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Bennett_Racing 06-21-2010 08:38 AM

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

AeroModder 06-21-2010 11:04 AM

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.

theycallmeebryan 06-21-2010 11:14 AM

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.

Bennett_Racing 06-21-2010 12:02 PM

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?

DonR 06-21-2010 01:28 PM

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.

JasonG 06-21-2010 02:14 PM

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.

AeroModder 06-21-2010 03:10 PM

Quote:

Originally Posted by DonR (Post 180034)
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.

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

aerohead 06-21-2010 05:39 PM

shape
 
Quote:

Originally Posted by Bennett_Racing (Post 180021)
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?

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!

Bennett_Racing 06-22-2010 06:25 AM

Quote:

Originally Posted by DonR (Post 180034)
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.


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.

Bennett_Racing 06-22-2010 06:28 AM

Quote:

Originally Posted by JasonG (Post 180038)
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.

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?


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