Propeller Design Workshop

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Propeller Design Workshop

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

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Propeller Design Workshop

• Theory and design of practical propellers
  Introduction

Introduction
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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 Im an expert

Introduction
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Evidence

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

Introduction
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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
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Evidence

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

Introduction
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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. Larrabees 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 Larrabees method.

Introduction
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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
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Evidence

• I asked myself Where can I learn how to design
  props that are six percent more efficient?
• Whatever Larrabees 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
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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, Ive come to learn that designing that
  best prop is quite a different matter entirely!
• Daunting, but not insurmountable

Introduction
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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, Ive ended up designing my own design tools

Introduction
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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
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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