Every day, hundreds of jets fly over Columbia, Md., somewhere between 5,000 and 39,000 feet above the head of Sir Frank Whittle -- short, spry and 74 -- who half a century ago in his native England was granted the first patent for the jet engine.

Sir Frank did not come to Columbia in 1974 just because it happens to lie under one of the most heavily traveled jet corridors in the world. In fact, his move had nothing to do with hardware. "I fell in love with this woman," he says, gesturing to his wife.

Even as he makes his admission, Sir Frank and his World War II rival, Herr Dr. Hans von Ohain, are being beckoned over to a 9,155-pound Pratt & Whitney JT 9D turbofan jet engine that is suspended from the ceiling in room 106 at the National Air and Space Museum. This 4 1/2-ton hunk is one of the stars -- along with four actual aircraft -- of a new gallery devoted to jet aviation.It opens today, just in time to mark the museum's fifth anniversary.

The question at hand is a simple one: How do jet engines work? As fascinating as the gallery is, it doesn't quite explain why there are so many moving parts in this behemoth Pratt & Whitney number. A display in the gallery shows that an inflated balloon released into the air is the basic model of the jet, but. . .

"Yes, the balloon," says Sir Frank, "is a fair model, but the idea is as old as nature: the squid." And with this he uses his gnarled hands to mimic the action/reaction movement of the sea animal. "It's very simple, all based on Newton's third law: If you push air back then you push yourself forward."

"This is a three-stage jet," adds Herr Dr. von Ohain, now 69 and living in Dayton, Ohio, the home of the Wright brothers.

While Sir Frank was over in England trying to develop a jet for the Allies, von Ohain was furiously working at the Heinkel factory in Nazi Germany, coming up with an engine that would send the He 178 V1 screaming into the skies on Aug. 27, 1939, and thus begain the jet age that exacerbated aerial combat, created the DC10 and made commuter romance a part of everyday life. Now both of them are living in the land of deregulated airlines. Von Ohain retired from the U.S. Air Force in 1979 and now is associated with the University of Dayton Research Institute. Sir Frank is still an adviser with the U.S. Air Force Academy.

Anyway, back to the big jet engine, the type that fell off the DC10 in Chicago in 1979, but appears to be well fastened to the ceiling at Air and Space:

"The whole thing can't turn at the same speed . . .," says Sir Frank.

". . . or it would blow up," adds the Herr Doktor.

"So there are different stages. The air comes in the front and is heated i the combustion chamber in the middle. Hot air at a certain temperature has more energy than cold air. . ."

". . . But the pressure from the air just flowing in is too low for efficiency," interrupts von Ohain. "So you need all these turbines to speed it up. Some engines use gears.This one has two shafts, one inside the other, which isn't very good in my opinion. THIS IS JUST MY OPINION. They crucify you when you say these things sometimes. . ."

". . . You want higher and higher pressures," says Sir Frank.

"Sir Frank had four atmospheres [of pressure]," says von Ohain. "We had three. These have 30 or 40. Incredible."

Sir Frank's four atmospheres of pressure didn't get proven until May 15, 1941, when the Gloster E28/39 became the first Allied jet to leave the tarmac. Why so long after the Germans, when Sir Frank had enjoyed such a big head start, beginning with his 1928 RAF Flight Cadet science thesis on jet engines, and von Ohain hadn't arrived at Heinkel until 1936?

"It was amazingly quick, what we did," says the Herr Doktor, "so we must have had good spies. Yes, now I recall seeing your patent, but I didn't remember it being '30 -- maybe '32, I thought."

"No, published in '30," says Sir Frank. "But nobody believed it would work."

"UGH!" says von Ohain. "The English bureaucracy."

And did these prophets of the wild blue yonder profit?

"I'd settle for one cent per passenger mile," says Sir Frank, with a twinkle in his eye.

"At least he got to fly," says von Ohain. "And let me tell you, he was a juvenile delinquent in the air. The things he did with planes. Me, I knew how dangerous these jets were and wouldn't go near them. I'm only sorry we can't spend more time together, though. We live 600 miles apart."

600 MILES! In the JET AGE?

"It's very expensive to fly," says the Herr Doktor. "Inflation is terrible, and the two of us getting together is not considered a business expense."