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-   -   Roof Spoiler on Pick-Up Truck Cab - Phase-1 (https://ecomodder.com/forum/showthread.php/roof-spoiler-pick-up-truck-cab-phase-1-a-19525.html)

kach22i 11-18-2011 02:48 PM

Roof Spoiler on Pick-Up Truck Cab - Phase-1
 
1 Attachment(s)
I need some extra eyes on this little experiment. I've been reading that a sharp edge on the roof of a pick up truck is even more effective than a bed cover, and works best with a cover (I have one).

The situation is that I've beveled the underside of the smoked acrylic spoiler/wing to mount flush with the rolled edge of the roof. I fully intended to use silicone caulk and hold the tips down with some tape while it set up. Should that fail or pop up later, I would resort to a fastener of some kind.

However, prior to gluing it all down and caulking I'd like to consider all of my options. To my eyes I currently have a wing, a strange inverted wing to say the least.

Please note that the rear edge of the roof spoiler/wing is a 90 degree cut, no bevel, cant, or angle involved.

S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...WING-ABOVE.jpg
http://i184.photobucket.com/albums/x...OVE-DETAIL.jpg
http://i184.photobucket.com/albums/x...WING-BELOW.jpg
http://i184.photobucket.com/albums/x...LOW-DETAIL.jpg
EDIT IMAGE ABOVE: A connector on the leading wing edge has since changed the angle to zero, matching the aluminum support.
http://i184.photobucket.com/albums/x...ING-FINGER.jpg
http://i184.photobucket.com/albums/x...GER-DETAIL.jpg

Should I bend those tips down and caulk as planned?

I'm thinking of doing a little test driving first. I'll have to zip tie the leading edge of the roof spoiler to the aluminum channels to prevent wing/spoiler flapping as there is only a single thru-bolt near the rear edge and it could act as a hinge at speed.

THE QUESTION.................and options.

1. Leave "as is" and hope it's a wing or spoiler.

2. Bend down and caulk.

3. Gorilla tape the existing open joint, that way the gap is closed and level with the aluminum channel spar and roof plane. If this works, work on making it better in the spring.

EDIT-1: Maybe this flow chart will help.
MORE random pics...... - Page 1955 - Pelican Parts Technical BBS
http://forums.pelicanparts.com/uploa...1321567231.jpg

EDIT-2:

I did not want to mess with messy caulk or temporary tape until I did some road testing. I added a thru-bolt and lock nut to the spoiler/wing to prevent it from acting like a hinge. I may have to put couple more holes in my roof to secure the aluminum channels and prevent some see-saw action. The existing screws are only 6" apart and can be rocked via the deflection in the thin sheet metal roof. I will use automotive plugs and sealant to close up the holes in the roof when the experiment is over. I have similar plastic plugs in the tailgate from a NASCAR style spoiler I installed a couple of years ago and have since trimmed down.

More photos, about a dozen more in link:
S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...k%20Up/wn6.jpg
http://i184.photobucket.com/albums/x...k%20Up/wn9.jpg
http://i184.photobucket.com/albums/x...%20Up/wn10.jpg
http://i184.photobucket.com/albums/x...%20Up/wn13.jpg
http://i184.photobucket.com/albums/x...k%20Up/wn1.jpg
http://i184.photobucket.com/albums/x...k%20Up/wn2.jpg

EDIT-3:
This is the thread and image which got me going.
http://ecomodder.com/forum/showthrea...ver-124-2.html

aerohead 11-19-2011 03:03 PM

spoiler
 
The 'cab wings' tested by Texas Tech were no shorter than 24-inches if memory serves me.And they were all angled downward.
Optimums of length and inclination varied as a function of short-bed/long-bed.
I can put my hands on that paper,but Al is closing for the Thanksgiving holiday next weekend.I'll try to get in during the week and post.

kach22i 11-19-2011 03:56 PM

Quote:

Originally Posted by aerohead (Post 271021)
The 'cab wings' tested by Texas Tech were no shorter than 24-inches

I had no idea it could be that large, I had trouble finding images on my own and the ones I did find were not much larger than what I ended up with. The other thread offered no photos, just the tiny diagram images.

