How would you do front wheel skirts ?

[edenstrang]

Originally Posted by skewbe

I'd drive that aptera, are they working on a kit?

It's going to be a production car, but registered as a motorcycle, I think. They're taking deposits right now..

Originally Posted by Mighty Mira

I've got to teach myself how to fibreglass. Good luck with it!

Remember to account for potholes with your design, leave more clearance than you want. It could get really ugly to have your cowl sandwiched between the wheel and the road, in busy traffic.

Fiberglass is ugly... itchy, smelly, sticky, it' papier mache's evil twin. It's anything but difficult, though, just helps to have familiarity.

You're right about the clearance, especially if I intend to lower the car! I think if I make the shroud (and it's mount) sturdy enough I can keep it really tight on the tire--accounting for diameter change at speed. I'll probably use a version of the brush idea between the shroud and tire, to keep rocks from doing Pachinko inside.

It would really suck to get a flat tire and have the weight of the car distorting my carefully made shroud...

[Mighty Mira]

In that case, I wonder If just a partial front skirt wouldn't do the same thing. The idea behind this is to flare the front just enough to catch most of the air flung forward to diver it down and back, with nothing at the rear.

[Mighty Mira]

My original idea was just to make two sheet aluminium pieces (or one big one), possibly with something to brace them out a bit underneath, maybe not. The idea was to give the maximum length of rubber so that an outwards stretch does not encounter much resistance and hence lowers wear.

[Dynamically Aero]

Originally Posted by Mighty Mira

I've been searching for that brush strip material in vain. Has anyone else had better luck?

You might get some ideas if you research the Formula 1 cars of the late 1970s when sliding skirts were legal. A good one to start with would be the Lotus 79 which Mario Andretti drove to the 1978 World Championship. Be sure to click on the "ground effect" link.

[edenstrang]

Originally Posted by Mighty Mira

In that case, I wonder If just a partial front skirt wouldn't do the same thing. The idea behind this is to flare the front just enough to catch most of the air flung forward to diver it down and back, with nothing at the rear.

I'm thinking if I shroud it all, it'll take care of turbulent air entering the wheel well from under the sides as well, and just provide that much less disturbed air underneath. Also, if I "bubble out" the wheel shrouds, I can have them flush to a partial rubber skirt around the wheel well. I'll have to draw that for clarity..

[Mighty Mira]

Well, I spent four hours and managed to do something similar to CO ZX2's skirts. All the contact area is rubber, and underneath are two aluminum fairings to give enough clearance for the wheels at highway speeds while not adding much pressure drag. They appear to be rubbing very little.

We'll see how my next tank goes. Haven't yet tested it with both of them on.

[edenstrang]

That's cool! Your grill looks good, too.

When I saw cozx2's skirts, I was trying to think of the best surface to contact the wheel when it turns, and I thought of this slick synthetic bristle stuff you sometimes see on the backside of conveyor belt rubber, so it can slide over metal.

Does the tire grab the rubber much? I'm really curious.

If it's an issue, maybe it could help to put aluminum tape (or something better) around the outer wall of the tire, right down to the contact patch, so that when the spinning wheel pushes out against the rubber it's not rubbing the shroud raw.

[Mighty Mira]

Originally Posted by edenstrang

That's cool! Your grill looks good, too.

Thanks very much! I thought that seeing as I was covering the grille area, I might as well smooth the contours a bit.

When I saw cozx2's skirts, I was trying to think of the best surface to contact the wheel when it turns, and I thought of this slick synthetic bristle stuff you sometimes see on the backside of conveyor belt rubber, so it can slide over metal.

That would work, if it could stretch, otherwise you'd have to have two segments of bristly stuff. The idea with this is that the rubber is so long that it doesn't need to stretch much. If I could use a more stretchy material, I would. I thought it would be easier and cheaper (over the short run) than to go with the more complex but complete Basjoos type solution. As to put something more abrasion resistant there, I thought I'd try and minimize the abrasion first (maximize the length of rubber) and see how long it holds up. It was only $30, and I used only half of it.

Does the tire grab the rubber much? I'm really curious.

No, it doesn't (as far as I can tell). Not anywhere near what I was expecting. I should probably have someone look at it. The thing is, at extreme angles the speed is always relatively slow, that's got to help.

If it's an issue, maybe it could help to put aluminum tape (or something better) around the outer wall of the tire, right down to the contact patch, so that when the spinning wheel pushes out against the rubber it's not rubbing the shroud raw.

I'd worry about the tape getting cut and developing a more abrasive edge than the tire.

What I'd really like to figure out is a way to cover the leading edge of the rubber skirt without looking overly tacky. At the moment, the bits in between the screws can catch a bit of air. Got any ideas? I'm not sure if I've even seen aluminium tape, maybe that would work. I was thinking of something to either match the paintwork or the rubber.

[Mighty Mira]

A few updates: Coast down testing yields something in the area of 0.22-0.25 area. I really need to get elevation data to do proper testing. I just checked bom and at the moment there is a 13kph headwind in the area I did the testing(gotten by averaging two sites in that vicinity), virtually a straight headwind. Note I only did it in one direction, starting at sections of the road that were roughly flat I thought.

If I take that into account (by increasing my speed in my simulation to account for the increased headwind), I get a drag coefficient of 0.17 to 0.19. It's possible that the wind has picked up since then, but it was only an hour ago since I got home.

Suffice to say, I think front skirts are a definite improvement. The lower road noise is noticeable, and coasting seems more effortless than it was. Probably the acid test will be when I do some terminal velocity glides down some hills on my commute - typically I see 80-85kph going down them.

Someone yelled out "What's the go with the car, mate!?" at a set of traffic lights. I said (before doing the testing) "The drag coefficient is about 0.22". He probably didn't know what I meant. I guess I should have said "fuel economy!". Oh well.

I still have had no issues with rubbing.

And I think my solution to the front of the rubber/car join will be industrial strength UV proof clear tape.

[Mighty Mira]

Originally Posted by theclencher

better than a UFE-II? yes but mostly no

What do you mean by that?

The UFE-II is smooth, but it's not a miracle. There are several glaring concessions to fashion.

The grille area is approximately 5 or 6 times as large as mine. That's 5 or 6 times as much air that has no choice but to create more turbulence, and hence heat, and hence, wasted energy that game from the car's kinetic energy. Small in area, large in Cd.

The front wheels are not only unfaired, they are also egg beater style. Not only that, they are relatively large. This creates drag, a lot.

You also have the rear of the vehicle that is no less than 2/3 of the car's total frontal area. This is comparable to the back of my vehicle.

My car is not going to win any auto salon prizes any time soon though.

Do note that I will be retesting my frontal area, and most probably, the coast down. But as far as I can tell, there is a noticeable improvement by doing the front skirts, which is what you would expect.