Jeep Cherokee "Aeromatics" (Kammback / partial boat tail)
 

Ok, I've been on this site for a while now, but I've really only adjusted the nut, courtesy of the ScanGauge II (which is still awesome). And I decided to make my first aeromod starting in the back of my Cherokee (oh, and sorry FastPlastic, it's not going to be very stealthy like yours). I don't know what to call it, it's partially a Kamm, and also like a partial boattail, just with no bottom because I still tow pretty often and use my cargo carrier (in the picture). I also wanted to make this thing easily removable so when I want to go out on the trails, I can take it off without destroying it. Lets just call it a JeepKamm for now

I decided to make it from 1/2 inch PVC pipe for the frame and 6 mil black plastic as the skin. I've also sourced some scrap lexan to "window" my taillights so as not to need to add auxiliary lights to the JeepKamm (for now anyway). I'm also custom forming some poly gutter hangers into the mechisms to hold on the mod (second picture).

So here is where it sits at tonight, as I have to go to bed to be up in about three hours for work. I hope to finish tomorrow evening and start road testing it this weekend.:D

JeepKamm
 

You're definitely working on the correct end of the Jeep.
It's hard to tell what the curvature is without a side photo.The Aerodynamic Streamlining Template can help you with that.
I hope you are using schedule-40 PVC,as it will be strongest,and that the weight is actually supported by the cargo carrier.
I would recommend as much triangulation as you can get for rigidity.You may be relying on the 4-mil skin for carrying quite a bit of the load.
If the plastic pipe fractures and fails,it may occur elsewhere rapidly,accelerating into a complete collapse.
Work your speed up in increments and mentally rehearse for what you might do should you experience a failure.
And use a lot of attachment points,spreading stresses over many locations.

;)Yep, I'm using schedule 40 and am going to be cementing everything together when I'm satisfied with the rigidity. I bought 6 mil plastic for the skin, so we'll see where that gets me. I reconfigured the frame this morning to function better. Models pictures to follow when I have the frame finished.

Update!
 

OK, posting some pics of where I'm at now. I more or less redesigned it on the fly this afternoon for more rigidity and am pleased with where it is at and where it is going. Still would like to get it skinned tonight but we'll see. Quality is more important than haste.
http://i745.photobucket.com/albums/x...bucket_67_.jpg
http://i745.photobucket.com/albums/x...bucket_65_.jpg

Looks good! I've considered a foldable plexiglass Kammback for mine that I can clip onto the back of the factory roof rack for long trips, and store easily the rest of the time. Of course, it would be smaller, and probably less effective than yours.

Removable jeepkamm is finished!!
 

... except heat gunning the last few wrinkles out, but I'm out of patience tonight. Here are the last few shots of the build (especially the one with it on the tail, showing the bar assembly). I can literally wiggle my jeep through it and it doesn't budge! It only weighs maybe 25lbs, and that's my best guess (comparing it to a 20lb sack of potatoes).

I'm not going to bench test it yet (I've not gotten the last few wrinkles out), but I am overdue seeing my relatives about 84 miles away of "rolling hills". I consistantly get between 23.2 and 23.6 MPG on this route rain or shine without the jeepkamm, so I'm eager to see what I get tonight. I will post the update as soon as I get there and hopefully I have good news.

http://i745.photobucket.com/albums/x...ucket_283_.jpg
http://i745.photobucket.com/albums/x...ucket_285_.jpg
http://i745.photobucket.com/albums/x...ucket_287_.jpg
http://i745.photobucket.com/albums/x...ucket_288_.jpg

I didn't even have to put in those light windows, because you can clearly see both lenses at any angle. Just in case I might put in my utility carrier below it until I can get some lights mounted on it and paint the underbars black. Got to keep it clean and sexy! ;)

very nice work, it's inspirational for certain!
what are you using for attachment points?

Test results are in:
 

Trip mpg:24.7=6.5% (based off these numbers)...

While not conclusive, it ar least gives me some heart to see an improvement. While driving I noticed an issue with how the skin being not completely taught is allowing air to form a bowl or trough at the end of the kamm. Not to mention that the whole rippling air bowl shakes the jeep from about 52 MPH on up. When I get home tomorrow I will make ribs for it out some thin coroplast sheets that I acquired a while back for trying on a small kamm. I sincerely hope that getting the skin taught will net a total of 15-20%. More modding for tomorrow I guess.

