"Is this thing real or not?" strangers ask when they see Bob Woodall preparing for departure at College Park Airport. His takeoff convinces them the sleek, sophisticated beauty he flies is indeed real.

What they don't know: He made it himself.

When Woodall, 59, saw the first of its kind, an eye-catcher of a plane called the VariEze, "I walked past this full-size, white plastic model that charmed and intrigued me." That was in 1974 and the plane had just emerged from the design table of California aeronautical engineer Burt Rutan, often credited with today's revolution in home-built airplanes.

The Experimental Aircraft Association (EAA) estimates that there are more than 18,000 home-built aircraft flying regularly and perhaps another 18,000-20,000 under construction.

EAA spokesman Henry Ogrodzinski says kit-airplane construction "is on the upswing." Builders range from blue-collar workers to bank presidents to housewives, from their twenties to senior citizens. "Some people don't even build them to fly, they do it just for the fun of it."

The assorted lot shares more than their love of flying. Their strong desire to build transforms this loner's avocation into a team effort. It's a club that many join, but few exit flying.

"The economy has priced a lot of people out of general aviation," says Ogrodzinski, so they are turning to the home-builts, ranging in price from around $5,000 to $40,000 and up. The Christen Eagle (designed by Californian Frank L. Christensen), $46,000, is usually considered the "Cadillac of home-builts."

Woodall, an aeronautical engineer, admired the VariEze's configuration--the unusual "canard" design--with the shortest wings in front, longest in back, propeller in the rear. The VariEze was given that name because Rutan, 39, considers it "very easy"; other builders suggest that it be renamed something like "moderately difficult."

Woodall was smitten. He ordered the 234-page "Manufacturer Manual" ($175) for the Styrofoam-and-plexiglass two-seater. "The plans were so complete that Rutan used to joke in his seminars that he tells you everything, including when to take a break, because if you don't you may not get another chance for two hours."

Three years, $12,000 and a lot of "sweat equity" later, Woodall, of Adelphi, Md., is flying around in a 170-mile-per-hour, home-built plane that gets 30-35 m.p.g. (A four-passenger Cessna 172 flies at 128 m.p.h. and gets 17.5 m.p.g.)

"Building an airplane," Woodall claims, "is no harder than building a house. The average person who is a moderately skilled home mechanic would have no trouble."

Says EAA's Ogrodzinski, "A modern version kit-airplane built by an average American will beat any commercially built aircraft as far as comfort, speed and efficiency." FAA certification of new commercial designs, he notes, can take "a raft of paperwork, legions of lawyers, millions of dollars and years of effort."

Woodall stresses that you can't build the aircraft alone: "Roughly 90 percent can be built by yourself. For approximately 10 percent you need others." Home-built aircraft by law must be more than 50 percent constructed by owners. It takes a solo license to fly one and a private license to take up nonpaying passengers. Paying passengers are not allowed.

At 21, George Newbery, Bethesda, is perhaps the youngest builder in the area. He began his single-seater, the Quickie, while a senior in high school and now is about six months away from completion. The project, he says, has helped him define interests before selecting a college major. He's now considering engineering.

His Quickie, another Rutan design, arrives in a basic-materials kit with the basic cost, $4,500 for a single-seater, paid in advance.

Newbery's two-car garage is neatly arranged with most of the necessary tools--scales, knife, buckets, hacksaw, scissors--basic in many households. A hot-wire saw--used during the initial stages to shape the wings from Styrofoam blocks--might be the exception. The process of "sandwiching" the Styrofoam, fiberglass and epoxy gives these planes the nickname "sandwich composites" or "composites."

"The day I fly my plane," says Newbery, "will be the happiest day of my life." He will soon "mate" the wings to the fuselage, but first his plane must be inspected.

"Home-built airplanes are classified as experimental aircraft," says FAA air worthiness inspector Bill O'Brien.

"There are a minimum of two inspections: the 'pre-cover' and the 'pre-flight,' which is very, very thorough." The term "pre-cover" is a holdover from the days when home-builts were fabric-covered; today's planes are inspected before painting since the translucent epoxy exposes the structure.

To expedite inspection of the 300-plus home-builts under construction in the Northern Virginia and Maryland area, O'Brien recommends that current and potential builders join local EAA chapters. "From my experience, they are very generous as far as giving help."

Informal advisers in local EAA chapters, such as Fred Wimberly, are called "designee inspectors." An experienced private pilot in his mid-forties, Wimberly completed his VariEze in 1980.

"This plane," he emphasizes, "isn't for beginners. It's a fast-landing plane and therefore not very forgiving. Also each plane flies a little bit differently and without a copilot there's no room for error." The passenger sits directly behind the pilot.

The completion of a home-built is a significant accomplishment, as O'Brien points out: "Only 8 out of 10 people who begin them ever finish."

Meanwhile, there are devotees like designer David Smith, 47, of Harford County, Md., who has built five planes: "This plane," he sighs, "is my last. That's what I promised my wife under forfeiture of my life."

The popularity of the EAA's 30th annual fly-in last year is perhaps the best testimony to the growing kit-airplane movement. More than 750,000 participants and spectators in more than 14,000 aircraft made it the biggest aviation event in the world, 10 times larger than the famous Paris Air Show.

During its eight-day run, Wittman Field in Oshkosh, Wis., was four times busier than Chicago's O'Hare Airport.