Flying ultralights can be exhilarating. It's grass-roots aviation using modern technology, and it's inexpensive compared to most other forms of flight. These appealing facts draw participants into the fold by the hundreds. But it's still flying. Despite the lack of regulatory burden, ultralight flying requires the same degree of good judgment as any other form of aviation.
Bad assumption - I am a private (commercial, airline, instrument rated, military, you-name-it ) pilot. I can handle one of these "toy" airplanes.
Better assumption - I've never flown one of these airplanes. I'll invest some time in study and training.
Aw, come on. Stall speed is less than 24 knots. Maximum speed is less than 55 knots. The whole machine weighs only a couple of hundred pounds. How risky can it be? Remember, it's usually not the flying that injures people and damages airplanes, it's contact with the ground. Ultralight airplanes have certain flying characteristics that require extra vigilance to avoid taking a pilot from the flying part to the ground contact part.
Mixed Breeds
Virtually all light general aviation (GA) airplanes have a single engine in front driving a tractor propeller. Physical variety is essentially limited to high/low wing, nose/tail wheel and high/low horizontal tail. The pilot usually sits under or over the wing and is usually surrounded by an enclosed cockpit.
Ultralight (U/L) airplanes (the FAA calls them "vehicles," but pilots still call them "airplanes") abound in physical variety. Some resemble conventional GA airplanes, others are quite different. From tail-less flying wings to Rogallo-type wings, U/L configurations span the appearance spectrum from hang glider to traditional airplane. Engines are often located above the pilot, either in front with a tractor propeller or behind with a pusher prop. The pilot is often at the very front of the machine. In fact, several U/Ls sit on their tail booms until the pilot climbs aboard and his (or her) weight lowers the nosewheel to the ground. Some employ traditional three-axis control, while others rely on the pilot to shift his weight for pitch and roll control.
These physical differences can significantly affect how the airplane flies and influence its flying qualities. Equally important, such differences influence the pilot's perceptions.
Imagine flying your Cessna 152. Now trade places with the propeller. You are now at the tip of the spear. No wing to obstruct your view to either side. No greenhouse effect of summer sun through Plexiglas. Possibly no physical visual obstruction of any kind.
This lack of visual obstruction is one feature that makes U/L flying so exciting. Like Rose on the railing of the Titanic's bow, you're as close to personal flying as you can get. The view is hard to beat, but it means you don't have all that airplane structure to give you a visual reference. No glareshield for pitch and roll attitude reference - certainly no artificial horizon. In fact, many of those instruments you've come to rely on are gone. It's needle, ball, and airspeed flying but, generally, without the needle, and perhaps without the ball.
Before you don your Icarus mindset based on the assumption of competence, you should be aware that these machines are different. They feel, behave, react, perform, and fly differently from even light GA airplanes. To explore some of the differences between U/L and GA airplane flying qualities, we visited Kolb Aircraft, which produces a series of ultralight and very light airplanes in kit form. We flew the FireFly, an ultralight that comes as a kit or completely assembled. It was a high-wing taildragger powered by a 40-horsepower, two-stroke engine mounted backward on top of the wing to drive its pusher propeller. The pilot sits in front of it all in a cockpit narrow enough to leave elbows in the breeze and behind a windscreen that reaches chin level.
Inertia and Drag
By definition ultralights are light-weight. They don't have a lot of inertia, the tendency of an object to resist a change in its motion. An airplane with low inertia accelerates and decelerates more quickly than an airplane with high inertia.
Drag always acts to slow an airplane. It delays acceleration and hastens deceleration. Ultralights can have a fairly high drag count. In fact, some U/Ls actually are designed with extra drag to help them meet the Federal Aviation Regulation Part 103 maximum speed restriction. Overcoming this drag is one reason U/Ls often use high power settings. The high drag also contributes to the rapid airspeed decay when the pilot reduces power.
As an illustration we compared the airspeed decay of a Cessna 152 with the FireFly. Initially both airplanes were flying straight and level at normal cruise. We retarded the throttle to simulate an engine failure and maintained level flight. The 152 stalled 25 to 30 seconds after the power went to idle. The FireFly stalled in a little more than 10 seconds after we reduced the power from 5,500 rpm (cruise) to 3,000 rpm. We didn't reduce power to idle because the two-stroke engine would not continue to run reliably at low power settings. An actual engine failure would surely result in less time until stall.
