Aircraft rigging and alignment

[azblackbird]

For all the airframe guys here...

I’ve seen many cars, trucks, motorcycles over the years going down the road in a sideways cant. Either they are way out of alignment, or they’ve been in an accident and the frame is tweaked.

I would imagine there are planes that are the same way also. Just wondering what methods you use to ensure a plane is properly rigged and is in perfect alignment so to speak?

Do you just eyeball it, use some sort of laser system, or perhaps maybe a flow tunnel to verify that everything is true?

Just curious...

 

[GRG55]

Plumb bob, spirit level and a tape measure. Along with the manufacturers rigging instructions. Not all light airplanes have adjustments where you may want them (e.g. wing to fuselage connections). They are riveted and bolted together in jigs and what you got is what you got, even if there is no damage history.

Trim for ball centered in calm air, hands off.

 

[GlennAB1]

Manufacturer's instructions first cable tensiometer(s), push-pull fish scales, rig beams, protractor, 6 inch rule, feeler guages for most normal rigging. If you suspect the airframe is tweaked most aircraft I've worked on have alignment check procedures utilizing a plumb bob. You level the aircraft and drop the plumb bob to ground from specific points and start measuring and comparing, and refer to the manual or manufacturer if you find problems.

 

[James331]

I see how it stalls, shows a bit.

Also the position of the controls and what the plane wants to do in a normal cruise setting.

 

[coloradobluesky]

Due to the assymetrical thrust of the propeller, many of these little GA airplanes almost always fly "a little" out of total symmetry. Left wing low does occur. Frequently things can only be made perfect at one speed/load point. If they were rigged right at the factory, don't mess with them. Mechanics have tried, and made it worse. They have to doument how many turns of the screw to be able to undo it. Ultimately, its how the airplane flies that determines the finest adjustment.

 

[flyingron]

As mentioned, the manufacturer provides guidance for cable tensions and what the positioning and angles that the various surfaces are supposed to be. Then there's a little tweaking that can be done to adjust them as airframes wear and get a little deformed over time.

The Navion actually has a few STCs and service letters for adjusting the rigging to change the way things were from the factory. As Colorado says above, there's often things that behave differently at different speeds (it's not just singles which do have an issue with the combination of forces between p-Factor, torque, spiralling slipstream, etc...). Most of these mods are set up to make things work better at cruise over low speed performance. One involves moving the entire horizontal stabilizer (tilting the front edge up about two inches). Others involve resetting the vertical fin as well.

 

[Bill Watson]

As a builder of a Vans kit,I would observe that good design married to modern CNC fabrication can produce straight and true aircraft in spite of amateur assembly capabilities - with essentially no jigs and only minor rigging tasks. The early kits required much more of the builder but the current kits are precision cut and drilled requiring mainly a lot of assembly and mastery of basic riveting. (The fiberglass work is another matter but doesn't play a role in airframe alignment and rigging)

The most challenging alignment task experienced during my RV10 build was aligning the 2 elevator halves with each other (not difficult but I screwed it). The most challenging rigging task was getting the wheel pants and fairings in line - but that task pays off with a well documented 15+ knot airspeed increase compared to naked gear legs and wheels.

 

[zodiacflyguy]

On the cessna 100 series light singles it is mostly accomplished by making sure it is level. (i.e. plumb Bob hung from datum) sometimes have to deflate the nose tire a bit as a final level adjustment. Then using a tape measure, check the distance between sets of specific points on the airframe. Example: distance from top of vert stab to each end of the horizontal. (After making sure the horizontal was straight first of course.) For the wings, there is an eccentric cam the wing attach bolts pass through to adjust the angle of incidenc. (The relationship between the chord line and the center of the fuselage.)

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