Definitive Elevator / Stab ajustment

[Binty]

Iv spent some hours trawling the forums about this topic and there is some conjecture on the setup... I need some definitive answers but first I will share what I know and have found; (Please correct if you see an error) See pics.

I have installed the Dakota Trim assembly (Yoke, Jack Screw and Pulley);
*The Bungee Cable fitting is approx 1" closer to the top of the Yoke than the Piper Yoke. This means the Bungee Cable needs shortening by about an inch.
*Also, unless slim fitting Bolts and Nuts are used, it can limit the UP travel of the yoke (nose down trim) against the Turret structure.
*The LOWER elevator spring and bungee cable is generally removed from PA18s.
*The UPPER spring is hotly debated to be for reasons of Certification, Stability or Trim assist and many prefer to fly without it installed.

Questions
1. ELEVATOR CABLE TENSION. Given that I didn’t pay much attention to my Elevator Cables prior to stripping, Im now wondering what sort of tension they should be under? The turn buckles (both) are fully wound in but the Cables still sag to the point they touch the rear cross tube. See pic. I have checked the cable lengths against the originals and they match.


2. ELEVATOR TRAVEL. The lower Elevator cable attach plate (red in drawing) protrudes rearward from the elevator horn and hits the stop limiting the elevator UP travel. It looks as if this plate has been previously fabricated and Im interested to know what size the stock ones are. Being 'shorter' would give me greater adjustment for the above issue...


3. STABILIZER WASHERS. I found a washer/shim on each front Stab attachment where the stab fits on the carry through. As I have a brand new carry through tube which needs to be drilled, Do I need a gap and washers or should I make it so the stab pushes hard up against the carry through fitting?


4. SPRING TENSION. Given I must now shorten my Bungee cable to allow for Dakotas different Yoke mounting, how much spring tension should there be… ie if the STAB is neutral, how much pull is on the Elevators (not flying). Should they too be in a neutral position? Should the Spring slacken and touch the Upper Elev cable when Back stick is applied? see pic below

 

[Steve Pierce]

Yes you have to shorten the upper bungee cable by 1" with the new Dakoat Cub jack screw and yoke. I just make a new cable. You also need to use low profile hardware to keep the bungee cable attachment from hitting the jack screw tower. Piper says the cables should be 30 lbs. I do it by feel and yours look loose.

 

[Steve Pierce]

Do not use washers on the liner tube at the front of the stabs.

 

[Binty]

Further to this... Im curious to know if the 'Zero' or Neutral trim position on the indicator plate coincides with; 1.Stab being in the Horizontal Reference Line Plane or 2. when the Stab and Elev are in the same plane (dependent on bungee spring tension), Or 3. something else?

Iv just rigged all my Empennage and have been setting up the Trim, Stab and Elev. Since the cockpit is in pieces, I havent got the indicator plate to see the various positions (not that they matter- Im just being fussy)

 

[Longwinglover]

As far as I know it coincides with nothing in particular except full nose down stab position.

The way to "set" the indicator is crank in full nose down trim (stab l.e. up) and then attach the indicator cable to the indicator button/spring with the spring fully relaxed and the button fully forward in the slot.

John Scott

 

[Glidertow]

Also seeking help with question 4 above.

 

[mike mcs repair]

Further to this... Im curious to know if the 'Zero' or Neutral trim position on the indicator plate coincides with; 1.Stab being in the Horizontal Reference Line Plane .....

as far as degree travel listed on the TCDS its from level flight....

 

[Glidertow]

My real question has to do with the spring being so slack that it lays down on the elevator cable when full back. Just does not seem safe.