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Propeller Design Workshop. Presented by David J. Gall Gall Aerospace David@Gall.com www.PropellerDesignWorkshop.com. Theory and design of practical propellers, Part 3. Practical Prop Design. Propeller Design Workshop. Practical Propeller Design. Introduction.
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Propeller Design Workshop Presented by David J. Gall Gall Aerospace David@Gall.com www.PropellerDesignWorkshop.com
Theory and design of practical propellers, Part 3. Practical Prop Design Propeller Design Workshop 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??? Practical Propeller Design
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 Practical Propeller Design
Introduction 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 Practical Propeller Design Practical Propeller Design
1. Physical Constraints • Diameter • Number of Blades • Hub Thickness • Thickness of the Blank • Machine Capacity Practical Propeller Design
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 Practical Propeller Design
2. Reynolds and Mach Numbers Practical Propeller Design
2. Reynolds and Mach Numbers Practical Propeller Design
2. Reynolds and Mach Numbers Practical Propeller Design
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 Practical 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 Practical Propeller Design
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 Practical Propeller Design
6. Optimum Propellers Practical Propeller Design
7. Airfoil Choices • The Traditional Airfoil Choices • Clark ‘Y’ • RAF 6 • NACA “One” series • NACA “Six” series • Eppler • Others? Practical Propeller Design
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 Practical Propeller Design
7. Airfoil Choices Practical Propeller Design
7. Airfoil Choices Practical Propeller Design
7. Airfoil Choices Practical Propeller Design
7. Airfoil Choices Practical Propeller Design
7. Airfoil Choices Practical Propeller Design
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 Practical Propeller Design
8. How to Make a Prop(er) Hub Practical Propeller Design
8. How to Make a Prop(er) Hub Practical Propeller Design
8. How to Make a Prop(er) Hub Practical Propeller Design
8. How to Make a Prop(er) Hub Practical Propeller Design
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…) Practical Propeller Design
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) Practical Propeller Design
10. Adjustable Pitch/Const. Speed • Discussion Practical Propeller Design
11. Structural Requirements • ANC-9 Practical Propeller Design
11. Structural Requirements Practical Propeller Design
11. Structural Requirements Practical Propeller Design
11. Structural Requirements Practical Propeller Design
11. Structural Requirements Practical Propeller Design
11. Structural Requirements Practical Propeller Design
12. By Request • Airfoils • Sweep • Twist • Noise • Resonance • Materials • Contra-Rotating (Dual Rotation) • Shrouded • Ducted Practical Propeller Design
Propeller Design Workshop David J. Gall Gall Aerospace David@Gall.com www.PropellerDesignWorkshop.com
