VAF Forums

VAF Forums (http://www.vansairforce.com/community/index.php)
-   RV-12 (http://www.vansairforce.com/community/forumdisplay.php?f=73)
-   -   Flaperon - induced roll issue (http://www.vansairforce.com/community/showthread.php?t=154025)

gossend 10-07-2017 12:29 PM

Flaperon - induced roll issue
 
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 10-07-2017 01:43 PM

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

videobobk 10-07-2017 02:14 PM

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 10-07-2017 03:01 PM

I would check on the ground when you lower the flaps thatís 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 10-07-2017 09:05 PM

Quote:

Originally Posted by JBPILOT (Post 1209292)
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 10-08-2017 06:06 AM

Question for Scott.....
 
My airplane has always had a slight tendency to roll when the flaperons are deployed if Iím 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 10-08-2017 06:16 AM

Big John - -
 
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 10-08-2017 06:40 AM

Quote:

Originally Posted by JBPILOT (Post 1209414)
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 10-08-2017 09:56 PM

Quote:

Originally Posted by rvbuilder2002 (Post 1209380)
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. Iíll pull up the floor panels and have a look.
Thanks Scott

gossend 10-14-2017 04:17 PM

Update!
 
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 :)


All times are GMT -6. The time now is 04:20 AM.