Wind buffeting screen

[snookwheel]

We took a trip today (about 150 miles) and used it as an opportunity to try somthing to cut down on the wind buffeting. I cut down an old window screen to fit across the roll bar, zip tied it on and the difference was pretty significant.

 

I removed the screen at a rest stop at the start of on the Skyway Bridge, (a 5.5 mile bridge that spans Tampa Bay) to see if I could tell the difference. Boy could we.... as soon as we got to the other side it went back on! Next step is to have one made that I can roll up and Velcro on. I do have a fairly high windshield and wind wings which may have combined to give me the favorable results I saw today. Well worth the effort to reduce buffeting!

 

I had searched this forum and read some less than favorable results from some folks. That was not the case for us.

http://img.photobucket.com/albums/v640/snookwheel/Windbuffettest1.jpg

http://img.photobucket.com/albums/v640/snookwheel/windbuffettest.jpg

 

And a pic. of my 78 year old Dad who we were visiting. He is an ex Commercial Pilot, Aerobatics Pilot and Alaskan Bush Pilot. He'd love the Stalker, but those skinny seats make it a bit rough for him to get in and out of these days.

http://img.photobucket.com/albums/v640/snookwheel/DaddyLyleandScott.jpg

[MHKflyer52]

And a pic. of my 78 year old Dad who we were visiting. He is an ex Commercial Pilot, Aerobatics Pilot and Alaskan Bush Pilot. He'd love the Stalker, but those skinny seats make it a bit rough for him to get in and out of these days.

http://img.photobucket.com/albums/v640/snookwheel/DaddyLyleandScott.jpg

The smile on both of your faces says it all and I don't think the seats were that big of a deal for your dad from the smile on his face.

Very cool.:cooldude:

[slngsht]

Awesome picture right there :thumbs:

[pi7ot]

I have used the wind blocker from a BMW Z3 roadster and I also use a piece of smoked lexan that I trimmed to shape. It was originally a Gila rear window tint from a 77-81 Camaro.

 

For me, Neither work that well for wind blocking, but the latter works well at cutting down the back draft of fumes from my rear exit exhaust.

I think the success of a wind blocker behind the seat backs is more likely if you are really low in the car...I'm too high up.

 

m

[DeanG]

There was a device built, I think, by Mike Costin (of Lotus then Cosworth) that smoothed the airflow around the windshield. Unfortunately, Collin Chapman hated it. I've never seen a picture.

[Mondo]

I wonder if your sunshades, on top of the windshield help as well. I wanted to do that but I have that 7 mirror across the top (don't need side mirrors with it).

[snookwheel]

I wonder if your sunshades, on top of the windshield help as well. I wanted to do that but I have that 7 mirror across the top (don't need side mirrors with it).

 

Funny you mentioned that. We tried that as well. Zero effect. Then, I moved the sunshades to the side, effectively increasing the height of the wind wing. That did help with the outside ear buffeting. I can post a picture if you want a visual. Cheap from Pep Boys Auto Parts. I think $5.00.

 

Scott

[lancylad]

Love the pic of you and your Dad, makes me happy to see you sharing your passion with your Dad. His smile is awesome..

[Dave W]

Reducing Buffeting in a Seven

I have experimented with reducing wind buffeting on my Locost for several years now. The high vacuum “ low-pressure area” behind the front windshield is worst then if you are on a bike at the same relative road speed. I have tried several approaches to reduce the buffeting. Some worked, others did not, I have no way of measuring buffeting but these are my general findings for the various modifications.

Winglets will reduce buffeting around 10 to 15% depending on size. The attachment should allow some air to pass between the screen and the winglet.

Laying back the front windshield an addition 5* reduced buffeting by about 10%. It helped mostly at lower speeds and no change at higher speeds.

A solid Plexiglas wind screen behind the seats, attached across the full width of the roll bar and at head height did not help. I also experimented with cutting down the screen with a gap on the top, gap at the bottom, and both top and bottom gaps to allow some air to fill the low-pressure air behind the windshield. Using solid Plexiglas did not help, It actually made it worst.

Side doors, without the top. My doors are a lot longer then most. They run from the front of the windshield all the way to the roll bar. They reduce buffeting a good 40 to 50% when compared to an open cockpit.

A Bikini top, you still have high vacuum area, but a high percentage of the air flow is behind your head. It reduced buffeting in the 30 to 40% range.

