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

[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.

[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.

[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 (http://boardroom.wscc.co.uk/cgi-bin/ikonboard.cgi?act=ST&f=1&t=73536&st=#entry732213) the ones you mean?

[Alaskossie]

John,

Those are very close. I do not remember them as being quite that tall, but that is the general idea of the ones i tried to buy four years ago.

Based on my blat yesterday, I find that with half doors and no top, angling the standard CC wings outward just an inch or so makes a noticeable difference in how much wind buffeting hits your face.

[scannon]

Based on my blat yesterday, I find that with half doors and no top, angling the standard CC wings outward just an inch or so makes a noticeable difference in how much wind buffeting hits your face.
That's what I noticed a couple of years ago on my Caterham. I made standoffs out of 1/2" clear plastic dowel and used superglue to attach them to the bottom of the wind wings. I put a soft rubber bumper on the end to protect the sheet metal. They significantly reduce the buffeting.

[Croc]

That's what I noticed a couple of years ago on my Caterham. I made standoffs out of 1/2" clear plastic dowel and used superglue to attach them to the bottom of the wind wings. I put a soft rubber bumper on the end to protect the sheet metal. They significantly reduce the buffeting.

Skip - Do you have a pic that illustrates what you did? I am struggling to imagine what you did. Many thanks

[scannon]

Skip - Do you have a pic that illustrates what you did? I am struggling to imagine what you did. Many thanks
Mike,

Here's a few pictures of it.

[Croc]

Skip - Now that I see the pic I can see what a brilliantly simple and effective idea you came up with. Why didn't I think of that ..duh! :leaving:

[slomove]

Well, I would not call it a flaming failure as earlier suspected but anyway I was not satisfied with the results. Polycarbonate is pretty tricky to work with and I suspect even with industrial equipment it may not be possible to shape a sheet on a mold with good optical clarity.

So I built a mold:
http://lh6.ggpht.com/_242PlvPtVpE/TOnNLy9Nn3I/AAAAAAAACMQ/ymWvvkCXkPY/s1152/P1020474.JPG

Put it into a heater box (a.k.a. oven) with air baffles:

http://lh3.ggpht.com/_242PlvPtVpE/TOnNPNxtqHI/AAAAAAAACMU/sejQ1sdNMEA/s1152/P1020478.JPG

Blew in 6 kW of hot air to get to 365 degrees:

http://lh4.ggpht.com/_242PlvPtVpE/TOnNSrR0R-I/AAAAAAAACMY/7cnhBr0LZf4/s1152/P1020480.JPG

Got a properly shaped sheet for the sidescreen but the optical clarity was disappointing:

http://lh6.ggpht.com/_242PlvPtVpE/TOnNXBvoaMI/AAAAAAAACMc/-CFTIcWdfFs/s1152/P1020503.JPG

Oh well, some things are more difficult than expected.
I did several experiments with different temperatures and soaking time but eventually had to give up and go back to the previous concept with the frame (see next post).

[slomove]

After that thermoforming failure I formed a new sidescreen frame from thin walled stainless tubing:
http://lh5.ggpht.com/_242PlvPtVpE/TOnNdkjxFcI/AAAAAAAACMg/mJVaRB8CLgk/s800/P1020482.JPG

Put a flexible 1/16" sheet of polycarbonate on and wrapped the edges around the frame with a hot air gun:

http://lh5.ggpht.com/_242PlvPtVpE/TOnNj_i8HLI/AAAAAAAACMk/_6mK30-bhb8/s1152/P1020486.JPG

Result is much more pleasing:

http://lh6.ggpht.com/_242PlvPtVpE/TOnNqz7ls2I/AAAAAAAACMs/p4JrfDXtyeg/s1152/P1020507.JPG

New frame is not too obtrusive, good wind and weather protection and still the feeling of an open car. I like it....

http://lh4.ggpht.com/_242PlvPtVpE/TOnNyN1q0JI/AAAAAAAACMw/QUiC9Sejg7Q/s1152/P1020509.JPG

[slomove]

More pics....This is with screens open:

http://lh3.ggpht.com/_242PlvPtVpE/TOnODRGYLaI/AAAAAAAACNE/qVvLcyBSYr4/s1152/P1020520.JPG

And I ended up with satin black mirrors (instead of the the matching yellow):

http://lh6.ggpht.com/_242PlvPtVpE/TOnN2QCP1PI/AAAAAAAACM0/IpgSzjxUIbI/s1152/P1020511.JPG

Anyway, given the difficulties, I think I can not provide sidescreens to other interested parties :o but maybe the pictures help come up with new and better ideas.

[scannon]

Gert,

It looks great. I think I like it better with the frame. Can you make me a set for the Caterham?

[Paul Hill]

Gert....
Interesting headlights.
Care to share the details?

[lancylad]

I'd like a pair of those for my Westfield. Love the way they tilt forward for entry and exit. Mirrors look good in black.

[slomove]

Gert....
Interesting headlights.
Care to share the details?

That was last year's project:
http://www.usa7s.com/vb/showthread.php?t=4498

In the meantime I ditched the separate swivel stem and re-mounted the headlights a little lower on the shock bracket from the newly installed Birkin widetrack kit. Looks more integrated and less vibration.

[slomove]

Gert,

It looks great. I think I like it better with the frame. Can you make me a set for the Caterham?

Unfortunately it is not a simple repeatable molding process as originally envisioned.

But doing the tube frame is actually not that difficult. It is 5/16 thin walled 304 stainless tubing that can easily be shaped with a tube bender by hand. One 6' stick plus 5" extension is sufficient for one side. It took me maybe 3 or 4 hours per side, bending, fitting, tweaking over and over until it was right. Since I don't have a jig this can only be done with frequent fitting on the car. Then I welded the swivel mounting plate, a dowel to hold on to the windscreen stanchion and a steel strap for the door sill. The swivel is a nylon ball joint in an aluminum shaft collar. Depending on the collar tightening the swivel has more or less friction.

[GBOLT]

Next time use a high quality pooltable felt on your form we do this all the time. It is also helpful to sandwich the material between a core and cavity, this will let you lower the material temp, and improve clarity,

[slomove]

Thanks for the tip. I heard about the felt method but I only found synthetic felt that would not have survived the temperature.

I am pretty sure I could have a achieved an acceptable result eventually with continued experimentation. But honestly my patience ran out and at $35 per 16x32" per sheet the experimentation gets expensive pretty soon.

I am quite satisfied with the result anyway. I don't regret giving the thermo-forming a try (old R&D wisdom: fail early, fail often) but the method with the frame is just much easier.

[Kess]

As a former Superformance owner (and now looking for a replacement 7) I thought the door/window that was offered on that car was a great design. The door was hard and snapped closed. It had a Lexan window that moved up and down in the door on a track. It used a knurled metal knob to hold the window in the desired position which worked great. With the door on and window down there was very little buffeting. With the door on and the window up rain was not a problem either. It sealed very well up to the top and the doors and top fit easily into the trunk. It was also very easy to lift the door off when I did not want it.