The Right Stuff, Simulator Style

To engineers at Environmental Tectonics Corp., the future of tactical flight simulation is crystal clear. Combat pilots, they say, need more than fancy computer graphics to simulate flight.

They need g-forces-lots of 'em. To accurately depict the feeling of hard tactical maneuvers, they say pilots need systems that quickly pile gravity forces on top of them-two, four, six, eight, even nine times the force of gravity in a matter of seconds-pinning their arms back, pushing the blood to their feet, turning every labored breath into a struggle for consciousness. They need systems that help them re-learn the simplest of skills-breathing, reaching, flicking a switch with a finger-all under a high onset of g-forces, and all the while maintaining their mental acuity and, oh yes, while flying an airplane, too. That last part-the flying of the airplane-is the key, the company says.

"Thousands of pilots have ridden in centrifuges," notes Ern Lewis, director of strategic development for Environmental Tectonics Corp. (Southampton, PA), as well as a former jet attack pilot, and former commanding officer of the U.S. Naval Training System Center (Orlando, FL). "But they've never controlled the centrifuge to recreate the experience of flying a tactical airplane." Until now, that is. Environmental Tectonics is aiming for a minor revolution in tactical military flight through the rollout of its Authentic Tactical Flight Simulator, a revolving centrifuge that incorporates a working cockpit. In one respect, it's a traditional human centrifuge, complete with a 25-ft revolving arm and a gondola perched on the end of it. On the other hand, it's a real flight simulator, with the gondola suspended inside a roll ring, and capable of pitching or rolling like a real airplane. What's more, inside the gondola there's the traditional stick and rudder, providing pilots with all the familiar controls.

"This is the first machine ever, anywhere, that allows a pilot to 'fly' a centrifuge," Lewis claims. "With this simulator, when the pilot pulls back on the stick, he feels those g-forces."

Creating G-Forces

Environmental Tectonics engineers say that there are good reasons for building such a simulator.

The most obvious is that combat pilots must experience the extraordinary forces of tactical maneuvers to develop the proper instincts in the air. The forces of gravity in fighter jets can build up in little more than the blink of an eye, engineers say, soaring from 2 or 3 g's to as high as 9 g's in less than two seconds. The results can be downright debilitating.

"Normal human beings with good muscle training can handle about 5.5 g's before they pass out," notes Bernhard Richter, vice president of development for Environmental Tectonics. "The idea of flight simulation is to get them ready for that situation. And to get them ready, you have to do g-training."

Indeed, Richter believes that if simulators don't prepare pilots for the onslaught of g-forces, then they are actually doing the pilot a disservice. That, however, is precisely what the military typically does by preparing pilots with graphically-intensive trainers, he says.

"There are simulators out there with millions of dollars worth of visual systems, but they don't move," Richter says. "So the pilots sit there and do all kinds of neat training on missile avoidance and weapons systems, but they're not moving. We consider that to be a negative form of training."

Environmental Tectonics engineers claim that by building a simulator that lets aviators "fly" while experiencing g-forces, they are providing pilots with the essential cues that are needed to recognize when they've reached the edge of the flight performance envelope. The relationships between the structural limitations of the aircraft and its speed are best experienced during seat-of-the-pants-type simulations, they say.

What's more, g-training also adds another ingredient: difficulty. The simple act of lifting an arm, moving a hand, or even flicking a switch is much harder when pilots struggle with six or seven times their normal weight. "If there are no g-forces (in the simulation), then it's too easy," Lewis says.

An Electric Solution

Up to now, however, the company says that military simulators haven't integrated high g-force centrifuges with cockpit realism in any significant way. Centrifuges have offered high g-force training-all the way back to the days of the Mercury astronauts-and simulators have added an impressive array of computer graphics, but the two have remained separate and distinct, mainly because of the engineering challenges involved.

To solve that problem, however, Environmental Tectonics' engineers have constructed a simulator of almost unbelievable size and force. The system's most essential component is a 25-ft-long, welded steel, A-frame-type arm that holds a gondola. The arm is attached to a huge power transmission system that provides the muscle to make it revolve. Spinning the unit's gondola at 10 rpm generates about 1.4 g's; 36 rpm creates 9 g's. And while that may not seem fast at first glance, the gondola at the end of the arm is said to hit speeds of 98 mph.

