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Flight is awesome. There is no rolling friction with flight,
just air friction.
The only problem with flight, is that you are so high in
the air, you can’t touch the ground and push yourself
forward. And so you are stuck with pushing air
backwards, to make yourself go forward with a propeller
or jet engine.
So what if you could combine the advantages of a train
and a plane? What if you could use wings to reduce
rolling friction between the train and the tracks,
between the bearings, and gears of the train? You have
wings, but you stay on the ground so you can push
against a solid surface (the earth), instead of trying to
push against air.
I think the best way to explain my idea is a thought
experiment. Let us say you load a train and a plane with
250 tons of cargo in Las Angeles. Then you have the
train drive its cargo to New York. The plane flies its
cargo to New York. Which method will use the least
amount of gas? I don’t care. What I’m interested in is
the return flight.
You load the train and the plane with 250 tons of cargo
again. Then you put Evil Kanevial Jr in the cockpit of the
plane, and tell him he is not allowed to turn on the
engine, but he is allowed to move the Ailerons to keep
the plane from crashing. Then you tie a cable from the
train to the plane. You pull the plane (with 250 tons of
cargo) in the train (with 250) tons of cargo back to Las
Angeles.
My question is this: which trip took the most amount of
gas. If I am right, the return flight would have taken less
gas, because it combines the advantages of lift, with the
advantage of pushing against the ground to move
yourself forward, in a train, instead of having to push
against air, in a plane, to move yourself forward.
My idea is to save Evil Kanevial a lot of stress, and
design a train with wings, recreating, in essence, the
thought experiment explained in the trip from New York
back to Las Angeles. However, when planes fly near the
ground, or near the water, the lift is improved, because
the air is compressed against the ground or water,
producing even more lift.
My idea would have the wings producing more than 250
tons of lift (the weight of the plane and the cargo), so
the track, gears, and bearings only see 250 tons of
weight.
Maglev
http://en.wikipedia.org/wiki/Maglev_train
[swimswim, Jun 28 2009]
Ground effect train
http://en.wikipedia...Ground_effect_train
Baked it seems [Twizz, Jun 29 2009]
Working prototype
http://www.ifs.toho...rain_outline-e.html
Baked as a bean. [Twizz, Jun 30 2009]
Laur monorail airplane
http://upload.wikim...f/Laur_monorail.jpg
"Is it practical? Maybe and maybe not." [jutta, Jan 14 2014]
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So, the question is, how much energy is expended in
overcoming rolling resistance? My guess is that it amounts to
less than 2% of the total energy expended by a heavily-laden
train over a long distance. And advance on
that? |
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Would this be cheaper than a maglev train? Using the cost-benefit analysis of which you spake. |
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Won't work. Period. The energy required to lift the weight will be greater than any energy saved in friction reduction, because wings are inefficient producers of lift - turbulence and drag as a side-effect.
The mass of the train is unchanged, even if it were carried on a wing, so no energy savings on acceleration either. |
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re: "The mass of the train is unchanged, even if it
were carried on a wing, so no energy savings on
acceleration either." |
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No one said the mass would somehow be changed.
Gravity pulls the train down putting stress in the
gears, on the track, in the wheels, and in the
bearings. The wings would produce lift. Gravity
pulling down. The lift pulling up. The same mass,
but the train track would feel less weight, because
the lift, lifts a portion of the weight upward. |
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re: "Won't work. Period. The energy required to
lift the weight will be greater than any energy
saved in friction reduction, because wings are
inefficient producers of lift - turbulence and drag
as a side-effect" |
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Its my idea, and I only give it a 2% chance of
working, but I think you are a little strong when
you say: "Won't work. Period." I think I would like
to see some calculations from someone before we
say that we are SURE. Lets just agree that it
probably won't work, but I think it would be cool if
it did. |
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This is my argument: If wings are "inefficient
producers of lift", who do we fly planes? |
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Wings are efficient producers of lift. And lift is so
cool, because it overcomes the problems of rolling
friction. Wings are such great producers of lift,
and do such a great job of overcoming rolling
friction, that we put up with crappy forward
thrust producers on plans, like propellers and jet
engines. |
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Propellers and jet engines are crappy producers of
forward thrust, or else we would use them on
trains. Wings are excellent producers of lift, or
else we would all just drive trains everywhere. If
we can use planes to overcome 1/2 of the rolling
friction, by putting wings on trains, we could have
the best of both worlds: reduced rolling friction
(that is proportional to the weight being carried),
and great forward thrust production from standard
train mechanisms. |
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Do a though experiment. Imagine a train pulling a
747 by a long cable from Las Angeles to New York.
