Aerospace Engines A to Z
Aerospace Engines A to Z

Updated: 08-Jan-2020

Barrel type engine displayed at the Smithsonian Museum. It has 18 cylinders in two groups of 9 horizontally opposed cylinders.

-This was the 4th prototype. Almen was located in Seattle, Washington.

-This engine model was the A4 and dates back to 1920. The small frontal area together with its 425 hp was one of the advantages of this system.

-Below we show another illustration from 1921 with the engine seen from behind. It is said that a gun could be installed inside the motor shaft.

Almen, 1920 y 1921
Almen, 1920 y 1921 Fig.2
"Almen, 1920 y 1921"

-You can find more information in the US National Archives, "Sarah. B. Clark" with number 3105/452.8.

-A new picture of the Almen barrel engine as exhibited at the NASM.

-These engines were designed between 1921 and 1925 by J.O. Almen and developed in collaboration with the US Army Air Service.

-It seems that there were several models. The model shown here is the A-2.

-The  A-3 and A-3a models had constructive improvements.

Almen, model A
"Almen, model A"

Almen diagram
"Almen diagram"

-In this publication there is enough information on this barrel engine but there are still appearing new illustrations such as the patent applied for by John O. Almen.

-Here in the simplest form, liquid-cooled, normal swash plate, it looks like some kind of a "spider".

Patent engine diagram
"Patent engine diagram"

-Engines that were implemented had a double swash plate and double-piston cylinders. "Wabbler Kinematics"

-But in a great imagination exercise, Almen designed an engine with a big amount of cylinders, without doubt aiming to obtain high powers.

A powerful imaginative Almen mounting
"A powerful imaginative Almen mounting"

-We received more information about this characteristic barrel engine, models A-1 and A-4.

-Unlike other engines of this type, it has a central inclined disk and therefore it does not use the common combustion chamber for every two cylinders, that are doing other engines of this type.

-Schematically it can be represented as follows:

Cinemática Wabbler
"Wabbler Kinematics"

-Implemented, in the A-1 it was defined as follows.

Almen A-1 schematic diagram
"Almen A-1 schematic diagram"

-More information about the evolution of Almen models are described in the main text.

-The illustrations in this extension come from the "Aircraft Engine Historical Society", from an article by its President Kimble D. McCutcheon.

-To compare the differences between the A1 and the A-4 in 1924, we offer a cutaway diagram of the latter engine.

A-4 cutaway diagram
"A-4 cutaway diagram"

-And a photograph of the full outside.

The Almen A-4
"The Almen A-4"

From Appendix 10: Photos from the German "Flugsport" magazine from before WWII, showing the revolver engine assembly, and without the cover next to the oscillating plate.

Detalle del motor sin cubierta
“Uncovered Almen engine details” (PiP-Flu)

Engines of ALMEN

Model: A-1

Arquitecture: 18-cylinder Barrel
Cooling:
Total Displacement:
Bore / Stroke:
Power: @ rpm
Weight:

Other details:
Model: A-2

Arquitecture: 18-cylinder Barrel
Cooling:
Total Displacement:
Bore / Stroke:
Power: @ rpm
Weight:

Other details:
Model: A-3, A-3a

Arquitecture: 18-cylinder Barrel
Cooling:
Total Displacement:
Bore / Stroke:
Power: @ rpm
Weight:

Other details:
Model: A-4

Arquitecture: 18-cylinder Barrel
Cooling: Liquid
Total Displacement:
Bore / Stroke:
Power: 450 @ rpm
Weight:

Other details:

The A-4 dates back to 1920. The small frontal area together with its 425 hp was one of the advantages of this system.

Almen A-4

"Almen A-4"