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The Future of Flight
Roland Piquepaille writes "With "High Times," the Economist delivers a very long and extremely well-documented article about the future of aviation during the next fifty years. It tells us about pilotless planes, with 32 countries currently developing more than 250 models of unmanned aerial vehicles (UAV), primarily for combat purposes. The article also looks at future civilian pilotless planes and at the future of personal aviation. But what captivated my attention in this article was the last part about future commercial supersonic and hypersonic (at least five times the speed of sound) planes. In particular, the Economist describes the HyperSoar. "The HyperSoar is a concept for a craft flying at ten times the speed of sound and able to reach any point on the globe within two hours." This overview contains more details and references about the HyperSoar which would fly from Los Angeles to New York in 35 minutes."
Remarkably bad math. Escape velocity is closer to Mach 25.
Oh, and flying upside down doesn't have a magical affect on whether or not you escape or not.
Eclipse Aviation of Albuquerque, New Mexico have produced a Air taxi capable of carring 5 people upto 1500 Km, but for this to be widely adopted 'free flight' must first exist. This allows piolts to plot there own jouneys, cutting distances and utlising more airspace. 'free flight' relies on each aircraft having it's own computer that allows aircraft to avoid each other. For more information see this weeks (13/12/03) New Scientist p28-33.
Before someone posts about how rockets are fuel-inefficient compared to other engines, I'd like to point out that it mostly depends on the cruise speed of the aircraft.
If the plane completes the flight in ten times less time than a conventional subsonic plane, then its engines are burning fuel for ten times less time as well.
Modern high-bypass turbofan engines have a specific fuel consumption (SFC) rate around 0.5 lb of fuel per lb of thrust per hour. Current liquid fuel rockets' SFC is around 10, and solid / hybrid rockets' SFC is around 5. But the concept of "pound of thrust" evolves with speed: for example, a reciprocating engine with a propeller will give you much more (approximately four times as much) pounds of thrust than the number of HP the engine develops, _at low speeds_. At 375 mph, you get one pound of thrust per HP. And beyond, you get much less. That's why high subsonic planes use turbofans and the slower planes still use propellers.
At supersonic speeds the fuel consumption per distance covered of a turbofan engine can grow as high as 3+, but that of a rocket engine does not grow with speed, so there's a given speed beyond which rockets are more efficient than turbofans.
Maybe we deserve this world ?
Airplanes are stable or unstable due to their roles.
Fighters are inherently unstable, to allow the radical combat sequences dictated by dogfighting. It's true some of the current fighters are unflyable without constant computer assisted tuning.
Large passenger jets ARE inherently stable. The use of computers to control the flight surfaces are dictated by demands for maximum fuel economy, which means constant re-adjustment of CG's, trim, and other parameters.
Nothing in their design prevents them from being flown on purely hydraulic controls in an emergency.
Actually, the energy cost for travel by flight is really no higher than for other transport methods. Consider a quick calculation:
A 747-400 has a range of about 8400 miles, and a fuel capacity of about 57,000 gallons. Multiply that by 410 seats, you get around 60 mpg per passenger. And Boeing's new 7E7 "Dreaminer" is touting much higher efficiency than any of their previous jets. Airbus is doing well too, with the new A380 and Rolls Royce Trent 900 engines. Fuel capacity of 82,000 gallons, range of 8000 miles, 555 seats. Thats around 55 mpg per passenger.
So those numbers are way better than the CAFE (Corporate Average Fuel Economy) standards in the US, currently 20.6 mpg I believe, not including the SUV's buzzing around the suburbs that aren't subject to those rules.
Hydrogen fuel cells would be great, but they're nowhere near production status for commercial transport flight.