Aero on Drag racing cars

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SventheGreat2
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Aero on Drag racing cars

Post by SventheGreat2 » Wed Feb 01, 2017 8:43 pm

First off I am new to Aerodynamics and such but I am still very interested. I have been recently taken more interest in studying Aero on cars and while doing this I have realized that apart from big wings there is little aero on drag cars. If I am wrong Please Explain!

Thank you,
SventheGreat2

cramr
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Re: Aero on Drag racing cars

Post by cramr » Thu Feb 02, 2017 11:46 am

I don't know much about Dragsters, but in terms of aero modelling I guess the challenge would be to model the big massive rotating rear tyre

Facts Only
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Re: Aero on Drag racing cars

Post by Facts Only » Thu Feb 02, 2017 12:13 pm

My first port of call would be to look up the actual rules. Top fuel is an FIA series so there should be a readily available rule list. its easier to understand the 'why' when you know the 'must'

With top fuel dragsters I have always wondered why the rear wing is behind the rear axle, the big challenge seem to be keeping the front wheels on the ground so having the rear wing behind the rear axle makes the rear wheels a pivot point to lift the front wheels when there is downforce and drag on the rear wing? Surely there is a point somehere along the length of the car where the intersection of the downforce and the drag is acting almost 100% on the rear wheels and leaving the front wheels neutral?

I'm probably just being stupid or missing something obvious though.
"A pretentious quote taken out of context to make me look deep" - Some old racing driver

Pierce89
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Re: Aero on Drag racing cars

Post by Pierce89 » Thu Feb 02, 2017 2:49 pm

Facts Only wrote:My first port of call would be to look up the actual rules. Top fuel is an FIA series so there should be a readily available rule list. its easier to understand the 'why' when you know the 'must'

With top fuel dragsters I have always wondered why the rear wing is behind the rear axle, the big challenge seem to be keeping the front wheels on the ground so having the rear wing behind the rear axle makes the rear wheels a pivot point to lift the front wheels when there is downforce and drag on the rear wing? Surely there is a point somehere along the length of the car where the intersection of the downforce and the drag is acting almost 100% on the rear wheels and leaving the front wheels neutral?

I'm probably just being stupid or missing something obvious though.
I think you're missing the big front wing that they also use.
“To be able to actually make something is awfully nice”
Bruce McLaren on building his first McLaren racecars, 1970

“I've got to be careful what I say, but possibly to probably Juan would have had a bigger go”
Sir Frank Williams after the 2003 Canadian GP, where Ralf hesitated to pass brother M. Schumacher

SventheGreat2
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Re: Aero on Drag racing cars

Post by SventheGreat2 » Thu Feb 02, 2017 3:50 pm

Facts Only wrote:My first port of call would be to look up the actual rules. Top fuel is an FIA series so there should be a readily available rule list. its easier to understand the 'why' when you know the 'must'
I'll look.

Facts Only
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Re: Aero on Drag racing cars

Post by Facts Only » Thu Feb 02, 2017 4:22 pm

Pierce89 wrote:
Facts Only wrote:My first port of call would be to look up the actual rules. Top fuel is an FIA series so there should be a readily available rule list. its easier to understand the 'why' when you know the 'must'

With top fuel dragsters I have always wondered why the rear wing is behind the rear axle, the big challenge seem to be keeping the front wheels on the ground so having the rear wing behind the rear axle makes the rear wheels a pivot point to lift the front wheels when there is downforce and drag on the rear wing? Surely there is a point somehere along the length of the car where the intersection of the downforce and the drag is acting almost 100% on the rear wheels and leaving the front wheels neutral?

I'm probably just being stupid or missing something obvious though.
I think you're missing the big front wing that they also use.
I'm certainly not, I know they have a big front wing as well... which is to keep the front wheels down. My point was that the position of the rear wing acts to lift the front wheels by pivoting about the rear wheels. If the rear wing was further forward it would lift the front wheels less and so the front wing could be smaller, so less drag.

I don't know much of the rules though, perhaps the rear wing has to be behind the rear axle or something like that. I assume its so high and far back to get it away from the dirty air off the tyres and exhausts.
"A pretentious quote taken out of context to make me look deep" - Some old racing driver

Pierce89
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Re: Aero on Drag racing cars

Post by Pierce89 » Thu Feb 02, 2017 4:34 pm

Facts Only wrote:
Pierce89 wrote:
Facts Only wrote:My first port of call would be to look up the actual rules. Top fuel is an FIA series so there should be a readily available rule list. its easier to understand the 'why' when you know the 'must'

With top fuel dragsters I have always wondered why the rear wing is behind the rear axle, the big challenge seem to be keeping the front wheels on the ground so having the rear wing behind the rear axle makes the rear wheels a pivot point to lift the front wheels when there is downforce and drag on the rear wing? Surely there is a point somehere along the length of the car where the intersection of the downforce and the drag is acting almost 100% on the rear wheels and leaving the front wheels neutral?

