Of all birds, winged mammals, and insects, very few have mastered the skill of pausing in midair and going backward as well as forward, so anything capable of such flight is, ipso facto, a rare beast. The ruby-throated hummingbird, which can hover with sewing-machine-like precision and also fly more than 500 miles across the Gulf of Mexico without a rest, is one such improbability. Helicopters are another unlikelihood. Explaining how the parts work together to do the unlikely is best approached by treating the helicopter as terra incognita, exploring it from the headland of its cabin to the archipelago of its tail boom.
This particular helicopter is white, and composed mostly of high-strength steel and aluminum. It is thirty-one feet long and seats two people, typically a wary instructor on the left and a trainee on the right, but it is also suitable for aerial photography and other daily errands. Anyone renting a Schweizer 300 CBi for weekend travel will be traveling lightly, because there is no trunk for baggage. I required a formal introduction to the Schweizer, because I would be flying one. The instructor I secured from Hummingbird Aviation, John Lancaster, had been a professional skiing instructor for twenty years in Vail, Colorado. Skiing injuries and a love of flight prompted him to seek out a new, and statistically safer, profession. He learned to fly helicopters in Florida at the world's largest privately run helicopter school1 and came to Minnesota to share his knowledge. Typical students were those planning to fly for police departments, tourist outfits, or offshore oil companies. He favored shorts and sport shirts and, before getting down to business, displayed the cheery demeanor of a camp counselor. But he also had nearly a thousand hours of helicopter time and we were both mindful that I was not here to interview him; he was now my instructor. As when dealing with any rookie, his first job was to explain important parts of the ship.
Lancaster began my first lesson in the flight-school office by picking up a black-and-white toy police helicopter from a shelf and explaining basic principles of flight. Then he sold me a set of pilot books out of a glass showcase that looked to have been bought from a going-out-of-business sale at a jewelry store.
The helicopter he would train me to fly is of recent vintage but a lineal descendant of a 1956 model invented by the Aircraft Division of Hughes Tool. Beginning in 1964, the army used a military version called the TH-55 Osage* to drive thousands of new pilots through eighty hours of basic flying at Fort Wolters, Texas. The TH-55 was a light piston-engine helicopter and cost much less than a turbine-powered model to operate.
This session lasted an hour and was devoted to a four-page inspection checklist. It required a close look at every side of this helicopter, including the underside. It was so thorough that we might as well have been hunting for a small bomb that someone has tucked away on the aircraft. With this guidance, Lancaster said, I would know how to check out the machine for my own flights. It seemed to this novice that the whole machine is so small and so open to view that it can be taken in with a quick glance followed by a nod or a frown, but this is considered bad form.
Still, an open-minded, undistracted glance from thirty feet away is not a bad way to begin a preflight, Lancaster said. Sometimes it reveals immediately that something is out of whack, or missing, and a mechanic can be summoned sooner rather than later. We folded our arms and took it in, top to bottom. For all the publicity about helicopters black and deadly, this ranked no more than a "1" on the intimidation scale. It has the look of a dragonfly carrying saddlebags, which in this case are twin fuel tanks. It also doesn't look radically more elaborate than a car, so I had to wonder why it costs a quarter-million dollars if purchased new. With an instructor, each hour in the air costs $300 in rental fees. Since helicopter pilots need to fly regularly to stay on top of their skills, winning the license is comparable to buying a fancy boat: the initial expenditure is steep and leads to still more spending.
The Schweizer sits on tubular landing skids that hold it high off the ground, giving it a poised and alert look. Above the cabin is an elaborate-looking hub gripping three airfoils that droop slightly. Each airfoil is a "rotor blade," taken together they make a "rotor." The extreme engineering challenges that are posed by spinning such large weights atop a hovering aircraft came as a complete surprise to the early inventors. When in operation the rotor rotates nearly eight times every second. Unlike airplane wings, which have a more generous curve on the upper side than the lower side, the cross-section of each rotor blade at the end is nearly symmetrical.
