PIPER  RIGGING - Frank Rush - Reprint from SWPC news

I personally don't like to see sheet metal trim tabs screwed to ailerons and/or rudder on fabric covered Pipers with all that rigging adjustment available.  If you have metalized wings, it should have been installed with the wings warped to the 2-½ degrees washout position with them on the aircraft in the properly rigged position.  If you try to change wash-in/washout the skin will start to wrinkle if twisted in either direction from the position at which the skin was installed.  If it is necessary to correct a wing heavy condition on a metalized wing, then the trim tab on the aileron is probably the best way to go.

All the rag Pipers that I am familiar with up to the Tri-Pacer had "leveling and rigging" printed in the owners handbook that told you how to level the aircraft, set the dihedral angle, set the washout, level and plumb the tail surfaces, then listed the control surface travels and that's where it left you.  On the Tri-Pacer, they did add a "control system rigging" section for the rudder interconnecting cables and has steps for checking the trim of the aircraft inflight before tightening the rudder interconnecting cable turnbuckles, but that is where they leave you, and there is no maintenance manual that gives detailed rigging instructions on each control or how to adjust for inflight trim discrepancies.

I rigged my PA-20 by following the Piper instructions for leveling, setting the dihedral angle, adjusting the washout and leveling and plumbing the tail in that order.  From this point we are on our own until we get to the control surface travels.

START the rigging by placing a straight edge across the bottom of the aileron control wheels and clamp in position to hold one in neutral.  Now tension the aileron cable loop in the fuselage to 30-35 lbs, using the three turnbuckles on the control column fwd. of the instrument panel.  Adjust the horizontal turnbuckles on the top of the column between the cable drums, or the bicycle type chain and sprockets to maintain both control wheels in neutral and adjust the turnbuckles along the vertical portion of the column to bring up the tension and maintain the aileron bridle cable just aft of the rear spar carry-through tube in the center of the fuselage so it will have equal travel in both directions.  With both control wheels in neutral, the bridal cable in the center of its travel and the tension between 30-35 lbs., safety these turnbuckles.  Check the entire cable run to insure that it is in pulley grooves and is not on tip of guard pins or riding on the structure.  Remove the straight edge and make sure wheels operate smoothly and reinstall straight edge for rigging ailerons in neutral later.

I rig the flaps next to provide a neutral reference at the inboard end of the ailerons when I reach that point.  The flaps are held in the up position by a spring on each flap bellcrank.  With the spring holding the bellcrank against the up stop, adjust the flap pushrod ends to position the flap trailing edge to neutral.  Use a straightedge on the bottom of the wing to the bottom of the flap.  If the flap is warped, I suggest you average this out to half on each end.  With the flap handle in the down position and the left flap in neutral against the up stop, tighten the turnbuckle in the fuselage aft of the baggage compartment to take up all the slack without pulling the flap bellcrank off the stop and safety this turnbuckle.  With the right flap in neutral, adjust the turnbuckle inside the right wing to take up all slack in this cable without pulling the bellcrank off the up stop and safety.  This should complete flap rigging, check cable runs to make sure there are no riding conditions and flaps operate smoothly in the down direction when the flap handle is pulled up.

The rest of the aileron system is now rigged.  With the straight edge still holding the control wheels in the neutral position, adjust the two turnbuckles in each wing to position the aileron in neutral, inboard end aligned with flap and outboard end aligned with trailing edge of wing.  As with the flaps, if the aileron is warped, I suggest that the difference is divided to half on each end.  Tension cables to 30-35 lbs.  Check cable runs in wing for clearance and to see that they are not wrapped around one another.  Remove the straight edge from control wheels and turn wheel to the right.  The trailing edge of the right aileron should go up and the left should go down.  Check for smooth operation and safety turnbuckles.

Aileron throws are set by the stops mounted on hinge at each aileron horn and are adjusted by moving stop fore and aft on hinge and for fine adjustment, filing ends on stops.  

The elevator cables run from a bellcrank under the front seat, aft to the elevator horns, and have turnbuckles in the tail just ahead of the elevator horns.  These cables are differentially adjusted so that the elevator horns hit the primary stops in the tail before running out of travel at the forward bellcrank or hitting secondary stops forward of the instrument panel.  The tension should be 30-35 lbs.  The pushrod between the lower end of the control column and the forward bellcrank is also adjustable at one end.

