Why don't vehicles have aerofoils to partially take the weight of the car?

[freebeard]

Originally Posted by OP

Freebeard, I think lifting the rear wheel is clever but not really what I am talking about here, because that would be quite susceptible to the PIT maneuver, or potholes, or crosswinds

If you're subject to the PIT Maneuver someone wants you to stop.

A trike would be less susceptible to potholes if the third wheel is flying.

Crosswinds suggest a vertical stabilizer.

edit:
aerohead's post is relevant: ecomodder.com/forum/showthread.php/race-action-world-solar-challenge-aero-39414.html

Worst case for crosswinds is driving into a dust devil (whirly-whirly).

[Tahoe_Hybrid]

Originally Posted by AeroMcAeroFace

In the Tahoe hybrid thread the car would only ever get 60mpg(US) due to rolling resistance, in the insight thread half of the drag was rolling resistance.

Theoretically rolling resistance is proportional to force applied, so a lighter car would have lower rolling resistance.

A car that generates significant lift has lower rolling resistance at higher speed.
Low drag shapes in ground effect often have high lift coefficients.

I am imagining a car, a bit like an ekranoplan, but never leaves the ground so the wheels always drive the car. Steering angle sensors, wheel slip sensors and brake pedal sensors cause the lift to stop and spoilers to create downforce pop up. Turning at speed can be assisted by aerodynamic aids.

As long as it is aerodynamically stable, in all directions, can dump lift as necessary I see no reason why this wouldn't reduce rolling resistance.

Obviously this is really complex but looking at cars like the huayra, certainly possible. Is it the case though that by the time significant rolling resistance reduction occurs, the speed is so high that rolling resistance is a tiny fraction of total drag?

aerodynamic issues a small reduction will let me in the magic gear (EVT gear) which would significantly reduce powertrain losses



an
electrically variable transmission, which uses electric
motors to operate at nearly any speed ratio through the
transmission.





which would eliminate powertrain loss.... which would at lest get me 35MPG IRL in my city(with a totally dead exhausted hybrid battery that is 13 years old) with the 6.0L v8...

the engine is barely idling at 1,050 rpm at 45mph,55mph . in the magic gear which would get me 35-40MPG on the highway.....



Honesty GM really limited it on purpose as they knew it could get more they did not have an Eco mode button which would have configured the TCM to use the EVT gear more often(or stay longer) at the expense of acceleration..which is a non issue due to the massive amount of Torque available ..


if I had new batteries it's possible to spin the wheels with the electrical motor






when it's not in the magic gear the rpm is a bit higher and will top out at 25-27mpg(IRL) at 59mph



the BEST ever was 32MPG with a slight tail wind (I just got lucky on that round trip..)



the normal LS2 6.0L engine.(it has a slightly different CAM and crank though). gets barely gets 9mpg in the city and 13MPG highway on the 4 speed auto (4L70E) (IRL) MPG which is all lost in the powertrain..

here is a cool photo

[aerohead]

The transmission, driveline, and final drive together, eat 24% of the power. Very close to what CAR and DRIVER has calculated with, giving us insight into the reverse-engineering their data, presented for the 2015 GMC Yukon Denali long term test.

[freebeard]

Equal energy lost to engine cooling and brake drag?

[JulianEdgar]

Originally Posted by AeroMcAeroFace

Presumably you are talking about the mk1 audi TT, I don't believe you when you say that lift is the sole cause of the issue here, that is a simplification. The issue in that case was lift but also suspension issues.

No I am not talking about the Audi

The real issue is unequal lift and/or centre of pressures ahead of the centre of mass. Planes do not suddenly crash when they get to 50% of their weight on their tyres.

The proposition seems to keep changing a bit each post. From originally 'why don't cars fly' to now something quite different.

When you added those side fins on your insight, you got extra rear lift but because the centre of pressure moved rearwards the stability improved?

No I had true downforce both before and after fitting the fins, so I was able to assess the difference that downforce alone made.

