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Monday, December 1, 2014

The AW609 Tilt Rotor: 2014’s Best Ride  

By Ernie Stephens, Editor-at-Large

 In mid-February of this year, I received a call from the publisher of this magazine asking me the most ridiculous question I have ever been asked in the 25 years that I have been a pilot: “How would you like to be trained to fly the AgustaWestland AW609 Tilt Rotor?”

As it turned out, I would be the first person outside of the manufacturer’s own pilots to fly the current iteration of the civilian tilt rotor, the experimental aircraft that can fly like a helicopter then reconfigure to fly like an airplane. The offer was extra exciting because I was also one of the first people to fly the hybrid Airbus X3 (formerly the Eurocopter X3), and probably the only person in world who has flown both.


(Left) The author in flight at the controls of N609TR. Photo by Dan Wells, AW609 test pilot
(Middle) A slow, steep approach in the AW609. Nacelles are at 87 degrees to slow the aircraft during decent. Photo by Ernie Stephens
(Right) Adrian Board, pres. and CEO of AgustaWestland Tilt Rotor, presents Ernie Stephens with an official AW609 ball cap, post flight. Courtesy of AgustaWestland Tilt Rotor Co.

 

 

 

 

 

   


Being allowed to fly the AW609 was going to take more than the permission of Adrian Board, the president and CEO of the AgustaWestland Tilt Rotor Co (AWTRC), the wholly owned subsidiary of AgustaWestland created to focus on the AW609. I would have to get permission from the FAA to even touch the controls because the aircraft falls under the category of an experimental aircraft to be used for research and development. Therefore, it cannot be flown by anyone other than the company’s pilots “to conduct aircraft operations as a matter of research or to determine if an idea warrants further development.” But hold on, because it got more complicated than that.

First, the FAA had to come to Arlington Municipal Airport, the home of AWTRC, and recertify the tilt rotor as an experimental aircraft in the crew training category since I am not an employee of the company. It also meant that I had to be officially trained as second-in-command aboard the aircraft before being allowed to fly it. And that was fine with me. Normally, when I do an evaluation flight for Rotor & Wing, I get a thorough technical briefing – usually between 90 minutes and two hours, depending on the complexity of the aircraft - from one of the design engineers or company pilots before climbing aboard. But to get two full days of what amounted to a transition course, including simulator training, followed by official authorization to serve as a second-in-command of the AW609 was a nice situation.

The May 2014 issue of Rotor & Wing recounts the way the AW609 handles throughout its full range of configurations and during various maneuvers. But space limitations being what they are, I couldn’t write too much about what I learned about the aircraft’s systems. Here is what they taught me:

Wing and Stabilizers

The AgustaWestland Tilt Rotor serial #0001 shows off its new paint job at Heli-Expo 2014 in Anneheim, California.
It is one of three prototypes.
Image courtesy of AgustaWestland Tilt Rotor Co.

The 34-ft wing is attached to the top of the fuselage and sweeps several degrees forward. The trailing edge has flaperons – surfaces that double as flaps and ailerons. A manual control for the flaperons resides on the instrument panel, but is only used as a manual override to the automatic system that handles them under normal conditions.

Bringing up the rear of the 609 is a high-mounted horizontal stabilizer with an elevator atop a rudderless vertical stabilizer.

In helicopter mode, the proprotors will provide lift. The flaperons will be at a 66-degree down angle to reduce the amount of wing area exposed to the proprotor’s downwash. And since movement of the 609 will be zero, or at a hover-taxi speeds, the horizontal and vertical stabilizers will serve no real function on a calm day.

In airplane mode the wings provide the bulk of the lift, and the flaperons provide roll moments and additional lift at slow speeds. The vertical stab will help keep everything in line.

 

Nacelles

At the end of each wing is a nacelle that houses a Pratt and Whitney Canada PT6C-67A turbine engine. A pylon protruding from the wing serves as the primary load-bearing member for the weight of the engine, gearboxes and proprotor system. It is also the portion of the wing structure that the nacelles rotate around.

In helicopter mode, the nacelles will be somewhere between 75 degrees from horizontal, which takes the aircraft into translational lift speeds, to 95 degrees, which is just enough aft vectoring to create a braking force while on approach, or brisk reward flight when in a hover. An 87-degree angle, however, is where the aircraft prefers to hover because it counteracts the aerodynamic forces that tend to make the ship drift slowly backwards. When the nacelles are tilted beyond 75 degrees, the 609 is virtually an airplane. The farther the forward tilt, the greater the forward airspeed.

In either mode, an automatic system will “discourage” the pilot from exceeding the tilt angle/speed schedule.

Engines

A drive shaft connecting the power outputs of the engines runs through the wing’s pylon. So, when one engine is running, both proprotors will turn. If both quit, the 609 will autorotate.

Looking at the nacelles from the side while in airplane mode, the engines lay horizontally in the lower section of the nacelle and, of course, they stand on end when in helicopter mode. To keep the engine oil flowing, the engineers created two reservoirs, so that one or the other will be at the engine’s lowest point through its range of rotation.


Metamorphosis: N609TR transitions from a hover to its top-speed configuration.
Courtesy of AgustaWestland Tilt Rotor Co.


Proprotor System

The 3-bladed proprotor system occupies the top have of the nacelle when viewed in airplane mode, and is driven by a gearbox powered by a shaft coming from the front of the engine. When vertical, blade pitch is controlled by an assembly that looks and works like the swashplate and connecting rods in any helicopter. And the same blade pitch that gives the AW609 lift when the nacelles are vertical gives it thrust when horizontal.

To slide left, displacing the center stick to the left will add pitch to the right proprotor, dragging the aircraft to the left, and vice versa. Pedal inputs rotate the 609 about its yaw axis by creating what amounts to a forward cyclic input in one proprotor set and an aft input in the other.

One thing I can’t emphasis enough is the adrenaline rush I received when I looked out the window and saw those nacelles rotating, followed by the mix of vertical lift and fast-forward feels. What a ride!

Learn how to fly the AW609 at http://www.aviationtoday.com/rw/topstories/Pilot-Report-Flying-the-AW609_81992.html#.VGAJP_nF9Mg

 

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