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Here is my idea to try to cut down on some of the wind buffeting while driving my Locost. The thought is that the air displaced by the windshield curves around behind it, mainly where the driver is sitting. If the driver were a bit closer to the windshield, the flow would be more behind.

I've noticed that various British roadsters (Austin-Healey Sprite, MGA and Triumph TR-250) have the seat back about 36" behind the windshield. In my car, the seat back is about 42" behind, so the goal is to make a longer scuttle and move the windshield back.

I've included a couple of photos: a profile view of the car now and a retouched one of what I'm considering doing.

It might work, but you'd be going thru a lot of effort just to try it with unknown results. I think that your looking for the unobtainable. Have you tried adding a windscreen across the roll bar? Similar devices are used on later convertibles and are available for MGA's AH's etc as aftermarket accessories. They are called Windblockers and seem to work fairly well. Don't know how they work on Sevens though.

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Chuck.

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You need to close up the sides. The buffeting is around the sides of the windscreen through the open sides.

A lot of 7 owners tour with the doors/side curtains in place, just like I keep the windows up on my other roadsters to eliminate most of the buffeting. The last thing to add is the wind blocker in back to prevent the wind rolling in behind your head.

Ditto on Jon's comments, the doors and wind-blocker will go a long ways in reducing the buffeting. The wind block can not be a solid sheet of Lexan behind your head. You will need to add holes in the sheet that is equal to 30 to 40% of the area, or use a screen - mesh type material in your design which allows the low pressure area to bleed off behind your head.

It looks like a good idea to me; all I'd recommend are 1) you cut the outside edges of the scuttle to the plane of the dashboard, so your passengers don't kick the scuttle on their way in and out, and 2) you run your wind wings full length down to the bottom of the stanchions...or perhaps even down to the bottom of the scuttle.

One thing that surprised the heck out of me with my Lalo body...
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...was how, even though all I had for a windshield was a little opaque bump on the scuttle to direct air over my head, the buffeting was pretty well eliminated. So I too am convinced it's the air coming around the sides of the windshield (and sides of the scuttle) which buffets us.

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One of my buddies put my Locost model into a CFD program. If it matters at all Jack, the end result is pretty much right on par with your findings.

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-Andrew
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Wow! what a response for the first day!

I know I will not eliminate wind turbulence completely unless I put an enclosed cover on the car. This IS an open roadster, after all. This whole exercise is an experiment.

My plan now is to keep the old scuttle, so if I do make things worse, I can go back to the original configuration. There is another thread in this section about wind buffeting. One post described a screen behind the seat and said the buffeting was worse. Nothing seemed to help much except full doors on the side. Moving the windshield back was not discussed.

I'm still toying with the idea of small doors to fill the gap between the scuttle and the rear fender. This might help some, but I have also read of folks having a lot of trouble getting the doors to fit correctly. They would also make it more difficult to remove the scuttle for maintenance, since the doors would likely also have to be removed.

It will be a big enough project to build this scuttle and get it to fit the rest of the car without worrying too much about doors. I will probably build in some way to add doors relatively easily at some indefinite point in the future.

Jack's comment about reduced buffeting with just a small wind deflector does raise an interesting question. It might be worth a try to simply remove the windshield and test that to see what effect the windshield is actually having. Andrew, would it be possible to have your friend run a model of a Locost without a windshield through his CFD program?

I've had mine up to about 100mph with no windshield and it wasn't too bad with a full face helmet. A little hard to see anything when I tried without a helmet though. At more normal speeds (50 to 60mph) it seems fine. I have never had a windshield on mine though, so can't compare.
Kristian

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Lets face it, there are a lot of options with windshield placement, size, angle, shape. I know the Locost has a particular windshield, but we have talked about leaving a slot under for example. Also you can split it with an angle which makes it a little more wind-worthy.

I'd say doors or side curtains or both, plus some kind of venting which allows pressures in the cockpit to stablise.

It makes for an interesting exercise. One thing I've noted in my Miata is that the wind is most reduced when only one of the door windows is up, and the windblocker is in place. Put up both door windows, and the buffeting increases noticeably. Weird, huh? I even tried having both windows 1/2 way up, and it didn't improve the buffeting at all.

I'm guessing that each individual Locost will be a little different in the way it reacts to buffeting-reduction strategies. At one point, I considered running a vent from under the floor pan of the car up to the back of the windshield to eliminate the low pressure area there, but then it occurred to me that would eliminate any low-pressure area under the car - right where a partial vacuum is a good thing to have. I'm still messing with ideas on eliminating the back-of-the-windshield low pressure zone somehow, but I haven't got there yet.

I still think that by using side wings, blockers, etc. we're just treating various symptoms, not curing the basic problem of that partial vacuum at the back of the windshield...

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Probably the best approach to reduce the low pressure area behind the windshield is a cowling that attaches cross the top of the windshield and may be a little on the sides. It would help direct the air over the top plus if you could also direct airflow behind the windshield. It would have to have adjustable vents or replaceable mesh that you could use to fine tune the flow on the back side of the windshield. My problem is I think it would end up looking like a monstrosity.
Dave W

The streamlines on the CFD output also suggest that fairing in the front of the rear fenders (as on the last photo of the Kimini bodywork mock-up on the site) might reduce biuffeting - it looks like the fenders are damming the flow and increasing the amount of sideflow into the cockpit from the windscreen.

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
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If you look at most modern convertables the windscreen has a much higher rake. The top of the windscreen is usually over the drivers head or close to it.
I think properly placed engine vents could be extended backwards and help divert the air away from the rear fenders as well.
Dale

Getting off-topic. I'm actually counting on the air piling up in front of the rear fenders so it'll head into the engine compartment.

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I'll ask and see what can be done.

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-Andrew
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