Pointing to the rear is a slender, tubular tail boom with a second set of rotor blades at the end, much smaller than the big blades on the main rotor. The tail rotor looks like an afterthought, but it is a technological survivor despite many attempts by helicopter innovators to get rid of it. The tail rotor's side-thrust overcomes the powerful twisting force that would result if a helicopter had only one rotor atop its fuselage and nothing to oppose it.* Single-propeller airplanes would also have a torque problem were it not for the fact that their wings have enough leverage in flight to keep the comparatively small propeller under control.
Lancaster closed in to work the checklist. He squatted to point out the engine and its associated parts, nestled in a stout tubular frame under the cabin. It's an aircraft engine, built for dependability and costing much more than a car engine. It burns eleven gallons of aviation gasoline per hour.2 We drained a pint of blue fuel into a plastic jar, checked for water that could kill the engine, then poured it back into the gas tank. Lancaster rapped on the tank, starting high to low, stopping when the sound changed from boom to thump. This verified the actual fuel level. He warned me not to place all my faith in the fuel gauge inside the cabin.
Of all the mistakes helicopter pilots can make, leaving the ground with too little gas for the trip is among the most embarrassing and avoidable. Despite the early freewheeling style of helicoptrians of the 1950s, who felt they could land about anywhere, today it is not acceptable to plan on refilling at a convenience store. That leaves mostly airports, except for the very few cities in the nation offering public heliports. A modified helicopters have flown for six hours or more, but more typical is two to three hours of operation on a full tank.
We peered into the cabin to make sure the fire extinguisher and paperwork were where they belonged. The view of the outside world is impressive from the pilot's seat, which in helicopters is on the right side of the cabin. The reason is that most pilots are right-handed and this arrangement allows these pilots to control the cyclic lever, which requires the most finesse, with their favored hand. In many conventional airplanes the pilot's visibility is narrow, comparable to looking out from a foxhole with a low roof, but not so with helicopters. The control panel and instruments are kept to a minimum so they all can be packed onto a pedestal in the center. Everything else within sight is a plastic bubble or just open air, since pilots prefer to fly without doors whenever the weather permits. The seat belts are comparable to those in race cars.
Lancaster prompted me to check the engine oil, the transmission bolts, the emergency transmitter, the door hinges, and even the welds in the landing gear. We lit up the beacons and wiped the housings with rags. We wiggled cables, belts, rods, and ball joints. We looked at a frame holding the belts for the transmission; Lancaster recalled a case from the National Transportation Safety Board files where that frame broke and killed the pilot. Unlike gasoline-powered airplanes, where the propeller is bolted directly to the crankshaft, all helicopters must have reduction gears so that the rotor turns only a tenth as fast (or even less) as the engine. The reason is that slow-turning rotors are more efficient than fast rotors.*
"Reading through the NTSB cases makes for an instructive evening," said Lancaster, "but it can dampen your enthusiasm."
We proceeded along the tail boom to the rear of the aircraft. Lancaster stopped for a lengthy discussion about the health and well-being of the tail rotor, which from our first glance at a distance looked to be little more than a set of striped lawn-mower blades. It's not, said Lancaster. There are little rods and bearings that allow the tail-rotor blades to change their angle a little, or a lot, as the pilot steps on the tail-rotor pedals. It has its own gearbox and oil supply.
The tail assembly is so delicate and essential to flight that pilots have to order passengers to be mindful of anything that wind might scour from the cabin, in flight, when the doors are off. Murphy's Law dictates that the slipstream will carry any such object straight into the tail rotor rather than allow it to tumble ineffectually to the ground. While there are verifiable wartime stories of Huey pilots who slashed through branches, even four-inch limbs, with their main rotors on the way down to a landing zone, no sane pilot would plan on chopping or even brushing anything lightly with the tail rotor.
