The moment ancient man carved the first wheel from stone, he ignited an insatiable appetite for transportation, greater speed, more power, better economics and finer luxury.

But the road to effective engines has had its share of detours and dead ends. Many revolutionary concepts never quite lived up to their expectations. Were these ideas failures or just ahead of their time?

FLYING TEAPOTS

The Stanleys' steamer British inventor Thomas Savery introduced the world's first steam engine in 1698. By 1769, Joseph Cugnot had built the first stream-driven vehicle: a crude, cumbersome truck used to move cannons. With the promise of steam power, engineers in Germany, Denmark, Sweden, France and America worked feverishly to develop a more practical steam-driven vehicle. But the vehicles were heavy, slow and loud. In the 1890s, the Stanley brothers of America built a number of lightweight steam-powered automobiles known as the Flying Teapots. But their necessary startup time was two minutes, and the engine required a stop every 10 minutes to refill with water. The advent of gasoline internal combustion engines strangled further development of steam-powered automobiles. But the steam concept was revived in the 1970s by William Lear, an innovator and aviation magnate who spent a fortune attempting to develop a nonpolluting steam engine.

ONLY 768 POUNDS OF BATTERIES

William Morrison's electric auto It is believed that William Morrison built the first four-wheeled electric automobile in 1891. The vehicle used 24 storage batteries delivering 112 amps at 48 volts. Each battery weighed 32 pounds, for an overall battery weight of 768 pounds. Though the batteries provided an instant start, charging the system took more than 10 hours - all for a driving range of only 40 miles. By the 1890s, many manufacturers were producing electrically powered carriages, and by the turn of the century, electric vehicles accounted for nearly 40 percent of the market. Their instant mobility proved a serious advantage over the internal combustion engine, which had to be cranked in order to start. But the introduction of the electric starter in 1911 nipped that advantage. The final mass producer of the era, Detroit Electric, ceased operations in 1939. Electric vehicle technology returned with the oil crisis of the 1970s. Electric powertrains are emerging again, but they still have a restricted range of operation. Hybrid combustion and electric vehicles are proving more promising, and r&d work is under way at all major auto suppliers.

IT'S A CAR! IT'S A PLANE!

The Pitcairn AC-35 Although "The Jetsons" didn't arrive until 1962, engineers already were thinking about flying cars in 1935 when the U.S. Bureau of Commerce's Experimental Division Section awarded a contract to Autogiro Co. to build the Pitcairn AC-35. The AC-35 was equipped with a single propeller and rotor blades for flight. The gear could be folded back over the fuselage to accommodate ground movement. Two passengers could sit side by side, and there was a small baggage storage area behind the seats. For road use, the 90-hp engine was connected to the tail wheel by a shaft that was put in gear when the propeller was disengaged. The vehicle reached a top speed of 25 mph. Testing began in 1936 and continued until Skyway Engineering Co. obtained the exclusive rights to the C-35 in 1961. The company dissolved in the mid-1960s, and no other C-35s were ever built.

TOO GOOD TO BE TRUE

Turbine-powered Chryslers In the early 1950s, Chrysler Corp. turned its attention to turbine-powered automobiles. Chrysler engineers developed a rotating heat exchanger that recovered heat from exhaust gases and lowered running temperatures. The engine was tested successfully on a Plymouth Belvidere hardtop in 1957, and in 1962 Chrysler developed the CR2A turbine with a variable fuel nozzle mechanism for better engine braking. Turbine engines offered several advantages. They were simple in design and contained one-fifth the number of moving parts of a piston V-8. They weighed 25 percent to 50 percent less. They didn't require tuneups, burn oil, stall or need to warm up. But there were shortcomings. The cost of machining the components was high. It had poor fuel efficiency, and engine braking was difficult. Chrysler built 50 turbine automobiles in 1963 and field-tested them until 1966. Although the results showed that the turbines required little or no maintenance compared with piston engines, the high fuel consumption remained a problem.

DOWN WITH PISTONS

Felix Wankel's rotary Felix Wankel built the first running rotary engine, the DKM 54, in 1957. The first design had an inner rotating housing and rotor moving around a central shaft. Rotaries were smaller and lighter than their piston counterparts while still capable of delivering necessary horsepower and high rpms with turbinelike smoothness. But rotaries had problems. The original motors had to be disassembled to change the spark plugs. Early models had problems with combustion chamber sealing and poor emission performance. And their noncylindrical parts were difficult and expensive to mass-produce. General Motors heavily promoted the technology in 1973 but abruptly cancelled its testing program in 1974. Mazda continued to endorse rotary technology, but only the Mazda RX-7 continues to use the Wankel engine. Mazda plans to release a dual rotary RX-8 in 2003. Today the Wankel has new potential as a hydrogen-powered engine. Its design lends itself to use with hydrogen, which would virtually eliminate harmful emissions. Mazda is developing and testing hydrogen rotary engines.

EIGHT WASN'T ENOUGH

Cadillac's variable displacement In 1981 Cadillac introduced what appeared to be the ideal power source: a V-8-6-4 variable displacement engine. With power on demand, the engine ideally would run on eight, six or four cylinders to optimize fuel efficiency. In theory, it was genius. Making the concept work was a different matter. The cylinders shut off without a problem, but re-engagement proved disastrous. Cars stalled in the middle of freeways or while climbing steep hills. In the end, the only fix was to override the system completely, returning the engine to operation of all eight cylinders. Despite its failure, the concept is back. Variable displacement technology has seen a major resurgence among automakers. Since 2001, the Mercedes S600 comes equipped with Active Cylinder Control, which deactivates the left-hand bank of cylinders when peak power is not required.