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Old 02-27-2007, 02:32 PM   #1
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front wheel fairing experiment

right now i'm building a pair of front wheel fairings.... they look like this so far... you're looking at them upside down so what's now on top will face the road aver it's covered with an aditional sheet



I noticed that on most modern cars the bumper covers about 60% of the wheel height, sometimes even more with the aid of these little straight black "what-are-they-called" flaps.
they all seemd to have better bumper designs than my car, but than i came across this picture of a kadett GSI.
i notised it's bumper seemd to extend further downward and lo and behold! there was an additional extention in front of the wheels!:


mine looks like this:



ok in the picture it actually look lower but in reality i feel there's a lot of engine rumble exposed to the airflow. on the other hand i think mine will allow the air to flow around the car easyer... the GSI one looks really angular

another thing that didn't look right to me was the "see trough" effect of the wheelwells:


they basically open up into the front bumper that's just a bit chunk of plastic that makes up the airdam, bumper and front grill. on the previous model of the kadett this was still all metal, so i'm sure at the time it was a clever way to make the car easier to produce, restyle and save weight.
apart from not looking right they did not present me with any horizontal surface to attach anything to, so if i wanted a simple flap in front of the wheel i would have to build some sort of shelve... so i might take it a step further...
For a while i sat planning how i could lower the whole things, yet these wild plans came to nothing due to lack of a suitable material... i thought about sheet metal, but that would be to expensive to experiment with....


so finally i desided to build something from "unsuitable" material, the only thing i had readily available where stiff card backing pads from A4 paper pads...

i figured this material had potential.... and i used it in the past to construct scale model planes so i know what it can and can not do. i decited to build a prototype and see how durable i could make it.
i've assembeled the fairings using pva (white wood glue), covered all parts in a layer of pva

to seal the parts and than painted them black with thick acrylic paint.

i'm paying special attention to the seems wich are all covered with extra pva. when they're finished i intend to spraypaint them with automotive paint. or perhaps something else... the more the better i think. if i can pervent water from getting to the card these might be quite durable.

they have taken a while to build becouse of all the paint and glue that has to dry, but i don't want to rush things since the weather is stiff rather humid so they will see their share of splasches... howerver thanks to the pva coat they have a real "rubbery" feel to it...

i've thought about a slope but decited this shape was better... it would be stronger and i didn't want to much pressure on the bottom... i think a lot of the time sloped fairings might be dictated by ground clearance, but that won't be a problem. one thing i am worried about is sidewinds.... in front view there's not extra surface, but there is to the side nothing huge though so we'll see...


the vertical edge around the "spoiler" part will be used to screw it to the bottom of the bumer that has a short "lip" that curves inward...



any bets/educated guesses on how much fuel they might save me?
(or how long it will take for them to fall of and have me run over my own aeromods?)
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Old 02-27-2007, 03:01 PM   #2
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Go to your local body shop and ask if they have any destroyed old bumpers that you can have, Cut off sections of plastic and bolt securely to the bottom of the car. These will drag on the ground often. Build them with that in mind.
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Old 02-27-2007, 03:28 PM   #3
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lunarhighway -

The workmanship is fantastic but I think that everyone's right, the road will chew them up over time. I would mount them for an ABA test and then look for other tougher materials.

Alot of people here use cardboard first in order to test the mod, and then move on to a more durable flavor of plastic.

On the other hand, maybe you know your material better than we do .

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Old 02-27-2007, 06:44 PM   #4
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i wonder what the point is where it doesnt matter that you block off the wheel because you would be increasing the frontal area.

before you reply to this, remember that at any given tim the very bottom of the wheel or tire is not moving and only the fore most and aft most part are going the speed of the car, if the tire has traction.

this also means that if the block is closer to being perpendicular to the direction of flow than the surface of the tire itself then it is worse for aerodynamics. time for some calculus...
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Old 02-28-2007, 04:01 AM   #5
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@cfg83

we'll see... this will be as much a test of the concept of the fairings than of their material.
i'm quite convinced propperly designed shapes of card will have a comparable sturctural strenght to plastic. for as long as they can be kept dry... right now i'm trying to coat the parts with a waterproof layer that should do the trick for as long as it's not penetrated. if the card could be saturated with some sort of varnish or resin i think it would have great potential.

