Aerodynamics Intuition Proven Wrong Again
 

To paraphrase Brad Richards, Exterior Design Manager for the new Ford F-150 in this USA Today video on the new aerodynamic Ford F-150, at the 40 second mark, that they angled it much more thinking it was going to get better aerodynamics, but it did not. Instead, they gave it a harder edge which worked better.

This proves once again prove that I know less than I thought I did about aerodynamics. His discovery makes me think that those flat air dams on the front of semi tractors might not be as bad as they look.

In everyone's wanderings around and musings on aerodynamics, are there any good aerodynamics cheat sheets? Yes, I know people get Ph.D.s and spend decades of their lives studying these phenomenon, so I am possibly asking for the impossible. After all, aerodynamics, is a subfield of fluid dynamics which in turn is a subfield of fluid mechanics. That is lots of material to cover. But I have had a lot of college and graduate science and I have found short intense summaries can sometimes be a quicker way to occasional insight.

Yes, I could pick up an aerodynamics text book. Its just, just that....they are so heavy.

My brother told me this about the F150 a few weeks ago, I ment to look up what he was talking about so thanks for the link.

I wondered at the scooplike ridges at the side of the bumpers of many modern cars. As if they were designed to create drag.
I believe they do, and that it is a good thing.
Because if the sides were smooth the air would flow swiftly over it at an angle.
It would not be able to make a smooth transition to the side and become turbulent.

Now those scoops and ridges effectively slow the air down (relative to the car!), so they create a high(er) pressure. This affects the general air flow to move over rather than along the sides of the car.
Apparently, that works out better. The line over the roof approaches the template on many cars. The sides are more or less straight and have ridges, wheels, mirrors, etc.

Another example can be seen in the prototype of the new Honda Fit.
http://media.autoweek.nl/m/m1oycupbpxhc.jpg
Notice the A pillars. They protrude ahead of the windscreen, and their base continues over the hood. Why? To force air over rather than along the car.
It has the bumper scoops on the sides too, as almost all new cars do.

" In everyone's wanderings around and musings on aerodynamics, are there any good aerodynamics cheat sheets?"

Just look up the posts here on this site by Aerohead ( " Aerohead aerodynamic seminars " )
http://ecomodder.com/forum/showthrea...ists-7118.html

As far as the shape of the front of the truck. I took it to mean that the blunt shape was as efficient as the sloped front end - not better than.

As far as the 'scoops' on the sides of the bumpers on cars, some do indeed act as 'air curtains'. In fact, it was even mentioned in the video of the truck about the 'air curtain' effect on the truck (at 2:10 in the video ). What i found interesting though is that they seem to be using the gap in between the bumper and the front end to channel the air around the wheels, versus sealing this gap.

Here is another link I just found :http://www.ford-trucks.com/articles/...015-ford-f150/

http://www.ford-trucks.com/wp-conten...50_Aero640.jpg
http://www.ford-trucks.com/wp-conten..._Aero2-640.jpg

BTW : If you lay a line along the sides of that image of the top of the truck, you will see that there is quite a bit of taper to the rear of the truck. I'm more interested in what is happening back there versus the front of the truck.

In the written article it says he said better then not as good as.

You're right.
I was wrong. Thanks for the correction.

So what is the cD of the truck ?

True, just like Mercedes does on the CLA.

Both the Merc and the F150 have a relatively straight front bumper, so I think this is mainly done to shape the overall flow pattern, it may be less effective when the bumper sides are slanted. Not saying uneffective!

The Merc and the F150 have bigger air dams than other cars, another thing that makes the passage through the bumper more effective.
Without an airdam the air trapped under the car will squeeze out through the front wheel wells.
That's why there is so much more brake dust on your front alloys than on the back ones: the air gets forced out of the front wheels and sucked in through the rear ones.
The fronts are not twice as dirty as you'd expect from a front biased brake balance, but ten times so.
The airdam blocks that flow, making the bumper vents more effective. I bet the help cool the brakes too.

I wish they would just say the cd as well. I think why the more squared "shoulders might help is they steer the air off that outside frontal area off the side and under the mirror rather then over the top.

I'd assert just the opposite. The protrusion dies out with the curve of the bottom of the windshield. The creases in the hood are in a pronounced V-shape. It's like a 'bug deflector' that cause the air close to the hood to divert to the sides. Maybe to energize the air around the rear-view mirror?

They need to come together somewhat, the pressure over the slanted hood makes the air flow go sideways anyway,even more than those lines indicate.
If they went straight over the hood they would have a large angle compared to the direction of air flow, that would cause extra friction and turbulence.
Like an aircraft wing, the optimal angle of attack is not the maximal one.
This angle just nudges the air upwards without blocking it too much.

When I first saw cars with protruding A pillars I thought they had misplaced the windscreen. It went completely against my intuition.
As more and more models employ this trick I had to accept here must be a reason for it, and I believe it to be what I've explained in this thread.

I'm probably biased because I had a 1958 VW Beetle convertible. The frame stood proud of the flat glass. The wiper couldn't move snow out of it's normal range, let alone clear the whole thing.

I'm sure most of you know about the effect dimples have on golf balls.Check this out Morphable surfaces could cut air resistance | MIT News Office

I was reading about something similar just the other day:

Elastomeric camouflage switches texture and colour

That guy should be fired for those headlights. Now I can't get a new F150.

wrong
 

Bear in mind,that in the forebody,the boundary layer is in the most favorable pressure gradient,and is essentially held against the body as long as it is 'attacking' the flow field.
And as Ford aerodynamicists essentially said decades ago,"there is no magic radius",just enough softening and you've got full attachment.
This isn't so for the aft-body which is the major source of drag with road vehicles.Back there you've got to be especially careful with your contours or the whole thing goes to the worms.Control of aft-body separation is the premise for aerodynamic streamlining.

Once upon a time the car body was designed first (for aesthetic reasons) and then they began thinking how they could fit the passengers, engine, suspension, etc. inside it.

Now they (a lame committee) decide the layout and then think on how they can fit a not-so-ugly somewhat aerodynamic body over it. Yes most modern cars are ugly and boring IMO.

They should do it backwards again. First design an eye-catching aero body and let Marquis de Sade design the ergonomics!

When? Certainly not before Harley Earle. The stylist was always handed a set of parameters. Cowl height, for instance is set early on.

http://ecomodder.com/forum/member-fr...24-628x392.jpg

Some committees as less lame than others. :)

http://ecomodder.com/forum/member-fr...21-956x597.jpg

This committee took an extremely aerodynamic body and stuffed a Ducati V-twin in it.

Aerohead, your answer combined with your aero lessons have already improved my understanding significantly. Thank you.