I just used my largest scrap left over from my hovercraft elevator project.

Pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...ch22i/FIN2.jpg
http://i184.photobucket.com/albums/x...ch22i/FIN1.jpg

On the hovercraft the sheets of acrylic help straighten out the swirling flow from the fan blades.

Back to the truck:
In theory, vortexes will form at the top of cab corners. The tips of the wing stop short of the top corners by about 2 inches. Either this is a good thing by getting out of the way, or I missed the boat on influencing/controlling vortex generation.

aerohead 11-19-2011 04:35 PM

large
 
Quote:

Originally Posted by kach22i (Post 271032)
I had no idea it could be that large, I had trouble finding images on my own and the ones I did find were not much larger than what I ended up with. The other thread offered no photos, just the tiny diagram images.

I just used my largest scrap left over from my hovercraft elevator project.

Pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...ch22i/FIN2.jpg
http://i184.photobucket.com/albums/x...ch22i/FIN1.jpg

On the hovercraft the sheets of acrylic help straighten out the swirling flow from the fan blades.

Back to the truck:
In theory, vortexes will form at the top of cab corners. The tips of the wing stop short of the top corners by about 2 inches. Either this is a good thing by getting out of the way, or I missed the boat on influencing/controlling vortex generation.

Some of the wings were as large as 32-inches in length.
Doing top and sides would be better than just the top,but it would impact bed utility.

kach22i 11-19-2011 10:36 PM

Did some more research. Pages 55-58, the conclusion on "rear roof garnish" is not exactly what I had in mind. Their "garnish" is set at a 12 degree downward angle, and I'm guessing about 6 inches deep.

PDF link:
http://csus-dspace.calstate.edu/xmlu...pdf?sequence=1

Quote:

Table 4.2.1 presents the overall effect of using rear roof garnish. It shows that by attaching Rear Roof Garnish to the baseline truck model, aerodynamic drag coefficient Cd was reduced by about 2.4%;
however, the lift coefficient Cl was increased by about 33%
I think that if I were to bend my roof spoiler down 12 degrees and caulk or foil tape the joint/connection I could expect similar results.

Right now my spoiler/wing/garnish is flat, and allows boundary air under it. I should not get the same amount of lift, but that remains to be seen. I'll take safety over mpg gains any day of the week.

EDIT 11/21/11: This is pretty close to what I am first testing. Tonight I get to do some serious highway driving, will be doing more driving tomorrow as well (I work from home).

The Recumbent Bicycle and Human Powered Vehicle Information Center
http://www.recumbents.com/car_aerody...an_spoiler.png
Quote:

Additional mods for Vans and SUVs::
A new spoiler design has been shown to reduce drag and lift significantly on bluff-backed vehicles such as minivans and SUVs. Simulations showed that aerodynamic drag on a mini-van moving at 67 mph were reduced by 5% when the new spoiler was attached. This rear spoiler acts like a diffuser when it is attached to the back of a vehicle, making the pressure on the back of the vehicle higher than without it. That's a good thing!

Full technical paper ($22)
A Rear Spoiler of a New Type that Reduces the Aerodynamic Forces on a Mini-Van
NOTE: Last night I added plastic automotive button head plugs to the open holes on the trailing wing edge. I snipped and did some grinding to make it flush on the bottom (they were too long). I used a butane torch lighter to soften the plastic plugs before inserting, as they were a bit tight and got stuck half way in a test fitting.

aerohead 11-22-2011 04:51 PM

Texas Tech data
 
These values were published in Texas Tech's SAE Paper# 881874:'Pickup Truck Drag Reduction-Devices That Reduce Drag Without Limiting Truck Utility'
* For short bed pickup,drag min was achieved with a 24-inch wing @ 12-degrees ( a 19" wing @ 11-degrees was almost as low) and 1/2 tonneau cover [ back 1/2 ].
*For a long bed pickup,a 32" wing @ 8-degrees had the drag minimum when combined with the 1/2-tonneau.
*17 % drag reductions were measured.
* An 'aeroshell' provided a 20% drag reduction.

Sven7 11-22-2011 05:11 PM

The truck looks beefy! Nice.

