Windshield should be more inclined than the hood?

[aerohead]

Originally Posted by Big time

By more inclined I mean that the windshield has lesser angle to the vertical than the hood.

Thus you have to either make the windshield more inclined and/or make the hood less inclined i.e. less horizontal?

Some of the research which has been published shows the drag reduction asymptotic around 60-degrees of inclination,with no further gains if any steeper.
Some Lamborghinis and Hondas have gone closer to 70-degrees,but you pick up internal reflections.
At very steep angles,you actually get refraction.
The air prefers a 'bulbous' front,although Hucho mentions that this requires very expensive curved (compound) glass.Used mainly in concept,record,or full-race cars.
It usually means 'fixed' side windows on the doors,as they can't roll up or down inside the door cavity.
Where I live it wouldn't matter.People dress for the opposite season year round,running heat or AC to compensate.
Selective coatings,as NASA uses on spacesuit face shields can help mitigate solar loads.Ford Motor Co. has already done this with Taurus/Sable if I remember correctly.
The nose of an AKULA or VICTOR Class USSR submarine will give you an idea of an 'ideal' nose/windshield architecture.

[drmiller100]

the angle of the windshield is relatively trivial in terms of effect on vehicle's overall drag.

if the angle is too steep (vertical), air stacks up on the bottom of the windshield until it forms a bubble, and air flows around it.

if the angle is too shallow (laid down horizontal) internal relflections are an issue for the driver in differing light conditions - you get nasty reflections off the dash.

frontal area is king. back of the car is form drag, which is queen. The rest of the car are merely pawn upon the winds of drag.

[Frank Lee]

Good summary Doug

[Tesla]

Originally Posted by drmiller100

the angle of the windshield is relatively trivial in terms of effect on vehicle's overall drag.

if the angle is too steep (vertical), air stacks up on the bottom of the windshield until it forms a bubble, and air flows around it.

if the angle is too shallow (laid down horizontal) internal relflections are an issue for the driver in differing light conditions - you get nasty reflections off the dash.

frontal area is king. back of the car is form drag, which is queen. The rest of the car are merely pawn upon the winds of drag.

So are you saying all the modifications outside frontal area and rear drag are not worth the effort?

[drmiller100]

Originally Posted by Tesla

So are you saying all the modifications outside frontal area and rear drag are not worth the effort?

something truly obnoxious, like wheel openings, are worth covering for some people.

I bet covering the wheels, perfectly, is worth less then 5 percent reduction in overall drag for most cars. This adds up to less then 2 percent mileage.

If you are getting 49 mpg, and your time is worth 10 cents an hour, and you REALLY WANT 50 mpg, then it might be worth it for you.

Learning to drive is MUCH more important then all the aero changes made to any existing vehicle.

and everything in front of the front doors of the vehicle, other then wheel openings, is not measurable.

[Sven7]

Simply, it's very hard to alter the frontal area aside from removing mirrors and lowering the car. What is left aero-wise? Improving flow around the vehicle. It comes down to the "low hanging fruit" we all talk about. It takes but an hour or two to add rear skirts, and a little longer to make a coroplast partial belly pan. If you like doing projects as much as I do, you'll probably jump at the opportunity to optimize the aerodynamics. For some people it's not worth it.

Aeromods augment your driving technique by letting you coast longer. Phil has posted studies that show full belly pans improving car aero by up to 15%. Yes, aero mods make a difference. To say they do jack squat would be ridiculous. You've got to put the time in, though.

[Tesla]

I've done a grille block and extended the angle a bit so it is not so vertical, I've also put an airdam on the front and done a partial belly pan at the front, This is to improve aerodynamics as well as improve airflow through the engine bay.
The results from the engine bay re temperatures have definately improved, the aerodynamics seem to have a placebo improvement, will wait to see FE numbers on the next couple of tanks.
Good to get some insight on the windscreen issue so I can focus my attentions on the bigger fish.

[aerohead]

Originally Posted by Tesla

So are you saying all the modifications outside frontal area and rear drag are not worth the effort?

If you'll take a look at Sticky#4,there is a drag reduction breakdown for mods tested over the years.

[hoopty_yo]

Originally Posted by crexcrex

Very good............shim your hood at the hinges increasing the incline till you are satisfied.................when your point re hood incline is proven drop me a line for a permanent fix...........you will be surprised

crexcrex

Just an FYI: if you decide to drive around after shimming the hinges, make sure the hooks near the hinges engage somewhat in the front body area. They are there to keep you from eating the hood in a frontal collision.

[aerohead]

I stumbled onto some tasty little numbers when re-visiting Walter Lays wind tunnel work of 1933.
Lay tested a 'pumpkin seed' model car,which for all intents and purposes IS the 1987 GM Sunraycer,with matching Cd 0.12.
By installing a completely vertical windscreen with square edged header and A-Pillars he doubled the drag to Cd 0.24! Hucho refers to this in his book(s) when mentioning that no amount of boat-tailing will reap benefits if the forebody isn't 'clean'.
What's remarkable about Lay's research,is that by tilting the windscreen back only to 50-degrees from vertical,all the turbulence was killed,and the car was as low-drag as if it had the 'ideal' compound windshield.
Of course,this is only at zero-yaw,and the 'ideal' windshield WOULD have an advantage in a crosswind,but it kinda drives home Hucho's point,that most contemporary automobiles have adequate forebodies,from which to streamline from.
I think we'd be hard pressed to find any modern vehicle,except maybe Hummer H-1 and some Land Rovers,which didn't meet Hucho's criteria for acceptable forebody.