Five days a week, Maynard L. Hill takes scraps of fiberboard, a discarded engine part or two and top-secret electronic gear and creates tiny, inexpensive spy planes that delight cost-conscious Defense Department brass.

On weekends, however, he takes the same kinds of materials--minus the radar and surveillance equipment, of course--and builds 11-pound wonders that set world aviation records on thimblefuls of gasoline.

Hill, 57, is a model airplane fanatic, a soft-spoken scientist whose professional life and hobby have merged into a lifelong passion for things that fly.

"Sometimes, I get the work and the hobby mixed up in my mind," Hill said during a stroll around the grounds of the Applied Physics Lab, the Johns Hopkins University facility where he designs lightweight warplanes for the Army and Marine Corps. "I suppose it's because I apply the one to the other--all the time."

On the Fourth of July, for instance, while most folks enjoyed the holiday with picnics and fireworks, Hill stood for nine hours and 17 minutes in a Montgomery County pasture to break a distance record set four years ago by his archrivals, a pair of Russian model plane enthusiasts.

Hill, of Silver Spring, flew a radio-controlled plane 765 kilometers (475 miles) to break the Soviet record of 749 kilometers. The flight nearly was canceled when a squall line moved through the staging area, forcing Hill gingerly to steer his 6-foot-long plane through 40-mph gusts.

The plane, which has a tough skin of orange plastic, survived the storm, burning less than half a gallon of unleaded gas to fly 1,530 times around two pylons spaced 500 meters apart. The flight, Hill's eighth attempt at the record, was witnessed by top officials from the Academy of Model Aeronautics, the Reston-based association that certifies record flights to a French body called the Federation Aeronautique Internationale.

"Some think we're too serious about model planes, but there's a lot of fun to it, too," said Hill, who has set 14 other world records for model airplane flights. His altitude record, made in 1970 in a glorious swoop to 27,000 feet, still stands.

"People like Maynard are mind-benders," said academy spokesman Geoffrey Styles, a close friend. "They're ingenious, of course, but then they stretch their talents as far as they can. It's hard to explain how oustanding it is to have set 15 world records."

The world records are pleasant, if somewhat ephemeral achievements, Hill said. They don't count, however, on those days when generals and colonels wait impatiently for him to build a better warplane.

"Many of the principles are the same with a model plane and one with a military purpose," said Hill, his voice accented by a boyhood spent in Pennsylvania Dutch country near Allentown. But, he added, "the applications of the two are different, totally.

"With the hobby, you make a plane, set a record. If it crashes, you rebuild. With this job, though, there is pressure to met certain requirements--battlefield conditions, budgets, deadlines."

Hill's creations for the military are not unlike those he flies in his spare time: lightweight, sturdy and inexpensive. But put a radar-jamming device or a camera in the nose of a radio-controlled plane and the drone becomes an airborne spy capable of fouling an enemy's early-warning system or tank radios.

In last year's combat with Syrian forces, the Israeli military used a drone to pinpoint troop movements on the ground. (Some Israeli officers had visited Hill at his laboratory.)

"We are bringing the price of these military planes down to the cost of a used Toyota--about $2,000," said Hill, pointing to a snub-nosed model painted olive drab and stenciled with Army insignia. "Just think of how many expensive missles it takes to shoot one of these little things down."

Hill's approach to the weapons of war and the flying toys of grown-ups are virtually the same: cool, precise, methodical. Yet he insists he lives for the weekends, for other shots at the record book.

"I want to break the cross-country record," he said, smiling at the prospect. "The current record is 265 miles, held by an American.

"I figure I can fly a plane from Hagerstown to Roanoke. You know, I could follow it in a convertible."