Perhaps it's better to approach this as a partial Kammback, not a spoiler?
http://4.bp.blogspot.com/_Ak_mOrsdsx...x_kammback.jpg

kach22i 11-22-2011 11:12 PM

Tonight I drove an hour in the rain on a secondary road, speeds 45-55 mph to get to a hovercraft owner's meeting (1/2 hr there, 1/2 hr back). Just a seat of the pants feeling tells me I'm getting a little down-force in lieu of a lot of lift.

I'll be doing some distance driving for Thanksgiving and will start calculating fuel consumption.

Here are some photos of the holes I plugged up.

S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...top-detail.jpg
http://i184.photobucket.com/albums/x...der-detail.jpg
http://i184.photobucket.com/albums/x...verall-top.jpg
http://i184.photobucket.com/albums/x...i-close-up.jpg

Quote:

Originally Posted by Sven7 (Post 271418)
Perhaps it's better to approach this as a partial Kammback, not a spoiler?

I think that would work on a S-10 Blazer very well, but could look a little weird on my truck. I'll be thinking about it, thanks for the idea.

Quote:

Originally Posted by aerohead (Post 271417)
These values were published in Texas Tech's SAE Paper# 881874:'Pickup Truck Drag Reduction-Devices That Reduce Drag Without Limiting Truck Utility'................

Does that data mention lift? The thesis I found talked about a lot of lift created which is typical of drag reducing devices.

Do you have anything on roof wings verses these flush plane spoilers?

I think my current state is acting as a wing, but I require more seat time to be sure.

kach22i 11-25-2011 11:43 AM

It is too early too tell for sure exactly the results of my experiment are so far, but I have an idea where I am headed. I drove 100 miles last night, mostly highway. About half the trip was 70 mph with some construction slowing us down to 60 mph for limited amounts of time. The second half is secondary highway 45-55 mph. This is the same route I took two years ago to get to work when I first started my spoiler experiments.

I am defiantly getting down-force, and lots of it. When I drove in the rain a few nights ago at around 50 mph I did not fear for my life and want to pull over to lock the hubs into 4WD as is typically the case. This was my first clue.

Last night I'd guess the down-force increase was close to 200 lbs at 70 mph, and 100 lbs at 50 mph. This is about half-way in between the force I remember experiencing when I installed a really tall rear spoiler with support spars (see Photobucket album picture - http://i184.photobucket.com/albums/x...20Up/GUR-4.jpg).

I'd like to take the truck up to 85 mph for a short blast after obtaining my fuel mileage estimates. I bet the down-force would be massive, as it increases a lot with speed.

Right now I 'm pretty sure that I'm consuming more gas than normal. However it could save me gas this winter if it extends 2WD use and has me locking it into 4WD less often. Kind of a draw really, just a thought at this point.

Here is a diagram with my thoughts of what is occurring.

S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...ck-diagram.jpg

The diagram is not totally arbitrary or "made up". I did notice more deflection and rippling in the tonneau cover (in the last two support spar areas) as I looked in my rear view mirror, a speed spike at 75 mph while passing made things even more obvious.

My wife said she could feel the difference too. She said the truck felt more planted. Even though the truck is an automatic it felt to me as if I needed to shift up a gear. This is kind of similar to the torque hold down force I get in my old Porsche 911 by keeping it revved up at 5,500 rpm in a turn or while driving in the rain. The lower gear with high rpm's just keeps the car planted, the truck was getting similar results aerodynamically and not through torque. I was also impervious to cross winds last night which was nice. No lane wandering, the truck tracked nicely.

What is the best way I can verify this flow diagram? I have no wind-tunnel, no smoke generator. I don't think wool tufts are going to tell me much, or will they?

aerohead 11-28-2011 06:50 PM

lift
 
Quote:

Originally Posted by kach22i (Post 271485)
Tonight I drove an hour in the rain on a secondary road, speeds 45-55 mph to get to a hovercraft owner's meeting (1/2 hr there, 1/2 hr back). Just a seat of the pants feeling tells me I'm getting a little down-force in lieu of a lot of lift.

