HKStallion

so i had a thought the other day.
probably a thought that alot of people have had and have answered themselves.
but i havent had the time to really disect it, so here goes.

Cars weigh alot. anywhere from 2500-6000+ lbs.
if a car has enough traction at 2500 lbs to cruise, turn, stop, etc.
why not create a wing (similar to a Porsche) that automatically lifts at a certain speed and actually creates lift?
So a 6000 lb Hummer now only requires the engine to propel 3000 lb of weight at highway speeds. when you slow down, the wing will descend back and regular dynamics will be achieved.
maybe partner this with cylinder deactivation and you could achieve quite a bit of efficiency.

tell me why this i dumb, i am sure there is a very easy explanation i am not thinking of.

thanks

Dave

Apollo

Well, I'd be thinking of two issues with that: momentum and available traction. The mass of vehicle is the same whether it has the wing or not, so momentum stays the same. However, a lift producing wing reduces the force on the road and thus reduces available traction. Long braking distances at high speed with large ass vehicles = not good.

The Gasman

Lots of things.

Like Apollo said, lift would cause braking problems.

If you lift you have the undercarriage of the vehicle to cause wind resistance as opposed to a drag wing that keeps the vehicle low to direct unneeded air over the car.

The actual answer is to reduce the coeficcient (sp) of friction like in vehicles like the Prius.

I also believe if you have a good coat of slippery wax that that should help because it reduces wind resistance.

ZDan

Aerodynamic drag is the number one enemy at highway speeds.
Generating lift induces more DRAG.
You will lose much much more from the additional induced drag than you will gain from reduced rolling resistance due to less weight supported by the wheels/tires.

It is documented that reducing lift on a 240Z (which has a fair amount of lift stock) with the use of chin and deck spoilers reduces aero drag a measurable amount and results in greater fuel efficiency.

For minimum drag/maximum fuel economy, zero lift and zero downforce is the ideal.

C6400hp

A couple of things, Weight is not nearly as important to hwy fuel effiency as good aero. Having a wing whether producing downforce or lift increases aero drag, decreasing mileage. Weight is a very large factor in stop and go driving where getting a heavy vehicle moving requires more fuel. Having a wing in that situation will do nothing. Reducing weight, improving aero, decreasing rolling resistence is the way to go.

spdemon12384

a couple of ways to reduce the energy required to move a car at highway speeds:

#1) Decrese coefficient of drag from wind
#2) Decrease coefficient of kinetic friction between the tires in the road (aka rolling resistance of the tire).

the effect of mass is much less than the effect of velocity on kinetic energy when there is an opposing force i.e. friction.
however, the amount of force required to get a car moving is the mass times the acceleration of the vehicle

its all about a compromise between minimizing forces of resistance and maximizing traction.

txjeepn

Now the question is if you had enough power would the car take off if it was on a treadmill that would match its speed?

Kremlin

Mass != Weight.

If, like in your example, a spoiler were added to intentionally create lift to effectively reduce half a 6000lb hummer's weight, it would still have 6000 pounds of MASS. Your Hummer will still be just as slow, but it will have half the traction and additional aerodynamic drag.

When we say "weight reduction" on a car, we're really referring to MASS reduction. If weight were what we were trying to reduce I'd fill my trunk with helium balloons everywhere I went

Lice Locket

At high speeds you actually want less aerodynamics so the car can grip the ground a lot more (so you actually want it to weight a lot at high speeds).

A Hummer w/ aerodynamics that makes it lighter will lose traction at high speeds, which isn't so great, and it is actually local driving that eats tons of gas, not freeway driving.

Spec_Ops2087

for a vehicle that is driven by the wheels, no it would not take off.