grill "shield" rather than block?
 

would it be possible to create a grill shield, rather than a full grillblock?

something that sits in front of the grill, but doesn't actually reduce the open area of the grill, or at least doesn't seal the grill but rather prevent a direct ram effect.

the idea is that at speeds the air would not be rammed into the grill but bounce of the shield, skip over the openings at the side and continue around the car, just like a full grillblock

at low speeds when airflow is requires and the fan kicks in it will suck in the air along the sides, as if the block would not be there.


now is this possible?, because the pressure in front of the car will be higher than the pressure in the engine bay, so will air still be forced around the block and enter the radiator, or will the air in fact skip over the edges...

does anyone know the science behind it?

also as an extention of this it might be possible trough a removal of my grill incert etc, to relocate my topgrill opening from a forward faceing position to an upward faceing position... this would bring it into an area where the flow accelerates over the hood... this might bring the pressure below that of the engine bay so that at speeds the air entering the bottom grill would be sucked out trough the topgrill... it would pass over the radiator rather than trough it...wich seems like a much lower drag path... would this be desirable, from an aerodynamic perspective and how much would this impact cooling?

I would think it would be possible, but not as effective as a partial grill block. Try it out and get back to us. :)

You have to get air through the radiator to use all the surface area it is designed to provide. Adding turns and reducing pressure differentials will reduce air flow and require power from the fan and engine. To minimize losses, use ram air in and low pressure extraction, with a continuous smooth duct, and control the size of the entrance, reducing it in winter.

maybe i should specify what my personal goals are and why i'd like this setup to work.

my car already has an optimised grill with a small lower grill and a partly factory blocked topgrill that sits rather deep, further blocking from behind on the topgrill alone worked nicely (i haven't touched the bottom one), but it showed that on a normal day with nice weather the car will get very hot only when stuck in traffic and not moveing... at a normal speed the temp will brop and stay quite acceptable... so basically what i'd need is an additional air intake for those occasions when the fan comes on. these are very rare so even if a grillblock would increase the fan on time it's still a fraction of my overall driving. still when it does come on i want it to be able to do it's job.... i'm not to keen on relying on electronics for this; but as there's no ram effect when the fan comes on the new opening would not have to be set up for this... the fan should just be able to suck in the factory spec ammount of air.

Kinda like this? My former daily driver, now semi-retired.

http://i188.photobucket.com/albums/z...gThumbnail.jpg

This one's 2.7 mm lauan plywood (about 1/8 inch for the metrically challenged), primed with oil-base house primer and then an appropriate shade of blue automotive touch up spray paint. It flexes easily; is mounted onto stud blocks on the radiator support at the four corners. Those four points force the curve.

sort of

in my case i think it might look like this
http://i77.photobucket.com/albums/j5...ay/grill-1.png
http://i77.photobucket.com/albums/j5...way/grill2.png
in this pic you see the actual open grill so the open area of the top grill is much smaller than it visually looks, therefore if the "shield" would stand only a short distance before the grill, the resulting opening would be about the same as the open grill. you also see that the totall grill opening on my car is really not that big so i have to be carefull as the car gets hot pretty fast

i did something like this

http://ecomodder.com/forum/showthrea...lock-7508.html

shield
 

Ford of Australia created a grill in the 1980s which behaved as you describe.As velocity increased,the airfoil sections which made up the grill would begin to stall.The turbulence created a formidable barrier to increased flow volume,effectively pinching off the airstream to the required minimum.

that's the sort of thing i'm looking for....you wouldn't by any chance have a picture off this setup? i've been looking for images of stalling wings for inspiration but a totally different leading edge would be needed for the sort of separation a grill would require.

i assume some premium carmakers comming out with low drag cars secretly employ these tricks to arrive at such a low Cd with quite large grills

I think that was the XE Falcon -
Ford Falcon XE

Ford still make Falcons here in Australia.

Mi24 Hind helicopters have a shield like that on the engine.

http://www.asiatradingonline.com/Mi24-Hind.jpg

Isn't that to keep birds out? Hmm, maybe that is what Lunar is up to ;)

most likely they're more interested in keeping bullets and chrapnell out, but provided they make it trough the rotor in one piece birds could down the thing too.... belgian SAR seakings have a truck style deflector in front of the engines to keep seabirds out, though it's probably not designed for what i want the hind shields actually describe the setup i had in mind best....

since these engines suck in their air they probably don't rely much on ram effect... sort of the same as the radiator with the fan on!

that falcon grill looks deceptively simple... some 80's cars had surprising good aero despite their boxy looks, perhaps i might also esperiment with adding some vertical slats in front of the grill...

i've also considdered a double grill, where there's two rows of vertical slats where the second row visually blocks the first but there's a space between them so the theoretical volume of air that could enter is the same.

