Wing slot effect

Rear wing formula continental

made up of 3 wings, the gap between top wing and middle wing is 5mm on one of my wings and on my backup wing it is wider gap at 15mm, what effect does this have? More or less downforce, drag etc

thanks
steve

Google 'Rear wing slot design pdf' and you will find more than you want to know.

Brian

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Originally Posted by steve everard

Rear wing formula continental

made up of 3 wings, the gap between top wing and middle wing is 5mm on one of my wings and on my backup wing it is wider gap at 15mm, what effect does this have? More or less downforce, drag etc

thanks
steve

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Short version: It all depends. Wing shape. Angle of attack (including relative to each other.) Speed. There's probably more, but I never achieved my boyhood dream of becoming an aeronautical engineer so not an expert.

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Originally Posted by steve everard

Rear wing formula continental

made up of 3 wings, the gap between top wing and middle wing is 5mm on one of my wings and on my backup wing it is wider gap at 15mm, what effect does this have? More or less downforce, drag etc

thanks
steve

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A wider gap reduces drag with a somewhat smaller reduction in downforce. My current rear wing has a 15 mm gap.

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Originally Posted by DaveW

A wider gap reduces drag with a somewhat smaller reduction in downforce. My current rear wing has a 15 mm gap.

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When I was with Audi and their LMP program my middle finger was "calibrated" as the optimum slot gap for their rear wing. My finger became the official "go/no go" gauge for the team!! (LoL)

PS: My finger measures 16mm.

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Short version: It all depends. Wing shape. Angle of attack (including relative to each other.) Speed.

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A wider gap reduces drag with a somewhat smaller reduction in downforce.

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A lot depends on what you are trying to do.

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made up of 3 wings, the gap between top wing and middle wing is 5mm on one of my wings and on my backup wing it is wider gap at 15mm, what effect does this have? More or less downforce, drag etc

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Is a lot like an airfoil with leading edge slats and flaps. When are these used? Low speed, high AOA landing.

Now turn it "upside down" for downforce. Tailoring that slot is going to depend on where you want that maximum effectiveness. At one particular turn - or at a few? The speed regime at that point on a circuit; the HP available for he remainder of the track; advantage for grip at a critical point, many factors. It goes on, and on, and on, and on.

A lot of possibilities - and fun to explore the varied options. Sorry I don't have a quantifiable answer. Like before:
"..it Depends"

Balance the downforce. If the nose lifts - yer-done.

Cheers - Jim

BTW - that is why active-aero is such a great idea! We could "trick" slats could do their job at high AOA - and gain advantage in a fight - all in fun.

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Originally Posted by DaveW

A wider gap reduces drag with a somewhat smaller reduction in downforce. My current rear wing has a 15 mm gap.

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Mine is 15mm as well.

The effect of the gap varies with the design. On a 1997-1999 Dallara Indycar, widening the gap increases downforce and drag, which was not what we were expecting at the time. So you have to test it to know for sure.


Sent from my iPhone using Tapatalk

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Originally Posted by GAC

The effect of the gap varies with the design. On a 1997-1999 Dallara Indycar, widening the gap increases downforce and drag, which was not what we were expecting at the time. So you have to test it to know for sure.


Sent from my iPhone using Tapatalk

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I spent some time testing various wing - flap assemblies in a small wind tunnel and in cfd using full car drawings. It turns out that not only is the gap important, but so in the fore - aft location......and that is specific to the main plane upper profile.

The Van Dieman upper pair is pretty good as it is normally found....about 12 to 15 mm gap.....at any reasonable angle of attack.

The VD lower element needs a small wicker (.25 inch) to be very effective.

Remember the angle of attack is relative to the air flow direction as it comes off the car. That is usually downward at some angle.
Therefore an angle of attack that works best on one brand of car will usually be different on some other car. Frankly, at the lower formula, most of the manufacture will not know (they sometimes don't even know what spring rates to run) so do your own testing.

Every wing profile will generate downforce at some angle of attack. The trick is to get the best downforce vs drag ratio.
There is a thing called the "drag bucket".....a range of angle of attack where the downforce can be adjusted without changing the drag significantly. Beyond that bucket, the drag goes up very quickly. In general lower angle of attack is better.
When you reach the drag bucket upper point, a slotted flap (or at least small wicker) is better than more angle of attack,.

However, the flap chord should be no more that 50% of the main plane chord. That brings up a front wing flap discussion which I will save for a later time. I will just say this: very large outboard flaps are only ok if directly in front of the tire (same for dive planes on the end plate). To do that would require a very narrow track, or a wing to wide to comply with the rules.

Jerry Hodges
JDR Race Cars

Jerry, good stuff here.

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Originally Posted by JerryH

I spent some time testing various wing - flap assemblies in a small wind tunnel and in cfd using full car drawings. It turns out that not only is the gap important, but so in the fore - aft location......and that is specific to the main plane upper profile.

The Van Dieman upper pair is pretty good as it is normally found....about 12 to 15 mm gap.....at any reasonable angle of attack.

The VD lower element needs a small wicker (.25 inch) to be very effective.

Remember the angle of attack is relative to the air flow direction as it comes off the car. That is usually downward at some angle.
Therefore an angle of attack that works best on one brand of car will usually be different on some other car. Frankly, at the lower formula, most of the manufacture will not know (they sometimes don't even know what spring rates to run) so do your own testing.

Every wing profile will generate downforce at some angle of attack. The trick is to get the best downforce vs drag ratio.
There is a thing called the "drag bucket".....a range of angle of attack where the downforce can be adjusted without changing the drag significantly. Beyond that bucket, the drag goes up very quickly. In general lower angle of attack is better.
When you reach the drag bucket upper point, a slotted flap (or at least small wicker) is better than more angle of attack,.

However, the flap chord should be no more that 50% of the main plane chord. That brings up a front wing flap discussion which I will save for a later time. I will just say this: very large outboard flaps are only ok if directly in front of the tire (same for dive planes on the end plate). To do that would require a very narrow track, or a wing to wide to comply with the rules.

Jerry Hodges
JDR Race Cars

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