Chin spoiler question

[Recumpence]

Hey Guys,

I am planning on installing a chin spoiler/nose pan combo on my C-Max. The car has a partial pan right now. However, the stock chin overhang is higher than the rear portion of the pan (just behind the radiator). So, the air accellerates as it is forced under the nose of the car. So, I am planning on making a modest air dam that terminates into a flat pan under the engine compartment. This pan will be parallel with the ground to eliminate this air accelleration.

Does this sound correct?

Oh, eventually I will do an entire belly pan. But, for now, I have to start somewhere.

Matt

[aerohead]

The SAE has recommendations for approach,breakover,and ramp clearances so none of a cars naughty bits are torn off,scraping on a driveway ramp,railroad crossing,etc..
For the front of a car,a 16-degree approach angle is recommended,as measured from where you can just see daylight between the front tire tread and road surface and any part of the car ahead of that point.
If the airdam extends too much your drag will go back up as you add frontal area.
If you're willing to modify your driving technique you can suffer through with a lower dam,but you'll have to approach some road hazards obliquely so as not to encounter a ground strike.

[Recumpence]

I would not be increasing the frontal area. What I would be doing is lowering the chin portion of the nose to the minimum level of the front pan area at the front suspension. The chin of the car is currently a couple inches higher than the area near the front axle. That is the point of my question in this tread. Right now, the air in compressed and accelerated as it goes from the chin area to a narrower area (lower) near the axles. If I lower the chin down a touch, the air will not compress because the nose pan will be level due to lowering the chin.

Does that make sense?

Matt

[mcrews]

pictures really would help

[aerohead]

Originally Posted by Recumpence

I would not be increasing the frontal area. What I would be doing is lowering the chin portion of the nose to the minimum level of the front pan area at the front suspension. The chin of the car is currently a couple inches higher than the area near the front axle. That is the point of my question in this tread. Right now, the air in compressed and accelerated as it goes from the chin area to a narrower area (lower) near the axles. If I lower the chin down a touch, the air will not compress because the nose pan will be level due to lowering the chin.

Does that make sense?

Matt

Ah,since the plan is top lower,get a scrap piece of cardboard,take a protractor and create a 16-degree template,short side as tall as your bumper bottom.
Slide it under the car until it contacts the front tires.
The line of the hypotenuse of the angle describes the 'clearance' elevation of which no portion of the car can be below or else it will be struck by things civil engineers design.
As to 'compression,' that actually doesn't begin to occur until your going about 250mph.
A proper chin spoiler will shear off the airstream at the lower edge with no velocity increase,and send the rest of the air over or around the nose.

[Recumpence]

Originally Posted by aerohead

A proper chin spoiler will shear off the airstream at the lower edge with no velocity increase,and send the rest of the air over or around the nose.

That is my goal.

Right now air is forced under the nose of the car, more than I would like. I would prefer seeing more of it diverted around the car.

Matt

[ECONORAM]

Originally Posted by aerohead

The SAE has recommendations for approach,breakover,and ramp clearances so none of a cars naughty bits are torn off,scraping on a driveway ramp,railroad crossing,etc..
For the front of a car,a 16-degree approach angle is recommended,as measured from where you can just see daylight between the front tire tread and road surface and any part of the car ahead of that point.
If the airdam extends too much your drag will go back up as you add frontal area.
If you're willing to modify your driving technique you can suffer through with a lower dam,but you'll have to approach some road hazards obliquely so as not to encounter a ground strike.

That crossed my mind when I saw a RAM truck modified for the Salt Lake flats a couple years ago. It had a ground dragging air dam, and I thought that would add too much frontal area... I kept that in mind when I made my front wheel fairings. I tried to keep them inline with the tires, slightly wider.
If your revised air dam is lower in the front, but doesn't go below the height of other items under the vehicle, I think that will work well. Perhaps if it were shaped a bit like a wedge, with the center the most forward and the rest trailing back to the front wheels it might benefit you even more.

[Recumpence]

I measured the nose of my car (finally) and what I found was; the nose of the car is 9.5 inches off the ground. However, the belly pan under the engine is only 5 inches off the ground. To complicate things, there are also air deflectors that narrow the opening between the front wheels. So, to the best of my calculation, the air is forced into about 40% of its innitial area. So, I will try the chin spoiler at various heights to see what affect it has on the aero efficiency of the car. Obviously, a 5 inch high chin spoiler may be a bit too low for normal driving, but, then again, maybe not. It all depends on the areas I drive in. Maybe I will make a very cheap (I.E. Choroplast) chin spoiler that I don't care if I wreck to test before I make a pretty one.

I also found quite a few ways to clean up the air flow around the nose of the car and under the rear end of the car as well. In fact, a few of these mods will probably look really cool too!

Matt

[SlideWRX]

Originally Posted by Recumpence

That is my goal.

Right now air is forced under the nose of the car, more than I would like. I would prefer seeing more of it diverted around the car.

Matt

Forcing it to go over or around the car will require MUCH more acceleration. Afterall, isn't the car around 50-60 inches high? 60-70 inches wide? The airflow under the car may be tuned to help balance the downforce at highway speeds, besides. If there is a belly pan, that is fixing the primary reason to divert air from the underbody.

I'd suggest adding to the belly pan more than diverting air from the underbody.

[Recumpence]

I completely disagree. The underside of the car is much more turbulent than the top side and the road compresses air against the underside of the car. Minimizing air flow under the car is much more beneficial than the air flow above it.