Propeller Design Workshop

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Propeller Design Workshop

• Presented by
• David J. Gall
• Gall Aerospace
• David_at_Gall.com
• www.PropellerDesignWorkshop.com

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Propeller Design Workshop

• Theory and design of practical propellers, Part
  3. Practical Prop Design

Practical Propeller Design
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Introduction

• H. Dietsius, N.A.C.A. TN-127 (1923)
• The Air Propeller, Its Strength and Correct
  Shape, (Translated)
• F. Weick, N.A.C.A. TN-238 (1926)
• A Simple Method for Determining the Strength of
  Propellers, fourth in a series TN-235 thru
  TN-238
• ANC-9 (1956)
• Available Where???

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Introduction

• These are the ONLY References Ive Found
• None of them account for the in-plane forces
  caused by modern high-compression internal
  combustion engines

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Introduction
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Practical Propeller Design

• Outline Theory and design of practical
  propellers, Part 3.
• Reality check Those darn physical constraints
• Reynolds' number and Mach number
• What about those tips?
• From minimum induced loss to maximum efficiency
  The effect of viscosity on all those theories
• Fuselage/nacelle blockage (a.k.a. "Source-sink
  slowdown")
• Optimum Propellers
• Airfoil choices
• How to make a proper hub
• Proper design of pusher props
• Ground and in-flight adjustable pitch and
  constant speed props
• Structural requirements
• By Request

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1. Physical Constraints

• Diameter
• Number of Blades
• Hub Thickness
• Thickness of the Blank
• Machine Capacity

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2. Reynolds and Mach Numbers

• Subsonic Propellers
• Use Rules-of-Thumb or
• Calculate Your Critical Mach Number then
• Adjust Diameter to Keep Tip Speeds Below MCR
• Transonic Propellers
• See NASA for Un-Ducted Fans, etc.
• Supersonic Propellers
• Yes, NASA went there, too

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2. Reynolds and Mach Numbers
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2. Reynolds and Mach Numbers
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2. Reynolds and Mach Numbers
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3. What About Those Tips?

• What do you have after you cut off the tip?
• Winglets
• Hoerner Tips
• Curving Up
• Curving Down
• Elliptical Tips
• Round Tips
• Sheared Wingtip

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4. Viscosity

• Theodorsen (and all prior) adds the viscous
  effects after the fact
• Thats OK, especially with round blade shanks
• The coefficient of drag is constant at any RPM
• The effect of viscosity is minimal so long as the
  coefficient of drag isnt too high
• (Ohh, those round blade shanks are soooo bad!)
• However, they are in the place of least harm

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5. Fuselage/Nacelle Blockage

• Larrabee et. al De-Pitch after the fact to
  accommodate the reduced inflow velocity
• This loses part of the relative wind thats used
  in the algorithm
• So, it deviates from the Goldstein distribution

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6. Optimum Propellers
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7. Airfoil Choices

• The Traditional Airfoil Choices
• Clark Y
• RAF 6
• NACA One series
• NACA Six series
• Eppler
• Others?

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7. Airfoil Choices

• Can You Manufacture It?
• Design to What Coefficient of Lift?
• No Sharp Leading Edges
• Watch Out for Thin Trailing Edges
• Try to Stay Within a Family
• Ease of Thickness Scaling
• Ease of Performance Prediction (Modeling)
• Ease of Manufacture

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7. Airfoil Choices
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7. Airfoil Choices
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7. Airfoil Choices
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7. Airfoil Choices
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7. Airfoil Choices
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8. How to Make a Prop(er) Hub

• Must Carry ALL Loads
• Must Mate Mechanically to Engine
• Prop Flange and/or Extension
• Must Deliver Engine Power to Propeller
• See Sport Aviation archives

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8. How to Make a Prop(er) Hub
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8. How to Make a Prop(er) Hub
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8. How to Make a Prop(er) Hub
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8. How to Make a Prop(er) Hub
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8. How to Make a Prop(er) Hub

• Sensenich Website Wood Propellers
  Installation, Operation, Maintenance
• Drive Lugs DO NOT Drive the Prop
• Static Friction Drives the Prop
• Static Friction Must be Greater Than the Torque
  Forces Developed in Power Pulses
• PLUS A LARGE MARGIN for Prop Strikes from Lost
  Exhaust Pipes, etc. (Silver Bullet ppt)

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9. Design of Pusher Propellers

• Hub Goes on Backwards
• Center Bore on Front Face
• Drive Lug Bores on Front Face
• Aerodynamics Much More Difficult
• NO, I dont want to do a partially-ducted
  channel-wing contra-rotating asymmetrical pusher
  propeller with winglets
• (I might consider it if it were symmetrical) ?

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10. Adjustable Pitch/Const. Speed

• Discussion

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11. Structural Requirements

• ANC-9

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11. Structural Requirements
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11. Structural Requirements
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11. Structural Requirements
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11. Structural Requirements
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11. Structural Requirements
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12. By Request

• Airfoils
• Sweep
• Twist
• Noise
• Resonance
• Materials
• Contra-Rotating (Dual Rotation)
• Shrouded
• Ducted

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Propeller Design Workshop

• David J. Gall
• Gall Aerospace
• David_at_Gall.com
• www.PropellerDesignWorkshop.com