New bug, .38 CD why?

[bnmorgan]

i'm with you on the HHO/Brown's Gas. The lips may do nothing for the cars, but they helped my bike. I was just wondering if something similar as a break point at the top of the rear hatch window would do anything beneficial. Was looking at the VG stuff on autospeed, wondering about that sort of thing too.

I could see lift as a problem if i was trying to stay at 120mph average, but i don't even get up to 80, ever. no need for it. 75 on the 4 lane, 60 on the 2 lane. the whole idea of drag reduction may be moot with return on investment, which is what i'm trying to figure. I still aint sure if i'm better to break the flow clean or try to glue it down further. If that beetle flow illustration on the first page of the thread is right, it's a mushy break point, so either should be better, at least if i understand.

anyone have any data or online reading material on that kinda thing? something detailed but not rocket science would be nice.

[ChazInMT]

Morgan, You DO NOT want to keep airflow attached. VG’s are used to try and keep flow attached when a rear shape tries to change too quickly for it to remain attached but not quickly enough for it to be a clean break. VG's would be useless here, the slope of the Bugs back is such that flow is remaining attached way too long already.

Understand that when I say you are generating too much lift, it is not all in the straight up direction, a very good portion of the lift is in the backwards direction, which is a huge drag load on your car. This is why you want it to separate at the top of the windshield. If you fear that you are creating a huge area of dead air that is starting at the top of your windshield, you should not worry about it, because this “Dead Air” drag will be there no matter what you do to your car....I hope that makes sense.

Below is a basic illustration of what I’m trying to say. By keeping the air from moving down the rear window, you eliminate the large lift, (Black Arrow) and it’s associated Drag Vector (Red Arrow).



The "Dead Air" drag is about the same as "Aerodynamically Shaped Perfect" drag. As soon as the air on your bug starts going down past the top of the rear window, it is costing you. So VG’s would do no good since the flow is already attached.

Go with a roof spoiler as I suggested earlier, it will yield the best results.

The dead air that forms will be less drag than the lift.

[bnmorgan]

*cue the Aha moment* that makes sense now. our problem isn't "ballistic drag" which i understand. We've got a stalling wing! we're creating more lift than the "wingspeed" is capable of......right??

That's the answer i was hunting I think. We want it detached because there's nothing useful left for it to do for us, IE no spoilers or other flow-dependant airfoils or benefits to be had. we want it to be come the stable chunk of air following us, energized once and carried by momentum (like the car it's self) only adding enough energy to maintain momentm. otherwise we are constantly swaping out large amounts of air mass and having to re-energize it not only to push it out of the way, but to add it to our "sled" and get it accelerated back up to our speed as well.

Much obliged!

[Frank Lee]

;p

[ChazInMT]

OK Frank, yer gonna have to help me out here. I can be pretty sarcastic myself, so what are you really trying to say here? Do you think Boat Tailers are really wrong? Are you agreeing with my assessment of this or do you think I'm way off base here?

If you think I'm wrong please explain why? It's sure easy to just sit back and say "I think that's Bull Crap!" without giving a well thought out reason for it, let's not be that guy.

[Frank Lee]

;p

[bnmorgan]

great way to kill a topic. How do you manage to have such a sun-shiny attitude all the time? is it chemically enhanced somehow? at least he last paragraph is somewhat constructive. Otherwise, you're abrasive as steel wool underwear.

[Frank Lee]

Aerohead, where are you???

[bnmorgan]

you prove my point for me. All i ask for is information, the attitude is useless, and makes me, at least, if not others, doubt the validity of what ever actual information you may have. Quantity does not equal quality. Whatever problems you have are not my fault, or likely that of anyone else here, so keep it to yourself and stop taking it out on the rest of the world.

Back to the matter at hand, since you do appear to have knowledge, would you make some useful suggestions of what i CAN do in the airflow department to help the bug get better mileage? you have given lots of negative feedback on what won't work, and how wrong everything is, so tell us what is right.

[Frank Lee]

Oh no, I wouldn't want to further burden you.