Lexan Gullwing Half-Doors - anybody interested?

[slomove]

I have been using self-made transparent half-doors/wind-deflectors (picture below) for several years and can not imagine touring without. They almost eliminate wind buffeting in the face and keep rain out of the cockpit. To open they swivel forward over the bonnet around the mirror stem. So, not really gullwing but kind of.

 

The ones that I made are pretty much beat up after 6 years and need to be replaced. Now I am wondering if I should just re-do them as they are (flexing and attaching thin Lexan onto the metal frame) or if I should go through the trouble of building a mold and thermo-forming thicker Lexan (i.e. 3/16") into shape, thus getting rid of the metal frame. Obviously more elegant but much more cost, work and risk of failure.

 

Anyway, just wondering if somebody else would be interested in such half-doors (please PM). If I would make 3 or 4 sets the cost of material, labor and amortization of equipment would be about $350 per set. No commitment necessary, just looking for serious interest to get me motivated.

 

Bad news: This is most likely for Birkin S3 only. I don't know if the screen angle and door cutout of a Caterham is even close (but could find out). While I have special tripod mirrors right now, I will switch back to single stem mirrors soon.

 

http://lh4.ggpht.com/_242PlvPtVpE/S8KJvfB0hDI/AAAAAAAABgU/lzP3bqgHGOU/s720/P1010819.JPG

 

http://lh4.ggpht.com/_242PlvPtVpE/SxHSehEgPPI/AAAAAAAAA0Q/5-yHWpGIvcw/s800/Hwy166_2.JPG

Edited October 21, 2010 by slomove

[Kitcat]

Gert:

 

Interesting/tempting. My concern, aside from whether it wld fit a Cat, is heat. In my car, the key to survival in weather above 70 degrees is lots of air flow thru the cockpit (doors off, or bottom 1/2 of both doors flipped up). Your design seems to insulate the driver from the elements but does that mean it also traps the heat???

 

Mike

[slomove]

Well, it insulates to a degree. While the buffeting is much reduced (actually the turbulent zone is rather moved backward behind the driver's head) there is still significant air flow in the cockpit. After all I live in Southern California and I use the car rather comfortably in the 90's. Only when it get above 100 degrees I prefer a car with A/C.

 

These screens don't help or hurt with the common problem of feet roasting. For that I have separate forced footwell ventilation and firewall insulation.

 

Edited to say....when it over 80 degrees I also use the sun roof.

Edited October 21, 2010 by slomove

[DeanG]

Great pictures. Interesting idea. They give the car a classic (retro?) look.

[supersportsp]

For Caterham owers: I would think with a set of the small Caterham deflectors and the Caterham half-doors, you would have the same effect. I ran my deflectors and a hastily made cardboard half-door as a test earlier this fall and it worked pretty well.

 

Ben at Caterham USA told me that most of the buffeting is due to wind hitting the rear wings and forcing air pressure into the cockpit. Thus, having something at that level to block that air flow out helps significantly.

 

I have also been experimenting with Airtabs. http://www.airtab.com/en/. I placed a couple just ahead of the cockpit opening in several positions. It was an improvement, but hard to say how much.

 

That all being said, this is an interesting potential option. JohnCH has made some super side deflectors for his Westfield. I am sure he will chime in.

[slomove]

The discussion about reduction of buffeting is probably as old as the Seven. So far I have seen only practical experiments with varying and very subjective results and no scientific data. I read somewhere that Lotus experimented in the wind tunnel in the 60s but did not implement any improvements after that. Caterham is said to have done some wind tunnel experiments for the overall aerodynamics but probably did not look at the buffeting?

 

Anyway, I don't think the buffeting has anything to do with the rear wings. After all it is known to go mostly away when you remove the windshield or install Brooklands (you still have the air stream but not the wild turbulence). But since I don't want to wear face/head protection in the car this is just not an option for me.

 

The steep windscreen forces the air to go up and over the cockpit (think aircraft wing) creating lots of vortices (google Karman-effect). My theory is that closing the side openings at least partially does not eliminate that problem but moves it backward out of the driver's face.

 

Whatever it is, these half doors have done an excellent job of keeping the hat on for the last 6 years.

[JohnCh]

There are a few threads on here about my enormous wind deflectors. They aren’t particularly attractive and must make the car’s poor aerodynamics even worse (see below), but they work great and add a measure of protection. Specifically, there is a good chance that if I didn’t have those, my wife and I would have been killed or seriously injured on the way back from USA2005. The lexan deflector prevented a tire carcass from hitting me in the shoulder (best case) or head (worst case) at 70mph on a dark freeway. The deflector redirected the carcass so it “only” ripped off the driver’s side rear wing and cracked the tub. Had it hit me, we most likely would have crashed.

 

I recently experimented with half doors that I mocked up out of cardboard and noticed a big difference compared to my deflectors. The half doors did a much better job reducing turbulence in the cockpit from about mid torso down, but they didn’t do much to stop the wind from hitting me square in the face – an area where my deflectors excel. The lack of wind through the lower part of the cabin with the half doors was nice, but I’m concerned that it would be a negative on warmer days when the hot air would just build up. I’ll probably continue to experiment in this area over the winter.

 

http://john15.web.officelive.com/Documents/993westfield.jpg

 

-John

[supersportsp]

Anyway, I don't think the buffeting has anything to do with the rear wings.

