Aileron Cable Tension

[22LD]

I am in the process of roughing in my aileron and balance cables. I recall reading (cannot find the post now) that tensions are typically set at approx 30 lbs but that less on the aileron cables (25 -26lbs) makes for lighter stick pressures in roll. However, when I set my aileron cables to 26 lbs tension, I am getting 39-40 lbs at the balance cable. Is this typical?

Also, no matter what adjustments I make, I am seeing 25 degrees up and 20 degrees down aileron deflection. I've tried adjust the push rods but that doesn't seem to make any difference. Any ideas?

Thanks.

[PaulSA]

My first reaction was "that can't possibly be" but then my schoolboy physics kicked in. I don't have my plans to hand but if the aileron bellcrank arms are different lengths, then the tension (force) in the cables will have to be different to balance the torque at the pivot point.

[22LD]

My first reaction was "that can't possibly be" but then my schoolboy physics kicked in. I don't have my plans to hand but if the aileron bellcrank arms are different lengths, then the tension (force) in the cables will have to be different to balance the torque at the pivot point.

Paul, that makes sense. I was thinking it had to do with the difference in lengths of cables. The balance cable is shorter, thus less stretch, albeit minimal. But very slight turns on the turn buckles can make big changes in tension. So it doesn't take much.

[Collin Campbell]

Just some thoughts on the aileron cable rigging. I’m not sure I am understanding the situation as you describe it. The lever arms of the bellcranks can make the tensions of the cables different. I think that another problem that may aggravate the situation is not having the bellcranks aligned properly. In the neutral position, the bellcranks should be parallel with each other. In other words the short arms of the bellcrank that the balance cable attaches to should be pointed exactly rearward. I like to clamp the bellcranks in this position and then fabricate the cables to fit. The drawing of the bellcranks on the plans IS the neutral position and they should look this way AFTER the cables are tensioned. The short push rod has nothing to do with cable tension, it is used to adjust the ailerons…don’t try to adjust the ailerons by altering the cables or you will get the geometry all out of whack and tensions will change throughout the range of movement of the bellcranks. At least that's the way it seems to me....

[Aero_tango]

I'm not sure why you are getting different tension, but regarding the aileron deflection, i had the same exact problem couple weeks ago when i did my flaps and aileron rigging.
I rigged everything per plan, and got +24 / -20 degree . Then i tried different setting with the aileron bellcrank, but no matter what I did, i was always getting the same aileron deflection. After fooling around for more than a day, i went back and looked at the plan in a greater detail.
Then i realized that by design, the deflection is not +/-20 degree, but something close to +24/-20...look at dwg10, pull a compass drafting tool, ruler and a protractor. Using the drawing, mimic a 20 degree down aileron deflection and measure how much the end of the push tube (the end that attach to the bellcrank) moves. Now, still working on the drawing, sketch the pushrod movement in the other direction, using the same numbers as measured previously. This will pull the aileron up. Measure the aileron deflection and you'll get close to 24 degrees. This sound complicated but takes only few minute to do on the existing drawing.

[Collin Campbell]

Yes, that is interesting to me. The differential aileron movement is designed into the aileron hinges...not the bellcranks. The same movement of the pushrod produces more up than down movement of the aileron. It is easy so see if you study the drawing (as you have done)...not too complicated really! It's fun to figure out how things work....I find the words lacking sometimes to explain things in a way that will be understood, but like you, I can see how it works by sketching things out...

[marcusofcotton]

My first reaction was "that can't possibly be" but then my schoolboy physics kicked in. I don't have my plans to hand but if the aileron bellcrank arms are different lengths, then the tension (force) in the cables will have to be different to balance the torque at the pivot point.

Have to agree with Paul on the basic physics....and the differential aileron movement helps reduce adverse yaw.

[22LD]

Thanks, everyone. Glad to hear about the difference in deflection. As for tension, my bellcranks are aligned as depicted in drawings when ailerons are in neutral position... basically the long arm perpendicular to the tension tube and the short arm parallel to it, but I will recheck everything.

[Battson]

Yes that is totally normal.

You might typically aim for 30 lbs in the direct cables, and 40 lbs in the carry-through cable. As you say, you can go lower to reduce stick forces. I have been using 30 and 40 with no worries.

The difference is caused by the different lever arm lengths at the bellcrank.

I don't think the up-going and down-going angles can be adjusted independently. I don't think 20 and 25 degrees is a problem.

[Collin Campbell]

Battson, I think you are right. I first thought the tensions should be the same throughout the system as a closed loop... but I see now that the lever arms do make a difference. Guess I should give more thought to things before I comment. Going to edit my comment above...

[22LD]

After giving it more thought, agree completely that the different arm lengths on the bellcrank would account for the difference in tension. As for the difference in up vs. down aileron travel, I've learned after talking to numerous A&Ps and IAs that that is very typical in most aircraft. I was just concerned after seeing the notation of 20 up and 20 down on the first page of the plans.

Thanks, everyone, for taking the time to reply.