Drag Racing Aero Help
 

Hello all,

You have kindly helped us before so would like some more advice/help if possible.

We have just bought the body below. Its carbon fibre over honeycomb and is a very nice piece.

http://i47.tinypic.com/205rqqt.jpg

My question is this, how can we make this as aerodynamic and slip through the air the best that we can?

We have yet to add spill plates to the rear of the body and also a gurney flap at the back.

Few more photos at the bottom for reference but any advice would be great.

Many thanks

http://i47.tinypic.com/124g86d.jpg

http://i46.tinypic.com/zit7hc.jpg

http://i50.tinypic.com/jfua2f.jpg

Definitely make sure the underbody is smooth, and that it stays smooth all the way to the tail. A diffuser would do better than a rear wing for low-drag downforce.

Since you'll be running with slicks, tread induced drag won't be much of a concern, but it might be a good idea to add some tire spats.

Its difficult to clean up the underbody of the car because this is meant to drop on top of a rolling chassis.

The front end of the shell looks fine.

I'd say taper the rear end sides of the of the shell inwards starting about in the middle of the rear fenderwell. Then, taper the rear of the cockpit shell back more towards the rear of the car so that it meets a 10-12* slope.

The entire shape of the shell looks like a wedge shape. Its fine that the front of the car has an incline, but maybe start tapering the rear end of the shell downwards about midway down the shell.

Sorry I should of said that we can't change the overall shape of the body mainly adding to it.

One thing we did think was to add some pieces, where the bump is on the 'bonnet' so that it goes right to the edge to meet the outer edge of the windscreen. that make sense?

I assume by wheel spats that AeroModder is referring to bodywork that covers the openings in the body for the arches. Sometimes referred to as wheel skirts.

I would try to smooth out what appear "headlight pockets" in the front. As well as any recessed pockets.

I noticed the vertical rear edges are rounded. I believe it is an excepted truth that making these a sharp edge produces less drag. By allowing the airflow to seperate more cleanly reducing weird vortex generation. Extensions here could be straight back or angled slightly with a transition radius. This would give a very small Kammback affect.

Are you allowed to create venturi tunnels on the bottom of the car to utilize the ground affect? If you are you may consider using this to supplement the downforce from the rest of the body & rear spoiler/wing. It would require a smooth undertray opening at the front of the car as well as some side skirting (may be able to use existing bodywork). Please note this is very ride height dependant.

The first thing I noticed is where the hood rise meets the cowl there is a pocket on each side that could be radiused.

Second, where do the tires sit in relation to the rear fenders? They should be farther in then the leading fender. The rear of the front wheel opening is a goo example of an exit curve. I believe the rear lugs shall be accessible, so full covers are out.

You will have to watch your hinges and tilt angle but try and clean up the rear underbody. It will reduce drag and add a little downforce.

Actually, I meant those little flaps in front of tires.

shape
 

If the windscreen/A-pillar weren't so generous in radius I'd say go ahead and push the blister out to the edges,but from the photos she looks really slick and don't think you'd see improvement at the trap.
The blower and bug-catcher can be extremely dirty and a lot of guys at Bonneville are finding more speed with the pro-comp type aero scoop/fairing covering the whole shebang.
The headers are also a source for interference drag,both from the structure itself and from the exhaust blast.You might look at some of the P-51 Mustangs which run the Reno,Nevada air races and look at how they configure their exhaust.If the epoxy finish can't handle the Btus,you could skin the affected area with stainless.
Safety/directional stability is your biggest concern at the speeds you run.
I was looking at photos of the Crash of the Chicken Hawk.They lost a freeze plug,squirted the tires,and got sideways;went over and 'inside' the guardrails for a total wreck.Driver went to the hospital.That was at only 111 mph!
I'd be tempted to maintain the wide boot ( no tapering ) just to have the drogue effect of the wider transom back there,helping to keep the car straight in the lane.
One day they may have a rate-gyro to automatically fire the chutes if a car gets sideways.I suspect the drivers are already plenty absorbed,concentrating on going 'forwards.'
Race safe!

Which edges do you mean? We are yet to add spill plates to the rear, like photo here.

http://i47.tinypic.com/35mjfo1.jpg

No nothing allowed under the car sadly, we can run a belly pan though so will make a new one of those.

Thanks again all for the replies.

Which bit can be radiased? Can you show on photo?

Photo above will give idea where the rear tyres sit. Does it help?

I understand the term exit curve now, also the front have a 'flare' to it also. This should help too.


When you say clean up the rear underbody? Do you mean for air to exit from under the car cleanly?

