Good Idea: Swept Wing [Redux]

Early planes had “straight” wings: they jut out perpendicular to the fuselage. They’re easy to build and generate lots of lift. And yet no jet plane uses them. Why not?

The Sound Barrier (or as nerds pronounce it, “compressibility”). Physics predicts that going faster takes more power (black line). But close to the speed of sound, the air molecules have no time to get out of the way. Going a little faster takes way more power than predicted.

The answer is to trick the wind by “sweeping” the wing and tilting it backwards. Before, the wing hit the air at the same speed as the plane. Tilted, it is off-angle to the air and has an effective speed of the plane speed times the cosine of the tilt. This lower speed allows the plane to fly faster than the speed of sound without hitting the sound barrier.

450 mph. Planes slower than that have straight wings. Faster and it will have swept wings. The faster the plane, the steeper the sweep.


[This is a revised version of an earlier post. Fewer words, more illustrations, with bad drawing. Comments requested.]

Awesome Shuttle Planes

Normal 747 w/Instagram filter "Shuttle"

The Space Shuttle was a boondoggle: it was doomed to failure by economics and engineering before it began. But like most boondoggles, it came with some really awesome toys. And two of them happen to be airplanes.

Airplane humor

Shuttle Carrier Aircraft

The Space Shuttle itself cannot fly. It can rocket straight up, but so can wingless 1970’s era space capsules. And it can glide. But the Wright Brothers’ first aircraft can fly more than the Space Shuttle. So, when the Shuttle lands in California, the only way to get it back to Florida is to hitchhike. On top of a 747. NASA bought 2 jumbo jets and added supports and stabilizers to create the capable-but-unimaginatively-named Shuttle Carrier Aircraft.

I'm a Space Shuttle! I'm a Space Shuttle!

Shuttle Training Aircraft

Oh, about the Space Shuttle not flying? When landing, the Space Shuttle is the world’s largest glider. Winds too strong? A normal airplane would circle another five minutes. The Space Shuttle is going to succumb to gravity. If you’re piloting, you’d really prefer to put those 100 tons of metal down on a runway. That takes training. More realistic training than a simulator can give you. The answer: the (again, very unimaginatively named) Shuttle Training Aircraft.

NASA took a Gulfstream II (the great great grandfather of the G6 of “Like a G6” fame) and made it pretend to be a Space Shuttle. This is like making a Miata that handles like an 18-wheeler. Or a canine Freaky Friday where a Chihuahua acts like a St. Bernard. This confused identity requires three tricks:

"If your side's so great, Buzz, where's the cupholder?"

• avionics (brains) that react slower to commands.
• a less aerodynamic plane. Simulating the Shuttle includes lowering flaps and landing gear even at 37,000 feet to slow the plane down. But even with everything deployed, a Gulfstream is still too much plane and not enough brick so the STA has to reverse thrust to be sufficiently slow. Standing on the brakes isn’t enough to make a Miata into a truck; it has to floor the gas in reverse, too.
• a Mullet of a cockpit: business (jet) on the right; party/Space Shuttle on the left.

The Space Shuttle doesn’t fly anymore and so neither will these affronts to aerodynamics. But we’ll always be able to remember, and laugh at, them.

Nifty Travel Tool: SeatGuru

You’re booking a trip and you get to seat selection. Which seat is best? Or, let’s be honest, is least bad? Is it worth paying $15 for the “Preferred Plus” seat?

http://seatguru.com has the answer. It turns out, there are a lot of things that can make a seat good or bad, and SeatGuru considers them all:

• legroom (more is better)
• in-seat power (and whether it’s normal AC or cigarette lighter DC)
• closer to front of plane (first to deplane)
• exit row (more legroom, but tray tables in armrests make them narrower and some don’t recline)
• proximity to galley and/or lavatory (flight attendants and passengers gather noisily)
• in-flight entertainment hardware that takes up space under the seat in front of you
• air-conditioning vents that can’t be adjusted over one seat on the airplane (why?)
• seat likely to be bumped by food cart
• extra storage space for window seats

You’ve certainly considered some of these. But do your future self a favor: don’t get stuck in a surprisingly bad seat.

Unfortunately, Airlines

Airplanes are Awesome. But Airlines are the only way to experience airplanes, and they are decidedly Less Awesome. Here’s my advice on how to survive in today’s age of baggage fees and delays.

There are two ways to pick a flight:

• Best (actually, Cheapest) Flight
• Best Airline

The first way is the easiest: you have a flight coming up, you put it into Kayak/Expedia/Travelocity (or Hipmunk, a new and better site) and pick the best (and by best you mean cheapest). Congratulations. You have saved $18. And had to learn a new airport terminal, paid a $25 bag fee, almost missed your flight, and got no frequent flier miles. In case I’m being too subtle, I don’t think this is a great option.

If you travel at all regularly (4 or more times a year), I recommend you pick an airline. You won’t fly this airline if it’s $500 more, but you will if it’s $5 more; if it’s $50 more you might go either way. And what do you get for this $5-50?

