h a l f b a k e r yMy hatstand runneth over
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
A lighter car means increased mpg. To "reduce" weight of the car without actually taking anything away from the car, add an inverted spoiler on top of car. Race cars often carry a spoiler which is actually inverted wing, which creates negative lift thus pressing the car on the ground thus increasing
traction.
However, idea here is to use a wing to create a positive lift, thus reducing net weight. Hence as the vehicle goes faster, wing will create more lift, thus making it lighter , hence faster. This is a positive feedback loop. Cars will keep going faster till aerodynamic drag balances out positive feedback.
Care must be taken that wing does not produce too much lift, but just enough so that car becomes lighter but still has enough traction.
Almost flying Automobiles
[xaviergisz, Jun 11 2011]
Top Gear does a tunnel loop
http://www.youtube....watch?v=-TbpgZ2Dt0A
[RayfordSteele, Jun 13 2011]
Mercedes does a tunnel loop
http://www.youtube....watch?v=izrNv4nMxAg
[DIYMatt, Jun 13 2011]
intersting link
http://www.youtube....2zk&feature=related
[VJW, Jul 11 2011]
[link]
|
| |
[+] A perfect H-B'ed idea. It sounds great, but I can't help but think something's fishy with it. |
|
| |
P.S. The etymology of the HB fishbone just clicked in my head. (I'm slow, I know.) |
|
| |
At moderate speed, the drag surpasses rolling friction. The inverted aerofoil will increase drag, thus reducing mpg. |
|
| |
The only time weight is a significant factor in efficiency is during acceleration and then it is the mass of the car that is important, not the weight. |
|
| |
Even at constant speed, gravity acts on the car, hence I think weight should matter. This weight/gravity causes friction at tires and axle friction. Hence we need engine power to counteract those that speed does not decrease. |
|
| |
[Marklar] quote some geezer in Colorado "As long as you stay on Earth, the difference is more philosophical than practical". |
|
| |
As mentioned above, during acceleration and hill climbing, it is the mass that is important. |
|
| |
In steady state motion, weight only makes any difference to rolling friction. Rolling friction represents only a small part of the total energy required to keep the car moving. Most of the energy is used to overcome aerodynamic drag. |
|
| |
A wing would reduce rolling resistance at the expense of aero drag. |
|
| |
Great efforts are made in vehicle design to reduce the lift that a car body shape naturally produces. |
|
| |
Reducing load on the wheels also reduces control, braking and traction. Drive a VW Beetle (original type) in high winds and you will soon know all about this. |
|
| |
Reducing traction results in increased slip at the driving wheels and consequent energy loss. |
|
| |
winged wheels for potholes. |
|
| |
[Twizz] Acceleration = gaining momentum by overcoming inertia of mass, hill climbing = gaining potential energy from gravitational weight. |
|
| |
Hill climbing is actually the only application where this wing would be useful, as long as you could reverse the effect for corners. |
|
| |
If you support part of the car's weight with an airfoil, rather than wheels, that portion of the weight doesn't go away. |
|
| |
So you've divvied up your weight into two portions: the one on the wheels, with a rolling resistance / weight ratio; and one on the wing, with a lift / drag ratio. |
|
| |
Your ability to control your motion vector - speed up, slow down, turn - is limited by how much friction you have at the wheels. UNLESS - you either a) provide control surfaces on your wing also - turn the wheels, turn the rudders, move the ailerons; or b) arrange the wing to go to negative lift when your inputs request control authority. |
|
| |
I'd suggest the following control set:
Steering wheel
Gear shift
Clutch
Brakes (differential)
Throttle
Wing lift
Joystick
Rudder pedals
Trim wheel
Options: drogue chute, ejection seat. |
|
| |
(I want it to be so complex it has to be fly-by-wire. Computer can glitch out and kill you, like, whenever. Retros = [++]) |
|
| |
It would be very bumpy once you had gotten fast enough to leave the ground. Because you would then slow down, and land again, probably lay rubber, speed up again and again take off, then slow down and land again. |
|
| |
Only on the Aston Martin DB5, and even then, only on the passenger side. |
|
| |
I wonder where the line is in car racing. |
|
| |
Most car manufacturers like to brag about how much downforce they create. |
|
| |
the idea is entirely worthless. The lift that is produced by an airfoil IS drag, it IS a loss in efficiency and causes a penalty to fuel economy. 100% without exception. |
