1. Propeller Design Workshop Presented by David J. Gall Gall Aerospace www.PropellerDesignWorkshop.com

2. PROPELLER DESIGN WORKSHOP Theory and design of practical propellers: Introduction Introduction

3. Motivation My objective is to equip my airplane with the “best” prop Early on, I realized that the experts were in disagreement Thus, my personal quest is to understand propeller design well enough to have an intelligent conversation with the experts Uh-oh, now I think I’m an “expert” Introduction

4. Evidence One of the first things that convinced me the experts were in disagreement was when I used Fred Weick’s (EAA #7882) December, 1960 EAA Sport Aviation article, “Design and Build Your Own Propeller,” based on Weick’s 1925 N.A.C.A. Technical Note 212, to help a friend choose a prop for his new design Introduction

5. Evidence Almost all of the propeller manufacturers recommended a 66” prop, but TN-212 indicated a 56” diameter would be best The 66” prop was used for the initial test flight, but the airplane was not happy! We cut the tips off to make it a 60” prop, then a 58” prop, and finally a 56” prop (54” pitch) Thank goodness it was ground-adjustable Introduction

6. It flew a lot faster after we cut and repitched Yeah, it was fun to fly, too! (Cruise 115 mph on 40 hp) Evidence Introduction

7. Evidence Further evidence was found in NASA Contractor Report 165938 “On the Design and Test of a Low Noise Propeller” by George Succi which reported that MIT professor E. E. Larrabee’s method was used to design a more efficient propeller for a C182, then the efficiency was “given back” in exchange for reduced noise from a subsequent prop, also designed using Larrabee’s method. Introduction

8. Evidence The desired result achieved was a quieter prop that gave the same performance as the original prop. Of particular note was that the efficiency increase “given back” in the interest of noise reduction was on the order of six percent or more. Hey, I could use that six percent to go faster or to save gas…! Introduction

9. Evidence I asked myself: “Where can I learn how to design props that are six percent more efficient?” Whatever “Larrabee’s method” was, I had to have it! (It turns out to be a very simple method, originally coded in the 1970s for a pocket calculator) Introduction

10. Premise Building the “best” prop for my airplane is no more difficult than building an “ordinary” propeller or a propeller designed using any of the “usual” methods However, I’ve come to learn that designing that “best” prop is quite a different matter entirely! Daunting, but not insurmountable Introduction

11. Overview There are good tools and there are “iffy” tools and I want to know the difference First, define what is meant by “best” prop Next, survey the existing tools (design methods), if necessary! Might be far simpler and easier to buy existing or order from established custom maker Might be good to know what design methods they use…. (hint: usually includes the word “proprietary”) So, I’ve ended up designing my own design tools Introduction

12. Status Report Welcome to my “Book Report” Still in amateur “hobby” status (“Amateur” means its a labor-of-love, not that its less-than-professional) It threatens to become a “Business” First propeller should fly late this year (RV-6) No, the promised spreadsheet is not ready  (but you may see parts of it in action here) It was supposed to be about designing airplanes! Lesson: The creation of “intellectual property” is more involved than it at first appears Introduction

13. Thanks Thank you, EAA! The camaraderie and spirit of community fostered by and within the Experimental Aircraft Association has been the catalyst and inspiration for this project The right to participate in such endeavors is truly a privilege, and the open exchange of information and ideas is profound This presentation is my little way of “giving back” Introduction