2002 NSX aerodynamics

[nsx4fun]

I posted the following on the Technical Forum, but this General Forum seems to get more action and still discusses a lot of technical topics, so here goes:

The new 2002 improved the coefficient of drag from 0.32 to 0.30
How???
Looking at the 2002, they added a lip under the wing. It looks like this can easily be added to my '92. Honda also changed the lower rear of the car, how much aerodynamic improvement is the new lower rear. Can it easily be bolted on to the earlier models? I think it also looks better, and the lower rear side skirts on my '92 have a fair amount of nicks from tire thrown rocks I presume, so a nice way to clean that up would be to replace with the 2002 design. I hope that someone has access to this info and can respond.

Regards, Fritz

 

[skim83]

I think the brunt of the decrease in drag comes from the deletion of the pop-up headlights. Please correct me if I'm wrong as I am about to get some shut-eye and can't refer to any articles.

 

[Jimbo]

I can't imagine the improvement came from the new headlights. The new units stick up more than the old flush pop-ups.

I think the improvement came from the front air dam, the rear valence and the lip on the trunk lid.

Just my opinion tho.

-Jim

------------------
1992 NSX Red/Blk 5 spd #0330
1991 NSX Blk/Blk Auto #3070 (Sold)
1974 Vette 454 4 spd Wht/Blk
Looking for 76-79 Honda Accords

 

[MAJOR STONER]

The leading edge of the 2002 front bumper is an inch higher than the 2001. Less downforce on the front of the car, but it slips through the air better. Top speed is up, but high speed cornering may be down.

 

[nsx4fun]

Jimbo, I'm sure all 3 contributed, but the front spoiler and the rear valence also have cosmetic effects, but the little spoiler under the wing is almost completely hidden. My question still remains how much of 0.02 improvement is a result of the little spoiler, & how much is the rear valence. These are the 2 areas I might consider changing, I've heard the little spoiler comes painted for $597. Another question would be, do they come painted in 1992 colors. I don't know if the new white is the same as the 1992 white. At work, a friend suggested getting it black, I wonder how that would look on a white car with Black roof and a black bra. I also have the window over the engine tinted Limo Black, hurts the nighttime visibility, but I think it makes the entire roof look much better.

------------------
Fritz

 

[1BADNSX]

My guess is that roughly half of the improvement is from the front bumper/air dam and the other half comes from the rear spoiler. I don't think the rear valance contributes much at all. Yes this is a guess, but based on years of experimental wind tunnel work and a PhD in engineering.

By the way, notice how Acura compared the top speed of the 91 model (168 mph) to the new model (175 mph). The new model needs both a 6% improvement in aero and 20 additional ponies to improve the top speed this much. It can be calculated and proven that neither the 6% improvement in aero or 20 additional HP will improve the top speed this much by themself because horsepower and Cd are functions of velocity cubed.

Bob

 

[nsxtasy]

Originally posted by nsx4fun:
Another question would be, do they come painted in 1992 colors. I don't know if the new white is the same as the 1992 white.

It is the same. However, paint can change color over time with the effects of the sun and the elements, so it's possible that it may not match precisely for that reason.

 

[nsx1164]

Originally posted by 1BADNSX:
It can be calculated and proven that neither the 6% improvement in aero or 20 additional HP will improve the top speed this much by themself because horsepower and Cd are functions of velocity cubed.

Add effective gearing (transmission and R&P plus the +1 wheel/tire setup) and I suspect you're there.

Interesting comment about downforce -- helps cornering but hurts top speed. Any info on comparative cornering ability ?

 

[nsx4fun]

Bob, I don't believe that Horsepower is a function of velocity cubed, and in fact, at those RPM's torque is decreasing. Friction from air drag though does increase drastically, although I thought it was velocity squared not cubed, but it has been years since Physics 11A. Could you provide me with the equation for Air Friction as a function of velocity? I presume it to be some constant times frontal area times coefficient of drag times air density times velocity (cubed or squared).

Fritz

 

[Number9]

Total drag is indeed proportional to Cd, A, and v^2. (Appropriate for spheres, cylinders, and automobiles.) I think you misunderstood Bob's remark about HP, as he seemed to be relating v to the HP required to achieve v.

