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None of the electric aircraft you mention will have performance approaching that of any commercial jetliner. Not in speed, range, and definitely not on cost. It

None of the electric aircraft you mention will have performance approaching that of any commercial jetliner. Not in speed, range, and definitely not on cost. It will be that way for a very long time due to the dismal energy density of batteries next to fossil fuels. You know how most powerplants generate power? Turbines, like these GE ones derived from their own jet engines: http://www.ge-energy.com/products_and_services/services/gas_turbines_power_generation_services/index.jsp http://www.ge-energy.com/products_and_services/services/gas_... . Higher altitude isn't everything for speed. You need to generate high-speed exhaust to produce thrust. A gas turbine compresses air and burns it so that explosively shoots out the back. How do you generate this electrically without combustion to raise the pressure? You can't just spin the turbine faster; the blade tips will go supersonic and efficiency will plummet, not to mention material stresses. Supersonic wind tunnels mechanically compress air into huge tanks, sometimes taking weeks to store enough pressure for minutes of runtime, but that obviously wouldn't work for aircraft. Jets already produce power efficiently (constantly running at nearly the same RPM, never idling in traffic) so there's much less incentive to create electric aircraft. The cost of energy from an electric aircraft in $/joule could be higher than that of a fueled one because you're introducing an additional energy conversion. Gas/coal -> turbine -> battery -> turbine versus gas -> turbine. You're also not getting the range benefit from burning off fuel and lightening the aircraft. You shift argument from "aircraft are too slow" to "aircraft are too inefficient," going electric won't fix either. There are applications for electric aircraft, mainly low-speed, long-endurance aircraft that can recharge from solar power without landing, and perhaps more maintainable private aircraft. These will not be challengers to the 0.85 mach 747 though.

caf 14y ago
A gas turbine compresses air and burns it so that explosively shoots out the back The high-bypass turbofans used on jet airliners produce most of their thrust by using shaft power to drive a fan that directly accelerates the air. Thrust from the engine exhaust itself contributes a smaller fraction. With electric ducted fans, presumably you would have a higher number of smaller-diameter fans. (That's not to say that I think that large electric passenger aircraft are going to be feasible anytime soon - I don't).
dredmorbius 14y ago
You don't need high-speed exhaust, and in fact there are good reasons (mostly noise abatement, but also efficiency improvements) to reduce exhaust speeds, which is precisely what turbofans and exhaust bypass systems on modern day commercial jets do (military planes don't, but they operate without noise controls and in a high-performance envelope in which efficiency is a secondary concern). What jets offer over propeller-driven aircraft isn't efficiency, but speed, and power-to-weight ratios. Propeller aircraft are limited by the tip speed of propellers (they have to be below the speed of sound), but are often much more efficient especially at lower flight speeds. In terms of efficiency, jet aviation has largely just managed to catch up to where propeller-driven aircraft were in the 1950s, when general-aviation jet aircraft first came into general use (barring a few failed Comets). I agree with you that electric aircraft are not particularly feasible, small drones excepted.

caf 14y ago

A gas turbine compresses air and burns it so that explosively shoots out the back The high-bypass turbofans used on jet airliners produce most of their thrust by using shaft power to drive a fan that directly accelerates the air. Thrust from the engine exhaust itself contributes a smaller fraction. With electric ducted fans, presumably you would have a higher number of smaller-diameter fans. (That's not to say that I think that large electric passenger aircraft are going to be feasible anytime soon - I don't).

dredmorbius 14y ago

You don't need high-speed exhaust, and in fact there are good reasons (mostly noise abatement, but also efficiency improvements) to reduce exhaust speeds, which is precisely what turbofans and exhaust bypass systems on modern day commercial jets do (military planes don't, but they operate without noise controls and in a high-performance envelope in which efficiency is a secondary concern). What jets offer over propeller-driven aircraft isn't efficiency, but speed, and power-to-weight ratios. Propeller aircraft are limited by the tip speed of propellers (they have to be below the speed of sound), but are often much more efficient especially at lower flight speeds. In terms of efficiency, jet aviation has largely just managed to catch up to where propeller-driven aircraft were in the 1950s, when general-aviation jet aircraft first came into general use (barring a few failed Comets). I agree with you that electric aircraft are not particularly feasible, small drones excepted.