Thanks for reply, sorry but what is a drogue effect?

I was referring to the side of the car as it goes rear past the tail lights. Which would be just a few inches outside of what I think you called a spill plate. I don't know how they would work being so close to the spill plate.

Exactly. If the air is turbulent as it leaves the car, it creates drag. The ideal situation is to disturb the air as little as possible, keeping the flow as clean as you can.

Would it help if the spill plates go past the rear of the body? How much overhang? Will it help?

Ok that makes alot of sense.

So at the back of the car, do we leave the surface flat or add a gurney flap to detatch the air?

drogue
 

If the car had a full tapered tail it would be prone to behave more like a lake canoe or racing kayak,requiring constant inputs of the oars to maintain direction.
With the tail chopped off,the base pressure created behind the chop acts in a 'drogue'( braking ) effect directly opposed to the direction of travel,as the drogue-chutes do at the end of the run.
This drag is a trade-off for directional stability,keeping the boot going same direction as bonnet.

On the underside, leave it flat. A lip spoiler on the boot is the equivalent of a gurney flap, just turned upside-down.

If the rules allow, a diffuser at the end of a smooth undertray would be ideal, like this:

http://www.revozport.com/webpics/FER...s-diffuser.jpg

http://www.kwaninternational.com/ima...car%20race.jpg

This has two ideas that are good. the hood hump goes out to the edge of the windshield, and the air intake is almost embedded in the hood of the vehicle (think LARGE NACA duct). The red and black car also has canards in front of the exhaust (barely visible).


I am not sure what the rules are for the underbody/undertail. I would say that the number one thing that you can do is to create as much down force using the shape of the vehicle so that you don't have to have a wing create that force (which is also providing aero braking). Making air take the long way underneath and the short route above (low and high pressure, respectively) Sounds like a fun project.

I would test that rear "wind shield" area to make sure the air stays attached. The angle looks a bit steep, you might have some turbulence that can be resolved via vortex generators.

That makes alot of sense, thanks for that.

Also we researched this body shape, (its a 2003 Pontiac Firebird)

And the photos we found, they actually dont use spill plates....

Is this because the body is effient enough?

Nah nothing like that allowed, here is part of the rules copied...

BODY
Any modification to body not expressly permitted in this Rulebook is prohibited. Any body that meets the Funny Car body requirements in their entirety is acceptable for TMFC. These bodies must be run as they come from the FIA-accepted molds. Any modification not expressly permitted in the Funny Car (Section 5) body requirements is prohibited. Body model must be no older than 15 years maximum. All bodies must be 2-door sports car, 2-door coupe, or 2-door sedan body of a type originally mass-produced by automobile manufacturer. Must have originally measured 63 inches (160.0 cm) wide or more at centerline of front and rear axle. Maximum body and/or roof width cannot exceed stock dimensions. Duplications of production bodies of fiberglass or carbon fiber permitted. Body may be lengthened or shortened. Front and rear contour of body must resemble same configuration and design for specific body used; holes for air passage prohibited.
Maximum body width variation from front to rear is 6 inches (152 mm). Minimum body width is 60 inches (152.4 cm) when mounted. Bodies are measured at centerline of front and rear axles. Enclosing the wheel wells or the use of wheel fairings is prohibited. Fender flares or lips (maximum 1 inch [25.4 mm]) not on original factory-produced bodies will not be considered in any width measurement.
Wheelwell openings: front, minimum 5 inches (127 mm)
measured vertically from centerline of the front axle to wheelwell opening; rear, minimum 8 inches (203 mm) measured vertically from centerline of rear axle to wheelwell opening. Trailing edge of rocker minimum of 18 inches (45.7 cm) measured directly from centerline of rear axle. Front overhang not to exceed 40 inches (101.6 cm) from centerline of front axle. Beltline moldings (if on stock vehicle), headlight and tail light housings or indentations must be incorporated into body. Tail light area may be hinged (top only) for air venting, maximum 100 square inches (645 cm2) per side; any other holes in rear of body prohibited. Hood scoops prohibited; injector must protrude through hood. Maximum dimensions of hood cowling, 26 inches wide (660 mm) by 5 inches (127 mm) high. Opening for blower hat must have a minimum 2.500-inch (63.50 mm) clearance between body and throttle linkage.
Rocker panel extensions may not be more than 1 inch (25.4 mm) wide. Ground effects of any description prohibited. Ground effects include, but are not limited to, rocker skirts, belly pans, sheetmetal work under the body that produces a «tunnel» for the passage of air, etc. Final determination on all body modifications rests with FIA Technical Services Department.
Bodies must be removable from a rear-release mechanism that must be accessible in the taillight panel area. The rear-release mechanism must be the pin and cable type. The mechanism must be unobstructed and easily visible and not located within 3 inches (76 mm) of any other opening. Release handle must be T-handle design with minimum measurement of 3 inches (76 mm) in length. Contact FIA Technical Services Department for acceptable design, operation, and installation.
Body (hood) burst panel, minimum 288 square inches (1858 cm2), mandatory on all screw-supercharger-equipped cars. Body burst panel must be secured with plastic screws and two 1/8-inch (3.2mm) stainless steel wires, with body pad bolted with plate on both sides of panel.
Any new body designs or concepts must receive approval from FIA prior to competition. Plans, drawings, pictures, etc., must be submitted to the FIA Technical Department for approval. Body specifications may vary for certain exhibition vehicles; prior FIA approval necessary. Underside of body, including roof area and all composite components such as timer boxes etc, must be covered with an FIA-accepted SFI Spec. 54.1 flame retardant covering or coating. Must be applied according to the manufacturer’s specifications and recommendations.
All bolts and fasteners on body, windows, etc. must have button heads toward outside of body. All stiffeners must be placed on the inside of the body, whether on windows, spoiler, etc.
Mounting trees for body may not be adjustable. The framing must be a permanent fixture, with no adjustments.


