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Article and photos by the author. Featured in the Spring 2008 issue of Park Pilot.
The control system in a control-line model is far less complicated than that of an RC model — no electronics to deal with and in most cases, only one moving control surface. Simple does not mean insignificant, so everything that goes into the model must be installed correctly. Also, there are many adjustments that can be made if you’d like to fine-tune your model’s control system to your taste. The control system consists of eight components. There’s the bellcrank, a pushrod, a pushrod guide, a control horn (two control horns if the model has flaps), two leadout wires, a leadout guide, flying lines and a handle that the pilot uses to control the model. The bellcrank is the heart of the control system, and three pieces of wire are attached to it. The two leadout wires attach through the holes in the outer lips of the “bell.” The leadouts run out the inboard wing (usually the left) and pass through a leadout guide, which I will address later.
For small and light park-type CL models, the leadouts can be made from two pieces of .025-inch-diameter music wire with loops on both ends. One end will attach to the bellcrank, and the other will have a loop at the end to accept the line clip. The clips attach the flying lines to the model. All wires in the control system must be bent using round-nose pliers. If you bend wire around a flat platen, as found on regular square-nose pliers, you run the risk of fracturing the wire at the bends. The round-nose pliers yields a smooth, even radius. The third piece of wire to the bellcrank is the pushrod, which is made from a piece of 1/16-inch diameter (.062) music wire. The pushrod will usually have a 90-degree bend at each end. One end will fit into one of the holes in the bellcrank, and the other end fits into a hole in the control horn. The control horn is mounted on the movable elevator control surface at the rear of the model, and the movement of the pushrod drives the elevator up and down. The bellcrank is screwed or bolted to a plywood mount. It rotates on a bushing to transfer the up/down control commands from the control handle to the elevator. The amount of motion induced at the handle results in a proportional amount of movement at the elevator. The idea is to make tiny or large, smooth inputs as required to precisely control the path of flight on the inside face of the “hemisphere” in which a CL model is flown. With practice, you will be able to scribe very accurate maneuver shapes on the face of this flight hemisphere. All that control is transferred from your hand to the control surface(s) through the bellcrank and control horn mechanisms. The pushrod and leadout wires both require guides. When up control is applied, the pushrod is under a compression load. It will bow if too much air load pressure builds up on the elevator. If it does bow, control is diminished or momentarily lost, and the result could be a crash. Installing a simple plywood or bent-wire guide between the bellcrank and the control horn solves the problem.
The leadout guide should be positioned near the inboard tip of the wing. Install the guide so that the front leadout is approximately 3 degrees behind the center of gravity as viewed from above. If you were to hold the model by the two leadout ends and let it hang, the nose of the model should point slightly toward what would be the outside of the circle. The leadout guide can be made to be adjustable so you can fine-tune the model’s angle of tangency to the path of the circle in which you will fly. Only by trial and error will you find the leadout position that is optimal for your airplane. For all of these components to work together properly, they must be installed properly. Your control system must be free of binding or springing. The bends must be accurate, and the pushrod and leadout wires must not rub against anything. Take extra time to install everything properly and you will be rewarded with a model that is easy to fly. While the model should be balanced at the recommended center of gravity, the feeling of control authority that each pilot prefers can be adjusted by moving the point at which the pushrod is attached to the bellcrank and the control horn. If you move the pushrod attachment point at the bellcrank end farther away from the bellcrank pivot point, more pushrod motion and greater elevator travel are achieved. If you move the attachment point closer to the bellcrank pivot point, the travel of the pushrod and the elevator is reduced.
You can also adjust the ratio of travel at the control horn end. The closer to the pivot point you attach the pushrod at the horn end, the greater the elevator travel that is realized from a given amount of bellcrank travel. Conversely, the farther from the pivot point you attach the pushrod at the control horn end, the less the elevator travel from a given amount of bellcrank arm travel. Everyone is “wired” differently when it comes to perception of sensitivity. Some will like quick controls, where just a tiny bit of hand movement will result in lots of control surface movement. Others will prefer a slower control feel, where a lot of hand movement is required to produce results. Neither is right nor wrong; it’s a personal thing. By using the adjustments available to us, we can fine-tune our model to be an extension of our mind and arm, and go exactly where we want it to go. There are dozens of commercially available handles on the market, but when shopping, ask for the 1/2A type, and also ask for steel-cable 1/2A lines. In the past, many modelers have opted to fly their small, glow-powered models on Dacron lines. Be advised that your AMA insurance does not cover models flown on these synthetic lines. Choose good steel lines and a good 1/2A handle.
Article and photos by the author. Featured in the Spring 2008 issue of Park Pilot.
The control system in a control-line model is far less complicated than that of an RC model — no electronics to deal with and in most cases, only one moving control surface. Simple does not mean insignificant, so everything that goes into the model must be installed correctly. Also, there are many adjustments that can be made if you’d like to fine-tune your model’s control system to your taste. The control system consists of eight components. There’s the bellcrank, a pushrod, a pushrod guide, a control horn (two control horns if the model has flaps), two leadout wires, a leadout guide, flying lines and a handle that the pilot uses to control the model. The bellcrank is the heart of the control system, and three pieces of wire are attached to it. The two leadout wires attach through the holes in the outer lips of the “bell.” The leadouts run out the inboard wing (usually the left) and pass through a leadout guide, which I will address later.
