Me playing around with the airspeed sensor and some mixer to make an auto throttle while retracts are up and normal throttle when retracts are up. You will probably want to be in chase mode to see my control inputs.

What I made is basically a airspeed requestor listening to the throttle if the airspeed drops the throttle increases to regain airspeed or if airspeed goes higher than what you requested the throttle decreases. Also it will add power below some speed to prevent stalling, but this is optional feature.

All you need is one airspeed sensor, one mixer and one signal modifier for the auto throttle, and three more mixers if you want a on/off switch.