@thisisntjared

you're right but i think the probem is more complex than that . The horizontal speed of a point on the tire will travel at the same speed of the car, when this point emerges from the wheelwell and slow down to 0 where it touches the road... from that point of view everythings that extends below the upper half of the wheel will cause extra drag. like you said.

however how will a pointed object at a given speed compare to a blunt object at a lower speed... when the difference is not too great the pointed object will have an advantage i think. this might explain why modern bumpers cover about 60% of the total frontal area of the wheel

the main reason why i desited to install something is front of my wheels is that i read somewhere a lot of the wheel dragg is associated with the fact that their spinning will cause air to enter at the rear of the weelwhell and be carried up and forward (the speed of the tire at this point is twise that of the car so that could make sence)

however this air is expelled again at the front of the wheelwell where it collides wich the oncomming air. This would cause the majority of the dragg. that might explain the little back tabs in front of the wheel on some cars. aerodynamicaly they offer little improvement over the tire surface... in fact they're moving at the car's speed while the tire at this point should be moveing slightly slower.
yet if they serve as a barrier to prevent collision between 2 airflows their shape starts making sence.

that's what i initially intended to maken but ad air trapped under my bumper might have caused lift so i desided to present the air with a smooth obstacle to go around rather than an blunt one later on.

that's my resoning behind the design... i might be lightyears off but i suppose that when i'll test them that will become clear...
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Old 02-28-2007, 05:20 PM   #6
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i am not looking to contradict you i was just typing what i was thinking, hence wondering.

anyway, wouldnt denting in the fenders behind the tire be a better way to aleviate the high pressure in the wheel well?
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Old 02-28-2007, 05:33 PM   #7
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Cardboard is a great resource for testing. I like the look, it will be interesting to see if they make a measurable difference.

I think you could have possibly used a polyurethane based adhesive, to give them a coating. That stuff sets up with moisture and it doesn't seem to come off, except with wear. Additionally, it is pretty flexible, so it might seal the cardboard, better, even if it's flexed.
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Old 02-28-2007, 07:28 PM   #8
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Quote:
Originally Posted by theclencher View Post
Sorry, I'm going to vote for them falling off and getting run over (been there!). That's a tough environment up there- way easy to smack 'em into something. I've been thinking of making something like that out of an old tire- if it's attached well enough it should flex and barely even scuff the surface.
In March I am going to make mine out of an old truck mudflap. Using a boxcutter to make them to size. I believe an old truck mudflap will holdup.
I need to decide on how low to make them (how close to the ground) for my Yaris hatchback.
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Old 03-01-2007, 03:04 PM   #9
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@thisisntjared
sorry if i sounded to defensive... i'm basically just thinking out loud too, so any comments are appreciated
btw i think you're spot on with the indented fenders !

the opel eco speedster has this... it has a Cd of 0.2 ,runs on diesel and only uses 2.5L/100km that's 94mpg!!!
of course it's ultra low weight...the interior is veeery empty. but appart from that the overall shape could be upscaled to a good looking family car.
eco speedster

the front of the car is also interesting. the center half of the airdam seems to allow some air to enter underneath while it's blocked in front of the wheels.
the sharp corners are also interesing. i wonder is such a shape will motivate the air to go over the car rather than split to the sides?

@roadrunner
nice car! I?d be carefull to add something to the underside though? it looks like the bumpers pretty aerodynammic as it is? it already covers the area i?m trying to improve. I don?t want to discourage you from trying though, but i?d keep them relatively small...

tonight i worked some more on my fairings... i reinforced certain parts, shaped the bottom panels, and made the holes for the screws. now the glue's drying again.... hopefully they can be tested on the road this month
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