Flight Training - May 2021 - 15

HOW IT WORKS

BY IAN J. TWOMBLY

FRANKENCOPTER
INTERMESHING ROTOR SYSTEMS

IT'S SO BONKERS YOU WOULD THINK THE INSPIRA-

tion came from a kid's drawing. Two giant rotors,
spinning inside each other's plane. An intermeshing rotor system, or synchropter, operates on the
assumption that two main rotors are better than one.
It turns out to generally be true.
One of a helicopter's biggest inherent drawbacks
is that power for lifting must be siphoned off to a tail
rotor to counteract torque. Designs with two main
counterrotating rotors can use more of the power for
lifting, making the most efficient use of engine power.
Kaman helicopters is the leader in designing and
manufacturing intermeshing rotor helicopters, and
former lead designer Anton Flettner invented the
concept. Their designs mount two rotors on individual masts, canted slightly outward, mere feet apart.
When turning, the rotors intermesh, sort of like the

eggbeater in your grandmother's utensil drawer. To keep the
blades from smashing into each other, manufacturers use a sync
shaft with gearing that connects the two masts to maintain the
separation and timing. If that fails, as it has a few times on the
similar configuration of the heavy-lift Chinook helicopters, it's
more or less a disaster.
The design has some other advantages beyond efficiency,
including better safety on the ground, and less maintenance and
weight because of the lack of tail rotor. For some, however, the
complexity of the intermeshing system and unique training and
maintenance requirements tip the balance away from the design.
How much do two main rotors help in terms of lifting capacity? With an empty weight of 5,145 pounds, and an external load
capacity of 6,000 pounds, the single-seat K-Max can haul its
entire weight in external cargo.
ian.twombly@aopa.org

TAIL ROTOR?

STEVE KARP

We don't need no stinkin' tail rotor
Getting rid of the tail rotor isn't a popular
design option, but there have been some unique
attempts over the years:
Coaxial rotors. Favored by Russian engineers,
coaxial rotor helicopters have two counterrotating
main rotors on one mast.
Tandem rotors. Probably the most recognizable design without a tail rotor, the Boeing
Chinook uses tandem rotors, or two main rotors
mounted in tandem along the longitudinal axis

of the fuselage. Like the Kaman designs, these
rotors usually intermesh, but not as dramatically.
Transverse rotors. Like a multiengine airplane
with the engines mounted straight up, a transverse rotor helicopter has two main rotor blades
mounted on the lateral axis that don't intermesh.
Notar. MD Helicopters is the purveyor of this
technology that ejects low-pressure air out of
a tail boom to create the same effect as a tail
rotor. -IJT

AOPA.ORG/FT  15


http://www.AOPA.ORG/FT

Flight Training - May 2021

Table of Contents for the Digital Edition of Flight Training - May 2021

Contents
Flight Training - May 2021 - Intro
Flight Training - May 2021 - Cover1
Flight Training - May 2021 - Cover2
Flight Training - May 2021 - Contents
Flight Training - May 2021 - 2
Flight Training - May 2021 - 3
Flight Training - May 2021 - 4
Flight Training - May 2021 - 5
Flight Training - May 2021 - 6
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Flight Training - May 2021 - Cover3
Flight Training - May 2021 - Cover4
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