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-   -   windshield (https://ecomodder.com/forum/showthread.php/windshield-19325.html)

muffildy 10-29-2011 12:58 PM

windshield
 
So i am looking into the windshield angle mod listed in the efficiency mods section, and i was wondering what windshield would be the best replacement for a mazda miata to maintain best visibility with the new windshield angle?

if i just kept it stock, i expect i would be seeing 20% less of the road.

ChazInMT 10-29-2011 01:03 PM

Modifying the windshield for what? You will see very little gain in efficiency by changing it, and it sounds like a galactic pain in the butt if you want it to look and work good. Your efforts would be better spent elsewhere on the car.

mcrews 10-29-2011 01:28 PM

unless your building a showcar/hotrod.....why would you start at the windshield?
I would look at a body kit to get a lower profile withuot scraficing the ride quality by lowering the suspension.

muffildy 10-29-2011 02:29 PM

total conversion
 
its a total conversion project
im harvesting the mazda miata drivetrain/suspesion and building a sandrail style chassis, attaching a body to it. So the amount of work is astronomical and wouldnt be reduced by keeping the old windshield. But i want it to be more aerodynamic, so i need a windshield which is the approximate width of the stock miata but a little bit taller so that the angle can be changed with no ill effects on visibility.

kach22i 10-29-2011 02:40 PM

I think a lot of people are going to start posting images of that green teardrop template if you don't clarify that you are doing this so that it "looks" faster and more aerodynamic.

muffildy 10-29-2011 02:58 PM

reasons
 
it doesnt have to look anything
it needs to be more aerodynamic
the stock miata is something like .37 coef of drag
frontal area should be pretty much stock miata though since the width/height are being determined by a lot of the harvested parts, but the aerodynamics can hopefully be improved to be a .25 or so coef of drag.
So to do that i basically need to follow almost all of the aeromods listed on this website, which includes changing the angle the windshield meets the hood at to be less severe of a change. to do that i think i will need a taller windshield.

I was thinking of switching to the toyota prius windshield, which is slightly wider as well so the wheels would end up being slightly recessed which would be ok since then i can cover them with panels without there being a bump.
but im open to other options.

aerohead 10-29-2011 04:31 PM

windshield
 
Quote:

Originally Posted by muffildy (Post 267874)
it doesnt have to look anything
it needs to be more aerodynamic
the stock miata is something like .37 coef of drag
frontal area should be pretty much stock miata though since the width/height are being determined by a lot of the harvested parts, but the aerodynamics can hopefully be improved to be a .25 or so coef of drag.
So to do that i basically need to follow almost all of the aeromods listed on this website, which includes changing the angle the windshield meets the hood at to be less severe of a change. to do that i think i will need a taller windshield.

I was thinking of switching to the toyota prius windshield, which is slightly wider as well so the wheels would end up being slightly recessed which would be ok since then i can cover them with panels without there being a bump.
but im open to other options.

If you were going to go to all the trouble to re-engineer your windshield you'd want to all the way to something like a GTP windshield,as Venom and McClaren,Mercedes C-111 III,etc. run.These are $ 3,000 windshield and would require massive modifications to the entire cowl area.
My neighbor ditched his Miata ,got a CRX and picked up 12 mpg without lifting a finger.

Frank Lee 10-29-2011 04:35 PM

People still think the hood/windshield junction is the problem :rolleyes:

brucepick 10-29-2011 10:51 PM

Have a look here, for some basics on the ideal shape to strive for.

http://ecomodder.com/forum/showthrea...rt-c-9287.html

Yes you'll want to optimize your windshield - but I would think you would want to optimize the entire 3 dimensional shape of the vehicle.

Ryland 10-30-2011 12:15 AM

But isn't most of the drag from the rear of the vehicle and from the underside, the amount of drag from the shape of the front is such a small percentage it's hardly even worth worrying about if you are ignoring the rest.

muffildy 10-30-2011 02:52 AM

not
 
the rest will not be ignored
the only things im basically stuck with are a 66 inch width, and a wheelbase of 89 inches because of the drivetrain. So that means yes, there will be rear mods, underside mods, tire mods etc.
Think i found a better fit for the windshield now, the honda insight is 66.7 inches wide so i wouldnt be gaining as many inches for the windshield mod.

for the creation of the boat tail as linked in that picture, i find it difficult to read. are the numbers the change in degree or are they coordinates on a x/y grid? Basically, for every 1 foot towards the back of the car how many inches towards the ground should it advance?

jime57 10-30-2011 02:54 AM

Quote:

Originally Posted by aerohead (Post 267887)
My neighbor ditched his Miata ,got a CRX and picked up 12 mpg without lifting a finger.

