The craft had a non-standard 9-cylinder engine, and two counter-rotating propellers.

C.444 - first version with counter-rotating propellers, adopted on all later versions (17 built)

Counter-rotating propellers generally spin clockwise on the left engine, and counter-clockwise on the right.

Counter-rotating propellers are sometimes used on twin-, and other multi-engine, propeller-driven aircraft.

The S.55 had two inline counter-rotating propellers, achieved by mounting the twin engines back to back.

The following aircraft have counter-rotating propellers:

The 4-cylinder Miller fan engine drove two wooden two-blade counter-rotating propellers by means of two roller chains.

The engines used by Ark Angel are electric motors driving counter-rotating propellers, mounted in pods below the hull.

According to NASA, counter-rotating propellers are up to 10 percent more efficient than single propeller designs.

The advantage of counter-rotating propellers is to balance out the effects of torque and p-factor, eliminating the problem of the critical engine.

Counter-rotating propellers should not be confused with contra-rotating propellers (propellers that share a common axis).

Bossi concluded, erroneously, that a successful human-powered aircraft would therefore require two counter-rotating propellers to cancel out the effects of torque.

A large duct at the fuselage's rear contains two counter-rotating propellers, which would be driven by two large electric motors.

Another issue with the P-38 arose from its unique design feature of outwardly rotating (at the "tops" of the propeller arcs) counter-rotating propellers.

The advantage of such designs is that counter-rotating propellers balance the effects of torque and P-factor, meaning such aircraft do not have a critical engine.

The aircraft uses four brushless electric motors with counter-rotating propellers, which makes the aircraft one of the world's smallest four-engine aircraft.

Counter-rotating propellers, also referred to as CRP, found on twin- and multi-engine propeller-driven aircraft, spin in directions opposite one another.

A variant with counter-rotating propellers was designated the Piper PA-39 Twin Comanche C/R.

His test rig, with two wheels and handlebars, resembled a wheelbarrow with an engine mounted in it, with a tall vertical shaft driving two counter-rotating propellers.

Contra-rotating propellers should not be confused with counter-rotating propellers, a term which describes non-coaxial propellers on separate shafts; one turning clockwise and the other counter-clockwise.

The National Physical Laboratory helped design and test her twin counter-rotating propellers and underwater fittings, while Decca Radar oversaw trials of her survey systems.

The history of stern drive power begins in the First World War with the production of the MAS of Isotta-Fraschini, with two counter-rotating propellers.

The important difference is that, with counter-rotating propellers, one propeller cancels out the side force effects of the other when both are turning at the same RPMs, either ahead or astern.

Unique to the propulsion system of this airplane are the counter-rotating propellers on both wings; both propellers on each wing rotate in opposite direction to each other, down in-between.