Counter-rotating propellers
Counter-rotating
propellers are sometimes used on twin-, and other multi-engine, propeller-driven aircraft. The propellers of
these wing-mounted engines turn in opposite directions from those on the other
wing. Generally, the propellers on both engines of most conventional twin-engined aircraft spin clockwise (as viewed from the
rear of the aircraft). Counter-rotating propellers generally spin clockwise on
the left engine, and counter-clockwise on the right. The advantage of
counter-rotating propellers is to balance out the torque effects of high-power piston engine as
well as gyroscopic precession effects (p-factor) during flight manoeuvres, eliminating the
problem of the critical
engine. These
are sometimes referred to as "handed" propellers since there are left
hand and right hand versions of each prop.
Counter-rotating
propellers,
also referred to as CRP, found on twin- and multi-engine propeller-driven aircraft, spin in directions opposite one another.
The propellers
on both engines of most conventional twin-engined aircraft
spin clockwise (as viewed from behind the engine). Counter-rotating propellers
generally spin clockwise on the left engine and counter-clockwise on the right.
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.
In designing
the Lockheed P-38
Lightning, the
decision was made to reverse the counter-rotation such that the "tops"
of the propeller arcs move outwards, away from each other. Tests on the initial
XP-38 prototype demonstrated greater accuracy in gunnery with the unusual
configuration. The counter-rotating powerplants of
the German World War II Junkers Ju 288 prototype series (as the Bomber B contract winning
design), the Gotha Go
244 light
transport, Henschel Hs
129 ground
attack aircraft, Heinkel He 177A heavy bomber and Messerschmitt Me 323 transport used the
same rotational "sense" as the production P-38 did – this has also
been done for the modern American Bell
Boeing V-22 Osprey tiltrotor
VTOL military aircraft design.
Drawbacks of
counter-rotating propellers come from the fact that, in order to reverse sense
of rotation of one propeller, a gearbox needs to be used or the engine
installation must be different. This may increase weight (gearbox), or
maintenance and spare parts costs for the engines and propellers, as different
spare parts need to be produced in lower numbers, compared to a conventional
installation.
Opposing-rotation aircraft propellers that share a common axis are known as contra-rotating propellers, rather than counter-rotating.
World War I Linke-Hofmann
R.I German heavy bomber (1917) with
counter-rotating propellers
Gotha Go 244 German WW
II light transport with counter-rotating propellers
He 177A Greif with
counter-rotating propellers
Single
engine, roller chain driven propellers
(one chain's path crossed to enable counter-rotation):
● The Wright Flyer — and nearly all
aircraft designed and built by the Wright
Company (1909–1916)
Twin-engine, one
engine per wing :
● Beechcraft 76 Duchess
● Bell Boeing V-22 Osprey tiltrotor
● Cessna T303 Crusader
● de Havilland Hornet
● Fokker G1 prototype
● Heinkel He 177A Greif (fourth
prototype onwards)
● Henschel Hs 129
● Gotha Go 244
● Junkers Ju 288
● Lockheed P-38 Lightning
● North American Rockwell OV-10 Bronco
● Piaggio P.180 Avanti
● Piper PA-31 Navajo (some variants)
● Piper PA-34 Seneca
● Piper PA-39 Twin Comanche C/R
● Piper PA-40 Arapaho
● Piper PA-44 Seminole
● Vought V-173 Flying Pancake
At least four
engines, two or more on each wing :
● Messerschmitt Me 323 Gigant transport
● Airbus A400M Atlas - first aircraft with
propellers in counter-rotating pairs on each wing
Four engines in
fuselage, with one propeller per side:
● Linke-Hofmann R.I
The following
German World War II aviation engines were designed as opposing-rotation pairs
for counter-rotation needs:
● BMW 801A and B, and G/H subtypes
● Daimler-Benz DB 604
● Daimler-Benz DB 606
● Daimler-Benz DB 610
● Junkers Jumo 222