Sizing scenarios and design drivers

Written by Marc Budinger (INSA Toulouse), Scott Delbecq (ISAE-SUPAERO) and Félix Pollet (ISAE-SUPAERO), Toulouse, France.

The preliminary sizing of UAVs aims at defining the main drone characteristics and selecting the components based on a few sizing scenarios. The sizing scenarios are part of the specification process and may include both transient and endurance criteria, such as maximum rate of climb and hover flight endurance. The final overall design has to consider simultaneously the various sizing scenarios that may impact the components selection through design drivers.

Design drivers

Design drivers are physical factors that influence the design process of a component. For example, the propeller design is driven, among others, by the maximum thrust it can provide.

Table 1 summarizes the main system components.

Sizing scenarios

Endurance scenarios, like hover flight need to be taken into account for the selection of the battery endurance and the evaluation of the motor temperature rise. Extreme performance criteria, such as maximum transitory acceleration or maximum rate of climb are fundamental to determine the maximum rotational speed, maximum propeller torque, Electronic Speed Controller (ESC) corner power, battery voltage and power, and mechanical stress.

Table 1: Design drivers and sizing scenarios

Components	Design drivers	Parameters involved	Sizing scenarios
Propeller	Max thrust	Diameter, tip speed	Takeoff
			Climb
	Efficiency	Pitch	Hover
			Cruise
Motor	Temperature rise	Nominal torque, Resistance	Hover
			Cruise
	Max. voltage	Torque constant, Resistance	Takeoff
			Climb
Electronic Speed Controller	Temperature rise	Max power, Max current	Takeoff
			Climb
Battery	Energy	Voltage, Capacity	Hover (autonomy)
			Cruise (range)
	Power	Voltage, Max discharge rate	Takeoff
			Climb
Frame	Stress	Mechanical strength	Takeoff
			Landing
			Crash

In the rest of this lab, only the hover and takeoff scenarios will be covered.

Table 2: Design drivers and sizing scenarios with focus on hover and takeoff scenarios

Components	Design drivers	Parameters involved	Sizing scenarios
Propeller	Max thrust	Diameter, tip speed	Takeoff
	Efficiency	Pitch	Hover
Motor	Temperature rise	Nominal torque, Resistance	Hover
	Max. voltage	Torque constant, Resistance	Takeoff
Electronic Speed Controller	Temperature rise	Max power, Max current	Takeoff
Battery	Energy	Voltage, Capacity	Hover (autonomy)
	Power	Voltage, Max discharge rate	Takeoff
Frame	Stress	Mechanical strength	Takeoff