propeller design workshop part iii.pps

Propeller Design Workshop

Presented byDavid J. Gall

Gall [email protected]

www.PropellerDesignWorkshop.com

mailto:[email protected]

http://www.propellerdesignworkshop.com/

PROPELLER DESIGN WORKSHOPTheory and design of practical propellers, Part 3. Practical Prop Design

Practical Propeller Design

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???


Introduction

• These are the ONLY References I’ve Found• None of them account for the in-plane forces

caused by modern high-compression internal combustion engines


Introduction


PRACTICAL PROPELLER DESIGN

Outline: Theory and design of practical propellers, Part 3.

1.Reality check: Those darn physical constraints 2.Reynolds' number and Mach number3.What about those tips?4.From minimum induced loss to maximum efficiency: The effect of viscosity on all those theories5.Fuselage/nacelle blockage (a.k.a. "Source-sink slowdown")6.Optimum Propellers7.Airfoil choices8.How to make a proper hub9.Proper design of pusher props10.Ground and in-flight adjustable pitch and constant speed props11.Structural requirements12.By Request


1. Physical Constraints

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


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


2. Reynolds and Mach Numbers


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” WingtipPractical Propeller Design

4. Viscosity

• Theodorsen (and all prior) adds the viscous effects after the fact

• That’s 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 isn’t too high…– (Ohh, those round blade shanks are soooo bad!)– However, they are in the place of least harm


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 that’s used in the algorithm

• So, it deviates from the Goldstein distribution


6. Optimum Propellers


7. Airfoil Choices

• The Traditional Airfoil Choices– Clark ‘Y’– RAF 6– NACA “One” series– NACA “Six” series– Eppler– Others?


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


7. Airfoil Choices


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




• 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…)

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 don’t want to do a partially-ducted channel-

wing contra-rotating asymmetrical pusher propeller with winglets

– (I might consider it if it were symmetrical)


10. Adjustable Pitch/Const. Speed

• Discussion


11. Structural Requirements

• ANC-9


11. Structural Requirements


12. By Request

• Airfoils• Sweep• Twist• Noise• Resonance• Materials• Contra-Rotating (Dual Rotation)• Shrouded• DuctedPractical Propeller Design

Propeller Design Workshop

David J. GallGall Aerospace

[email protected]

mailto:[email protected]

http://www.propellerdesignworkshop.com/

propeller design workshop part iii.pps

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