Plane always roll to the right. How to fix

[skorp_jon]

Hello. I have a showtime 4d 90 with OS 120AX

and i have to trim ailerons to the left, because my plane aways roll to the right.

What should i change to fix that. I don't want to have my plane so trimmed, because i know that's not right.

thank you for your help

[JetPlaneFlyer]

I believe this model has two piece wings which plug into a joiner tube that run through the fuselage and the two panels are aligned by a spiggot built into the rear of the wing root rib... am I right?
If so it sounds like there is a little misalignment somewhere such that the left wing is at a greater incidence than the right wing, it would not take much. Maybe the spiggots are not mounted at quite the same height in both wing panels or perhaps the holes in the fuselage are at slightly different levels?

I can’t think of anything else that is likely to cause it other than a twist in a wing but this would be unusual on an ARTF. Offset of the rudder or excessive thrust line offset (right thrust) would be worth checking for but not likely to be the cause.

[Brandano]

The first question that sprung to my mind was "under power or in the glide?", but I decided to leave the solution to the experts :)

[eflightray]

What you need is a wing incidence gage, (gauge?), to check for any discrepancy each side.

There are commercial ones , here's the Robart Incidence Meter (http://www.robart.com/how_to/incidence_meter.aspx)

If you do a google search on 'model incidence gage' (or gauge or meter), there are some descriptions of home made ones.

[Connexxion]

I had the same problem with a highwing trainer.

After measuring both wings I discovered the left wing had more wing incidence then the right one.Used an iron to clear that right up.

Get yourself a measuring tool,it pays itself right back!

[vintage1]

If its a flat bottom wing I get a couple of bits of spar or dowel, and band them to the wing undersides..band round spar over top of wing and round spar again at the other side. Then compare the two spars on each wing sighting from the side.

[JetPlaneFlyer]

If its a flat bottom wing.....

It's not... I believe that the model uses a symmetrical airfoil. You could perhaps still use a similar method. Just put a packer piece between the TE and the dowel making sure that the dowels were at exactly the same spanwise position on both wing panels and the packing pieces were the same thickness and in the same position chordwise.

Careful sighting with the good old Mk1 eyeball may be able to pick up the discrepancy without any dowels or other aids, though it is harder with a symmetrical airfoil than with a flat bottom one.

Steve

[Brandano]

Swapping the pieces of packing and repeating the check should also reduce any inaccuracies due to minor differences between them. Just a thought. However I still think that the most likely culprit is engine side-thrust, since while the plane is an ARTF the amount of side thrust needed might vary with different engine sizes?

[JetPlaneFlyer]

Thrust offset is worth checking but motor torque/prop wash issues usually produce a left roll, not right. On a model like this that is mid wing and has no dihedral even extreme right thust angle would be unlikely to produce a right roll.

It's easy enough to check out anyway; just see if the model still needs left aileron trim when flown with the motor at idle.

Steve

[vintage1]

on an electric, a windmilling prop tends to put a slight right roll moment onto the plane as well.

[hoppy]

Check left-right balance by holding prop spinner and supporting tail on a sharp object. Is the right side heavier?

Some articles on trimming:
http://www.cmfhobbies.com/How-To-trim-an-Aircraft!!/I60.htm
http://www.nsrca.org/TRIMA.HTM
http://www.rcplanetalk.com/trim.html

[Connexxion]

Check left-right balance by holding prop spinner and supporting tail on a sharp object. Is the right side heavier?


This trick will only do if the engine is bolted without a side/down thrust angle.

I've seen a lot of people using this trick to determine the left-right balance,without taking into account that the engine and thus the crankcase isn't inline with the fuselage!

[hoppy]

Good point - in that case, use any nose point that is centered to the fuselage.