Power System

Engines

Engines were selected based on following standards:

Enough thrust to compensate drag during the flight.
High reliability and easy to repair.
Proper size that can be suited under the wings.
The best performance altitude interval should be around the cruising altitude.
Reducing the fuel consumption as much as possible.
Low sound if needed.

Position

Front
- pros:
  - facilitate thrust vectoring, allows for better maneuverability and control, especially during takeoff and landing
  - high Aerodynamic Efficiency
  - low risk
  - high propeller efficiency
- cons:
  - add complexity
  - space consuming
  - influence first person view
Center
- pros:
  - provide better weight distribution
  - free up space in the fuselage
- cons:
  - add complexity to the UAV’s design
  - difficult with maintenance
  - generate significant vibration
Back
- pros:
  - reduce aerodynamic drag
  - help centralize the UAV’s weight
- cons:
  - require sufficient ground clearance to prevent damage during takeoff and landing
  - add complexity to the UAV’s structure, increasing manufacturing costs

Categories

Motor
- pros:
  - Versatility: could be used for Multi-Rotor, fixed wing, vtol, mini UAVs, especially for those that requires vertical take off and landing
  - Instant Torque
  - Precision Control
  - Compact and lightweight
- cons:
  - usually only suited to smaller UAVs
Correspondence with the propeller
- The relationship between the motor torque and propeller is closely intertwined, as they determine the power and performance of the aircraft. Many of these data are listed on the motor itself.
- Torque: torque measures the rotational force that a motor can produce. It indicates the turning power of the motor. A higher torque generally means that the motor can drive a larger or heavier propeller.
- Propeller Characteristics:
  - Diameter: The diameter of the propeller affects the thrust it generates. Generally, a larger diameter propeller can produce more lift and thrust, but it also requires greater torque to operate.
  - Pitch: The pitch refers to the angle at which the propeller blades are tilted relative to the direction of motion. A high-pitch propeller “bites” into the air more deeply, thus producing more thrust, but it also demands higher torque.
- Matching Principle: selecting the right combination of motor and propeller is crucial for achieving optimal flight performance. If the propeller is too large or has too high a pitch for the available motor torque, it may result in reduced RPM (revolutions per minute), decreased efficiency, and even motor overheating. Conversely, if the propeller is too small or has too low a pitch, the motor’s potential might not be fully utilized, leading to wasted resources.
- Calculation and Testing: to find the best match, theoretical calculations (such as using formulas to estimate the required torque) and actual flight testing may be necessary. There are many online tools available to help enthusiasts recommend suitable motor-propeller pairings based on specific needs.
- Other Considerations: factors such as battery voltage and current limits also affect the final selection. For example, with a given type of motor, increasing the battery voltage can boost output power, allowing for the use of a larger diameter or higher pitch propeller.
Ducted-fan
- pros:
  - Increased Thrust Efficiency in high speed
  - Reduction of Foreign Object Damage (FOD)
  - Noise Reduction
  - Improved Aerodynamics
  - Multi-Rotor Stability
  - Confined Space Operation
- cons:
  - Increased Weight
  - Reduced Efficiency at Low Speeds
  - Reduced Maneuverability
Turboprop engine
- Air enters the intake and is compressed by the compressor. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts. The hot combustion gases expand through the turbine stages, generating power at the point of exhaust.
- pros:
  - low fuel consumption
  - economic in low speed
- cons:
  - High fuel consumption at very low speed
Turbofan engine
- The word “turbofan” is a portmanteau of “turbine” and “fan”: the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion and the fan, a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components.
- pros:
  - Good in low speed
  - used in Civil aviation and Military aircraft
- cons:
  - require complex maintanece
  - higher production cost
  - suffer from reduced performance at low altitudes due to airframe drag penalties
Turbojet engine
- A turbojet engine consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine (that drives the compressor). The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust.
- pros:
  - economic in high speed
  - great High-altitude and high-speed performance
  - used in High speed aircraft
  - used in Subsonic aircraft
- cons:
  - High fuel consumption at very low speed

Power Supply

Categories

Batteries – when designing a drone, the decision to use battery power depends on several key factors:
- Purpose and Mission Requirements of the Drone: Different missions have varying power requirements. For instance, drones required for surveillance or aerial photography, which demand extended hovering or flight times, need batteries with high energy density and long endurance.
- Battery Performance: This includes the battery’s energy density, discharge rate, cycle life, and safety. A battery with high energy density can provide longer flight times, while a high discharge rate can supply the necessary current for takeoff or high-speed flight.
- Size and Weight Constraints of the Drone: The weight and volume of the battery also influence the drone’s design. Typically, there is a trade-off between battery capacity and weight in drone design.
- Cost Considerations: The cost of the battery is also an important factor. High-performance batteries tend to be more expensive, so a balance between performance and cost must be considered during the design phase.
- Environmental Factors: The operating environment of the drone, such as temperature and humidity, can also affect battery selection. For example, batteries that can withstand extreme temperatures might be necessary for drones operating in harsh conditions.
- Charging and Maintenance: The charging time, maintenance requirements, and ease of replacement of the battery are also considerations in the design.
Gasoline – when designing a UAV, the decision to use gasoline as its fuel source depends on several key factors:
- Energy Density: Gasoline has a high energy density, which is beneficial for long flight durations. However, the efficiency of the engine in converting this energy into propulsion is also critical.
- Emissions: Gasoline engines produce emissions that can be a concern for environmental impact and may also be subject to regulatory restrictions .
- Maintenance and Reliability: Gasoline engines require regular maintenance and may have more parts that can fail compared to some electric propulsion systems. The reliability and maintainability of the engine should be considered in the design phase.
- Weight and Balance: The weight of the fuel system, including tanks and pumps，can significantly affect the UAV’s center of gravity and overall weight, impacting flight performance.
- Availability and Supply: Gasoline must be readily available and easy to transport to refueling locations, which may be a consideration for long-term or remote operations.
- Cost: The cost of gasoline and the overall cost of ownership, including fuel consumption, should be considered in the economic viability of the UAV operation.
Hybrid – a combination of the previous two method