Installing the elevator bungees is almost impossible without help until you learn the knack of collecting one and, running the stabilizer trim all the way, lifting the elevators and holding them up with your legs, while you reach around the rudder and hook up elevator cable and bungee cable at the same time .(having the rudder removed would help.)  Check for smooth operation, cable clearance, and proper elevator throw and safety turnbuckles. 

The rudder cables, like the flaps have no tension on them.  A spring between the rudder pedal and the firewall holds pedals forward to keep it from falling backwards on the floor.  The cable at the rudder horns, have plates with several holes in a staggered line for adjustment.  Block the rudder in the neutral position and connect the cables at the rudder horns so that the rudder pedals are approximately vertical or slightly forward (but not so far forward that you cannot get full travel on the rudder before the pedal hits the firewall or structure) and the pedals are aligned with one another straight across.  

There are two different trim cables for stabilizer trim.  The older trim system has a shorter continuous cable that goes around the trim pulleys in the cabin and back at the trim screws only once with a small tension pulley just ahead of the trim screw.  The tension on this cable should be approximately 15-20 lbs., and I lean towards the lower tension and keeping the trim screw clean and lightly lubed.

The newer trim system has a longer continuous trim cable with a double wrap at the forward AND aft trim pulleys, with an idler pulley forward and aft and a spring at the forward idler to maintain tension on the system.  It is still important that you keep the trim screw clean and lightly lubed.

The test flight for checking trim should be performed in smooth air.  Level off and stabilize air speed and RPM at the value you intend to cruise the aircraft.  Remember that your trim is fixed and will be correct at only one airspeed without applying either left or right rudder to center the ball on the slip indicator.  If you have aileron/rudder interconnect, it should be disconnected at this time.  While holding the wings level, center the slip indicator ball with the rudder and note whether it takes left or right rudder (if any) and approximately how much is required.  While holding the slip indicator ball centered, release aileron control wheel and note if either wing is heavy and approximately how much.  Record which wing is heavy and going down and how much left or right rudder it took while the slip ball is centered.

To correct for a heavy wing, you need to adjust the rear strut on that wing by shortening the strut.  It can be done by yourself by first going to the fork end and loosening the jamb nut and back it off several turns, then remove the strut outboard attach bolt being VERY careful not to let the strut drop. (If it drops, fork will be bent and have to be replaced)  Lower the strut out of the wing fitting and turn it clockwise (looking inboard down the strut) to shorten the strut.  Only full turn corrections can be made from this end.  For the half turn corrections, the strut must be completely removed and one half turn taken at the fork end.  Remember - be very careful not to bend the fork ends in any way.  If you do, REPLACE IT.  Do not use a thread chaser on fork ends.  The units are manufactured with rolled threads and this procedure would ruin them.  Each ten degrees of wing heaviness inflight requires approximately one turn of the strut fitting.  Reinstall strut and tighten jamb nut on strut fitting.  

To adjust yaw trim, bend the leading edge of the vertical fin in the direction towards which the airplane skids, being careful not to depress the fin far enough to cause fabric wrinkles.  

Test fly the aircraft again and check trim and make adjustments as required above until it flies straight and level at your selected cruise speed without aileron or rudder applications.

Now if you have a Tri-Pacer with rudder/aileron interconnection, tighten the interconnecting cables with the coil springs just beginning to become extended.

Check the trim of the plane inflight again to see that the trim has not been affected by connecting the cables and to see that interconnecting cables are at correct tension to give properly coordinated controls.  If the interconnecting cable tension is excessive, too much rudder movement will result from the aileron movement, causing a skid.  If the cables are not tight enough, the rudder will not move far enough when the control wheel is rotated to give coordinated turns.  Proper tension will give coordinated turns at cruising speeds when either the wheel or the rudder controls are moved.

Everything I have talked about on the rigging will require A&P or IA signoff.  If you are still with me, - good flying to all!  
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Another place where rigging info can be found is piper service memo 20 and 21. Both are on the drawing CD. SM 20 tells how to rig the PA20 while SM 21 tells you the PA22 is rigged the same as a PA20 and also tells how to trim the interconnect. SM 20 tells you that 10 degrees of wing low will require about one turn of the strut fork so I do not believe you will be able to see that difference with the naked eye. It is also SM20 that will tell you if the planes skids while in level flight bend the leading edge of the vertical fin in the dirrection of the skid and not so much as to wrinkle the fabric.
Kenneth Aasand