Darby, how's the air tabs?

DarbyWalters · **Posted:** Wed Dec 12, 2007 10:17 pm

ATXKJ wrote:

Please note - armadillos are perfectly at home in Austin.
http://www.armadilloworldheadquarters.com/awhq.htm

But you always see them dead in the road...

I used to go to AWH back in the mid 70's and early 80's...saw some people in the early days...and raced cars in the parking lot and the road along the "river" of Municipal Auditorium Shores.

retmil46 · **Posted:** Thu Dec 13, 2007 3:03 am

DarbyWalters wrote:

I have considered some underbelly coverage...but the engine/tranny/transfercase skids do a pretty good job. I do think a lower front air dam would be a big benefit, especially if you covered more of the front tires. You could make it very easy to remove for offroad...I will be looking more at this very soon.

You can of course add many more air tabs...in fact the shape of the rear lights are like an air tab if you look closely. The AIRTAB site likes to tell you to locate the tabs much closer together...maybe to sell more. The thing is you don't want to over do it IMHO.

The problem mounting them by the wheel wells is the shape of the fender flairs...it makes it difficult to mount them properly and they a bit bigger than the flair is wide.

I am just trying to beat the 19city/21combined/23highway with a lifted CRD with armor. So far so good! I am actually beating the OLD EPA Estimates...including better than the 26 highway.

I think (I used 11) that you could order 20 and have a few to test with. Another way to attach them is using business card magnets cut to shape/size. Another guy has done this and they have stayed on at 65mpg or so. You have to figure that the air passing over them will keep them attached.

Matter of fact, on their website they list a minimum separation distance, something like 4 inches center to center. Any closer and they say they'll interfere with each other and cancel out the effect. They even admit closer spacing would allow them to sell more, but it wouldn't do any good.

As far as the fender flares, I was talking about putting them on the flat of the doors just in front of the fender flares, not on the actual flares themselves., and then only the rear wheels. But that would really be getting into the area of overkill. The way the fender flares are riveted together, might not be that tough of a job rigging up some actual skirts to at least cover the top part of the well and still not interfere with the tires.

With all the other mods I've done since my last trip, I'm looking to beat 33 mpg tank average highway on my next trip to your neck of the woods in a couple weeks.

The magnet idea sounds like a winner - besides protecting the paint, would allow you to move them easily to test different configurations. Anyone have any suggestions on where to find the magnet backing - sign maker perhaps?

ATXKJ · **Posted:** Thu Dec 13, 2007 11:26 am

DarbyWalters wrote:

ATXKJ wrote:

Please note - armadillos are perfectly at home in Austin.
http://www.armadilloworldheadquarters.com/awhq.htm

But you always see them dead in the road...

I used to go to AWH back in the mid 70's and early 80's...saw some people in the early days...and raced cars in the parking lot and the road along the "river" of Municipal Auditorium Shores.

My only legal pavement motorcycle race was on the road/ track around the Auditorium -
It's not the same since they decided it was only a music festival - and took away all of the fun stuff.

(okay I'm off topic - I need to order some Air Tabs and try them, but I don't think I'll see an mileage impact until I pull the MTR's)

DarbyWalters · **Posted:** Thu Dec 13, 2007 11:36 am

Yeah, the motorcycles were hitting the one "switchback on the southwest side of the "track"...fun to watch.

boilermaker2 · **Posted:** Thu Dec 13, 2007 11:42 am

Darby, you indicated that you used plasteel and my thoughts that any form of sheet metal, plastic or composite, even wood, will work as long as it doesn't catch fire or warp. :shock:

That said, could we (please) have some close-ups of how you mounted the air dam?

In addition, did you have to put any rubber seal around it to keep it from vibrating/buffetting behind the grill?

As you can tell, you're about to have another fellow "air warrior" (err guinea pig).

Boiler

retmil46 · **Posted:** Thu Dec 13, 2007 12:45 pm

Locally, Lowes and Home Depot sell smaller precut sheets of acrylic and lexan - about the size of a window pane - about a buck for acrylic, around $2 for lexan.

