PA-12 Leveling and Rigging Questions

[Paul Heinrich]

I have leveled my PA-12 using the alternative method and a digital level. I have the wings (uncovered) and tail (covered) both on at this point. I am checking my work before I cover the fuselage and wings, I have some questions that I hope someone could answer before it is too late.

Stabilator/Elevator

The TCDS says the Stabilator control surface movement is 1 degree, 15' "Up" and 5 Degrees, 30' "Down." Am I right to assume that "Up" means that the Stabilator yoke goes up which means the nose goes down and vise versa for "Down?"

With the aircraft leveled and my trim control yoke at the top of the jack screw, the Stabilator is dead level (+/- .01 Degree) according to the digital level. Is that what it is supposed to be?

If it is correct, if I run the trim yoke down 1 degree, 15', is that the point where I should mark the trim indicator as "neutral" (zero trim)?

If I continue to run the trim yoke all the way to the bottom of the jack screw, the level reads 6.9 degrees on the digital level, which is slightly more than the overall travel called out in the TCDS (6 Degrees, 45'). Is that, more or less, what it is supposed to be?

Assuming I'm good so far, in what position should the Stabilator be at in order to measure the Elevator travel? I am assuming that the elevator travel is measured in reference to the stabilator. Should the jack screw be trimmed Neutral for both Up (27 Degrees) and Down (32 Degrees) Elevator or should the Stabilator be trimmed to the top of the jack screw for Down Elevator and to the bottom of the jack screw for Up Elevator? Or does it not matter where the Stabilator is when you measure the deflection of the Elevators?

Assuming that the Stabilator and Elevator are properly rigged, should the Elevator assist spring and cable be set so that the Stabilator and Elevator are flat at Neutral trim?

Aileron

The TCDS calls for 25 Degree Down Aileron travel. I measured the difference in the angle of the bottom of the wing rib to the bottom of the Aileron when fully deflected down. The most I can get is 22 Degrees before the leading edge of the Aileron contacts the wing's false ribs. Is not being able to get a full 25 Degree movement something I should worry about?

Thanks for your advice.

 

[mike mcs repair]

I've had 6 beers, so take this with a grain of salt.... I could be wrong ;-)

Stabilator = what a cherokee has, a combined stabilizer and elevator..... you have a stabilizer on a -12.. and separate elevator..

you level the plane (firewall is close.. are you SURE your are in level flight position????, many pictures in my picasa album)

did you calibrate your level first???

Am I right to assume that "Up" means that the Stabilator yoke goes up

yes

With the aircraft leveled and my trim control yoke at the top of the jack screw, the Stabilator is dead level

not good...

If it is correct, if I run the trim yoke down 1 degree, 15', is that the point where I should mark the trim indicator as "neutral" (zero trim)?

not necessarily.... you will figure this out once it flies...

If I continue to run the trim yoke all the way to the bottom of the jack screw, the level reads 6.9 degrees on the digital level, which is slightly more than the overall travel called out in the TCDS (6 Degrees, 45'). Is that, more or less, what it is supposed to be?

above is your answer 5 '30 or = 5.5
(where'd you get "called out in the TCDS (6 Degrees, 45')."??)

Assuming I'm good so far, in what position should the Stabilator be at in order to measure the Elevator travel?

from the level flight position you are in already...

The TCDS calls for 25 Degree Down Aileron travel. I measured the difference in the angle of the bottom of the wing rib to the bottom of the Aileron when fully deflected down. The most I can get is 22 Degrees before the leading edge of the Aileron contacts the wing's false ribs. Is not being able to get a full 25 Degree movement something I should worry about?

did you use pa-12 ribs? -18 ribs are longer behind rear spar, and prevent full travel..... not a huge issue, I guess at this point.... but.......

 

[Paul Heinrich]

Thanks, Mike. What Degree should the Elevator be at with the plane leveled and when the trim yoke is at the top of its travel?

I get 6 Degree 45' total elevator travel by adding the 1 Degree 15' Up to the 5 Degree 45' Down called out in the TCDS. Is that wrong?

The wings were built new by Univair last month using their certified parts so I'm not sure why the aileron leading edge would hit the false spars.

 

[cubunltd]

You said with the airplane level and the jack screw all the way to the top, the stabilizer is level? Somethings wrong. Are you syre you don't have the trim yoke in upside down. V should point down.

John

 

[Paul Heinrich]

I must not have leveled it correctly or I have the yoke upside down.

This weekend I am going to level it per Mike's suggestion and make the firewall exactly 90 degrees and then see what the Stabilizer comes in at with the firewall vertical.

Would any of you know what the level SHOULD indicate with the PA-12 properly leveled and the trim yoke at the top of the jack screw? And what it should indicate at the bottom?

I need to know the correct readings to know if Mike's leveling means solves the problem or if I need to turn the yoke around.

Thanks.

 

[cubunltd]

With the aircraft properly leveled, level the stabilizer. it should not be topped out. Run the stab up and it should read 1 degree 15 min. as per TDC. run stab down and it should read 5 degrees 30 min. as per TDC. or very close to those numbers.
Check elevator travel with stab at 0 (leveled)

John

 

[Paul Heinrich]

OK, I leveled the 12 according to Mike's instructions. The firewall is exactly vertical.

Now, with the yoke at the top of the jack screw the stabilizer is ,02 degrees nose low. With the Yoke at the bottom of the jack screw the elevator is 7.2 degrees nose low.

With the firewall at 90 degrees, the bottom of the wing root rib is 1.2 degrees nose low.

The yoke is "V" down. Turning it upside down only makes it worse.

What the F#%* am I doing, or have done, wrong?!?

Please help!!!

 

[mike mcs repair]

OK, I leveled the 12 according to Mike's instructions. The firewall is exactly vertical.
....
What the F#%* am I doing, or have done, wrong?!?

Please help!!!

look at https://picasaweb.google.com/101445937433180427570/PA12ProjectForRussell that has various other locations/reading for 'level' when plumbed using plum bob...

on an old airplane you may/USUALLY have to use many to come up with an average of where 'level' should be... then make your stab numbers from that....

 

[skywagon8a]

It seems that there is some question of whether your PA-12 is level or not. With this being questionable I would go to the FAA data sheet http://rgl.faa.gov/Regulatory_and_G...0fe3b1c17780186256a61006c7931/$FILE/a-780.pdf
Then notice that the datum is the leading edge of the wing. This is at the bottom of page 2 under "Specifications Pertinent to All Models". Then notice on page 5 under "Landing Gear and Floats" item # 201. This is the weight and center of gravity of the main wheel. Since the main wheel is round it's center of gravity is the same as the center of the axle. This location is given as 1" aft of the datum. So, to level a PA-12, I would drop a plumb bob from the leading edge of the wing and would consider the plane to be level when the center of the axle measures 1" aft of the plumb line.

It seems to me that this would be the most accurate unless at some point in time your landing gear was mangled and improperly repaired.

 

[Longwinglover]

http://www.supercub.org/forum/showthread.php?33755-PA-12-rigging

John Scott