Front bumper shape
 

Time has come to redo my front bumper. Which is better for aerodynamics, a wedge shape or a rounded over shape?

I'm glad I noticed the "NEXT" button in that link, some interesting stuff.

Sort of on-topic adjacent, check out this rounded sail boat bow.

Radical new mini - Boat Design Forums

EDIT: I like these book scans, nice info.
http://ecomodder.com/forum/member-ae...strations.html

How can I navigate to this section of the site? Obviously, from the link notation, it is some ref material that Phil put onto the site, but I don't see a way to navigate to the material.

Do you mean the links don't work for you or what? :confused:

Go here to start.
Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - aerohead's Albums

http://ecomodder.com/forum/member-ae...enetration.jpg

http://ecomodder.com/forum/member-ae...oncept-car.jpg

http://farm6.static.flickr.com/5121/...17eda205_z.jpg

Looks like it's a balancing act between drag reduction (top) and downforce (bottom). With a street car downforce shouldn't be a problem.

If you want inspiration for a front end, look at modern current model cars. They seem to be an air dam type thing low, below midheight. The air dam tends to remain flatter out to the sides so it "pushes" the air out away from the messiness that is the front wheels. Above midpoint, it is all rounded radius to start the air on its trip over the top.

Like This.

http://i40.tinypic.com/vnpkz5.jpg

or This

http://i39.tinypic.com/k2mrkx.jpg

I wonder what the CD penalty is for the hood ornament???

That is a lot of help. Thanks. I have been looking at cars coming out now though, and what is with the flat front look. It just appears that having a tall flat bumper would actually cause a negative effect. Does anyone have data on how this effects aerodynamics?

The alternative is a sloping bumper and front end, which doesn't look as good. Bulldog noses are in fashion.

A bullet shape funnels air under the car which creates front end lift.

Front end lift is something I have been trying to avoid. I do the bulk of my driving at 60 plus and don't want to have issues sticking to the road. I am trying to bat around a lot of ideas, and reviewing stuff that people have already done to find out what works best. I don't like to do, then redo, then do again.

This is what I did and it paid off with almost 15% increase in FE.

http://ecomodder.com/forum/showthrea...job-17534.html

Hmmmm.

http://www.motivationalz.com/picture...ical_hippo.jpg

One of your relatives, CD? LOL:D

I'm just sayin' if you could indeed get that kind of a mileage increase with a simple rounding of a front end that already has attached flow, I'll gladly be the first to copy your efforts. :thumbup:

Here is an example of the attached flow on the bumper of my car during a tuft test. http://farm3.static.flickr.com/2321/...d68dd217_o.jpg

I'd like to see a picture of a front end without attached flow... Following your logic, you could take off the bumper and the whole front fascia, flow will still be attached, and drag won't change.

The problem with the silver bullet nose is that it directs so much air down below the car.

Under ? Don't you mean over ? ;)

Here is a site that has lots of useful information ( be sure to click the links to the other pages ! ) regarding blunt, versus wedge, versus bullet shaped noses.
Lots of good info such as lift and drag coefficients etc.

They even tried testing windshield shapes as well.

Winged Warriors/National B-Body Owners Association - Chrysler Winged Car Development and Testing

Thanks for the input. I am thinking about putting the front end on hold until I get the hubcaps and wheel skirts finished. I am doing the mirror relocation today, so I will see how I like that. I am not trying to go extreme, but 50+ to the gallon would help my finances out a lot.

No, I mean under. It's the opposite of an air dam. :confused:

Current cars also have a requirement for pedestrian friendly hoods for impact, which has been raising the hoodline at the front.

Car Design Online | Pedestrian Safety

He means that when the Point of Stagnation is halfway from the top and bottom, half of the air will go up and half will go under. The pressure of the air going under will want to push the car up into the air, creating lift (while a more or less equal force on the top pushes the car down). Lowering the PoS will let more air over the top than under the bottom, skewing the air pressure to create more downforce than lift.

:thumbup:

BTW, how does one go about making a strong stable, durable bullet nose? Perhaps I'll have to study the Aero Civic thread. :turtle:

I do know the answer to that. Styrofoam and fiberglass mat. Some people don't like to work with it, but it is relatively easy and very durable. You could also use a base layer of household screen and then fiberglass over it. It makes the fiberglass more durable.

I assumed that by " bullet nose " we were talking a half bullet nose, such as a Corvette, a Firebird, a Saturn SC coupe, or the car on page one.

http://ecomodder.com/forum/member-ae...oncept-car.jpg

Cars with bullet noses such as the Avion will of course have more of the air flowing under the car.

http://images.gizmag.com/hero/avion-1.jpg

http://i146.photobucket.com/albums/r...0212009001.jpg

There's a bit missing off the front of the Coupe, and yet this is the one (of 5 Tempos) that gets the best fe. I conclude the flow hasn't been compromised all that much, if at all.