I'll be doing some distance driving for Thanksgiving and will start calculating fuel consumption.

Here are some photos of the holes I plugged up.

S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...top-detail.jpg
http://i184.photobucket.com/albums/x...der-detail.jpg
http://i184.photobucket.com/albums/x...verall-top.jpg
http://i184.photobucket.com/albums/x...i-close-up.jpg



I think that would work on a S-10 Blazer very well, but could look a little weird on my truck. I'll be thinking about it, thanks for the idea.



Does that data mention lift? The thesis I found talked about a lot of lift created which is typical of drag reducing devices.

Do you have anything on roof wings verses these flush plane spoilers?

I think my current state is acting as a wing, but I require more seat time to be sure.

Reduced lift was a side benefit of the drag reduction.I don't have the paper with me so I can't give you any particulars.

kach22i 11-30-2011 01:01 PM

Quote:

Originally Posted by aerohead (Post 272222)
Reduced lift was a side benefit of the drag reduction.I don't have the paper with me so I can't give you any particulars.

If that is what you remember then I'm hopeful of doing more alternates on this basic design. I was under the impression that drag reduction typically means lift increases, and that drag increases are related to down-force generation.

Of course, there are always exceptions to the rules, and that is where my energies will be focused.

SvdM 12-09-2011 11:39 AM

Nice project. I have something similar planned for early 2012.

kach22i 12-09-2011 12:01 PM

Quote:

Originally Posted by SvdM (Post 273982)
Nice project. I have something similar planned for early 2012.

Great, I'm convinced there is great potential for increased safety with this approach, still working on that "saving gas" part myself.

When I hit potholes the wing does rock and tap on the roof a little, so those extra roof screws are going in soon.

The few times I've driven with ice and snow filling the gap I could have sworn there was less down force. I will need to foil tape the gap in the spring and do some real testing. Right now I'm pretty happy where I'm at on this project.

I just hope my vinyl bed cover survives the winter, this is the first winter I'm leaving it on.

EDIT: One inch of snow, sitting overnight and all day in dry air, driven at 45 mph for 1-2 miles to the gas station. There was quite the dust devil of swirling going on as I looked in my rear view mirror. Here is the resulting pattern it left.

S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...k%20Up/ts1.jpg
http://i184.photobucket.com/albums/x...k%20Up/ts2.jpg

To my eyes; the vortex of air coming off the cab corners is intact and healthy. The mysterious middle scoop of missing snow, and small drift against the glass might be the trapped vortex of rotating air I've shown in an earlier diagram.

I should note that the snow was only brushed off the front windshield and hood, the roof snow and tonneau cover snow was left virgin prior to driving off.


EDIT 12/10/11
S10 4x4 Pick Up pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...ck-diagram.jpg

http://s184.photobucket.com/albums/x...4%20Pick%20Up/
http://i184.photobucket.com/albums/x...of-swirl-1.jpg

kach22i 12-09-2011 11:37 PM

This VW Bug wing seems to have a few similarities to my own little experiment. I'd sure like to see a wind-tunnel of this to see how the gaps are contributing.

Automobile pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...e/DSCF4703.jpg
http://i184.photobucket.com/albums/x...e/DSCF4698.jpg
http://i184.photobucket.com/albums/x...e/DSCF4699.jpg
http://i184.photobucket.com/albums/x...e/DSCF4700.jpg
http://i184.photobucket.com/albums/x...e/DSCF4702.jpg
http://i184.photobucket.com/albums/x...e/DSCF4701.jpg

Sven7 12-10-2011 12:27 AM

Quote:

Originally Posted by kach22i (Post 273987)

To my eyes; the vortex of air coming off the cab corners is intact and healthy. The mysterious middle scoop of missing snow, and small drift against the glass might be the trapped vortex of rotating air I've shown in an earlier diagram.

I should note that the snow was only brushed off the front windshield and hood, the roof snow and tonneau cover snow was left virgin prior to driving off.

