It is well known that the force due to air resistance varies according to square of the speed so it requires a lot more bhp to go an extra 10 mph faster at 150 mph than it does at 50 mph.

So to overcome this, why don't car manufactures fit a big vacuum cleaner in front of the car to suck air out of the way so that the car is driving in a vacuum?

The amount of power required to reach high speed will be minimal - just overcoming the rolling resistance of the car - but a small amount of power would be used by the vacumm cleaner, and the air coming out of the vacuum cleaner can be channelled into a funnel to act as a rocket booster further improving performance and/or ecomomy.

So obvious really.

air resistance is just the effort required to move the air round the car. Thats exactly what the vacuum cleaner would be doing so you would save no effort.

Assume the front area of the car is 2 square metres and it is traveling at 50 miles per hour, 22 metres per second and it will have to shift 44 metres per second every second, reduce this through an intake port (rad grill) at say less the 0.25 square metres move it to the back of the car under pressure then let out to air again.

Can be done, but add a bit of fuel and a few fans to do the job and hey!!! you have a jet engine.

Cheers

Adrian

better sucking theai rom underneath the car to get more downforce Chaparel did this in the 70s it was so succesful it promptly got banned! No reason why not adapt a leaf blower for track days though

Caber

quote:

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Originally posted by AdrianH
Assume the front area of the car is 2 square metres and it is traveling at 50 miles per hour, 22 metres per second and it will have to shift 44 metres per second every second, reduce this through an intake port (rad grill) at say less the 0.25 square metres move it to the back of the car under pressure then let out to air again.

Can be done, but add a bit of fuel and a few fans to do the job and hey!!! you have a jet engine.

Cheers

Adrian

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A gas turbine makes a good vacuum cleaner - the exhaust helps with forward motion too!

How about if you have an engine-driven suction fan , maybe powered by hot exhaust gas , then you could push the air it sucks in from the front of the car through the engine and out the exhaust.......
I dont know if there would be that much air moved , but it may help generate a little extra power to overcome that pesky air resistance

Check the Grassroots Motorsports site in the US. There was a Corvette with a giant fan where the passenger was supposed to go, that did very well in autocross.

Many aircraft have been built with tiny holes in the wings, with a vacuum to keep the air as close to the surface as possible for just the reasons you mentioned. In a car, I think it would be too costly.

[Edited on 11/4/08 by RK]

and i thought the TD meant Turbo Diesel not Twin Dyson

Someone did once suggest something similar but they wanted to "throw" the wake of the car in front of it and so use its own slipstream to pull it along.

Another genius one was to fit a converging nozzle to the car. As the air accelerates through the throat of the nozzle it would behave like a jet engine and propel the car forwards, increasing the effect and moving the car ever faster.

These people had evidently not paid attention in science class at school.

quote:

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Originally posted by 02GF74
It is well known that the force due to air resistance varies according to square of the speed so it requires a lot more bhp to go an extra 10 mph faster at 150 mph than it does at 50 mph.

So to overcome this, why don't car manufactures fit a big vacuum cleaner in front of the car to suck air out of the way so that the car is driving in a vacuum?

The amount of power required to reach high speed will be minimal - just overcoming the rolling resistance of the car - but a small amount of power would be used by the vacumm cleaner, and the air coming out of the vacuum cleaner can be channelled into a funnel to act as a rocket booster further improving performance and/or ecomomy.

So obvious really.

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The tiny holes in wings are for suction but the reason for these is actually to maintain a laminer boundary and so prevent onset of turbulent boundary layer as that is more likely to seperate from the surface of the wing and increase drag.
Therefore this concept does not suck the vehicle along but I suppose you could blow the air out the back

I believe I said "for just the reasons you mentioned" which I had understood as, in a nutshell, "to reduce drag", which is what the holes in the wings are ultimately for!

Certainly, laminar flow is considered in F1 as well, which we see as "very shiny, smooth surfaced cars"!

Sorry but the reasoning here is the wrong way around. The idea of porous wings and boundary layer suction is to maintain laminar flow because it has a lower skin friction than turbulent flow and friction drag is a very large contributor to the overall drag of a plane. Turbulent boundary layer flow gives a higher friction drag but is much *more* resistant to separation than a laminar one, not less. This is why you get the dimples on a golf ball, for example, to force the flow to be turbulent when it would otherwise be laminar. It can then stay attached further around the circumference of the ball, leaving a smaller wake and lower overall drag. A friend of mine was doing a Phd on active boundary layer control for aeroplane wings but kept finding that it took too much power to suck the flow through the (necessaily really small) holes that it just wasn't worth doing (bearing in mind icing, dirt blockages and maintenance etc).

It's not really the reason they make F1 cars so shiny either, as that's primarily just for show. The associated aerodynamic benefit is small, because all the lifting surfaces are working so hard that they need turbulent flow from fairly early on along each surface for it to remain attached. The request for a highly polished finish comes from the marketing department, not the aero one.