PROPULSION

1
PROPULSION

• Final Design Report
• March 10, 2004

2
Propulsion -- Choices

• Electric Propulsion
• Electrothermal (Lack of thrust/altitude control)
• Electromagnetic (High power requirement)
• Electrostatic (For outer space missions)
• Air-Breathing
• Atmosphere Restrictions
• Propeller
• Further Investigation
• Chemical Propulsion
• Further Investigation

3
Propulsion

• Propellers
• Pros
• Controlled Flight
• Constant Flight Velocity
• More Reliable
• Longer Duration
• Ease of measurement
• Constant velocity constant height
• Cons
• Power Requirement

• Rockets
• Pros
• More Acceleration
• Higher Absolute Velocity
• Cons
• Stability
• Need more controls for height and measurements
• Possibility of explosion (low temperature
  behavior)
• Weight

4
Propulsion

• We chose propellers!!!

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Propulsion

• Propeller Design
• Number of blades 3
• Advantages
• Optimizing between efficiency, weight, and thrust
• Produces more thrust than a 2-blade propeller
• More efficient and lighter than a 4-blade
  propeller
• Position Pusher
• Advantages
• For low density flow, will not disturb the air
  prior to generating lift

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Propulsion- Calculations

• Drag Coefficient
• where CDP Parasite Drag
• CDI Induced Drag
• CDC Compressibility (neglected)

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Propulsion- Drag Calculations

• Assume minimum value of Re
• Use MACexp, the exposed main aerodynamic chord,
  to find wing dimensions CR root chord length,
  s taper ratio
• Product of wing platform ratio (s), exposed area
  of wing (wet)

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Propulsion- Drag Calculations

• From constants k and Cf (roughness based on Re),
• Induced Drag, CDI
• Total Drag

9
Propulsion

• Assuming a safety factor of 1.2
• Tcapable 3.77 N
• Tflight D 3.14 N for level flight
• Find V(l/Dmax) 130m/s
• Assume propeller efficiency 95
• Running power of engine 430 W
• Brake horsepower (max power of engine) 489.84 W
  0.675 hp

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Propulsion- Propeller Design

• Propeller Diameter
• Keep tip helical speed of propeller lt M0.85
• (velocity 195 m/s)
• Solving for n

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Propulsion- Propeller Design
n is approximately 20 rev/sec D 2.27 m Thrust
Coefficient Power Coefficient Advance
Ratio Propeller Efficiency
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Propulsion- Propeller Design

• Blade Design
• Spinner will be incorporated, to make up 10 of
  total diameter
• Want high aspect ratio
• Elliptical-shaped blade will give the best
  results
• Airfoil design
• Optimum airfoil thickness 15-18 near the root
• Thins to 10 at the tip
• Propeller tip
• Rounded to increase efficiency

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Propulsion- Propeller Design

• Propeller Pitch

• Fixed pitch
• Climb Propeller (lower pitch)
• Cruise Propeller (higher pitch)

• Variable/controllable pitch
• Pilot controls pitch setting
• Not feasible

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Propulsion- Motor Specifications

• Motor Specs
• Power requirement 0.67 hp
• 1200 rpm
• Must fit in cylinder casing of 0.1 m diameter
  (structure limitations)
• Lightweight

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Propulsion

• Flight Duration 1.43 hours
• Power 430 W
• Propulsion System Total Weight 7 kg
• Battery weight 4.2 kg
• Motor weight 1.8 kg
• Shaft Propeller weight 1 kg
• Distance 670 km
• Average Velocity 130 m/s
• Carbon Fiber Material

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Propulsion

• We will not be determining the following
• Concerning propeller blade
• Shape
• Twist
• Exact pitch
• Airfoil selection

Propellers are essentially a rotating wing, with
varying Reynolds number along the length of the
blade this exceeds our expertise and time
available.