[This message has been edited by Number9 (edited 01 April 2002).]

 

[1BADNSX]

Originally posted by nsx4fun:
Could you provide me with the equation for Air Friction as a function of velocity? I presume it to be some constant times frontal area times coefficient of drag times air density times velocity (cubed or squared).Fritz

You are correct about drag, but not power. Drag is proportional to velocity squared. The exact equation is D = Cd x A x density x VSquared / 2
Power is proportional to Cd multiplied by velocity cubed. It doesn't matter if you calculate top speed using drag and torque, or power. Just like acceleration, you get the same result using either method.

Bob

 

[Prancing Horse]

Very interesting discussion.
Bob pretty much nailed everything fairly well.

To understand the variables and its effects, and if your looking to get really technical here, I did a little research at the following site which has EVERYTHING relating to aerodynamics:
http://www.grc.nasa.gov/WWW/K-12/airplane/short.html

NASA has some excellent diagrams displaying the equations such as:

1. Definition of drag from NASA:

Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field or an electromagnetic field, where one object can affect another object without being in physical contact. For drag to be generated, the solid body must be in contact with the fluid. If there is no fluid, there is no drag. Drag is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid. If there is no motion, there is no drag. It makes no difference whether the object moves through a static fluid or whether the fluid moves past a static solid object. Drag acts in a direction that opposes the motion. (Lift acts perpendicular to the motion.)

2. Factors that affect lift (NASA also):

All that is necessary to create lift is to turn a flow of air. An aerodynamic, curved airfoil will turn a flow. But so will a simple flat plate, if it is inclined to the flow. The fuselage of an airplane will also generate lift if it is inclined to the flow. For that matter, an automobile body also turns the flow through which it moves, generating a force. (Lift is a big problem for NASCAR racing machines! Race cars now include spoilers on the roof to kill lift in a spin.) Any physical body moving through a fluid can create lift if it produces a net turning of the flow.

There are many factors that affect the turning of the flow, which creates lift. We can group these factors into(a) those associated with the object, (b) those associated with the motion of the object through the air, and (c) those associated with the air itself:

Object: At the top of the figure, aircraft wing geometry has a large effect on the amount of lift generated. The airfoil shape and wing size will both affect the amount of lift.
Motion: To generate lift, we have to move the object through the air. The lift then depends on the velocity of the air and how the object is inclined to the flow.
Air: Lift depends on the mass of the flow. The lift also depends in a complex way on two other properties of the air: its viscosity and its compressibility.
We can gather all of this information on the factors that affect lift into a single mathematical equation called the Lift Equation. With the lift equation we can predict how much lift force will be generated by a given body moving at a given speed.

I also found the amount of downforce on a CART car!!

:

2001 Penske-Reynard-Honda 2KI Indy Car Short oval configuration: Downforce:
2027 lbs. @ 165 mph, with 877 lbs. of drag
2978 lbs. @ 200 mph, with 1289 lbs. of drag
Lift-to-drag ratio: 2.31:1

Road track configuration: Downforce:
3328 lbs. @ 165 mph, with 1119 lbs. of drag
4888 lbs. @ 200 mph, with 1644 lbs. of drag
Lift-to-drag ratio: 2.97:1

Super-speedway configuration: Downforce:
1000 lbs. @ 225-230 mph, with 650 lbs. of drag
Lift-to-drag ratio: 1.54:1



I need to read up on wing geometry and velocity to see how that much downforce is generated!

-Nader

[This message has been edited by Prancing Horse (edited 03 April 2002).]

 

[MAJOR STONER]

It is official! The rear lip spoiler brings the drag down to .28 and the new lights bring it back up to .30.;-P

 

[nsx4fun]

OK Bob, now I understand what you meant. The drag is function of velocity squared (as I thought), & the rate of work done to push against that drag is a function of velocity cubed (as you stated). Thanks.

Major Stoner, where did you get your info? For me that is great news that the lip spoiler alone will make my '92 have less drag than the 2002. But I would like to verify your statement, before I pass it along to others as gospel.

Fritz

 

[millionshopper]

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David




[This message has been edited by gomaidy (edited 23 January 2003).]