Altitude and speed control in Loiter

Hi all,
My task is to test 2 different flying wing at relatively high speed (16 m/s) in order to find which is more energy efficient for payload lifting (1.5kg). I have manually tested the airfoils at those speeds and they fly well. Being new to ArduPlane, I have started looking into Loiter mode in order to automatically test them on a fixed circle path and for a certain amount of time. However I want the wing to stay at a constant altitude and the speed to be (relatively) constant during Loiter. Those two parameters being fixed I suppose that the only variable the auto mode will be able to play with is the angle of attack (the cost being increased drag). How can I achieve this, and what parameters can I use, as I am a bit lost with all the different settings? I have already tried Loiter but using stick mixing for throttle control in order to maintain altitude, this time I want the speed to be automatically controlled as well as altitude.
Thanks for the help!

NOTE: I have an airspeed sensor configured

I think if you designate the Loiter altitude (in the mission plan) and the Cruise airspeed (in the basic parameters) the aircraft will perform as you’re describing. This seems to be just the basic loiter behavior.

Have you tried this already? If so, what did you observe that wasn’t what you were hoping?

If you are interested in testing for energy efficiency, you really need to test with the payload. Changing other variables such as angle of attack is only possible at different airspeeds, otherwise it will result in climbs and additional energy loss. There are really only 2 things to set - altitude and airspeed. Other variables have to be tested. Fluid dynamics are inherently nonlinear, and it’s usually easier to just test instead of model when it comes to efficiency.

If you want to know some numbers about twin-engine airplanes, you can see my results here: Benchmark Test of the Twin Engine Mapping Planes

Thank you for the responses! The issue was that I had to override the throttle in order to make it stay at a constant altitude as it was loosing speed and thus loosing altitude. I believe I have found one of my issues. I am using a PixHawk Lite and recently try to connect an analog airspeed sensor however it seems like I can’t find the right pin number on MissionPlanner to read from the 3.3V ADC of the PixHawk Lite to which my analog sensor is connected to. And so I did not have any reading for airspeed from the sensor. I guess my question now is if I can use the board’s speed estimation and not the sensor’s in order to maintain constant speed? In absence of an airspeed sensor will the board’s speed reading be used to match the Cruise airspeed parameter? I will also continue searching for a way to hook up the analog sensor or buy a digital one.