Pulling on the rear leadout rotates the bellcrank, which in turn makes the pushrod move aft, forcing the elevator to move upward. When you pull the front leadout, the bellcrank rotates forward, the pushrod pulls on the control horn and the elevator is drawn down.
The bellcrank mechanism is really simple. The important thing is to install the entire control system so that there are no binds or “springing.” Everything must work smoothly.
For small and light park-type CL models, the leadouts can be made from two pieces of .025-inch-diameter music wire with loops on both ends. One end will attach to the bellcrank, and the other will have a loop at the end to accept the line clip. The clips attach the flying lines to the model. All wires in the control system must be bent using round-nose pliers. If you bend wire around a flat platen, as found on regular square-nose pliers, you run the risk of fracturing the wire at the bends. The round-nose pliers yields a smooth, even radius. The third piece of wire to the bellcrank is the pushrod, which is made from a piece of 1/16-inch diameter (.062) music wire. The pushrod will usually have a 90-degree bend at each end. One end will fit into one of the holes in the bellcrank, and the other end fits into a hole in the control horn. The control horn is mounted on the movable elevator control surface at the rear of the model, and the movement of the pushrod drives the elevator up and down. The bellcrank is screwed or bolted to a plywood mount. It rotates on a bushing to transfer the up/down control commands from the control handle to the elevator. The amount of motion induced at the handle results in a proportional amount of movement at the elevator. The idea is to make tiny or large, smooth inputs as required to precisely control the path of flight on the inside face of the “hemisphere” in which a CL model is flown. With practice, you will be able to scribe very accurate maneuver shapes on the face of this flight hemisphere. All that control is transferred from your hand to the control surface(s) through the bellcrank and control horn mechanisms. The pushrod and leadout wires both require guides. When up control is applied, the pushrod is under a compression load. It will bow if too much air load pressure builds up on the elevator. If it does bow, control is diminished or momentarily lost, and the result could be a crash. Installing a simple plywood or bent-wire guide between the bellcrank and the control horn solves the problem.
The pushrod is held to the control horn with a Du-Bro nylon keeper. This horn is mounted on the bottom of the elevator and the pushrod bend is positioned directly over the hinge line.
Install a pushrod guide halfway between the wing and tail. It prevents the pushrod from bowing under compression as up control is applied. The hole should allow free movement.
The leadout guide should be positioned near the inboard tip of the wing. Install the guide so that the front leadout is approximately 3 degrees behind the center of gravity as viewed from above. If you were to hold the model by the two leadout ends and let it hang, the nose of the model should point slightly toward what would be the outside of the circle. The leadout guide can be made to be adjustable so you can fine-tune the model’s angle of tangency to the path of the circle in which you will fly. Only by trial and error will you find the leadout position that is optimal for your airplane. For all of these components to work together properly, they must be installed properly. Your control system must be free of binding or springing. The bends must be accurate, and the pushrod and leadout wires must not rub against anything. Take extra time to install everything properly and you will be rewarded with a model that is easy to fly. While the model should be balanced at the recommended center of gravity, the feeling of control authority that each pilot prefers can be adjusted by moving the point at which the pushrod is attached to the bellcrank and the control horn. If you move the pushrod attachment point at the bellcrank end farther away from the bellcrank pivot point, more pushrod motion and greater elevator travel are achieved. If you move the attachment point closer to the bellcrank pivot point, the travel of the pushrod and the elevator is reduced.
The leadouts must exit the guide at the end of the inboard wing behind the center of gravity of the model. A good way to check this is to hang the model by the leadouts. The nose should hang slightly lower than the fin as a good starting point. An adjustable leadout guide allows you to fine-tune this feature for best flight performance.
You can also adjust the ratio of travel at the control horn end. The closer to the pivot point you attach the pushrod at the horn end, the greater the elevator travel that is realized from a given amount of bellcrank travel. Conversely, the farther from the pivot point you attach the pushrod at the control horn end, the less the elevator travel from a given amount of bellcrank arm travel. Everyone is “wired” differently when it comes to perception of sensitivity. Some will like quick controls, where just a tiny bit of hand movement will result in lots of control surface movement. Others will prefer a slower control feel, where a lot of hand movement is required to produce results. Neither is right nor wrong; it’s a personal thing. By using the adjustments available to us, we can fine-tune our model to be an extension of our mind and arm, and go exactly where we want it to go. There are dozens of commercially available handles on the market, but when shopping, ask for the 1/2A type, and also ask for steel-cable 1/2A lines. In the past, many modelers have opted to fly their small, glow-powered models on Dacron lines. Be advised that your AMA insurance does not cover models flown on these synthetic lines. Choose good steel lines and a good 1/2A handle.
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