab got tweaked in an overtight fabric situation?

Suggestions?

Skukum12,
Did you fix your problem?
I have a 12 with a similar issue and would like to chat with you.
Kind Regards Jeff


Sent from my iPad using SuperCub.Org mobile app
 
One thing to keep in mind when recovering a fuselage is that it's REALLY easy to "tweak" the vertical fin when shrinking fabric. And, that can induce yaw.

MTV
 
Look forward over the top of the vertical stabilizer. Does it point slightly to the left of the fuselage centerline? Experienced mechanics here may know the exact amount of "slightly" I've run a string across the stabilizer's C/L to the skylight C/L and a 3/8-1/2" offset from the skylight seemed to work. Probably depends on the plane.

Edit: Ball to left move front of vert stab to right? Opposite for ball to right?

Maybe vertical stab got tweaked in an overtight fabric situation?

Gary
 
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Zero thrust line on the engine requires the leading edge of the vertical stabilizer to be off set. The Bearhawk offset is 3/4” from centerline.


Sent from my iPad using Tapatalk Pro
 
This isn't complicated just step on the ball. As Mike says if the ball is out to the right we step on the ball to recenter it by adding right rudder. Then match the fin offset to the rudder offset C/L-move front of the fin to the left and retest. If the ball is out to the left add left rudder and then match the fin to the rudder and retest. This usually assumes a steady airspeed and power like cruise and proper rigging for the airframe and engine. Just an observation from the planes I've owned. There may be other options like a rudder trim fixed or variable.

Example: https://www.youtube.com/watch?v=gzaqRyNFdc0

Gary
 
I found an -18 one time which flew perfectly, except that the ball was out by 1/2. The fuselage was hanging from the wings crooked. Both forks were into the struts on one side and out from the struts on the other. Moved both front and rear strut forks the same amount in, and out on the other side. The rigging did not change, the ball went to the middle.
 
Wings need to be equal. Washout - flap and aileron position - dihedral - incidence at fuselage...things like that before the rudder or fin is messed with. With a digital level it's easier now to measure. The skid-slip indicator ball should be checked for centering when the fuselage is leveled laterally on the ground. I've seen rudders that were bent/curved maybe from uneven fabric shrink or impact. A non-centered tailwheel in flight can turn the plane and require rudder correction.

Gary
 
And if and when you put it on floats, (especially with dual water rudders), don't mess with the aircraft rigging if it doesn't fly straight. Simply adjust the water rudders to bring it back into shape. Doesn't take much. When you return to wheels it will be right where you left it.
 
Make absolutely certain that it is correct before you install the floats. If you don't, you will not have a clue where the error is.
 
I found an -18 one time which flew perfectly, except that the ball was out by 1/2. The fuselage was hanging from the wings crooked. Both forks were into the struts on one side and out from the struts on the other. Moved both front and rear strut forks the same amount in, and out on the other side. The rigging did not change, the ball went to the middle.

Sky wagon
I have a similar situation to what you are describing above
I am showing ball out by 1/2 to the right
On the L/H side both forks are all the way in, on the R/H both forks are out 5/8”
What do you suggest
Move both out on the LH? (Increases dihedral) Or
Move both in on the R/H? (Decrease dihedral)
I triple checked level, & dihedral (currently 3 1/8” measured with string) washout, tail feathers etc.
I don’t want to add a trim tab if I can help it.
Appreciate your feedback

Jeff


Sent from my iPad using SuperCub.Org mobile app
 
Sorry Sky-wagon, I just re-read your post, I see now you moved both sides the same amount. How many turns?


Sent from my iPad using SuperCub.Org
 
Sorry Sky-wagon, I just re-read your post, I see now you moved both sides the same amount. How many turns?
However many turns makes the two front strut fittings or total strut length bolt to bolt match. The rear strut lengths control the wash in/out effecting wing heaviness. When you turn the rears in this situation make sure that it is the same number of turns as it's respective front strut. Also check that the screws on the T&B instrument are parallel to the upper front spar carry through tube. The instrument also has to be straight. If you have a twisted fuselage you may have to make an adjustment to suit.
 
PA-12 discussed here: https://www.youtube.com/watch?v=J3u_46RPrXk&feature=youtu.be

Looking back to front at 0:48 as the camera swings around it appears the horizontal tail is tipped to the right. The upper slots in the fairings are different but might be their attachment varies. Rudder is offset so it's hard to sight across the vertical stabilizer to the C/L of the cockpit. Dihedral appears equal.

Gary
 
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Jeff could be optical delusion. If you have any flat pavement around for a quickie measure from the gear or lower engine bolts to ground, then ends of horizontal stab or elevators. Try to get it level in other words then check the tail surfaces. You can also measure from the upper wing strut bolts to ground with a plumb bob to check equal dihedral.

It sure looks off but pictures lie. I'm no where near as short and fat as I appear.

Gary
 
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