Amazing Technology Now Being Fielded Worldwide (Part II)

By ANN Correspondent Kevin "Hognose" O'Brien

• READ PART ONE

What the Centrifuge Adds

The point of the centrifuge is to increase the realism of flight simulation. Or, as ETC puts it, the "continuous motion cueing and sustained G cueing in real time flight." There has been a great deal of to-controversy in the training and human factors worlds over the last few years on the value of motion cueing. Some studies indicate that it has little value. The difference may be one of degree: traditional simulators can provide motion cueing that hints at what the airplane can do, but they can't sustain acceleration (G), they can't do negative G, they can't reverse from positive to negative - all things an actual airplane can do. Even the momentary, transient accelerations felt in an ordinary full-motion simulator are strictly limited.

Now for the first time, there is a simulator that shakes off some of these limitations. It doesn't come cheap, but it makes it possible for pilots to do things that they have not only been unable to do in previous simulators, but also have been unable to do in airplanes. 

The centrifugal flight simulator provides acceleration - a "G Vector" - that matches the visual and aural cues, as well as responds to pilot control. ETC calls this alignment of cues and vectors "G-Pointing."

As ETC puts it:

Tactical flight simulation provides an authentic learning environment that exposes the pilot to the same stresses, including continuous motion and high G, that are experienced in actual combat flying, but in a safe controlled environment and at 1/20 the cost of flying the aircraft.

As we'll see, the training and operational uses to which this technology can be put are limited only by the imagination. And the beauty of it is, for a military that trains extensively in combat jets, the device can literally pay for itself in savings on direct operations costs and aircraft wear and tear (the G-FET-II has a service life of 30 years if maintained on schedule). Not to mention that evolutions that were once considered too risky to execute in training now can be done, with no fear of losing a valuable aircraft or a priceless pilot.

Some G-FET-II Design Features

The centrifuge consists of a gimbaled cockpit gondola made of aluminum aircraft alloy, cradled in an arm made of steel - construction grade steel near the hub, and aircraft grade steel further out. The steel frame of the arm has large, man-sized access holes so that it can easily be maintained. As you might imagine, the machine rides on a bearing that would do a battleship's turret proud. The pad the bearing is set in is made of reinforced concrete and attached by massive tie rods to a massive steel and concrete foundation fixture deep underground. In between is the machinery room, which contains the regenerative brakes and the drivetrain. Motive power comes from a monstrous, high-torque DC motor with a horizontal output shaft, driving a massive gearbox that turns the power from the motor 90º to vertical. The machinery, it turns out, is built of standard kinds of parts that are well known to industrial power systems engineers. The system delivers a million foot-pounds of torque. That's the equivalent of a couple thousand 2003 8.0 liter Dodge Vipers at peak.

"I imagine," I said, showing off my education, "that the arm is counterweighted to reduce asymmetric stresses." 

"No way," said mechanical engineer Ron Averill, showing off his education. "That wouldn't be good. Nope, we just design it to swing the weight around out there… see, a counterweight would add more mass, and that would interfere with the acceleration we need."

What kind of acceleration?

Well, I saw the thing pull 15 G, and as I mentioned, Glenn easily pulled 6.5 G in it. (He was using the F-18D air data model, and flying a realistic combat profile, including a SAM evasion maneuver). While 15G will send most humans to the Land of Nod, what really matters is how quickly you can put the G on and how long you can sustain it. Well, you can put G on at a rate of 15 G/second and work up to a sustained level of 25G. It can decelerate abruptly or steadily as well, and its regenerative braking system ensures that most braking energy is not lost, but remains available to the system. This means that it's energy-efficient; ETC claims 80% energy recovery.

A rare feature of this type of centrifuge is its ability to operate in the negative as well as the positive G range, and to transition smoothly and realistically from one to the other.
 
The pod, or gondola in official ETC-speak, looks like it moves freely about all axes. There are actually limits, but they are not extremely limiting. It can pitch up and over 180º and can pitch down 90º. Its roll limits are a little less than that, but to the pilot it creates the illusion of motion in 360º in all axes. The gondola is built, logically enough, with aircraft technology of aluminum and the "back" of the pod drops down to form a sort of airstair door for boarding, and then locks up to seal the pilot inside.

