Homebuilt aircraft

Also known as amateur-built aircraft, homebuilt aircraft are constructed by persons for whom this is not a professional activity. These aircraft may be constructed from "scratch," from plans, or from assembly kits. Although the aircraft is constructed by an amateur, the finished product is often of good quality; the safety record of homebuilt aircraft is generally comparable to that of certified aircraft, once out of the testing phase that is required after construction is complete.

Overview

In the United States, homebuilt aircraft may be licensed Experimental under FAA regulations, provided that the owner has done at least 51% of the construction work. The first aircraft to be offered for sale as plans, rather than a completed airframe, was the Ace Baby Ace in the late 1920s. Homebuilt aircraft gained in popularity in the US in the 1950s with the formation of the Experimental Aircraft Association and with a large demand for light aircraft created by ex-military pilots after World War II.

Homebuilt aircraft are typically small, one- to four-seat sportsplanes, and employ simple methods of construction. Fabric-covered wood or metal frames and plywood are common in the aircraft structure, but increasingly, fiberglass is being used. Engines are often either the same as or similar to the engines used in certified aircraft or converted from automobile engines, with Volkswagen air-cooled flat-4s and Subaru-based liquid-cooled engines proving popular. The use of automotive engines helps to keep costs down, but many builders use dedicated aircraft engines which typically give better performance and/or reliability. There are some newer aircraft engines becoming common, such as those from Rotax and Jabiru, that use modern technology to keep costs and fuel burn down compared to the small Lycoming or Continental engines.

A combination of litigation, which has discouraged general aviation manufacturers from introducing new designs, and cost has led to homebuilts outselling factory types by five to one. In 2003, the number of homebuilt aircraft produced in the USA exceeded the number produced by any single certified manufacturer.

History

The history of amateur-built aircraft can be traced to the beginning of aviation itself. Even if the Wright brothers, Clément Ader, and their successors had commercial objectives in mind, the first aircraft were amateur-built, constructed by passionate enthusiasts whose goal was to fly.

Early years

Aviation took a leap forward with the industrialization that accompanied the First World War (1914-1918). In the post-war period, manufacturers needed to find new markets and introduced models designed for tourism. However, these machines were affordable only by the very rich.

Many U.S. aircraft designed and registered in the 1920s onward were considered "experimental" by the then-CAA, the same registration modern homebuilts are certified under. Many of these were prototypes, but designs such as Bernard H. Pietenpol's first, 1923 design were some of the first homebuilt aircraft. In 1928 Henri Mignet published plans for the HM-8 aircraft, as did Pietenpol for his Air Camper. Pietenpol later constructed a factory, and in 1933 began creating and selling partially-constructed aircraft kits.

In 1936 an association of amateur aviation enthusiasts was created in France. Many types of amateur aircraft began to make an appearance, and in 1938 legislation was amended to provide for a Certificat de navigabilité restreint d'aéronef (CNRA, "restricted operating certificate for aircraft"). 1946 saw the birth of the Ultralight Aircraft Association which later in 1952 became the Popular Flying Association in the United Kingdom, followed the next year by the Experimental Aircraft Association in the United States.

Technology and innovation

Until the late 1950s, builders had mainly kept to traditional wood-and-cloth and steel tube-and-cloth design. Borrowing from improving technology in the manufacturing side of aviation, homebuilders showed great creativity in introducing innovations. Metal construction in kitplanes was taken to a new level by Richard VanGrunsven in his RV series, while Burt Rutan pioneered composite construction and introduced the canard design to the homebuilding world. Standardized components from production aircraft, such as autopilots and more advanced navigation instruments became common.

Litigation during the 1970s and 1980s caused much stagnation in the production small aircraft market, forcing the surviving companies to stick to older, proven designs. In recent years, the less restrictive regulations for homebuilts allowed a number of manufacturers to develop new and innovative designs; many can considerably outperform certified production aircraft in their class.

A prime example of high-end homebuilt design is Lancair, which has developed a number of high-performance kits. The most powerful is the Lancair PropJet, a four-place kit with cabin pressurization and a turboprop engine, cruising at 24,000 feet and 370 knots. The only production aircraft of similar size and performance, the Extra 500, is still undergoing certification in the U.S. and will cost $1.5 million.

A small number of jet kitplanes have been built since the 1970's, including the tiny Bede BD-5J.

Building materials

Homebuilt aircraft can be constructed out of any material, provided it is light and strong enough for flight. Several common construction methods are detailed below.

Wood and cloth

This is the oldest construction, seen in the first aircraft and hence the best known. For that reason amateur-built aircraft associations will have more specialists for this type of craft than other kinds.

