Sprint Car Difusser Help!

[Berggie]

Ok im new to this site and i believe it could help solve my problem. I race a sprint car. We have a front wing and a top wing(located above the driver). Those are our two main points of downforce. The area i have been thinking about is below the car. The bottom of the race car is NOT enclosed. only the front 1/4 of the car has a belly pan. therefor all the air after that is very dirty. I cannot find any rules on having a full length belly pan so i am going to make a stab at it. The only real place i have no idea what im doing is at the rear(difusser). How do i exactly go about designing the difusser? If you have a side view of the racecar the entire bottom (or belly pan line) is flat or parallel to the ground except the last foot at the rear has a bend upwards of about 3 inches. So when making a belly pan do i follow the curve upward or do i make it stay flat? once again this is the area for the difusser. Please help me.

 

[SRE24]

In my response I must make assumptions about your post. I assume by doing this you are trying to create added downforce for the car? There is a slight problem with this theory in a sprint car application. A diffuser is designed to speed airflow up at the rear of the car i.e. the air flows in a forward to backward direction. However, in a sprint car, the time when you need downforce is invariably in the turns. During this time airflow under the body of the car will be traveling perpendicular to the body/diffuser because you are sliding creating nothing more than the drag you were trying to avoid. Add the belly pan to clean up the air, but a diffuser will not work in your application. Let me know if you have any other question.

Andrew~BSME

 

[GregLocock]

So, you need an assymetric diffuser.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Berggie]

Ok SRE24 so my best bet would be just add a flat belly pan the length of the car. At the back should I keep it flat(level with the ground) or should i follow the chassis which has a upward curve of about 4 inchs within a 1 foot distance? But you are right im looking to basically clean up the air flow around the body. Also what about adding like a runner to the bottom. What am i talking about? say a 1/2'' x 1/2'' piece of alum. or plastic that would go from the fron tto back of the car. will that keep the air flowing parallel to the cars motions better? and would this help if i did the same on top of the wings? I hope you understand. Im just trying to use a method that would keep the air flowing straighter while on the sirface of the car. will this help? thank you for your help once again.

 

[patprimmer]

I think Greg is right.

Sprint cars have asymmetric wings and asymmetric tyre size (stager) so why not design the belly pan and diffuser presuming airflow at a diagonal. I think perpendicular is to much as if the axis of the chassis is perpendicular to direction of travel, you are very close to going backward.

I would think 46 to 60 deg is typical attitude on the turns, but that is just my guess from occasionally watching a race.

Regards

eng-tips, by professional engineers for professional engineers
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[SRE24]

I would like to start off by stating that I dont feel an asymmetric diffuser is even applicable to this case. In racing , especially dirt track, cars are all over the track. Its not like Nascar or Formula One, guys run high, low, and around slower cars. (And more importantly, we assume perpendicular to airflow) This means that it would be entirely impossible to establish a proper angle for an asymmetric diffuser. In theory, its a great idea. So is the Carnot cycle. In practice, I dont feel it is possible to achieve anything other than a negligible result.

With that being said, I have though about how to achieve a more "laminar" flow of air on a sprint car. As a visualize the air traveling over this car, I dont see how it would be possible to achieve better flow on an object as aerodynamically unclean as a Sprint Car. I believe the top part of aluminum on the wing is called a wicker bill? Which I know has been outlawed in some classes (ASCS). Does that mean it is not possible to achieve the results you are looking for? Absolutely not. Part of being a good engineer is knowing that you dont really know it all. So I must say that I don't have any more ideas for you. I dont think the improvements you are talking about making to your car would make a noticable improvement to your performance. Keep up that thinking though and eventually you'll hit on something.

Andrew~BSME

 

[GregLocock]

So presumably the assymetric top wing is a waste of time as well?

How bizarre.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SRE24]

In response to GregLocock, I am not sure if you are using sarcasm but in an attempt to help others learn yes it is a waste of time...this is a SPRINT CAR. Therefore strict sanctioning body rules prohibit any such device. I speak of only North American sanctioning bodies, WoO, ASCS, NCRA.

 

[GregLocock]

If it is illegal, fine. Bu that is not the impression you gave in your previous posts. If it is illegal then you don't need a technical argument about the airflow direction.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Berggie never said where he was from. Why do you just presume he is North American. This is the World Wide Web. That actually does extend beyond California and New England.

A technical question was asked. No rules were mentioned. The OP asked specifically about diffusers. Have I missed anything.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Berggie]

patprimmer i am from north america/northeast. The reason for not mentioning any rules is that our rules are pretty gray. gray meaning i dont think they care about or dont know what they would be talking about when making rule as such. My goal is to take this division to the next level before the compitition. im looking to basically clean up all the air around the body with minimal drag and maximize my top wings and downforce.

 

[MikeHalloran]

Okay, then, I'd make the bellypan asymmetrical, with a rounded 'leading edge' on the starboard side of the car, and a tapered 'trailing edge', with a sharp edge like a Kammback, on the port side, and similarly on the back.

Effectively, you want to build a wing on the bottom that will be effective when the car is sliding.

So it would have minimum ground clearance along a line parallel to the car's axis, but displaced to the starboard side.

If you also tilted the motor to the left a bit, biasing the oilpan into the deeper area of the bellypan, you might be able to disguise the pan's actual intended purpose.



Mike Halloran
Pembroke Pines, FL, USA

 

[Berggie]

So Mike what you are saying is if im looking at the racecar from the rear or from behind the front and right side of the belly pan whould be rounded and the left side and rear would have a trailing edge hangging off?

 

[MikeHalloran]

Pretty much. Imagine splicing an airplane wing, upside down, to the bottom of the car, with the wing's span going fore/aft, or LF/RR, or somewhere in between.

If you do it subtly, you may be able to run a few races before it gets noticed, and maybe a couple more before it gets banned.





Mike Halloran
Pembroke Pines, FL, USA

 

[evelrod]

If you do it subtly, you may be able to run a few races before it gets noticed, and maybe a couple more before it gets banned.

"Mike (NASCAR) Halloran" LOL !!!

A man after my own heart! I, too, am a "Smokey" fan.


Rod

 

[MikeHalloran]

He was indeed a hero of mine.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

It won't be noticed until you start to noticeably improve, then everything will be noticed and objected to.

Many years ago, I was involved with a formula ford. We normally ran them in and then optimised them on a dyno. We decided to "run it in" on oil supplied by a sponsor, but we did not normally use the oil as it was not race quality.

We did one power run on the supplied oil. It gave 114 HP. Our best previous engine was 110. We changed oil, back to 110.

Needless to say we raced on the thin oil.

We had our engine examined after every race that season as it is very unusual in FF to be able to just pull out on the straight and drive past opposition, so it was presumed we must be cheating.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Berggie]

ok sorry if i keep posting with a reply about this. im here to try and learn a bit. I understand what you are saying but the trailing edge of the drivers side how would the edge be? should it have a trailing edge that hangs past the body work? i wish some how we coupld put drawings on here lol.

 

[MikeHalloran]

The way I imagine it is, standing alongside the car:

The bottom of the starboard side would look rounded/ tucked in, in the classical way.

The bottom of the port side would look cut off, sharp and square, at a level about midway up the stbd side's curve.
Sort of like this:

port side stbd side
| |
| |
| /
| /
--------__________ /
--------_______/


Section lkg fwd



Mike Halloran
Pembroke Pines, FL, USA