Fixed sun visors that help defect the wind up over the top of the cockpit did help about 10%, but the visors probably need to 6 to 8” wide. My visors are only 4 ¼” wide, and worked the best when set about 20* from horizontal.

Make up air, I have a defroster, and a 5 speed heater fan, but I can not feel any difference in buffeting with the system running. I would venture to say that it would take a lot more air volume then a typical heater fan could put out. For the 5% of the Sevens that use bikini tops, I just installed a rear window that attached across the full width of the roll bar just a couple inches behind your head. The car was tested with Winglets and a bikini top installed. With a full width windscreen i.e. rear window, installed it increased the wind buffeting.” This is without doors” and the results where basically the same that I had with a solid wind screen tested without the top installed. But with the bikini top installed the air flow is back and forth alternating from the left side to the right side. Air flow was verified by using a single turf hanging from the roof bow. I design the rear window with center sliding section this allowed me to adjust the center opening. Adjusting the rear opening 1 or 2 inches wide in the center section had almost no effect on the buffeting. I next tested the windscreen with about 20 to 25% of the total rear window area opened in the center section to allow air to suck out into the low-pressure area behind the windscreen. A moderate 20-25% area opening actually reduces the total wind buffeting probably in the 10 to 15% range Vs a completely open rear area. It was more effective the higher the speeds. It was tested to 100+ mph and it prove to be even more effective at reducing the buffeting at those speeds when compared to a completely open rear area. Using an opening in the center area of the rear wind screen appears to work much better then trimming off the top and bottom of the full width Plexiglas windscreen and warrants further testing without a top installed or the used of an open mesh type wind screen which allows air flow.

Your results may vary; Dave W

If anyone would like pictures just drop a PM to me.

[Croc]

Dave - your results are interesting. They confirm my preference for reducing buffetting:

1) Use the side screens/doors with top off. Minor buffetting and pretty comfortable on long highway drives.

2) Use a bikini top, clear polycarb winglets and a mesh screen between the two seats (a soft bits for sevens design). My winglets were a modified Westfield UK design although I plan to modify them further so they stick out further from the car. In their current guise, holding them out while driving demonstrates to me the buffetting point from the airflow moves back behind the driver and the reduction of buffetting is significant. With the winglet modifications, option 2) would be the most comfortable. Without the winglet mods, option 1 is more comfortable.

 

I would be curious to see the pictures of your set up, particularly the winglet design to compare with the results of my experimentation.

[JohnCh]

Great info Dave. I experimented a lot with winglets on my car and discovered that to maximize effectiveness they need to be long, extending below the door cutout, be fairly wide, and sit at a pretty steep angle. The shape below is what I finally settled on after making a number of mockups out of reinforced cardboard. Not the most attractive add-on, but they split the difference between running with and without sidescreens, and unlike sidescreens, they don’t trap cockpit heat at low speeds. Work pretty well in the rain too.

 

http://john15.web.officelive.com/Documents/windwing%20front.jpg

 

-John

[snookwheel]

Neat idea John! How is the panel attached?

 

Scott

[JohnCh]

I used a spare set of male sidescreen hinges spaced the same as the female counterpart on the windscreen pillars. Makes it very easy to swap between sidescreens and windwings: lift one out, drop in the other.

 

-John

[lancylad]

Hi John

Your deflector design looks really good, what thickness Lexan did you use? I'm sure you have been asked that question before, as well as many more. So, just one more time.... Thanks John. Steve

[JohnCh]

I think I used 1/4" but I'll have to measure tonight when I get home. They are shockingly strong though The driver's side unit took a tire carcass hit at 70mph that destroyed the rear wing, but left the deflector unfazed. If the deflector hadn't been there, I might not be here to write this...

 

-John

[snookwheel]

If it is not too much trouble, I would love to see some pictures from different angles. It looks like you curved it to fit. Is that a bar across the middle of the shield? I bet those could slide behind my seat when not in use.

 

Scott

[JohnCh]

It’s one piece of lexan with two bends (middle and bottom) that can be seen in these photos. I made the final mockup out of MDF and then handed that off to the plastics shop who cut and bent it to match.

 

http://john15.web.officelive.com/Documents/trans%20tunnel%20015.jpg

 

http://john15.web.officelive.com/Documents/windwing.jpg

 

-John

[lancylad]

Good pics John, looks like 1/4 " material. Thanks for the info. Off to start playing with some MDF..:smash: