So yesterday I was stuck in traffic and saw a late 90s model Hilux with one of those upside-down trailing edge spoiler thingies. For anyone who doesn't know they're meant to scoop air into the low pressure area over a vehicles rear glass, or at the very back of the vehicle, and decrease the drag the vehicle produces by killing this low pressure area. Here you can see one on this Lancia Stratos:
Although nowhere near the extreme angle of the one I saw on the back of the Hilux...
The downsides are that the device itself creates some drag (although a lot less than it gets rid of) and it creates lift (which in the case of liftbacks like the Stratos, is also less than it gets rid of). I got to thinking, what if a "back end scoop" and spoiler device could be combined? It would create even more drag than usual but if it could kill it's own lift, that would make the wing purely a drag-reducing device (on the back of big blocky vehicles).
Such a device would work well on the back of my Sammy, which has the aerodynamics of a washing machine, and it hits high speeds regularly, whether I'm flying down the highway or flying down a trail (yeah we do some ridiculous speed on trails in competition....).
Think I should give it a shot? It could always use a higher top speed and better efficiency. I figure the wing will cost about $150 overall. If it makes a noticeable reduction in fuel consumption I'll call it worthwhile.
Yeah, you see those things on the STI and EVO now. Or you did at least. I don't remember what they look like now.
Go for it. Remember: lift is produced two ways. Relative lift comes from the angle of attack of the wing. This is why those tiny wooden planes can fly, even without airfoils. It's also produced by the pressure difference between the top side and the bottom side of the wing (the airfoil). So, if you mount an airfoil upside-down, you may counteract some of the lift while maximizing the effect you're after and minimizing drag.
I guess I always just thought those were to keep the dust from collecting on the back window of a station wagon or suv...
They're certainly effective at that.
Clem
I think the two go hand-in-hand. What's a great way to keep the dust off the back window? Keep airflow smoothly attached to the surface, rather than swirling around in turbulence somewhere behind the back window.
For highway efficiency, I think you are on the right track with thinking about small details. You could also consider smaller sideview mirrors, removing antenna, closing up gaps above or below with additional panels, and working on underhood airflow with ducting around the radiator/drop vent hood, etc.
YaNi
New Reader
10/2/08 9:58 a.m.
Check out Autospeed. It's an Australian internet magazine and the guy is very grassroots. He is interested in aerodynamics and has a ton of interesting articles and gadgets.