I'm probably just being stupid or missing something obvious though.
I think you're missing the big front wing that they also use.
I'm certainly not, I know they have a big front wing as well... which is to keep the front wheels down. My point was that the position of the rear wing acts to lift the front wheels by pivoting about the rear wheels. If the rear wing was further forward it would lift the front wheels less and so the front wing could be smaller, so less drag.

I don't know much of the rules though, perhaps the rear wing has to be behind the rear axle or something like that. I assume its so high and far back to get it away from the dirty air off the tyres and exhausts.
The dragsters have a long nose full of ballast so wheelspin is actually a bigger problem than lifting the front. So yeah the rear wing is important.
“To be able to actually make something is awfully nice”
Bruce McLaren on building his first McLaren racecars, 1970

“I've got to be careful what I say, but possibly to probably Juan would have had a bigger go”
Sir Frank Williams after the 2003 Canadian GP, where Ralf hesitated to pass brother M. Schumacher

Facts Only
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Re: Aero on Drag racing cars

Post by Facts Only » Thu Feb 02, 2017 5:38 pm

The rules are here:

http://www.fia.com/regulation/category/101

Its a long document so I have picked out a couple of things of interest for Top Fuel Dragster aero:

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. Air deflector plates located behind cockpit restricted to maximum 17 inches by 17 inches (432 mm by 432 mm). Leading edges, fairing in or rounding off corners, etc. prohibited. Maximum 1.25-inch (32 mm) lip for stiffening permitted. Mud flap may be located in front of or behind exhaust headers.

FRONT-WHEEL FAIRINGS
Prohibited.


WINGS & SUPPORTS
Rear wing supports must meet SFI Spec 2.3P. Rear wing must meet SFI Spec 49.1. SFI tag must be affixed to the main wing element, on the underside, adjacent to the right spill plate. Wing configuration limited to one only, with three elements, and must be FIA Drag Racing Commission accepted for competition. Combined total area of rear wing (total of all stages and/ or elements) is restricted to a minimum 1,450 square inches (9354 cm2) and a maximum of 1,500 square inches (9677 cm2). Trailing edge of rear wing may not extend more than 50 inches (1270 mm) behind centerline of rear axle. Maximum height of any wing as measured vertically from the trailing edge of wing to ground is 90 inches (2286 mm). Strut mounting points may not be forward of motor plate. Distance from main to secondary mounting points must be 30 inches (762 mm) minimum. No part of the wing or wing supports may attach to any engine, bellhousing or transmission components.

Spill plates must be flat, vertical, and inner and outer surfaces must be parallel. Maximum thickness including trailing edge of wicker 0.650 inch (16.51 mm). Wicker permitted on trailing edge only. Must be flat/straight, not to exceed 31 inches (787 mm) measured diagonally from the front leading edge at the bottom of the spill plate to the top trailing edge at the back of the spill plate. Lips of any other kind prohibited. Length and width of spill plate optional, provided spill plate fits within the confines of a 22-inch by 22-inch (559 mm by 559 mm) square box

All Top Fuel rear wing main elements must be positioned with a positive 2-degree angle maximum (no minimum) relative to the racing


FRONT WINGS
Front wing must meet SFI Spec 49.2. Front wing design must be FIA Drag Racing Commission accepted prior to competition. Front-wing element(s) maximum width 63 inches (1600 mm) total. Total width of front wing, including spill plates, maximum 66.5 inches (1689 mm). Spill plates must be flat, vertical, and inner and outer surfaces must be parallel. Maximum thickness of spill plates including trailing edge of wicker .550-inch (14 mm). Wicker permitted on trailing edge only.


So basically its spec wings and the rules on mounting points force them to be behind the engine. No ground effects and no end-plate shaping.

its all on page 92-94 of the technical regulations

And people think F1 is restrictive.
"A pretentious quote taken out of context to make me look deep" - Some old racing driver

Pierce89
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Re: Aero on Drag racing cars

Post by Pierce89 » Thu Feb 02, 2017 8:47 pm

Facts Only wrote:The rules are here:

http://www.fia.com/regulation/category/101

Its a long document so I have picked out a couple of things of interest for Top Fuel Dragster aero:

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. Air deflector plates located behind cockpit restricted to maximum 17 inches by 17 inches (432 mm by 432 mm). Leading edges, fairing in or rounding off corners, etc. prohibited. Maximum 1.25-inch (32 mm) lip for stiffening permitted. Mud flap may be located in front of or behind exhaust headers.

FRONT-WHEEL FAIRINGS
Prohibited.


WINGS & SUPPORTS
Rear wing supports must meet SFI Spec 2.3P. Rear wing must meet SFI Spec 49.1. SFI tag must be affixed to the main wing element, on the underside, adjacent to the right spill plate. Wing configuration limited to one only, with three elements, and must be FIA Drag Racing Commission accepted for competition. Combined total area of rear wing (total of all stages and/ or elements) is restricted to a minimum 1,450 square inches (9354 cm2) and a maximum of 1,500 square inches (9677 cm2). Trailing edge of rear wing may not extend more than 50 inches (1270 mm) behind centerline of rear axle. Maximum height of any wing as measured vertically from the trailing edge of wing to ground is 90 inches (2286 mm). Strut mounting points may not be forward of motor plate. Distance from main to secondary mounting points must be 30 inches (762 mm) minimum. No part of the wing or wing supports may attach to any engine, bellhousing or transmission components.

