Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - Drag reduction

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Drag reduction - Racecar

I am working on some drag reduction on our endurance racecar and I wanted to pick some brains from the hypermile'r world.

Our rules allow us to repurpose material from the car in other areas. If we use wood, metal or plastic stock then we are charged "points". We basically have no points left, so we are reusing some of the rear bumper, a splash sheild and door cards. I also have some metal from the bottom of the fenders and some trim pieces.

The biggest area I see is the rear of the car. I can extend out to 12" from the rear of the car and I already have a diffuser at a max angle that extends out that far.

I am running an airdam, splitter, flat floor, diffuser and a custom fast back (reused bumper). The radiator is sealed and ducted and I have a vented hood with gurney flaps to improve extraction. I also have vented fenders, on the top for pressure reduction and reduced lift and the rear of the fenders vented to relieve well pressure.

I have a mock up here of what I want to do in the rear with a splash shield and door cards. I have an approximate 14 degree slope off of the fast back.

I don't want to cover the fenders because of brake cooling and we need to change tires.

We are only at 145whp, so drag reduction is important for overall lap times.

Does anyone have any other tips and tricks, additional input would be greatly appreciated.

Are you allowed to enclose the rear quarter panels to create some boat-tailing on the sides, while still allowing sufficient wiggle room for fast tire changes?
I'm not a racer except for Bonneville, but I believe that your diffuser would be more effective if enclosed, along with welcome drag reduction.

Quote:

Originally Posted by LuckyKid (Post 633865)

The biggest area I see is the rear of the car. I can extend out to 12" from the rear of the car and I already have a diffuser at a max angle that extends out that far. ............

You don't have to follow the original silhouette of the car it sounds like.

I'd try something like Ferrari did in 1962 - worked back then.

See Post#2
Porsche Boxster Shooting Brake, Yes or No? - Pelican Parts Forums
https://upload.wikimedia.org/wikiped...readvan%27.jpg

Very close to the aerodynamic template Part-C most often discussed in this forum and is a sticky at the top.

I think the rear (box cavity) can remain 100% open so all the repurposed metal can go to the sides, top and belly.

Quote:

Originally Posted by aerohead (Post 634229)

I thought that if the back of the rear tire is enclosed that it creates drag. Maybe I could leave a cavity behind the tire but extend the rear quarter panel downward?

Many ways to vent that rear wheel well, from the slot of the 1962 Ferrari Breadbox to the 993 Porsche below.

https://www.vanthulldevelopment.com/...-gt2-widebody/

Have you tested it without the wing?

Quote:

Originally Posted by LuckyKid (Post 634275)

I thought that if the back of the rear tire is enclosed that it creates drag. Maybe I could leave a cavity behind the tire but extend the rear quarter panel downward?

Enclosing will definitely reduce drag if the panels are boat-tailed, when viewed from above, however, you will lose the drogue effect of the exposed wheels, affecting high-speed stability. This has been known since before 1940.
Historically, if the rulebook allows, the body will be streamlined as much as possible, then 'sail' area will be added for directional stability, of which will be partly supplied by the paneling.

Quote:

Enclosing will definitely reduce drag if the panels are boat-tailed, when viewed from above, however, you will lose the drogue effect of the exposed wheels, affecting high-speed stability. This has been known since before 1940.

Do you have a cite or example? TIA.

Quote:

Originally Posted by freebeard (Post 634448)

Do you have a cite or example? TIA.

Fachsenfeld, who did the research at the FKFS, addresses the relationship in his book,' AERODYNAMICS DES KRAFTFAHRZEUGS', 1951.
The turbulent wake behind the wheel acts in a stabilizing fashion, like the wake behind the transom of a ship / boat, tends to 'center' the stern in the direction of travel.
If you look at a recent ROLEX' 24-HOURS of DAYTONA race car, you'll see a fin behind the Jaray greenhouse, running the total length of the aft-body. Exactly like Fachsenfeld had done prior to the beginning of WW-II in Europe. This weather-vane compensates for some of the loss of the exposed wheel wake, and with zero drag penalty.:)