If you're thinking this isn't a realistic scenario, you're right. Following an engine failure most of us are mentally prepared to establish the maximum glide-range airspeed as a first order of business. Here are those numbers. The 152 slowed from cruise speed to glide speed in 12 seconds. The FireFly took less than three seconds (3,000 rpm again). The U/L pilot must take positive action quickly to avoid decelerating below glide speed and thereby reducing his emergency landing field options. Time is not a luxury in the 152 either, but temporary deviations from the optimum airspeed are less likely to cause a significant glide-range penalty.
Inertia also applies to rotation. An airplane with a lot of roll inertia (say, full tip tanks) takes longer for its roll rate to build than a lower roll inertia airplane. It also takes longer for the high-roll-inertia airplane to stop rolling after the pilot removes the aileron deflection.
U/L airplane inertia is generally low in all three axes. The U/L's response to control stick or rudder pedal displacements is often much quicker than you may be accustomed to in the GA airplane you fly. This feature adds to the fun of U/L flying, but you must apply your control inputs more thoughtfully to avoid over-controlling the airplane.
The same low rotational inertia helps account for the U/L's sensitivity to gusts. Even little gusts can drop a U/L's wing or swing the nose right or left to a greater degree than in GA airplanes. Returning the airplane to coordinated, wings-level flight can require a lot of control deflection and a little patience under certain conditions. At altitude, this usually isn't a problem - just another side of the U/L's personality. Near the ground, however, most pilots are short on patience where aircraft control is involved. Gusty conditions are not the best time for U/L flying.
Just how susceptible the U/L is to gusts and how responsive it is to the pilot's control inputs depends on the airplane. Just as U/Ls come in a variety of configurations, there is a variety of control authority among the myriad designs.
Stability is another arena best described as varietal among various U/L designs. Because these airplanes are exempt from meeting any airworthiness standards, the degree of longitudinal and lateral-directional stability is left to the manufacturer.
Throttle-Pitch Relationship
Ultralights designed to resemble GA airplanes generally have the same pitch-power relationship. More power usually raises the nose and vice versa. But once the location of the engine changes, the relationship can reverse.
With its high-wing-mounted engine and pusher propeller, the FireFly is representative of several U/L designs. Advancing the throttle results in more thrust, but that thrust acts above the airplane's center of gravity. That means the nose pitches down when you add power and pitches up when you reduce power.
In most GA airplanes the thrust line is pretty close to the center of gravity. Reducing power generally lowers the nose gently. This is a nice self-preservation feature because the airplane seeks the same angle of attack it had before the power reduction. Reducing the power in a high-thrustline U/L unbalances the pitching moments and results in a higher angle of attack. How high depends on the airplane and the flight condition, but the pilot of a high-thrustline U/L quickly learns to associate back stick with power additions and forward stick with power reductions.
Many U/Ls use two-stroke engines. These lightweight powerplants typically run best at 5,000 to 6,000 rpm, where they develop their rated power. The four-stroke engine in your GA airplane can idle below 1000 rpm; the two-stroke probably won't. It'll try, but it's clearly not happy there. It may continue to run roughly and shake the entire airplane, or it might quit running altogether.
Two-stroke reliability is always a controversial topic, but there's general agreement on two-stroke engine handling. Two techniques you are generally advised to avoid are:
This holds true for air-cooled four-stroke engines also, but the two-stroke generally is less tolerant of this kind of handling. Engine failures have been attributed to thermal expansion and contraction of internal parts associated with engine mis-handling. Proponents say two-stroke engines are just as reliable as the familiar four-strokes when properly maintained and operated.
If the engine does quit in flight, the propeller will probably stop rotating. Without a windmilling propeller, the only way to accomplish an air start is the same method used on the ground. For many popular two-stroke engines, this means a hefty tug on a lawnmower-type rope handle. The utility of this system depends on the location of the handle relative to the pilot. Access may necessitate loosening your harness or releasing the flight controls.
