Ultralight aircraft

Definition: A minimal aircraft, requiring minimum power and with slow cruise and landing speeds.
Significance: Minimal aircraft, whether purchased or home-built, are the least expensive entry into the pleasures of flight—an affordable option for experiencing the sheer exhilaration of bird-like freedom in the air.
In the United States, the Federal Aviation Administration (FAA) in Part 103 of the Federal Aviation Regulations (FARs) has defined a basic powered ultralight vehicle as one that has a single seat, an empty weight of less than 254 pounds (with exemptions for pontoons and an emergency parachute), has a fuel capacity of 5 gallons or less, has a maximum calibrated airspeed of 55 knots (63 miles per hour), and a power-off calibrated airspeed of 24 knots (28 miles per hour) or less. For training purposes only, Exemption 3783 of July, 1983, permitted the use of two-place ultralights for in-flight instruction. The structure, control system, and stability of an ultralight are the responsibility of the designer and builder because an ultralight is not a certificated aircraft. In Europe, this type of minimal aircraft is called a microlight, A microlight is defined as a one-or two-seat airplane with a specified takeoff weight, wing loading (number of pounds of weight per square foot of wing area), and fuel capacity.
In the United States, an operator of an ultralight is not required to possess either a medical certificate or a pilot’s license, and this has opened up the possibility of flight for thousands of pilots who either cannot afford the expense of certificated aircraft or who are no longer able to pass the medical exam. Because they have such short takeoff and landing capabilities, ultralights can be stored and flown from small grass strips in the country, further reducing the cost of owning and flying them. In England and in Europe, on the other hand, a microlight pilot must possess a valid Declaration of Health and must have passed an examination on applicable regulations, flight procedures, navigation, and weather. Tens of thousands of ultralights and microlights have been sold and are being flown.


Origins

Perhaps history’s first ultralight was Alberto Santos-Dumont’s 1909 Demoiselle; it had an empty weight of about 215 pounds and a 35-horsepower engine. Plans for the Demoiselle were offered in the 1910 issue of Popular Mechanics, but the machine required a very light pilot to get off the ground because of its very small wing. A little later, in the Great Depression, the United States could point to Bernie Pietenpol’s 1929 homebuilt Air Camper, powered by a Model A Ford engine, as a practical minimal aircraft.
However, the modern ultralight/microlight movement had its origins in a reinvention of the airplane, repeating in the early 1970′sthe hang gliding pioneered by Germany’s Otto Lilienthal in the 1890′s. (Hang gliding relies on weight shift by the pilot hanging below the wing for control of its flight path.) The revival was started by the invention of the Rogallo wing, a flexible-wing glider intended for space or military applications, by Francis Melvin Rogallo of the National Aeronautics and Space Administration (NASA). It was quickly adopted for sport flying in Australia and came to the United States as a towed glider behind a speedboat. Hang gliding became very popular and thousands were sold, especially on the West Coast where winds flowing up seaside hills generated lift and the seashore sand cushioned hard landings.
However, fliers soon tired of lugging their gliders back up the hill after what sometimes were very short flights; the ultralight movement can be said to have begun with John Moody’s flight demonstrations at the July, 1976, Experimental Aircraft Association Fly-In of an Icarus II biplane hang glider powered by a 12-horsepower engine strapped to his back. When the December, 1976, issue of Popular Science magazine featured this powered hang glider, the revolution was on. The Icarus II became the Easy Riser when an engine was added, and thousands were sold.
Initially, the FAA decided to exempt powered hang gliders from the certification and pilot requirements ofthe FARs so long as they were foot-launched, or at least foot-launchable. That was not very practical, as powered gliders inevitably became more sophisticated and used larger engines (mostly adapted chain-saw and snowmobile engines). In October, 1982, Part 103 became effective and established the basic ultralight definition, requirements, and flight restrictions, and these continue in effect.
The early ultralight pilots taught themselves to fly much as did pioneer pilots; they gradually increased taxi speeds, then made short straight-ahead hops, and then made their first tentative turning flights. The slow speeds involved usually minimized injuries. However, the FAA realized that instructionby a competent instructor in a two-place ultralight would certainly increase safety, and authorized the production and sale of uncertificated, two-seat ultralights so long as only authorized instructors used them for instruction or proficiency and their weight did not exceed 350 pounds and their stall speed did not exceed 29 knots (49 miles per hour).
By 1982, the hang-glider manufacturer Quicksilver was selling two thousand ultralights a year and had introduced a model that used three-axis control (the MX) in place of the much less effective weight-shift control used by unpowered hang gliders. Chuck Slusarczyk had introduced his CGS Hawk with a fully-enclosed cockpit, standard flight controls, and flaps, and was selling an average of forty ultralights every month.
In the United States, however, the bubble burst in November, 1983, when the television program 20/20 aired an expose of ultralight aircraft in which an ultralight suffered a structural failure, resulting in the death of the pilot. That caused ultralight sales to plummet by about a factor of eight. However, it also caused marginal designs to go out of business, and since then ultralights have continued a healthy growth. In addition to original “lawn chair under a wing” designs such as the Quicksilver, many airplanelike designs such as the Mini-Max are available. Ultralights can be built from plans (least expensively), from kits, or (most expensively) purchased ready-to-fly.

