Sikorsky S-97 Raider

https://en.wikipedia.org/wiki/Sikorsky_S-97_Raider

The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter
based on the Advancing Blade Concept (ABC) with a coaxial rotor system under
development by Sikorsky Aircraft. Sikorsky planned to offer it for the United
States Army's Armed Aerial Scout program, along with other possible uses. The
S-97 made its maiden flight on 22 May 2015.

Background

Sikorsky's earliest attempt at a fast compound helicopter with stiff coaxial
rotors was the Sikorsky S-69 (XH-59A) flown in the 1970s. Its top speed was over
260 knots but its excessive fuel consumption, vibration and complexity requiring
the full-time attention of two pilots led to the program's cancellation. These
problems were largely solved on another attempt by the Sikorsky X2 technology
demonstrator in 2010. First proposed in response to a Request for Information
for the Armed Aerial Scout (AAS) program in March 2010, the S-97 was formally
launched on 20 October 2010. It was intended as a contender for a United States
Army's requirement to replace the Bell OH-58D Kiowa Warrior. Other military
roles are possible, the U.S. Special Operations Command having expressed
interest in the S-97 as a replacement for the MH-6 Little Bird, and the
possibility of adapting it for civilian applications also exists.

Design

The S-97 design includes variable speed rigid coaxial main rotors and a
variable-pitch pusher propeller, making the S-97 a compound helicopter. Like the
X2, it has fly-by-wire control and dynamic anti-vibration actuators to cancel
out shaking. The main rotors have hingeless hubs and stiff blades, to improve
low-speed handling and efficiency of hover. At high speeds, the close spacing of
the hubs reduces drag. The stiff blades allow each rotor to have low lift on the
retreating side of its rotor disk (reducing drag), whereas each rotor on a
conventional coaxial rotor with "floppy" blades needs nearly equal lift
distribution. The propeller relieves the rotor of propulsion, further reducing
drag.

Maneuverability is improved compared with earlier helicopters because of the
ability to tilt the coaxial rotors together or tilt each one differently, and
because of the variable pitch propulsor and active elevons. At low speed the
S-97 maneuvers by differential torque of the upper and lower rotor, at high
speed it uses rudders.

The S-97 will be capable of carrying up to six passengers, in addition to a
flight crew of two in a side-by-side cockpit. However, the production S-97 is
projected to be capable of flying with either one or two pilots, or
autonomously. Space for a targeting sensor has been reserved, however it will
not be installed in the prototype aircraft.

Based on the technology from the Sikorsky X2 demonstrator, the prototype S-97s
will be powered by a General Electric YT706 turboshaft (the same engine used on
the MH-60M Black Hawk). A more powerful engine, developed under the Improved
Turbine Engine Program, is expected to become available. Compared to the OH-58D
Kiowa, the S-97 has significantly increased performance goals, such as cruising
speeds upwards of 200 knots while carrying weapons, turning at three times the
force of gravity at 220kt, and a high hover efficiency (Figure of merit).
Sikorsky also aims for an operating cost of $1,400 per flight hour.

Role
Reconnaissance and attack compound helicopter

National origin
United States

Manufacturer
Sikorsky Aircraft

First flight
22 May 2015

Status
Under development

Number built
3

Program cost
US$200 million

Unit cost

US$15 million, projected

Developed from
Sikorsky X2

Developed into
Sikorsky Raider X

Operational history

The first flight of the S-97 occurred on 22 May 2015. It flew for 1 hour instead
of the planned 30 minutes, completing three takeoffs and landings; forward,
rearward and sideward. For this initial flight, the Raider was flown with its
triplex fly-by-wire flight control system in backup degraded mode so as to focus
on basic airworthiness in the low-speed regime. This begins a year-long flight
test program of about 100 flight-hours to expand the flight envelope to meet
Sikorsky's key targets of 220-knot cruise speed carrying weapons, hover at 6,000
feet on a 95F day and 3g maneuverability at speed. Toward the end of Phase 1
testing, software will be upgraded to Block 2, bringing in the propulsor and
articulating tail to increase speed and enable the full flight envelope. The
second prototype (P2) was displayed to the public in October 2015. After two
flight hours and a few months of testbench validation of the propulsion
drivetrain, P1 is scheduled for higher speed some time in 2016.

On 3 August 2017, an S-97 prototype suffered what Sikorsky described as a
hard-landing at their flight test facility in West Palm Beach, Florida; both
airline transport pilots received minor injuries. The NTSB factual report on the
incident stated that the helicopter lifted into a low hover and immediately
experienced excessive roll oscillations which lead to intermeshing of the
counter-rotating coaxial rotor system, and a hard landing. Damage to the
helicopter included collapsed landing gear, structural cabin damage, and dynamic
component damage, including rotor blade tip separation of all rotor blades.
Video of the accident sequence showed aircraft roll oscillations exceeding
60–degree angle of bank during the course of 5 seconds, during which the upper
and lower rotors collided at the 1 o'clock position.

On 25 June 2019, the S-97 returned to flight testing and reached a speed of 190
knots.

Specifications

General characteristics
Crew: 0-2 pilots
Capacity: 6 troops
Length: 35 ft (11 m)
Gross weight: 8,945 lb (4,057 kg)
Max takeoff weight: 11,000 lb (4,990 kg)
Powerplant: 1 × General Electric YT706 , 2,600 shp (1,900 kW)
Main rotor diameter: 1 (2 coaxial)× 34 ft (10 m)
Propellers: 6-bladed variable-pitch, clutchable pusher propeller, 7 ft (2.1 m)
diameter

Performance
Cruise speed: 250 mph (410 km/h, 220 kn) (with external weapons)
Never exceed speed: 280 mph (440 km/h, 240 kn)
Range: 350 mi (570 km, 310 nmi)
Endurance: 2hr40min
Service ceiling: 10,000 ft (3,000 m) at 95 °F (35 °C)

Armament

Guns: .50 cal gun w/500 rounds
Rockets: 7-shot rocket pod(s)




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