One thing I forgot to mention is that one huge benefit of this design is that it still leaves the rear hatch fully functional, albeit a few pounds heavier and you have to hold it or prop it somehow. It does look kind of neat stuck up in the air. I'll take a picture of that tomorrow when I construct those ribs.

30 mpg or bust!

Issues: Round 1 (because I'm sure there will be more
 

This morning when I went out to get ready to go, I was inspecting how everything had held up overnight. Apparently, the top hatch mounts were losing their shape and had streched about an inch (probably from the sun and the 12 hours of sitting bearing the full weight after a 78 mile drive).

http://i745.photobucket.com/albums/x...ucket_468_.jpg

So I made a temporary mod to hold it on for the trip home and still managed 24.4 mpg with HORRIBLE RV stop and go traffic. I'll post the video later that I took.

http://i745.photobucket.com/albums/x...ucket_470_.jpg

And to give it some rigidity, I added the bungie cord to hold the frame down to the cargo carrier:

http://i745.photobucket.com/albums/x...ucket_471_.jpg

Here you can see how loose the plastic really is, I'm going to shore it up with either some cloroplast ribs or underbody or replace it all together with a kind of "shingled cloroplast skin" that I dreamt up this morning.

http://i745.photobucket.com/albums/x...ucket_469_.jpg

I still haven't gotten that picture of the hatch up, but I will after I get the mounting reworked.

Mounting
 

ShadeTreeMech:

They are vinyl raingutter mounts that I reshaped with my heatgun (you can see the streched top ones in a picture in the previous post) They were the longer of the two sets, the others are sealed and taped into the frame, they held up just fine. BTW, the lower mounts attach to the hatch right above the taillight, essentially sandwiching the top 2/3 of the carrier with the two mountings. It held on just fine yesterday at 70mph. Again, more to follow when I get the upgraded mounting and rib structures installed.

26.6 MPG on an out and back round trip!
 

Ok, I'll admit that I'm grinning from ear to ear, I got a lot finished today:

I spliced together a lot of 24x20 inch cloroplast signs that were donated to me by the local fort here, to make a "undershell" in the place of ribs to give the plastic skin some structure.

http://i745.photobucket.com/albums/x...ucket_491_.jpg

I liked it so much, I finally finished it all of with my heatgun and here is the cleaned up results:

http://i745.photobucket.com/albums/x...ucket_543_.jpg

Then I took a trip down to a friends house in Olympia, just off of the freeway (about 25 miles each way), stopped and picked up a couple of things, and left ten minutes later to come back home. No drafting or other stranage driving (except honking at a few rubberneckers so they wouldn't wreck), but my Jeep can now NC (Neutral Coast) and not lose any speed while going down two hills on the freeway, where it would lose a considerable amount before. And even better: Normally I drive at 60-62mph with the TPS reading 16 the whole time, now I hold it at 13-14 for the same sustained speed! So, "the proof is in the pudding" as they would say, and the whole trip averaged 26.6 mpg. EPA average for my vehicle is only 14 in town and 18 on the highway. Thats just shy of 50% better than highway!

Side note: Does anyone know how to interpret the IGN number on the scangauge? the highest I've been able to see is 40, but it's been everything below that.

Ok, enough tooting my own horn (even though it is my build thread). I make another trip out to the peninsula in the next two weeks, so I'll make another comparison to that old tried and true run. Oh, and here's a picture from tonight showing the fully funtional rear hatch as promised:

http://i745.photobucket.com/albums/x...ucket_544_.jpg

I suppose next for me is figuring out a better solution for the top mounts of the JeepKamm rather than the ratchet strap currently being employed. Then it's on to doing something about my ridicoulous front end. 30 mpg is in sight baby!:D

Dang Dude, You work fast.

I like what you've done but my hunch is it could be improved. The length seems a tad long, you could build it shorter I think and get similar results. It looks like it may be cumbersome in the long run and foul weather, and I wonder about legalities with the covered rear lights and length.

I know Aerohed put a 3 foot (+ or-) flow collector on back of an old 67 (+ or-) VW Transporter van and improved its performance a bunch.

The shape seems to initially drop too quickly. The transition should be more subtle.

Here is my take on it.

http://ecomodder.com/forum/attachmen...1&d=1279524701

The sides should curve in equally as well since a bunch of air is moving there too.

