Aerodynamic Streamlining Template: Part-C

[MN Driver]

I'm still a little lost though looking at this form that we are all talking about. Wouldn't it be more ideal to round the front so the wind goes around the object? It seems like such a flat fist shoving its way into the wind?

I suppose I've always thought the front end would look like the 1980 GM Epcot 2003. Back seats!?
http://www.gmphotostore.com/1980-GM-...tinfo/53217393


...or the Synraycer
http://www.gmphotostore.com/1988-GM-...tinfo/53217373

Possibly round the back off of this 1986 Corvette Indy Concept


I found these through the GM PhotoStore
Concept Vehicles-GM PhotoStore

Why would having a flat front be superior? I'd figure you'd be better off having the back and front be at least somewhat similar for airflow.

[aerohead]

Originally Posted by MN Driver

I'm still a little lost though looking at this form that we are all talking about. Wouldn't it be more ideal to round the front so the wind goes around the object? It seems like such a flat fist shoving its way into the wind?

I suppose I've always thought the front end would look like the 1980 GM Epcot 2003. Back seats!?
1980 GM Epcot 2003-GM PhotoStore


...or the Synraycer
1988 GM Sunraycer-GM PhotoStore

Possibly round the back off of this 1986 Corvette Indy Concept


I found these through the GM PhotoStore
Concept Vehicles-GM PhotoStore

Why would having a flat front be superior? I'd figure you'd be better off having the back and front be at least somewhat similar for airflow.

MN,if you were above the Template looking down,the front of the vehicle and its sides would have the same 'roundness' and curvature as the side elevation view of the Template,just like an NFL regulation football viewed from any 'side.' The windshield would have compound 3-dimensional curvature as on Sunraycer and the sides would taper to the rear just like the Hindenburg.
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In road vehicle aerodynamics it's easy to get good flow attachment with rather blunt noses.The challenge is to eliminate flow separation at the back,killing the wake,and the only way to do that is to extend the body back.
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The curvature and 'steepness' of the Template is right near the ragged edge for flow attachment.If you go any steeper,you end up with a Granville Bros'.Gee Bee R-1 racer which flat-spins because of its separated flow ahead of the tail/rudder,due to the 25-degree body taper.This 'steepness' kills pilots,and it kills fuel economy.
-------------------------------------------------------------------------- The GM/AeroVironment Sunraycer IS a "Template" vehicle.It projects to 89 % of the template length,with a little reflex camber to accommodate for solar insolation on the PV array.With wheel fairings Sunraycer has Cd 0.089 and 400 mpg equivalency with 10-Bhp I.C. engine.
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Your correct about a 'flat' front although the Template doesn't produce that.Typically in fluid dynamics,for lowest drag,the body structure disrupts the flow within the 1st 1/3rd of body length,then uses the remaining 2/3rds to permit the flow field to re-combine without turbulence,which is exactly the purpose of the Template.
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The PROBE-IV concept used an unusually long nose and short tail to achieve Cd 0.152,although to go lower it would require an extended tail.
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The PROBE-V with Cd 0.137as you will notice,has more tail.
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Fully 'boat-tailed' composite structures,as the NUNA-3 solar racer have Cds reaching below Cd 0.09.That's a long way from 0.152.

[t vago]

I saw some interesting sights during this last winter snowstorm a few days ago. People around here generally don't brush off more than the bare minimum of snow from their cars, and of course they like to drive on the interstate with all of this snow blowing off.

On quite a few of these cars, I happened to see snow aerodynamically shape itself to the roofs of these cars, such that the roof was effectively raised a few inches. That makes me think that for maximum gain, maybe the leading edge of this template ought to be matched to the windsheild of a given vehicle, and then aero extensions ought to be built to match the template (even if it raises the roof a bit).

Then again, that may drop C(d) at the expense of increased frontal area. Just a thought...

[MGB=MPG]

interesting ,, air foils
do not air foils have design speed ,
what is design speed on image 1
airfoils are wings . wings produce lift , at some speed and wind condition would they not fly off the road?

lot of a NACA 0015 foil, generated from formula




Plot of a NACA 2312 foil, generated from formula

[3-Wheeler]

Originally Posted by t vago

....On quite a few of these cars, I happened to see snow aerodynamically shape itself to the roofs of these cars, such that the roof was effectively raised a few inches. That makes me think that for maximum gain, maybe the leading edge of this template ought to be matched to the windsheild of a given vehicle, and then aero extensions ought to be built to match the template (even if it raises the roof a bit)....

You might be on to something here.

