Sikorsky S-64 Skycrane could lift move than 20,000 pounds (9,072
Helicopters have many
commercial uses. One of the most unusual
is serving as an aerial crane. In this capacity, helicopters carry loads
slung beneath their fuselages on cables. The first helicopters were used
in this capacity in the 1950s, although it was not until the 1960s that
they were heavily used for this purpose in the construction industry.
There have also been numerous proposals for very large, hybrid
helicopter-blimps to carry massive loads, but these have not been
Helicopter skycranes offer several
advantages over conventional cranes. First, they can reach areas that may
be hundreds of miles from the nearest roads or on inhospitable terrain.
For instance, they are often used to erect communications towers on top of
mountains or electrical transmission towers far from cities and towns.
Large skycranes are often used in the lumber business to lift large trees
out of terrain that is too rugged for a ground-based vehicle.
They can also reach locations that a
conventional crane cannot easily reach. For instance, skycranes are often
used to replace equipment such as transmission towers and large air
conditioning units atop tall buildings. While they are not practical for
the construction of the buildings themselves, skycranes are highly useful
when a single piece of equipment, such a large pump, needs to be brought
in or removed. In addition, some large factories have equipment mounted on
their roofs far from the edge. A conventional crane could not reach over
the building far enough to place or remove this equipment, but a skycrane
has no problem doing it.
Many different types of helicopters are
used as aerial cranes. The first aerial cranes were lightweight Bell Model
47s used in the early 1950s. The Model 47 could never carry more than a
few hundred pounds. In the 1960s, the Sikorsky S-58, known as the H-34 in
military service was used in this capacity, and many S-58s are still in
use today carrying medium-size loads.
The Bell UH-1
Huey and Jet Ranger are both commonly used to carry light and
medium loads to inaccessible areas—for instance, to carry telephone poles
along the side of a mountain. The Model 211 HueyTug was a commercial
flying crane version of the military UH-1C equipped with a new
transmission, longer main rotor, larger tailboom, strengthened fuselage,
stability augmentation system, and a 2,650-shaft-horsepower
(1,976-kilowatt) T55-L-7 turboshaft engine. It entered service in the
Larger helicopters were used for more
demanding tasks beginning in the 1970s. Commercial versions of the Boeing-Vertol
CH-46 and CH-47 helicopters have been used to carry heavier payloads, such
as logs for the lumber industry.
But the heaviest loads require the
Sikorsky S-64 Skycrane, which in military service was known as the CH-54
Tarhe. The Tarhe, which had its first flight in 1962, was used during the
Vietnam War to recover downed aircraft, transport artillery pieces, and
even drop large “blockbuster” bombs. The S-64 has two Pratt & Whitney
T73-P-1 turboshaft engines providing 4,500 shaft horsepower (3,356
kilowatts). The Tarhe could lift up to 20,000 pounds (9,072 kilograms) and
has six large rotor blades. No military Tarhe's are currently in service;
the U.S. Army uses the CH-47 Chinook for its heavy-lifting needs. Other
armies also use the Chinook for this purpose.
A later version of the S-64 was equipped
with two 4,800-shaft-horsepower (3,579-kilowatt) T73-P-700 engines.
Civilian versions were built, and a number of ex-military versions were
remanufactured for civil use for the Erickson
Air Crane Company, which first began operations in 1971. Evergreen
Helicopters, Inc. also flies the S-64. Civilian skycranes can lift up to
25,000 pounds (11,340 kilograms).
civilian version of the Sikorsky CH-54 Tarhe is the S-64 Skycrane.
Later versions were built by Erickson Air Crane Company.
The skycrane is exactly as its name
implies—an aerial crane, nothing more. It has a cockpit pod at the front
of a long boom equipped with landing gear mounted on outriggers. This
provides a large open area under which the carried load is connected to
Skycranes were used in 1972 when the
Chesapeake Bay Bridge connecting Maryland and the Eastern Shore was being
built to bring concrete and other supplies to the construction site. In
1993, an Erickson aerial Skycrane, normally used for hauling lumber in
Oregon, was used to remove the “Statue of Freedom” from the top of the
Capitol dome in Washington, D.C. The statue was placed on the ground while
it was being cleaned and restored before being gently returned to the top
of the dome, once again with a Skycrane.
During many lifting operations, pilots
often move their helicopters very little. They usually lift off, hover
while the load is attached, and immediately—but slowly—move over to where
they will lower the load. If anything goes wrong, such as an engine
warning light coming on, they are under orders to immediately drop their
load so as not to risk the aircraft. For this reason, the area underneath
the flight path has to be empty. If the Skycrane is lifting an air
conditioning unit to the middle of the roof of a large factory, for
instance, the area inside the factory under the flight path has to be
empty. A piece of machinery dropped from the helicopter would likely crash
straight through the roof and kill anyone underneath. Many of these
operations are also conducted at such low altitude that a total engine
failure would be fatal.
Several companies have proposed merging
blimps with helicopters, usually by attaching rotors to outriggers mounted
below and to either side of a blimp. In this way, an extremely large load
could theoretically be carried, with the rotors providing additional lift
to the blimp. The purpose of these aircraft is usually to lift large loads
of logs for the lumber industry, although other transport missions have
also been proposed. An aircraft called the Heli-Stat was built in the
1980s to attempt this mission. It used the fuselage and rotors of four old
Sikorsky H-34 helicopters. But the Heli-Stat crashed. Other proposals for
such aircraft have been proposed but never progressed very far.