|
| |
Hey, don't feel like you need to hold back, [WcW]. Go ahead, say
what you think. |
|
| |
ignorance is slavery to mediocrity. |
|
| |
The good is the enemy of the excellent. |
|
| |
Close cover before striking. |
|
| |
Packed by weight, not volume. Contents may settle during
shipping. |
|
| |
There is neither good nor evil in the world, but that thinking
makes it so. |
|
| |
Do not inflate beyond 2.3 Bar. |
|
| |
/The good is the enemy of the excellent./ |
|
| |
My money still is on the good. |
|
| |
//lift that is produced by an airfoil IS drag, [...] 100% without exception// |
|
| |
Which is why albatrosses walk. |
|
| |
They don't have airplanes where you are? |
|
| |
No, they get attacked by the Pterodactyls. |
|
| |
// why albatrosses walk // |
|
| |
Because the tube and the buses stop at 2300, and cab drivers
won't take a large fish-eating avian south of the river at that time
of night. |
|
| |
But don't car manufactureres also brag about how lighter their car is? How their car uses titanium/alminium to reduce weight ? |
|
| |
If a car is a front wheel drive, then traction is actually needed only for front wheels as far as propulsion/direction control is concerned. How about providing positive lift to rear wheel axle where most of the cargo weight resides ? |
|
| |
Wing can have a negative feedback so that if it produces lift more than a preset-threshold, it self-adjusts to keep lift undercontrol. |
|
| |
Taking it to the logical extreme, airplanes must have infinite mpg as they lift off and thus eliminate weight altogether. |
|
| |
But they still have wind drag to overcome, just like cars. Air planes have to spend gallons just to stay at a constant altitude unlike cars and zepplins. |
|
| |
The question is how much drag will the wing introduce as it produces lift. One solution could be to sweep back wings like Jumbo Jets (and unlike spoilers) to reduce drag keeping the lift same. |
|
| |
RRC (rolling resistance coefficient) for road car tyres is typically between 0.007 an 0.014. This means that (ignoring other sorces of friction such as drivetrain - which will be present regardless of weight / load) a car would roll down a slope of 1 in 100. |
|
| |
The best gliders have a glide angle of 1 in 60. |
|
| |
Road car wheels are nearly twice as effecient at carrying weight. |
|
| |
Albatrosses don't get run over. |
|
| |
//The best gliders have a glide angle of 1 in 60.// |
|
| |
That is, at a 1 in 60 slope, they can maintain a velocity higher than the craft's stall speed. |
|
| |
I highly doubt that an automobile would maintain 50kph on a 1 in 100 - or even 1 in 60 - slope. |
|
| |
"reduce drag keeping the lift same" : increasing the efficiency at which drag is converted into lift. |
|
| |
a wheel might roll down a 1% slope but a car will not. In a perfect world a perfect wheel would reach and infinite speed. Friction is the killer of speed and kinetic energy. The function of the car as a wing, ether of upforce or downforce is clearly a result of friction which can only be seen as converting the energy of motion into some other form. I cannot save energy this way. I will not try. |
|
| |
Build a maglev car and then we'll talk. Until then, the wing is useless for fuel efficiency. |
|
| |
Ground effects are there for improving the aero. There are cars with active aero wings which are there for increased stability under changing aero conditions at higher speeds, but deploying them only hurts fuel economy, and it wouldn't get better by turning it upside down. It's a drag source, regardless of orientation. |
|
| |
Maglev provides support, propulsion and guidance from on
contactless wear-free system. |
|
| |
So-called "ground-effect trains" are in fact a sort of hovercraft
derivative. Sort of. |
|
| |
There's always the Ekranoplan … |
|
| |
Focus on reducing the turbulence produced by the vehicle as it passes through the air. As you increase speed there is a breakaway point where the waste energy of the native airfoil is adequate to produce lift. Then you may float on the waste energy. Up to that point i forbid it. |
|
| |
//Ekranoplan// That's true, WIG effect increases lift coefficient. |
|
| |
//Then you may float on the waste energy. Up to that point i forbid it.// |
|
| |
Nice to meet you God. Nice universe you've got here. It'd be a shame if something were to "happen" to it. ;) |
|
| |
There must be some sort of way to cheat and work around the laws of thermodynamics. Nobody has set them down in letters of fire on top of a burning mountain yet, or am I mistaken? |
|
| |
