perforated grill block?
 

I'm new here, I was searching the net looking for information on posssibly using perforated sheet metal for a grille block on my 2001 Ford F150. To avoid overheating the truck during hot weather and towing I'm thinking of using this type of material which is 30% open. Any thoughts on whether this is worthwhile to do to reduce the air pocket in the grille?

Thanks
Rick

http://www.made-in-china.com/image/2...etal-Sheet.jpg

I have no idea is this instinct is correct or not, but I would say that perf metal is prolly less aero than an equivalent bit of solid metal with an open hole for the necessary cooling parts.

yes, I would go with a solid sheet of metal for places unused. Right now I've got a duct tape grille block over the part of the grille where the intake is, so now it draws in air from the engine bay, warming the engine faster and running it about 10 degrees warmer, since it's below freezing right now, this is good. But for the summer, I'll probably remove that and block the rest of the grille. perf probably would just restrict and harm more than help.

A perforated grille block will do no harm.

well that clears that up :D it was just a guess ^_^"

Perforated screens are velocity sensitive; at low speeds they let in about what you'd expect- say, a 30% open screen will let in 30% of what an unobstructed vent would- and at higher speeds they "close up" to the oncoming flow and appear to the air to be more "solid".

Without experimenting, I believe this is completely correct. Fluids have a tendency to adhere to a surface as they sheer off it. As you increase your speed there will be a build up of air around the surface of each hole's entrance that is an area of localized slow or stagnate air. So as you increase velocity, more air will be blocked from entering due to this.

So a perforated block would work good for some trucks then maybe? When you are going slow and hauling really heavy stuff it gets air flow. But when you are going fast on the highway it acts like a flat panel.

Sounds good to me :)

Well... in that scenario overheating sounds like a real possibility, but less so than with a solid grille block.

Some trucks achieve a similar result by using a thermostat to control the opening of the grille slats ahead of the radiator.
At low temperatures the grill opening is small and at higher temperatures the opening change to allow more airflow.

Rolls-Royce used the same principle as far back as the 1920's for the same reason.

Rick : Welcome to the place and and enjoy your stay.

Cheers , Pete.

I remember being in stop and go traffic beside a large Autocar truck and its grill opened and closed with it's throttle. Every time pulling up 15 - 20' it opened, then closed while slowing or idling. Seemed pretty clever and this was even pre-internet.

Frank -

This is cool because I think you may end up creating an "aesthetic" that is also MPG efficient. Aaaaaaaaand ..... it's a passive design. No moving parts means uber-reliability and cheap to make.

CarloSW2

I made this thought experiment to visualize it: imagine a pail with a 30% open screen covering it. Let a small stream of water flow onto it; all the water easily goes through the screen and into the bucket. Turn a deluge of water onto it and most of the water flies off all around the bucket, yet some gets through, but probably not a whole lot more than the small stream.

Has anyone noticed that the newer vehicles are using honeycomb grills that imitate a perforated grille? I've noticed this on newer dodge trucks and dodge vehicles.

This is the stuff auto manufacturers need to start doing and shutting their mouths about the 35mpg fleet average they have to meet. Couldn't they just make one that is controlled by air so the electrical system doesn't have to work so much? it's open whenever your at low speeds, but go fast enough and the flaps are caused to lift up from the force of air and cover the grille openings.

Basically, there are flaps that lay down on the front bumper on hinges, and is bent at the tip at an angle. At slow speeds, they stay down, but when you go fast enough air is forced under the flaps because the bend at the tip is at an upward angle. The air being forced under it lifts the flap into the air, and is pressed up against the grille opening until you have to stop, where they fall back down onto the front bumper.

Maybe not the best idea, but it's a start.

There was a Ford car from the 70's which had a normal grille with horizontal slats which achieved the same result with no moving parts.

The slats were shaped like an aerofoil / teardrop shape in profile. At slow speeds the air went through the openings but at higher speeds the shape sent air over the grille slats and over the bonnet / hood.

The material was a simple injection molded plastic and at a quick glance it wasn't even visible but the shape could clearly be felt with your fingers.

Pete.

That would be the early '80's Tempo.

DifferentPointofView -

I like it. I was thinking the same thing but I was being more complex because I was thinking of a flap that was hinged at the top and "pushed" by the air in a similar way. But, a flap that just falls back down is nicer because gravity helps out (mine would have needed a spring). That sounds really easy to do. Hinge some plastic and put little bumpers to raise the flap :

Attachment 193

CarloSW2

Mine would be iced up half the year. The other half, it would pound against the stops, one way or the other, because of the strong gusty winds and every passing semi.

my take on the perforated sheet metal grill is yes it will work but round holes are a very inefficient way to duct in air.
We might pushing a lot of air around all the time when we don't need it.
If we divert all the air with a smooth airfoil and then have an NACA intake duct that opens only as much as we need, it would only induce extra drag when we need lots of air instead of all the time. does that make sense.
note the shape of the intakes on the hood of this red car.

It is a Ferrari, 0.0 F40 at that, So I'm not surprised on the smart design :thumbsup: why don't we just do full grille blocks and have intake ducts like that? one of those things that could benefit more vehicles out there.

Sure about that?

perforated sheetmetal
 

I'm in the,use solid material where your going to block,and leave open the areas your not going to block camp.The perforated metal shown,has no leading edge radii for the openings,and will result in what is known in fluid dynamics as high vena-contrata losses .Its virtually an aerodynamic abomination,a torture chamber,if you will, with regions of separated flow in either laminar or turbulent boundary layer conditions at each and every opening,and imparts the very drag your attempting to abate.Keep it simple.

That's kind of the fancy way of saying what I said in #6.

Frank -

At what speeds do you think the holes will "close up"?

CarloSW2

I have an opinion, and we all know what that's worth!

It also depends on the screen. Some are much less restrictive than others.

But it's sort of an educated guess, and of course there is no "open/closed" behavior to this- it gradually goes from acting unrestricted to acting very restricted. To assign a speed value to when it acts "closed", then, we must decide when the most noticeable change of behavior is noted.

So, I really shouldn't even put a number out there, but for the off-road vehicles I used to design, I figured this occurred around 40 mph.

Part of this discussion is based on the idea that less cooling air is needed at high speed.
Which is why the perforated panel holds some promise.

False premise.
Actually at highway speeds cars (my car, at least) need MORE cooling air.

I do appreciate the explanations of how/why the perforated panel tends to pass a lower percentage of air at higher speeds. Good stuff to know.

I built the grill cover panel you see in my avatar this past Sept. and installed it just before an early October road trip, 300 miles each way. With temps around 75 deg. F, it was fine in town but got a bit hot on the highway doing mostly 60-65. Frequently the temp gauge went up about 3/16" to 1/4" over the center point where it usually rests, and the elec rad fan came on to help cool things down. A few times, I ran the heater to cool it.

With cooler weather its been fine all winter. I'll be building a new one with a larger opening for summer.

variable grill block, i got two runners for a kitchen drawer and i just havn't gotten around to building yet. my plan is to have a NACA opening with a sliding cover that will start uncovering at the bottom first and gradually openup either by a choke cable and linkage or automatic by a temperature sensitive cylinder and linkage.