pitot tubes on race cars

[Mike Arman]

>From: Ado Sigal <a.sigal at bluewin.ch>
>Subject: Re: pitot tubes on race cars


>  Marketing techniques have been mastered times over,
>while the aerodynamic expertise still produces aero designs that do
>exactly opposite than required, and where highly paid and appreciated
>car aero experts still have 'grey areas' within their aero expertise,
>even after spending decades designing and testing their creations.
>Strange that.
>Cheers,
>Ado


A hundred years after Orville and Wilbur, aerodynamics are *still* not as 
well understood as some of the experts would have us believe.

Examples from the aviation world - in the search for better and more 
predictable LOW speed performance on single engine Cessnas, there are four 
approaches.

1) A set of wing tips that droop down at the ends (almost a foot!). These 
increase the effective span, and create a high pressure area near the 
ailerons, giving a more stable ride and better roll control at low 
airspeeds. ("Madras" wingtips.)

2) A set of wing tips that are cut upward from the bottom (wedge shaped), 
and do not extend downward at all. These give *exactly* the same results as 
#1, and the stall seems more predictable. ("Hoerner" wingtips.)

3) Vortex generators glued (!) to the upper surface of the wing. These 
re-energize the boundary layer air flow, and delay the stall by keeping the 
airflow more "attached" to the wing surface.

4) Drooped and re-contoured leading edges, plus drooped flaps. This 
increases the camber of the wing, but is an expensive way to go, especially 
when option #3 gives 95% of the results at 20% of the cost.

Air acts somewhat like a FLUID, and thus airflow is sometimes unpredictable 
and often surprising.

At low speeds in a car (like 55 mph), it doesn't make a heck of a lot of 
difference, so all the wings and ground effects panels on Grand Prix's, 
Jeep Cherokees. and H*ndas don't really do much of anything beyond making a 
statement about the owner. (Remember that cars are not supported by air 
flow, and airplanes are, so this is not contradictory to the previous 
statement.) In the automotive world, 55 mph is the domain of the stylists, 
the marketing department, and the bean counters

At 155 mph, however, since drag goes up as the SQUARE of the air velocity, 
these things become much more important. The "breeze" under a car at 55 mph 
is not a major factor in its' handling or "flyability", but at 155 mph, it 
becomes another story entirely. You have a lot more than three times the 
pressure at three times the speed, and yes, you can probably get Grandma's 
Sentra airborne if you can get it going fast enough. 155 mph belongs to the 
engineers.


Best Regards,
Mike Arman