Task 1

Experimental Determination of Trims

Matthew Berk

Two different methods for attempting to determine trim values for different airspeeds were performed in the interest of obtaining a baseline trim setting for our controls systems.

Bixler 2

For the Bixler 2 an initial attempt was made to find trim settings by using our proportional controller design to hold heading and altitude with different initial pitch trims and try to allow the final steady state error to define the other control positions to maintain this trimmed flight. In this scheme basically the throttle trim was picked, then hopefully the control system would trim velocity, rudder, and aileron.

This generally worked in the sense that a relative steady state condition within a perturbational range was obtained, however the data output ended up being too noisy to actually determine a reasonable "average" trim location. It became apparent that this attempt to use a control system to determine control system trims was unfortunately hampered by the system's immediate response to any perturbation adding noise to the trim values. Ultimately trim locations were never obtained for the Bixler 2 as equipment was moved to our prototype.

Sparrow 1

On the Sparrow 1 prototype a much more conventional manual flight technique was performed in relatively calm conditions to determine trims. In this case rather than setting throttle, the surface deflections were determined initially.

First, rudder and aileron were picked to maintain straight flight. Fortunately our airplane surfaces seemed well-aligned enough that during testing there was no velocity dependence noted for the lateral-directional trims and they were held constant over all airspeeds.

With lateral-directional trims selected, the elevator was trimmed, the velocity noted from QGroundControl, and throttle was picked to maintain altitude. This was achieved by a ground control station manager calling to the pilot to increase or decrease throttle based on the rate of change of altitude reported from QGroundControl.

Unfortunately, due to a lack of time only one set of flights was able to be performed for trim determination. Additionally, due to the very limited airspeed range possible with the Sparrow 1 for level flight, many of the attempted trims showed overlap in airspeeds near each other, requiring fairly stringent checks on the data to ensure truly straight and level flight. This resulted in only 3 trims which the team could consider supported enough by flight data to report. 11m/s was reported as the top achievable speed of the aircraft in level flight. The trim attempts for 9 and 10 m/s were determined in analysis to have either overall altitude gain or loss, meaning they were not representative for level flight trim.

The trims that were found and reasonably accurate are shown below as a function of airspeed:

Figure 1: Trim of throttle and control surfaces at different airspeeds.