Given the choice, most pilots would opt for more power. Engine power in U/Ls often is limited by the FAR's maximum weight limit. Smaller, lightweight engines are less powerful than larger, heavier engines. GA pilots accustomed to relying on excess available power to solve judgment errors should re-think this potentially dangerous habit before flying an U/L, because that excess power may not be there. Some U/Ls, like the FireFly, seem to have plenty of power, but others may not.
Just because U/Ls are lightweight, slow flyers doesn't mean they glide forever. With all that drag, the only way to maintain the recommended maximum glide-range airspeed following an engine failure is to lower the nose substantially. Under these conditions the forward view can be quite intimidating. Without that big old GA instrument panel in front, the U/L appears to be even more nose-low.
Takeoffs and Landings
The low inertia and relatively high power of some U/Ls enable impressive takeoff performance compared to typical GA airplanes. In a light airplane the takeoff roll can be 15 to 30 seconds, depending on its loading, runway, and atmospheric conditions. The FireFly gets airborne in three to five seconds, and it's a taildragger. That's only three "potatoes" to raise the tail, sort out any directional control issues, check the instruments, and rotate for takeoff. Takeoffs in any airplane require the pilot to be prepared, but in a U/L you have very little time for mistakes and corrections.
Not every U/L gets airborne in three seconds. Some use smaller, less powerful engines to keep the overall airplane weight within limits. These airplanes are still capable of safe takeoffs, but their performance is more along the lines of GA airplanes than the FireFly's STOL performance.
Once in the air, the combination of pilot exposure to the elements, steep climb angle, limited pitch attitude reference, and possibly high-revving two-stroke engine nearby can make the pilot feel, well, anxious. A 12 to 15 degree climb angle is not unusual in some U/Ls. Compare that with a typical Cessna 152 climb angle of around six degrees. The fairly slow climb airspeed coupled with an excellent climb rate can have the U/L at pattern altitude well before the departure end of the runway.
For normal landings, Dan Kurkjian, Kolb's director of training, recommends power-on approaches. Kurkjian is also an EAA-certified U/L instructor, an ATP, a CFII, and he holds a helicopter rating. We found 3,500 rpm produced a comfortable base leg and final approach. Carrying this power through the round-out allowed the airspeed decay to resemble that of a power-off GA flare. Reducing the throttle after the round-out plopped the FireFly onto the grass runway nicely, with the power reduction providing just a trace of nose-up pitch.
Kurkjian said landings pose the biggest challenge to GA pilots learning to fly U/Ls. Where a GA airplane may be flown at 1.3 VS on final, 1.5 or 1.6 VS is more common in U/Ls. That extra energy helps carry the airplane through the airspeed decay of the round-out. GA pilots naturally want to attempt full stall landings, but, again, the rapid airspeed decay can quickly eliminate the pilot's options during such a maneuver. Flaring high is another GA pilot tendency that is driven by the U/L's typically lower seat height, steeper final approach pitch attitude, and tremendous field of view over the nose (if there is one).
Power-off final approaches in a GA airplane are fairly common. When it comes time for the round-out and flare, the GA airplane's extra inertia helps. It slows the airspeed decay, leaving the pilot with some energy for last minute corrections. Opting for a power-off final approach in a U/L illustrates its low inertia and high drag in fairly dramatic fashion. The glide path is steep and appears even steeper. The U/L pilot basically has one shot at getting the flare right. The pilot must make a larger pitch attitude change because of the steeper nose-down glide attitude. The low inertia and high drag result in a fairly rapid airspeed decay that begins as soon as the pilot begins the round-out. We observed three seconds from round-out initiation until touch down. The good news here is the low inertia and high drag characteristics also mean a short landing roll.
Ultralight flying is fun. It may be the ultimate form of aviation therapy. The airplanes are reasonably inexpensive and - burning two to four gallons per hour - operating costs are low. You can use any field of reasonable size as an airport, and you can fold most U/Ls and trailer them home.
You should take learning to fly a U/L as seriously as learning to fly any other airplane. The burden is on you to obtain this training. Some insurance companies may require training from a registered U/L instructor, but no federal requirements are in effect for training of any kind, nor does an FAA written or practical test exist. So, exercise the same good judgment that brought you this far in your aviation pursuits. Get the training from a certified U/L instructor, and get ready to enjoy one of the most thrilling kinds of flying you'll ever experience.
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