vehicle efficiency

I would think in terms of mass not weight if I were you. Your idea would probably reduce tyre hysteretic loss at the expense (IMO) of greater aerodynamic losses and (seriously) loss of braking ability.

And at such speeds the wing would be very large.

Well, first of all, it would not reduce the mass and would increase air drag.

The second problem is whether you really want to lift up a car since you would go into a turn with the same old mass but a lot less road traction. Kind of like driving on ice.

1st, the wing will generate drag. The more aggressive the attack angle of the wing, the more drag. Think of an aircraft and the principles that determine flight (gravity, drag, propulsion forces). Run the numbers through the formulas and you will see that a wing (in any attack angle) will make the car work harder.

2nd, the car still has momentum. So acceleration requires force (gas) to overcome the tendency for an object that is at rest to remain at rest or at its initial velocity.

You could just take the bus.

Not sure you could call those fins aerofoils but the monu-mental overhangs prevalent at the time had horrible handling effects and certainly lift at the rear would have been a factor, but not sepcifically because of the fins, just that surface area.

PS I wouldn't say this was badly off topic.

I was first going to reply with similar comments to above about reduced control, and high drag, as I do think they are valid points but someone needs to run the numbers.

Instead of going down this track I want to point out some positive things about the idea.

Racing boats use this concept in a design called a Tunnel Hull to go quite fast, although I have no idea about fuel use. The graph in the article shows the drag is much less than the lift.

What I am not sure of is how well this would work in a car at normal highway speeds since you need to go quite fast to get decent lift. I also don't know what effect on fuel use it would have. Wheel bearings on a car do a good job of reducing friction, and cars have to go up hills where boats are always on a level surface.

I imagine if it did work out that you could get increased gas mileage, creating a wing that automatically adjusted to give you the handling when you needed it might be possible. I would hate to see a car flip in front of me, like you sometimes see those racing boats do on TV.

Thank you for your vote of confidence frankd20. Much appreciated.

I accept all the other member comments, about handling etc. and, admittedly,
there would be a lot of "changes" to the handling of a vehicle. However;

a) I don't think these would be insurmountable; because, it would be simply
like driving a much lighter car than one would normally drive. (easier) and,

b) It could possibly become the "norm" and be accepted like other things; like, auto
gear changes, cruise control. etc. - even possibly insisted upon by customers!

I could not see the "flaw" (if any) in my idea of using a "spoiler wing" to "lift"
reduce the weight of the car, which could reduce the fuel used. (costs)

Remember, the car would be perfectly normal at parking and slow speeds; and the
variable wing only come into effect as the speed increases. The car would also return
to normal handling upon braking, with even a possible increased braking effect. (drag)

There is no free lunch; but the benefits just might, outweigh any downsides.
I would like for some manufacturer to give it a shot in their R & D; who knows?

It is reassuring to hear they use it for boats; so it must have some credibility.

If the members cannot find fault, I will contact some manufacturers and
see what they think of my offering. Who knows, one day we may be driving
along on a wing, and a prayer! (sorry for that, couldn't resist!)

jt.

Have a free notice board in 30 seconds - http://www.mfnb.at

Ever experience the nightmare of hydroplaning?

Funny feeling!

When I woke up, they cut me out of the wreck with hydraulic scissors.

From the impact traces, we conclude that I did 9 complete-rollovers.

Glad to hear you were okay!

Why would they wait till you woke up? If you hadn't would they have saved their energy and gone home?

In a boat it makes a lot of sense to get as much of the hull above the water line as possible due to the high drag. The friction from water is orders of magnitude higher than air at STP.

When you look at automotive fuel economy, aerodynamics factor in only when speed exceeds a certain limit (i.e., 25 – 35 mph). Aerodynamic drag increases with the square of velocity, ignoring turbulence. Rolling resistance is pretty much linear with speed! In city driving, stopping and acceleration eat into fuel economy. For city driving aerodynamics has little impact if you drive the speed limit.

For highway driving, even a simple whip antenna for your radio has an impact. Rolling friction only accounts for a small percentage of total forces acting upon a vehicle. At highway speeds accelerating the vehicle is done once, and then you run at a cruise velocity. This is what gives us better gas mileage on the highway. Let's look at the two most prominent factors in fuel economy; aerodynamic drag and rolling resistance.