That's some great real world experimentation right there. I reckon with the spoiler pointed down 10 degrees and some buttress type fairings on the side it could really reduce the wake you're seeing on there. Of course you probably won't get the extra downforce of your current spoiler but you'd get gas savings! There's a thread somewhere of a Toyota Sienna with the side fairings. I'm not even going to attempt finding it. :p

kach22i 12-12-2011 11:28 AM

Quote:

Originally Posted by Sven7 (Post 274079)
That's some great real world experimentation right there.

The basis of all science is observation (and experimentation), right? Once you learn to keep your eyes open, you will see many things which you would normally not.

I did not plan nor expect this to happen, but when I was walking toward the truck that morning I had a hope, and that hope was confirmed.

Phase II?......smaller less energy robbing vortexes?
Industrial Design - Transportation pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...ortex-ts2b.jpg

Boeing 737 Advanced Blended Winglets
http://www.b737.org.uk/images/737winglets.jpg
http://www.b737.org.uk/images/winglet_side.jpg


As The Croft Flies: December 2010 Archives
Quote:

#MEBA10: Winglets 101
By John Croft on December 6, 2010 12:36 PM

Walking the ramp here at the Dubai International airport on the eve of the Middle East Business Aviation (MEBA) show, I happened on a good example to show the difference between blended winglets and elliptical winglets.

http://www.flightglobal.com/blogs/as...ts_compare.JPG

Blended winglets are the intellectual property via patent law of Seattle-based Aviation Partners..

Elliptical Winglets are the intellectual property via patent law of Wichita-based Winglet Technology, the founder of which used to work for the former.

Needless to say, they don't like it when you get the two technologies mixed up, despite the fact that both increase maximum load and increase cruise range.

So here's the deal:

Blended winglets as seen on the Boeing Business Jet (B737) in the background consist of a straight winglet joined to a straight wing via a curved joint.
Elliptical winglets, shown in the foreground on a Cessna Citation X, consist of a constantly curving winglet joined to a straight wing.
.

kach22i 12-12-2011 01:05 PM

Phase III...............winglets/fins on rear

Inspiration.
GALLERY>>ICONIC PORSCHE LIVERIES - Speedhunters
http://ll.speedhunters.com/u/f/eagam...viers_pink.jpg
Quote:

The Porsche 917 is a beautiful car, even better in coupe trim. In 1971 Porsche commissioned an Aerodynamics company, SERA to analysis the 917 and develop a more efficient car. The organisation discovered that by making the car wider, the wheels would be inboard and be create less turbulent air. The car made its debut at a test in plain white. The bulging bodywork with the inset wheels reminded journalists of a Pig with its relatively small feet and thus, the idea of the Pink Pig was born.
One possible application; Scheme 4-Corner Winglets
Industrial Design - Transportation pictures by kach22i - Photobucket
http://i184.photobucket.com/albums/x...nglets-ts1.jpg

EDIT-1
At the risk of sending my own thread into the "Off Topic" zone, I post this.

Saab: phoenix at geneva motor show 2011
saab: phoenix at geneva motor show 2011
Quote:

Based on a highly aerodynamic, 'aeromotional' design that highlights the aviation roots of the company,
the car features a low front and cabin, which flows into a hood and tapered rear deck.
side and roof-mounted winglets, modeled after the flying buttresses of architectural planning,
channel airflow from the sides of the vehicle across the rear deck to reduce lift.
http://www.designboom.com/cms/images.../phoenix01.jpg
http://www.designboom.com/cms/images...nix-geneva.jpg

These winglets or what every they are, seem to form a second skin which controls vortex formation.

Perhaps a hollow cylinder, half cylinder or hoop which is aerofoil in section and set at the locations I've already indicated would work at controlling vortexes.

http://www.designboom.com/cms/images...nix-detail.jpg

EDIT 12/13/11
Something like this on the back of a pick-up truck cab would be clean and simple.

http://www.fitfreak.net/forums/gauge...o-spoiler.html
http://i53.photobucket.com/albums/g5...mageFromDB.jpg

EDIT again 12/13/11..............more fins on a car.
http://www.metaphorsinmotion.com/pos...-Chaparral-2-C
http://www.metaphorsinmotion.com/upl...jpg?1226443276
http://www.metaphorsinmotion.com/upl...jpg?1226443214