To reach such speeds, the system must generate extraordinary forces. It does so by employing an electric motor from GE Motors and Industrial Systems (Salem, VA) and a gearbox from Flender Corp. (Elgin, IL). The motor, capable of generating 1,850 and 6,000 hp, combines with the Flender speed reducer to develop more than 1 million ft-lb of torque.

Power to drive the unit is located at the center of the centrifuge. There, it is transmitted from the motor, through the gearbox, and through a 52-inch-diameter shaft that rotates the arm.

Engineers say that the motor-gearbox combination is big, but they add that it must be in order to move the centrifuge's 11-ton steel arm. "I'm six feet tall and I'm still not as tall as this motor," Richter says.

Along with the main power transmission system, the centrifuge also employs dual motors for pitch and dual motors for roll motions of the gondola.

The two roll motors, made by Kollmorgen (Radford, VA), are mounted at the front and back of the roll ring at the end of the 25-ft arm. Both motors are coupled with gearboxes from Sumitomo Machinery Corp. of America (Chesapeake, VA). They provide the force to rotate the roll ring.

Similarly, 24-hp pitch motors are located at the left and right sides of the gondola, enabling it to pitch up and down. The pitch motors and their associated gearboxes are also supplied by Kollmorgen and Sumitomo, respectively.

Controlling Motion

Pilots using the simulator sit in the gondola, which can accommodate several different kinds of cockpits. The company's engineers say that the simulator's price, which ranges from about $20 million to $30 million, depends on the type and number of available cockpits. Some military customers, they say, have talked to the company about providing as many as three different cockpits, which could be changed out to represent different aircraft.

Visual displays for the cockpits are controlled by up to three Pentium 4-based computers, all of which are remotely located in a separate control room.

Three more computers, located on board the gondola, handle the graphical user inter-faces (GUI), simulate the airplane cockpit, and perform the motion control duties. The motion control computers send commands to a three-axis Kollmorgen motion controller, which in turn transmits signals the amplifiers responsible for managing the pitch and roll motors.

Despite the amount of on-board motion control, Environmental Tectonic's engineers say that the real challenge in building the new simulator was in maintaining structural stiffness in the unit's 25-ft-long main arm. By doing so, they say, they were able to create a simulator that that not only produces high g-forces, but reaches seven, eight, or even nine g's in a matter of seconds, thus reproducing the so-called "high onset" of g-forces that occurs in real tactical flight.

The ability to mimic high onset could be a boon to pilots, they say, because it simulates the hair-raising and frequently debilitating conditions-pushing of blood into the pilot's legs and away from the stomach, followed by loss of blood flow to the brain-that ultimately leads to the dreaded GLOC ("g" loss of consciousness). By providing a system that's light and stiff, the company's engineers believe they can help pilots to recognize the high g-force onset and deal with the physiological issues while they fly.

"This arm is very, very stiff," Richter says. "It has to be that way to accurately simulate flight."

Indeed, Richter claims that total deflection at the outermost tip of the 25-ft arm is a mere 0.003 inches, despite its 11-ton weight. Furthermore, he says, the 11-ton weight is an achievement in itself, considering that existing U.S. Navy centrifuges weigh between 150 to 180 tons.

"We had to do some fancy modeling and some intense FEA (finite element analysis) work to get the stiffness we needed from this arm," Richter says.

The company's engineering team is convinced that the ability to combine g-force training with simulated flying will produce a better brand of tactical pilot. What they don't yet know is whether the U.S. military will change over to their new breed of simulator.

"People say the simulator is expensive, but a real airplane is more expensive," Richter says. "An hour in an F-16 costs between $6,000 and $7,000, whereas an hour on the simulator is about $250.

Moreover, the simulator, even at $20 million, is a fraction of the cost of a modern fighter aircraft, which can run $70 million or more in some cases.

"If you can recreate the authentic environment of the aircraft, then the pilot can learn the authentic skills that are needed to fly it," notes Lewis. "And if you can do that while eliminating the risk, creating greater access to the equipment, and lowering the cost, then we believe the military should see the value in it."

To respond to this story, Karen Auguston Field can be reached at[email protected].