The United States Army procured 713,717 aircraft propellers from 1940 through 1945 propellers. The graph below only includes complex pitch controllable blades which were difficult to manufacture. It excludes those seen on puddle jumpers or manufactured from expensive steel or fixed-pitch blades fitted to some trainers. These complex propellers were part of the equation driving improved performance. The US aircraft manufacturers were driving improved performance across the board via engines, aerodynamics, as well as propellers. A small performance gain by itself did not amount to much but when combined with multiple gains across the aircraft system performance leapt.
Table of Contents
Propeller design began early in the process. The propeller was part of an overall system where changes elsewhere could affect the propeller’s performance. Design considerations included:
- Type of plane. Bomber, fighter, and cargo all had different characteristics. Fighters were concerned with speed versus a cargo plane’s need for endurance and fuel conservation.
- Plane model. With each aircraft iteration weight and fuselage changes could occur requiring potential propeller adaptations.
- Engine: manufacturer, number of engines used, propeller gear ratios, engine ratings at various altitudes from sea level to planned operating altitudes, and shaft size.
- Planned airspeeds.
- Maximum allowable diameter.
- Propeller type – pusher or puller.
- Performance parameters and priority for the parameters: take off, climb, cruise, dive, or some combination.
The 1920s and 1930s saw changes in propeller design utilizing blade pitch control. Take offs required a greater pitch angle generating more power than the lesser angle at cruise when conserving fuel was paramount. The on-ground analogy of pitch control is shifting gears in a car. Initially these designs utilized mechanical systems requiring great exertions by pilots to overcome the centrifugal forces of the blades in motion.
In 1929 a two-position hydraulic pitch control system was introduced allowing easier pitch change. An additional feature of these variable pitch blades allowed pilots to feather a blade on a disabled plane reducing drag. This saved fuel and allowed better aircraft control. Propeller design continued to evolve and in 1935 constant speed propellers were introduced. Use of these propellers allowed engines to perform at a constant speed which also was a fuel saver.
In fact, propeller performance was deemed so important that Frank W. Caldwell of Hamilton Standard was awarded the 1933 Collier Trophy for the hydraulically controllable propeller. The Robert J. Collier Trophy is an annual aviation award administered by the U.S. National Aeronautic Association, presented to those who have made “the greatest achievement in aeronautics or astronautics in America.
US Aircraft Propeller Production: 1940-45 Data
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Abstracted from Table PR-17, Crawford and Cook, Statistics: Procurement, p. 79. The figures are for controllable pitch types only. Source: Holley , Irving Brinton, Jr. “United States Army In World War II Special Studies Buying Aircraft: Materiel Procurement For The Army Air Forces.” 1964, Page 549, Center of Military History United States Army, Library of Congress Catalog Card Number: 64-60000, https://history.army.mil/html/books/011/11-2/index.html, Data accessed on July 12, 2022
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