\\Nobody has set them down in letters of fire on top of a burning mountain yet, or am I mistaken?\\ |
|
| |
Unless that was what the whole "We apologize for the inconvenience" thing was all about. |
|
| |
//There must be some sort of way to cheat and work around the laws of thermodynamics// Quote of the year! |
|
| |
You'll have to ask Q, he's the one who does all that messing with physical laws stuff. |
|
| |
In simple terms, lift is a side effect of drag; it's just the drag vector pointed in a convenient direction. ANY lift force (up or down or sideways, depending on whether it's a wing, a rudder, a spoiler...) is because of increased drag. And more drag = more fuel used. |
|
| |
I suddenly have this urge to write "Don't Panic" in large yellow letters on the cover of my calculator. |
|
| |
Aerodynamic drag is substantially the result of turbulence which increases with velocity. If you propelled a glider to high speed you would do so with a tremendous penalty in efficiency. This also motivates the tremendous wingspan, at low speed there is so little force imparted by the air to become lift that it must be used to maximal effect. In effect the glider maximizes drag in the airfoil itself; this drag efficiently changes force in one vector into force in a different vector. If the goal was simply to fall as fast as possible (high economy of velocity) then the design of the glider is a complete flop. Since the goal here is to minimize the loss of kinetic energy over time while traveling the nape of the earth it can be inferred that we desire that no forces of any sort be applied against that, even if those forces are deflected into a different vector. |
|
| |
I'm really struggling with how people aren't clear on this. Migraine isn't helping. |
|
| |
How about AOA (angle of attack) and camber ?; With proper use of camber (curvedness of wing surface), is it possible to increase lift without increasing drag ?. A wing with a certain amount of camber will always produce more lift compared a both-sides-flat wing which produces same amount of drag. It is possible to have an object in the fluid flow with absolutely no lift but certain amount of drag. |
|
| |
My earlier post comparing lift/drag ratio with coeffecient of rolling resistance appears to have been universally misunderstood. |
|
| |
Using a wing to unload the tyres is a simple exchange between aero drag and tyre drag. The wheel bearings, driveshaft, transmission etc. all still turn and are not affected by tyre load. |
|
| |
Wings are less effecicent at carrying load than tyres. There's no getting around it. |
|
| |
I'm not sure what the problem is here. Let's start with no gravity, and no road, and say that there is a force applied to a vehicle in the direction of some vector labelled i. |
|
| |
Now add some gravity - let's forget about wheels, and instead have a single blade and make the road out of perfectly smooth ice. Let's have some perfectly still air too. Our force i is opposed now only by the air, by another force j that probably increases with the overall speed of the vehicle, balancing out the total amount of force i at some terminal velocity. Let's also add the force k pushing downwards which is applied by gravity on the whole thing, counteracted by the force l which is the equal and opposite force applied by the road/ice pushing upwards - let's continue to assume no friction for now... |
|
| |
Now add a wing. This converts some of the force delivered by i into a perpendicular force m pushing the vehicle upwards. This redirection of force is a transformation of some of the horizontal driving force i, the horizontal component of which we can model by an overall increase in the wind-resistance force j. The actual force applied by the wing is probably at an angle to the horizontal, it just makes sense to think about it in its horizontal and vertical components. |
|
| |
So far, we've assumed a frictionless system, and seen a horizontal force applied counter to the driving force i, which would lower the terminal velocity and the reactionary force k applied by the road to the sliding blade. What's required next is a way to model the friction forces between the vehicle and the road - which would vary as a function of the force of the vehicle pushing into the road according to gravity. But I think that's the point towards which everyone is arguing, isn't it? |
|
| |
There seems to be some disagreement on whether the drain on the horizontal i-force caused by the wing would be enough to counteract the reduction of the drain on the i-force due to friction by the enlightened vehicle - but as [bigsleep] says, what's required is "quantitative evaluation" - as the problem is a question of optimisation. |