I think Phil has this right. Better to ditch the Miata while it looks good and is in stock form, retaining its value. Switch to something which is basically more promising like a CRX or even a first gen Insight, if you can find it.

Get your objectives straight in your mind. Do you want to work the usual ecomodding approach to improved fuel economy, or do you want a custom street rod?

Making basic changes such as windshield angle are very difficult technically, and the associated adaptations, such top, seats, doors, side glass, etc. just ripple on forever.

If you are determined to proceed with the Miata, I'd buy a good front spoiler such a the one by flyingmiata.com, built a complete smooth belly pan, remove the right side mirror, possibly add rear tire spats. Then I'd look at constructing a template derived extension of the hardtop rear, with new rear window.

Can such a thing pass road safety inspection in your state?????

Patrick 10-30-2011 10:34 AM

1 Attachment(s)
Muffildy, if you're gonna go all-out, use the rear hatch glass from a 1984 Camaro:

muffildy 10-30-2011 11:05 AM

all out
 
yes, this is an all out project
none of the unibody will be re-used, we are going to be bending/welding a completely new body and attaching it to a tube frame chassis.
the 1984 camero rear window is a good idea, only problem is that the camero is 72 inches wide, which is 6 inches more wide than the miata; since we are using the A-arms/differential etc that would mean i would need to get longer CV joints which can be pricey; do you know of a similar rear window thats made for a 66 inch wide car? If i used the insight front windshield i would be at 66.7 wide instead so between 66 and 67 would be good. 68 might be pushing the CV joint issue.
also a 3000 dollar windshield is out of the question - budget is not that big.

jime57 10-30-2011 11:55 AM

Check out using an Insight hatch. It should be about the right width. Any Insight parts you can hang on your tube frame will put you ahead of the game weight wise. If you could use the entire roof and A pillar assembly you would get the windshield and the nice shallow angle that it has. Just one of many options I'm sure.

brucepick 10-30-2011 12:01 PM

Put an Insight body on your sandrail chasis?

Or get a junked Insight and give it the power train you want it to have. You'll start with really good aero and a lightweight shell.

muffildy 10-30-2011 07:05 PM

food for thought
 
hrm, may do just that; i was going to go more for a full boat tail but i cant seem to find glass for that option.

brucepick 10-30-2011 07:35 PM

Quote:

Originally Posted by muffildy (Post 268029)
hrm, may do just that; i was going to go more for a full boat tail but i cant seem to find glass for that option.

Just a quick guess - but the Gen 1 Insight might be a good candidate for a boattail add-on. Maybe you could find a way to keep the rear glass functional with the added tail?
http://media.ed.edmunds-media.com/pi...ght.5074-E.jpg

Patrick 10-30-2011 08:23 PM

Quote:

Originally Posted by muffildy (Post 267978)
yes, this is an all out project
none of the unibody will be re-used, we are going to be bending/welding a completely new body and attaching it to a tube frame chassis.
the 1984 camero rear window is a good idea, only problem is that the camero is 72 inches wide, which is 6 inches more wide than the miata; since we are using the A-arms/differential etc that would mean i would need to get longer CV joints which can be pricey; do you know of a similar rear window thats made for a 66 inch wide car? If i used the insight front windshield i would be at 66.7 wide instead so between 66 and 67 would be good. 68 might be pushing the CV joint issue.
also a 3000 dollar windshield is out of the question - budget is not that big.

Well the Camaro glass isn't as wide as the car. I think it's very close to the overall width of a Ford Probe. It might be just the size you need.

Another option might be a Corvette hatch glass. But I imagine it would cost more than a Camaro hatch.

CFECO 10-31-2011 10:09 AM

Nissan Murano rear glass looks good, though the glass is not laminated windshield glass = not legal for use as one. Has a wiper already built in though.

euromodder 10-31-2011 02:52 PM

Quote:

Originally Posted by Frank Lee (Post 267889)
People still think the hood/windshield junction is the problem :rolleyes:

The main benefit of a shallow windshield angle, is the equally shallow transition angle to the roof .
It'll help the streamlining beyond the windshield-roof transition.

Clev 10-31-2011 04:09 PM

Quote:

Originally Posted by CFECO (Post 268126)
Nissan Murano rear glass looks good, though the glass is not laminated windshield glass = not legal for use as one. Has a wiper already built in though.

Yeah, I'd avoid using rear hatch glass as a windshield. I get rocks bouncing off my windshield at least once a month that would shatter a back hatch at freeway speeds.

kach22i 10-31-2011 04:11 PM

Quote:

Originally Posted by euromodder (Post 268163)
The main benefit of a shallow windshield angle, is the equally shallow transition angle to the roof .
It'll help the streamlining beyond the windshield-roof transition.