Spill plates must be flat, vertical, and inner and outer surfaces must be parallel. Maximum thickness including trailing edge of wicker 0.650 inch (16.51 mm). Wicker permitted on trailing edge only. Must be flat/straight, not to exceed 31 inches (787 mm) measured diagonally from the front leading edge at the bottom of the spill plate to the top trailing edge at the back of the spill plate. Lips of any other kind prohibited. Length and width of spill plate optional, provided spill plate fits within the confines of a 22-inch by 22-inch (559 mm by 559 mm) square box

All Top Fuel rear wing main elements must be positioned with a positive 2-degree angle maximum (no minimum) relative to the racing


FRONT WINGS
Front wing must meet SFI Spec 49.2. Front wing design must be FIA Drag Racing Commission accepted prior to competition. Front-wing element(s) maximum width 63 inches (1600 mm) total. Total width of front wing, including spill plates, maximum 66.5 inches (1689 mm). Spill plates must be flat, vertical, and inner and outer surfaces must be parallel. Maximum thickness of spill plates including trailing edge of wicker .550-inch (14 mm). Wicker permitted on trailing edge only.


So basically its spec wings and the rules on mounting points force them to be behind the engine. No ground effects and no end-plate shaping.

its all on page 92-94 of the technical regulations

And people think F1 is restrictive.
The wings aren't quite spec. Different suppliers use slightly different foils but, to get approved your performance must be similar to current wings in use. I read an article where one company went through like 15 iterations before their wing performed poorly enough to be approved for top fuelers.
“To be able to actually make something is awfully nice”
Bruce McLaren on building his first McLaren racecars, 1970

“I've got to be careful what I say, but possibly to probably Juan would have had a bigger go”
Sir Frank Williams after the 2003 Canadian GP, where Ralf hesitated to pass brother M. Schumacher

LVDH
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Re: Aero on Drag racing cars

Post by LVDH » Fri Feb 03, 2017 3:32 pm

Maybe the rear wing position is just a compromise. I agree that the location creates an unwanted pitching moment. But as the front seems to contain ballast and the front wing creates down force, these two forces together with the large leverage maybe easily compensate for the disadvantages. I guess due to the exhaust location the air gets extremely disturbed where you would think the rear wing should go. The engines blow out enormous amounts of gasses. Also I can imagine that the end plates help stabilize the car. If the end plate sizes are very restricted I can see how placing the rear wing further backwards helps more than the mentioned disadvantages.

SteveRacer
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Re: Aero on Drag racing cars

Post by SteveRacer » Fri Feb 03, 2017 4:25 pm

https://www.youtube.com/watch?v=B_3QPlrxebk

I remember this kind of stuff being more common at one time. Maybe this has something to do with its placement.

Brian Coat
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Re: Aero on Drag racing cars

Post by Brian Coat » Fri Feb 03, 2017 11:47 pm

As suggested above, the wing is where it is to try to get clean air. Look at how the exhaust pulsations impact it. And look at how tall the tyres are (and distorted! If you want a science project, explain that shape!) .

Image

The rear wing downforce moment does not give a wheelie problem.

Early in the run when the wheelie moment is highest the wing forces are low and the main rear downforce comes from the exhaust, whilst the long wheelbase and ballast hold the nose down.

Later in the run the wheelie moment is a little lower and the rear wing moment will rise but the front wing can excert a huge counter-moment because it is ~6x as far from the pivot point as the rear wing (300" wb).

The wheelie+rearwing moment and front wing counter-lever cause a massive bending load in the chassis which is why the car "arches its back" at the top end.

Image

There is a good reason for "spec aero" in TF. Safety.

The (spec) tyre is only rated to about 340 mph at current downforce levels. Any increase in downforce or top speed would require a massive (i.e. Unaffordable) tyre development programme.

These cars effectively run top speed limiters through ignition retard devices. This season the closed-bodied cars started pushing over 335mph and the regulators bought in a mid-season change to the retarder spec.

roon
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Re: Aero on Drag racing cars

Post by roon » Sat Feb 04, 2017 12:51 am

If they were any longer they would begin to resemble F1 cars.

SteveRacer
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Re: Aero on Drag racing cars

Post by SteveRacer » Sat Feb 04, 2017 1:42 am


Brian Coat
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Re: Aero on Drag racing cars

Post by Brian Coat » Sun Feb 05, 2017 10:15 am

So what could we play with???

Is it true that only the spill plates are required to be vertical?

The assymetry of the rear wing attack angle under load appears to be sub-optimal to me and may offer scope for development of the mountings to ensure a flat wing under load?

http://rebilasphoto.photoshelter.com/im ... HHY&GI_ID=

Similarly, a change in attack angle with speed is apparent and exploring ways to 'tune' this using the mounts could be beneficial?