Also, if you're not using the roof rack, figure out a way to lose that, it can't be helping you.

Great Job!!:thumbup:

You might want to get a 3rd brake light for the kammback, you could hang it from the back or glue a magnet to it and stick it just above the plate or on the back skid.

Now that I relooked at your pics you should be able to wire the lights on the skid to your 3rd light.

Hey Jeep, ran across this today, great stuff that shows a bit more what I was trying to say. Check it out, it's right in the sweet spot of what your doing.

Cheers.

http://ecomodder.com/forum/showthrea...info-2072.html

By skid I'll assume that you mean the hitch carrier, I've already got plans to install lights on the kamm so I don't have to use the hitch carrier to stay legal. I definitely agree that a third brake light is needed asap.

The next problem ive found is to use the hatch with the kamm installed is a giant pain so I need to fashion some kind of clip-on cable system that essentially extends the handle to the rear or side of the kamm.

Thanks for the suggestions guys and gals. I thought this thing would be a weekend project but it has taken on a life all to itself.

Thanks man. I agree that in the pictures it looks like it has a really abrupt droppoff at the end of the roofline, but I can assure you, it's not as bad a transition as the photo's make it out to be. The sides are tapered in quite a bit and the whole backend turns into a half circle shape instead of keeping the square geometry that the vehicle has (Thanks to MetroMPG for that inspiration). I'm attaching a photo of the kamm sitting vehicle side down on the ground to illustrate the side profile tapering.

As far as length goes, it's exactly 48 inches further out than my bumper. I parked next to a extended cab Ford F-150 today and my rig with kamm was two inches longer. I'm also used to pulling a trailer with the Jeep, so having a little extra on the arse isn't out there for me.

Again, thank you for the well intentioned comments, and please keep them coming.

http://i745.photobucket.com/albums/x...ucket_586_.jpg

See, roof racks can be good for mpg.

You'll probably want to tuft test it eventually to find out where you have attached flow and where your angles are too steep / abrupt. I think you'll have flow detachment at the sudden transition from square to angled, especially near the top corners. But if you're seeing an mpg improvement, it's obviously better than stock. :thumbup:

Dude that's awesome! I hope you have better luck with yours than I did with mine.

I love using bungee cords too. Its funny to hear bungee cord and rigidity in the same sentence though.

A-B-A testing
 

Hey guys and gals, I just found a great spot for A-B-A testing really close to me! It's a nearly four mile stretch of "tree-tunnel" so winds should be minor, and on the weekend and at night, there is very little traffic. I don't have cruise control, but I'm used to holding my right foot steady while watching the TPS on my Scanguage. So if you are following this thread and waiting for proof, I should have some definative results posted by this weekend.:thumbup:

:thumbup::thumbup::D
I am impressed at what you're doing with a Jeep!

Good luck with the A-B-A testing. I can't wait to see the results.

BTW: If you have the time, try to sqeeze in an extra 'B', so your testing is A-B-A-B.

This definitely gives me inspiration. Jeeps are such practical, fun vehicles, but the MPG sucks. If there's a way to at least fix the highway mpg a bit, then that makes it even better!

When addressing aerodynamics to my Jeep, I look at all the research and developments being done in commercial trucking, since they too are boxes on wheels, albeit much larger.

Check this idea:

Trailer Innovations: Aerodynamic Enhancement Products for Tractor Trailers

test and verify 1st,make claims afterwards
 

I anticipate that they will be very disappointed with their results.They should have proved it out before they smelled green.
Also,they should have done a more thorough patent search,as this form has already been investigated,if not already within a patent application.

A-B-A Testing - Saturday
 

Sorry guys, I didn't have the time or money to spend on the gas to do some proper testing last week. But I've got a full tank and plenty of time on saturday to try it out again. I'll post the results here as soon as they are finished.

U.S.Patent # 4,257,641
 

Edgar L. Keedy of Liberty Center,Ohio received this Utility patent in Mar.24,1981,for a very similar invention.

Defiantly not stealthy, but from the initial testing you may just fly by my numbers in a matter of no time. :thumbup:

I would suspect he's done his turn with "B" testing. (AKA "beforehand" testing)

let him catch up with a few "A" tests. :D

Check out my wooden spoiler! It has a definate effect on my FE
 

Ok, I'll admit I got derailed this weekend, but it isn't over yet. I have still some time tonight to get that test in. But in the meantime, wanted to bring up something, mostly usefull for us "hatchies" but for everyone else out there that just wants to haul some stuff that's oddly shaped. I picked up a hitch carrier on Craigslist for $20 a few months back and it has been integral in my initial aeromod designing, as well as simple utility.

Today is a prime example: I wanted to pick up an 80lb computer desk/hutch, and while I drive a box, it's not a very large box.

http://i745.photobucket.com/albums/x...cket_2890_.jpg

That carrier gets itself right behind the bumper, and doesn't really affect the airstream, and as long as nothing protrudes beyond the profile of the vehicle, it's almost like nothing is there, except for the added weight. Notice in the photo below that tbe desk in all of it's ratchet-strapped glory sits about eight inches above my roofline. had to drive 40 miles to get the thing so--- here's the results:

going to Seattle FE: 25.1 (almost my best ever)
coming from Seattle FE: 23.5 (not too shaby)

While this is not conclusive, it is demonstrating one thing to me: my normal pulling a trailer FE ONLY on the freeway is between 16-20. This is much better, as it only affects one leg of the trip, and even then, for much less of a penalty.

Ok, I'm getting ready to head out in a minute, strap on the kamm, and get some testing done.

Kamm A-B-A tests are in
 

Ok, so this was my methodology for these tests so I can control everything as much as possible:

1. accelerate to 50 mph holding the throttle at 16% open the whole time
2. use gps/scangauge to keep speed as even as possible (49-51) and keep foot even and steady (TPS on scangauge and listening to the engine).
3. 4 mile course, no traffic, no wind, two turns but nothing to slow down for, very little elevation change
4. prewarmed/driven vehicle

The course is 4 miles out, check fuel, turn around, reset, 4 miles back.... rinse repeat

So here's my results for this 50 mph test (in gallons of fuel used per run):

First A Sets (Kamm attached):

.17
.15
.16
.15
.16
.14
.16
.14

Average: .15375 gallons for 4 miles or 26.02 MPG

B Sets (no Kamm):

.17
.16
.17
.16
.17
.15
.17
.16

Average .1625 gallons for 4 miles or 24.62 MPG

Second A Set (Kamm back on):

.16
.15
.16
.15
.16
.14
.16
.15

Average: .15375 gallons for 4 miles or 26.02 MPG... again

In conclusion, there is a difference, but I doubt it would normally be this great at 50 MPH. I need to find a longer test track where I could maybe go ten miles and get more accurate fuel usage/run data. This data shows a 5.6% increase in FE with Kamm on versus Kamm off. When compared to what the EPA average is for this vehicle of 15MPG, 1.4 MPG extra is 9.3%. Also, I know this aeromod should perform better when comparing it at 60-65 MPH, where aero is more of a factor.

Bottom line: there are improvements to be made to my design, especially in the neighborhood of transitions. I'm thinking for starts - a second layor of 6 mil plastic, attached with black tape and heat shrunk to fit right might improve a lot of places.

I'm worn out, and going to bed. I probably didn't explain myself clearly enough on everything tonight, so post a question and I'll get back to you tomorrow.

BTW: I'm still rocking that ratchet strap to hold on the top of the kamm. I managed to hide the bulk of the mechanism a lot better from the wind this time though.

Since you have a Scangauge, just use it to calculate mpg. I think those fillup numbers are way too small to get anything meaningful out of them.

- Update -

I haven't been on here in a while, had some personal emergencies come up, and moved, blah blah blah...

I hate to say it, but in my earlier testing I think my foot was still a little biased and the track was too short. I did drive with it on for a couple of longer trips (80 miles each way) and now I think the mileage increase is more around the 2%, rather than %8 or so.

Even worse, is somehow it got hit while my car was parked back in October and subsequentially tossed (although I did take it to get recycled as it's all plastic) as it was beyond repair. While I didn't get my money's worth in the investment, it was nice to build such a concept piece and try it out. I might make another in the future now that I've learned some lessons and from my early mistakes. I think I'm going to stick to cleaning up my undercarriage first before I go and mod the rear end (again).

Sorry to hear about the Kamm:( Hopefully version #2 will be even better, and cleaning the flow under the car will also help the new Kamm. Good luck:)

Get a full width skid plate, then build off of that.

