By the time the Korean War ended in 1953,
helicopters such as the Piasecki H-25 and the Sikorsky H-19 Chickasaw had become a staple
of the United States Air Force. But getting there wasn't achieved without its difficulties.
To overcome some of the operational challenges brought on by perilous mountains and unpredictable
weather, the Bureau of Aeronautics, Sikorsky Aircraft, Reaction Motors,
and the Marine Corps developed the Rocket On Rotor power plant.
The auxiliary power boost system, which could be activated with a switch installed in the cockpit,
employed rocket engines mounted on rotor blade tips.
If successful, this innovative device would render American
helicopters capable of performing maneuvers no other aircraft could.
Helicopters In Korea
Helicopters proved a game-changer during the Korean War.
Used primarily for medical evacuation, search and rescue missions, and critical resupply delivery,
they had become an essential battlefield tool for the United States Armed Forces by war's end.
According to a 1955 article published in the Redstone Rocket [QUOTE]:
"Just as fixed-winged aircraft earned its place in the Army unit during World War II,
helicopters earned their "wings" in Korea."
Despite the revolutionary achievement that changed the Armed Forces forever, getting
there wasn’t easy. The choppers showed constant operational limitations due to Korea's weather
conditions and harsh terrains in which take-off and landing space required a vertical flight.
High-altitude mountains proved to be a particular hindrance. The aircraft's gross
weight had to be significantly reduced, limiting the number of combat troops,
patients, or material that the helicopter could accommodate.
As the war came to an end, the US government recognized the need for improvements on its
helicopters. A more powerful engine would not solve the altitude problem,
as the aircraft would still fall off proportionately.
According to the engineers of the Bureau of Aeronautics and members of the Marine Corps,
what the choppers needed was a lightweight, efficient auxiliary power source that could
be used in case of an emergency with the simple turn of a switch.
The supplemental power plant was required to successfully operate at different altitudes.
The answer was a rocket-powered device.
ROR
To solve the helicopters’ operational issues, the Bureau of Aeronautics joined forces with Sikorsky
Aircraft, Reaction Motors, and the Marine Corps to develop the Rocket On Rotor system. Known as ROR,
the device involved placing a set of rockets on the tips of the helicopter's rotor blade.
90% unstabilized hydrogen peroxide fueled the device with a propellant tank mounted
on top of the rotor assembly. The fuel was supplied to each of the engines by
a centrifugal pumping method produced by rotating the helicopter’s rotor.
The combustible then entered the rocket engines at the blade's tips.
As the hydrogen peroxide came into contact with a metal catalyst inside each engine,
the substance decomposed into oxygen and steam, producing the necessary thrust.
The ROR power plant had a dry weight of 75 pounds
and could hold up to 300 pounds of fuel, enough for about 7 minutes of rocket-powered operation
regulated with an on-and-off switch located in the cockpit.
This short operation time would give the helicopter an extra power boost at take-off,
allowing for weightier loads, improved autorotation performance, an improved
rate of climb, and hover ceiling. The device could also assist in case the main power plant failed.
Testing
The ROR was first tested on Sikorsky H-19 Chickasaw helicopters on March 9, 1954.
The aircraft were fitted with the small 1-pound rocket motors in the rotor blades' tips,
adding 35 pounds of thrust to each.
To test the device's pilot adaptability, over 30 airmen tried their hand at the system.
According to the test pilots, the Rocket On Rotor power plant was efficient and practical.
The ROR proved to be an excellent auxiliary power system for helicopters operating high altitudes
and under all sorts of weather conditions. The additional power
also improved the aircraft’s safety by allowing to decrease the rate of descent.
After half a year of developmental testing, the Marines finally showcased the state-of-the-art
device to the public at the Naval Support Facility Anacostia Washington, D.C., in September.
A year later, a 21-minute video with footage of the rotor rocket was released
by Reaction Motors Incorporation. In the video, the company declared the device
could be adapted to any type of operating helicopter with minimal design changes.
But although the development tests were successful and provided several benefits
at the cost of a modest weight increase, the system was never used in any helicopter.
The reason is still unknown, and the ROR device faded into the void
of unfinished army designs of the mid-twentieth century.