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MAX Update No. 35: Nose Job for Better Aerodynamics

10/1/2009 12:52:10 PM

Tags: MAX, 100 mpg, aerodynamics, horesepower

The new MAX body is getting a new nose. Cardboard and computers are working hand in hand on this aspect of the design. Don’t worry, the finished nose won't look like this, we’re just seeing how small an air inlet we can get away with.

For drag reduction, the less air that goes through the car, the better. Properly guided, air that goes around, over and even below the car can have relatively low air resistance, but air that goes through will always be a big drag, to coin a phrase. If you assume that all the air MAX nosethat goes through a radiator is converted to drag, you won't be far wrong. If you go back to Update No. 16, you can see that MAX’s radiator opening is substantial — a full square foot of MAX’s frontal area. Is that enough area to be worth messing with?

Dynamic pressure (shown by the letter ‘q’ in the aerodynamics biz, for reasons shrouded in mystery) is the pressure of air in motion. For horseback calculation of car performance you can use q = 1 pound at 20 mph. Dynamic pressure (q) increases at the square of airspeed (if you double your speed, you hit twice as many air molecules and you hit them each twice as hard, etc.) so q at 40 mph (20 mph x 2) is 4 pounds per square foot (2 squared). At 60 mph (20 mph x 3) q is 9 pounds per square foot (3 squared). I’ll spare you the math, but it takes 1.5 horsepower to exert 9 pounds of force at 60 mph. If we could reduce the size of the radiator opening to one-third of a square foot (as shown in the photo), MAX’s “cooling drag” would only be 3 pounds, would only take one-half horsepower to overcome, and would save us one full horsepower at 60 miles an hour.

Testing will show how little air MAX needs for cooling, but my guess is not very much. While Kinetic Vehicles encourages even our high performance customers to build their cars with four cylinder engines, we have a few who have put Chevy V-8s in cars that look just like MAX — same nose and everything — and they cool just fine. Still, one test is worth a thousand guesses, all it takes is some cardboard zip-tied to the grill and a keen eye on the temperature gauge, and when we’re done we can recycle the cardboard!

 


Photo by Jack McCornack 

 


Browse previous MAX Updates.
Check out the 100-mpg Car page for all things MAX.


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Post a comment below.

 

Jack McCornack
4/15/2010 2:42:57 AM
Hi Steve P, I may need to do a follow-up on this update but MAX is proving sufficiently cool on a smaller inlet than a license plate. I like the idea of a blowback license plate but a local gendarme already busted me for it and it looks unlikely that law will change here in Oregon. Covering license plates with clear plastic is also prohibited in many states. Maybe when gas gets to ten bucks a gallon they'll lighten up on front license plate rules around here, and many states recognize that a front license plate needn't be visible at speed; really, all they're good for is writing parking tickets without getting out of one's vehicle and/or walking to the back of the offending car. But the way our culture is headed, we're more likely to see front license plate light requirements rather than improving mileage by getting rid of the things.

Steve P_3
4/13/2010 2:48:22 AM
Jack, Wouldn't it be ironic if the area needed to cool Max would be exactly this same size as a american license plate. Put the license plate on a butterfly baffle to regulate the cooling temp, if even necessary. I don't like the idea of pulling air from near the road. I would think waste heat from other cars and radiant heat the pavement would have some effect and reduce cooling capacity. Also, I like the idea of enclosing the bottom of the vehicle. I has positive several effects. Keeping the engine compartment cleaner and reducing bottom drag. Ducting air from the side or top of the bonnet thru the radiator and fan back out the bottom or sides would be best.

Jack McCornack
10/7/2009 2:54:05 PM
It would indeed, Lee (see Lee's comment below), and while I think this test will show how small a grill opening we need (if any; see previous comments), there are other limits to how far to lower the nose. While getting the nose lower (and longer too) will reduce drag, there's a practical limit when you come to a driveway, plus in most states you need to deal with a front license plate. But some of the driveway and speed bump difficulties can be reduced by raising the whole car. One reason cars showed such reduced drag in Ye Olde Days when they had "air dams" hanging down from the front bumpers is, cars were such a mess underneath. I'd think a smooth flat belly pan could skate over 6" of air as easily as over 3" of air. So maybe lowering the nose -relative- to the rest of the body will give the front end ground clearence we need, with the low grill opening we want.

Lee_18
10/7/2009 1:28:50 PM
In the image, the area under the opening looks as large as the opening in the grill, and it looks like it is angled to push the air under the car. If you're redesigning the nose, would it make sense to lower the opening in the "nose", to reduce the air pushed under Max?

Jack McCornack
10/5/2009 8:53:57 PM
Interesting thoughts, those. I haven't done it yet but I intend(ed) to block the bottom of the engine compartment completely and duct the air through the radiator and out the sides of the car, but Michael, your experience is making me rethink that. Perhaps airflow under the car--which is already turbulent--would be better used as cooling air than trying to smooth it out with a full length belly pan, if it would mean I could mount a rounded nose with no air intake at all. Time to buy some cheap electronic indoor-outdoor thermomenters so I can see how hot it is in there with the nose completely blocked. That plus a cable operated louver and an if-all-else-fails fan should make it easy to test...and if it works, that would be one serious source of drag eliminated.

mOrloff
10/4/2009 10:29:46 PM
Or better yet (to improve on the improvement suggested to the suggestion), activate the electric fan by said louver cable. :o)

jeff dean
10/3/2009 9:52:41 PM
I agree with michael, you probably don't need any air flow. Just in case you get into a hot situation, how about putting cable operated louvers in the front grill opening. If the engine gets hot, just pull the cable and turn on the electric fan.

Michael_82
10/2/2009 9:08:41 PM
How about just closing it all the way up? Diesels transfer heat so slow when under light loads that there should be enough air circulation from under the engine to refresh the under hood temp. The air flow (as long as the engine compartment is not sealed off under the engine) will get pulled through the radiator down under the engine, mix with the air flowing under the engine, then sucked back up to the front of the radiator. I'm willing to bet they would have no trouble at all! For over 2 years now I have been driving my F250 diesel with the front of the grill completely, and I mean COMPLETELY BLOCKED OFF and have had no cooling issues at all in the summer. I don't pull a trailer with 20,000 lbs up steep grades in it, but the bed fully loaded to max GVWR is not an issue @ 100 degrees in the summer.







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