Roof Spoiler on Pick-Up Truck Cab - Phase-1

[kach22i]

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




EDIT IMAGE ABOVE: A connector on the leading wing edge has since changed the angle to zero, matching the aluminum support.



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


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







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

[aerohead]

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]

Originally Posted by aerohead

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



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]

Originally Posted by kach22i

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



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]

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

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

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]

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]

The truck looks beefy! Nice.

Perhaps it's better to approach this as a partial Kammback, not a spoiler?

[kach22i]

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

Originally Posted by Sven7

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.

Originally Posted by aerohead

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]

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


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]

Originally Posted by kach22i

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







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.