EDIT .....................wild thing.
http://forums.nasioc.com/forums/show....php?t=2233025
http://www.thedetroitbureau.com/wp-c...ce-drawing.jpg

EDIT.....this may actually work - who would have thunk?
http://www.indiancarsbikes.in/auto-n...tures-2-18171/
http://www.indiancarsbikes.in/wp-con...wing-image.jpg
http://www.indiancarsbikes.in/wp-con...rear-image.jpg

aerohead 12-13-2011 06:40 PM

Ferrari
 
See if you can find an image of Ferrari's 599 XX car.It has C-pillar buttress winglets which help get air onto the rear spoiler with minimum drag.
They spent a couple hundred hours in the wind tunnel ( $2oo,ooo) to dial them in.They would be an example of current-think which actually performs.
You're going down a lonely path.There's very little literature on such things.Good luck!

KamperBob 12-13-2011 07:31 PM

Kach22i. when I look at the snow pattern on your tonneau it seems intuitive. Snow deposited behind the cab could be explained by a pair of mirror symmetric separation bubbles. Think about boundary conditions and flow balance as a visual. Flow wants to converge convexly over the bed. Given the rear wing likely reattachment there. In between lies a typical open bed bubble but shallower due to the raised bottom with the tonneau and, moreover, cleaved down the middle by forward flow. The forward stream could drop its load up against the back of the cab in the sharp turns and reduced velocity. (This same principle is used in wood working in the form of a chip separator can before the dust collector bag on table saw exhaust port for example.) The assymetry left to right could be explained by a bit of cross wind effect. I'm skeptical about much roof corner vortex because that edge is radiused a couple inches, but experimenting will tell for sure. Either way I look forward to more. Nice contribution. Rock on!

kach22i 12-13-2011 08:55 PM

Thanks for the leads and encouragement guys.

Ferrari 599XX side wing photo
http://media.caranddriver.com/images...-s-520x318.jpg
http://media.caranddriver.com/images...s-1280x782.jpg

Ferrari 599XX winglet Wallpaper | Walltor
http://www.walltor.com/images/wallpa...glet-24296.jpg

EDIT.....some more ideas floating around in my head, Stratos inspired.

http://s184.photobucket.com/albums/x...4%20Pick%20Up/
http://i184.photobucket.com/albums/x...k-foil-ts2.jpg
http://i184.photobucket.com/albums/x...rear-truck.jpg

EDIT-2............this plane fence gives me ideas.
http://www.a2wt.com/Pictures.htm
http://www.a2wt.com/images/A2web/A2%...20COT%2006.JPG

EDIT-3: ....another roof wing
http://www.iwsti.com/forums/gr-vendo...-2008-sti.html
http://i206.photobucket.com/albums/b...tex/P1-2-2.jpg
http://i206.photobucket.com/albums/b...oltex/p1-3.jpg

...........and another.
http://www.iwsti.com/forums/styling-...-all-sale.html
http://www.z1auto.com/images/roofvanezerosports.jpg

aerohead 12-15-2011 06:38 PM

Lebu
 
You may also want to dig up NASA's 'Large Eddy Break Up device,investigated for aircraft fuselage many years ago.I don't remember that they had any success with it,but the more info the better.

ChazInMT 12-15-2011 07:46 PM

I hate to be a wet rag on your fire here, but keep in mind that these winglets you are discussing are all fine tuning enhancements on vehicles which are very aerodynamic to begin with. They effect only a small amount of airflow around the vehicles. Putting these things on a pick-up truck which has the aerodynamics of a shaped brick is IMHO a waste of time and energy. You need to do things that affect mass amounts of air in order to see anything that is going to make an appreciable difference. Building a 2 ft kamm sorta thing on the front of your cargo box would probably net you the biggest easiest gain, a full on aerocap, would be better yet. Anything you do will be optimized by following the template.

Just sayin.

http://i41.tinypic.com/5efvvp.jpg

kach22i 12-15-2011 10:40 PM

Quote:

Originally Posted by ChazInMT (Post 274959)
I hate to be a wet rag on your fire here, but keep in mind that these winglets you are discussing are all fine tuning enhancements on vehicles which are very aerodynamic to begin with. They effect only a small amount of airflow around the vehicles.

