Flaperon - induced roll issue

[gossend]

I've been flying N218DG for 18 mos now - 265 happy hours! Except:
When I deploy the first notch of flaps for landing, I've always gotten a pronounced right roll that I have to correct with left stick force. The airplane flies straight and wings level in cruise. Since pulling the flap handle pushes both pushrods rearward equally, how can this happen?

[JBPILOT]

With rear most baggage floor plate off, are arms in equal position when flaps appear to be in proper position for level flight ?

[videobobk]

I would expand a little on what John has said. See Section 32, Page 9, Figure 2. Put that AN3-21A (or longer) bolt in place. With the flaps up, the push tube rear ends should be in the same location, relative to fore and aft. If not, you may have found your problem. If this bolt wasn't in place during the build, or if the flap handle was in another position, you would very probably have to redo this. Big job!

Also look at the flaperons while this bolt is in place. They should be in the same position relative to the wings. While it would seem possible to adjust any misalignment out, it really isn't. I am pretty sure some weird flight characteristics could occur. Perhaps what you mention. I would also expect higher maximum roll rates in one direction than the other.

We take special precautions while doing this part of the build process. I don't believe it would be possible for this to happen after all the holes were drilled, but you say you have considerable hours, and I assume it has happened every time. That is where I would check first. Autopilot linkage should be looked at, also.

Bob

[Azjulian]

I would check on the ground when you lower the flaps that?s the flaperon stays parallel with the wing along its length and that with a straight edge the edge of the flaperon is straight. Check that for both sides

[rvbuilder2002]

Originally Posted by JBPILOT

With rear most baggage floor plate off, are arms in equal position when flaps appear to be in proper position for level flight ?

Yup.

The flapperons are inducing a force back into the control system.
If when they are neutral, the arms aren't aligned, each has a different amount of leverage influence on the system which then induces a displacement that causes a roll.
If they are not aligned at neutral, the flapperons will also deflect slightly different amounts when flaps are deployed.

[BigJohn]

My airplane has always had a slight tendency to roll when the flaperons are deployed if I?m above final approach speed. Easily overcome with slight stick pressure and not a problem at all when below 50 or 55 kts. I have never been concerned enough about it to try and do anything about it.

My question is, If I wanted to play around to get rid of this tendency, could it be done by adjusting rod ends and such, or would it require replacing parts and redrilling holes?

[JBPILOT]

If the original drilling of the torque tubes were not correct, you can not adjust it out. You could buy one side or the other and make them match. What Bob said above would be best. Put the alignment bolt in place per building instructions and the 'horns' of the torque tubes should be in near perfect alignment.

[BigJohn]

Originally Posted by JBPILOT

If the original drilling of the torque tubes were not correct, you can not adjust it out. You could buy one side or the other and make them match. What Bob said above would be best. Put the alignment bolt in place per building instructions and the 'horns' of the torque tubes should be in near perfect alignment.

Hi John. Well, I did that seven years ago when I built the aiplane and I have to think I did that part correctly. I fear if I went to all the trouble of repeating that step the results would be the same. Not worth it for such a minor issue. However, if there was another simple adjustment that might remove the roll tendency I might try it at the next CI.

[gossend]

Originally Posted by rvbuilder2002

Yup.

The flapperons are inducing a force back into the control system.
If when they are neutral, the arms aren't aligned, each has a different amount of leverage influence on the system which then induces a displacement that causes a roll.
If they are not aligned at neutral, the flapperons will also deflect slightly different amounts when flaps are deployed.

Of course! In fact the differential would be sinusoidal. I?ll pull up the floor panels and have a look.
Thanks Scott

[gossend]

Nope, everything's square and aligned as per the book. In fact, I remember now that I actually discarded a set of flaperon torque tubes and aligned and drilled the new ones to make them right.

1. That ain't it.
2. It wouldn't make any difference anyway.

As to point two - remember these are not flaps. Flaps are rigidly coupled, and if thru rigging or differential deflection they become misaligned, you've got a roll moment and only ailerons can correct that roll in flight. This requires constant stick pressure.
But these are not flaps; these are ailerons - deflected, but they're still ailerons. A roll tendency is corrected by moving the stick, like in the case of differential flaps, but there is no residual moment. That is, move the stick to one side a half an inch and the moment goes away. Hands off!
So, within reason, small mis-rigging of the flaperon/mixer assemblies cannot produce a residual rolling moment - just level the wings and let go of the stick!
.....so "OK smartass - what is the problem then?" (you might ask).
The problem will be solved in my next post