Principles of Flight

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Objective

Describe how various RPA generate lift and thrust, and how propeller pitch influences performance.

A. Lift Production

Core Principles

  • Fixed-Wing Lift
    • Airfoil shape and AoA deflect airflow downward (Newton’s 3rd Law) and create pressure differential (Bernoulli).
  • Rotor/Wing Lift (Multirotor & Helicopter)
    • Rotary wings act as rotating airfoils, producing lift everywhere along the disk.
  • Ducted Fans & Coaxials
    • Enclosed shrouds increase static pressure and reduce tip losses for more efficient lift.

Method

  1. Inspect wing/rotor airfoil geometry.
  2. Verify proper pitch setting to achieve design AoA at hover or cruise speed.
  3. Monitor lift distribution via hover-height or cruise speed consistency.

B. Propeller Pitch & Performance

Core Principles

  • Pitch Definition: Theoretical distance a propeller would move forward in one revolution in a solid medium.
  • Low Pitch: “Coarse” low-pitch blades allow high RPM at low forward speed—better for hover and climb.
  • High Pitch: “Fine” high-pitch blades bite more air per rev—better cruise efficiency but require more torque.

Method

  1. Select propeller pitch matching mission profile:
    • Hover-intensive → lower pitch for torque.
    • Cruise mission → higher pitch for speed.
  2. Conduct static-thrust test: measure thrust vs. motor current to confirm optimum pitch.

C. Thrust Creation

Core Principles

  • Momentum Theory: Propeller accelerates a mass of air rearward; thrust = mass flow × velocity change.
  • Blade Element Theory: Each blade section produces differential lift and drag; integrated along radius yields total thrust.

Method

  1. Review manufacturer thrust vs. RPM curves.
  2. Check motor/ESC combo delivers rated RPM under load.
  3. Ensure intake and exhaust flows are unobstructed to maintain mass flow.

Aerodynamics Checklist

  • [ ] Airfoil and rotor geometry inspected
  • [ ] Pitch selection aligns with mission profile
  • [ ] Static-thrust tests performed
  • [ ] Motor/RPM monitoring within expected range