"It remains a fundamental aerodynamic axiom, by the way, that a plane will not stay in the air without its tail." That's a line that appeared in this space on Nov. 19, and that, as these things go, wrought a flurry of protests.
"I have several things I would like to point out relative to this statement," says Steve Willie, writing from Olympia, Wash. Letters beginning like this have a way of putting me quickly to sleep, the subtleties of aerodynamic theory not being among the topics that get my turbines turning.
"Several recent aircraft designs," writes Willie, "don't have a tail." He cites so-called flying-wing concepts like that of the B-2 bomber and the tailless X-45, an unmanned combat air vehicle, or UCAV. Several of the Wright brothers' experimental prototypes also were built without tails.
The key being, they weren't supposed to have them. What got this discussion running was the crash of American Airlines Flight 587, an Airbus A300 that parted company with its tail after a crew member overreacted to a wake turbulence encounter. The blueprints of a B-2 or a Wright brothers box kite from 1902 simply don't necessitate a vertical stabilizer. (That's the more technical term for tail, and I'll be using the terms interchangeably from this point.) The A300, like virtually every modern airliner, is a different story, and should that stabilizer be abruptly separated from the rest of the plane, well, my initial statement stands.
But wait a minute, and hang on tight ...
"Any aircraft with digital flight controls, including large commercial airliners, can theoretically be programmed to fly without a vertical stabilizer. I cannot guarantee that existing onboard computers would be sufficiently powerful to make the necessary control corrections, but recent simulations suggest that differential thrust could provide any missing directional stability. The plane cannot be allowed to bank, because any non-symmetric aileron input will result in uncontrollable adverse yaw, which needs rudder input and cannot be corrected quickly enough by differential thrust."
That's Willie talking again. I have no idea if this is true, or even what he's saying, exactly, except to know that it can't possibly apply to an airliner's day-to-day operations. In the interest of saving coffee, I won't be looking into it.
I should have learned my lesson. In one of the very first Ask the Pilot question-and-answer sessions, a seemingly straightforward illumination of how a plane gets off the ground brought forth a veritable pounding of wait-a-minutes from annoyed readers. My explanation, so went the dissenting letters, was overly bogged down in the principles of Daniel Bernoulli, the 18th century Swiss mathematician whose experiments with velocity and pressure form a staple of Aviation 101: high pressure beneath a wing, low pressure above. (See Chapter 1 of my book -- that's the boring chapter -- for a slightly more nuanced look at this.)
But while the laws of Bernoulli are not in dispute, theirs is only half the story. Or more, or less, depending whom you ask and how much they happen to care. "Bernoulli is so old school," countered one flight instructor. The simple matter of deflection, he and others insist -- the act of an airfoil pushing against the oncoming current of air -- is the more "true" reason a plane stays aloft. If nothing else this is more intuitively graspable, easily demonstrated by angling your hand out the window of a speeding car, your arm held aloft by an ample molecular cushion.
It's amusing, charming, romantic -- and possibly embarrassing -- that the very premise of lift, the most basic kernel of flight itself, is debatable in 2004. "But either way," I once wrote, "it's all in the wing."
Wrong again. When I dared state the implausibility of an airplane flying with a missing wing, I was promptly sent a photo of an Israeli Air Force F-15 fighter that managed a safe touchdown after its entire right wing had been torn away during a combat exercise. McDonnell Douglas, maker of the F-15, dispatched a team of engineers to have a look at the miracle plane and concluded that the jet's wide, flat body and powerful rudders were able to provide just enough control to allow the survivable emergency landing. Difficult enough for an F-15, and -- here we go -- a full 100 percent impossible when applied to your civilian passenger plane.
For ease in sorting my mail, please include the word "bullshit" in your subject line.
Truth be told, nearly anything from a Frisbee to a cannonball can be hurled through the air, often with a surprising degree of grace. Arcing across the sky and flying, however, are, different things, the latter implying an aircraft's ability to maneuver and remain aloft on more or less its own terms. In accomplishing this, we're accustomed to a traditional layout -- the tubular fuselage, the rear stabilizers and the cantilever wing. Our image of the airplane is thus universally conventional, identically replicated by every 5-year-old's doodlings or the rote memory of folding a paper airplane. Yet wild variations on this orthodoxy are not only possible but proven.