With clear panels, you could have a "stealth" version - would look stock at anything but close-up inspection.

boilermaker2 · **Posted:** Thu Dec 13, 2007 6:01 pm

Very good idea remil, thanks. A couple of light layers of black paint over the lexan should make it look like smoked black glass (my KJ is black).

Thanks,
Boiler

DarbyWalters · **Posted:** Thu Dec 13, 2007 6:23 pm

Whatever you do KEEP IT CHEAP!!! Definitely use a dremmel or something similiar to cut. You HAVE to cut them our as single plates and notice that between each slot there is a big ABS insert...so they have to be cut to allow for this to slip between the slots. It is really not hard at all.

retmil46 · **Posted:** Fri Dec 14, 2007 2:21 pm

Did a little measuring last night at 2 AM after I got home from work (yes, I know, I need a life). Based on their minimum spacing of 4" between centers or 3 per linear foot, and dimensions of 3.25" wide, 4.75" long, I came up with the following -

On the sides, you could fit 6 between the roof and tailights, and another 2 in front of the tailights. Any lower and you'd be behind the fender flares where I doubt they'd do much good. On the drivers side, it might be tricky fitting the lower 2 due to the fuel filler cap.

On the rear doors, you could fit 2 on the lower panel below the trim strip and 1 on the upper panel in front of the fender flares, if you wanted to try and reduce drag from the rear wheel wells.

On the roof, 5 might be the practical limit for easy install due to the roof ridges. The ridges extend back just far enough to prevent a flat flush install for any mounted behind them. Otherwise, with 38" in between the roof rails, you could fit upwards of 9.

DarbyWalters · **Posted:** Fri Dec 14, 2007 3:01 pm

To be effective you have to mount the ones for the rear wheel well on the flairs themselves to catch the air you are directing. If they are on the door skin, the air aill just hit the fender flair and be right back where you started.

Now get some sleep :wink:

retmil46 · **Posted:** Fri Dec 14, 2007 3:51 pm

Then I guess the grand total if you wanted to do a full loadout would be 21 - 8 per side and 5 on the roof.

Darby, did you paint yours or is that the standard white airtab they sell? Got the same paint job on mine - stone white. If no painting is involved, so much the better. Paint and I have an understanding - I don't mess with it, and it doesn't make a mess all over me. :roll:

DarbyWalters · **Posted:** Fri Dec 14, 2007 4:26 pm

They come in White and Black. It is not the "exact" same white but it blends in pretty good.

JIMMY JEEP · **Posted:** Fri Dec 14, 2007 9:07 pm

Am i expected to believe a few stick on lumps of shaped plastic are gonna improve mpg via areodynamics on something the shape of a brick. Me no think so!!!!.

DarbyWalters · **Posted:** Fri Dec 14, 2007 11:15 pm

Nobody is twisting your arm to buy any. :lol:

I can tell you that small things can make differences...duct tape on sprint Karts...diffusers on race cars...splitters on trailers...tact in comments...

retmil46 · **Posted:** Sat Dec 15, 2007 3:15 am

Hey, for $50 (less than a tank of fuel), it's worth a shot. Not to mention it'll be one of the less expensive mods I've done to this Jeep.

At least they have a basis in a proven scientific field (aerodynamics), not just a 30 minute infomercial flinging pseudoscientific babble and nonsense at you like that freakin' Tornado sheet-metal POS and the ever-popular "magnets around the fuel line" crap.

JIMMY JEEP · **Posted:** Sat Dec 15, 2007 8:55 am

Seriously kj weighs over 2 tons its shaped like a brick, it will rarely get driven at speeds over 100mph were aerodynamics start to make a real difference. I'm not having a pop at you ,any improvement in mpg would be a relief to us all either petrol or diesel owners. But i personally feel they would be of no benefit on our kj's. They look good though and if anyone wants to style the vehicle individually i'm all for that.

DarbyWalters · **Posted:** Sat Dec 15, 2007 10:23 am

JIMMY JEEP wrote:

Seriously kj weighs over 2 tons its shaped like a brick, it will rarely get driven at speeds over 100mph were aerodynamics start to make a real difference.

