Reattaching wake and drag penalty

[micondie]

Originally Posted by dwtaylorpdx

On a lot of sedan race cars we add spacers under the hood hinges to let the high pressure area in front of the firewall loose. It often ads 4 or 5 mph down the straightaway. Anybody tried it for mileage?

Dave

How high do you space the hood? Is it high enough to direct some of the air flow upward so it gets a head start flowing over the roof or is it just high enough to bleed off some of the high pressure air into the engine compartment?

[botsapper]

This thread has piqued my interest because I have been playing around with an extending Kamm-rear spoiler idea. The critical downstream rear angles could always benefit to a long-tail configuration. The idea is very similar to reconfigurable/extending airplane wing flaps. The move-able wing extend & become flush/fixed to the fastback surface & additional wingtips deploy downwards to clean up some side flow. I've considered these add. tips to deploy outside the rear light assembly but would compromise the safety equipment. The wingtips always could be made w/ clear polycarbonate to passed safety reqs. Lower speeds & parking maneuvers needs retracting the wings. 'Active' wing flap angles become too complicated.
Also another idea, a model specific (Prius 2010) rear wheel covers extend to very clean flows sharply detaching at the bottom & rear edges...

[pstrbrc]

OK, this is something I'm working on for my Escort. And one of the limitations that I have is that TOWMBO will not tolerate any public display of eccentricity.
So, a belly pan is acceptable, but a boat tail is not. Wheel discs are borderline acceptable, rear wheel pants are clearly not. So, I might get away with vg's, but...
So, my back glass is ~30* from horizontal, and a line from the back of the roof line to deck height at 14* says I need a 8"+ shelf attached.
What does the collective mind know about the +/- of rear window dust deflectors? I know, those are usually only for "wagon" backs, but a deflector with an included arc of 25* would certainly be a place to start. Yes, this would cause lift at high speeds, but at econ speeds, what would be the down side? Would a smooth deflector blade cause more drag than 8 vg's across the back edge?

[aerohead]

Originally Posted by pstrbrc

OK, this is something I'm working on for my Escort. And one of the limitations that I have is that TOWMBO will not tolerate any public display of eccentricity.
So, a belly pan is acceptable, but a boat tail is not. Wheel discs are borderline acceptable, rear wheel pants are clearly not. So, I might get away with vg's, but...
So, my back glass is ~30* from horizontal, and a line from the back of the roof line to deck height at 14* says I need a 8"+ shelf attached.
What does the collective mind know about the +/- of rear window dust deflectors? I know, those are usually only for "wagon" backs, but a deflector with an included arc of 25* would certainly be a place to start. Yes, this would cause lift at high speeds, but at econ speeds, what would be the down side? Would a smooth deflector blade cause more drag than 8 vg's across the back edge?

What I've read about them is that the act of directing air towards the wake is good,but air separates off the back side of the deflector for a net drag increase overall.--------- simple flat plates extending straight back,which capture vortices along a quasi-Kamm profile have been demonstated to help,although you have the "length" issue.

[MetroMPG]

Cd: "damned pressure bubble"... thanks for the laugh.

[botsapper]

"Out damn bubble, out!" Seems to be common running joke 'round these parts...so has anyone done the obvious & 'attacked' it with something like this...

http://www.team-bhp.com/forum/attach...s-dsc02307.jpg

Looks like bug deflectors moved backyards but smoke tests & tuft testing would be interesting to see.

[chuckm]

Originally Posted by aerohead

What I've read about them is that the act of directing air towards the wake is good,but air separates off the back side of the deflector for a net drag increase overall.--------- simple flat plates extending straight back,which capture vortices along a quasi-Kamm profile have been demonstated to help,although you have the "length" issue.

I hope I'm not misunderstanding you... if I attached a short Kamm profile lip to the top of my rear windshield area, I might gain a little benefit?

[Cd]

Originally Posted by botsapper

"Out damn bubble, out!" Seems to be common running joke 'round these parts...so has anyone done the obvious & 'attacked' it with something like this...

http://www.team-bhp.com/forum/attach...s-dsc02307.jpg

Looks like bug deflectors moved backyards but smoke tests & tuft testing would be interesting to see.

Both Aerohead and Basjoos created air deflectors for their wipers. I'll let them eloborate on any gains. I tufted my car and noticed that the turbulent bubble on my car only extended a couple of inches past the arm of the wiper.




.

Also look here. This is a very good article on tufting the wiper area : http://autospeed.com/cms/title_Silen...5/article.html

[Cd]

Originally Posted by chuckm

I hope I'm not misunderstanding you... if I attached a short Kamm profile lip to the top of my rear windshield area, I might gain a little benefit?

I'll let Aerohead answer this one.
I added a small lip spoiler to the edge of the roofline on Franks' car due to the fact that his back glass has such a steep angle. His car is almost like a hatchback with a trunk.

( I hope I understand your question. )

[dwtaylorpdx]

Originally Posted by micondie

How high do you space the hood? Is it high enough to direct some of the air flow upward so it gets a head start flowing over the roof or is it just high enough to bleed off some of the high pressure air into the engine compartment?

Usually the rear edge of the hood is 1" higher. Much more and latches and such get hard to use. I also pull the gasket off the rear edge of the hood to really open up the gap.

Dave