One of the more ingenious parts of the system, to a non-mechanical-engineer, was the slip-ring umbilical that passes such things as electricity through the spinning hub of the centrifuge arm. It turns out, ingenious or not, that it is another piece from the engineer's standard toolkit.

Now, the way that the pilot's action on the flight controls turns into motion of the centrifuge and the gimbaled pod is, as you might expect, controlled by software, and by electric motors. The software comes mostly from ETC Turkey, although the air data model comes from ETC Poland. Turkish engineers do a lot of the integration. If the pilot, for instance, pulls back on the stick, the software notes the motion, and sends it to the air data model. The air data model knows the airspeed and the type of aircraft, and decides what control deflection would result, and how it would move the aircraft. The simulator software receives a command from the air data software, to produce A amount of G in B axis. The simulator software calculates that it must gimbal the cabin to X orientation while producing Y degree of acceleration or deceleration on the centrifugal arm. Oh, yeah, and it has to do this just about instantly, so that the pilot doesn't feel any unnatural lag when he displaces the stick.  To the pilot, he feels that he reefed back on the stick and some G pressed him down in his seat.

Of course, this is a gross oversimplification. Of a simple maneuver.

"It's simple!" engineer Alper Kus told me.

Uh-huh. To him, maybe.

The genius is only half used on the centrifuge itself, even factoring in the software. There is also the control room. In the control room, a controller can talk to and monitor (on video and physiologically) the pilot. The picture at left was taken during one of Glenn's flights. Through the windows in the background, you can see the gyro frantically spinning around. In front of the controller, you can see Glenn on the video screen. In addition, a bank of computers monitors all of the many parameters measured during the flight. (Over time, a number of them might prove unnecessary. But on the very first G-FET-II, the engineers wanted to measure everything. And they did.

Safety is a matter of constant concern, and it was considered at every stage of the design. Dozens of interlocks prevent the machine from starting in an unsafe state. Should some safety condition change while the machine is in operation, it is designed to stop as quickly and safely as possible. Components and systems are engineered so that any failure fails in a safe condition.

The G-FET-II is an amalgam of computer, aeronautical, and battleship technology - it embodies the software of the 21st century, the riveted alloy monocoque of the 20th and the massive steel of the 19th. It is a dead certainty that no one in the world could have developed this, except for ETC. Indeed, this machine was postulated long ago. "The idea's been around a long time," an ETC executive told me, resolutely refusing to take credit for what seemed to me to be a brilliant innovation. Well, the idea might have been out there, but it took several of ETC's specialized international business units to build this device, and it took ETCs credibility to get an air force to plunk down money for the first machine before it was built.

What's it like Inside?

I "flew" the simulator bit of the FET II centrifugal flight trainer, without the centrifuge or gondola moving (ETC's executives told me that they weren't comfortable with anyone but their own pilots flying the machine, until they have a few more hours on it). When you sit in the seat, it's close enough to an actual airplane cockpit that you quickly forget you're in a simulator - a definite indicator of a well-done sim. The switches aren't exact copies of the cockpit (in the case of the one I was in, the F/A-18D) but they're close enough for the switchology to be transferable. What I mean is, the cockpit as currently configured doesn't have ruggedized military gorilla-proof switches, but they're all in the right places.

In front of you is a panoramic viewscreen, which lets you see what's going on in a field of view of 120º by 50º. When you first sit in the seat and strap in, it seems that the screen will be something you notice in "flight." Nothing could be further from the truth. The minute the screen lights up and you're sitting on a runway idling, all doubt vanishes and you're for all intents and purposes in the real airplane.

There didn't seem to be anything wrong with the F/A-18 air data model, not that I have any time in a real F-18 to compare it to. If you did stuff the airplane would let you do, you got away with it, and if you tried to do things where a real airplane would bite you, you got bit. The big advantage of a simulator, of course, is in what you do after the machine bites you - in a real one, you'd eject; in the G-FET-II, you sheepishly request a reset. I won't tell you how many resets I needed. Let's just say that the Navy isn't missing a real hot rock F/A-18D pilot.

FMI: www.etcusa.com