GRILLE
Must be equipped with a simulated grille of same configuration and design for specific body used, holes for air passage prohibited.


7.7 REAR BUMPER
Must be equipped with rear bumper consisting of a minimum vertical surface of 3-inches (7.65 cm); maximum allowable cutout for parachute shroud lines 4-inches (10.2 cm) by 30-inches (76.2 cm). The trailing edge of rear bumper may not extend more than 54-inches (137.2 cm) from the centerline of the rear axle. Maximum measurement from trailing edge of the rear bumper to ground, 29-inches (73.6 cm) at rear tire pressure of 4.5 PSI (.64 bar). Maximum 1-inch (2.54 cm) lip permitted on rear bumper as a stiffener, not included in overall measurement.


7.8 SPOILERS
Permitted front and rear. Rear spoiler cannot be “built-in” to body. Rear deck relocation cannot extend more than one-third of the as-produced replica body’s rear window. Side surfaces of elevated decks must be completely covered by spoiler spill plates.
Maximum rear spoiler width, including spill plates and attachment points, 54-inches (137.2 cm). Rear spoiler spill plates cannot be located forward of the centerline of the rear axle and onto rear quarter. Spill plates cannot be more than 5-inches (12.7 cm) above the roof line. Rear-most point of spill plate may not exceed 60-inches (152.4 cm) past the centerline of the rear axle. Spill plate supports permitted on one side of spill plate only, not both. Lip on rear edge of spill plate (vertical) .5-inch (1.27 cm) maximum.
The trailing edge of rear spoiler may not extend more than 56-inches (142.2 cm) past the centerline of the rear axle, may not be over 3-inches (7.65 cm) above the roof line, and the forward and trailing edge may not be mounted so as to preclude a “wing” configuration. Wicker on spoiler not to exceed 2-inches (5.1 cm) forward or back. The installation of vortex generators is permitted on the spoiler assembly only; prohibited on car body. Any adjustment or movement during run prohibited. Air flow through spoiler or past the underside of spoiler, other than hinged tail light area, prohibited.


7.9 WINDOWS
Windshield mandatory. Side windows optional. If windows are used they must be clear. Side windows must have a minimum 6-inch (15.2 cm) diameter opening adjacent to driver. See General Regulations 7.8.


GROUND CLEARANCE
Minimum 3-inches (7.6 cmm) from front of car to 12-inches (30.5 cm) behind centerline of front axle, 2-inches (5.1 cm) for remainder of car, except oil pan and exhaust headers.


INJECTOR SCOOP
Injector scoop may not extend more than 18 inches (45.7 cm) forward of the center of the forward engine cylinder, may not extend more than 12 inches (30.5 cm) behind the center of the rear engine cylinder, may not be higher than the top of the windshield, may not have more than 1 square foot (929 cm2) of opening area, and may not be more than 24-inches (61.0 cm) wide.

Canards in front of the exhaust is a very good idea. Something easy to do too.

We wont need to use a huge wing at all I dont think. Google Pontiac Firebird funny cars, none of them seem to use one.

Thanks again all

How could I test it?? Drips of oil ??? See if it runs??

Those rules don't leave you much of anything... Undertrays are definitely out. So are vortex generators.