The weight has NOTHING to do with aero dynamics for one...Yes, it does affect mpg but that is not what AirTabs address. I guess car makers can stop using wind tunnels since no street cars consistenly do over 100mph. I think you are confusing downforce with aero dynamics. While it is true that huge amounts of downforce occur mostly at higher speeds, aero improvements happen at much lower speeds. If this was not true than our KJs would get similiar mpg at 70mpg as they do at 55mph...they don't and the main culprit is aero...if it wasn't the mpg would act in a more linear fashion.

It is very hard to measure mpg perfectly the way we all have to fill up at service stations...but over a period of fillups the error becomes very small. My mileage did increase after adding the extra side AIR TABS...it is not a big jump but I will take the extra ~.5mpg or ~10 miles per tank. It all adds up and at just $3.00 per gallon getting 22 mpg city, the $1.38 per tank will pay for these in ~20 tanks of diesel. If you do even more highway driving, I think you will gain a bit more and recover the investment faster.

Anyway, I am not going to get into a long drawn out debate over this...it is what it is...and for me it seems to be working.

DarbyWalters · **Posted:** Sat Dec 15, 2007 1:32 pm

As for the "FULL GRILL BLOCK"...it hurt mileage. I got great mileage with 4 blocked off (2 on each side), but with all them blocked the mileage dropped significantly. I think the computer adjusted for possible rising temps by limiting power somehow. I also think the intercooler like fresh clean cool air.

retmil46 · **Posted:** Sat Dec 15, 2007 1:52 pm

JIMMY JEEP wrote:

Seriously kj weighs over 2 tons its shaped like a brick, it will rarely get driven at speeds over 100mph were aerodynamics start to make a real difference. I'm not having a pop at you ,any improvement in mpg would be a relief to us all either petrol or diesel owners. But i personally feel they would be of no benefit on our kj's. They look good though and if anyone wants to style the vehicle individually i'm all for that.

What's presented on the Airtab website agrees with every engineering text I've read on the subject of aerodynamics and motor vehicles (where's Reflex when you really need him? :lol:

)

I believe Darby is correct, you're confusing downforce with wind resistance. As a general rule, above 45 mph wind resistance becomes the primary load factor that the engine has to overcome to keep the vehicle moving at a constant speed and a major player in determining fuel economy. Below 45 mph, where wind resistance isn't a factor, the major factor in fuel economy actually becomes the gearing and gear ratios of the drivetrain, along with factors such as tire rolling resistance, mechanical losses in the drivetrain, the base efficiency of the engine and what rpm it's most efficient at, etc.

Weight only comes into play when we're talking about acceleration - either forcing the vehicle up to a higher speed or taking off from a stop, or uphill against gravity. And acceleration is the rate of change of speed, something we can easily influence as drivers - accelerate moderately and use less fuel, or burn rubber and gulp it down.

For a modern POV at highway speeds on level ground, it only takes on the order of 12 to 15 HP to keep it moving at a constant speed - less HP than you find in most riding lawnmowers. The reasons we have 200 HP diesels in our vehicles instead of 20 HP lawnmower engines are that the world and it's roads aren't perfectly flat, we can't drive all the time at a constant speed, and we humans like doing other things wih our vehicles besides moving from point A to point B with the cruise control on.

So for highway driving, anything you can do to reduce wind resistance will have benefits.

BTW, put my order in last night for 21 white airtabs. If they get here in time, I'll install them before the trip to TX and give them a good long distance trial on the interstate.

DarbyWalters · **Posted:** Sat Dec 15, 2007 3:30 pm

Three Grill Blockers installed: Two (2) on the driver side and One (1) on the passenger side. Next to the one on the passenger side is the other half of the air duct so 4 are really blocked off kinda. Now the "scoop" is the second slot and the first slot is blocked...hope this direct more air up.

Oh Yeah, painted them gunmetal grey.

Darby, how's the air tabs?

Who is online