Tiltrotors: an unparalleled capability
Aug 06, 2023
Dr Joetey Attariwala gets first-hand experience of flight in a tiltrotor and discovers what makes them a superlative alternative to helicopter or fixed-wing aircraft for special missions
Tiltrotor aircraft are amazing platforms that combine the vertical take-off and landing (VTOL) capabilities of a helicopter with the speed, range, service ceiling and comfort of a turboprop airplane. Simply stated, tiltrotor technology is transformational technology that provides operators an incredible versatility in virtually all operating regimes, austere or otherwise.
Today there are two key players who are marketing tiltrotor platforms – Bell and Leonardo; and there are a number of startups who are working on their own tiltrotor technology; however, the majority of these efforts are still at the concept phase.
One of the key selling features of tiltrotor aircraft is their independence from traditional runways. This capability unlocks significant potential for tiltrotor aircraft to be used in a number of military and emergency medical services (EMS) roles. These aircraft also have the ability to redefine numerous missions like offshore, VIP/corporate transport, search and rescue (SAR), and para-public operations for private, commercial and government users.
One can easily conceptualize the benefits of tiltrotor aircraft, however, the proof is in the pudding: having flown in a tiltrotor – a US Marine Corps MV-22 Osprey – I can speak first-hand about the incredible capability they deliver. The flight that I took launched out of the Farnborough aerodrome, and what was immediately evident to me was the versatility that tiltrotors provide and their impressive performance.
With a simple toggle of a pilot’s thumb switch, a tiltrotor transitions between flight modes. In the case of the V-22, toggle forward and the proprotors translate to deliver speed, which is nothing like the experience of a helicopter or a fixed wing aircraft because, true to tiltrotor capability, it is both. Once in ‘airplane mode’ the tiltrotor gains efficiency as its stubby wings provide lift, and the engines propel the aircraft to fixed-wing speeds.
Why then, are tiltrotors not everywhere yet? The simple answer has been cost, and original equipment manufacturers (OEMs) are acutely aware that this needs to change if tiltrotors are to succeed.
“You can’t singularly compare the cost or expense of a tiltrotor to a helicopter, or a tiltrotor to a fixed wing,” said Kurt Fuller, Vice President and Program Director for the V-22 at Bell. “You really have to look at the mission capability comparison, and then look at your expenses.”
The V-22 Osprey is the world’s first production tiltrotor aircraft, and is manufactured in a 50/50 joint venture between Bell Textron and Boeing. With over 700,000 flight hours across the fleet, the V-22 has proven itself to be an extremely versatile platform that can self-deploy anywhere in the world utilizing internal fuel and aerial refueling capabilities.
The V-22 first entered service with the US Marine Corps, who use their MV-22 variant as an assault transport for troops, equipment and supplies; these aircraft are optimized for operating from ships or expeditionary airfields ashore.
The US Air Force Special Operations Command was the second operator of the Osprey; its CV-22 variant is used for long-range infiltration, exfiltration and resupply of non-conventional special operation forces. The CV-22 carries more internal fuel and is a more sensor laden aircraft with the addition of a multi-mode radar and an integrated, active electronic warfare suite that facilitates its special operations role.
The newest operators of the Osprey are the US Navy, whose CMV-22 variant is used in the carrier onboard delivery (COD) mission; and Japan, who is the first international operator of the Osprey – its aircraft are largely aligned with the Marine Corps variant.
The V-22 has a two-seat cockpit and an open passenger and cargo cabin with a rear-loading ramp for easy access. The aircraft is fitted with triple redundant fly-by-wire flight controls, a triple-redundant hydraulic system, and triple-redundant hydraulic motors that drive the actuators that tilt the engine nacelles.
© Joetey Attariwala
Inside each nacelle is a Rolls-Royce AE 1107C engine, which produces 6,150shp. These engines share many parts and functions with the AE 2100 series engines found on the Lockheed-Martin C-130J. This common core approach provides the V-22 with performance and affordability benefits from common spare parts supply, shared lessons-learned, training, maintenance procedures, and tools. Both engines are connected to each other via an interconnect driveshaft. Under normal twin engine operations, only a small amount of power is transferred through the interconnect driveshaft to drive components on the mid-wing gearbox. If one engine becomes inoperable, power is distributed from the remaining engine to both proprotors through the interconnect driveshaft.