It makes sense that if the angle between the top edge of the windshield and the top of the car body is too abrupt, that the snow accumulated in this area because of the localized lower air pressure in that spot.

Jim.

[KamperBob]

Snow forms should be taken with a grain of salt so to speak. Pressure and flow cause erosion. In an open truck box, for example, reverse flow of the detached eddy bubble carves just as easily. With snow piled on a flat tonneau or flatbed trailer I've seen carving from turbulent wake as well. Just because snow is missing doesn't make it best for that region to be vacuous. However, in most (all?) places where snow remains "filled in" it seems a good bet that material wants to be there. Of course this is just my opinion. Maybe I'll learn something from someone who disagrees with better backed science.

[aerohead]

Originally Posted by t vago

I saw some interesting sights during this last winter snowstorm a few days ago. People around here generally don't brush off more than the bare minimum of snow from their cars, and of course they like to drive on the interstate with all of this snow blowing off.

On quite a few of these cars, I happened to see snow aerodynamically shape itself to the roofs of these cars, such that the roof was effectively raised a few inches. That makes me think that for maximum gain, maybe the leading edge of this template ought to be matched to the windsheild of a given vehicle, and then aero extensions ought to be built to match the template (even if it raises the roof a bit).

Then again, that may drop C(d) at the expense of increased frontal area. Just a thought...

t vago,I intentionally left the 'front' of the template simplified to honor pure fluid dynamic minimum drag for sub-transonic flow road vehicle aerodynamics.
Any modern vehicle has a 'good enough' front end for attached flow.
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The importance of the Template is its treatment of the vehicle aft-body.This is where the drag is.
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As an ecommodder though,the question is,are you going to totally re-design the front of your car,or clean up the back.
Front mods may do little for performance,as I proved to myself at Bonneville.
Rear mods however will make tremendous difference to performance,and I also proved that to myself at Bonneville,and the open road.

[aerohead]

Originally Posted by MGB=MPG

interesting ,, air foils
do not air foils have design speed ,
what is design speed on image 1
airfoils are wings . wings produce lift , at some speed and wind condition would they not fly off the road?

lot of a NACA 0015 foil, generated from formula




Plot of a NACA 2312 foil, generated from formula

MGB,at some given airspeed,anything will be airborne.
The Template is designed for zero separation and continuous static pressure regain the further you go back down the tail.
Remember,a spoiler is designed to re-attach separated flow onto the car body to spoil lift.The Template produces no separation,no lift.
It's funny that you show the 1957 MG EX-181 LSR streamliner.This car IS one of the 'Template-cars',which goes out to 80% of the original Template.It does embody reflex-camber and over-shoots the template,however,at Cd 0.12,you see the value of the aft-body streamlining.
-------------------------------------------------------------------------- Since the late 1970s lift is not really a stability issue for 'everyday' road velocities.Dr.Alberto Morelli's work at Pininfarina figured to how to design for zero-lift.It's not a problem for those looking at mpg savings.

[aerohead]

Originally Posted by t vago

I saw some interesting sights during this last winter snowstorm a few days ago. People around here generally don't brush off more than the bare minimum of snow from their cars, and of course they like to drive on the interstate with all of this snow blowing off.

On quite a few of these cars, I happened to see snow aerodynamically shape itself to the roofs of these cars, such that the roof was effectively raised a few inches. That makes me think that for maximum gain, maybe the leading edge of this template ought to be matched to the windsheild of a given vehicle, and then aero extensions ought to be built to match the template (even if it raises the roof a bit).

Then again, that may drop C(d) at the expense of increased frontal area. Just a thought...

Here's something to consider.
*The lowest Cd for a streamline body of revolution in free-air is 0.04.
* The Template,in free-air,has Cd 0.04.
* When the Template is 'split' in ground-reflection it is Cd 0.07
* When the 'ground-clearance' is cut away from the 'half-body' the Cd is 0.08.
* When skinny wheels are added to it the Cd jumps to 0.12.
* When wheel fairings are arranged around the wheels/tires,the Cd drops to 0.089.
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All this is based on exhaustive wind tunnel research,at a cost of billions of dollars now.
It may not serve us to follow what the snow does,All this has been tested already ( yes aerodynamacists are that crazy!) to no avail.
It's taken me over 35 years to come up with a tool as simple as the Template,at a personal cost of tens of thousands of dollars.
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Smart money is on good science.

[some_other_dave]

Originally Posted by aerohead

MGB,at some given airspeed,anything will be airborne.

Ah, yes--the "F-104 Aerodynamic Theory", now known as the "Space Shuttle Aerodynamic Theory". Simply stated as, "Throw anything hard enough, and it will fly."

-soD