|
| |
I have heard thatsports cars with spoilers can go upside down inside circular tunnel, at sufficiently high speeds, because spoiler bears all the weight of car and pushes it on upper surface of tunnel. |
|
| |
I'm having lots of doubts. Cars that could do that would need to double their spring rates. |
|
| |
It's not exactly the car's weight that's the problem, it's getting the mass moving. Adding a wing isn't going to change that. |
|
| |
Batmobils can do that, I am sure. |
|
| |
KITT in Super Pursuit mode. |
|
| |
Right, now there's another problem here - if the horizontal force we've been describing earlier (in my earlier anno, it was described as i) is applied by rocket, or rubber-band, or some other non-friction-requiring method, then all's fine and dandy. |
|
| |
In order to apply horizontal force i (which we need to continue to do as the force of air-resistance j - (wing or no wing) increases as our speed increases) - We need to be maintaining enough friction (normally provided by gravity/downforce etc) in order to lay that force down on the road. |
|
| |
If we are successfull in reducing the friction to some nominally small amount, then we are also reducing our ability to continue to impart our force into the road via the wheels. |
|
| |
The whole point of the downforce producing wings in F1 is not to improve fuel economy, but to glue the car onto the road - not just to go around corners - but also in order to allow the exceedingly powerful engine to continue accelarating, rather than have its wheels spinning around generating lots of smoke, but no useful thrust. |
|
| |
For a car to be able to go upside down, its spoiler has to be above its CG and not at its rear end I think, since, otherwise there is no support for front portion of the car in up-side down mode. |
|
| |
As the motorcycle globe of death demonstrates, it is possible to get a motor vehicle upside down purely based on centrifugal acceleration (I know, but it's easier than saying the reaction force to the centripetal acceleration imparted by the wall of the sphere/tunnel). Obviously, the longer travel path of a tunnel loop would require much higher speed. |
|
| |
The addition of a spoiler to increase the downforce on the rear wheels to keep them from breaking free would presumably be just as useful in this as in any active road maneuver. |
|
| |
If you were trying to loop based on aeordynamic down force, then yes, you would need multiple spoilers or a spoiler located between the wheels (not over the CG, neccesarily, although that would probably be most efficient). |
|
| |
well although numerous persons here have voted against this wikipedia says of the opposite, an aeroplane with wheels: Under continuous motorised flight at 225 km/h, a Pipistrel Sinus burns 11 liters of fuel per flight hour. that is kind of like 139 miles at 2.4 gallons. Or over 50 MPG |
|
| |
The plane is much lighter however, plus traffic light stalls kind of mess with things, yet I suspect that if there were a way to remove noise a hovercraft could get better mileage than many cars. with a hovercraft wing translates as "rotating airfoil" |
|
| |
Those claims are not idiotic, they are based upon
a formula developed by the EPA and the industry
for hybrids. I have it in my hybrid class notes. For
EPA test conditions, they align. |
|
| |
The plane is not shaped like a car; it has a Cd
nearly an order of magnitude different. And ask
what mileage that plane gets while taxiing. |
|
| |
If you manage to actually get the wheels off the
ground, then you have quite changed the
equation. But simply adding a wing to provide
lifting force is going to cost you in fuel. |
|
| |
[spidermother] - //The best wings are just a little bit worse than ordinary car wheels.// I think you should think that through a bit more. |
|
| |
You're using, I assume, your 60 v. 67 numbers you posted up above; however, there's a discontinuity between the two. The lift/drag ratio for the glider is at its best operating speed - which is, perforce, a non-zero velocity and thus has air resistance as one of its factors, built in. The numbers for the road wheel are simply for motion on ground, and no accounting is done for air resistance - it can't be until you've defined the rest of the vehicle and its motion. |
|
| |
When you get the road vehicle moving the same speed as the glider, there will be *substantial* air resistance, and whatever advantage it had will be long gone. |
|
| |