Source: http://www.atmosphere.mpg.de/enid/Information_ss/Velocity___air_drag_507.html

What the graph tells us is that rolling resistance is far outweighed by aerodynamic drag by more than 5 times at 60 mph (100 km/h). Adding a wing to offset rolling resistance is a loosing proposition. The problem gets worse with velocity. No matter what attack angle the wing is set to the wing adds drag. As you increase the attack angle you increase drag drastically. The drag introduced by the wing will overcome any small benefit you may get from rolling resistance.

Let me add one more thing. Almost all cars get positive lift when they are driven at speed. Wings are added to cars (like mine) to remove that lift component. It makes my car safer at speed, but it is designed for top speeds in excess of 190 mph. Still I get 27 mpg at 80 mph highway and 29 at 65 mph. Not bad for 400 hp, eh?

Most cars on the road that have wings have them to make the driver feel good (ego). They are not functional and in fact impact your highway mileage negatively. You need to drive at some serious speed to get a benefit from a wing as far as countering lift.

I also fly sailplanes and you need to get above 40 mph to get enough lift with those huge 12 meter wings to get airborne. That translates to a lot of drag and force to lift 400-500 pounds of plane and another 150 pounds of pilot to neutral buoyancy.

Cars weigh in excess of 3,000 pounds. If rolling resistance is 20% of the total drag on a car you need a huge amount of wing to lift 3,000 lbs!!! I can assure you that the aerodynamic drag introduced by any wing will be many times higher than the rolling resistance of a car.

A fly in the ointment if you please; Let me relate something to you. A piper J 3 cub weighs in at arround 600 lbs. On 65 hp it can do about 80 mph. That same 65 hp engine in a tail wind will do closer to 140 mph. The biggest differance is streamlining. Both planes are two seaters both weigh about the same,but because one is cleaner aerodynamicly it will go faster for the same power input. Your idea of putting a wing on a production car to do what you were describing would only add to the cost, not preformance. Design a car that is aerodynamicly cleaner and you won't need as much power/fuel consumption or wings to lift the weight of the car. Lifting any of the weight from the tires will only reduce traction and make cars more prone to accidents. All high preformance cars are designed to go fast(streamlined), not for the family comfort or safety(boxy and heavy). Now if you want to design a truely high preformance family car, go for it.

Be aware that the De Havilland Tiger Moth aircraft has a take-off speed of about 50mph!

So, if a vehicle with significant lift is lifting while its road wheels are persuaded to take a corner, what happens?

Hope to clear the hedge/tree/house parked on the bend.

May I thank all the members for pointing out the flaws; and
especially the guest with excellent graphs, link, etc.

The increased drag, seems to be exactly that; a drag! (on the idea)
In so far as it would be greater than any benefit obtained.

Another case of sticking to what one does, and leaving the design
(of the vehicles) to the professionals. But it was worth asking.

Thanks to one and all. Back to the drawing board for me.

jt.

Have a free notice board in 30 seconds - http://www.mfnb.at

Even though the idea was flawed, never stop reaching for new ideas.

Eddison said "Ideas are like baseballs. Throw enough of them in the air and you are bound to catch one." Or something like that ;-)

There's merit in your idea but you also need to take other things into consideration.

In Formula 1, the wings are primarily intended to keep the car on the road (lifting it won't do any good for the car, much less for the driver). However, it is adjustable.

In a twisty racetrack, they adjust the wings for maximum down-force. You want that grip when negotiating corners. The downside to this is less speed and not-so-good fuel economy.

However, in a racetrack where the track is mostly straight (few curves with a couple high speed curves too), you'd want less down-force. Note, less not "no down-force". This allows you to go faster and improves your fuel economy.

So, your wings (automated at that) can give you better performance. When you brake at high speed, your wings push the car down to give the tires more grip.

The downside.

Your proposal is to put the wing on the roof. That much area will increase drag, but somebody's already said that. What I haven't read is that such a wing is also a big sail.

When you're driving in a crosswind, you'll be fighting to keep the car in your lane. If the wind blows just right, it may lift your car up and roll you several times.