Originally Posted by
jtpitkin06
Wing rigging
One might ask, “Why adjust the folded position when the flight position is perfectly adjusted?”
If you could be sure the flight position is perfect then I would agree there is no reason to adjust the folded position unless there is a problem with wing and stab clearance.
Most would agree that the goal is to rig the airplane for flight. But what reference do we use? Some builders use fuselage references for leveling the airplane, such as the door thresholds or upper spar carry through tubes. Those may not be the ideal aerodynamic reference.
The one flight surface that cannot be adjusted is the vertical stab. If we want the flight surfaces aligned with reference to all the others we must start with the non-adjustable surface. For leveling the airplane start with the vertical stab. Use a plumb bob or a level against the rudder hinges. Be sure your vertical stab is, in fact, vertical to the fuselage. Some vertical stabs are a bit warped from the welding process and need to be straightened. If your airplane is already covered then you will have to live with it until the next recover.
Next adjust the dihedral to get both wings rigged in relation to the vertical stab. Then the wing tip washout is set. Finally, the horizontal stab is adjusted to be level when the vertical stab is plumb.
With the airplane now rigged for flight it is time to check the wings folded position. My wing tips were off by two inches. I would have to change each side by one inch. With wings over 13 feet long a one inch change would be about 0.38 degrees. Would that make a significant difference in the alignment or how the airplane flew? As we will see, the flight characteristics are not measurably affected.
The builder must decide which course of action to take.
I could adjust the wings to be near even in the folded position. Aligning the wingtips in the folded position does put the vertical stab slightly out of vertical in relation to the wings. But the amount is small. Readjusted wings would put the vertical stab out of alignment the same 0.38 degrees. However the vertical stab is only about 40 inches tall. That 0.38 degree figure is just 1/4 inch displacement at the tip of the vertical stab. Thus, In my case, the wings were close enough that aligning the wing tips in the folded position did not appreciably affect the aircraft rigging. Remember, these figures are for my wings that were 2 inches out of alignment when folded. If your folded wings are off by as much as four inches you would have a vertical stab displacement of just 1/2 inch.
The final decision, if adjusting the wings for the folded position, is what to do with the horizontal stab. Should it be aligned referenced to the vertical stab, or the wing? I elected to keep it aligned with the vertical stab for purely visual reasons. It is possible that some sharp eyed observer could detect a slight tilt to the horizontal stab if it were aligned with the wing instead of the vertical stab. Aligning the horizontal stab to the vertical stab does put the entire empanage in a small tilt to the wing. Aerodynamically it would not add any measurable undesired yawing moment.
My other choice is to do nothing and live with the wing folded misalignment. The folded position does not affect the flight of the airplane. Visually, it is a minor defect. Mechanically, it is a minor inconvenience. It is possible some of the transport kit bracing would need to be modified with braces of different lengths and noted as left and right.
Thus it is up to the builder to decide which path to take. Adjusting the wings to be near even when folded is possible without affecting the aerodynamics in a negative way. Or, if you prefer alignment perfection with all three flight surfaces, align the wings and horizontal stab referenced to the vertical stab and ignore the folded wing position.
John Pitkin
Greenville, TX
Re: wing alignment
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