How about an equally angled hood leading to the windshield?

Previa Thread
http://joshp77.files.wordpress.com/2...agestima31.jpg

aerohead 10-31-2011 06:50 PM

Camaro
 
Quote:

Originally Posted by Patrick (Post 267976)
Muffildy, if you're gonna go all-out, use the rear hatch glass from a 1984 Camaro:

Patrick,I have one of these for the T-100 for demonstration purposes only,as it is 'safety glass',but not 'laminated safety glass.'
They won't even let me,or anyone else run one of these at Bonneville.Glass shards all over the course should they break.
And State Inspections won't pass them for passenger vehicles as they're not DOT rated for windshield service.
RATS!!!!!!!!!!!!!!!!

aerohead 10-31-2011 06:53 PM

Dodge Viper?
 
Quote:

Originally Posted by muffildy (Post 267978)
yes, this is an all out project
none of the unibody will be re-used, we are going to be bending/welding a completely new body and attaching it to a tube frame chassis.
the 1984 camero rear window is a good idea, only problem is that the camero is 72 inches wide, which is 6 inches more wide than the miata; since we are using the A-arms/differential etc that would mean i would need to get longer CV joints which can be pricey; do you know of a similar rear window thats made for a 66 inch wide car? If i used the insight front windshield i would be at 66.7 wide instead so between 66 and 67 would be good. 68 might be pushing the CV joint issue.
also a 3000 dollar windshield is out of the question - budget is not that big.

The Dodge Viper has as good a windshield as we're likely to run across.About $600.Check the dimensions.

Frank Lee 10-31-2011 07:20 PM

Quote:

Originally Posted by kach22i (Post 268174)
How about an equally angled hood leading to the windshield?

That affects the windshield/roof transition how?

CFECO 11-01-2011 12:07 AM

Less of a sharp edge the air has to break over. IF the template is the ideal, then the rounder and smoother we make the front of the car the better the rear will work, yes? If one took a vertical flat plate and the rear was the template from max camber, would "that" be just as good as the full template? If the windshield is of no matter, why do the better aero cars all have laid back windshields? Prius...

Frank Lee 11-01-2011 12:09 AM

Rumpler.

Quote:

Less of a sharp edge the air has to break over.
The angle of the hood/windshield has no influence over the angle of the windshield/roof. The ws/roof junction is the important one, and angle has less to do with it than how generous the radius at the junction is.

If the flow is decent as far back as the A-pillars/windshield header it doesn't matter what's going on ahead of them.

CFECO 11-01-2011 08:50 AM

Rumpler, .28 so? It follows your template in plan view, if it was template in side view, it would be really something.

"If the flow is decent as far back as the A-pillars/windshield header it doesn't matter what's going on ahead of them."

Prove it. Vertical flat plate with template rear = full template, I don't think so.

Patrick 11-01-2011 11:14 AM

Here's what Hucho (1987, pp. 133, 135, 136) has to say about windshield angle:

As the windshield becomes flatter, the aerodynamic drag decreases. ... From all these data it can be concluded that the direct influence of windshield inclination on drag is only moderate. The effect is assumed to be more pronounced the more the flow is routed over the windshield.

Windshield inclination angles of more than 60 degrees are not practical because of light diffusion. In addition, large, highly inclined windshields lead to increased solar heating of the passenger compartment.

Two effects are responsible for the favourable, though moderate, influence of a highly inclined windshield on drag. First, the excessive speed in the area of the A-pillar is reduced so that the momentum loss occurring at that point is smaller. Second, the deflection of the flow at the transition from the windshield to the roof is weaker. The low pressure peak occurring there is therefore smaller and the positive pressure gradient in the remaining flow is less steep. Hence the momentum loss in the boundary layer is lower, allowing greater pressure recovery in the area of the rear end. . . . Therefore, even if a strongly inclined windshield does not contribute to a local drag reduction, it helps to improve the flow over the rear part of the car and thus to reduce the overall drag.

muffildy 11-01-2011 01:30 PM

buick riviera
 
found the buick riviera has a really nice looking rear glass
problem is i cant seem to find any information on the dimensions of it so i dont know if it will even fit.
also, cant find anyplace that sells it in particular except ebay.

botsapper 11-01-2011 01:53 PM

Recommend cleaning up the trailing flow...and it'll look way cooler!

http://pic90.picturetrail.com/VOL237.../387846677.jpg

http://www.paul-davis.com/vehicles/miata/fasback.jpg

http://lh5.ggpht.com/_e9GW4M7g5Rk/Sv...miatalhMOD.JPG

http://www.autokonexion.com/images/f...epic%20589.jpg

euromodder 11-01-2011 01:55 PM

Quote:

Originally Posted by Frank Lee (Post 268233)
The angle of the hood/windshield has no influence over the angle of the windshield/roof.

