May 6

What Is An RC Plane Setup About?

All Present & Correct

My last post took us through the various installations needed to complete the radio and power train. Now that all of the essential components are installed, (I have to say it looks pretty busy in there)  I need to go through a full setup procedure to make the model ready for its first trial flights.

So what is an rc plane setup all about? Well really its just a matter of checking and making sure all of the active functions are correctly connected and operating as they should. Let us go through some of these checks together.

Arranging Aileron Differential

I have decided to use this arrangement as in the past I have found it beneficial in certain circumstance. If you visit my previous post entitled Differential on Ailerons for Radio Control Aeroplanes you will learn why this feature makes life easier when flying models that suffer from ‘Adverse Yaw’.Servo Offset Aileron Diff

Now, I’m not suggesting that the Hawklett is one such model but I have found that a little aileron differential helps the roll function of most planes.

Here in this diagram the differential is arranged by setting the servo output arm a few degrees forward of the vertical. As the arm moves in a circular arc, the forward linear movement is less than the rearward movement.

When this is transferred to the control surface horn the difference in linear movement causes the upward deflection to be greater than the downward deflection (As > Bs therefore Ah > Bh). Hence we have ‘Aileron Differential’.

Now I know that I could have arranged this with the two wing mounted aileron servos connected to two receiver sockets (aileron & auxiliary) along with a mixing facility but I prefer to keep the spare sixth channel for another function if needed. Consequently I find this mechanical option equally as effective.

Single Servo Rudder & Steering Control

Rudder & Steering Servo

As you can see from this diagram, there are two ways to arrange the pushrods to achieve control of both Rudder and Steering from a single servo.

In the first instance the steering horn on the nose leg is connected on the same side as the servo output arm connection. To have the rudder turn in the same sense as the wheel the closed loop cables have to cross over in front of the fin inside the fuselage.

In case two the steering pushrod crosses over from one side to the other so that the wheel turns in the opposite direction. but the closed loop cables do not cross over. Alternatively the ball link connector to the wheel could be moved over to the other side of the servo output arm whilst leaving the steering leg linkage as in the first diagram.

Separate Elevator Control Arrangement

I thought that it was worth spending a little time on an explanation of this arrangement. I personally have never seen this done before on any commercially available model kits or plans. Having said this, it does work very well and could be applied to other projects where rear fuselage space is at a premium.

Elevator Pushrod & Drive Yoke assembly

The basis of this arrangement is the clever little yoke that connects the two halves of the elevators together. It comprises a wire ‘U’ with a ‘Z’ bend soldered to the bottom of the ‘U’. This fits into a standard clevis pin hole in the horizontal leg of the bell crank. The upright leg of the bell crank is connected to the pushrod that runs the full length of the rear fuselage to where the servos are located under the cockpit.

On each end of the Yoke arms are ball link sockets that mate with the balls attached to ply extensions on the trailing edge of the elevators.

In use this arrangement gives very positive and easily adjusted elevator movement.  As there are at least three points at which the movement ratios can be adjusted (servo & bell crank x 2) the range of movement is adjustable to the Nth degree. The all important consideration is that all linkages are a good fit into the drive components to eliminate unwanted slop.

The final ball link connections on the elevators give fine adjustment to ensure the elevator halves are exactly in alignment on each side.

Setting Up The Retracts

The important thing to ensure when installing and operating mechanical retracts is:

a) That the travel of the pushrod(s) do not exceed the operating range of the servo(s).

b) That the travel is sufficient to locate the pushrod and actuator in the locked leg position.

Retract leg up

Retract leg down

In the two diagrams above you can see that the pushrod link/activator moves horizontally sliding a bar in the activation slot from one end to the other. This in turn pivots the leg mounting block, shown mainly in dashed lines, so that the leg travels in a 90 degree arc from the retracted position to the down position.

I have shown the pin that sits in the activation slot short of the maximum travel. This prevents the servo from being put under continuous load. Having said that, I have checked that the amount of travel is sufficient to ensure that the position of this pin at full travel locks the leg in the required position.

The main adjustment is made via selection of the correct pushrod connecting hole in the servo output arm. With some radio gear that does not have a ‘travel adjust’ programme, this is the only method available. Most modern digital gear has this facility so final adjustment can be made by reducing or increasing the travel slightly at each end. I have set mine at 95% at each extremity.

The drawings here show the nose leg where the mounting plate is hidden inside the fuselage. On the wing units the leg extends from the opposite side of the block so that the mounting plate sits flat against the wing surface.

Final Testing

At the beginning of this post I asked the question; “what is an rc plane setup about”? I hope that this has been answered for you in the above explanations.Digital Wattmeter

Now that all of the active controls are setup the next task is to do some motor run tests using different propellers and monitoring the current draw and logging the static power readings. This is where that invaluable piece of kit, the Power Meter or Watt Meter comes into its own.

I very strongly suggest that if you intend to go down the electric flight route, you should invest in one of these meters. It will save you not only a lot of time but also the money you could lose in burnt out motors, ESCs and blown Lipos. It will also help you select the best propeller for your plane.

I’ll catch you next week with some test results. Don’t forget to mention my website if you know anyone who’s just getting started. Also, if you want to follow the full series of my Hawklett build posts, the first is here.



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Posted May 6, 2016 by Colin Bedson in category "Modelling Skills

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