Skidplate
 

I'm looking at this one from DPG Offroad - either that or I'll get a local shop to bend one for me based on these pictures and some custom measurements.

From the side:
http://www.dpgoff-road.com/images/pr...yinstalled.jpg

From the back:
http://www.dpgoff-road.com/images/pr...installed1.jpg

Instaling the plate won't be all that hard; building around the driveshaft, springs and axles will be the tough part. Not to mention insulating the area around the exhaust. Maybe I'll get lucky and find some place that has recycled street signs like I saw on a post here with a Subaru STi. I'll open another build thread when I do get to that point.

updates! we need updates! we care!

Updates
 

Moved to GA for some job training, but last weekend I starting fabricating a front air dam to push the airflow under my front suspension out of black coroplast, aluminum angle stock and rivets. Pictures to follow later on today of where I'm at on it. Here is my shopping list so far:

$14 - (1) 4x8 sheet coroplast
$8 - (2) 16GA aluminum angle 8 ft stock
$4 - (2) 3/16 aluminum rivets 50 pack
$2 - (1) small angle bracket pack
$3 - (1) small 90 degree joice pack

The prices are each so the total investment is $43.

FastPlastic: I wish I had your skills with sheet metal, but I'm going to have to live with my beating/hacking on coroplast for this one.

Clean up the front end
 

Well, my plan was to finish the pics last night, but I got distracted as always. :D

http://ecomodder.com/forum/attachmen...1&d=1308394506

The first pic is just the naked front end, but you'll notice that since I don't have a stock front end anymore (below, courtesy of FastPlastic), I lack the air dam that kept most of the air out of my suspension.

http://ecomodder.com/forum/attachmen...1&d=1308394506

so this is my remedy for that. It's actually a square sheet, but the picture makes it look odd. Also it should be noted that it will clear my tires at full turn by about 2 inches

http://ecomodder.com/forum/attachmen...1&d=1308394506

As far as attachment points, in the front I plan to tie into the built in ones behind the bumper face (normally where you would relocate the vacuum ball from the stock setup). As far as the rear end goes, I will either drill and make a bracket on the front end of the lower control arm mounts and allow it to self-adjust based on suspension travel. Or else I may have to hang the piece off of the framerail before the suspension and find another way to support it.

Looks good:thumbup: I don't remember if I really showed it but my panel actually gets smaller the father back it goes(Kind of a V shape), gave me more surface area in the front that way. I also found on the frame is a threaded hole, after a few quick test bolts I found the one that fits. here's the bracket I made, but I would recommend a little beefer one if go this route as mine is all bent out of shape and needs to be redone(plowed too many snow drifts).http://ecomodder.com/forum/attachmen...p;d=1215721692

Cherokee Air Dam Installation
 

Down to business

Here's the bracket I made using an existing hole in the body:
http://ecomodder.com/forum/attachmen...1&d=1308426651

Both brackets in a frontal view:
http://ecomodder.com/forum/attachmen...1&d=1308426651

Here's a shot of the top of the pan:
*The larger hole on the right hand side, that is so that I can still access the winch clutch.
http://ecomodder.com/forum/attachmen...1&d=1308426651

Partially hung dam, still mocking up the side panels:
http://ecomodder.com/forum/attachmen...1&d=1308426651

Completed side panel:
*There were small spaces in the back of the bumper to fit those 'tabs' into, almost like it was a part of the design!
http://ecomodder.com/forum/attachmen...1&d=1308426651

Everything buttoned up on the ground:
http://ecomodder.com/forum/attachmen...1&d=1308426651

http://ecomodder.com/forum/attachmen...1&d=1308426651

http://ecomodder.com/forum/attachmen...1&d=1308426651

I thought I was going to sweat to death getting this thing together, but it all worked out. Overall I'm absolutely pleased and cannot wait to see where this puts my highway mileage. I've only taken it up to 75 MPH for about ten miles to feel for any shimy and check to ensure it's safe to operate the vehicle. I will say that the Jeep seems to coast A LOT further when I NC (Neutral Coast). I'd love to do some A-B-A Testing with it, but it's a total PITA to put on and I'll assume take off. It is nice to only have the very bottom of the front differential and the lower portion of the control arm exposed. The lower edge sits about .75 of an inch lower than the axle.:D