 

According to Ben, that is not the case. He was on the team that took a Caterham to the wind tunnel in the early 2000's to see if they could make any major improvements in getting it to cut through the air. He was an engineering intern with Caterham UK at the time.There is an article someone posted out of Car (UK) magazine that covered this project. It talks about Ben in the article I believe.

 

Anyway, I was talking to him specifically about cockpit buffeting solutions and that his when he brought up the comment about the rear wings.

 

I believe the reason buffeting 'improves' with a brooklands or aero screen is that you are in much more direct and consistent airflow.

Edited October 22, 2010 by supersportsp

[Alaskossie]

i had plenty of time to think about wind buffeting on my 6100-mile drive from Colorado to Alaska in August.

 

Most of the time, I ran with CC windwings, a SoftBits bikini top and SoftBits rear wind deflector/filter (stretched between the headrests), and SoftBits canvas half doors. The wind buffeting was still present, but the combination of half-doors, bikini top and windwings reduced it to some degree. The only exception was not really buffeting, but stiff crosswinds, like crossing the Mojave Desert. it was such a hot, drying wind ( and 100 degrees F. +) that I had trouble with my eyes drying out, and had to resort to goggles.

 

Of course, for those who want to run without any top, the buffeting would be increased with this combination, any time the top would be removed. I did notice quite a bit of flex and rippling of the bikini top at interstate highway speeds, which put me to thinking about adding 3 or 4 removable carbon-fiber tent-pole sections as stiffeners.

 

Also, some spring-loaded hinges for the CC windwings would keep them from rapping against the body when luffing in a trailing wind. (You have lots of time to think about Seven mods and projects on a trip like that!).

 

After a while (like when I started up the Alaska Highway), I removed the half-doors and windwings, and put on the contoured Caterham full doors. This really cut the buffeting, of course, and gave me more elbow room than the flat canvas half-doors (as well as a better latching system, with the CC armrest/latches).

 

I'm thinking of a winter project that consists of new c/f half doors from Mog, and then adding a removable flat lexan window panel that wopuld hing on the windwing hinges like the full doors, so that assembled, you would have a full door, and disassembled, you would have a half-door with elbow room and an armrest/latch assembly. Storing the flat Lexan panels in the boot would be a lot easier than storing the full CC doors, which take up much of the boot.

 

John, do you think that buffeting would be reduced on your windwings if the top and side edges had a return of an inch or so, rather than just an narrow vertical edge? Hard for an amateur like me to know what the aerodynamics do here...

 

Alaskossie

[slomove]

When I got my car in 2003 I tried the regular half doors with and without deflectors and while it helped it just struck me as a jury-rigged solution. Larger deflectors are esthetically a compromise and the button-up half doors are cumbersome. I really prefer to get in and out without hassle.

 

That niggle is what got me to fabricate the transparent swiveling half doors in the first place. Opens and closes in a second, no need to stow away and does not impede the open feeling like the regular tall doors.

 

I decided to give the frame-less thermoformed version anyway a try. If I don't have a challenging project I will drive my wife crazy..... and if I get that to work I will post a few more pics.

[scannon]

Gert,

 

Do you know anyone with a Caterham near you that you could use to test fit the doors? If they can be made to work on a Caterham I'm in for a set.

[slomove]

The only guy with an SV in the area is Magnus F. but he went Aeroscreen a while ago.

 

Given the tooling effort I will make 2 sets at least, if for nothing else as a spare. Then I can send you a set for a test fit and you can try if it works.

 

But I think I am getting ahead of myself here. Let me first see if I can shape the screens properly at all. Maybe it ends up in flaming failure and Rosie is laughing her rear end off. :willy_nilly:

[scannon]

That works for me. Give Rosie a hug for me once she stops laughing.

[lancylad]

I'm following this thread with great interest, I love the sensation of driving with no doors but of course the face pounding is not to much fun. The thought of clear sidescreens is appealing and I am very interested in your project, not to sure if they would fit my Westfield? Measurement time...

[solder_guy]

JohnCh:

 

Your big deflectors look like a set of lexan I bought from the UK. Did you also? I have yet to mount mine on my Rotus.

 

Rob

[JohnCh]

Rob, mine were made to my specs. After hearing very good reports about the deflectors you bought, I experimented with mockups in various sizes and angles before settling on the final shape.

 

-John

[Alaskossie]

There was a fellow in UK who was mentioned on Blatchat as making custom windwings. They were a bit taller than normal, and the bottom edge had a horizontal angle that turned in at right angles to the windwing, and held the windwings away from the body a bit.

 

I contacted him, and he told me that unfortunately he was no longer making these windwings; so I deleted his bookmarked information. Perhaps this is where you got your windwings, solder_guy?

[lancylad]

Are these the ones you mean. http://boardroom.wscc.co.uk/cgi-bin/ikonboard.cgi?act=Print;f=4;t=42466

[Alaskossie]

lancylad,

 

No, those are not the ones. The ones you linked from the Westfield site are wider but shorter than the ones I saw in 2007. I looked in my messages, and found that the fellow's name was Tony. His windwings were tall enough that one side needed a cutout for the kill switch. I will e-mail him to se if i can get dimensions, etc.

[JohnCh]

Tom, are these the ones you mean?