Frequent Flier Miles. For 25,000 miles, you can get a ticket that would cost $500. That’s 2 cents per mile, which means a New York-LA round trip (round-trip distance 4,950 miles) gets you $99 of frequent flier miles. But you can only redeem the miles if you earn enough. It’s worth paying $25 to get a free $74.

Frequent Flier Status. The more you fly an airline, the better they treat you. They don’t charge you bag fees, they let you through security faster, they throw extra miles at you. Sometimes, they’ll even put you in first class for free (or discounted). And, best of all, when the weather goes wonky or the plane needs maintenance, you’re first in line to get home. The threshold for this kind of treatment is lower than you might think. (And new credit cards offer many of these perks even if you only travel once a year.)

Familiarity. Maybe I’m making too big a deal of this, but I like the familiarity. You know how boarding works, you know which airport restaurant is the least greasy. On a trip that’s going to wear you out, I like knowing what to expect.

Next I’ll help you figure out with Airline is Best for You.

Every 50 Seats

You will never see a plane with 51 seats. Why? The FAA requires one flight attendant per 50 seats. That 51st seat can generate 2% more revenue (on a sold out flight) but requires 100% more flight attendant cost (on every flight). 52 seats offers 4% more revenue, 53 6% more. How many seats does it take to make enough money to justify a second flight attendant?

You’re looking at a histogram of number of planes with a number of seats. The horizontal axis is number of seats on a plane; the vertical axis the number of commercial planes in the US with that number of seats. I collected this data from Wikipedia (e.g., American Airlines Fleet) into a Google Spreadsheet. For instance: the “40” column goes up to 116. There are 116 planes with 31-40 seats. What does this graph (detailed, interactive version) tell us?

There are ten times as many planes with 41-50 seats (1112) as there are with 31-40 seats (116). Once you’re paying a flight attendant, you want to get your money’s worth.

There are no planes with 51-60 seats. In fact, the next plane has 64 seats. Without talking to accountants, we know it takes 14 seats of revenue to offset the cost of one flight attendant.

The same cliff happens at 100 seats and 150 seats. The effect weakens at 200 seats and beyond because of first and business class. Premium service requires more flight attendants, so the FAA requirements are less demanding than first class customers.

Popular planes make their own peaks. The 140 bump is due to Southwest’s 587 (!) identical 737-300s. The bump at 180 and 190 is the venerable 757 (it’s split over two values because different airlines put in different size first class cabins).

Ahead of its Time: the de Havilland Comet

The de Havilland Comet was the Neanderthal Icarus of jetliners. “Neanderthal” in that it came first, but rooted no family trees. “Icarus” because it flew too high and failed.

The Comet was the first jetliner. It first flew in 1949 and carried paying passengers in 1952. It looks modern enough (all-metal body, swept wings, pressurized cabin) but for the engines and the windows. It has 4 (instead of 2), small (instead of large) jets mounted inside the wings (instead of podded) and rectangular (instead of rounded) windows.

Those windows were the Achilles Heel of the wax of its Icaru-- Wait. Too many metaphors. More simply: you’ve never head of the Comet because it windows were critically flawed. Pressurization pushed each window out with a ton of pressure (16.6 inches wide * 14 inches high * 8.25 psi). The window’s glass held, but passed the weight to the metal frame unevenly: the square shape pushed much more at the corners. Like bending a paper clip back and forth, it fatigued the frame until even a small force could break the metal.

Two Comets blew apart in mid-air in 1954. Authorities blamed sabotage, until forensic evidence proved the planes failed in the same way. Very smart people figured out what I described above and De Havilland spent 4 years reengineering the Comet. On October 4th, 1958, a Comet operated the first London-New York passenger jet flight. The Comet’s monopoly didn’t last long: later that month, Pan Am flew the same route with the larger, faster, more efficient, better looking, more popular 707. The Comet’s biggest contribution to aviation is a stark reminder that, at 30,000 feet, little details matter.

Life of a Jetliner

A well-maintained Jetliner can last 30 or 40 years. What happens over the course of those decades?

Shiny and New (0-5 years)
Fresh off the assembly line, this plane has the latest technology. Today, this includes at-seat electrical power, in-flight WiFi, LED lighting, swivel bins, fancy seats. All the gadgets still work. The little touches combine to make an atmosphere: when you walk through the entrance, you look up and smile. This flight will be a little less dreary. Virgin America’s planes still have this shine on them.

Settling In (5-10 years)
Everything works. It... works. Your seat works. The in-flight-entertainment works, but it’s showing its age. The screen’s too small, the graphics too blocky. You’re happy to fly this plane, because it could be worse. Think JetBlue.

Journeyman (10-20 years)
No one claims this is still a new plane. But it’s cheaper to keep flying than to replace. The plane isn’t too old to learn new tricks: new seats inside so the airline can sell more tickets, winglets on the outside to improve efficiency, perhaps a new paint job to match the latest fashion. These overhauls fit well during a “D” maintenance check: every 5 years check the plane by taking it all the way apart and putting it back together.

Second career (20 years)
It may happen after 10 years, or after 30. But there comes a point that the first owner of a plane is done with it. In our next post, we’ll see what becomes of second-hand planes.