Structure

A very low wing loading (the ratio of weight to wing area) is the key to the ultralight’s very slow stall speed, and therefore its ability to land in very short, unpaved fields. A legal ultralight, with a 175-pound pilot and full fuel, requires a wing area of around 160 square feet, about the same as a much heavier, certificated two-seat trainer. This very low wing loading means that even moderate air turbulence and surface winds can make for unpleasant and potentially hazardous ultralight flying, and so most ultralight pilots prefer to fly in the early morning or late evening.
Excellent short takeoff performance is added to this short field landing capability by matching the low wing loading with a lightweight, powerful engine, yielding a low power loading. This has made the two-stroke engine the engine of choice for most ultralights, but engines more powerful than about 35 horsepower quickly put an ultralight over the weight limit. Two-stroke engines are more sensitive to the fuel mixture, the installation may not be well engineered, and deterioration can occur during winter storage, causing many ultralight pilots to become familiar with forced landings. These should not be a problem so long as the pilot is ready to transition to a steep nose-down attitude for gliding and a suitable short landing area is available. The steep glide angle is required because ultralights have a great deal of airframe drag from wing bracing and unstreamlined cockpits.


Safety

Many thousands of ultralights are now flying in the United States, but the absence of registration means that the exact number is not known. Similarly, because there is no reporting requirement, it is not known how many ultralight accidents occur. Some ultralights, perhaps especially those with engines behind the pilot, may not provide very good protection for the pilot in the event of a sudden stop. However, there is no doubt that a careful ultralight pilot with a carefully maintained flying machine, flying in good weather with light winds and always within gliding distance of a suitable landing area, can fly safely and with a great deal of personal pleasure and satisfaction. A good helmet and a ballistic parachute also enhance safety. Good hearing protection is vital because the engine is very close to the pilot.
The FAA’s 5-gallon fuel limitation was intended to insure only local flying by ultralights, so they and their pilots would not be exposed to the navigation and weather challenges of cross-country flight. However, challenge is just what stimulates and inspires some fliers, and by 1979 two ultralights had successfully been flown from coast to coast. Short cross-country trips have become very common. Ultralights need to be extra alert for the faster certificated aircraft because they often are not very visible from the air.
The greatest legal threat to ultralight flying is probably the liability problem, because most are not insured. Furthermore, almost all single-seat ultralights are much heavier than allowed by Part 103 and the more popular two-place ultralights are mostly used for passenger carrying rather than for the instruction of students. Some of these problems may be solved by sport pilot and sport airplane proposals that promise to extend low-cost flying into the two-place, lightweight, four-stroke powered, relatively slow planes, such as the first Cubs, while retaining minimal aircraft and pilot requirements.

Trikes and Power Parachutes

Trikes are flexible-wing, delta-shaped, powered hang gliders that are controlled by weight shift, using a bar that extends in front of the pilot. The operation of a control bar works opposite to that of a control stick: The nose is raised by forward motion (“pushing it up”). There are even fewer easy attitude references for the pilot than in the usual ultralight, and the pilots’s senses can provide initially conflicting information. Using a pusher engine, trikes are particularly vulnerable to anything that gets blown back from the structure and into the propeller. Handling turbulence is a considerably different and demanding task. Trikes are particularly popular in Europe but are also becoming more common in the United States.
Latecomers in the ultralight field, powered parachutes have established themselves as a popular form of recreational flying. They are very sensitive to atmospheric turbulence, requiring smooth air and very light winds for safe operation. With such a lightweight “wing,” the parachute “cart” for the pilot can be extra strong and still be legally ultralight, although the high drag of the parachute requires a relatively large engine. When ready to fly, the parachute is behind the cart and must be carefully inflated by a blast of air from the propeller before a commitment to a takeoff is made.

Other Applications

Thanks to their ability to fly very slowly and safely at low altitudes, ultralights have proved to be very useful for photography and for law enforcement all around the world. They are also the only piloted flying machine that flies as slowly as birds. In a well-publicized experiment (dramatized in the film Fly Away Home), Canada goose goslings were raised alongside an ultralight, taught to fly behind it, and then led on a desired migration pattern from Toronto, Canada, to Virginia in 1993. The same experiment has been successfully accomplished with sandhill cranes, and it is hoped that the population of the rare whooping crane can be increased through similarimprint-ing techniques.

Next post:

Previous post: