An elbow engine is a

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...

-based

steam engine A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder. This pushing force can be trans ...

typically fed by

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...

compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...

to drive a flywheel and/or mechanical load. It is based on a mechanism known as a

Hobson's joint A Hobson's joint or Hobson's coupling is a type of right-angle constant-velocity joint; rods bent 90° are able to transmit torque around a corner because they are all free to turn in their mounting holes in both legs of the coupling. Hobson's joi ...

. Although not commonly used today for practical purposes, it is still built by hobbyists for its rarity and unconventionality.

Principle of operation

Elbow engines have two rotating, circular, cylinder blocks. Each block contains a ring of parallel cylinders and can itself rotate on a central axis, similar to a revolver cylinder. The two blocks are placed at 90° to each other. Each piston is L-shaped, and circular in cross section with one end fitted into each cylinder block. The two cylinder blocks rotate together, coupled only by the pistons. Engine output is taken from the rotation of one cylinder block. Pressure is supplied to each cylinder by means of a fixed plate forming a plain

thrust bearing A thrust bearing is a particular type of rotary bearing. Like other bearings they permanently rotate between parts, but they are designed to support a predominantly axial load. Thrust bearings come in several varieties. *''Thrust ball bearing ...

with the back of the cylinder block. This has two openings in it which supply and exhaust steam to and from the cylinder; as the cylinder block rotates it opens and closes communication with each pipe. This method of valveless steam admission is also used on many basic

oscillating cylinder An oscillating cylinder steam engine (also known as a wobbler in the US) is a simple steam-engine design (proposed by William Murdoch at the end of 18th century) that requires no valve gear. Instead the cylinder rocks, or oscillates, as the cra ...

engines. This arrangement results in a compact engine with a low part count, at the expense of including a large frictional surface.

Problems

Despite their apparent simplicity, elbow engines can be difficult to troubleshoot. They are also known to splatter oil when operating.

References

* Jeremy Harris, Willard Slay.
You Can Make This Incredible Elbow Engine
''Popular Mechanics'' July 1965 p.166

External links

Video of (6-cylinder) elbow engine in operation

3D simulation of elbow engine construction and operation
Steam engines by layout