Task 5

Minimum Turn Radius, Manual and Auto

Matthew Berk

Obtaining the flight performance characteristics is necessary for the mission planning team to finalize its waypoint algorithm as well as obtain better control gains for line transition and navigation. The methodology was to simply try to continually tighten a turn at full power for the manual mode, and to try various gain values on turns for automated control.

Manual Mode:

Figure 1: In the trajectory plot one can see that during the sustained turn the model is drifting downwind. By taking the cross-wind diameter of the turn the radius can be seen to vary from around 11-13m when under manual control.

Figure 2: Looking at the state variables, one can see that they generally make sense. The turn is sustained at an average of about 8 m/s and a bank angle around 45 degrees. CL hovers near the estimated CLmax of 1.2, and the g-loading is in the range of 1.25-1.5. Note that due to the off-axis position of the Pixhawk in the model it is possible for the z-accelerometer to have errors stemming from roll rate, which should explain the points which exceed CLmax but stall does not occur.

Figure 3: The controls show a similar story, indicating full throttle power (with its corresponding power consumption) and an aileron and elevator trim which are typical of a steady turn on a model with light dihedral. Since there is no rudder, that data was not included.

Automated Mode:

Figure 4: In automatic mode a very tight turning radius was obtained by allowing an overbank and tip stall for large angle deviations. This allows for extremely tight turns with radii in the territory of 3m, but with about 5m of altitude loss as shown in the color bar. This altitude loss may be worth it as the aircraft can return to cruise altitude within a few seconds of the turn, but this is for the mission planning team to decide. The gains can always be reduced for a normal level turn.

Figure 5: The data shows the tip stall and the subsequent tuck and dive at 75.5s which leads to a velocity increase thereafter. After the dive a 3g loading is induced in the pullout to steady state.

Figure 6: Again, the controls settings show a reasonable response to this condition. Thrust increases in the turn and then drops off rapidly as speed is gained in the dive in order to reduce the velocity gain in the dive. The ailerons engage the dive then restore to level after the maneuver is completed. The elevator makes sense in order to quickly pull out of the dive.

Overall the turn performance seems quite good, and with further tuning to the control system it is expected that it will be able to provide sub-10m level turns and potentially sub-5m stall turns. Which is chosen will depend on interaction between the mission planning and controls teams, as well as a substantial amount of testing to determine the tradeoffs for each.