NSX aerodynamics

The first gen Insight (ZE1) is one of the best examples of an extrem wind slippery car. BUT the car is very, very sensitive to crosswinds above 50 mph. It needs the amount of correction trying to go straight in heavy crosswinds that you have to reduce the speed to feel more or less safe. It's not lift front or rear I guess. The car is very light, the wheelbase is quite narrow and the tires are narrow. Honda engineers went at one extrem between air drag and high-speed stability. Noone would accept the behaviour of such a car nowadays. But up to the 70ies most of the cars were like that BUT NOT aero at all. :)
For vintage car testing fans (I really love these true kind of car testing videos): https://www.youtube.com/watch?v=5M1Y7gC0vkE FF to 9:15 a car is running at 62 mph in a crosswind section with also 62 mph. The deviation is mesured without correction via the steering wheel.
 
The first gen Insight (ZE1) is one of the best examples of an extrem wind slippery car. BUT the car is very, very sensitive to crosswinds above 50 mph.

Good video! At 9:15 you can see how the Opel Kadett's nose is pushed off course by the crosswind more than its tail is. That happens when a car's aerodynamic center of pressure is located further forward than its center of gravity. Think of an arrow. With feathers at the back, it will tend to point into a side wind. If the feathers were at the front instead, the nose would get deflected and it would be very unstable. If the center of pressure coincides with the center of gravity, a car will just get laterally displaced in a crosswind. Supposedly one of the reasons why the NSX's tail was made long was specifically to improve its stability in crosswinds. (source: Brian Long's book "Acura NSX, Honda’s Supercar", page 22)

In a side wind, does the first generation Insight get laterally displaced with the nose still pointing in the right direction? If the nose gets pushed off course more than the tail, I hope Honda does a better job designing the new NSX. Low drag does not have to go hand in hand with susceptibility to side winds!
 
Supposedly one of the reasons why the NSX's tail was made long was specifically to improve its stability in crosswinds. (source: Brian Long's book "Acura NSX, Honda’s Supercar", page 22)
I remind Honda also stating/advertising that the differential in the gearbox corrects for crosswind influences.

Low drag does not have to go hand in hand with susceptibility to side winds!
It's a big trade-off. It would be interesting to see an XL-1 in a crosswind test. Being lower and wider I guess it would be much more stable than an ZE1. But this is a bit OT in a sportscar forum.
Andreas, I think you're one of the very fastest drivers in the world. How does the NSX behave at 300 km/h? :wink:
 
The lighter the car and the larger its side area, the more easily it will get deflected by cross winds. However, I think the trick is for the front to get deflected the same as or less than the rear. If the car is designed so that the center of pressure lies at or behind the center of gravity, the car will either just get displaced laterally or actually kind of self correct because the nose will want to point a bit into the side wind. Arrows and missiles are both aerodynamic and stable – the two are not mutually exclusive.

I agree, it would be interesting how a VW XL1 reacts to cross winds and whether Volkswagen even paid attention to that when designing a slow car.

In my experience, with its nice long tail, our aerodynamic NSX is stable at 300 km/h. A colleague of mine drove my NSX at almost 300 km/h when it had a completely stock underbody and he said the car felt more stable at that speed than his BMW did at 250. I have found my NSX can get a bit twitchy at 300 km/h if the alignment is off, however.


Edit: just a thought – to improve crosswind stability, you could try playing with the alignment settings. When a crosswind hits a car, it doesn't just push the car at the front and back, it also tries to tip it. That reduces the load on the wheels facing the wind so the wheels on the downwind side carry a higher percentage of the car's weight. If you increase front toe-in, the load-bearing downwind front wheel will try to steer a bit into the wind. Theoretically, at least. I don't know how much of an impact that would really have.
 
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Alignement can help I'm sure but in a ZE1 it's a mpg-hit going toe-in or toe-out (toe is Zero from the factory). You could also Mount tires with more grip but again that's a big hit in mpg. But this is a very different car for a very different task. But interesting to see that Honda ever built such an extreme car.
 
sure, but when the NSX was designed and into the 90's it's aero ranked amongst the best for downforce vs drag, especially the NSX-R. Comparing with recent designs seems pointless.

And anyway, they look absolutely terrible and very boring !
 