Lunar, I just remembered that a few days ago cfg83 started this thread showing how he made a spring loaded grill block. At small speeds it is in the open position, but when going faster the wind closes it. When slowing down it opens again. This is pretty much what you are looking for, only your thread was about the block being stationary.
I've been thinking about both types for my car, since they are much less complicated than an electromechanical opening mechanism, but my diesel is almost always running cold. Today is the first day here with temps around 15*C, so maybe shortly I'll hear my fan (haven't heard it yet) and start unblocking the grill and thinking about something permanent. I really wonder how this static grill "shield" will perform. When are you going to try it?

Something like this?
Attachment 3112

What you are talking about sounds like a screen mesh.
Depending on the size of the openings in the mesh, air flow slows way down at higher speeds.
During a hurricane, a screen mesh satellite dish has almost the same wind loading as a solid metal dish.

So, one could use a small aperture mesh that looks almost solid at 55 MPH
and higher, but allows air to be pulled in by the fan while in slow city traffic.


It's likely that the radiator air flow is limited by the apertures of the honeycomb.
Very high speed air rammed in the nose might just flow around it.

I was about to post about meshes. An angled mesh can work like a plain angled surface for air to flow around, but the radiator fan can still suck through it.

lunarhighway - so the problem is that you seem to get enough air while driving, but not at idle? how hot does it actually get in traffic? does the fan cycle on and off, or run constant as the temp continues to rise? are you certain the cars temps dont do the exact same thing w/o any grill block?

if the fan can run and cool ya off easy enough when stopped, i would think that everything is normal.

now i know lots of gm cars live by the airdam. for me, my 99 saturn sc1 sports a full grill block, and only gets what air bounces up off the airdam. temps didnt change at all when i blocked it, only difference was better mileage

@Piwoslaw yup that's exactly the effect i had in mind
@Xringer i considdered mesh a while back...i think i made a post about it, i'll look it up, but what i could find on the web didn't say much about a speed related block effect, the most important thing i learend is that the air tends to travle as laminar flow (if that's the right term)... some distance beyond the mesh... but that's a different story.
@2000mc

it def isn't a bottom breather... the airflow was originally in no way forced up into the radiator... there are some holes in a support beam below and in front of the rad, but after some speculation i concluded they where structural. my undertray completely covers these and this has not changed cooling in any visible way... on the other hand these could serve as an additional intake when the fan comes on... than again at speed with the holes direcly behind the little airdam, some low pressure might actually such out air before it goes trough the rad...

i've only once had a near panic moment when a short distance from my home trafic came to a stop... the weather had been quite good that day but my full winter grillblock for the topgrill was still there and the temp would just go into the redline... fontunately shortly after that traffic resolved and i made it home, and pulled out the block....

so for now i'd like an all season block i can forget about
even if it's slightly worse in winter, being able to leave it in place in summer should mean a net improvement, or at worst the same effect without all the worries

picture
 

lunarhighway,I should have a two-color image of Ford's grill.I'll see about locating it and getting it scanned and posted.I couldn't find it with my materials here at ecomodder,and I believe someone posted it at maxmpg a few years back,a site which is no longer active.

thanks, that would be realy nice... thus far google hasn't turned up much interesting pictures... i suppose the actual grill might not be all that shocking but if some plain pieces are set at the right angles and spaceing etc they might help aero in ways something that looks "about the same" couldn't

I've been wondering about an extended nose. The front of my truck is pretty flat - not 1986 Ford F150 flat, but a bluff bow to be sure. Adding some nosecone would bring the airflow up smoothly over the front.

There's enough acreage of airspace underneath to get cooling air from under the car.

I've been thinking about radiators too - and I have this forum to thank for that. Why does the radiator have to be the big, flat panel? What if the radiator were a duct filled with tubes and fins, shaped something like the A-coil in your home air conditioner? Have the circulator fan be a vanaxial blower at the apex of the A, pulling in from the front and blowing down and out at the A's rear leg. This would negate the need for a forward-facing air inlet at all, all the air would come in from below the front of the car.

that's sort of what they did to the Plymouth SuperBird... back than the front end of any car was basically flat.

you could go pretty low with the nose and than add an airdam to scoop up air into the original grill should that be needed the additional advantage is that you could leave the "grill" area onaffected so you don't risk overheating, but the aerodynamif profile will change drasticly when the vehicles moving.

sorry if i'm beating a dead horse, but it doesnt make sense (atleast to me) that you would have enough airflow to cool while driving but not at idle.

have you visually checked that the fan is spinning when it should? not just making noise?

with the hood open, and the fan running, does the fan produce a strong hot blast of air?which would be normal

is the air flow weak, and extremely hot? this would be expected if the there was very little airflow due to the grill opening or a weak fan.

