Designing/building front wheel skirts v.1.0 (Geo Metro)
 

Well, after doing the tuft testing video (http://ecomodder.com/forum/showthrea...etro-5403.html ), I'm definitely sold on the idea of fabricating a set of front wheel skirts for the Flea.

In an ideal world, my next step would have been to head out to my ideal test road to do some A-B-A runs with a set of cardboard and duct tape skirts to get some data on the actual difference I might expect to see. But my cruise control isn't working reliably enough to commit the time to that.

So based on the tufts alone, I'm going to skip ahead to fabrication. This'll likely be the last mod project on the car before cold weather sets in.

Here's what I'm thinking...

Top hinged, like Mike did:

http://ecomodder.com/forum/attachmen...1&d=1223512997
http://ecomodder.com/forum/attachmen...1&d=1223512997

I think this is the best route to take. Attach a hinge to the wheel arch, build a light metal frame that swings from the hinge, and attach the skirt material to the frame.

Thing is, as with my rear skirts, I don't want to drill into metal in a rust prone spot. Fortunately, I had a quick look this evening, and there are already two screws in a good position to use as mounting points:

http://ecomodder.com/forum/attachmen...1&d=1223512997

http://ecomodder.com/forum/attachmen...1&d=1223512997

(No, the tire won't hit the hinge when the suspension compresses - it's offset slightly outward from the side of the tire.)

As for the skirt material, I think I'm going to consider this "version 1.0" and do black coroplast. If they work well, I'll consider building an aesthetically nicer set from fiberglass in the future...

So first step is to make the hinge brackets that will span those two screws...

EDIT: front wheel skirts tested: http://ecomodder.com/forum/showthrea...light=skirt%2A

You my friend are Aero-crazed. Keep up the good work. Depending on Mileage difference I may do this on mine in future, I am still getting used to the stares from rear skirts.

You have to ease into these things. (Unless you're basjoos.)

I remember being pretty self-conscious when I first put the rear wheel skirts on. That went away after a little while. Now, with the rear skirts AND the Kammback, people just mistake the car for a Honda Insight. :D Seriously - it's happened.

But the front skirts might be more of a hard core aeromod. We'll see what kind of comments they generate...

Drink it in, bbjsw10. I live for those looks. Makes me remember I'm a creative, independent thinker... Or is it that i'm cheap?

Just a small detail but I would put those hinges as far apart as possible. Would be nice to make the covers easily removeable.

Can't wait to see what you come up with.

Good point, orange. I'll try to get them as close to the mounting points (those screws) as possible for strength.

What will fill the gap above the hinge? I would assume coroplast, but then you will need to have a gap between the pieces to allow movement of the lower piece...

I was actually hoping to make things so the skirt is one piece, but tilts into the wheel well above the pivot, and out of the well below it.

hmmmm.... good idea.

You would still need to have a gap between the metal and the coroplast to allow it to move... you could try adding something along the edge of the wheel well that overlaps over the coroplast? unless you're not OCD on basjoosing.

if you could offset the angle of the hinge slightly so than the door hinges forward-upwards, instead of just upwards you may have an aditional aerodynamic benefit, as the air won't be scooped in the open door when the weels are at a more pronounced angle. does that make sense?

perhaps just a few degrees offset form horizontal in the hinges won't present much additional construction problems (just drill the frontal bolt hole as low as possible in the bracket and the rear one higher) but could yield a slightly better aerodynamic configuration when the doors are opening. in addition the airflow will in part force the doors close at speed

just a thought, it won't make or break the design, but when you go as far as makeing front wheelskirts you light consider these little details as well. respect for attempting front wheel skirts anyway!!!

[QUOTE=lunarhighway;66147]
in addition the airflow will in part force the doors close at speed

QUOTE]

Brilliant !
So true.

( Also, you plan to have the front lip curve inward into the wheel well ... right ? )

I am curious to see how you get around the problem of having the tires rub against the skirt when you turn the wheel.

I think Basjoos' idea of the conveyer belt wheels is brilliant, but I would be worried that the rubbing would eventually wear into the tires.
I know it won't, but it would if I built it !:o

As long as the inside surface is smooth i don't think there would be any issues with the tire getting rubbed through.

Maybe an aluminum plate with a hinge, rubber to cover the space above, and small springs near the hinges to prevent any flapping.

I can't wait for the results. I might have to try it with my car.

Found a new "front wheel skirted" car:

http://ecomodder.com/forum/attachmen...1&d=1223657619

Source: PAMVEC: Parametric Modelling of Road Vehicle Energy Consumption

I am looking forward to seeing how this turns out. All of your other aeromods ended up looking great.

