Defying Physics

A parachute can go up—if you add an engine

September 1, 2000

Bill Graves looks over his shoulder at me as I sit snugly behind him. "You ready?" he asks. An instant later the idling Rotax two-cycle, 65-horsepower engine behind my head screams, our three-wheel Six Chuter powered parachute cockpit shoots forward, and the parachute lying in the grass behind us is snapped off the ground as its shrouds are pulled tight. As the parachute fills, it acts like a huge drag chute that nearly pulls us to a stop before suddenly soaring overhead to become a nonrigid wing.

With the canopy no longer acting as a brake, we lurch forward. Just as we accelerate, Graves pulls back the power and looks up to check that the parachute's lines are clear of sticks and tangles. Following his glance, I take in the beauty of the multicolored canopy as the fabric arches across the blue sky. Through the intercom, Graves, who holds an instructor rating for powered parachutes, can barely be heard over the engine. "You want to make sure your lines are clear before you leave the ground. You don't want to be 50 feet up and realize you have a problem." Satisfied that all is well, he adds full throttle and the Six Chuter jumps off the ground to climb with a sensation unlike that of any aircraft I've ever known.

Hanging beneath the parachute during the climb, the cockpit gently rocks back and forth, looking for equilibrium as the engine tries to push it out in front of the canopy. Passing above the tree line, a crosswind adds a slight twisting action to the rocking motion. It was like being a small kid again, riding a swing with unequal ropes, and for the first time going higher than the swing really wanted to go. For the first couple of trips around the pattern, I'm that small kid again, wondering if I've gone too high.

The first powered parachute that could take off under its own power flew in 1981 when Steve Snyder, Dan Thompson, and Adrian vandenBurg combined their talents and inspiration. Snyder, who recently died while flying his F–86 at a New Jersey airport, was an avid skydiver who helped pioneer ram-air parachutes in skydiving. With an interest in remotely piloted vehicles (RPVs), it was Snyder's idea to take skydiving's new parafoil designs and add an engine. Thompson brought to the project his experience as an ultralight-aircraft designer and small-engine mechanic, while vandenBurg's skills as a machinist were critical to building the cockpit frame. Over the next two years, the three worked on refining and developing the powered-parachute concept.

Snyder's goal was to create an aerial vehicle that could be safely flown by an average person with only a few hours of training. It was the third prototype, P–3, that put all the aerodynamic requirements together. Design and construction of the P–3 started on February 26, 1983. On March 19, Snyder piloted the maiden flight. Several months later at Oshkosh, six production units were displayed for sale. Seventeen years later, it's estimated that as many as 15,000 powered parachutes are prowling the skies around the globe. Sales in 2000 are expected to be as high as 1,800 aircraft, and 90 to 95 percent of those could be two-passenger units. These look like a cross between a parafoil, the rectangular-shape parachute that is highly maneuverable, and an airboat from the swamp minus its hull.

Powered parachutes operate under the ultralight guidelines of FAR Part 103. As such, they are limited to five gallons of fuel, 254 pounds of empty weight, and one passenger. Like ultralights in general, few powered parachutes actually meet those requirements. Of 25 different models listed in a recent buyer's guide, fewer than half shown were "103 legal." Most are two-passenger, carrying eight to 10 gallons of fuel, and weighing closer to 300 pounds. The only ultralight restriction that all powered parachutes seem to meet is speed. "These are single-speed vehicles from the time you break ground till the time you touch down," says Graves. Powered parachutes take off, cruise, and land at 25 to 28 mph. With such slow speeds, they don't tend to fly in gusts over 10 knots and are most often seen around sunrise and sunset. "Anything above 10 to 12 knots takes all the fun out of it," says Graves. "It's safe up to 15 knots, but it's rock and roll." The only thing fast about powered parachutes is their growth in the aviation community. Some argue that powered parachutes are currently the fastest-growing segment in all of general aviation. And costs are a big factor in that growth.

A new powered parachute will set you back anywhere from $8,000 to $17,000, with the average being just under $12,000. Maintenance costs are minimal because there are no expensive avionics or elaborate airframes. Fuel burns are on the order of 2.5 to 3.5 gph of auto gas. Since the parafoil fits into a stuff sack, powered parachutes are easy to store. Many owners acquire small trailers to hangar and transport their aircraft. These trailers typically carry extra fuel, oil, and all the gear needed to support and maintain the aircraft. Because of the delicate nature of the nylon canopy fabric, most pilots fly off grass because asphalt, with its rough, abrasive surface, tends to rip and tear the fabric. Takeoff rolls tend to be 50 to 100 feet, so a large lawn or small field is often all the airport required.

Money issues aren't the only draws to this form of aviation. Freedom from FAA scrutiny, escape from the complexities of modern GA aircraft, and the "wind in the face" factor are reasons so many find ultralights in general—and powered parachutes in particular—to be appealing. Perhaps the biggest reason for growth in the powered-parachute community is that after five hours of training almost anyone can be turned loose in the skies.

Steve Snyder's goal was to create an aircraft that would be so safe and simple that a person with little training could fly one competently. Statistics indicate he succeeded. Since the beginning of powered parachutes in 1983, only 18 people have been killed in accidents, says Jim Stephenson, president and CEO of the Aero Sports Connection, an umbrella organization for ultralight aircraft. That's an average of about one death per year since the sport began. In comparison, Stephenson points out that snowmobile accidents in just the Upper Peninsula region of Michigan took 39 lives last year.

