Question for the Aero guys
 

I have an old CJ7, most times it doesn't get driven very fast (35-40, often not more than 10) but occasionally I take it down the freeway.

I was wondering if installing a bug deflector on the hood to divert the air up over the rather vertical windshield might help.

Yer pretty much doomed by the fact that you're driving a cube down the road.

A brick has so much room for aerodynamic improvement, but I don't believe a bug deflector is one.

I agree; most of the gurus would say to work on other areas first; wheel openings, underside, maybe, and the rear.
A bugflector could work, but I have doubts about the one designed to effectively work for your jeep; those things push out a huge bubble much larger than your windshield to reduce bug splat. You would want one that's smaller or less severe, I think.

The wheel openings arent much of an option, the tires move arround too much and the tires barely clear at full travel as it is.

I am already considering a set of smooth skid plates which also get better clearance than the current one I have.

I can't really do much to the front or rear because whatever I add would just get smashed on the rocks.

I was figuring on making a deflector just big enough to get the air over the windshield.

The goal isn't to make this thing a super high FE vehicle, just to improve its road maners a bit.

first of this thing will never have good aero... it's designed to be perfect off road, and just that, so on road it will always be handicapped. So not driving it sensible and slow is your best bet...

but here's an idea that might be inspiring... it's not too extreme,cheaply doable and testable, and for the most part won't compromise the vehicles off road performance... plus i don't think it would be to noticable to other drivers if propperly done..
it's mostly for inspiration, so i went all the way, but taking parts from it that are more subtle should also help

http://i77.photobucket.com/albums/j5...y/dams/cj7.png

stock, modded, and highlighted.

main thing is an angled plate in front of the grill... this will deflect air over the grill, but basically not block it, as the sides are open, so it shoudld retain full off road cooling.

than you see that the front tires are virtually fully exposed.. what this vehicle could use is a huge airdam, so perhaps fabric or rubber "inverse mudflaps' that connect the mudguards to the bumper could be a start, than closing the bullbar (or whatever you have) and extending it as far down as possible...

if you really whant to go low you could make the lower part hinged so you could fold it up offroad.

or retain a sensible height and make the lowest part from strong rubber so that when it does hit something it will fold back....

a vehicle this aero dirty i think has the best fighting chance when the air is deflected as clean as possible around it... once that's done there's not much clean surface to keep the flow attached to and the vehicle's to short for much boattailing.

Interesting ideas there.

I'm not so sure about the grill ramp, it would still be a pretty steep angle and it would still slow the air when off road. I already have mild temperature issues as it is (even at highway speed). Ambient +120f and ambient this weekend got up to 108f. :mad: I'm going to vent the hood and see if it helps.

The air dam, were you visualizing that as vertical or slightly sloped? If its sloped I could make it solid and able to slide up on rocks.

Closing up the gap between the fender and the bumper would still be pretty steep, but should be better than a gap, and should strengthen the fender considering I'm going to remove some material above the tire to fix some mild rubbing.

Btw, that the same color as mine, but its not near as shiny, and I don't have a 4" body lift.

as for the angle of the grill block, it doesn't really matter, it could even be flat, but what is important is the corner radius at the top (if you want to optimise) if you want to streamline a brick the first thing to do is round the corners. most gains will come from the fact air is forced around the car rather than trough the messy engine and out the bottom. alternatively you could make a grillblock that's adjustable... or removable off road.

a sloped fairing would work, as with the grond clearance on your car the air that goes underneath isn't as restricted... some larger dams "mud flap" style perhaps, in front of the tires could also give an improvement at speed...

perhaps look at the lates generations of suvs and picups for inspiration on airdam heights etc

Just had an odd image pass through my mind,

Build a large fiberglass nose to put on it when going some where, shaped like a nose of course.:D with the air inlets for the radiator beig the nostrils.

Ill take a look at some of the newer SUV's (oversized station waggon's), but no guarantees, most of the new ones don't exactly scream off roadable to us.

Cj-7
 

Dr. Paul MacCready got a patent for a windshield fairing for JEEP-type vehicles.
Looking at it,you'd swear it was a parachute.The device attached to the face of the windshield framew like a 3/4 window frame with shallow tunnel inside, projecting forward as deep as the distance to the frame edge with a semicircular sweeping radius curving back around to the A-pillars,and up to the header.Looked like a rectangular fiberglass inner tube split in half.
This greater radius prevented flow separation around the otherwise squared off frame.The semicircular form prevented formation of blind spots.No one would believe that such a thing could help but I believe that something like this is one of the few things which would help you.
In a wind tunnel,at zero yaw,after painstaking work you might get the air deflected around the frame,but with any crosswind,you'd be right back with separation.
I'd look for some PVC pipe of proper size, rip it into half tube sections,miter the corners, and attach firmly.

Aerohead: do you have a link to any pictures I could look at?

Lunar: I have been looking at any newer SUV I came across, it looks like the best option (for this one) is a sloped front skidplate going from the bumper to just in front of the front axlethat pushes the air down below the front axle, then smooth skid plates underneath. Still looking at the fender extentions, they should be pretty easy to do and still look relatively normal.

just a few more loose thoughts... moon discs... just any round plate that could seal of the rims basically... if they help on normal cars where the wheels look fairly aero friendly they should do something on these big wheels... than again they'd have to be strong for off road stuff.

next, perhaps a bridge to far, but not impossible is just make a whole new roof/windshield. it's involving, but given the fact the windshield will just unbolt (right?) and the vehicle doesn't have a fixed roof, means it won't involve gutting the original vehicle.... a plexiglass bubble would be cool (but like i said, probably not really practical)

on a more modest basis perhaps you could redesign the windshield to have more curved sides.... maby it's possible to saw the whole windshield assembly including the a pillars from a wrecked car and fix that? a saab 900 (don't gut a good one please) would be an interesting candidate, but a crashed metro might be nice too.

another idea is to install two lengthwise rollbars that from the A pillars and curve back all the way.. a fabric cover over these would also form a nice aero shape...

picture
 

TheEnemy,sorry,I saw it on micofilm in the patent section at Dallas Public Library long ago and did not think to print it.
No doubt,you could probably see it online now if you new the correct search field.
If you can envision a life-preserver from the Titanic,only rectangular,you've got it!

Thanks Aero, I have tried looking for it but without any luck, I think I understand what you are talking about now.

We had some good winds on Friday gusts 25-30mph, so I took it out to an open area and used a stick with a plastic streamer on the end of it to do some "wind tunnel" testing. Saturday was better, gusts 50-60mph but I didn't get a chance.

The air going over the hood was pretty stable, up until it got close to the windshield, then it kind of stalled, or bounced arround (left right or up).

The air over the top of the windshield was only deflected up by about 6 inches and had huge amounts of turbulance. Edit to add: A bug deflector would probably have to be huge to be effective, and ruin the flow over the hood.

I don't remember what it did on the sides of the windshield.

At the doors the airflow was slightly down.

In front of the rear tires the air flowed up at about a 45deg angle, then into the back seat and forwards between the front seats.

Airflow on the back/behind the rear tires was pretty unsteady, but what there was looked turbulent.

There appeard to be lots of flow going into the radiator, makes me wonder why it runs hot.

Link to USPTO MacCready Patent
 

Hi All,

Here is a link that will bring up MacCready's surface vehicle aero aid patent:

United States Patent: 4057280

If you have a TIF viewer add-in in your browser, just click on Images, and then each page in succession....