2-servo Elevator
 

A.M.,

I'm setting up a Cap with dual elevator servos. I connected one to channel 2 and the other to channel 7. I am using a Futaba 9C.

The 2 servos are mounted in the fuselage on either side of the rudder servo and the control arms point to the fuselage sides. Clearance between them and the rudder servo would make changing their directions very difficult and because of this I'm virtually forced to mix the channels instead of y-connecting them. This of course means that when I set the MIX up between elevator and aux1 I have to reverse the direction of aux1 in relationship to the elevator channel.

I've done this and my problem is I'm getting a significant difference between the 2 elevator deflections (difference will definetely effect the trim of the airplane). The push rods cross each other in the fuselage, they are of a nyrod design with a carbon arrow shaft as the sleeve -- virtually no side flexing, and they are virtually identical in size. Right now I'm attributing the deflection difference to the servo deflections.

Here's the rub: Neutral for both servos are not currently 90 degrees to the servo case. They actually point slightly aft of 90 degrees to the case. If I was to modify the clevis' so that they both are exactly 90 degrees to the case will I elliminate the deflection difference or is the difference due to one servo going in one direction and the other going in the reverse?

Is there anything I can do with the 9C programming that would help to even out the deflection of these 2 servos? They aren't digital so I know I can't program their deadpans.

I'm asking this question but will not stand still -- I will be modifying the clevises to make them both 90 degrees to the servo case. I will also refine the adjustment to get as close as I can to neutral on both servos without using the subtrims. Since I also own the Hitec servo programmer I will verify that the pulse widths between channel 2 and 7 are the same. Unfortunately, since these are analog servos I won't be able to adjust their deadpan.

I plan on asking Mike at Hitec a similar version of this question because the servos we are talking about are Hitec 425s. I will be asking him if it is normal for the deflection of 2 same-model servos to be off enough to cause a noticeable deflection difference between 2 surfaces on 2 channels.

2-servo Elevator
 

Hill,
The arms don't need to be 90 to the case; the pushrod MUST repeat MUST be 90 to the servo arm itself, then square to the case has very minimal effect. Please makesure your servo arms are 90 to your pushrods, that may well solve the problem, ro the problem may be total range of one servo vs the other, in which case use ATV to adjust it.

Any reason not to use the Ailevator function and use channel 8?

2-servo Elevator
 

I will explore this -- was not familiar with it because the name seems to refer to using the airlons as both elevator and airlon, something I do with my Zagi.

BTW, I did adjust the arms on the servos and the control horns and came up with a close synchronization. We flew it this evening and I was not too dissapointed in the results -- more work is needed to refine the control.

Your suggestion about the servo arm being 90 degrees to the pushrod sounds promising -- got the same recommendation on another forum. Since my pushrods cross each other in an 'X' pattern I would expect the servo arms to be slightly aft of 90 degrees to the servo case at the neutral position.

2-servo Elevator
 

Don't confuse ailevator with elevon....elevon is for flying wings which have ONLY one pair of surfaces used for both; ailevator is the tail version of flaperon -- work as elevators and if you dont' set the aileron travels to 0 in the function then it also works with your ailerons.

2-servo Elevator
 

Thanks A.M. Someone else explained this to me and then it made sense.

I just go back from a great weekend at the Summersville, WV Walley's Squadron Fly-In and will now attend to this.