Question

Critically think about the difference in fixed-wing vs multi-rotor maneuvering flight dynamics and possible configuration changes to answer the following discussion topic:

When considering turning and climbing flight, compare and contrast fixed-wing and rotary-wing UAV performance and its implications for flight planning capabilities and limitations. Additionally, discuss the advantages/disadvantages of configuration changes such as adding a heavy payload or extra onboard sensors and if this will affect performance and path planning considerations.

Answer 1

Fixed Wing aircraft

The fixed-wing aircraft uses the wings (airfoil) to produce lift by moving faster through the air by means of generating thrust by using a propeller-motor combination or a jet engine. The fixed-wing aircraft are generally are larger in size compared to rotorcrafts and require runways or a launching system to generate lift for taking off from the ground. Once it's launched the aircraft requires minimal control and inherently stable during flight. The aircraft has more flight time compared to the rotorcrafts. The flight speed of the fixed-wing aircraft is higher compared to rotorcrafts as it's not limited by the rotor speed (for the jet planes). The fixed-wing aircraft can carry a larger payload over longer distances and requires less power than a rotorcraft.

Rotary Wing aircraft.

The rotary-wing aircraft or rotorcraft uses the blades (which also have the airfoil shape) which rotate at very RPMs to generate lift and uses Cyclic pitch controls( for a helicopter) or differential thrust (for a drone) for moving around. The rotorcraft has a major advantage over the fixed-wing aircraft, as all rotorcrafts can hover and the fixed-wing can't and can take off and land without any launching system or runways as the lift generated by the rotorcraft is vertical and lifts the entire vehicle at once. But the rotorcrafts require a complex mechanical system for cyclic controls as in the case of helicopters and inertial measuring unit, flight controller, etc for a drone and are not inherently stable during the flight, but the drone has higher maneuverability over the other aircraft. The rotorcraft require more power to stay in the air and its range is also limited compared to the fixed-wing aircraft.

Turning and Climbing Flight

The fixed-wing aircraft usually has a larger turning radius and slower turn rate compared to the rotorcrafts and uses the control surfaces for performing a turn (rudder). The rotorcrafts have higher turn rates due to higher maneuverability, the drones vary the speed of the opposing or adjacent rotors to generate a differential thrust in the desired direction. Drones also have a lower moment of inertia compared to a fixed-wing aircraft which makes it much easier to perform a turn. For a helicopter, the turning is performed by varying the speed of the tail rotor and introducing a torque on the vehicle which initiates a turn in the desired direction.

During the climbing flight, the fixed-wing aircraft either increase the thrust of the engine/rotor to generate more lift or uses the control surfaces to direct the airflow downwards (elevator) or use both for climbing. On the other hand, rotorcrafts increase the thrust by spinning the rotors at higher rpm or uses the collective pitch (in helicopters). The rotorcraft has higher climb rates compared to the fixed-wing aircraft at a given altitude, as the entire thrust is used for its vertical climb but the service ceiling (the maximum altitude the aircraft can fly) is limited compared to the fixed-wing aircraft.

Flight planning capabilities and limitations.

The fixed-wing aircraft have a higher range and uses less power/fuel due to the lift generation of the wing and the power is only used for increasing the forward speed of the aircraft. The limitation of the fixed-wing aircraft is it cannot hover over one place to deliver payload safely while flying instead, it makes circular flights for surveillance activities. The fixed-wing aircraft are generally much faster than the rotorcrafts and can cover a long-range in a quick time.

The rotorcrafts have limited range and have higher power/ fuel consumption, flight time is also limited due to the hovering nature of the rotorcraft as more power is consumed for staying in the air. Due to the limited range, the rotorcrafts are capable of only short distant flights. The flight speed is also limited due to the compressibility effects occurs in the rotor, as the tip speed of the blades reaches the speed of sound, flow separation occurs on the blade, in turn, reducing the lift generated by the blades.

Effects of heavy payloads on flight performance

The fixed-wing aircraft can handle heavy payloads and can deliver to longer range, which makes it ideal for delivering payloads of bulky and robust in nature. The addition of onboard sensors will not affect the flight performance and some types of equipment will improve the path planning for the fixed-wing aircraft like onboard airspeed sensors, GPS modules, cameras, etc.

The rotorcraft's payload capability is limited but they can deliver heavy payloads over a short-range. The rotorcrafts can deliver the payloads which require more handling without any damage. The heavy payload will definitely affect the flight performance of the rotorcraft and the placement of the payload is also will affect the center of gravity of the rotorcraft. Some of the onboard sensors will improve the flight performance of the rotorcraft like accelerometers, IMU (which are built into the drone), Time of flight sensors, Laser Range Finder (LRF), etc. For path planning applications, ultrasonic sensors will help to detect the distance between objects and the drone.