Now fully two pages into the checklist, we reversed course and worked back toward the nose, along the right side of the helicopter. Lancaster pointed out a little window built into the tail boom and prodded it with a finger. It's there for inspection of the tail-rotor driveshaft dampers. These are doughnut-shaped bearings that keep the tail-rotor driveshaft from wobbling, which was one of many problems to vex early helicopters. This brings up a principle applying to helicopter components and helps explain why everything in this avocation costs so much. Let's say Part A is vital to flight. But Part A vibrates if left to its own devices and will crack if neglected, so we need a little Part B nearby, keeping Part A safe. But Part B is dogged by problems of its own, so we need a Part C, and sometimes even a Part D, to guard Part C.
Lancaster had me slide my fingers along a skein of steel control cables under the cabin to see if they had unraveled since the last pilot checked them an hour ago. They haven't. Now it was time to clamber up the rotor mast. Lancaster showed me where to put my feet so I could get a good look at the rotor hub without snapping something by stepping on it.
Sometimes places and machines are said to have a "heart," which in a home could be a cozy kitchen. If helicopters have a heart, something that is unique and important to them in the way that a nuclear reactor is to a ballistic-missile submarine, it would be the rotor hub.
At the high point of this Schweizer, eight feet above the ground, three rotor blades are held in the bolted grip of a metal hub. Each nut has a little loop of safety wire to prevent it from wiggling loose. The white blades have the shape of long, slender wings, which is exactly what they are. The hub not only holds on to the blades despite extreme centripetal forces at full speed, the hub also allows the pilot down in the cabin to alter the angle of each blade in flight with extraordinary delicacy. The hub is arranged so that commands from the cyclic and collective controls can pass through a rotating mechanism called the swashplate and out to the blades. The idea of the swashplate originated with windmill builders in the nineteenth century. If the lower swashplate pushes straight up or down, that changes the collective pitch of all the blades. If the lower swashplate tilts to one side, each blade must change pitch while it goes around.
The notion of two plates rotating against each other and forcing the upper one to follow the tilts and pushes of the lower one sounds cumbersome, but in a well-maintained helicopter the linkage is so precise that even imperceptible hand movements of the pilot have a prompt effect.
During flight, the entire loaded weight of the helicopter hangs from the hammer-forged assemblage of parts called the rotor hub. Turbulence or extreme maneuvers multiply that weight by G-forces, such that the hub of the massive Mi-26 cargo copter must be able to tolerate more than 100 tons hanging below. As Igor Sikorsky once said to a reporter who asked him what would happen if the rotor came off in flight: "That is not recommended." The importance of a light, intricate, and yet strong rotor hub is another reason why helicopters cost ten to twenty times more than a car. There was only room up here for one person to stand and Lancaster called up for me to shove the rotor around by hand, looking for anything wrong with something called the lead-lag dampers. These look like small, black hydraulic cylinders and sit near the base of each rotor blade. These humble devices keep the rotor blades from finding synchrony with the landing gear. Without them the helicopter would be at risk of going into a manic dance and rolling over on its side while just sitting on the ground and idling its rotors. Missing or failed dampers would pose a risk in the air also. We finished the preflight in a little less than an hour. This seemed like a lot, but never fear, said Lancaster: After I gain more practice in peering, tugging, and wiggling, a thorough inspection at the start of a flying day will take only fifteen minutes. According to veterans, any time spent by a pilot in knowing every part of his or her aircraft will not be wasted. "They say you can teach a monkey to fly, but to know the systems is very important," Alaskan pilot Mel Campbell told me while steering across the North Slope. "If you know what the aircraft will do in all circumstances you can save yourself."
Lancaster escorted me to the school's trailer-sized computer flight simulator, which at $100 per hour costs only a third as much as a real helicopter. We climbed into the miniature cockpit and I buckled my seat belt on the right side. The buckling amused Lancaster because the simulator offers no fancy actuators to make the little cabin rock and roll, as in an amusement ride. It has no more inclination to roll over than does my easy chair at home. The big image of a simulated Chicago O'Hare International Airport was bright and the computer was prepared to make the controls realistically frustrating to the novice. My job, he said, would be to maneuver around a simulated white bus, not hitting anything and not touching the ground.