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Old 02-15-2009, 01:55 AM   #21 (permalink)
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You are right- gusting. Well that's still wind ya gotta cut through even if periodically.

Metro: good find!

I thought this was interesting: "Fadler said: “Zero to 180 degrees is oncoming wind, and anything from 180 to 360 degrees is going to help you.” I'd think that the 90 deg xwinds and tailwinds close to that would hurt and not help. I mean- to pull numbers from the air to illustrate- I'd think it would be "Zero to 180 degrees is oncoming wind, and anything from 200 to 340 degrees is going to help you.”

Guess I'll keep yammering about yaw when it comes up.

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Old 02-15-2009, 06:04 AM   #22 (permalink)
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Hmmmm.....
most of the 90's british touring cars had single wipers, parked in the central position. I guess since then rules have changed?

Perhaps the difference varies car to car?



Infact on that picture i cant see one with standard 2 piece wipers
Ok so a few of those are in use as it's raining, but you can see.....
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Old 02-15-2009, 06:29 AM   #23 (permalink)
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cool, my car is in the lead

here's another one, the extensively greenpeace ecomodded twingo... but this is a one box design, with virtually no break between the window and the hood... on the speedster i think the windshield is much more bubble shaped, so a great portion of the air goes round the sides... this curve may make it difficult to install normal wipers.

what i do notice is that on modern cars the A pillars sometimes extend before the window, especially at the base... now this could be to trap rain, but on some cars it looks a bit much... perhaps this is to contain a high pressure bubble to shield the wipers, feed the air intake for cabin cooling etc, but in a controlled manner so the bubble becomes part of the cars "ideal" aero profile

the benefit of a single wiper will greatly depend on the size and pressure of the bubble and what goes on at the sides near the A pillars
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Old 02-15-2009, 06:35 AM   #24 (permalink)
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Aye,
Or a place to put the wipers (at the sides of the screen )


The wipers are so low profile on those cars ^
Also i dont really know if it needs to have the wipers sat there, as the trailing edge of the bonnet is already raised and there is a big step from bonnet to screen , height wise.


Regarding the greenpeace twingo :

I wonder how well the twingo's wiper works? surely it leaves the bottom corners un-wiped? Thats more hazardous than the top corners...
Also does where the wiper drive attach , not look like it may increasing the frontal area slightly above the car( might just be photo angle )
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Old 02-15-2009, 07:50 AM   #25 (permalink)
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Quote:
Originally Posted by aerohead View Post
During development of their PNGV Car,GM noticed during windtunnel evaluations,that the windshield wiper had virtually no impact on drag.-------- I eliminated the wipers on my CRX at Bonneville and it had no effect on top speed.It's possible that the high-pressure bubble just ahead of the windshield "shields" the wipers from the outer flow.
I would like to direct you back to my first post on this thread and the raising bonnet thread....

Quoting myself now :
"At higher speed my wipers start to get pushed up the screen - almost as far as half way lol . It seems a common problem, a few people from crx uk raise the bonnet, making the air flow over the wiper. Some other members move their wipers as far down as possible... so they are sitting on the black plastic trim.
The other members just buy new wiper arms lol "


Before i " fixed " the wipers, they would get pushed to about 45* , then the wiper sensor/motor would kick in and make them do their full sweep. At high speed i had no option but to have the wipers ON lol.

I would say that the airflow is hitting the wipers to pull them from their original resting place.

The way i got around that was sitting the wipers so that they point downwards, slightly towards the bonnet, which forces any force to be taken away from the tip of the wiper.....

I guess if you speed tested the crx, then 0.78mph is not worth much on a road car.
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Old 02-15-2009, 08:12 AM   #26 (permalink)
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I would also like to say that this problem seems to affect the phase 2 mark 2 crx. I have not heard of ph1 mk2 owners having the problem with their wipers being pushed up the screen.

For your info : the american ( and uk D series ) crx's which i refer to as phase 1, have a totally different front end ( headlights ,bumper, hood ...and suspension, track dimensions, wheel offset, crossmember etc etc - which makes my phase2 harder to get aftermarket parts for ! My phase2 was only available in the uk for 2 years)

American / d series / "normal " crx front end :



My " phase2 " front end :





Note the difference between headlights, center raised bonnet ( i think this is the wiper problem - although you would expect it to be the other way around ?!?! ) , bumper etc.

Many people dont realise the differences until they see the cars side by side
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Old 12-04-2009, 01:55 AM   #27 (permalink)
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yawn- more yaw!

the following two examples demonstrate the generic trends, but are not necessarily accurate for any particular vehicle.



For the first example, let us examine a generic sports sedan. Its top view is shown in Fig. 6.14 (this data is for a 20% scale model, at Re L = 3.0 x 10 6 , with smooth underbody). The graph depicts the effect of wind side-slip angle ▀ W on the aerodynamic coefficients. In order to explain the source of these aerodynamic loads let us observe the generic flow field depicted in Fig. 6.15. Basically, for the small, near-zero side-slip conditions the flow is attached on the vehicleĺs sides, and the pressure distribution (from a top view) resembles the pressure distribution on a thick airfoil.



The pressure distribution data of Fig. 6.16 (after SAE paper 73-0232) reinforces this comparison. This analogy to the airfoil case explains the almost linear increase of side force, C Y , with side-slip angle ▀ W , which eventually stalls at about ▀ W ~ 25░ (see also Fig. 5.16).

Returning to Fig. 6.15, you can see that at the larger side-slip angles the flow separates at the side of the vehicle, and when combined with the separation at the back, creates a much larger separation bubble. Because of the low pressure inside this separated zone, and the increase of the frontal area with increasing ▀ W , the drag coefficient increases sharply, as shown in Fig. 6.14. Usually, the larger separation bubble created by the side slip increases the velocity above the vehicle, resulting in a smaller increase in the lift. At very large side-slip angles (of over 35░), the separated area behind the rear window is reduced by the momentum of the side flow, causing a reversal of this trend in the lift (e.g., a local reduction in the lift).

Race Car Aerodynamics - Designing for Speed *-* Bentley Publishers - Repair Manuals and Automotive Books

Relevant even at lower speeds...
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Old 12-04-2009, 04:08 AM   #28 (permalink)
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my XT was single from the factory. I don't think they considered styling much at all so there must have been a reason for it.. (it IS very flashy though!)
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Old 12-05-2009, 03:57 PM   #29 (permalink)
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wiper

I can tell you categorically that below 100 mph they make no difference whatsoever.I suggest you put your energy elsewhere.Really,it's a dead end.

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