Designing lead out guides

[Christoph Holtermann]

It may not be worth to open a new threat on this bcause everyone has built in his career hundreds of lead out guides. However, I want to reduce friction in the lead-out guides as much as possible because electric planes for sure may have more need for frictionless lead-outs than IC powered planes. Two questions here:

Which material combination offers the lowest friction? I want to use cable lead out wires, 0.8mm in diameter (approx. 30/1000"). In the past I used 1/8" copper tube . Worked well on IC powered planes. How does polyamid/nylon work and for how long?

How does the lead-out guide, assume it is a tube, needs to align with the lead-out wire? The lines form a bow due to their air-drag when flying. The front lead out wire probably already has the correct direction in relation to the connected flying lines. The rear lead-out wire however probably causes drag in the lead-out guide because it is bent. Is there a program or formula that tells me the lines-angle at the lead-out exit as function of plane-weight centrifugal force and line diameter? Should the copper tube then have a bow to avoid excessive friction at the tube edges?

I have seen for instance Gilbert Beringer having installed a pulley (most probably on the rear lead out only) to reduce excessive friction on his twin-engined Caudron.

Many thanks for your thoughts!

Christoph Holtermann

[Jim Thomerson]

I use the yellow tubing from inside a golden rod. Years ago a couple of short pieces came in the Perfect leadout packages.  I make them about a half inch long.  I use saltwater fishing leader, cable with nylon coating, for leadouts.  I have never seen any evidence of wear on yellow tube or leadouts. 

[Tim Wescott]

First, I suspect that you're over-thinking this.  As long as the action is smooth, I don't think that the leadout guide friction comes close to dominating the total effect of all forces in a control system, particularly after launch.  If it's already good enough, why not put your effort into making things better elsewhere?

Second, I think brass against steel is a good combination.  Whether the brass is tubing, a block with holes, rivets or screws, I think it's a good choice of leadout guide material if you're using plain steel wire.

Third, Google for Line III (or Line 3).  It's really about telling you where to put your leadouts, but a line drawn from the plane center of gravity to the leadout will probably be about as close as you can get to the actual exit angle of the lines without careful camera work on a flying plane.

Fourth, I don't think that your friction will go up with a straight tube in back, but the system may wear better if you put in your suggested bow.

[Howard Rush]

Minimizing side force on leadout guides is difficult.  Putting the bellcrank on the CG helps, but the bellcrank width is greater than the optimal leadout spacing, so there will still be some side load.  I orient the direction of the leadout tubes to match the leadout angle near neutral as best I can.  That might help, too.  I have been using leadout guides made from Delrin acetal plastic (I think that's the material.  Roy Trantham gave some to Paul Walker and Bob Hunt.  I stole some from both.).  I typically use .031-inch (.79 mm) 7-strand stainless steel cable, but it is pretty rough.  I am reluctant to try 19-strand cable, because people have warned me of broken strands.  I haven't tried the combination that Jim recommends, but I have seen evil happen with nylon-coated leadout wire and metal leadout guides. 

Something I plan to try for leadout guides is iglidur J bar stock from Igus,  http://www.igus.de/ .  I use bushings made from this material in the control system of my current airplane.  It works well.  I don't know how the material would work for the leadout application, but the Igus people seem willing to provide technical assistance for even the smallest projects. 

[Christoph Holtermann]

Thanks for your feedbacks.

@ Howard: If I can help getting some of that bar-stock material (they are located in Cologne, no 45min from me) tell me.

[Igor Burger]

I use 49 strand wire in standard Brodak LO guide with some white plastic. Never had problems with hunting, Also on reworker IC to electric. But once I had to replace it because of broken strands as Howard mentioned, I think it was some faulty cable because it was model only 2 years old. I have much older and all works well.

Alex uses copper tube in hole, but the tube is not attached inside the hole, it is free with rings on end, may be you saw it. I think Richie has the same. It can adapt to wire angle.

However yes, move bellcrank rather front, it will limit friction.

[Dave_Trible]

Thought I'd show my method.  These are for adjustable lead outs but a stationary guide could be made similar.  I buy a hunk of 3/16" Delrin sheet at a plastics supply house. It's not cheap- the 12x24 sheet seen in the photo was over $60.00 but it's a life time supply.   I make my bellcranks and horn uprights from the same sheet.  It's a self-lubricating bearing material and is pretty tough to cut but lasts forever.  I route the strips shown laying on the wing.  These are cut and drilled then assembled as shown in the plywood slider bar with set screw.  Being only 3/16 " thick leadout alignment and wear are simply not a problem.  The unit shown has been removed from an old airplane and it about to be reinstalled in my new build.  No wear can be seen on guide or leadouts.

Dave

[Tim Wescott]

Igor:  Do you really mean 49, or was that a slip of the fingers trying to type 19?

Dave:  Do you just thread the Delrin, or do you use a T-nut or something?

[Igor Burger]

well .. Idid not count them, but they say it is 7x7 so I hope it was 49 :- ))

[Dave_Trible]

Tim neither. The hole is drilled about the shank size of the Allen head sheet metal screw (less the threads) and just screwed in.  The screw makes its own threads and stays tight wherever you put it.  I have made separately adjustable units too with a separate screw for both parts.
By the way Hi Igor.  Congrats on your win.
Dave

Added note:  in most cases my final leadout location is about 1 degree behind the CG. If you think you can predict about where that will fall,  I'd mount the centerline of the fixed lead outs there.

[Jim Thomerson]

Years ago I carved a slider for a 1/2A airplane out of a toothbrush handle.  It worked fine.  I'll see if I still have it and can post a picture.