A car propelled by a turbine air jet has acceptable efficiency?

Question

So, I know that there are vehicles that use gas turbines as their engines, but they are connected to the wheels. What I'm asking is that if a turbine with reasonable size (small enough to fit in a car without taking its majority of space) could propel a normal car (something like a Ferrari) with only the air jet coming out of it.

The only type of car I could find that uses such a system are vehicles that are used to break speed records, and they can't make curves nor travel over irregular terrain.

I know that if it was that simple, there would be a lot more jet powered vehicles. But I can't stop but wonder which benefits such vehicle could have.

I could only think about the M35 Mako from Mass Effect, which uses its jet air propulsion to climb mountains.

Answer 1

Could be done

But there's a lot of reasons why it would be a bad idea, at least for commuter city traffic.

• jet exhaust would pose a hazard to anything behind the vehicle, like pedestrians and other vehicles, nearby buildings.. etc
• loud -- obnoxiously so. Would require hearing protection both for the pilot and anyone nearby
• unless the thrust : weight ratio was high then it would be cumbersome going from 0 to say 60mph, which describes most commuter traffic.
• the engine controller / throttle would have to be governed such that the car's top speed is limited to say, an aircraft at high taxi speed (~120 knots). Otherwise it will stop being a ground vehicle and achieve fixed-wing flight just with the lift generated by its body shape.
• would need a significant amount of road to come to a stop. At high speed a caliper style brake on the wheels will not stop that vehicle in time. It will just pop the wheels. You'd need airbrake surfaces (which might clip nearby cars / pedestrians, bikes..), maybe even a thrust inverter from the jet engine to stop it.
• so much more complex and expensive. This engine will also need an accessory section: hydraulic pump and generator. And if you want it to be able to start itself without external support equipment, it will need an APU (think smaller, second engine).
• if FOD gets into the air intake, it will get chewed up by the compressor sections, shattering them and sending deadly pieces of sharp, flying metal in all directions. So placement of the air intake matters. If it's close to the pavement, as most air manifolds are, it is likely to suck up any loose crud on the road -- from pebbles to soda cans. Blam, there goes a $1,000,000 engine.

Answer 2

Well, a car only propelled by the jet stream of air it would not be that effective on a day to day basis..

But I you come to use the jet stream to spin an electrical generator or some fanblades that in some way could transfert the rotation movement to the wheels, you have an altenative to the good old piston engine.

This way allows you to even re-use the heat produced by the jet engine to aliment itself, in a "turbo-ish" way, and direct the exaust gases to no be harmfull to pedestrian or the car behind. Pointing it upward could even give you downforce required at high speeds.

The biggest negatives points would be the engine noise, vibrations and heat. Also, the air intake would create a huge vacuum effect, and you also should prevent anything, from dust to small things suchpaper trash or pigeons to by sucked by, if you don't want the engine to blow up.

And yeah, good old Mako rocks !