Control Line handle/Bellcrank/control ho...

After reading the post on the porportional control line handle a week ago I did some experements. I never realized that rotating the control line handle reduced the amount of line pull. I just never gave it any thought.

The lines on my control line handle are 4.5" apart. I did the math on it and here are the results rotating the handle 10 degrees at a time.

10 deg............line pull .750".............movement 100%
20 deg............line pull .718".............movement 95.7%
30 deg............line pull .687".............movement 91.6%
40 deg............line pull .625".............movement 83.3%
50 deg............line pull .562".............movement 74.9%
60 deg............line pull .437".............movement 58.2%

The bellcrank and the elevator control horn operate on the same physics as the control line handle. The bellcrank that I tested was a Sig, 3.5" between control lines, 5/8" offset to the control rod.

10 deg............line pull .125".............movement 100%
20 deg............line pull .119".............movement 95.7%
30 deg............line pull .114".............movement 91.6%
40 deg............line pull .104".............movement 83.3%
50 deg............line pull .093".............movement 74.9%
60 deg............line pull .072".............movement 58.2%

The control horn has the control rod connected at 5/8" from the center of rotation.

10 deg............line pull .125".............movement 100%
20 deg............line pull .119".............movement 95.7%
30 deg............line pull .114".............movement 91.6%
40 deg............line pull .104".............movement 83.3%
50 deg............line pull .093".............movement 74.9%
60 deg............line pull .072".............movement 58.2%

The problem is compounded by a factor of 3 from the control line handle, bellcrank and the control horn which all reduce movement as they rotate. A round disk on the control line handle will correct only the movement of the control line handle but will do nothing to correct the bellcrank and the control horn.

It took me about 30 minutes to find a formula in my old college trig book, how to calculate the radius of a irregular shape curve. I came up with a radius for the control line handle that will add line pull at the same rate that its lost at the bellcrank and the control horn. Movement at the control line handle will be 1 to 1 ratio at the airplane elevator.

My first control line handle used a 4" disk. Control lines are 4" apart. As the handle rotates in either direction the control line spacing changes to about 5" giving it more line pull. My first test flight shows sensitivity flying straight and level has not changed. The airplane is much quicker to make a turn with a given amount of rotation on the handle.

My second control line handle uses a 3" disk. Control lines are 3" apart. As the handle rotates the control line spacing changes to about 4". Over all sensitivity is reduces. It is much easier to fly straight and level. The airplane turns very sharp when I want it to. I have plenty of movement in my hand and wrist to do manovers. I use to have a problem with not having enough movement in my hand and wrist to do a loop. Now its not a problem. The controls are no longer too sensitive flying level and I have lots of control doing manovers.

My control line handle is really stupid looking. Its heavy and aquaward but it works better than expected. I think some type of amplifier bellcrank would work better. The bellcrank needs to be designed to increase movement to make up for lost movement in the control handle and elevator control horn that way a normal control line handle can be used.

I'd like to see a picture of your handle(s)

Thanks
John Jolley

Sorry I could not get this pic online last night my boys both needed the internet for school homework.

The control line handle is made from 1/4" plywood. 2 pieces of plywood are 5.5" x 7.25". There is a 4" diameter plywood circle glues inbetween these 2 pieces. There is a 2" x 5.5" piece of plywood glued inbetween at the hand grip. I glued it together with epoxy. I drilled 4 holes 1" diameter each 7/8" apart for the hand grip. I cut a 3" diameter hole inside the 4" diameter circle to reduce weight. I routered the edges and sanded it. I drilled a 1/4" hole for the cable adjustment and clamp. The cable rotates around the 4" circle which makes the cable pull exactly the same all the time.

The only difference in the other 2 handles is the circle in the middle of the 2 pieces of plywood. The circle is a perfect circle near the hand grip. The other half of the circle is egg shaped. The circle is 4" diameter in one direction and 5" diameter in the other direction. The other control handle that I made has a smaller circle that measures 3" in one direction and 4" in the other direction. As the handle rotated to 10 degrees the cable rotates on the perfect circle. When the handle rotates past 10 degrees the cable has to run up hill on the egg shaped circle which increases the line pull.