If unequal loading was the sole cause of the problem we wouldn't have cars with weight distributions up to 70/30.

You are constantly equating aerodynamic lift forces with static weight distribution but the published research on car stability and aero lift doesn't agree with this.

But it isn't, because my cars aren't designed with aerodynamic stability in mind, they are aerodynamically unstable and rely on the tyres to stop the car from going sideways. This is a thought experiment about a car that is aerodynamically stable.

I don't know why you say this - it varies from car to car. Some cars are quite aerodynamically stable in yaw.

I have driven cars with front end lift, and I know it isn't pleasant, but then I have flown planes and gliders with much more lift and they have no directional stability issues. As I mentioned earlier the real issue is directional stability, rather than specifically lift.

Again, look at the published research. Front end lift on cars is of far less importance than rear lift.

Drop a plane and it will point in the correct direction, drop a car and it will tumble. Why? Aerodynamic directional stability.


On typical road cars maybe, but a plane becomes more stable as more lift occurs, due to more corrective aerodynamic pressure. Handling, again on a typical car, but this imaginary car can cut the lift, and has control surfaces so that evidence doesn't apply. Braking, air brakes would be employed, lift cutting and added downforce would be employed.

I am not saying that it would be in any way easy to do, or legal to do, but I still see no reason why a car specifically designed for it, such as in a university challenge like a solar challenge, wouldn't work.

Again, go read the research. In fact, it as a solar car that I was referring to above that had handling control problems with 14 per cent rear lift. Do you honestly believe that the solar teams have overlooked something like you suggest? Given that many of these cars have aerodynamic lift, it would have been obvious in their testing if total resistance fell with speed - especially if there were no downsides.

Another thing you're ignoring: total aero drag normally goes up with increased ride height.

Tyre grip is not linear no, but I was approximating it to linear because the linear region is where most car tyres are. However, the graph you provided suggests that halving the force on the tyres leads to only a 25% reduction in grip.

I don't think you are considering where cars are on the tyre grip versus load curve.

I think what you are suggesting is a very bad idea, and it doesn't get much better as you keep altering the proposition. To be honest I am pretty surprised that you've put this idea forward as there's plenty in the published literature (that you normally read) to show how such an approach would be nightmarish in the real world.

[freebeard]

Here is your use case:

https://www.youtube.com/watch?v=BrCdsj_UrX8

[j-c-c]

Originally Posted by aerohead

The transmission, driveline, and final drive together, eat 24% of the power. Very close to what CAR and DRIVER has calculated with, giving us insight into the reverse-engineering their data, presented for the 2015 GMC Yukon Denali long term test.

Everybody knows heat is energy. If you want a quick lesson in efficiency, place your hand, only very momentarily on a rear differential after driving at high speed over any distance past say 50? miles. It is amazing how much internal friction there must be to generate that amount of heat in such a massive unit that has a large surface area open to the moving air, at speed. Don't forget that heat directly starts from the energy in the gas tank.

[j-c-c]

Originally Posted by JulianEdgar

N
Another thing you're ignoring: total aero drag normally goes up with increased ride height.
.

Maybe, but at some point when ground effect is overcome, ride height matters little, especially with an aero designed undercarriage?

[Isaac Zachary]

Originally Posted by j-c-c

Maybe, but at some point when ground effect is overcome, ride height matters little, especially with an aero designed undercarriage?

I believed you are right.

Streamlined half bodies get twice the coefficient of drag than a fully streamlined body.

Maybe a streamlined half body makes up for some of the loss with ground effects, but I'm sure it's not going to cut its Cd in half.

[JulianEdgar]

Originally Posted by j-c-c

Maybe, but at some point when ground effect is overcome, ride height matters little, especially with an aero designed undercarriage?

It's hard to keep up but last thing I noticed AeroMcAeroFace was talking about a 50 per cent reduction in vehicle weight through aero lift. That would certainly increase total aerodynamic drag.