super silhouette race car aero stuffs.

Ok, I LOVE the old Japanese super silhouette race car aero... and I was wondering: what is the advantage to the wings/blades/things on the top of the fenders?

would I be able to see any benefit (at autoX and track days) from putting them on my miata... aside from awesome swag points?

pic for reference:

If actually functional, they can assist with flow control.
The flow around a 3D object is also 3D.
The fences on the fender would (hopefully) prevent air flow spilling laterally over the edges,
and direct it up the hood and over windshield, promoting greater pressure and downforce up front.
Or not.
Actual airflow testing and analysis in a tunnel beats human intuition every time, but it ain't cheap.
OTOH, nowdays data acquisition and sensors ARE cheap, and so it's possible to make and try out changes
on the car and measure relative effect.

Bottom line is lap times, what's faster?

may also reduce drag at high speeds. Similar to the 'winglets' on most commercial jets now (the up-turn at the end of the wing), if you can stop the "spilling" of high pressure air over the sides of the hood, you will reduce the vortexes that are created by that spilling. The vortexes are high drag.

You probably will not achieve those speeds at an autox.

So basically the same as end plates on a wing, then. It would be pretty easy to mock up using the Miata fender bolts, then do some tuft testing to see what changes on the airflow. You can definitely see how the pressures on the top of the hood drop off towards the side.

I think those chanel are to keep air from flowing down to the sides, therefore improving downforce on the front end

Works for these guys

Not sure how much those effects scale, since slot cars are incredibly lightly loaded per tire as compared to a real car, but I am sure there is a nonzero benefit. That said, they are not often used now, so it may not be worth the tradeoff in drag.

When I think of those fender thingys, I can't help but think of the batmobile.

I wonder if any modern production type (or silhouette type) cars use them and if not, why not. Perhaps they just look cool and don't add much value.

The Batmobile aero is obviously working completely backwards in that picture

Or its working well, otherwise the thing would be twice that far off the ground

Stock cars use roof rails:

My (worthless) intuition suggested: 1. The roof rails helped channel air to the rear spoiler, improving downforce, and 2. Eliminating flow variability. (I guessed) Airflow moving along the roofline/side window edge might sometimes slip over the roof, and sometimes along the window, depending on whether the car is traveling straight or turning, and more randomly from wind changes, adding variability to the handling. The roof fence would eliminate that variability.

Number two might be a case of useless aerodynamic intuition. YMMV. Article below says roof fences are to reduce lift when the car gets sideways.

NASCAR Aero

Roof rails might be totally irrelevant to the discussion at hand; sorry. ;-)

David

It is relevant to the discussion... Just not to me (I has no roof)

Has to be functional. Otherwise all the wind tunnel R&D those race spent would be for not.

Currentl LMP's are using this. As mentioned though, unless it's a track car achieving VERY high trap speed, it won't work for you.

All together now, as forum: "at what speed do aerodynamics become active?"

But, but.. Swag.

Wait.... Why am I 2 different people.

I am the op.

Trackmouse wrote: Has to be functional. Otherwise all the wind tunnel R&D those race spent would be for not. Currentl LMP's are using this. As mentioned though, unless it's a track car achieving VERY high trap speed, it won't work for you. All together now, as forum: "at what speed do aerodynamics become active?"

At 1 mph. It just has to be more aggressive at lower speeds.

I read somewhere (legitimate) that one of the secrets of the classic Mini's cornering was the rain gutters. With slip angle and the resulting skewed airflow, they had an aero effect of stabilizing the car. I can see the roof strakes doing the same. Those NASCAR guys spend a lot of time traveling at high speed in at odd angles of attack.

I think the hood strakes would be a downforce generator and they probably generate a couple of vortices over the windshield. It would be an interesting test, I might have to give this a shot at some point.

Blobs of paint or oil can show airflow as well.

I have used dirt, and road grime. Also, diy car washes (the ones with the high pressure spray wands.)

That was how I aimed my canards... When the water went over the mirrors, I was happy.

One of these with a piece of string on the end actually works very well to get an idea of airflow.

Yeah... But I would also need an air compressor... And perhaps a garage.

Yeah, I am one of those "supercharged, flared, miata guys, built in a parking lot, with hand tools" guys

IIRC those rails on top of the Cup car are also so when it gets sideways, it doesn't roll so easy. They also have strips on the rear window. I think that at the speeds you would see on an autocross course, those rails on the fenders would be nearly useless unless they were really tall.