Another reason for wing heaviness

[videobobk]

Okay, so this one was my fault, I admit it. But I had a heavy right wing from the first flight. Not too bad, but bad enough. The electric trim had to be almost all the way left when the tanks were even, and if the right one had more than the left, trim wasn't possible.

I had noticed that when you let go of the stick, it would move a bit right, starting a gentle right turn. If you held the ailerons centered (by watching their alignment with the flaps) the plane continues on level.

I pulled the wing inspection plates yesterday and found that the right aileron bellcrank wasn't centered properly--when the gage was in place, the aileron showed a left turn position, off about 1/4". I readjusted the linkage. Now the trim is just a little off center to the left and I plan on checking it again with the help of another person as I may not have it exactly correct just yet.

To correct the heavy right wing, I shortened the right aileron push tube by screwing it in (and readjusted the long tube to bring both ailerons even with the flaps.) I would put this on the list of things to check when dealing with a heavy wing. The change in leverage is substantial to the trim!

Bob Kelly

 

[Kevin Horton]

This is interesting. Adjusting the linkage like that would certainly affect the aileron positions when the trim was in the neutral position, which could cause a wing heavy tendency with neutral trim. But, I would be very surprised if it would affect wing heaviness if the trim system was not connected. If you change a pushrod length to raise one aileron, the airflow will tend to push it back down, which forces the other aileron to raise. The ailerons will seek a position that balances the forces on the two ailerons. I would expect that the only effect of such a change would be to affect the height of the aileron trailing edges, and the left-right position of the stick when the roll rate is zero.

Trim systems that use springs can mask other problems. It would actually be better to access wing heaviness with the trim spring completely disconnected from the flight controls. That way you can clearly see whether any wing heaviness is due to things like aileron trailing edge, flap angle, aileron height, etc. Once the aircraft is rigged so it flies straight and true without the trim connected, then you can hook up the trim and fiddle with it until the aircraft flies straight and true when the trim is in the neutral position.

 

[rvbuilder2002]

Kevin,
I think it actually can. Both ailerons have positive pressure on their bottom surfaces. This exerts a slight load on the aileron control system.
The system is so low in friction (if properly built) that if the bell crank positions are not matched, a difference in moment is developed between the two sides which can allow the pressure of the one aileron to drive the other.
When the two forces equalize it will be with the ailerons positioned for a slight roll.

As a side note...in an RV this can be used to advantage. The very slight elasticity in the RV control system allows this positive pressure on the aileron bottom to push the ailerons up slightly and make the T.E. up compared to ideal alignment.
If the ailerons are rigged very slightly T.E. down (between 1/32 and 1/16 ") the system elasticity will allow them to be properly in trail, in flight.

I totally agree with Kevin in reguards to roll trim checking / adjustments, and trim system. You should disconnect the trim system before working on trim roll trim problems.

 

[flyeyes]

This is interesting. (snip) If you change a pushrod length to raise one aileron, the airflow will tend to push it back down, which forces the other aileron to raise. The ailerons will seek a position that balances the forces on the two ailerons. I would expect that the only effect of such a change would be to affect the height of the aileron trailing edges, and the left-right position of the stick when the roll rate is zero.

Kevin, I should know better than to disagree with you on an aerodynamics question, but this one makes sense to me;-)

The way you are describing the system is accurate, but only if the force necessary to deflect the aileron up is the same as the force needed to deflect the aileron down.

By slightly altering the level arm where the aerodynamic forces on the aileron are pushing the control system "backwards," I can easily understand a little wing heaviness might resulting from having the bellcranks indexed differently.

Am I wrong in how I'm thinking this through? Unless you can convince me otherwise (which is pretty likely, given your background) I'm heading out to the airport to look at my bellcranks again;-)

 

[Kevin Horton]

Hmm. I need to ponder this a bit more. I may have posted a bit too quickly. I hadn't properly considered the effect of the differential action of the bellcranks. I now see that it could be possible that changing pushrod lengths such that the neutral position of a bellcrank is changed could change the rolling moment with zero stick force.

If you "fix" a wing heaviness by rigging the pushrods to put the two bellcranks at different angles, it seems that this could result in the two ailerons having different travels, giving different control authority to the left than to the right. I would hope to avoid this if possible.

I still believe that any wing heaviness should be diagnosed with the trim springs disconnected. A misrigged trim spring could either mask wing heaviness, or make a properly rigged aircraft look as if it had a heavy wing.

I'll buy Scott and James a beer next time we meet.

 

[RV8N]

Tried it, didn't work for me.

I had a heavy wing during my early flight testing and tried to lengthen and shorten the aileron push/pull tubes. All it did was move the neutral point of the stick left or right. I finally put it back in the middle and left it alone.

Your reason for a heavy wing may be different but I agree with Kevin. After trying it and thinking about it for quite some time, I don't see how it could do anything but move both ailerons slightly up or slightly down.

Karl

 

[rv72004]

I dont have heavy wing, BUT my rhs aileron rides a bit below the wing tip and flap. the lhs used to ride high and lhs was perfectly flush, after adjusting the pushrods, the lhs now rides low and the rhs is flush. The trim didnt change. Aircraft still flies straight with no wing heaviness.This all whilst solo on lhs.

Here what confuses me; when doing stalls solo, the rhs wing drops quite significantly [30to45degrees]. I sit on the lhs ,therefore heavier, so why the rhs wing drop.All the time the aircraft does not have a heavy wing.

Also if the aircraft does not have a heavy wing ,why is the one aileron out of alignment??? [about 1/8"] .

EJ
RV7

 

[jdmunzell]

What about the VS alignment?

I know I am way ahead of myself since I'm only on the wings but, how about the alignment of the vertical stabilizer? I would think that a vertical stabilizer slightly off from where it's supposed to be in the initial installation on the fuse would contribute greatly to a "heavy wing". I haven't seen anyone mention this as a possibility.