7 Aerodynamics and wind deflectors

[FerneyO]

Is anyone aware of any wind tunnel data for a 7?

I'm experimenting with wind deflectors. I've made some marginal progress, but I am struggling with the wind that comes up over the rear wings(fenders) and into the side/back of the driver. I tried some side screens and see some improvement, but at this rate I'll be back to the standard side screens.

You can check out my attempts at http://fernlahone.wordpress.com/2014...nd-deflectors/

....Dave.

[Doug Liedblad]

Caterham did some wind tunnel testing years ago. I believe I have a scanned image of the magazine article.

I will post or email to you.

As soon as I can find it.

[FerneyO]

Caterham did some wind tunnel testing years ago. I believe I have a scanned image of the magazine article.

I will post or email to you.

As soon as I can find it.

I found one article from ~2007 that Magnus posted. It was concerned more with reducing drag & improving downforce. But no pictures of smoke flowing around a model.

I'm interested in the airflow around the sides of the 7 and what is the flow like immediately in front of the rear wheels.

[Doug Liedblad]

That will be the same one I have. I probably stole if from Magnus.

You'll need to get out your checkbook and find a wind tunnel.....

I don't think it's been done.

If you have a rear exit exhaust, change to side. TADTS with rear exit.

Change to the Aeroscreen like Magnus or Morgan has. This reduces buffeting in the car dramatically. Go figure.

Or drive it with the full windscreen, hood, and side curtains. Maybe the heater on too.

[FerneyO]

My theory is that the windscreen forces air upwards and creates a partial vacuum in the passenger space. Air moving up, in front of the rear wheels is compressed and therefore moves into the partial vacuum of the passenger space (around the side & back of my head). The Aeroscreen would create less pressure and less of a vacuum, thus reducing the rear/side turbulence. See my attached sketch.

7_aero_theory.jpg


I tried putting a side screen to fill the space next to my head & roll bar and see some partial success. I'm now wondering about diverting the wind about 3' in front of the rear wheels, (level with the rear of the engine) using a bigger version of the front winglets that the CSR has on the nose.

[prabjohns]

I have temporarily put a plexiglass rear window inside the space that the roll bar encloses. It was to cut down the large amount of exhaust fumes that blew into the cabin until I could do a proper side exit exhaust. It made a huge difference.

[moosetestbestanden]

Ditch the windshield, er, windscreen.

[JohnCh]

I've experimented with different solutions on my Westfield. Half doors helped, and didn’t trap cockpit heat to anywhere near the same degree as side curtains, but things still got pretty toasty insde from the waist down. A wind block placed in the main hoop of the roll bar made no difference. From what I've read, the distance between the headrest and the wind block is critical, so my guess is that it's a bit longer in my car than in Paul's. Apparently the best option is to place it in the same plane as the headrests.

After experimenting quite a bit with both size and positioning, I finally settled on some rather large wind deflectors custom made from polycarbonate. They reduce buffeting much better than the half doors, and allow enough cabin airflow that heat buildup when driving is never an issue. The downside is that they look rather ungainly, and because the mounting angle to the windscreen is pretty shallow, they create an even bigger wind brake.

Here are a couple of pictures that show the size and positioning:
2010-2.jpgwestfield-993.jpg

BTW they also saved my wife and I from potential serious injury on the way back from USA2005. It was oh-dark-thirty in the morning when we hit a tire carcass at over 70mph on an undulating piece of freeway. I didn’t see it in time to react, and hit it full on with the left front wheel, which kicked it up into the wind (tire?) deflector, then down to the rear wing which was comprehensively destroyed. Looking at the rubber marks, it's clear that if the deflector wasn’t there, best case the carcass would have taken out my left shoulder, worse case would have been a head shot. At that speed, a crash was a likely outcome. Obviously a pretty edge case scenario, but it has helped endear them to me.

-John