or is it a strong blast of fairly cool air? could be caused by partially blocked radiator, or coolant not circulating at low rpm due to low coolant level

hold your hand infront of the grill opening with the fan running. assuming everything else is functionng normally, and the problem is the grill opening size, you should be able to feel alot of air moving. if the grill opening is the restriction, i'd think it would feel a little like holding your hand infront of a vacuum.

when the car's at speed the high pressure area in front of it forces air trough the grill and the radiator, and to a lesser extend some suction underneath the car, gets the air out of the engine bay... but when it's static or at slow speed this airflow needs to be forced by the fan... and a fan basically just moves air... it doesn't create a real pressure difference...
the fan in the car is made to move air trough the original opening and trough the radiator, but if this openig is reduced by lets say 50% your fan would have to be 50% stronger in simple terms... since the grill is calculated for a worst case scenario ,under normal conditions it's to big, so partly blocking it will still deliver enough air to the rad to keep things withing normal parameters.

this is also the reason why some sportsplanes tend to overheat while when they're taxing.
their rads are relatively small and placed in housings designed to deliver the right airflow at the average speed the plane will travel... on the ground there's not enough airflow trough the radcore and things can get to hot.

picture
 

lunarhighway,I located the article(s) on the grille I remembered.My memory isn't what I think it is,so here's some corrections: The original article appeared in the July 1976 issue of POPULAR SCIENCE,page 60.------------------------------- The "lamellar" grille was developed by Ford of Cologne,Germany.It appeared on an experimental Ford Capri.The grille cut drag by 12% and cut lift by 30%.-------------------------------------------------------------------- The grille is comprised of five ( 5 ) horizontal airfoil sections,layed back at a 21-degree angle,and each airfoil element is configured "nose-down",with the cord line of the highly cambered foils angled,tail-up,at 30-degrees.----------------------------------------------------------- At low speeds,there is no boundary layer effects,and the air goes through unimpeded.At an undisclosed speed above "moderate",the boundary layer thickens and stalling takes place,with the stalled region acting as a barrier to flow.----------------------------------------------------------------- The grille showed up in the 1978 Capri III,Ford Fiesta,and Ford Granada.The grille was "de-raked" and is vertical rather than angled back,and it's performance deteriorated.--------------------------------------------- On the third gen Capri,the lamellar grille,along with a front airdam is only good for a 6 % drag reduction,unlike the 12 % reduction with the original grille by itself in 1976.--------------------------------------------------------- I attempted to "join" Photobucket,so I could post the photo and it seized the computer and we had to shut-down and re-boot the computer to get rid of it.------------------------------------------------------------------ If anyone can recommend an alternate hosting site,I'll try that.In the meantime,if you'll send me a PM here at ecomodder,I'll either try and scan and email the image,or mail it to you the old way.------------------------------------------------------------------ It looks like this type of grille technology is very finicky,and might require a windtunnel to set up.

aerohead -

Assuming for the moment that you have Windows XP, you can use MSPaint to make the image smaller (If I remember correctly, I don't think this will work for Windows 95 because MSPaint doesn't store JPEG files) :

Check if the file is below ~110,000 bytes. If yes, then you can upload it to this forum. If no, then you will have to repeat the process until the file is small enough.

CarloSW2

That grille aerohead is talking about was used on the 1st gen Tempos. At least, I dimly recall reading that one time.

MSPaint
 

Thanks CarloSW2.The fella that owns the business here where I use the computer says when he scans a photo,it goes into Photoshop.I've been able to download photos from my camera and email them to friends,but don't know where to send them for ecomodder.com,as an attachment.Help?

Frank -

Wiki agrees :

Ford Tempo - Wikipedia, the free encyclopedia
CarloSW2

Why would widening the rear track improve aero?

I'm sure it wouldn't and that's an erroneous claim.

Maybe they meant pushing the wheels outward to make them more flush with the flanks of the car

Making the wheels more flush seems likely to help, but when it comes to details in aerodynamics, there seem to be very few hard rules. The Corvair Greenbrier wagon looked like it was intended to appeal to Japan as a rolling pagoda, but it turned out to be far more streamlined than other, similar vans.

No, the whole reason for the Tempo/Topaz was to provide a lil step up from the Escort with seating for 3 in the back. T/Ts use much Escort stuff from the firewall forward and so have the same front track width but the butt end is wider.

Aerohead: When I post photos I first upload the photo as an attachment, then I refer to the photo using the image link to reference the attached document. It gets the photo to show up enlarged very nicely.

based on this description i made the following sketch... i hope i interpreted things right here

http://i77.photobucket.com/albums/j5...l/path2446.png

is this somewhat what it should look like?

what's missing from the description is the relation of the length and the spacing of the foils.

than again, the angles give enough indication to try and build some sort of prototype

That's pretty much it.