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A propeller works by pushing off of the air. A jet works by exploding fuel. It's not clear how you'll get super-fast in thin air without the exploding fuel part

by Retra 8y ago

A propeller works by pushing off of the air. A jet works by exploding fuel. It's not clear how you'll get super-fast in thin air without the exploding fuel part?

Robotbeat 8y ago
That’s not true. You’re describing a rocket, not a turbofan or even a turbojet. Fundamentally, modern high bypass turbofans are just shrouded propellers. Could reach supersonic speeds in the same way using electric. Lift to drag is about half as good at low supersonic speeds as transonic, so cut your range in half, but fundamentally there’s no reason you can’t achieve supersonic electric flight. Just need good batteries to get that range...
- deleted 8y ago
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Johnny555 8y ago
I thought that most commercial jet engines derived most of their thrust from the turbo-fan pushing air through the engine, not direct thrust from the fuel combustion?
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RandallBrown 8y ago
Ion thrusters? Not sure if they're at all practical yet, but that seems like a decent solution, especially if you can ionize the air you're flying through.
- Zak 8y ago
  Air-breathing ion thrusters for aircraft are not at all practical yet. The first demonstration flight of a self-contained unmanned non-payload-carrying aircraft using one took place last year.
mpweiher 8y ago
Well actually...modern jet engines tend to be high-bypass turbofans, with the PW1000G geared turbofan achieving a bypass ratio of 12.5:1. In a turbofan, as the name suggests, the (vast) majority of thrust actually comes from the fan in front, and the turbine is really just used to turn the fan. That's what the bypass ratio means. https://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan https://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan
holoduke 8y ago
With one or multiple ductfans in a row you can create enormous pressure differences and thrust. Its less efficient than a regular propellor, at least at low altitudes

by Retra 8y ago

A propeller works by pushing off of the air. A jet works by exploding fuel. It's not clear how you'll get super-fast in thin air without the exploding fuel part?

Robotbeat 8y ago

That’s not true. You’re describing a rocket, not a turbofan or even a turbojet. Fundamentally, modern high bypass turbofans are just shrouded propellers. Could reach supersonic speeds in the same way using electric. Lift to drag is about half as good at low supersonic speeds as transonic, so cut your range in half, but fundamentally there’s no reason you can’t achieve supersonic electric flight. Just need good batteries to get that range...

deleted 8y ago
[deleted]

Johnny555 8y ago

I thought that most commercial jet engines derived most of their thrust from the turbo-fan pushing air through the engine, not direct thrust from the fuel combustion?

deleted 8y ago

[deleted]

RandallBrown 8y ago

Ion thrusters? Not sure if they're at all practical yet, but that seems like a decent solution, especially if you can ionize the air you're flying through.

Zak 8y ago
Air-breathing ion thrusters for aircraft are not at all practical yet. The first demonstration flight of a self-contained unmanned non-payload-carrying aircraft using one took place last year.

mpweiher 8y ago

Well actually...modern jet engines tend to be high-bypass turbofans, with the PW1000G geared turbofan achieving a bypass ratio of 12.5:1. In a turbofan, as the name suggests, the (vast) majority of thrust actually comes from the fan in front, and the turbine is really just used to turn the fan. That's what the bypass ratio means. https://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan https://en.wikipedia.org/wiki/Turbofan#High-bypass_turbofan

holoduke 8y ago

With one or multiple ductfans in a row you can create enormous pressure differences and thrust. Its less efficient than a regular propellor, at least at low altitudes