Already mentioned is the B-2, essentially a modernized version of some decades-old "flying wing" prototypes. We have the airplane and airfoil as a single, integrated unit. Short of a dearth of window seats, there is nothing inherent to this shape that outright precludes a commercial adaptation. It ain't for lack of imagination that we don't have one. Engineers have submitted passenger-carrying proposals. Making it impractical are eight decades of entrenched civil aviation mindset and infrastructure.
A variant of the flying wing is the "lifting body," employing a more blended wing and fuselage. Look carefully and shades of these applications can be noticed in existing civilian models. The Shorts 330 and 360, a pair of commuter turboprops built in Northern Ireland, borrow from the lifting-body concept to aid their stubby wings. Note also how the 330 uses a twin-tail design, seen from time to time and prompting a question for Willie: Will a Shorts 330 remain airborne if one of its two tails falls off?
If you haven't noticed thus far, appreciating some of flight's more exotic potentials dictates a journey past Ask the Pilot's carefully monitored DMZ. Combat aviation is generally off-limits in this space, but I'm allowing a temporary excursion.
For the record, my general infatuation with airplanes has included one or two from the armed forces realm. My favorites as a kid, replicated in scale from the boxes of Revell and Monogram, were the McDonnell Douglas F-4 Phantom and the Boeing B-52 bomber. The Phantom, a staple of the Vietnam War and one of the sexiest planes ever made, is a rare breed nowadays, but the eight-engine B-52, itself a 48-year-old design, continues to pull its weight over Afghanistan and the Middle East. A B-52 was the star of Stanley Kubrick's "Dr. Strangelove" (1964), if that helps you to picture one.
(Getting back to the B-2 for a moment: Is it just me, or does this plane look like it just flew out of the pages of Revelation? Am I the only one creeped out? Only the F-117, perhaps, is more fiendishly apocalyptic.)
Aviation, like many other industries, is rich with civilian-military crossovers. The 747 was originally conceived as a military transport; early Soviet passenger liners descended from bombers. Perhaps more intriguingly, it can work the other way too: The U.S. Air Force's KC-10 refueler is an adaptation of the civilian DC-10. The 767 is also in line to become a refueling platform. Lockheed's P-3 Orion, more than 200 of which are still used by the U.S. Navy, emerged from the L-188 Electra. The Brits turned their Comet and VC10 into a maritime patrol vessel and tanker respectively, while Boeing just announced that its 737 will become a naval patrol bomber.
And so on.
It remains to be seen how radically different commercial airliners of the next century will look. And be forewarned that pleasant aesthetics and efficient aerodynamics are at times mutually exclusive. Those who've seen renderings of Boeing's upcoming 7E7 Dreamliner will note its eccentric, to put it politely, appearance. It has "a forehead like a porpoise," one wag put it. Consider also the cartoonish blended winglets of the 737-800.
Then again, the A380, the new Airbus behemoth preparing for debut in 2006, is pretty damn unattractive -- and conventional.
Just how revolutionary can we get? Well, have a look at this, and be certain to watch the videos, which I assure you are not fakes.
Great fun, but deserving of a disclaimer. Is there really such a thing as a flying lawn mower? Sure, so long as it's not really a lawn mower. Look closely and you'll discover a lightweight airfoil body and a "handle" that acts as a vertical and horizontal stabilizer. The entire machine is carefully balanced and arranged -- if not elegantly so -- to fly. Though only a toy, it's an aircraft, not a mower. Rigging a propeller to your John Deere will not have the same results and is liable to hurt somebody.
"Air does not yield to style," an aircraft designer once said. What it does yield to, as we can see, depends mostly on our imagination.
Icarus had it all wrong, but others, maybe, were on the better track. It's without irony that for years the logo for All Nippon Airways depicted Leonardo da Vinci's 16th century "helicopter" design -- a corkscrewing flying machine that, while an impressive statement of the artist's vision and intellect, could never get off the ground.
Or could it?
It's best I remain clear of certain blanket statements from this point on. Can a lawn mower fly? Can a plane stay in the air without wings or a tail? I'm keeping my mouth shut, lest I crank up the mental wind tunnels of all the aerodynamic free thinkers out there.
- - - - - - - - - - - -
Do you have questions for Salon's aviation expert? Send them to AskThePilot and look for answers in a future column.
Shares