Car mpg figures are based on normal driving with stop/starting. While 50mpg might sound impressive for a car, it's less than most cars get cruising at 80km/h (I drove a 5.7l Durango that cruised at 5l/100km, but went to 12l/100km for normal driving). Also, if you remove the gearbox of a car and attach the engine directly to a propellor, you might get better efficiency (although I doubt it). There are other differences to consider apart from the wings. |
|
| |
<aside>I hate the SI unit l/100km, it implies that you've tested for 100km, just like mpg implies you've put in a gallon and seen how far you could get. I think ml/km would be better (of course, cl/km would give you the same number as l/100km so would be an easier transition). |
|
| |
[spider], there's a well-studied distribution of how many miles a typical operator of, say 70th percentile, will travel during any given trip, and the figure targets a certain percentile driver, (I think it's around 70-75 %. Of course there are the 90th percentile users and 99th percentile users that frequently drive cross-country. But the curve is well-known. |
|
| |
Standard EPA numbers suffer from the same problem, economy / consumption ratings are sensitive to how you drive, which is why there are standard EPA cycle tests to try and capture the 'typical' driver behavior and serve as a comparative rating. Incidentally, the US government and EPA actually write the rules using l/100 km numbers, which are then 'translated' into MPG for the general public. |
|
| |
I think that the original idea is a bad one, and have a slightly different way to look at it: |
|
| |
Imagine a perfectly efficient wing, with pure powerful lift, adding no drag at all. It would promptly hoick up the back of the car, taking away all traction from the wheels. The remaining drag, from front wheels and from the body of the car, would keep the car from moving. I want to extrapolate from that and say there no point at which lift is good, but there may be cases--however, with the wing's drag a real issue, I don't see it working out. |
|
| |
Now, imagine a purely flexible tire, made of super-supple marmoset leather crossed with Damascus steel. It would have no operating friction at all, except for the bearings it turns on and the gnarly super-tread that it suctions on the tarmac. No matter how much weight it carried, it would have no difference in drag (so adding a wing to reduce the car's weight would be pointless). |
|
| |
In short, improving the tire would make this idea useless, and practically, adding a wing would slow the car a couple of different ways. |
|
| |
(BTW, there's a gyrocopter trainer that is towed behind a truck. It had a very bad lift/drag ratio, but it was technically this idea. I rode in it and I towed it, and I wouldn't recommend it for improving MPG. (Or handling.)) |
|
| |
[baconbrain], I know you were talking theoretically, but you can't have lift without drag - the lift energy has to come from somewhere; it comes from slowing the vehicle down. |
|
| |
//gyrocopter// more of a glider I'd think. [bb] great tire concept. |
|
| |
Your description of lift induced drag is accurate and illustrates the point that you can't have lift without drag. |
|
| |
At it's theoretical best, a body might produce lift equal to it's drag. If this were not the case, where would the extra energy be coming from? |
|
| |
Lift is not caused by drag, but drag is certainly caused by lift. |
|
| |
A wing generates lift by moving air. You can't have lift without work. If you aren't leaving a wake of downward moving air behind you--no matter how wide and tenuous--you are not getting lift. |
|
| |
And a wing strapped on top of a car is just about as far as one can get from a theoretical ideal wing. It is going to have limited wingspan, be covered with bugs, and operating in very turbulent air. |
|
| |
Arguments based on ideal wings in an idea for a car spoiler. We are certainly winging it. |
|
| |
I posted the same idea years ago. It doesn't work |
|
| |
Lift force = mass of accelerated air x acceleration of air. Air is accelerated, so work is done. |
|
| |
YOU CAN'T GET LIFT FOR FREE! |
|
| |
I think this can work for road trains better. Engine has no wing. Only trailing cars being pulled have those, since they don't care about traction (as much). |
|
| |
But then again, the current argument is about whether the lift from wing is worth the drag it causes ? |
|
| |
// the current argument is about whether the lift from
wing is worth the drag it causes // |
|
| |
Why isn't the argument about the lift from this proposed
'wing' reducing traction and sending the car spinning off the
road?! |
|
| |
Yes, spoilers and other downforce-producing gizmos
increase drag. Yes, high-performance car builders are
always looking for ways to reduce weight... CURB WEIGHT!
