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Old 08-07-2007 | 09:48 PM
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khodges
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Joined: Jul 2003
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From: newton, NC
Default RE: Balsa USA Bristol M-1

The rudder is your basic, 2-wire pull-pull, routed through the outer tubes of a flexible control rod setup (Sullivan Goldenrods). This allows more latitude in servo placement and the exit points of the wires through the fuse than you'd get running the wires straight from servo to control horn. The tubes can be routed to the desired exit points and secured to the framework just under the covering (Koverall on this plane). I wanted the servo ends of the wires to be on the centerline so I could make them all equal length to keep the geometry so that the wires stay taught and don't bind.

The elevator was the one that took some creative engineering, to allow one servo at the side of the fuse to control 2 sets of pull-pull wires, and keep the servo forward as possible for weight distribution. The crossways rod with the control arm is a carbon fiber rod; I drilled out the center of 2 servo control arms (DuBro heavy duty) and fit them over the rod, and pinned them with 2-56 screws as well as Ca. This way, the screws keep thwm from rotating on the rod if the CA gives. The single arm goes to a rod with ball joints to the servo. The double arm has ball-type swivel connectors to the wires that go to the elevator; these wires also feed through tubes for the same reason as the rudder's. You can see in the tail shot where they exit the fuse, which are scale locations on the M-1.

The carbon tube has to be free to rotate and is cut just about 1/8" shorter than the width of the fuse box so it has little side-play; I used brass tubing of an inside diameter just larger than the carbon rod. I made two "sleeves" with a flat brass plate soldered to one end of each. The sleeves are slid over each end of the rod and screwed to the sides of the fuse box structure in a location that allows the double arm to align with the tubes for the wires. The outside of the box has a small lite-ply plate with blind nuts where the sleeves mount. The servo, linked to the rod, rotates it back and forth to move the elevators. The wires are still adjustable for tension, and are equal length so that there is no change in tension with up and down movement of the control surface. If you look at the pic below, you can see where the c/g location is (marks on the edge of the wing saddle). The servos and Rx are all located near the c/g, the battery is under one end of the rod. This plane has a short front, so keeping the weight forward was a concern.
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