4 inch bellcrank vs. 3 inch bellcrank in a Pathfinder profile ARF

[Allen Eshleman]

I need to replace the leadout lines in a Pathfinder ARF.  I inadvertently ordered a 3 inch bellcrank instead of a 4 inch bellcrank.  I presume it has a 4 inch bellcrank.  What would the difference be if I installed a 3 inch bellcrank?  It is one of the Tom Morris style from Oki-Air.

The one lead out wire tore inside the plane in an on- the-ground accident.

Thanks.

[John Paris]

Allen,
It will be much easier to replace the lead outs than the whole bellcrank.  I just did this on one I am assembling and with the top and bottom anchors it will require a fair amount of surgery.  This point aside and to your question, your   controls will be faster with the same handle setting and  you may run into some of the ribs with the lead out cable.  I suppose that some may argue that there may not be sufficient torque to overcome elevator and flap loading, but I would guess you will still be okay at reasonable stunt speeds.

Good luck on your project.

John

[Allen Eshleman]

This plane was gifted to me with over 100 flights and it still has the original bell crank. 

Is the bell crank installation solid in these?  I have read complaints about the lead out lines.

If the bell crank installation is fine, I agree that it would be better just to replace the lines.

[Peter in Fairfax, VA]

Just did this job last week.  Plane flew great and I flew the pattern with it ten times Friday evening.

I removed a small amount of covering on the bottom, then used a Sullivan C/D leadout kit, wrapping it with tie wire.  Didn't need to cut any wood at all.

The basic complaint of the older Brodak ARFs is that the leadout wire is brittle and fatigues, breaking.  This was exactly my experience.  The newer ARFs may not require this.

Could I have done a fancier job, like bending brass tubing through enlarged holes or changing the bellcrank?  Yes, but I didn't.

Peter

[Randy.Birt]

I had problems with one that had the original lead-outs. It had been hanging on the wall in the garage for five years or so, when I noticed that one of the lead outs was hanging out of the wing about 18 inches. i pulled on it and it pulled out of the wing. I pulled on the other one and with a little tug it also broke free from the bellcrank. I always wondered how that could have happened. I replaced them and the plane is still flying today.

Randy

[Allen Eshleman]

At this point, I am just going to replace the leadouts. 

[Ken Culbertson]

At this point, I am just going to replace the leadouts.

Good choice.  If you are not hitting the "N" wall with your 3" then going to 4" will make things better but you don't *need* it and the work to change a bellcrank, especially a floating one, is enough to have you ask any children to leave the room or cover their ears.

Ken

[Phil Spillman]

Hi Allen, Sorry we didn't get to see eachother last year at Lebanon, PA! Hope to back again next year at the same spot in the "Big Room"! As to your dilemma, just replacing the leadouts is the quick answer! Hope you're now using an adjustable handle as to line/leadout widths. If 3" bell crank is too fast simply squeeze the handles' leadouts' smaller to remove some of the sensitivity. That's one of the main advantages of using 4" bell cranks: more leverage with less movement!

Phil Spillman

[Howard Rush]

If you are not hitting the "N" wall with your 3" then going to 4" will make things better but you don't *need* it...

That wall is squishy. 4" is better, but the benefit is nonlinear.  There is a point of diminishing returns.  I can't tell you yet where it diminishes, but I'm working on it.

[Howard Rush]

That's one of the main advantages of using 4" bell cranks: more leverage with less movement!

More leverage with the same angular movement.  Less angular movement for the same leverage.  For the same leverage, different size bellcranks will make different swaths in the wing that you have to keep clear of spars and ribs. 

[Ken Culbertson]

[quote author=Howard Rush link=topic=57131.msg590847#msg590847 date=1596763643
different size bellcranks will make different swaths in the wing that you have to keep clear of spars and ribs.
[/quote]
Probably the mistake most often made by otherwise expert builders.

Ken

[bob branch]

I just opened a pathfinder kit today. It comes with a 3 inch bellcrank. The plans make a 4 inch a problematic idea. I think the mount would have to be relocated. Has anyone actually put a 4 inch in one of these?

[Brent Williams]

I just opened a pathfinder kit today. It comes with a 3 inch bellcrank. The plans make a 4 inch a problematic idea. I think the mount would have to be relocated. Has anyone actually put a 4 inch in one of these?

The latest bunch of Pathfinder's to come out of Gordan Delaney's underground lair have all had 4" bellcranks.  Easy enough to relocate the mount. 

[Allen Eshleman]

Well, we replaced the leadout wire which was torn.  It actually tore half way through the wing - not at either of the crimps.  The cirucumstances were due to careless thinking.  I parked the Pathfinder in front of the next plane - a Shark 402 and left the lines laying across the path of the 402 on take-off.  The propeller of the 402 picked up one of the lines of the Pathfinder and wrapped it around the crankshaft of the Magnum 25 and stopped. 

What we have done to the Pathfinder is to open it up at the bellcrank which is a 4 inch bellcrank.  I replaced the line by sawing the outside part of the bellcrank with a hacksaw type saw.  I slid one of the beautifully wound leadouts from a 3 inch Okie bellcrank into the bellcrank and repaired the bellcrank with thick CA glue.  My brother has patched it up.  However, I am now tormented by the fact that the other leadout wire - the one toward the front should also be replaced.  The plane was gifted to me by a fine flier and stays at the end of the line better than any plane I have ever built.  The former owner says that he flew it over 100 times with no problem.

[Peter in Fairfax, VA]

Allen,

My Pathfinder ARF continues to fly well, too.  Just flew it yesterday.

Interesting technique, cutting a slit in the bellcrank to work in a leadout.  Don't know that I'll have any call to try that, but I can see that the leadout bears against the bellcrank along a fairly narrow angle, so it should work.  To be 100% sure, I'd tie the leadouts to a cinderblock and see if I could lift it with the plane.

Regarding the front leadout, if you cut off some of the covering, you can work in a leadout and tie it, without cutting any wood.  The tie job is in close quarters, but can be done with some patience. Are you comfortable with your technique to tie lines?  If not, practice using the old leadouts off the plane.

Peter

[Allen Eshleman]

I can't say I am comfortable with my technique.  It was original with me.  However, it was the back side or the outside side that got the slit.  I can't imagine that the uncut edge of the bellcrank toward the  pilot would ever tear.  Biggest worry is that the bellcrank would break but I doubt that. I know there have been problems with the crimps on these ARF's so it's the other one toward the motor, undoctored, that could give way.

[Allen Eshleman]

I worked the wire with its copper tubing in.