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Elevator Pull Pull system

Sopwith Pup

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barryt06/04/2020 13:14:48
70 forum posts
21 photos

Looking for some advice please. I have installed closed loop rudder systems before and I have seen the drawings explaining the geometry. My problem is with the elevator system. I can't find much helpful information.

The Pup elevator control wires exit half way between the trailing edge of the lower wing and the leading edge of the stabiliser, but at a significant angle to the fuselage centre line. Using a vertically mounted servo, could I use bent tubes to change the angle of the control wires from the servo as they exit the fuselage? I am concerned about excess friction as there will be four tubes in total. How would I alleviate this?

Could someone direct me to a resource showing how this should be done or suggest a better way of achieving a 'semi' scale solution?

pup line drawings.jpg

Ron Gray06/04/2020 13:17:59
1927 forum posts
803 photos

If you cross the wires over in the fuse the angle will be much reduced.

Mike T06/04/2020 13:26:19
489 forum posts
37 photos

In my Pup, I used thin alloy tube mounted in balsa blocks above and below the top longeron. The inner portion of the tubes bend down to point at the servos (which are installed upright). Using nylon covered trace wire, friction is not a problem.

Nigel R06/04/2020 13:30:42
3750 forum posts
587 photos

Barry, my personal experience of closed loop is that they work just fine when run through a snake inner, so I would do exactly as you are thinking, don't sweat the friction as those plastic coated cables will still operate nice and smoothly. Installing the cables is then a piece of cake, after covering, when you have a handy tube going from near the servo to near the control surface.

barryt07/04/2020 09:18:05
70 forum posts
21 photos

Thank you gentlemen, your advice is much appreciated. The long snake inners sounds like the optimum solution in this case as access will be very limited after the fuselage is covered. I'd better get started!

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