GRM Exclusive Reveal: Exocet Spec-A

Well, an 18 inch tall windshield 48 inches wide (about right for an Exocet) is 6 square feet, so the windshield assembly should (in my horseback opinion) be able to withstand 300 pounds spread evenly over the glass. An aluminum channel with an external brace atop the top might be all it needs, but my channel (see http://www.kineticvehicles.com/ExtrusionW.html) is 6061 T6, 5/8" x 5/8" with 1/8" walls, and I don't think it could handle that load by itself. So I'm going with an external stiffener before I even set up a test stand.

If you want any 'field research' done on a Sport model, let me know !!

Good luck, Jack! A full surround was a little more than I wanted to take on, especially after I did the aerodynamic force calculations. It can be done, but the surround needs to be supported and/or very stiff, and I didn't see a way that didn't involve prepreg carbon and a windshield cost approaching the kit itself. The lack of curvature in the glass makes strength hard to come by, but other cars out there have accomplished the challenge.

I just keep thinking "they have done it like this for years on the Super 7 ... why not here"

[edit: I clearly haven't figured out how to do footnotes; the first is a reference to "mice" and the second refers to "...don't calculate much"]

Warren v wrote: Good luck, Jack! A full surround was a little more than I wanted to take on...

Thank you, Warren. I suspect that as acceptance grows, you'll find more of us mice* in Exocets, and you had more than enough to take on, just getting the Exocet ready for prime time.

Warren v wrote: ...especially after I did the aerodynamic force calculations.

If you still have those calculations, I'd love to see them. On projects of this nature, I don't calculate much**, or more accurately, I rough out the calculations and then test to see if I got it right. As they say, you trust your mother but you cut the cards.

einy wrote: I just keep thinking "they have done it like this for years on the Super 7 ... why not here"

Because an Exocet Sport windshield is twice the area of a Se7en windshield, and it's taller and further between the stanchions, so there's more leverage on the support structure. Warren is right, this ain't gonna be easy--by my (slide rule on horseback) calculations, an Exocet windshield at 100mph is roughly (load x leverage) equivalent to a Se7en windshield at 200mph. And since I don't trust -my- calculations enough to stake -your- life on them, I'll build a fixture and do a 220*** pound (100 kilogram for you sophisticates) sandbag test before offering this windshield kit to the motoring public.

*I hope I'm using that word correctly--I'm elderly and unhip; heck, first time I saw "Because race car," I thought it was a typo.

**Mostly because I'm not that good at it. I did my structural book learnin' with a slide rule, and you young whippersnappers today have FEA, and phones in your pocket that are smarter than NASA was when we sent men to the moon.

*** Warren, please advise if you'd recommend a different test load.

I'd have to do a CFD to give you any real drag numbers. Be aware that a thin flat plane at a small angle will throw a lot of laminar flow up, generating drag coefficients that substantially exceed 1. Even worse, your force will be concentrated on the middle of the top, and that part of the glass will be subject to crazy vibrations from the eddy currents. So your greatest static load, your greatest dynamic load, and your weakest point are all coincident. A structure like that is doable, but you'll need some thick glass if you insist on a flat shape. Double curvature is a powerful thing. If there's any way for you to integrate a curved windshield, the stress decreases by a few orders of magnitude.

Warren, I'm not asking you to do my job for me--and certainly not for free--but if you're a CDFer for Hire let me know, I have other projects that might be better suited to your skills and talents. I just thought, since you'd done the permanent-mount windshield for the Race chassis, you'd know if my calculations (and upcoming tests) were off base in comparison to your calculations (and your tests).

I was not aware that a thin flat plane at a small angle will throw a lot of laminar flow up, indeed I'm not even aware of what 'throw a lot of laminar flow up' means. Mind you, my formal aero training goes back to the days when MIGs had tube radios; I've tried to stay up to date but haven't been in an aerodynamics/structures classroom for (gulp) close to four decades (though I think subsonic aerodynamics were pretty well figured out by then).

Anyway, you went for a flat windshield in your design, and I don't know that you insisted on a flat shape or if it just made good business sense to go flat instead of curved, but I have neither the budget nor the inclination to have custom double curved windshields formed. Double curvature is indeed a powerful thing, but (in my opinion) it wouldn't decrease stress by 1000+, it would decrease stress by maybe 20% (though strain is a different story).

I want my windshields to be safe and effective and economical and 50 state legal, and I want them to make Exocet owners even happier than they already are.

I don't know how the widths and shape would match up but a Porsche 550/356 windshield looks cool and is available in 3 different heights. (Speedster, Convertible, and Coupe). I've used it in a number of builds. If I remember correctly its 49 inches wide.

Me too! It's a good general purpose windshield for (us) folks building classic replicas/knockoffs/inspiredbys. That windshield is about perfect for the width of the chassis (that is, the chassis side rails are also 49" center to center) but it's an awkward mount, and I don't feel it's in the character of the Exocet...plus there's my personal objection to selling a $495 dollar windshield mount kit with instructions that say, "Now, spend $600+ on glass."

Besides, I think I can do it with flat AS1 50-state-approved-and-price-competative-with-dirt windshield glass. To quote Nevil Shute, An engineer is someone who can do for ten shillings what any fool can do for a pound.

This isn't going to impress the ghost of Nevil Shute--this isn't costing 10 shillings, or even a pound (truth is, it's a whole sheepload of pounds sterling for the tooling and the initial 500 pounds aluminum, which is enough for a whole bunch of windshield frames...so keep selling those Exocet kits, Kevin!) but in reasonable kit-car quantity, it sure beats machining them out of billet.

