I usually put the spoiler on the throttle channel and use a program mix to adjust the elevator as the spoiler changes. No problem with a conventional tail. But with a V-tail only one side of the tail moves.

I am using a Futaba 7CAP. Futaba support answered my e-mail telling me the answer was to put 2 programmable mixes on one switch. Both with the throttle [activating spoiler] as master and one with aileron and the other with elevator as the slave channels. This works fine.

From : Don Stackhouse

As far as the need for mixing from spoilers to elevator, we attempted to keep that to a minimum in the aerodynamic design of the spoilers. The spoilers originally started further inboard, but their airflow interacted with the tail (both the conventional tail and to a lesser extent the V-tail), causing a fairly pronounced nose-down pitch change when the spoilers were open.

We changed the design, moving the spoilers further outboard, to minimize the effect. However, we decided that keeping a little bit of nose-down pitch change was good, because it gave positive indication that the spoilers had opened, even from a long distance. Also, because spoilers destroy lifting ability over a portion of the wing, they do raise the stall speed slightly when open. We felt that a slight nose-down pitch change would help encourage beginners to keep their speed up on final approach to allow for this. In addition, that extra speed could come in handy if they left the spoilers open too much or too long, resulting in getting too low while still too far out. The extra speed would allow them to stretch the glide a little after closing the spoilers.

Don Stackhouse
DJ Aerotech