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and the Cruze handles rough weather and crosswinds way better than the Honda (Acura) NSX.

And if you think the NSX is the epitome of aerodynamic efficiency, you would be wrong. This guy right here, the Nissan GT-R, may not look the right shape for an aerodynamic supercar, but it still achieves a coefficient of drag of just 0.26, among the best of a car in production today, and unlike the NSX, the GT-R is a mass-produced supercar

In the case of Cd as Sparky mentions the NSX design dates back over 25 years and much has been learned about drag and lift since then.
Back in the late eighties most sports cars had Cd's in the low 30's which reflected the need to control lift at high speeds.
High speed stability was a very high priority back in the day.

New designs can deal with managing lift without a corresponding increase in drag.

It's not uncommon these days to see very low Cd's from passenger sedans like the Cruze ,Toyota Corolla etc. as they are low speed machines and the designers can focus on reducing drag without being concerned with lift.

I find it a bit hard to believe a car with the side profile of a Cruze could handle crosswinds better than an NSX.
Is your comment based on a comparison of your NSX and your Cruze?
 
CD is only half of the drag equation. Total drag is CD*Frontal Area. While the GTR has a low CD, it has a very high Frontal Area.

As JD mentioned, CD can be reduced by accepting lift in a car. The NSXs aerodynamics was a compromise of drag, cross wind stability, and minimal lift. With almost zero lift and, a good CD, and small frontal area, its a pretty good design. You can't be narrowly focused solely on CD.
 
KEY:
frontal surface area (A)
cw (cd)
air drag index (cd x A)
at 200km/h (125mph)
lift front axle
lift rear axle

Honda NSX-R (2002)
(A): 1.7800 m²
(cd): 0.34
(cd × A): 0.60
at 200km/h
downforce front 32kg
downforce rear 5kg

Another source:
NSX-R - 1.78 sq.m (Announced)
0.32cd =
0.57cda

Ford GT
(A) 1.92 m²
(cd) 0.35
(cd × A) 0.67
at 200km/h
downforce front 44kg
lift rear 2kg
http://www.automobile-catalog.com/auta_details1.php

This site says the 05-06 Ford GT was:
1.82m^2
0.31 CD
0.565 CDA

New 2017 Ford GT:
1.779m^2
0.35-0.388CD
0.623-0.690 CDA

http://www.suzukaracing.com/GTR page/racetoroadgtr.pdf

Frontal area:

NSX-R - 1.78 sq.m (Announced) X 0.32cd = 0.57
Carrera GT - 1.9 sq.m (Calculated) X 0.39cd = 0.74
Porsche GT2 - 1.9 sq. m (Estimated) X 0.32cd = 0.61
360 Modena - 1.906 sq. m (Calculated) X 0.34cd = 0.65
Nissan GTR - 2.09 sq.m (Estimated) = X 0.27cd = 0.56


2007 Lamborghini Gallardo
Cd 0.34
Frontal area 1.95 meters^2
CdA = 0.663

2009-2011 GT-R
Cd 0.27
Frontal area 2.09 meters^2
CdA = 0.564

2011 Turbo and Turbo S Coupe
Cd 0.31
Frontal area 2.05 meters^2
CdA = 0.635

C6 Z06
Cd 0.34
Frontal area 2.07 meters^2
CdA = 0.703

Veyron
Cd 0.36
Frontal area 2.07 meters^2
CdA = 0.745

http://press.nissan-global.com/PRESSKIT/NISSANGTR/0710/ENGLISH/index.html

Cd: 0.27
 
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http://www.automobile-catalog.com/auta_details1.php

This site says the 05-06 Ford GT was:
1.82m^2
0.31 CD
0.565 CDA

New 2017 Ford GT:
1.779m^2
0.388CD
0.690 CDA

Nice quote :)

I already had the numbers (they are from the German Sportauto magazine) for the NSX-R, but did not have the GT numbers.

A lot of sports cars end up with much more drag (and lift) then the original NA1 and/or NA2 NSX, either by their size or Cd-values.
And most of them don't generate any downforce at all at high speeds.

Lots of people tend to dismiss the original NSX just because it's an 'old' car by now, but many people forget how much work Honda put into its design.
 
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