You can see the pic at. [photo not recovered: handle01.jpg]

I will post a pic of the other 2 handles later today, I have to leave for work in 5 minutes.

That's very similar to my handle that I've been using for 10 years. The only difference is that I cut off two pieces of the circle, one next to my knuckles and the other at the end of the handle. This reduced the overhang some. I have found that I can get used to the overhang, but I would eliminate it if I could.
My next experiment will be to put the grip inside the circle, but I will have to make a very large bellcrank, 5.5" or 6" so that I can get my hand into the handle.

Here is a pic from a different angle. It might make it easier for everyone to understand how it works.

>After reading the post on the porportional control line
>handle a week ago I did some experements. I never realized
>that rotating the control line handle reduced the amount of
>line pull. I just never gave it any thought.

I was really mystified about this statement until I realized that "line pull" wasn't the same thing as "line tension".

Over the years, people have tried all sorts of things to counteract this, usually at the airplane end. I remember seeing some sort of sun and planet gear arrangement at the bellcrank, for one. And the RC people have what they call "Exponential".

>My control line handle is really stupid looking. Its heavy
>and aquaward but it works better than expected. I think
>some type of amplifier bellcrank would work better. The
>bellcrank needs to be designed to increase movement to make
>up for lost movement in the control handle and elevator
>control horn that way a normal control line handle can be
>used.

I would love to see a picture of this, too.

Iskandar,
It took me a while too to figure out why the pull was in inches and not in pounds. I guess I don't speak American english. I think the handle in the picture would be slow in response and tiring to use because you would be constantly pulling the model towards you.
I remember that Brian Horrocks used to use a diecast Aussie handle which was very similar to this except that the handle part was inside the circle. It also doubled as a line reel.

Here is the other picture. The 2 cardboard pieces are my templates. I did all the math on the cardboard then cut them out with scissors. I laid the template on the plywood and drew around it with a pencil. Cut an glue the plywood and its finished.

When the handle rotates the distance between the cables increases which increases the rates at which the lines are pulling on the bellcrank of the airplane. 110 degrees of the plywood circle is a perfect circle. The rest of the circle gets larger as it rotates.

Its a stupid looking handle but it seems to work very well. Its no harder to use than a regular handle. Its a little heaver but this is only an experemental handle. Now that I know that it works I will make a nice handle with 1/8" plywood to reduce the weight. The donut plywood cam ring doesn't need to be any thicker than 1/8" plywood 1/4" wide. 3 sheets of 1/8" plywood glued to a handle won't be much weight, probably less than 1 ounce of weight.

Gary,

I would think the overhang would kill you. What if you moved the part you hold to the inside of the ring? Or done so that you grip the portion of the ring farthest from the plane?

I'll try it if you can figure out how to eliminate the cables and not bend the controlines. I think bigger gains can be made by getting the bellcrank/flap pushrod parallel and the flap horn and elevator horn geometry corrected. Folks (like me) will still screw up the neutral adjustment at the handle and make things way harder than they need to be. Steve

Steve,

Ya know, I've been a good boy in keeping quiet about your whack-job neutral adjustment at the handle end of the Mutant Magnum. Mr. Walker was not impressed. Or so I am told...

>I'll try it if you can figure out how to eliminate the
>cables and not bend the controlines.>

Steve, the cables bend less in this set up than in most conventional handles.

>I think bigger gains
>can be made by getting the bellcrank/flap pushrod parallel
>and the flap horn and elevator horn geometry corrected.>

You should do all of the above anyway, but that doesn't produce the same effect as a disk in the handle. An expo crank does produce the effect, but I have been reluctant to try an expo crank because of the complexity.

>I would think the overhang would kill you. What if you moved
>the part you hold to the inside of the ring? Or done so that
>you grip the portion of the ring farthest from the plane?

Yeah, the first thing that came to mind when I saw this was overhang, too.

Is there such thing as too little overhang? I suspect in Stunt you want some, in Combat I've seen handles with almost none.

Isky,

As little as possible, at least for me. I've tried handles with considerable overhang and it just kills the control feel (my opinion, I know guys that like it).

I like this idea for a lot of the same reasons I liked Ted Fancher's roundy round bellcrank.