Leadout movement differential

[Ken Culbertson]

I am re-posting this here because the thread I posted it on went off into the weeds before answering any of my questions!  Since the surgery is scheduled for tonight I thought I might give it one more shot to get some expert advice or get talked off of the ledge.

I got a completed and covered wing from a reputable source that already had the controls installed.  Contrary to my own advice I just left the controls alone and never really measured the movement.  BIG mistake.  I test flew the plane yesterday (electric so I fly them as soon as the airframe is sealed).  It was super sensitive around neutral even with the line spacing down to 2 1/2" at the handle.  1 1/2" leadout line differential gives me 45 degrees flap.  We won't discuss how this went unnoticed until I was wrapping the leadouts.

So,  my question, since I am going to have to do major surgery is what is the preferred line differential.  I can get to about 3, 3 1/2" by moving the connection to the bellcrank in about 1/4"which would put it at about 3/4" which still seems like a bit too far from the pivot. For several reasons, I cannot change the flap horn).  I also can't find any "standard" on how many degrees the bellcrank should rotate.  I would think somewhere around 60 in either direction should be a maximum.

Someone suggested a 4" differential in another thread which is near impossible with a 4" bellcrank.  I got close to 3" on a 3" bellcrank my classic and it over-centered.  The flap pushrod is currently 1" from the bellcrank pivot which is excessive and probably costing me leverage.

If I know what the differential should be I can figure out where to put the hole.

I normally use a rather large line spacing. I realize that much of that is personal but there must be some "rule of thumb" where to put the drive hole on a 4" bellcrank.

I am willing to bet, given our extensive archives that these questions have been answered multiple times, I just can't find them.

Thanks

[Dave_Trible]

Ken the dimensions I’ve been comfortable with for a long while are these:

Bellcrank bolt to flap pushrod hole ( center to center)  5/8”
Bellcrank to flap pushrod in flap horn 3/4”
Rear pushrod flap 1” to elevator 15/16”

This will give a good handle range line spacing from 2 1/2” to 3 1/2” that gives a feel of too quick to too slow on your adjustable handle and the airplane balanced in a normal range.  From what you said here I’d get to the bellcrank and cut that throw down to 1/2”-5/8”.  I don’t know how your lead out dimensions come out with that ( never thought about measuring it that way) but it will put you in a comfortable range.  I get more than enough control ‘power’ with these measurements on my 74-75 ounce, .76 powered airplanes so longer arms just aren’t necessary,  and require a longer bellcrank arm and/or more travel.

Dave

[Ken Culbertson]

Ken the dimensions I’ve been comfortable with for a long while are these:

Bellcrank bolt to flap pushrod hole ( center to center)  5/8”
Bellcrank to flap pushrod in flap horn 3/4”
Rear pushrod flap 1” to elevator 15/16”

This will give a good handle range line spacing from 2 1/2” to 3 1/2” that gives a feel of too quick to too slow on your adjustable handle and the airplane balanced in a normal range.  From what you said here I’d get to the bellcrank and cut that throw down to 1/2”-5/8”.  I don’t know how your lead out dimensions come out with that ( never thought about measuring it that way) but it will put you in a comfortable range.  I get more than enough control ‘power’ with these measurements on my 74-75 ounce, .76 powered airplanes so longer arms just aren’t necessary,  and require a longer bellcrank arm and/or more travel.

Dave

Thank you sir!

Ken

[Paul Walker]

If you are conversant in Excel, get the Howard Rush program for control system geometry.

All you have to do is e-mail him and he will send it to you. It's
a VERY GOOD tool to have at your disposal. It will answer all these questions.

[Ken Culbertson]

...Since the surgery is scheduled for tonight I thought I might give it one more shot to get some expert advice or get talked off of the ledge.

Thanks for all the help folks - surgery successful, patient is in recovery.  As soon as the stitches heal I will perform the plastic surgery to cover the scars.

45 degrees movement both directions.  3" differential,  1 1/2" leadout movement each way from neutral to full up/down.  Lesson learned - check things out even if they come from one of the elites.

Ken

Need to add a PS:

When I went to re-trim neutral on the elevator I an having to unscrew the ball link quite a bit.  Since we didn't use these "back in the day" I don't have a feel yet for how many threads (or turns) you have to have into the link to be safe.  I would think a 1/8" would be good but I don't know for sure.  If I have to lengthen the pushrod threads (it cannot be replaced) is there a simple way?  I am hoping there is a simple 4-40 extension out there I could just thread on.  Does anyone make a long ball link or Clevis?  If not I will just have to invent something.

Thanks again - Ken

[Curare]

There are some longer ones, but you may already be using a long one, what's in there now?

[Curare]

The push rod should be screwed in almost all the way when you are at the right setting.


Motorman

Obviously the more threads that are engaged the better it is, but don't go overboard. I've seen models lost because the builder screwed the ball link on so far that the threads were pushing the ball link head off. It probably wasn't apparent when he screwed it on, but it certainly was after he'd hit the deck from a broken link!

[Ken Culbertson]

There are some longer ones, but you may already be using a long one, what's in there now?

DuBro heavy duty.  It is about 1/4" in now.  I think it will be OK.  I didn't have to move it out as much as I thought.

ken