Fool's Errand (Aeromodding GMC 2500HD)

[darcane]

Originally Posted by vskid3

darcane- Nice belly pan! I'm going to try to get away with mainly using zip ties, but your way looks like a good option.

Zip ties are adequate when the coroplast is supported and there are lots of places to attach to. Under the bumper, I found that it was just a lot of open space and I had to build some sort of frame. I was also concerned that if a zip tie or two in the wrong spot broke, it would act as a parachute and rip the remaining zip ties losing the whole belly pan. Using the screws and fender washers also makes it a very robust connection.

[vskid3]

I put the skirts on pause for now. What do you guys think about the amount of flapping I'm getting and what would be the best way to stop it if it's too much?

Started working on the belly pan. I did from the running boards under the cab on the driver's side to the frame. There's a bit of a lip under the outside of the running board that it's resting on and I cut out where the transmission brace is so it's kinda wedged up there. Zip tied it at 8 points to various brackets and holes. Tried to take a picture but it was too dark for it to show much with the flash, I'll post one tomorrow morning. I'll finish tightening the zip ties and take it for a test drive and hopefully return with it still attached.

I'm thinking of having the front piece rest on the bottom lip of the bumper so it can't get the parachute effect going if the front zip ties break. It'll be next after doing under the running boards on the passenger side.

I'm going to see about attaching smooth wheel covers to the center caps. Would a kammback on the back of the cab be helpful or would it hurt the existing air bubble that's formed in the bed? Kammback would be easier than a full aero cap to collapse and store for towing.

[BabyDiesel]

Originally Posted by vskid3

I put the skirts on pause for now. What do you guys think about the amount of flapping I'm getting and what would be the best way to stop it if it's too much?

IMO the flapping is better than it was, but is still less than optimal. To me, the flapping would still disrupt the airflow to a certain degree.

My design has had no flapping in over 6 months of being attached. I used 1/4" aluminum bar for a bottom frame, and 90* tabs drilled into the fender as attachment points.



The tabs used. These are from Lowe's


I cut the coroplast to fit, and then painted black. Painting the coroplast helps it last longer when it is exposed to sunlight constantly.


They have been at speeds of up to and maybe past 80 mph with no signs of distress

I'll finish tightening the zip ties and take it for a test drive and hopefully return with it still attached.

Zip ties will work. I have had my front and rear pans zip tied for around 6 months and they have held up great. Just make sure they are tight! Pic for reference.

I'm thinking of having the front piece rest on the bottom lip of the bumper so it can't get the parachute effect going if the front zip ties break.

Exactly what I did. I drilled a screw into the bottom of the front bumper through the coroplast, angled up towards the radiator. I have it rigged in such a way that when I tighten the zip ties down, it pulls and holds the coroplast down on this screw. The duct tape is no longer there FYI

I'm going to see about attaching smooth wheel covers to the center caps. Would a kammback on the back of the cab be helpful or would it hurt the existing air bubble that's formed in the bed? Kammback would be easier than a full aero cap to collapse and store for towing.

Phil (aerohead) has data showing that a 2/3 bed cover (open space at the front) is a better choice than a full cover and it is much easier to design than a kammback. If it proves itself, you could remake a more permanent version that folds up and stores away in your bed for the instances you tow with your 5-th wheel. Easy on, easy off

[kafer65]

vskid3, the gap filler on the front wouldn't have to be much different that what you did in the back.


BabyDiesel here is what I used from Lowes to stop the flaps on my skirt.

Its slotted and you can see in the picture on it that its slightly folded which gives you the ability to bow it for clearance and retain rigidity. I mounted it on the bottom of the skirt so the folded part tapers back toward the tire. Everything is nice and tight and slender in its cross section.

[vskid3]

Probably won't be much belly pan progress today, it's pretty windy out and that doesn't go well with large sheets of plastic. :/

A little more about the truck. It has 4.10 gears out back, so the RPMs are high on the freeway. Just over 2k RPM at 60MPH and almost 3k at 75RPM. Not going to change them out as that would defeat the main purpose of this truck. On the trip to and from Home Depot to get the coroplast it averaged 16.5MPG doing 55-60MPH with the tailgate down on the return trip. At 75MPH it gets about 14MPG.

Here's some pictures of the belly pan so far. I also took a picture of the passenger side to give a better view of what was covered and the zip tie points.





BabyDiesel- I think I will just do a flat bed cover of some kind. Most of the gains while being easier to store.


kafer65- After looking at more gap fillers for the front wheel well, it looks like I should be able to cover more than I thought. I still need to do a video to see how far down I can go.

[aerohead]

Originally Posted by vskid3

Probably won't be much belly pan progress today, it's pretty windy out and that doesn't go well with large sheets of plastic. :/

A little more about the truck. It has 4.10 gears out back, so the RPMs are high on the freeway. Just over 2k RPM at 60MPH and almost 3k at 75RPM. Not going to change them out as that would defeat the main purpose of this truck. On the trip to and from Home Depot to get the coroplast it averaged 16.5MPG doing 55-60MPH with the tailgate down on the return trip. At 75MPH it gets about 14MPG.

Here's some pictures of the belly pan so far. I also took a picture of the passenger side to give a better view of what was covered and the zip tie points.





BabyDiesel- I think I will just do a flat bed cover of some kind. Most of the gains while being easier to store.


kafer65- After looking at more gap fillers for the front wheel well, it looks like I should be able to cover more than I thought. I still need to do a video to see how far down I can go.

Here is GM's patent illustration for their patented half-tonneau,including the drag table for different length configurations.
It's for a circa 1985 GMC/Chevy,so it's not a 1:1 comparison with modern trucks.

[vskid3]

Originally Posted by aerohead

Here is GM's patent illustration for their patented half-tonneau,including the drag table for different length configurations.
It's for a circa 1985 GMC/Chevy,so it's not a 1:1 comparison with modern trucks.

Here's a link to the patent text. It says the vertical bulkhead only offers a slight increase vs the partial tonneau alone. It looks like that truck is a long bed, so I'll have to adjust some for my short bed. If my logic is correct, it's the size of the open area that's the money maker, so for my truck I would probably be best with a 30-40% cover to provide an optimal vortex size. If the image is to scale, it looks like the 50% opening is the same length as the height from the floor of the bed to the top of the cab, maybe I should try the same? Does that sound right, aerohead?

[aerohead]

Originally Posted by vskid3

Here's a link to the patent text. It says the vertical bulkhead only offers a slight increase vs the partial tonneau alone. It looks like that truck is a long bed, so I'll have to adjust some for my short bed. If my logic is correct, it's the size of the open area that's the money maker, so for my truck I would probably be best with a 30-40% cover to provide an optimal vortex size. Does that sound right, aerohead?

I think it's a good guess,short of wind tunnel testing.
In a later article about pickup aero,it was mentioned that part of the performance criteria for the partial cover,was to have it open to the locked-vortex' low pressure core.
With the open cover,this low pressure was communicated under the cover to the inner face of the tailgate,where it increased the pressure differential across the gate.
It is this differential which is responsible for the drag reduction.

[vskid3]

Got the skirt flapping fixed. Put a piece of aluminum across and riveted it to the flare. Doesn't look the greatest, but it's high enough that it shouldn't interfere with changing the tires.




Wind wasn't quite as bad as the weather forecast predicted, so I did the belly pan on the passenger side. Pretty much just a mirror image of the other.




Front pan is next on the list.

[spacemanspif]

Everything looks great!!! Can't wait to see what results you get out of that tank.