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Vertical lift innovations

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Military developments have potential in the civilian market.


Bell Boeing V-22 Osprey tiltrotor is used by 4 branches of the US military. It excels in unconventional operations.
By Shannon Forrest
President, Turbine Mentor ATP/CFII.
Challenger 604/605, Gulfstream IV, MU2B

In the world of FAA pilot certificates, one qualification is so rare that few know it exists. A predictable but erroneous guess would be that it covers one of the forms of flying best described as more recreational than professional.

These include hot air balloon, glider, and gyrocopter. Professional pilots might venture a guess that the single-engine airline transport pilot certificate is the rarest of all, but that too would be incorrect.

The honor for the most obscure civilian certification – which can be obtained in the form of a private, commercial, or airline transport pilot certificate – is powered-lift.

According to the Code of Federal Regulations, an aircraft is defined as “a device that is used or intended to be used for flight in the air.” Moreover, powered-lift means “a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low-speed flight that depends primarily on engine-driven lift devices or engine thrust for lift during these flight regimes and on non-rotating airfoil(s) for lift during horizontal flight.”

In layman’s terms, a non-rotating airfoil is a wing which must remain in a fixed position and generate lift through conventional aerodynamic flow while the aircraft is moving horizontally. The reference to engine-driven lift devices or engine thrust to achieve vertical maneuvering can also be simplified to mean that an aircraft powered by either a propeller/rotor or a jet engine can be certified as powered-lift.

Vertical takeoff and landing

The most well-known jet engine powered-lift aircraft is the AV-8 Harrier, nicknamed “the jump jet” by the popular press. Development of the Harrier by Hawker Siddeley in the UK started in the 1960s, and the plane entered service with the British Royal Air Force and Royal Navy before eventually serving with the US Marine Corps after McDonnell Douglas began production in the 70s.

In 1985, Boeing produced a newer version of the aircraft, designated the AV-8B. Vertical takeoff and landing (VTOL) is accomplished by using a collection of angled nozzles to direct thrust.

The process of controlling the Harrier at low altitude and slow speed using this method is challenging – so much so that a former US Marine Corps test pilot, quoted in a 2014 Wired magazine article, compared it to “balancing a model airplane on the point of a pencil.”

To date, the AV-8B is still in service with the Marine Corps, but is scheduled to be retired in 2025 as the Lockheed Martin F-35 will replace both the Harrier and the F/A-18 fighter. Despite some tactical successes with the Harrier program, the overall safety record is grim.

The type suffered 143 non-combat accidents between 1971 and 2002. Perhaps that’s one reason why the vectored jet thrust paradigm of aircraft control never made the leap to civilian commercial applications. On the other hand, the outlook for propeller-/rotor-driven powered-lift aircraft in military service is promising, and the nascent civilian sector is expected to grow rapidly.

The first civilian production tiltrotor is the Leonardo AW609. It combines the capabilities of a helicopter and turboprop in a single airframe.

Rotor-based VTOL

If the Harrier is the epitome of powered-lift based on jet thrust, then the propeller/rotor counterpart is the Bell Boeing V-22 Osprey. The colloquial term for a propeller- or rotor-based vertical lift aircraft is “tiltrotor,” which describes exactly how it works.

During vertical flight, the Osprey’s rotors operate much like those on conventional helicopters. And in order to achieve horizontal flight, the same rotor tilts to perform like a propeller. The principle seems simple when described this way, but the engineering and aerodynamics are complex.

Proof-of-concept work on the tiltrotor started in the 1950s with the Bell XV-3. At first, Bell placed engines inside the fuselage and props on the wingtips. This setup necessitated that connecting driveshafts be run through the wing.

By 1977, engineers surmised that placing the entire engine and prop assembly on the wingtip was a better solution, and they applied the new design to the XV-15. Although the tiltrotor made sense theoretically, because it combined the takeoff and landing flexibility of a helicopter with the speed of an airplane, it would take an accident to demonstrate the practical use for it.

In 1980, the United States hatched a plan to rescue US citizens being held hostage in Tehran, Iran. Operation Eagle Claw called for US Navy helicopters to fly from the USS Nimitz, which was positioned in the Persian Gulf, to the Iranian capital. However, the helicopters would need to be refueled in the desert to complete the mission.

At the refueling staging area, one of the helicopters collided with a C-130 Hercules, and the rescue attempt was called off. The next year, the Pentagon put out a proposal request for a vertical lift aircraft, and 2 companies responded – Bell Helicopter Textron and Boeing Vertol.

Bell Boeing V-22 Osprey

In 1983, a contract for a tiltrotor aircraft that could be used by the US Army, Air Force, Navy, and Marine Corps was awarded to a combined Bell-Boeing design team. The effort resulted in the debut of the V-22 Osprey in 1988. The “standard” V-22 is 84 ft wide and 57 ft long, and is powered by 2 Rolls-Royce engines.

Bell advertises a speed of 266 kts and a maximum takeoff weight of 52,600 lb. Each of those 4 branches has a unique mission requirement. As a result, there’s some variation in capabilities as a function of which force is operating the aircraft. In nature, the Osprey is a tenacious member of the hawk family.

It’s a formidable predator, and having the V-22 aircraft as its namesake is appropriate. The Osprey program has survived many attempts at cancellation throughout the years.

Some were budget related (research and development costs were in the billions), while others involved design problems and a series of high-profile accidents early on. Fortunately, the safety record of the aircraft improved over time.