Unfortunately, that low accident rate for powered parachutes "is escalating due to stupidity," says coinventor Dan Thompson, who is currently president of the North American Powered Parachute Association and runs his own company making powered parachutes. "This aircraft is a very simple vehicle to fly, but maybe that fact is what causes problems. There's more than people perceive." Thompson cites recent examples where pilots have neglected checking weather, ignored equipment limitations, and used very bad judgment.

As with many aircraft, the riskiest portion of flight is the takeoff. For powered parachutes, the moment of greatest risk is while the parachute is filling and stabilizing. These aerial vehicles have no crosswind capability, so all landings and takeoffs must be into the wind. If not, the cockpit, or cart as it is often called, will be heading in one direction and the canopy in another. When that happens, the canopy can pull the cart over and drag it across the ground. Ironically, it's this same tendency to follow the canopy that makes the aircraft so stable in flight.

Powered parachutes are like a huge moving pendulum. The cart hangs beneath the wing, the pivot point of the pendulum, and the position of the cart relative to the suspension point determines the wing's angle of attack. When the pendulum's weight, in this case the cart containing the pilot and passenger, moves out from under the suspension point, the weight has a natural tendency to return to that point. When a wind gust hits, the larger and lighter canopy moves first and the cart will be momentarily displaced. After a slight delay, the cart swings back underneath the canopy, seeking the suspension point, and level flight resumes. This is why a powered parachute is constantly rocking and twisting during flight. It's an unsettling experience for someone new, but the feeling quickly fades. In some ways, it's very similar to riding a small boat on the ocean.

The wing itself is actually a series of ripstop nylon cells. It gets its structure from ram air entering the cells through openings in the leading edge. The nylon material allows very little air to leak through, so the only way for it to escape is to flow back out through the leading edge. When inflated, the air pressure inside the cells prevents outside air from flowing in, forcing it to flow around the leading edge and generate lift. Turns are started by exerting pressure on "push tubes" with your feet. When you push on the tubes, you're actually pulling on the shrouds connected to the trailing edge of the wing. A push on the tubes pulls down the trailing edge and creates additional drag that actually turns the aircraft. When both tubes are partially pushed, as in flaring for landing, the effect is more akin to that of flaps, and they can arrest descent for a soft landing.

While most powered parachutes have a traditional-looking stick, its only function is controlling the nosewheel during ground roll. Once you set the throttle for cruise, you can fly with your hands in your pockets as there is little else for them to do. Throttle usage is different than in most other aircraft because it has only one function: It controls how high you go and makes no difference in forward airspeed. It's best to think of the throttle as only an up/down control.

Once you break ground and settle into the rocking motion, flying a powered parachute can be very relaxing. With no avionics or radios and good weather, your attention naturally focuses on pure flying. At such low speeds, it's easy to stay ahead of the aircraft and spend time enjoying the scenery. Most folks fly 300 to 500 feet agl, bringing real meaning to the phrase "low and slow." Some pilots enjoy flying just above the trees, weaving among the treetops like they were cones on a test track.

Given the vagaries of the two-cycle powerplant, flying over areas with no place to land should always be avoided. However, a powered parachute is a parachute and can put down just about anywhere, including small parking lots and rooftops. With a dead engine, these aircraft still fly at 25 to 28 mph, with a glide ratio of about 3:1 and a descent rate of around 600 fpm. And if you're good with your feet, flaring with the push rods means that you should be able to land only slightly harder than normal. Even an engine failure on takeoff can be a nonevent with proper technique. A 180-degree turn back to the runway can be made as low as 50 feet if "chute surge" is handled properly. Chute surge is a pendulum effect caused by a loss of power. As the engine slows, the cart swings backward, leading to a reduced angle of attack and a loss of altitude.

Stalls, mainly the result of strong gusts, are rare. When a severe stall occurs, the aircraft descends too steeply for the cells to stay inflated. Meanwhile, the canopy acts as a braking device all the way to the ground. "Once in a steady-state stall," where the cart is too far forward of the chute, "there's virtually no way out of it. In talking with some folks who have gone through some of those," says Thompson, "they've impacted fairly hard and while they feel it for a while to come, they haven't done any serious damage to themselves." Much more common is a cell collapse on one end of the wing, again due to a wind gust. Because the cells are cross-fed they will reinflate, often without the pilot ever knowing there has been a collapse. In extreme examples, where two or more cells collapse, the important thing is to maintain directional stability. Graves, who also holds a private pilot certificate with an instrument rating, adds, "It's just like any other form of flying: It's practice, training, and practice. You've got to learn the limitations of the machine and the pilot."

In my first few circuits with Graves, I'd thought I'd met a personal limitation as we rocked and twisted through the pattern. But less than an hour later, I was beside myself as I repeatedly kissed the grass with the main wheels before climbing back into the pattern. When I finally rolled to a full stop and killed the engine, I laughed the same way I did on my very first solo.


Links to additional information about powered parachutes and ultralights may be found on AOPA Online ( www.aopa.org/pilot/links/links0009.shtml). Tim Wright of Richmond, Virginia, is a freelance writer and photographer.