Experienced SB-1 shortly after rollout
Boeing and Sikorsky, participating in the Pentagon’s Future Vertical Lift (FVL) and Future Long Range Assault Aircraft (FLRAA) programs, announce new successes in their joint development, the SB-1 Defiant helicopter. During a recent test flight, the machine again improved its speed record and showed compliance with the main requirement of promising programs. At the same time, the tests are not over yet, and new successes and achievements are expected in the future.
Faster than its predecessor
The next flight with the achievement of increased speed took place on June 9 at the West Palm Beach airfield (Florida). In the cockpit of the experienced SB-1 were Sikorsky test pilot Bill Fell and Boeing pilot Ed Hendersheid. The main task of the flight was acceleration in flight in a straight line with the specified operating modes of the systems, providing for some restrictions.
During acceleration, before measuring the speed, the power plant operated at half the power, which limited the thrust of the propellers. In these modes, the helicopter was able to reach a speed of 205 knots – 379.7 km / h. During acceleration and flight at such a speed, the pilots appreciated the operation of the control systems and the power plant.
It is noted that the flight on June 9 demonstrates the compliance of the SB-1 helicopter with one of the main requirements of the FVL program. The task of the project is to create a promising helicopter, superior in flight characteristics to the existing serial Sikorsky UH-60 Black Hawk. The maximum permissible speed of the Black Hawk Down is 360 km / h, or 194 knots. Thus, the new Defianf has already surpassed its predecessor in speed, and the maximum possible performance has not yet been reached.
Sequence of achievements
Tests of the experienced SB-1 are going at a fairly high rate. The overall complexity of the project and the emerging problems in general do not interfere with their implementation. The helicopter is tested in different modes and gradually shows an increase in flight performance. The achieved results look very interesting, and in the near future it is expected to reach the maximum indicators.
The prototype SB-1 Defiant began to be built in the mid-tenths, and its first flight was originally planned for 2017. In the future, the start of the tests was postponed several times due to the need to rework and improve the project. The finished car was rolled out of the workshop only in December 2018 and was soon transferred to ground tests.
Helicopter in “record” flight on June 9
In January 2019, the first taxis, runs and other tests were carried out on the ground. On March 21, the first flight took place, during which they checked the operation of the systems, maneuverable and limited speed characteristics. In the following months, SB-1 performed several new flights, incl. with a gradual increase in speed. In the summer, the car was sent for repairs due to a breakdown of the rotor hub. Flight tests resumed on September 24 and are still ongoing.
By now, the experienced helicopter, using half of the available power, has reached a speed of 205 knots. According to the development companies, the use of the full power of the engines and propellers should ensure a cruising speed of 250 knots (more than 460 km / h) and a maximum speed of at least 500 km / h. Achievement of such indicators is expected within the next few months, but the exact date can not yet be called.
In fact, the entire SB-1 Defiant project is built around the idea of increasing the maximum and cruising speeds of the project. To solve this problem, original ideas and designs are used, which were previously tested with the help of experienced Sikorsky X2 and S-97 helicopters.
The special propeller design makes a decisive contribution to flight performance. The SB-1 is equipped with two counter-rotating coaxial rotary rotors. The propeller design is optimized for high horizontal speeds. For this, blades of increased rigidity and a special shape with curved edges, as well as curved tips, are used. The original reinforced propeller hub is used, covered with a fairing.
In take-off and landing modes and at low flight speeds, the rotors are responsible for both the creation of lift and forward motion. However, a further increase in thrust to increase speed can be associated with negative phenomena on the blades. To avoid this, at high speeds, the helicopter generates lift with both the propellers and the tail stabilizer.
Acceleration to high speeds is carried out using a separate pusher propeller in the tail. All three screws of the machine are connected by a common transmission with several modes of operation, providing for the connection or disconnection of different units. All modes use two high power turboshaft engines.
In the experimental configuration, the SB-1 is equipped with Honeywell T55 engines with a take-off power of 4000 hp. Helicopters with a different power plant should go into serial production. In the interests of the FVL program, a new General Electric T901 engine with a capacity of over 5000 hp is being created, formerly known as the Future Affordable Turbine Engine (FATE).
Using T55 or T901 engines is estimated to provide a cruising speed of 250 knots. The introduction of advanced products will allow the flight range to be increased to 424 km, as required by the task for the FVL / FLRAA. In an experimental configuration, the Defiant helicopter has a shorter range. However, in both cases, the helicopter of the new scheme outperforms the army UH-60 in all main indicators.
A helicopter with high performance characteristics will be able to solve a wide range of tasks. Depending on its purpose and configuration, the crew can include up to four people. The closed cockpit provides for the installation of 12-14 seats for passengers or other equipment, weapons, etc.
It should be recalled that from the Sikorsky-Boeing SB-1 Defiant helicopter, not only high flight characteristics are required. This machine must bypass the competitor, get a contract of the armed forces and bring profit to its creators. Its rival in the FVL / FLRAA competition is the promising V-280 Valor tiltrotor developed by a group of companies led by Bell and Lockheed Martin.
Competitor SB-1: Bell-Lockheed Martin V-280 Valor
At the moment, the V-280 project is noticeably ahead of the SB-1. The first flight of this tiltrotor took place in December 2017, and just six months later, a horizontal speed of 190 knots (350 km / h) was obtained. In October 2018, a new personal best was set – 250 knots. Valor’s cruising speed is set at 280 knots (518 km / h), and this result was first achieved in January 2019. Trials are ongoing and new achievements are taking place. The maximum speed of the tiltrotor must exceed 500 km / h.
At the moment, two promising aircraft of the FVL and FLRAA programs show similar flight performance parameters, but there are significant structural and other differences. SB-1 and V-280 have certain advantages over each other, and there is no clear favorite yet.
According to current plans, flight design tests of the two aircraft will continue until 2022. After that, the customer will choose the most successful project for further development, which will last until the end of the decade. Serial production of new equipment will begin only in 2030. The deliveries of the winning FVL and FLRAA machines will allow starting the replacement of the outdated UH-60.
Thus, the companies participating in the project do not have too much time to demonstrate the capabilities of their developments. Therefore, we can expect that in the near future there will be new interesting news about certain achievements. But only in 2022 will it become clear whether the recent SB-1 flight was another step towards orders and series.