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Basic Fixed Wing Setup

Hai-Lee

Old and Bold RC PILOT
Mentor
#1
Setting up your first fixed wing aircraft can seem quite simple but there are a few misunderstandings around transmitter setup which can cause difficulty for some and so this is just a few simple pointers to clarify things a little and allow you to setup your plane and get it to fly reasonably at first attempt. Of course after the first flight you may need to adjust things a little to "Tweak" its performance.

Firstly I will state that ideally the point at which the pushrod, (or equivalent), connects to the control horn should be perpendicular to the control surface hinge line. This is important for getting balanced control response, especially with rudder and elevator. There can be times where a non-balanced response may be required but that can be normally achieved in "Post" setup changes to the transmitter settings.

Initial Transmitter Settings

1.The trims should be centred.
2.The sub-trims should also be checked to ensure that they are centred.
3. on the dual rate settings the "High" rate should be set to 100%
4. The end points should be set for +100% & -100%

Setting up the Servos
1. With the servos plugged into the Rx turn on the Transmitter and then turn on the Rx. This should centre the servos!
2. Fit the servo into its final position and secure such that it cannot move in its mounted position.
3. Now fit the output arm of the servo such that it is in parallel with the control horn. As servos will not align perfectly with the required angle initially you should endeavor to get the arm as close as it physically possible to the required angle.
Getting the angle exact: With the angle as close as you can get mechanically you can tweak the angle by using the sub-trim thereby keeping your trim range centred for your first flight. In the case of dual controls like ailerons/Flaps/Elevons and Flaperons
you can use the sub-trim to get IDENTICAL angles on the servo arms so you get balanced control surface deflections
which can be vital for stable and predictable operation of the plane.

4. Fit and tighten the securing screw to the top on the servo.
5. Fit the pushrod onto the servo in the hole closest to the securing screw. and then connect the other end of the pushrod into the hole in the control horn furthermost from the hinge line. Check the control throw or deflection. If insufficient deflection then shift the servo end of the pushrod outwards to a hole that is further away from the securing screw and re-check. Repeat until the required deflection is achieved.
6. Repeat step 5 for every control surface.
7. Centre each and every control surface and either adjust the length of the pushrod or tighten the linkage stopper to lock the control surface in its centred position with the servo in its centred position.

Setting up the Transmitter
1. Sub Trim is set during the initial setup to get the servos either properly and squarely centred, or to give identical servo arm angles for dual control surfaces.
2. Dual rate. With the High rate setup to give the recommended control surface deflection the rate switch is then moved to the low rate position and the low rate setting recommended setting is programmed in. Where no recommended low rate is given an setting of 80% is recommended as a starting point. Feel free to adjust to suit your own experience after the first flight.
3. Expo. This setting can vary significantly between brand of transmitters/ For an experienced pilot the setting recommended for the first flight is 30% whereas a beginner should consider a setting as high as 50%. Too much Expo can make the plane somewhat unresponsive at all but large control stick deflections. The significant differences in Transmitter Expo settings is that on some systems the settings you require will be "Positive" and on some others it will be "Negative" for the same effect. The effect you require is to flatten the response curve around the transmitter stick's centre position. For the same movement angle of the Tx stick the centre area should move the control surface less.
4. End Points. The setting of end points can provide a few special benefit for those who use them. When using 2 channels for the ailerons, rather than adding Differential mechanically you can provide a good facsimile by reducing the down deflection on each of the aileron channels. In addition where you find you have insufficient rudder in a single direction you can increase the overall rudder deflection mechanically and then cut the response in a single direction, (the working direction), by altering end point. Where your flap setup is driving the servos to their limits and causing the flap servos to stall and "Buzz" continuously you can reduce the range of the flap servo travel by adjusting their end points.
5. Mixes. I will not discuss the need for, or how to implement mixing as that can be an involved subject and a long post that may be transmitter specific.
6. Mix Ratios. When you are using a mix and find that you need to adjust the input rations of the channels, (the FT Viggen is a classic where the elevator input needs to be greater than the aileron input), you can adjust the amount of each channel into the mix. (For a Viggen the ratio would be approximately 60% elevator and 40% aileron).

I hope that answers a few questions and perhaps raise a few others!

Have fun!
 

mayan

Well-known member
#3
Great thread @Hai-Lee I think that this is a good starting point for those of us that don't understand this all yet. I know I need to understand all this better!