The most commonly-used woods are Sitka Spruce and Douglas Fir, which offer excellent strength-to-weight ratios. Wooden structural members are joined with adhesive, usually epoxy. Unlike the wood construction techniques used in other applications, virtually all wooden joints in aircraft are simple butt joints, with plywood gussets. Joints are designed to be stronger than the members.

After the structure has been completed, the aircraft is covered in fabric (usually aircraft-grade polyester) using typical aircraft methods.

The advantage of this type of construction is that it does not require a lot of complex tools and equipment, but rather such commonplace items as a saw, plane tool, file, sandpaper, and clamps are sufficient.

Amateur wood/cloth planes include:

The Ison miniMAX
the Jodel models including the bébé D-9, D-112, and the more D-18, D-19, and D-20
the Piel CP-30 or Émeraude
the motorized glider Fournier RF-5.

A modern trend is to build what could well be designated as wood-composite aircraft. The basic material is still wood, but it is combined with foam and other synthetic materials. An example of a wood-composite design would be this IBIS experimental aircraft project, designed by Roger Junqua.

Metal

Planes built from metal use similar techniques to more conventional factory-built aircraft. They can be more challenging to build, requiring metal-cutting, metal-shaping, and riveting. However, full or component assembly kits are relatively easy to obtain. A component assembly kit has the material needed to build part of the aircraft, such as the fuselage. Such kits are also available for the other types of aircraft construction.

There are three main types of metal construction: sheet aluminum, tube aluminum and welded steel tube. The tube structures are covered in fabric, much like wooden aircraft.

Examples of metal-based amateur aircraft include:

The Murphy Aircraft SR3500 Moose, Rebel, Maverick, Elite, JDM-8 and Yukon metal home-build kit aircraft. Murphy Aircraft is a Canadian Manufacturer that offers a complete line of aircraft construction kits for home/self construction.
The Vans RV-4, RV-8, RV-10 and other models produced by Van's Aircraft, are by far the most popular metal homebuilt aircraft. Van's is a U.S. manufacturer whose designs are available in kit form.
Those built by Chris Heintz's Zenith Aircraft Company
Jean Pottier's Pottier P-230 Panda
Sonex, Waiex, and Xenos kit planes and plans from Sonex Aircraft

Composite

"Composite material" structures are made of cloth with a high tensile strength (usually fibreglass or carbon, or occasionally Kevlar) combined with a structural plastic (usually epoxy, although vinylester is used in some aircraft). The fabric is saturated with the structural plastic in a liquid form; when the plastic cures and hardens, the part will hold its shape while possessing the strength characteristics of the fabric.

The two primary types of composite planes are molded composite, where major structures like wing skins and fuselage halves and prepared and cured in molds, and moldless, where shapes are carved out of foam and then covered with fiberglass or carbon fiber.

The advantages of this type of construction include smooth surfaces (without the drag of rivets), the ability to do virtually any compound curve, and the ability to place fiberglass or carbon fiber in optimal positions, orientations, and quantities. Drawbacks include the need to work with chemical products as well as low strength in material directions perpendicular to fiber. Composites provide superb strength to weight. Material stiffness dependant upon direction (as opposed to equal in all directions, as with metals) allows for advanced "elastic tailoring" of composite parts.

Examples of amateur craft made of composite materials include:

Canard designs such as the VariEze and Long EZ designed by Burt Rutan.
The Murphy Aircraft Renegade.
all Lancair designs
the MCR de Dyn'aero,a high-performance craft available in kit form.

External links

^* "Murphy Aircraft Mfg. Ltd. - Manufacturers of kit planes in the ultralight, experimental and sport-pilot categories."
Experimental Aircraft Association "EAA, the Experimental Aircraft Association, is a growing and diverse organization of members with a wide range of aviation interests and backgrounds."
Popular Flying Association "The Popular Flying Association is the representative body in the United Kingdom for amateur aircraft construction, recreational and sport flying."
Réseau du Sport de l'Air (In French) "Le Réseau du Sport de l'Air est la Fédération Nationale dédiée à la Construction et la Restauration d'aéronefs grandeur nature depuis 1947 (avions, planeurs, ulm, hélicoptères, ballons...)" ("The Air Enthusiasts Association is the national federation dedicated to the construction and restoration of heavier-than-air craft since 1947 (planes, gliders, ultra-lights, helicopters, balloons, ...)")
Igo Etrich Club The Igo Etrich Club was founded in 1987 by to provide a place for all Austrians interested in building aircraft. The association assists it members at the following tasks: own developments; building a copy using a plan; building a kit plane; restoration of an old plane or overhauling of an old-timer.
ExperCraft ExperCraft provides an oranized system for documenting and sharing homebuilt aircraft projects on the Internet. Visitors can browse and view projects under construction by builders all over the world.