Here's a drawing of the windshield surround extrusion; I'll have my first squeeze (a couple hundred Sport/Basic chassis windshields' worth) in the shop in mid/late May. Meanwhile I get to build a forming machine, and after the metal comes in, I get to build another forming machine when I figure out why my first forming machine doesn't work. [EDIT: Hmm. I followed the image-posting instructions, but the image comes through as broken. Here's the url if you want to see what I tried to post.]

https://www.dropbox.com/s/6q8mnn5ngys52q7/KV02Die.jpg?dl=0

Jack,

Is the extra 1.00 x 0.25 lip for stiffness? Also, what is the purpose of the 0.5" x 0.125" undercut in that lip?

Your basic profile is close to what I am fabricating now, but my setup is A36 steel.

>Is the extra 1.00 x 0.25 lip for stiffness?

Stiffness and strength.

>...the purpose of the 0.5" x 0.125" undercut...

Weight reduction, plus it can be used to pin the nuts for 5/16" bolts to attach the windshield surround to the stanchions. But I'll admit to some concern re how this shape is going to bend.

>Your basic profile is close to what I am fabricating now...

Clearly, great minds think alike.

>...but my setup is A36 steel.

Steel extrusion is beyond my budget.

I can imagine the die cost already is not insignificant!

In my case, the steel surround is a fabrication of C channel around the left side / top / right side, with angle iron (i.e. L channel) welded to the top run for increased bending stiffness. This will slot / bolt into the Exomotive offered Sport windshield frame, once I finish fabrication of that interface. Once I get a bit further on, I'll post some pics if I can figure out how to do that.

Hey GRM! The Exocet has been thriving since we last talked, and I want to thank the community again for their input, passion, and participation in the project. In the last few months, a customized V8 Exocet came 4th in the open wheel class at Pikes Peak, Matt Farah had a blast driving a customer's turbo Exocet in a One Take, Randy Pobst and completed the SCCA Targa Southland in a bone-stock Exocet, and the car has a received a considerable amount of press, even landing on the cover of S3 magazine. There's even a community-generated video series based on the build process: Crossthreaded

It's been fun watching it grow. SEMA took notice too, naming Kevin one of their Launchpad finalists. Tonight is the last night of voting. If you care about such things, your votes could help Kevin win the competition. Voting ends TONIGHT! Again, thanks for being such an awesome community and supporting this wacky grassroots project!

https://www.sema.org/launch-pad/vote

I have a buddy finishing his Exocet. He is having trouble getting it insured as a modified 2004 Miata. Does anyone here have any tips?

Thanks

Trying for regular insurance or specialty/collector car insurance?

This has probably already been brought up, but while convertibles are normally not acceptable in Rallycross, has anyone tried to get something like an Exocet in with a metal panel attached to the roll cage?

tuna55 wrote: I have a buddy finishing his Exocet. He is having trouble getting it insured as a modified 2004 Miata. Does anyone here have any tips? Thanks

It shouldn't be registered as one, it should be registered as an Exocet. I'd call up Hagerty and the other specialists.

In reply to NOHOME:

Regular. He wants to drive it to work.

Regular insurance companies wouldn't touch mine, even with an auto enthusiast independent agent shopping it for me. I ended up going with Infinity Insurance Company as a specialty vehicle.

tuna55 wrote: In reply to NOHOME: Regular. He wants to drive it to work.

That might be an issue. One that I expect I could run into with the Molvo. Regular insurance companies are becoming adverse to just about any modification, let alone the creative stuff. A part of me sympathizes since nobody builds a hoonmobile to not hoon.

Specialty insurance doesn't have to mean you can't drive it to work.

I'm going to sound like a broken record but call hagertys. They are simply the best customer service I've ever had in my life.

icaneat50eggs wrote: Specialty insurance doesn't have to mean you can't drive it to work. I'm going to sound like a broken record but call hagertys. They are simply the best customer service I've ever had in my life.

When I called Hagertys about Frankenfiat, they were very clear that the car had to be kept in the garage, had to be driven less than a certain mileage, had to be waxed at least twice a month, had to maintain tire pressures between 25 and 35 PSI... Ok, I'm joking, but the person seemed to be very clear that the policy was aimed at a gentleman driver who did little more than Cars and Coffee events. It was frankly off-puting. Allstate picked up the policy as a "normal" car.

Kreb wrote:

icaneat50eggs wrote: Specialty insurance doesn't have to mean you can't drive it to work. I'm going to sound like a broken record but call hagertys. They are simply the best customer service I've ever had in my life.

When I called Hagertys about Frankenfiat, they were very clear that the car had to be kept in the garage, had to be driven less than a certain mileage, had to be waxed at least twice a month, had to maintain tire pressures between 25 and 35 PSI... Ok, I'm joking, but the person seemed to be very clear that the policy was aimed at a gentleman driver who did little more than Cars and Coffee events. It was frankly off-puting. Allstate picked up the policy as a "normal" car.

Hagerty's was called, this was the relative feeling from my bud.

In reply to tuna55:

I had a Hagerty policy on my Stalker. never had to use it. Never thought to call them after I slid into a curb and damaged the front end. But I don't like fibbing about what I do. I'd rather pay a bit more and tell them the truth - that it will be in the garage - unless I've got another project in there. And while I may not drive it for 6 months, then I might drive the f--k out of it for two months.

edit: I don't really think about actually using my insurance when it comes to toys. I share a mountain cabin where we could have made a half-dozen claims over the years, but rather than whine about it to someone, I just call my cousins, throw a work party and deal with it. Insurance is more for the kid who wasn't supposed to be on my property in the first place, fell off the deck and has parents who think that because the cabin is next to a lake, that means we're rich.