[QUOTE=Cd;66262]I've been driving with mine for over a year and a half and over 40,000 miles with no problems with rubbing wear on the tires from the rollers.

[QUOTE
I've been driving with mine for over a year and a half and over 40,000 miles with no problems with rubbing wear on the tires from the rollers.[/QUOTE]

( I was just stating that if I personally did what you did, It never would have worked. I was never doubting your genious )

Where did you source those conveyor rollers from?

You can order them on-line at McMaster-Carr (McMaster-Carr).

Part# 2278T21
3/4" Diameter Conveyor Roller Aluminum, for 4-7/8" Between Frame Width, 20# Cap
$8.51 Each

They also sell longer versions of this 3/4" dia roller.

So do the rollers always make contact with the wheel, or just in a turn ?

They only make contact during a sharp turn, like turning into a driveway. They don't make contact during lane changes or when making moderate turns like from one 4-lane road onto another 4-lane road. They sometimes make contact when turning from one 1-lane road onto another 1-lane road.

hinges
 

Please,don't anyone attempt to do the skirt w/o hinges.The one I did for the T-100,even though blistered out to allow reduced turning radius,rubs at the slightest provocation and is a constant source of stress and displeasure! ------------------------- I'm going to do a double-articulated linkage for mounting the skirt,as it will move like a parallelogram,away and up simultaneously,the skirt always parallel to the side of the car.------------------------------ No benefit aerodynamically,but it will let me play with this mechanism,which I intend to also use for the canopy on the hyper-mini.

Bassjoos : Just curious : what does it sound like when they make contact ?

Metro : Dont't mean to hijack. Care to comment on the rubbing issue and how you will handle it ?

They sound very similar to the noise produced by a TIE fighter in Star Wars. The aluminum sheet covering picks up and transmits the noise produced by the rollers. The earlier coroplast covered version was a bit quieter.

I'm thinking of attaching some teflon sheet or other slippery plastic where the tire will contact things. It'll be mounted to the metal frame behind the skirt.

I think mine will be more sensitive than that. Not enough to contact in a lane change or gentle bend in the road (less than 1/4 turn of the wheel), but I'm going to try to get them fairly close to the tire to minimize frontal area and try to keep attached flow on the aft side of the skirt.

---

I worked on things a bit today - flattened a length of copper pipe to form the bracket that I'll mount the hinges on. I jacked up the a rear corner of the car to compress the front suspension on the opposite corner to double-check clearance to where I was going to run the bracket. Decided to position it up higher than I showed here:

http://ecomodder.com/forum/attachmen...1&d=1223512997

I've got it positioned at the halfway point between the bracket drawn above and the top of the wheel arch.

I also picked up some steel bar stock (fairly light) to make the frame. I'll work on that tomorrow and take some pics.

What about just filling in the gap between the wheel and the wheel well, make it solid, and leave the minimum clearance for turning. Then put some sort of rubber stripping around the rest that can basically seal it when the wheel is straight but will flex enough for the wheel to pass through it.

At first you might think it wont be nearly as effective because it doesnt cover the spinning side walls of the tire, but I bet most of the turbulence created from the spinning tire is actually from the tread part of the tire that is perpendicular to air flow.

This coupled with some hub covers should be very effective, and possibly even more then a full cover because it wont increase frontal area and might have better laminar air flow.

Could do another tuft test with a cardboard cutout to see ;)

It's not a bad idea.

Couple of issues: Don't forget the cutout has to accomodate the movement of the wheel with suspension travel too. So it can't just be a simple circle.

Also, the wheel cover/tire on my car isn't flush with the surrounding bodywork. It's recessed at the top & sticks out relative to the bodywork below the center of the wheel. Makes it more complicated to design a gap filler with smooth lines.

Ever see the "bristles" on transport trucks above the trailer wheels to keep spray down? Maybe that could work as the "gasket" bit that has to permit the tire to pass through when turning.

very interesting. I like the hinge bracket.

hinges & frame roughed in
 

Much more refining yet to do, but I got the hinges mounted on the flat copper pipe that uses existing screws in the wheel well lip. Need to drill one more screw hole in the forward part, but I can do that in the plastic bumper, so no rust issues there.

Need to trim the copper, and I may replace it with stainless if I don't think it's sturdy enough with the full weight of the completed frame & skirt:

http://ecomodder.com/forum/attachmen...1&d=1223946868

Below: side view. The frame is just tacked together at this point. Going to add some triangulation for strength.

http://ecomodder.com/forum/attachmen...1&d=1223946868

Below: view from above... There's about a 1 inch gap between the tire/hub cap and the frame. Accomodates 1/4 turn of the steering wheel before contact.

http://ecomodder.com/forum/attachmen...1&d=1223946868

Front view:

http://ecomodder.com/forum/attachmen...1&d=1223946890

Aside from the hinge being slightly front-mounted (you are still doing that, right?), you could add something on the front bumper right in front of the skirt to divert air around it to make sure air doesn't get under there and lift the skirt away from the car.
As for the slippery material backing or conveyor roller, what about using a layer of coroplast? I'm assuming you have lots of extra laying around like some of us do..

