An article in a left-leaning magazine ran a piece about a radical idea for airports. Building a new airport at the top of an incline, the article said, could save huge amounts of fuel because planes would be going downhill for takeoff, and uphill for landing.

Having once authored some music reviews for Utne -- oops, now you know -- I'm loath to bash their reportage. Plus the reviews were shitty (god, what I did to the Jazz Butcher's "Illuminate"!), so I owe them.

This is a tantalizing concept, but easier said than done. For one, planes normally take off and land in the same direction (into the wind, if possible), not head-on. You can't be upsloping and downsloping at the same time on the same strip without a conflict, so you'd have to have at least a pair of runways.

Further, planes need enough runway not just to reach takeoff speed, but to stop if a takeoff is aborted at high speed. Stopping along a downsloping surface commands more energy and distance than along a flat one. As you might recall from a few columns ago, existing runways with gently graded surfaces mandate slight penalties. With an overtly steep grade, a runway would need to be longer, probably much longer, to avoid incurring prohibitive weight sanctions. And no, one of those mountain-style turnoffs like those used for out-of-control trucks would not be helpful.

You're talking all sorts of revisions and asterisks to standard techniques that would, in the end, offset the benefits. Asking around, I was told the U.S. Air Force experimented with this concept back in the 1950s at Wright-Patterson Air Force Base near Dayton, Ohio. Seeing that the experimental runway has been used for the annual soapbox derby since then leads us to believe the idea was deemed impractical. Fuel savings, at any rate, would be minimal. A medium-size plane might use about 150 gallons more for your average non-slanted departure.

I used to know a guy -- he fixed furnaces for a living and thought he knew about "mechanics and stuff." It was his belief that the reason dragsters and hot-rod cars had big tires in the back was for better mileage, that the car's rear was higher and it would always "think" it was going downhill. He was a nice guy, so I never told him what an idiot he was. Now, if we could just put bigger tires on the main landing gear and small tires on the nose gear, the airplane would think it was taking off downhill all the time and save thousands of gallons of jet fuel.

Why do planes take off and land into the wind?

To understand this, recall how a plane stays in the air and imagine there's a 20-knot headwind pointing down a particular runway. Well, if a plane's intended takeoff or landing speed is 120 knots, then 20 of those knots are already taken care of.

For the sake of argument, imagine there's a hurricane blowing at 200 knots and you tow a 757 from the hangar and turn it toward the storm. Theoretically, the plane would lift off and "fly" just as would on the way to Denver. What would the cockpit airspeed gauges read? Two hundred knots. The plane does not care how fast, or in what direction, it is moving across the ground, only how fast it is moving through the air. That is the difference between airspeed and groundspeed, and by extension, yes, a plane can fly "backwards." Up in a two-seat Cessna you can point your nose into a strong wind, slow the machine to as little an airspeed as possible, and sure enough you might find yourself drifting backwards like a kite, relative to the ground.

What happens if the wind suddenly stops or changes direction? That's windshear. Winds are always gusty and whipping around, but in extreme cases a shear can be dangerous.

Some airports are laid out with local climates in mind, and flights will try to take advantage of prevailing winds. For reasons of traffic management or to avoid noisy overflights of neighborhoods, this isn't always possible, and then you're stuck with a crosswind or tailwind. Tailwinds are beneficial when cruising along at high altitudes, but they're not much fun when taking off or landing. Tailwinds are irrelevant to airspeed, but will increase groundspeed. Racing down a runway, a plane will be pushed along, using up valuable runway while its actual "speed" is unaffected. Maximum allowable tailwinds for takeoff or landing are very low for most planes, around 10 knots or so.

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