I can appreciate your point, it is a good one. I must have my fun trying the weird and implausible before surrendering to the tried and true.

From a post/thread back in 2004 talking about "LEX Fences" and such.

Question for the Aero Experts - Page 2 - Pelican Parts Technical BBS
http://www.aerospaceweb.org/question...f18-fence2.jpg
http://forums.pelicanparts.com/uploa...1109602866.jpg

I did some highway driving today, the thought of attaching 24" long x 6" dia. PVC tubes at the edge corners on the roof and at the tail of the bed top came to me. The idea would be to tunnel/tube shoot some ram air where vortexes would normally start to form. Not my best idea, but I go though a lot of them. Then one day the urge to build slams me and I do something nutty and rather spontaneous.

Stay tunned.;)
http://s184.photobucket.com/albums/x...4%20Pick%20Up/
http://i184.photobucket.com/albums/x...ubes-truck.jpg

The tube idea really started as a pod idea, sort of F-104 and Caddy Tail Light.

http://ckparis.blogspot.com/2009/05/...-fins-and.html
http://1.bp.blogspot.com/_AQP6ii7exN...caddy+fins.jpg

http://s184.photobucket.com/albums/x...4%20Pick%20Up/
http://i184.photobucket.com/albums/x...ch22i-pods.jpg

EDIT 12/16/11
I found a patent somewhat similar to the trail edge/corner thing I've been thinking about. Again, a wing, and not a box (truck cab).

http://www.wikipatents.com/US-Patent...ing-tip/Page-1
http://www.wikipatents.com/vortex-re...S4108403-1.jpg

http://www.britmodeller.com/forums/l...hp/t72943.html
http://gbg-pop.pixbox.se/arkivet/syn...0/32511335.jpg
http://gbg-pop.pixbox.se/arkivet/syn...0/32613672.jpg

sc2dave 12-15-2011 11:39 PM

IIRC, those fins you refer to as LEX fences are called vortex generators.I worked on these F/A-18 jets in the service back around '91

Frank Lee 12-15-2011 11:47 PM

200 lbs of downforce? I suspect that if I pressed down on that wing with 200 lbs of force you would hear your roof rippling.

kach22i 12-15-2011 11:50 PM

Quote:

Originally Posted by sc2dave (Post 274988)
IIRC, those fins you refer to as LEX fences are called vortex generators.I worked on these F/A-18 jets in the service back around '91

Read post #28
Question for the Aero Experts - Page 2 - Pelican Parts Technical BBS

You are right.

The concept or lesson here is that vortexes can be tools and do a job.

kach22i 12-15-2011 11:54 PM

Quote:

Originally Posted by Frank Lee (Post 274990)
200 lbs of downforce? I suspect that if I pressed down on that wing with 200 lbs of force you would hear your roof rippling.

I know what two, 65 lbs (130 lbs) of tube sand feels like over my rear axle.

I drew a diagram and stated that the increased down-force was because the rear spoiler was made more effective.

What part do you not understand Frank Lee?

Frank Lee 12-15-2011 11:59 PM

I guess that's the part I did not understand! Well, it takes 20 min for all those quoted pics to load. :rolleyes:

viio 03-08-2012 11:34 AM

Did you ever get this thing modelled in CFD? I could knock something up for you?

kach22i 03-08-2012 02:11 PM

Quote:

Originally Posted by viio (Post 292107)
Did you ever get this thing modelled in CFD? I could knock something up for you?

No I did not. Real life and seat of pants only, which is best, right?

I would be curious to see if CFD could handle the tiny air gap between roof and wing.

Do it up, I'll owe you a beer.:D

viio 03-08-2012 05:47 PM

Okay I put a couple of hours on this tonight - please excuse the model it's slightly ghetto but it'll do the job. I re-used a couple of parts from other models. I also couldn't quite get the curvatures of the roof right so I've curved the spoiler instead to create the same gap at the edges. There's a higher quality render running right now and I'll post up pic once thats done.