Leonardo AW609

Bringing new technology to market always seems to cost more than anticipated, and the Osprey program is no different. However, the high cost of engineering may not be so unpalatable if one considers the potential civilian spin-off from the military V-22.

The first civil powered-lift rating (ie, tiltrotor) was awarded in 1997 to V-22 chief test pilot Tom Macdonald. Since then, only a handful have been issued. Right now, it’s a case of an FAA qualification in search of an aircraft because there’s currently no FAA certified civilian tiltrotor to fly.

But that could change soon, as Italian aerospace company Leonardo is currently in the process of completing 2 production models of a civilian tiltrotor called the AW609. The aircraft has been on the drawing board since 1996, when, much like the Osprey, Bell and Boeing were also involved with the project.

Both companies subsequently left the team, leaving Agusta (now Leonardo) to go it alone. On paper the AW609 looks like a turboprop, with twin Pratt & Whitney PT6C-67A engines expected to deliver a maximum cruise speed of 275 kts and a service ceiling of 25,000 ft into known icing. At 46 ft long and 60 ft wide, the AW609 is smaller than the V-22.

Flight control is fly-by-wire. A crew of 2 is supported with a Collins Pro Line Fusion suite of avionics, and the pressurized fuselage can seat 9 passengers comfortably. A VIP seating configuration reduces the payload to 8 passengers but adds a refreshment center and bathroom.

Those who have flown the AW609, as well as the V-22, describe the flying characteristics as more airplane than helicopter. This statement makes sense, given both aircraft spend proportionally more time in horizontal flight.

Sikorsky-Boeing SB-1 Defiant is in contention to replace the US Army UH-60 Black Hawk. It is faster and more nimble than the existing fleet.

Target audiences

It’s not hard to see the advantages of an aircraft like the AW609 for transporting passengers to and from offshore oil platforms, or being used as a platform for emergency medical transport.

Other target audiences include corporate flight departments with a mixed fleet of fixed- and rotary-wing aircraft, and high-net-worth individuals.

Companies with a demonstrated need for a helicopter have always placed a premium on landing close to the office. In 2016, when General Electric was in talks to move its headquarters to downtown Boston, a helipad was touted as a necessity.

And when Amazon was entertaining the thought of building a second headquarters in Queens NY, part of the $3-billion incentive package included a helipad on the campus. In the event the helipad couldn’t be constructed at Amazon’s headquarters, the NYC Economic Development Corporation agreed to find Amazon one in “reasonable proximity to the development sites.”

Corporate flight departments with a rotary-wing component often use it to transport passengers to the local airport to get to a fixed-wing aircraft. If the corporate aircraft in question is a Gulfstream G650 getting ready for an Atlantic crossing, it’s a moot point.

In other scenarios, however, a company could justify the price premium of a tiltrotor, which is roughly 2 to 3 times that of a helicopter. If the fixed-wing aircraft is a turboprop, the answer is obvious – a tiltrotor is essentially 2 aircraft for the price of 1.

But even if the company plane is a jet, the economics of the tiltrotor could make sense on shorter legs, especially when factoring in the ground and transfer time when moving between the helicopter and fixed-wing aircraft, or vice versa.

The northeast corridor of the US could be the sweet spot for a civilian tiltrotor. An AW609 could take off vertically on or near a corporate campus, transition to horizontal flight, and then fly at high speed while staying low enough to remain below congested center-controlled airspace in the flight levels.

Airbus Helicopters has achieved faster rotorcraft speeds by adding 2 pusher propellers. Its RACER concept is an advanced technology demonstration platform.

Airbus RACER

Rotorcraft purists who want increased speed, but don’t want to add powered lift to their repertoire, might want to look to the Airbus RACER (an acronym for Rapid and Cost Effective Rotorcraft).

The technology demonstrator, which is expected to lead to a production prototype later this year, is designed with a main rotor and 2 pusher propellers mounted on thin box wings.

Unlike the AW609 and V-22, the engines on the RACER do not rotate up or down. The props allow the aircraft to fly at a higher speed (Airbus advertises 220 kts) because they augment the lift and propulsion of the main rotor.

A secondary effect is to counteract the torque in hover, which eliminates the need for a tail rotor. Futuristic looks aside, for regulatory and pilot certification purposes, the RACER is considered a helicopter.

Sikorsky-Boeing SB-1 Defiant

Sikorsky and Boeing have also embraced the pusher prop concept and applied it to their joint venture technology demonstrator – the SB-1 Defiant.

The Defiant is also classified as a helicopter, although, unlike the RACER, it uses 2 rotors stacked atop each other, and a single pusher propeller. The SB-1 Defiant is in contention to replace the UH-60 Black Hawk and become the future medium-lift platform for the US Army.

Bell V-280 Valor

Some naysayers contend that tiltrotors will never become part of the civilian infrastructure because they’re too costly and impractical. The truth is, Bell has already developed the V-280 Valor, a tiltrotor which outpaces the V-22 in terms of technology. One marked improvement is that only the props and driveshafts tilt, as opposed to tilting the entire engine like the Osprey.

The Valor is smaller and nimbler than the Osprey, which makes its footprint more suitable for smaller corporate flight departments. Bell also claims manufacturing techniques have lowered costs by 95% in some areas. As of now, more pilots are qualified to fly an airship than a civilian powered-lift platform.

But unlike transatlantic zeppelin pilots, the ranks of professional powered-lift pilots will continue to grow as flight departments embrace the utility of these platforms.


Shannon Forrest is a current line pilot, CRM facilitator, and aviation safety consultant. He has over 10,000 hours and holds a degree in behavioral psychology.

 

 

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