The train and 747 both carry the same cargo, lets
say they each carry 250 tons (the pilot does not
turn the jet engine on, but moves the wings to
keep the plane from crashing). I believe the gas
used by the train pulling the 747 would be less
than if the plane flew itself, and the train drove
itself. If so, than that proves my idea is a good
one. Because you could use the same
mass of the plane and train, but have a bigger
train with wings, throw away the extra parts, have
the same thing as a train pulling a 747... |
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Minor problem. 747 efficient cruising speed, mach .8 or
~850 kph. Take off speed of the same 747 ~290 kph. Best
high speed train to date ~220kph.
Admittedly the absolute minimum needed for a loaded 747
to take off appears to be down around 188 kph, but only
under ideal conditions. As such, you are going to have a
hard time getting this train to provide enough lift.
Oh, and as to why we fly things, its because its fast, not
because its efficient. A train, on flat ground, at a constant
speed, is by far the most fuel efficient transport mechanism ever devised (with the possible exception of a
bicycle under the same conditions). |
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I'm gonna take the existence of WIG's to postulate that lift-drag isn't as much as hull-drag, but as previously noted, trains are pretty awesome in efficiency department. |
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//I think I would like to see some calculations from someone before we say that we are SURE//
okay. |
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I do this every time. I have a throw away idea, but
when people start talking about it I really start
defending it... |
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re: "You'd lose traction and power with this, due
to the lift." |
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Trains have plenty of traction. They could loose
99% of their weight and still have enough
"traction". When the train is going slow, and wants
to speed up or slow down, there would be no lift.
Even at 60 miles per hour, the train would not
have "traction" problems. Even if it did, just
rotate your Ailerons and you have all the traction
you want. |
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re: "Minor problem. 747 efficient cruising speed,
mach .8 or ~850 kph. Take off speed of the same
747 ~290 kph. Best high speed train to date
~220kph" I'm not saying we use the exact same
wings as a 747. I have not done the calculation. I
do not have a wind tunnel. But you have
identified the whole question. If a wing can
produce very much lift at 60 miles per hour. |
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//Best high speed train to date ~220kph//
I've clocked a Eurostar at over 300. |
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Is this making anyone else want to parasail? |
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//Is this making anyone else want to parasail?//
Above/behind a train with an overhead 25kV pickup? No thanks. |
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See link - I was sure I'd seen this somewhere before. I'd guess it would ideally run on a concave track (like a drainage channel) so as to gain lateral location as well as support. Traction would not require the weight of the vehicle if it used pairs of wheels clamped to a central rail. Clamping force could also be adjusted according to the tractive force required. Tunnels should present no problem, so long as the train is properly designed. |
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What if there were a long rope connecting New York and Los Angeles with a mile or two of slack in it? Then the aeroplane could take off and fly as usual, but with the rope continuously passing through a pulley on the aeroplane. Then the power of the engines could be used to pull the aeroplane along the rope, which must be a more efficient use of power than pushing air out of the way, surely?