*** Thumbnails are for the clicking ***

The spoiler I've bodged together:
http://i4.photobucket.com/albums/y14...10_spoiler.png

The velocity in the right plane before:
http://i4.photobucket.com/albums/y14...rightplane.png

The velocity in the right plane with the spoiler:
http://i4.photobucket.com/albums/y14...e_wspoiler.png

kach22i 03-08-2012 06:11 PM

Forgive me if I don't see a huge difference in the overall. I see a tiny bit more yellow hitting the rear spoiler, but not much.

Would it help to bevel the leading edge of the roof wing (down) as I did in real life?

I think it's 3/16" thick.

The rear spoiler is 45 degrees or greater.

7" to 8" gap under the front chin spoiler.

I can tell you that there are depression wells in the bed cover fabric while at speed, mostly between the last spar and tailgate but some in the middle one too.

I'd really like to see those corner vortex's forming. That is my next modification, to tame those suckers.

viio 03-08-2012 06:25 PM

The red is where the air is at it's lowest velocity (i.e. most dragged). The roof spoiler is keeping that slow air out of the truck bed and actually directing it to (and over) your rear spoiler. If you didn't have that rear spoiler at all you'd have less drag as the roof spoiler would be sending air into the wake rather than into another object (rear spoiler).

viio 03-08-2012 06:53 PM

I don't think you'll be getting vortexes by the way, at least not like the big blue ones you drew on. There's too much laminar airflow coming down the sides of the vehicle, it'll just push the air into the truck bed. 3d model coming up to show you what I mean.

viio 03-08-2012 07:01 PM

It's hard to see in the 3d view, but those vortexes are just getting swamped by airflow down the side and over the top of the vehicle.
http://i4.photobucket.com/albums/y14...h_bed-flow.png

These 3 give a better picture of whats going on in the truck bed:
http://i4.photobucket.com/albums/y14...ntopplane3.png http://i4.photobucket.com/albums/y14...ntopplane2.png http://i4.photobucket.com/albums/y14...intopplane.png

kach22i 03-08-2012 09:57 PM

Quote:

Originally Posted by viio (Post 292203)
The red is where the air is at it's lowest velocity (i.e. most dragged). The roof spoiler is keeping that slow air out of the truck bed and actually directing it to (and over) your rear spoiler. If you didn't have that rear spoiler at all you'd have less drag as the roof spoiler would be sending air into the wake rather than into another object (rear spoiler).

This is the opposite of what I've experience though.

My roof wing is actually directing air downward, doing so (I theorize) by removing the boundary level air though the slot and drawing the air above it down with it. This flow goes into the rear spoiler sooner and with more mass than without the roof wing. And yes, this means more drag, but I love the extra safety in bad weather.

This is the only way I can explain all the extra down force.

I'd be getting some lift and less drag according to the computer flow diagrams, this matches all the other data on "garnish" I've read. I think you did an accurate enough job, still wonder if the cant to the leading edge of the wing is responsible for extra redirecting of surface/boundary air.

I will have to tape some tuffs or longer strings in that area and film what's going on.

There must be a safe way to generate a small amount of smoke in front of the wing to record what is happening. Any ideas?

redorchestra 03-08-2012 11:44 PM

smoker can for bee hives?

viio 03-09-2012 02:36 AM

Well if nothing else you've got a bit more science to look at there. Want me to do another version with the roof spoiler aimed down some?

SvdM 03-09-2012 04:15 AM

I'd like to see that too (I vote for spoiler aimed down ~ 12?)

kach22i 03-09-2012 09:15 AM

Quote:

Originally Posted by viio (Post 292306)
Well if nothing else you've got a Lot more science to look at there. Want me to do another version with the roof spoiler aimed down some?

From what I've read a 10 or 12 percent downward angle on the "garnish" will net a +20% reduction in drag, but a +30% increase in lift. This is one of the reasons I never angled it down.

I would be interested if your "science" can measure this reported "lift", or at least graphically represent it.

I think for the most part your program underestimates the suction/flow of air though the small air gap between the end of the roof and the beveled leading edge of the wing. I do need to find a way to measure this alleged flow, smoke bomb in a coffee can on the roof?


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