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i was wondering abt the eficiency of commercial jets when it occured to me that it is not at all efficient

now i m under the notion that commercial flying is a waste

i checked up the internet and found out abt various projects that combine maglev tech with turbo propulsion

e.g. Aerotrains

Since maglev tech is at such advanced stage that an addition of a turbojet is really possible

i checked up and found that all the projects that tried to use this fusion of tech failed either because of lack of funding or were just destroyed for no reason

Since none of the commercial jets are traveling faster than mach 1 except for the concorde which has also been scrapped

trains can or at least match to the speeds of commercial jets without flying at 30000 ft and probably safer that air travel and maybe more efficient due the high density air present at ground level

So i was hoping to have a paper presentation on this topic

Please if someone could enlighten me on this subject

I am doing Aero engineering in india

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A couple of thoughts, I am by no means qualified to specifically answer your questions.

 

Doesn't denser air also mean more friction, and therefore less efficiency?

 

I think, at least with the Concord, the reason that commercial jets are not typically designed to travel at supersonic speeds have a lot to do with noise pollution from sonic booms over populated areas. The Concord was profitable because it could fly the majority of its route over the Atlantic, with only short periods of subsonic flight over populated areas. If a jet designed to fly at supersonic speeds is required to fly slower over populated areas, and a significant portion of its flight path is over populated areas, then it will waste tremendous amounts of fuel at the less efficient subsonic speeds. I remember reading long ago in Popular Mechanics (?) about some really innovative airframe designs that were supposed to minimize the noise, but I don't know that anything ever came of it.

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i was wondering abt the eficiency of commercial jets when it occured to me that it is not at all efficient

now i m under the notion that commercial flying is a waste

Given their high speed and ability to cross oceans, large jet aircraft are surprising efficient. A Boeing 747-400 has a payload-distance to energy of about 0.087 kg m/J. This is comparable to the most energy efficient passenger cars, such as that of a Toyota Prius with two passengers, which is about 0.086 kg m/J.

 

The payload-distance to energy of the most popular commercial maglev train, the German-designed Transrapid, is strongly dependent on the number of cars in its train. For its usual 3 car train, it’s about 1.4 kg m/J. This is about 16 times that of a 747.

 

The most efficient modern low-speed freight trains have payload-distance to energies of about 5.2 kg m/J.

 

My source data for the above are all from wikipedia. I made these calculations quickly, so please make them on your own to confirm my results.

 

i checked up the internet and found out abt various projects that combine maglev tech with turbo propulsion

e.g. Aerotrains

I don’t think “aerotrain” is a good name for a jet or propeller driven maglev train, because it’s referred to a lightweight wheeled American train, the GM Aerotrain, and a French-designed prototype track-guided hovercraft, the Bertin Aérotrain.

 

I’d like to see your internet sources on jet or propeller driven maglev train, Devayan, as I’ve long followed maglev trains.

 

The only proposal for such a system of which I’m aware involves a favorite of mine, the Inductrack system. This system is unique in not requiring external power in its tracks, only passive loops of conducting material, such as inexpensive aluminum, and unpowered permanent magnets in the cars, converting a small fraction of the cars’ driving force into levitating force by inducing a current and magnetic field in the track with its moving permanent magnets. This is potentially a great advantage in regions where electric power is expensive to obtain, such as the American Midwest, as the system can potentially be built on existing tracks for less than the cost of improving the existing rails for conventional high speed (150-200 km/h) trains, such as Amtrak’s Acela.

 

trains can or at least match to the speeds of commercial jets without flying at 30000 ft and probably safer that air travel and maybe more efficient due the high density air present at ground level

According to the wikipedia article Maglev (transport), the speed record for a maglev train is 581 km/h, much slower than the 912 km/h cruising, 988 km/h maximum speed of a 747. The most popular commercial maglev train, the German-designed Transrapid, is normally operated at 400 km/h, with an engineered top speed of 500.

 

In short, I agree that maglev trains, especially the Inductrack sytem, are a promising and underdeveloped technology. Replacing present day air travel with high-speed rail is challenging, however, because of

  • High initial cost – you can fly a regular route between practically any two places on Earth for the startup cost of a couple of runways and an airplane – about US$300,000,000. High speed rail costs about $1,000,000/km, not including the cost of the trains. Maglev systems built to date (which don’t include Inductrack) increase the cost per track distance by about $100,000,000/km.
  • Geographic limitations – Airplanes can connect nearly any two places on Earth. For all practical purposes, rail can’t cross oceans, and can only cross mountainous terrain at many times its usual const of construction – the English Channel railroad tunnel, for example, cost about US$100,000,000/km, 100 times the usual cost.

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Thanks for the updates

well JMJONES denser air means more mass flow rate which is the driving force for any jet engine i agree drag will be more but the thrust produced is also proportional to it i think i ll have have to do more calculations on that and get back to you

 

As far as the speed is concerned i suppose once the jet engine are put we can catch upto the commercial jets

connecting places around the globe was not my point

i live in a country where electric lines cannot reach to all places and trains travel at 140 kmph

probably domestic travel is my target .In India for a 45 min flight one has to waste atleast 3 hrs which is a lot

But i see your point with the expenses which makes this project a theoritical one kind of useless

So i suppose the future lays in vactrains for high speed travel

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