George I just saw the thing about the yachts-really interesting!

And for whatever reason this quote seemed important:
:)

No worries!

http://bringatrailer.com/wp-content/...le_Front_1.jpg

You mean the sealed beam lights and those gaping holes don't make that much of a difference? :eek: (Is that your 27mpg Tempo?)

Are you being sarcastic Frank ?

No sarcasm, and that is the 35mpg Tempo (gaslog not on EM).

Maybe the radiator block is so good it more than cancels out the bad headlight areas/fender scoops?

all that much
 

It looks like the only issue would be the tiny leading edge on the fender sides where the turn signals were removed.The fenders have nice penetration curvature rear of that area,so those areas would still be in 'attack',with immediate re-attachment and little drag.
Hood edge and bumper radii look plenty smooth.
Makes sense to me Frank!

It is all good but the open areas around the headlights are not closed off; they lead to the inner fenders and after a labyrinth path, the engine compartment. Perhaps what I have is about the same flow through the engine compartment even with that nice big radiator block; or maybe the flow through all that nonsense is stifled such that there isn't really much flow entering those areas in the first place. At any rate, fe and probably top speed (not accurately tested) seem to not be negatively affected.

It would certainly be interesting to see a tuft test along the sides of those fenders Frank.
Thanks for posting the example.
I can certainly see what Aerohead was referring to about immediate reattachment along the sides.
As far as the little tabs that hold the side signal lights on, they might even function the same way that the creased sides do on the front end of the Prius.

Its hard to tell without tufting it though.

( I hope you do get around to fixing that front end ! Good luck passing inspection without the turn signal lights )

Here is my 'dead horse' that I keep bringing up from time to time.
This is proof that you can have a blunt 'barn door' front end and still have good aero.

This old '80 Camaro got down to a wind tunnel tested .201 Cd - or just over what the EV-1 achieved.

Chevy Camaro Aerodynamics Side View Photo 7

http://image.hotrod.com/f/10214169/1...+side_view.jpg

Also look at the attached flow with the 'barn door' flat front end on this '32 Coupe :

http://www.youtube.com/watch?v=z7Trx...eature=related

Notice the flow along the roofline as the smoke stream hits the vertical windshield.

http://www.youtube.com/watch?v=mqi6w...eature=related

Here is another '32 coupe - this one quite draggy by the looks of the smokestream.

Still, this video gives a good idea of how that a simple rounded edge can keep attached flow - for example along the roofline.

http://www.youtube.com/watch?v=8PoIo...eature=related

.201 even with that massive scoop??

It would be fun to tuft test vs one of my "complete" cars.

There are no inspections. There are turn signal lights.

" We did lots of hoodscoop testing with Harwood's scoop part numbers (left to right) 3161, 3164, and 3182 borrowed from Barnett Performance. We also tried our old 6-inch cowl hood and a bone-stock flat hood we borrowed from Camaro Specialty and taped all the scoops in place on that hood. All the scoops were swoopiest when extended back to the windshield. Believe it or not, the cowl and the PN 3182 aero scoop had the very same Cd as the flat hood, and the other two scoops were just 10 counts worse. Better yet, the ram-air of the aero scoop was estimated to give us 24 hp at 250 mph. "

Read more: Chevy Camaro Aerodynamics Hoodscoop Photo 5

Frank, your Tempo pic reminds me of the truck grille I have not finished yet.
I get to make a scratch bumper for the truck, and I've been watching this thread. Thanks for all the good info. It looks like I need to build something resembling Jay Leno's chin, yet tasteful. Seems like a tall order to me :D

While this is for the nose of a streamliner; it is still quite interesting.

http://www.aussieinvader.com/wp-cont..._design_dm.pdf

Phil has said this before and I'll repeat it for the sake of discussion. Attached flow is not the goal! The pressure at the front of a car is great enough to attach flow almost no matter the shape. In fact, if you show me a car without attached flow on the front panel I'll send you a nice drawing of your car. :thumbup:

Anyway. Reducing drag is the goal. Air will most likely prefer a nice, rounded front to a block front. And keep in mind that when you compare it to the EV1, you compare it to a stock car without the giant air dam or gap taping.

That's not to say a car with a flat front can't yield good numbers- the Camaro disproves that- but a smooth transition is preferable.

Carry on! :)

People continue to fixate on the front when the top of the windshield on back is where it's at.

Very interesting.

Looks like you have a choice of safe and slow, or fast and air-born.