Further airframe testing

For the last week and a half I have been doing further testing on the Sky Eye’s performance at my intended weight. Here are the general results thus far:

Payload – 720g (1.6lbs)
Best cruise efficiency – 60-75% Power
True Airspeed @ 4500ft, 65% Power – 37MPH
Climb Rate @ 4500ft, 100% Power – 424fpm
Climb Speed @4500ft, 100% Power – 31MPH
Efficiency @ 65% Power, 3S Battery – 4.8 mi/Ah
Climb Efficiency @ 4500ft, 3S Battery – .53Ah/1000ft
Climb Lateral Efficiency @ 4500ft, 3S Battery – 1.25 mi/1000ft

The cruise tests were done in a closed loop at 4000ft with winds speeds up to 9MPH. Due to the nature of a closed, fixed loop over a ground point, they reflect the reduced efficiency I will see due to wind  - more time is spent traveling against the wind than with the wind, resulting in a net efficiency loss.

An interesting observation was made during the climb tests, where I climbed at constant rate and then did a steep dive to climb again. Control of the airplane, especially aileron control, decreases substantially as airspeed increases. My guess is that the cheap pushrods that came with the kit are bending when the ailerons are deflected at these speeds. I saw this when I exceeded about 55mph groundspeed, but there was probably a significant vertical speed component to that as well. I am sure that while the tail surfaces remain controllable at this speed, their failure is not far behind the ailerons. Lesson: don’t do dives.

My mission plan is to carry a 9Ah battery load, use a maximum of 8Ah of that and cruise at 1000ft AGL. The fixed 30 mile round trip course should, according to these figures, consume 6.5Ah@12V of energy from the flight systems. This leaves some extra for stronger winds, autopilot power, and loitering time. The full mission should take approximately 65 minutes with no winds.

Up next is integrating an ArduPilot mount into the system and starting to tune the PID controllers. Stay tuned.

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