Also, you can test airflow by using short lengths of string taped to the body. It's known as "tuft testing."

They are quite restrictive, its why we want to make the absolute best we can with this body.

Oh I know I have read it on this forum, thanks.

Ok another way were aiming to help our elapsed time and mph is weight, were on a mission to lighten the car as much as we can.

Thanks for all replies, please keep suggestions coming.

Also just read about this too...worth doing?

Rear corner airflow trip feature - permalink

Airflow along the side of a vehicle tends to follow the curvature of the tail lights and bumper part way around to the rear of the car, which can cause more drag than a sharp corner "crease" that promotes clean separation at the trailing edge.

GM designers integrated such a crease at the rear of the Chevy Volt "production" concept, a feature that could be retrofitted onto existing vehicles.

Examples \ Info \ Threads:

efficient enough?
 

The body looks like a continuous wedge growing wider and wider to the rear.
The way the nose divides the airstream,the flow down the top and side,their respective velocities may be closely matched.If that is true then you'll have a nice clean separation to the turbulent wake without counter-rotating attached vortices at each side.So maybe on account of that they skip the spill plates, figuring the pilot chutes will find good air for which to yank the parachutes out of the packs and not just get slammed into the track.
I think we'll all suspect you've got some separation just behind the backlight but it sounds like the rulebook says you can't touch that area,and there's plenty of room for re-attachment,so with the exception of the small burble,the boot will be clean.
It would be nice if the body manufacturerer could provide you with a center of pressure location to compare to the center of gravity.You might want to run the spill plates just to have some weather-vane back there.If you somehow lost traction under power and one wrinkle-wall was centrifugally larger than the other,the rear end could try and steer into the smaller tire ( I don't know how effective the little drag tires are at the front for steering )and if you were getting crosswise,the weathervane might help coax the tail back,keeping you out of the guardrail.

Correct....in fact in the Hybrid version of the GMC Yukon, you will see that it uses extensions on the rear pillar and sharper profiled tail lamps to promote clean separation.....its a slight difference that the casual observer may not even notice. The regular Yukon is rounder.

But don't forget in your application you have vents/flaps where the tail lights normally are that feeds air into where the potential turbulent wake would be.....so I don't think its really an issue for you....again this can be tested using tufts.

It really is too bad that they don't allow for smooth under-bodies and rear diffusers...you would have a venerable guided missile if they did.

That makes sense, think what were likely to do is make the spill plates ready to fit and test the car, if its not nice to drive the fit them to try. But were going from this body below so believe me this new body will be like a Rolls Royce!!

http://i47.tinypic.com/r218wk.jpg

Ok I will leave these for now then, thanks for the info.

Really finding aerodynamics very interesting, bought a few books on it which I am reading at moment.

Well as for the smooth under-bodies, we can have a belly pan, and there is a flat pan under the greabox area too. I will try to find a photo...

Found a photo. Its a crach of another car but gives an idea of the underside.

http://i47.tinypic.com/2uo30ck.jpg

This is also worth a read

Hairy Glass - Hairy's History

safety
 

Great read,thanks!
Comforting to know they're not blinded by speed and driver safety and stability remains paramount.
A good Hairy Glass day and you live to race again!

As is this if you dont already have it:

Race Car Aerodynamics: Designing for Speed…

By Joseph Katz

http://www.amazon.com/Race-Car-Aerod.../dp/0837601428

Here is a novel idea...one that has come more into play with auto manufacturers with the advent of increased fuel economy.....since the body is pretty much optimized and has strict rules with how much you can do, how about improving the aerodynamics under the body. New car manufacturers are even more trying to improve the airflow under the hood, around components, smoothing things out and providing channels to evacuate air quickly and efficiently. F1 has been doing it for years, they place and design everything with aero in mind, even if it means slightly less than optimal location, from a mechanical standpoint.

I am wondering if your "cockpit" and all the mechanicals, if it were all enclosed in an optimized cocoon like shape, if then the airflow that does come in there would more readily leave that area and do so quicker with less resulting drag. Since air will inevitably make its was under the car, getting it out as fast as possible might help you shave off a few tenths. All those bars under there could slightly benefit from some carbon airfoil shrouds.....some downforce might also be found there. You probably would have to do some runs and see just what kind of airflow is going on under there...some tufts, and some onboard mini cameras might tell you a lot. To put it another way....perhaps designing the car without the body on it to be as aerodynamic as possible (keeping in mind the direction in which the air is coming in from) might help when the body is back on.

Thanks, got this one, great book