Very nice, MetroMPG. You mentioned using teflon instead of rollers. I've heard of the rock crawler guys making skid plates with the slick plastic stuff they make cutting boards out of. Maybe that'd work for ya. It'd be cheap and easy to cut/drill.
http://i337.photobucket.com/albums/n.../skidplate.jpg

I'm not relying on aerodynamics to keep the skirt closed - it'll have two springs fore & aft inside the wheel well to keep it in position. The tire will push against these springs when steering. (I think basjoos also has springs inside his.)

Tango - cutting board plastic is a great idea. Thanks. More durable than coroplast, for sure.

I think the main reason to go for rollers is the longevity of your hinges. Any
material you choose for rubbing pads will have much greater friction than rollers will.

(geek voice) Plus then, your thkirts will sound like tie-fighterth. That would be cool

Looks good so far. Looking forward to the next stage.

So far the frame of your design looks fairly similar to mine except I used a piano hinge that extended along the entire top of the movable portion of the frame and had more clearance over the tires since I needed the room to mount the rollers.

I got the frame pretty much finished. I will probably have to weld on a some "tabs" to mount the plastic that the tire will push when turning.

http://ecomodder.com/forum/attachmen...1&d=1224114815

So it's on to making the actual covering that will mount to the frame.

I was planning to use fiberglass because I have more experience with it than trying to form metal. And I'm the coroplast looks a bit too "coroplasty" for my tastes.

The plan was to shape the form of the skirt sculpting expanding spray foam over cardboard as the base, then glass it, then get rid of the foam/cardboard base.

Then I got the idea that if I could build a cardboard base fairly close to the shape I wanted, I'd use drywall mud instead of the foam because (1) it's really easy to sand, and (2) I had lousy luck with the spray foam last time I used it.

So...

http://ecomodder.com/forum/attachmen...1&d=1224114815

There's the mudded skirt, coat 1.

Unfortunately, the water content in the mud just caused the cardboard to warp terribly, so I scrapped that idea.

Plan C?

I'd make a template from one pice of cardboard and use pre made body filler that has shreds of fiberglass in it (IE long and strong or kitty hair). then you can build up your fiberglass from there.

Probably what I'll do. I went out on a cardboard run tonight - local furniture / appliance store dumpster. (It's supposed to rain later, so if I wanted a good piece I needed to go tonight.)

Couldn't you make a rough shape coroplast base? That would not warp, but then again the mud might not stick well.

Plain masking tape is also something you can work with fiberglass just like cardboard.

So get some cardboard and form it to shape and use masking tape to help hold the shape you are interested in. For compound curves use non corrugated cardboard and cut slits in it and tape them smooth. Construction paper also works good for some shapes. The resin will soak through the paper and the masking tape just like the cardboard. So after you get the shape like you want it put a single layer of fiberglass mat over it and resin and let it harden up enough to hold it's shape then put another layer on to make it strong enough to work with.

After that take it off the car and scrape any excess cardboard and tape off the back then put a layer of fiberglass over the back side to seal the cardboard in. If there are some areas that are not right you can sand them down where they need to be and repair any holes you cut in from sanding bad places out. Usually it only comes out a very tiny bit thicker but is just as strong making the parts this way. If you want it to be real thin just use thick paper like poster board paper instead of cardboard.

Also if I remember right, powdered graphite is what you mix in the resin to make the fiberglass black. That way it is black all the way through and scratches won't show up easily in it. It also hides the cardboard so you don't see it through the resin :)

Composite foam is a fantastic medium for building light, strong fibreglass and resin structures. It's a thin layer of foam on a fabric backing. It is used in boat building and it comes with one side cut into small cubes so it can flex. I can't remember the technical name for it but you could call boat builders or fibreglass supply places.

There is also honeycomb which the boat people would have as well.

Enjoying your mod. Becoming inspired.

More than one way to skin a cat.
 

Yuk. That's gross. Who'd wanna skin a cat?
Anyway, yet another way to do it would be to use pink or blue styrofoam from your local home improvement store. Cut, carve, and sand it to shape, then paint it with some latex paint. THEN fiberglass over that. The latex paint keeps the polyester resin from attacking the foam. Then remove the foam mechanically (grinding/sanding/ripping/tearing) or dissolve it with your favorite environmentally-unfriendly chemical.