Control horn sweet spot ?

[BigO]

m guessing that if you mount the control horn away from the hinge (closer to the edge of the control surface?) . It will shorten the through? ( that my tx will not be so sensitive? ) what do you thank ?

[Murman]

If you attach the control rod to the outermost hole on the horn, it will reduce the throw. If you mount it to the hole closest to the hinge, it will make the throws longer.
It's the opposite on the servo end though. Further out on the servo arm makes larger throws, further in reduces them.

If you have a computerized radio, you can reduce the servo travel to accomplish the same thing.

[Bill G]

I think he is referring to the location of the control horn on the control surface, relative to the hingeline. Offsetting the horn will decrease the sensitivity in one direction, but will increase it in the opposite direction, which is referred to as differential.

Before computerized radios with aileron differential and individual aileron servos, the horn location was physically offset to provide differential. If you move a control horn on an aileron (or any surface) such that the clevis is aft of the hinge line, you will have positive differential. Alfa models did this on their warbirds that use a single servo cable setup, to provide positive aileron differential.

Positive differential causes the surface to move upward more readily than downward. This is done to reduce adverse yaw effects on ailerons. If you want to reduce the sensitivity, then you will simply move the linkage to a further outward hole in the control horn.

[BigO]

Thanks Murman I had not considered that.

[BigO]

Thanks Bill thats what im referring to Thanks for the info

clevis is aft of the hinge line? so for positive differential? i need to move my central horn past the hinge

[kyleservicetech]

Originally Posted by BigO

Thanks Bill thats what im referring to Thanks for the info

clevis is aft of the hinge line? so for positive differential? i need to move my central horn past the hinge

What brand and model of transmitter do you have?

My Spektrum DX8 and older DX7 have the capability of exponential control that really softens up the control around the servo neutral position, and opens it up as the servo is moved to the full throw position.

Just about all computer type transmitters now days have this capability.

And, if you want differential, the DX8 transmitter makes easy to do, just a little more work for the DX7. Other higher quality transmitters usually have similar capabilities. Transmitter controlled differential usually requires two aileron servos.

Normally differential commands are required when the model has real "Yawing" problems, that occurs when as an example, the pilot gives right aileron control. And the model rolls right, but the fuselage noticeably "Yaws" to the left. I had a giant scale scratch built Piper Cub 14 years ago that really had this problem. Making an aileron turn demanded simultaneous application of a significant amount of rudder. My transmitters at the time did not have the differential capability.

Differential aileron is usually done by increasing the throw on the "UP Aileron" on one wing panel, and reducing the throw on the "Down Aileron" on the other wing panel. (With the same thing done with an opposite aileron roll command.)

[BigO]

I have cheap o Hobbyking t4a v2. about $30.00 with shipping and it came with a rx.
so far I have no complaints, Its done everythang Ive ask it to do.

Im going to move my push rod in closer to the servo then if the slow boat from china gets here Ill replace the Popsicle stick control horns and move them to the center of my rudder

thanks for the help

[fhhuber]

Always locate the horn in line with the hinge. Moving the pushrod connection forward or aft of the hinge (either) will reduce available control throw.

If doing mechanical differential offset the servo arm. Its far easier to adjust the amount of differential this way.

Keep the connection at the control surface on the furthest out hole practical. Adjust throw at the servo end. This puts the least load on the pushrod (less chance of pushrod flex) and this will reduce the amount the surface can move to to any slop in the linkages. (flutter prevention)

A good mechanical setup can make it so you don't need to use any of your computer radio features to correct the way the aircraft performs.

[BigO]

alright Now I understand what Bill g was trying to tell me well some of it

The sweet spot is wear the push rod and the control horn meet and i want that as close to the hing line as i can get it
Adjust throw at the servo end

I will eventually catch on Thanks for the help

[Wrench66]

I've never heard of moving the control horn/push rod pivot away from the hinge line......learn something new everyday
I've ALWAYS put my linkage pivot as close to the hinge line as possible and THEN toning down the throws if needed.
--Ray

[fhhuber]

"Give me a long enough lever and I'll move the world."

[Murman]

Originally Posted by BigO

alright Now I understand what Bill g was trying to tell me well some of it

The sweet spot is wear the push rod and the control horn meet and i want that as close to the hing line as i can get it
Adjust throw at the servo end

I will eventually catch on Thanks for the help

This is correct. The holes in your control horn should be directly (90 degrees) above the hinge line.

[BigO]

Huge Improvement it flies a lot more better I read up on how to trim it out it almost did a loop

[Bill G]

Originally Posted by BigO

alright Now I understand what Bill g was trying to tell me well some of it

The sweet spot is wear the push rod and the control horn meet and i want that as close to the hing line as i can get it
Adjust throw at the servo end

I will eventually catch on Thanks for the help

What I was trying to point out is that you don't always want to align the control horn center with the hinge line. You really need to sketch an enlarged diagram. This will allow you study the differential effect that offsetting an arm will cause, which is sometimes desirable.

Originally Posted by BigO

Thanks Bill thats what im referring to Thanks for the info

clevis is aft of the hinge line? so for positive differential? i need to move my central horn past the hinge

For positive differential, you will offset the control horn clevis point rearward of the hinge line. In simple terms, relocate the arm toward the trailing edge of the aileron. This is what Alfa Models has done. Off top of head the offset is probably in the 5-10mm range on my FW190. The offset distance depends on how much differential you want. With a single servo aileron setup, this is the most practical method to achieve positive differential.

Another method is to orient the servo arm to create positive differential. This is done by positioning the arm such that the majority of it's travel range is in the up-aileron direction. That method is less desirable however, as the response decreases exponentially with upward aileron travel. By offsetting the control horn, the response increases exponentially with travel, which is what you are trying to achieve with positive differential.

Another simple method is to simply raise both ailerons a bit from perfect alignment with the wing, when in center position. Some manufacturers recommend a mm or so at the trailing edge on park sized models. This also provides a crude form of washout that actually does work however.

With aileron torque rods, the linkage arms are spaced less than 180 degrees apart, offset toward the TE of the wing, for positive differential. This recommended in the instructions of the Ziroli designed HOB Texan that is currently being built on this forum. The orientation described would be seen while viewing the top surface of the wing, with the aileron torque rods bent upward.