(Yes, I realise I'm ignoring the massive weight of the rope, the unfeasible strength of rope needed, and the plight of millions of midwesterners who'll have this huge rope dropping on their heads every day) |
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//I'm gonna take the existence of WIG's to postulate that lift-drag isn't as much as hull-drag, but as previously noted, trains are pretty awesome in efficiency department.// |
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Actually, at the point of least total drag, form drag and induced drag are about the same. (Wikipedia: Drag). As Rolling friction is negligible compared to aerodynamic friction (form drag) in trains, and the wings would add induced drag to the amount of form drag, the idea is bad. |
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//Above/behind a train with an overhead 25kV pickup? No thanks.// |
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as long as you aren't grounded... |
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What would be easier, pulling a kite all rolled up on a skateboard behind you, or pulling the kite unfurled in the air behind you? Especially at high speeds. |
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// Trains have plenty of traction. They could loose 99% of their weight and still have enough "traction". // False statement. The amount of pulling power that a locomotive can apply to a train is, at best, about 1/4th the weight of the locomotive (that being the coefficient of static friction of steel on steel). That figure can drop to 1/10th in wet, icy, or cold (even with no water, the steel gets harder & less adhesion) conditions. |
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My mistake, I found a bad source for train speeds. It's
possible you could get a train above lift speed, but still
not up to a real cruising speed.
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Finding the right of way without bridges and overhangs to
do that in the US is improbable at best. It might be
possible in sections of the midwest, but the rockies would
be difficult, and the east coast corridor would be
impossible without a lot of political will, as it would
require truly massive uses of eminent domain and
construction money. (There's a reason we don't have
anything faster than the Accela there already, the right of
way just isn't available) |
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wikipedia: "The A-10 has superior maneuverability
at low speeds and altitude, thanks to large wing
area, high wing aspect ratio, and large ailerons.
The large high aspect ratio wing also allows for
short takeoffs and landings, permitting operations
from rugged, forward airfields near front lines. The
aircraft can loiter for extended periods of time
and operate under 1,000 feet (300 m) ceilings with
1.5-mile (2.4 km) visibility. It typically flies at a
relatively slow speed of 345 mph" |
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We would have different wings than the wort-hog,
designed for 60 miles per hour. |
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Hmm, no one has mentioned tunnels which would cause big problems... |
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In any case, as others have mentioned aerodynamic drag is much higher than rolling friction especially a train's steel on steel rolling friction when you have given up the planes slight advantage of flying high in thinner air. |
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So if you were crazy enough to do this there would be an advantage over flying but much less efficient than a train alone. |
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And all the things that make a warthog capable of flying at
low speeds also make it an inefficient flyer and a fuel hog.
Low speed, low altitude flight is inefficient, although you
might recover some of that through ground effect. |
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From what I find, the A-10 is very efficient... but
that is not my point... my point is that we can
make similar decisions to those they made for the
A-10. "thanks to large wing area, high wing aspect
ratio, and large ailerons" the A-10 is able to get
lots of lift at low speeds. That is my point. You can
make deign decisions that maximize low speed lift.
There is nothing to argue, I'm not saying it is a
good idea. I am not saying it will work. I'm just
saying if it does work, it will be the result of
maximizing lift at low speeds. |
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//I'm not saying it is a good idea. I am not saying it will work.//[marked-for-tagline] |
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Will the series of exercise videos be available first? |
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//the wort-hog//
A beer-drinking pig? |
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no. anyone who thinks that this is a good idea is completely uninformed as to the nature of friction and the energy consumed to produce flight. |
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The original idea mentions ground effect, which is more effecient than proper flight and has sufficient potential that prototypes have been buit and tested (see link). |
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Anyone who thinks this is unworkable is completely uninformed as to the nature of ground effect. ;-) |
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to reiterate : at point of lowest total drag, airplanes have 50/50 form and lift drag. trains have just form drag, with rolling 'drag' negligible. if trains fly, the lift drag will be as big as form drag -> bad idea. |
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ground effect leads to max 3x reduction in induced drag, so no joy there. |
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adding: the lower the velocities, the higher the lift drag, part of the explanation why the 'warthog' is a fuel guzzler. |
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The Japanese and French prototype ground effect trains (linked to from the Wikipedia article) are both pushed by propellors rather than wheels, so they don't quite make this idea baked. |
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A similar concept has been used with barges, where the propulsion comes from a person, animal, or vehicle on a towpath (pushing against the ground) rather than a propellor or oars on the barge (pushing against the water). |
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I also doubt that they were freight trains. There is a factor of scale and weight here. Bullet and "ground effect" trains can work because their density is relatively low. If they were carrying ore the amount of heat generated by the pressure required to keep them off the ground would completely defeat the system. |
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