The US Air Force is currently executing a nacelle improvement program to increase readiness, reliability and maintainability of the CV-22. Fuller described the initiative: “As we got to about 400,000 flight hours of tiltrotor operation, it gave us a wealth of data to go back and look at what we can do better relative to maintainability, and that really focused on the V-22 nacelles. We went in and redesigned a lot of the wiring architecture and construction, as well as some structural improvements. We’re currently in that upgrade effort with the Air Force – we’ve done about 20 per cent of their fleet so far where we bring those aircraft back into Amarillo, pull the nacelles off, upgrade them and then put brand new nacelles on the aircraft and get those back to the user.”
Numerous cabin and cargo systems have been designed for the V-22 and are available to satisfy a range of mission tasks. The cabin and rear ramp are capable of accepting cargo pallets or containers, and the usable cabin volume of 739 cubic feet is designed to carry up to 20,000 pounds internally. The cabin floor is fitted with flip rollers and a winch for handling palletized cargo. The standard troop transport role carries crashworthy seating in the cabin for one flight crewmember and 24 troops with full equipment – offloading troops can be accomplished within 15 seconds after the opening exits. Provision for aeromedical evacuation of up to 12 litters are in the aircraft.
One of the many areas where the Osprey shines is in SAR and humanitarian aid. No event showcased this capability more than that of Operation Unified Response in the wake of the earthquake that hit Haiti. In response to that natural disaster, the US Marine Corps mobilized numerous V-22 aircraft because they can cruise long distances quickly, and then assume a search posture using its sensors or visually by the crew. These V-22s were not reliant on runways or airfields to conduct operations, and operated in a myriad of roles from site survey; aerial reconnaissance of population centers and infrastructure; resupply; casualty evacuation; and transport, to name a few.
The Osprey also has provision for a rescue hoist that can be attached to the rear of the aircraft in the ceiling forward of the empennage bulkhead. The rescue hoist is installed as a kit and permits rescue and/or insertion/extraction of personnel when landing is not practical or desired. The hoist system is capable of hoisting devices into the cabin like a stokes litter, two-man rescue team, three-man forest penetrator, or a stokes litter with an attached floatation device. The rescue hoist has a lift capacity of 600 pounds, a continuously variable speed up to 225 feet per minute, and a maximum distance of 250 feet below the aircraft. The maximum load limit of the cable is 2,100 pounds.
“When you look at a tiltrotor medevac type mission, you combine the capabilities of VTOL which gives runway independence, along with the range and speed of a fixed wing,” said Fuller. “We saw that in a recent Navy deployment of USS Carl Vinson. They had a sailor that had an injury, but the ship was out of range for a helicopter to get from ship to shore. The injury was such that the medical staff didn’t feel the patient could survive a catapult shot off the aircraft carrier so they deployed a CMV-22 aircraft, which went out and picked up the patient from the aircraft carrier and flew them straight to a hospital.”
© Joetey Attariwala
The US Army recently selected the Bell V-280 Valor as the solution for its Future Long-Range Assault Aircraft (FLRAA) program, which is part of the Army’s Future Vertical Lift initiative. The award was based on Bell’s tiltrotor that was developed and tested as part of the Joint Multi-Role Technology Demonstrator (JMR TD) program that began in 2013.
As of writing, Sikorsky has filed a formal protest of the Army’s decision, so Bell was not in a position to speak directly about the V-280; however, they did speak about the JMR TD on which it is based.
Bell explained that they designed the JMR TD on lessons learned from the V-22. Speaking about this process was Frank Lazzara, Director, Sales and Strategy, Advanced Vertical Lift Systems, V-280 Valor/FLRAA: “The leadership at Bell told the team here that we have to design costs out of the next tiltrotor because we have to make it affordable, manufacturable, and we have to make an aircraft that can be maintained in the field with high availability rates.”
The V-280 is designed with side doors, which are approximately six feet wide, and the cabin has approximately 300–400 cubic feet more space than a Black Hawk.
Powering the V-280 is the Rolls-Royce AE 1107F turboshaft engine, which is very similar to the AE1107C engines powering V-22. Both turboshaft engine variants are part of the AE engine family and its common core. The V-280 design is such that only the proprotors translate, as opposed to the whole nacelle like that on the V-22. This allows passengers the ability to enter and exit through the side doors safely, while not having to deal with a nacelle hanging down or its hot exhaust.
“The size and efficiency of the V-280 tiltrotor platform has allowed us to use this combat-proven engine at a reduced horsepower level, providing extended time-on-wing,” shared Jena Wright, Senior Vice President, Strategic Campaigns, Rolls-Royce Defense. “This also allows for inherent growth to deliver ample power as aircraft capability or needs increase. Additionally, the level, non-rotating configuration of the engine nacelle in the V-280 simplifies the installation for improved maintainability and reliability. Our development of the ‘end-to-end’ solution with Bell includes use of an inlet barrier filter, which significantly improves the operational life of the engine. This allows us to achieve an increase in performance without risk to schedule.”
