Chris evans top gear downforce confussion.

jej_knowles

jej_knowles

jej_knowles

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When watching the new show last night i found chris's description of how a rear wing works a bit confusing!
Watching the programme on bbci player his description on the rear wing of the viper starts at 5.30 into the programme. I find it strange that he says there is over a tonne of air pressing down on the wing? Does it take one tonne of air to produce one tonne of downforce?
 
School physics. Interesting question.

I would have though it'd be the angle of attack and the speed you are going at.

So my guess would be no. Does the the same mass of air hitting the wing faster give a larger force? I'm thinking yes.

edit:

I reckon I'm wrong now. Will be interested in the answer.
 
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Ignoring that air is compressible for the sake of convenience, and given the density of air is 1.2 kg/m^3, a tonne (1000 kg) of air would yield a volume of 1000/1.2 = 833 m^3.

That's almost a cubic kilometre of air.

To picture a cube of air with a volume of 833 m^3, let's take the cube root. The cube root of 833 m^3 is around 9.4 m. So each side of that imaginary cube of air has length of 9.4 m.

So do you think (almost) a cubic kilometre of air is acting down on the wing?

I reckon all he's done is taken the force acting on the wing and divided it it by 9.91 m/s^2 to give an equivalent mass, which he says is a tonne (since force is analogous to but not the same as mass * acceleration [where in this case acceleration is due to mavity at 9.81 m/s^2]).

But then how would he know the force acting on the wing?

My conclusion? He's talking ********.
 
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No it was just really bad terminology. Makes no sense whatsoever to talk about an amount of air pushing on the wing as if it's all sitting on top of it weighing it down! I chuckled at that :).

Ricochet J said:
Ignoring that air is compressible for the sake of convenience, and given the density of air is 1.2 kg/m^3, a tonne (1000 kg) of air would yield a volume of 1000/1.2 = 833 m^3.

That's almost a cubic kilometre of air.

To picture a cube of air with a volume of 833 m^3, let's take the cube root. The cube root of 833 m^3 is around 9.4 m. So each side of that imaginary cube of air has length of 9.4 m.

So do you think (almost) a cubic kilometre of air is acting down on the wing?

I reckon all he's done is taken the force acting on the wing and divided it it by 9.91 m/s^2 to give an equivalent mass, which he says is a tonne (since force is analogous to but not the same as mass * acceleration [where in this case acceleration is due to mavity at 9.81 m/s^2]).

But then how would he know the force acting on the wing?

My conclusion? He's talking ********.
Click to expand...

But this imaginary 833 m^3 (1000 kg mass of air) is itself in air - so it weighs nothing! His statment is even wronger than you give it credit for! :)
 
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Thought it didnt sound right. If he had said "the rear wing creates over a tonne of downforce" i wouldnt of queried it.
I know im being pedantic but it was the first show and everything should have been double checked.... Not buying chris evans as a knowledgeable car enthusiast. Unless were talking ferraris.
 
He means the cars aero produces 1 tonne of downforce. Although he didn't mention at what speed which is quite important (its likely to be right at the top of its 170mph+ limit).

Its just a badly worded statement to try to describe something in an overly dumb way.
 
Whilst it might not be exactly what meant, it's not inaccurate

On average, a column of air one square centimeter in cross-section, measured from sea level to the top of the atmosphere, has a mass of about 1.03 kg
Click to expand...

If, for the sake of convenience, we say the wing is a meter wide and 10cm deep (it'll be wider that anyway) then that gives the wing an area of 1000cm^2. At just over 1kg per square centimeter there is about 1 metric ton of air sitting on top of the wing, even if the car isn't moving.
 
kaiowas said:
If, for the sake of convenience, we say the wing is a meter wide and 10cm deep (it'll be wider that anyway) then that gives the wing an area of 1000cm^2. At just over 1kg per square centimeter there is about 1 metric ton of air sitting on top of the wing, even if the car isn't moving.
Click to expand...

If you put a metric tonne on the rear wing, the rear of the car would be scraping along the deck and the uprights bolting the spoiler to the boot lid would make the boot lid buckle if not tear through the boot lid.

edit: I should have read the whole thread
 
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Whilst the car is stationary, there is an equal and opposite force acting on the wing due to atmospheric pressure being equal at that level. Nett effect = zero.

At speed the air moving under the wing is at a lower pressure than that moving over the wing hence negative lift or downforce.

He was confusing units of mass with units of force.
 
I think the old Viper ACR wing would generate over 1 tonne of downforce once it its 150mph, and may apply here, it just got lost in translation, possibly because it went over Evans head.
 
Ricochet J said:
Ignoring that air is compressible for the sake of convenience, and given the density of air is 1.2 kg/m^3, a tonne (1000 kg) of air would yield a volume of 1000/1.2 = 833 m^3.

That's almost a cubic kilometre of air.

To picture a cube of air with a volume of 833 m^3, let's take the cube root. The cube root of 833 m^3 is around 9.4 m. So each side of that imaginary cube of air has length of 9.4 m.

So do you think (almost) a cubic kilometre of air is acting down on the wing?

I reckon all he's done is taken the force acting on the wing and divided it it by 9.91 m/s^2 to give an equivalent mass, which he says is a tonne (since force is analogous to but not the same as mass * acceleration [where in this case acceleration is due to mavity at 9.81 m/s^2]).

But then how would he know the force acting on the wing?

**
******.
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Erm... Thats exactly what i was going to say.....
 
They always make silly errors like that. Back when Hammond was riding a Pinarello (that's a bicycle, car fans) in Moscow or wherever it was he claimed it weighed 700g... Erm, no, maybe the frame does, but I can guarantee the whole thing weighs more than that.
 
Siliconslave said:
I'm pretty sure he was just reading the car's press release for the majority of the segment, that part didn't come across very clearly at all :(
Click to expand...

yes someone else would have prepared something for him to read and he just read it out.

they need to just remove him as soon as possible.he is a utter **** :p
 
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