Do Rear Spoilers / Wings Help Any?

[Christ]

Originally Posted by cfg83

Christ -



Oooooh, lots of combos here :

1 - Lower the front by 2 inches.
2 - Lower the front by 1 inch and raise the rear by 1 inch.
3 - Reduce the diameter of the front wheels by 1 inch and increase the diameter of the rear wheels by 1 inch. You'd get the 2 inch net and you could *claim* you were going for a classic race car look.

The first is the probably the best, but there's room for more choices.

CarloSW2

Doing the highlighted option would only get you 1/2" lowering in the front, and 1/2" raise in the rear. You'd need to double your lift/lower in tire diameter to net the same gain as altering the suspension.

I'm sure you know that, but I'd like to make it clear for others.

(Increasing the Radius by the same number as a suspension mod would create the same overall lift/lower, but the diameter is R2, which is to say that R = 0.5*D.)

[darcane]

Originally Posted by Christ

Carlos - Downforce. They use them in NHRA/IHRA as well.

I don't remember the whole reason they work, but I think I remember something about Bernoulli in there, or maybe I was day dreaming during that lecture. Either way, they're there to produce downforce.

Land speed racing is a whole different animal than drag racing. That spoiler is undoubtedly designed to reduce drag as well as reduce lift. At Bonneville, reducing Cd is the number one goal of body design. Often ballast will be added instead of spoilers to add downforce for traction since you have a long distance to get up to your top speed.

I've got a book called Competition Car Aerodynamics that discusses the effect of angle and spoiler length in some detail. According to it, on a typical stock bodied car, a spoiler with an angle less than 20° can both reduce lift and reduce drag.

Mike

[aerohead]

without endplates it's already been emasculated by GM.It's not large enough to effect much change even if it was "complete",and without the car or a set of blueprints for the car, it would be hard to calculate anything.---------- If it were mine I'd keep it.If I were going to investigate drag reduction in that region of the car,I suspect the final spoiler would be quite different.

[TOOSTUBBORN2FAIL]

Originally Posted by darcane

Land speed racing is a whole different animal than drag racing. That spoiler is undoubtedly designed to reduce drag as well as reduce lift. At Bonneville, reducing Cd is the number one goal of body design. Often ballast will be added instead of spoilers to add downforce for traction since you have a long distance to get up to your top speed.

I've got a book called Competition Car Aerodynamics that discusses the effect of angle and spoiler length in some detail. According to it, on a typical stock bodied car, a spoiler with an angle less than 20° can both reduce lift and reduce drag.

Mike

awesome book, even if its more related to racing, some of the stuff in it can still help here

[radioranger]

I'm betting it's used to help kill some lift , without increasing the drag , or both could happen , lift induced drag, since the car is wing shaped,

[aerohead]

I've been wrapping up noodling on the HOT ROD Magazine Camaro Red Hat Project LSR, Ford Fusion 999 Hydrogen LSR , and Volkswagen Jetta Hybrid LSR cars.
* All used wiper delete
* All used mirror delete
* All were lowered
* All used narrow GOOD YEAR EAGLE racing tires
* All used the MOON Equipment, full, convex wheel covers
* Two of three used 100% grille blocks ( Jetta did not )
* Two of three used 100% belly pans ( Jetta did not )
* two of three used rear spoilers ( Jetta did not )
* All cars were allowed a 5.3% frontal area reduction ( mirrors, lowering, narrow tires)
* The apparent departure angle, from backlight-to- spoiler top, happen to match the streamlined 2013 template contour for the Camaro and Fusion
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* The Camaro went from Cd 0.467 to Cd 0.20
* The Fusion went from Cd 0.34 to Cd 0.21
* The Jetta went from Cd 0.28 to an estimated Cd 0.2706 ( reverse-engineered from Volkswagen data )
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* The Cobalt sedan SS, with high-mount rear 'wing' is published @ Cd 0.324
( I've seen no other reported Cds for the Cobalt
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* The Cobalt EcoTec LSR car used wiper delete
* The Cobalt used mirror delete
* The Cobalt is lowered
* The Cobalt used narrow GOOD YEAR EAGLE racing tires
* The Cobalt used the MOON wheel covers
* The Cobalt used a 100% grille block, except for a combustion-air inlet at the forward stagnation point
* The Cobalt used a 10-inch rear decklid extension spoiler identical to that of the Fusion
* The Cobalt would have been allowed the 5.3% frontal area reduction
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I've yet to find a 'blueprint' for the Cobalt.
Should I do so, and find that it also matches the same contour, the implication for me is that the Bonneville spoiler allows:
* altering the basic vehicle configuration to generate negative lift ( W.H. Hucho, page 281, 2nd-Edition)
* ' Additional force is obtained by positioning the rear positive pressure far back behind the rear axle... thereby producing a greater leverage about the center of gravity.' ( Hucho, page 282-3, 2nd-Edition )
* ' The attached spoiler ... provide(s) nearly the same drag and lift coefficients as raising the upper rear edge ( of the body ) [ Hucho, page 175, 2nd-Edition ]
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The spoiler constrains the flow, forcing it to follow a streamlined pathway, facilitating flow attachment, flow deceleration, pressure recovery, increased base pressure, pressure drag reduction, reduction of rear lift, and providing a robust flow environment for pilot-chute inflation/ main parachute deployment.
It's not as 'good' as just streamlined shaping of the car, but it does satisfy SCTA Rulebook body modification limitations.

[aerohead]

*I printed off a blueprint of the coupe and sized it to fit my contours.
* The sedan and coupe are identical in both width and height.
* They're within a fraction of an inch in length.
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* Without the rear wing, the upper trailing edge of the deck is a match for the 2013 template.
* I've no idea whether the SS high-mounted spoiler is decorative, intended for direct downforce, nor whether it reduces, or increases drag.
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* The only Cd available for the Cobalt is for the 4-door sedan SS, at 0.324.
* This SS also has 1-inch extensions to the rocker panels and both fascias.
* There is no brake-horsepower/drag-limited top speed data available for the car.

[aerohead]

Using available photographs of the ECOTEC LSR car, I modified the technical drawing, lowering the car, and adding the SCTA-spec rear spoiler with 'spill' plates ( as they refer to capping plates ).
Estimated race car dimensions:
Length- 185.59-inches ( 4714 mm )
Width- 67.91-inches ( 1724.91 mm ) published
Height- 53.21-inches ( 1351.53 mm )
Body height- 49.116-inches ( 1247.54 mm )
Forebody- 54.22% of total length
Aft-body - 45.77%
Ground clearance- 1.00-inch ( 25.4 mm )
Verjungungsverhaltnis- 1.7296
L/H- 3.48787
L/h- 3.7786
L/W- 2.7328
( Long-tail length )- 261.42-inches ( 6640 mm )
L/ square-root of Af = 3.2329
Estimated coefficient of aerodynamic drag- 0.21
Estimated frontal projected area- 22.885-sq-ft ( 2.126 meters-squared )
Estimated CdA- 4.8058 sq-ft ( 0.4464 meters-squared )
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*The OEM Cobalt backlight base slant angle is 19-degrees
*The deck relaxes the backlight-to- trailing edge exit angle to 12-degrees, intercepting the 2013 template contour.
*Addition of the high-mount spoiler relaxes the backlight-to-trailing edge exit angle to 7.3-degrees, with the implication for direct downforce.
* Deleting the high-mount spoiler, and extending the decklid 10-inches, intercepts the original, 'slower' template, which also matches the 1981 VW-Flow Body contour ( Cd 0.14 ) and 2019 GAC ENO. 146 contour ( Cd 0.146 )