Adding his perspective on the design of the aircraft, Lazzara said: “The wing is designed completely differently than the V-22 to reduce the cost of manufacturing and cost of the aircraft. The proprotor blades are remarkably simpler to produce, and cheaper. Approaches like these are throughout the aircraft, because the focus of the design effort went to reducing costs, increasing sustainability targets, while not compromising on performance or capability.”
Bell has designed the V-280 with consideration of size, weight and power (SWAP), and modularity to accommodate various mission sets. Speaking to the potential of medical evacuation, the organization said that they have worked with three companies to seek lessons from civilian applications of medevac configurations. “We did that to make sure we don’t accidentally design something out of it,” said Lazzara.
As the first civil tiltrotor that will be certified, the Leonardo AW609 represents a potential revolution in point-to-point air transportation. The AW609 has a capacity of two crew and nine passengers, and thanks to its long range (700nm) and high cruise speed (270kt), it requires fewer bases to provide the same coverage of traditional helicopters. This capability, along with a pressurized composite airframe, fly-by-wire flight control system and robust ice protection system, makes the AW609 ideal for a wide variety of missions including VIP and executive transport, parapublic, medical and rescue services, homeland security and more.
According to Bill Sunick, Head of Tiltrotor Marketing at Leonardo, the AW609 is poised to provide a revolutionary capability to the EMS market as it will reduce the transfer time between hospitals while granting a wider coverage area. At the same time, a high level of lifesaving care is ensured by a smooth flight profile with a pressurized cabin designed for cruising efficiently at 25,000ft.
A medically equipped AW609 can board up to five medical crew members and one patient on a stretcher. The low cabin floor height allows for easier patient loading and unloading from the aircraft.
The AW609 is powered by two Pratt & Whitney Canada PT6C-67A turboshaft engines. The PT6 series engine is renowned in its use in numerous airplanes and helicopters, with this variant being one of the most powerful versions. Additionally, for its use on the AW609, the engine has been qualified for operation in both horizontal and vertical orientations.
Timing of certification is not yet defined, but Sunick shared the following: “We refrain from speculating on the precise timing of certification, though having flown in excess of 1,900 flight hours we can definitely see the light at the end of the tunnel. In fact, Federal Aviation Administration (FAA) pilots recently flew the AW609 for the first time in preparation for Type Inspection Authorization, which will see additional FAA flights as the program moves to the final stages of the certification process.”
There is no doubt that tiltrotor aircraft provide amazing capability. What has limited their adoption has been cost, which one would expect with a new transformational capability. However, the capability is now mature, and companies like Bell and Leonardo are focused on making their platforms more affordable.
“Tiltrotors are not this kind of emerging thing anymore. It’s here, it’s mature, and it’s absolutely proven capability wise,” said Lazzara. “Will the V-280 be more accessible than the V-22 was? I think, absolutely, the answer is yes, and I think that really changes the conversation because the reason the world isn’t flying V-22’s is because it’s a fairly expensive capability to get, and if it wasn’t, everybody would be after it, because the capability has been proven.”
Operators like the US Coast Guard have expressed interest in tiltrotor technology; however, cost and size are factors that presumably shied the service away from adopting the capability. With that said, tiltrotor capabilities are beautifully suited to the Coast Guard mission, as Fuller described: “From a SAR perspective, you need to recover folks quickly, so tiltrotors give the speed of a fixed wing, but then you can convert to helicopter mode and rescue the folks that need saving. The right platform depends on the mission; the V-22 might be too big, but something smaller like a V-280 might be a great solution.”
In the meantime, research and development for tiltrotor platforms continues. Bell is pursuing research into its High Speed VTOL (HSVTOL) initiative, which is meant to provide the next generation of warfighters with runway flexibility and improved speed, range and survivability. This technology blends the low downwash hover capability of a helicopter with the speed (>400kts), range and survivability features of a combat aircraft.
“Bell’s HSVTOL aircraft are original, next-generation technology, capable of providing vertical lift speed, range and survivability. The aircraft are designed to significantly reduce rescue response time and mission risk by enabling access to contested areas at higher speeds and enhanced aircraft survivability,” said Lee Anderson, Director, Innovation, Bell.
Dr Attariwala trained as a medical doctor and has established himself as a highly regarded journalist who contributes to various aerospace, defense, training and simulation, and law enforcement publications around the world. He is a regular contributor to AirMed&Rescue magazine.V-22 Osprey – the beginning of the modern era of tiltrotorsV-280 is the next generation of tiltrotorLeonardo AW609 offers great potentialThe future of tiltrotors