They want to make the car lighter to offset the detriment
of the spoilers/air dams/whatever that keep it glued to
the road at high speeds. The goal isn't just light weight,
it's light weight and greater traction. |
|
| |
Cars drive on roads. Airplanes fly in the air. Experimental
attempts at combining the two cause test-driver shortages. |
|
| |
// lift-to-drag data for wing in ground effect ?// |
|
| |
As a generla rule I think it is roughly 3 times the regular lift. |
|
| |
Once again, it's not weight that the manufacturers
are worried about, it's mass, which affects how long
it takes the car to accelerate and how well it
corners. |
|
| |
So, instead of an antispoiler, which reduces
weight, without changing mass, what's needed is
something which reduces inertial mass, without
altering weight. That's not impossible as long as
"reduces"
is understood in the same way as for the
antispoiler, i.e. it works by applying a force to the
vehicle. |
|
| |
The simplest way to accomplish that might be
with aerodynamic control surfaces, as on an
airplane, though that would only work at high
speed, and would also get complicated in
crosswinds. Essentially, this same idea but
rotated 90 degrees. Shirly that's been tried
before? |
|
| |
A less elegant approach would be a propeller or
jet engine which was either orientable or had
orientable vanes or ducting. |
|
| |
With an absurd amount of apparatus, and a good
control system, it should be possible to give the
driver the "feel" of a car that was impossibly light,
but with very good traction. |
|
| |
Not useful, exactly, but serious sports car
enthusiasts might enjoy driving it. And races
would be fun to watch: the track could be
rectangular, and the cars would corner in a way
which seemed physically impossible. |
|
| |
(edit) this is more or less what [lurch] said. |
|
| |
//not useful, exactly// [marked-for-tagline] |
|
| |
// the track could be rectangular//
I suspect (but I could be wrong) that cornering would effectively be an explosion, to (almost) instantaneously change the direction of travel. You can possibly make it seem like the car has no weight, but mass is always there, and F=ma. |
|
| |
F = m a
let F = F_w + F_t
.......... w: wheels' traction on the
road
.......... t: thrust -- e.g. jets, control
surfaces |
|
| |
let F_t = f(a)
.......... Thruster force a function
of acceleration.
.......... (automated closed loop control system.) |
|
| |
F_w = ma - f(a)
let m_c = f(a)/a
.......... c: "compensatory" |
|
| |
F_w = a(m - m_c)
let m_e = m - m_c
.......... e: "effective"
|
|
| |
For a suitible function f(a), we can achieve
effective mass less than actual mass: m_e <
m. No violation of Newton's law, but to the driver
and spectators it seems as if the vehicle has
unphysically good cornering. |
|
| |
That's what I meant by //not impossible as long as
"reduces [mass]" is understood in the same way as
for the antispoiler, i.e. it works by applying a
force to the vehicle.// The antispoiler doesn't
really reduce weight, it just adds a force
proportional to weight, with opposite sign. |
|
| |
The major problem is that the driver would rattle
around inside the car like a dried pea in a maraca.
Perhaps some sort of permanently inflated airbags
would help. |
|
| |
re ^ , everybody's saying that's WIG effect; doubt it: too close to the ground, it's gotta be boundary layer... I'm not sure that'd be any more efficient than wheels. |
|
| |