If the hood/windshield angle is altered by angling the windshield, then it definitely does.

Quote:

The ws/roof junction is the important one, and angle has less to do with it than how generous the radius at the junction is.
A shallow transition angle makes it far easier to generously radius the junction.

botsapper 11-01-2011 02:02 PM

Instead of an angle change, modders easily chops the glass and lowers overall frontal area.
Even at SEMA 2011, they chopped the windshield for a Spyder concept.
http://www.autoevolution.com/images/...y-medium_4.jpg

euromodder 11-01-2011 02:02 PM

Quote:

Originally Posted by kach22i (Post 268174)
How about an equally angled hood leading to the windshield?

A way to get closer to the streamlining-template's bulbous nose shape.
The Previa ruins it through sheer size and its rear though.

On the Prius and Insight, Mercedes A and B, ... the angle between hood and windshield is also minimal.

California98Civic 11-01-2011 02:25 PM

Quote:

Originally Posted by euromodder (Post 268296)
If the hood/windshield angle is altered by angling the windshield, then it definitely does.


A shallow transition angle makes it far easier to generously radius the junction.

This would explain the design changes to the hood, windshield, roof design across the Prius generations?

First:
http://www.vonemdeheim.com/picture_library/P1270034.jpg

Third (latest):
http://priuschat.com/forums/attachme..._prius-prv.jpg

james

aerohead 11-02-2011 05:07 PM

Rumpler
 
Quote:

Originally Posted by CFECO (Post 268262)
Rumpler, .28 so? It follows your template in plan view, if it was template in side view, it would be really something.

"If the flow is decent as far back as the A-pillars/windshield header it doesn't matter what's going on ahead of them."

Prove it. Vertical flat plate with template rear = full template, I don't think so.

I have a complete analysis of the Rumpler car.I'll try and remember to snag it.

aerohead 11-02-2011 05:09 PM

Riviera
 
Quote:

Originally Posted by muffildy (Post 268292)
found the buick riviera has a really nice looking rear glass
problem is i cant seem to find any information on the dimensions of it so i dont know if it will even fit.
also, cant find anyplace that sells it in particular except ebay.

That glass won't pass a state safety inspection.Whatever you choose,it must be laminated safety glass and it must be etched to say so.

aerohead 11-05-2011 01:49 PM

Rumpler Tropfen-Auto
 
Quote:

Originally Posted by CFECO (Post 268262)
Rumpler, .28 so? It follows your template in plan view, if it was template in side view, it would be really something.

"If the flow is decent as far back as the A-pillars/windshield header it doesn't matter what's going on ahead of them."

Prove it. Vertical flat plate with template rear = full template, I don't think so.

The Rumpler Tropfen-Auto was produced as an open touring car in 1921,with Cd 0.54,and an enclosed limousine in 1924,with Cd 0.28( as measured in VW's modern tunnel.
A plan-view of the car appears in Baron Fachsenfeld's book of 1951.
The body is relying on a 2-D type of flow with the air going primarily around the body rather than over.
The body itself is a 3.044:1 streamline section with 100% aft-body.
*At maximum body camber point the tangent angle is of course zero.
*At 10% aft-body length the tangent angle is 4.5-degrees.
*At 20% aft-body 8.5-degrees.
*At 30% aft-body 14-degrees.
*And from there on to the terminus the tail maintains a 14-degree angle.
--------------------------------------------------------------------------
The roof in plan-view is a 2.164:1 streamline section of 0.89-width forebody and 1.27-width aft-body.
I've not put a protractor to the roof although the rear curvature is quite aggressive and just looking at the image I would presume the flow is separating by the rear axle centerline.
Flow over the roof is very good.It has a familiar architecture.
--------------------------------------------------------------------------
I believe that a 3.92:1 section has the lowest Cd in 2-D flow.And little is published about 'cars' based on sections.They are more like inverted boat hulls or wingtips than sections.
--------------------------------------------------------------------------
At Cd 0.28 the car was remarkable for its day however when compared to Jaray's 'pumpkin seed' of 1921 @ Cd 0.13,we have a better path to follow.

California98Civic 11-05-2011 02:14 PM

Quote:

Originally Posted by aerohead (Post 269006)
The Rumpler Tropfen-Auto was produced as an open touring car in 1921,with Cd 0.54,and an enclosed limousine in 1924,with Cd 0.28( as measured in VW\'s modern tunnel.

Here the 1924 enclosed limousine, I believe:

http://static1.carsablanca.de/files/...jpg?1280329052

Not so good over the top, is it. But most air, as you said went around the side. Maybe that was much cleaner, given the shapes.

james


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