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The AFResearchLab video AFRL Tech Museum Series: Propeller Development begins with the narrator standing in front of four propellers in a sequence transitioning from wood to metal, and what stands out to me at least is a very unusually-shaped two-blade propeller whose blades are extremely wide and thick near the base and taper to a point like a short, squat twisted candle flame.

There is a sign next to it that says something like (just guessing):

Olmstead High Efficiency Propeller

This unusual propeller was designed in 1918 by Olmstead Laboratories and tested at McCormick Field...

I assume that the designer is probably Aeronautical Engineer Charles M. Olmsted (1881-1948).

Here are several other photos of similar propellers:

Question: It's certainly beautiful to look at, but what aircraft was the Olmstead High Efficiency Propeller for? When and how was it used?


The "Olmstead High Efficiency Propeller" is the widest one, 2nd from the right:

screenshot from The AFResearchLab video "AFRL Tech Museum Series: Propeller Development" https://youtu.be/0Asa1iUFbMM The "Olmstead High Efficiency Propellor" is the widest one, 2nd from the right

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    $\begingroup$ It was probably tested on something like a Jenny and found to be not so efficient in actual application, and put away. It looks like an attempt at a blade that operates at a constant Reynolds number across its span. $\endgroup$
    – John K
    Commented Mar 6, 2022 at 13:55

3 Answers 3

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enter image description here
wikimedia.org

Propellers like tires can often be fitted to various vehicles. In this case, at least one (or more) Curtiss NC-4 (shown above), among other models:

The propeller design was eventually used for aircraft setting climb and world weight-carrying records and appeared on the Curtiss NC-4, on the first transatlantic flight [May 1919]. Olmsted deemed them his "secret weapon," and felt they would add even more interest to his aircraft when it was finally revealed to the public.

— Restoration: The 1912 Olmstead Pusher, smithsonianmag.com

Olmstead's own pusher plane with his signature propeller never took off (shown below), and then his lab went bankrupt too:

In 1912, work on the aircraft came to an abrupt halt when the Buffalo-Pitts Company went bankrupt. Although the aircraft was 90 percent finished, construction was never completed. Olmsted’s laboratory went bankrupt just two years later.

enter image description here

— Ibid.

Given that the lift equation has the speed squared, this propeller though may look nice, adds a lot of weight to an area that doesn't contribute to the majority of the thrust, so it's a design that focuses on only one aspect, like this famous comic.

If interested, this is the patent: Olmsted, Charles Morgan. "Aerial propeller." U.S. Patent No. 1,019,078. 5 Mar. 1912.

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  • $\begingroup$ Which leaves one burning question: Olmsted or Olmstead? The Smithsonian article uses Olmstead in the title but Olmsted in the body; the patent has Olmsted; the museum plaque has Olmstead… Wikipedia has him as Olmsted, with many references, so presumably correct; I guess the typo is so common just because -sted is a much less usual ending than -stead. $\endgroup$ Commented Mar 8, 2022 at 9:40
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    $\begingroup$ The pusher plane that "never took off" - do you mean that literally or figuratively? $\endgroup$ Commented Mar 8, 2022 at 15:24
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    $\begingroup$ @Toby: both! the following quotation explains what happened $\endgroup$
    – user14897
    Commented Mar 8, 2022 at 20:28
  • $\begingroup$ @Peter: the patent is probably the tiebreaker, good catch $\endgroup$
    – user14897
    Commented Mar 8, 2022 at 20:30
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This propeller shape is for general purpose use. It attempts to optimize the lift distribution across the prop to maximize efficiency by using chord along with other design parameters. Unfamiliarity with construction and installation combines with only a slight improvement in efficiency has limited its popularity. Modern takes on this shape were seen in Paul Lipps' winning Reno racer

enter image description here

and in the propulsor prop of the Carter Copter.

enter image description here

Propellers are often described as wings. Efficient wings have an elliptical (or close) lift distribution to minimize drag. This approach is extended to props and results in a wing like planform, but a prop flies very differently than a wing. Relative airspeed at a prop tip is twice that at midspan and four times that at quarterspan, where on a wing all the airflow is essentially the same speed.

Since lift is a function of speed squared the required coefficient of lift at the root is two orders of magnitude higher than at the tip. Shown is an example of a 72in dia prop with m0.8 at the tip.

enter image description here

The three main design parameters used to get the required CL are chord, camber and angle of attack (or twist). Most propellers designers can get the desired lift distribution using camber and twist, and forego the complications of using large changes in chord.

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If you zoom in on the video still, you can read it: "...was designed 1918 by Olmstead Laboratories ... for possible use on the Loening M-8 aircraft...".

screenshot from the AFResearchLab video "AFRL Tech Museum Series: Propeller Development" https://youtu.be/0Asa1iUFbMM

Thanks to @Walen for this better resolution: better screen shot of plaque

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    $\begingroup$ Full resolution image with clearly visible text at flickr.com/photos/156402454@N04/47673679042 confirms this. $\endgroup$
    – walen
    Commented Mar 7, 2022 at 9:05
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    $\begingroup$ This could have been a good 'before' and 'after' of that "zoom enhance"-feature they always use in the movies :) $\endgroup$
    – ROIMaison
    Commented Mar 10, 2022 at 12:54

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