Left Wing Heavy in Cruise

[Rob Simpson]

Hi All,
New to flying the 337 all be it that I have had the aircraft for a few years whilst updating panels and radios. The aircraft is S/N 1807, a 337G model and when we got the aircraft, the left aileron trim was set to max up deflection and the right to max down.
It has installed the no gear door mod, Horton STOL kit and lots of antenna on the roof as it was used as a survey aircraft for a while.
Rudder, aileron and flap rigging has been checked and nothing is showing up. we did find one of the stall fences slightly off set, so removed, made new mounts and reinstalled just in case.
Went through the rigging procedure in the manual for the rudders and set them to 1/4 inch to the left with the nose wheel off the ground and then went flying with the aileron tabs set to zero and found that the left wing is extremely heavy and requires a fair force input to get the aircraft to maintain wings level.
Reset the tabs to where they were when we got the aircraft and it will fly straight, but doesn't look right when you look at it on the ground.
The Horton wing cuffs look like they are equal, and when you slow the aircraft down, the forces to hold it decrease dramatically ( with the tabs in neutral)
With the tabs offset, the rudder trim is about 1/3 off to the left.

Any thoughts would be greatly appreciated.

regards

Rob

[kbecker]

Did you test for tail boom twist? As I recall you can measure in an "X" pattern as one of the methods to check for this.

Kevin

[pwolfehagen]

Interested to see where this goes. Full left rudder trim is required on mine to keep it straight, 1971 T337F. It came to me that way I only have about 20 hours of flight time in it. It was on the list of things to address but the front engine gave out before I got to it. She's been down for a bit but should be up again in a couple months.

[Rob Simpson]

Hi Kevin,
Havnt done the symmetry check on the booms as yet, but will put it on the list to look at and report further.

Paul,
Your issue might be the nose wheel steering interfering with the rigging of the rudders when the nose gear is retracted. There is a note in the manual after the rudder rigging procedure about after a check flight if you see the rudder trim out to the left, you have to check the interaction between steering and trim. Of interest, out of the 4 manuals I have for various models of the 337, only 2 of the manuals had the note about the trim. If you dont have that section in your manual, let me know and will send you a PDF of the relevant page.

And yes, we tried that and it made it better, but still heavy left wing.

Will advise if we know more

rob

[kbecker]

I know some Cessna's have an adjustment at the spar attachment with the wing that allows you to increase or decrease the pitch of the wing (I'm probably not describing that correctly), but if the wings aren't set the same, you can experience a heavy wing situation. There is some kind of cam shaped adjustment there that can be rotated to make this adjustment.

[kbecker]

Here is a video that explains it. I don't know if this is relevant to the 337.

https://www.youtube.com/watch?v=zJFFPa40Tpk

[Rob Simpson]

Hi Kbecker,
Yep, thats how its done on the 100 series strutted aircraft, alas the 337 does not have the cam system used on it so cannot adjust, Thanks for thinking of us though.
Rob