Need help with Aerocap for 05 Dodge Ram.

[ChazInMT]

OK, So here's what I get.



Higher Res Version Here

The Red Line is as you said, right to the top of the gate and I see that as 11° overall, the yellow straight line is 8°, and the orange line is essentially a template curve section to smoothly transition over 8°. Now mind you that the angle above the gate, the maximum slope, on the 11° arc is 16° and 14° for the 8° arc, for whatever that's worth.

So my reasoning is this, From the chart, we see that 10-12° is pretty much the same for lowering the Cd, but the CL goes up a not so insignificant amount at 12° losing 44%. I gotta believe that at 8°, your CL will look great and the Cd will only be slightly affected. But you gain 4" of covered space.

Now, I see you live in Michigan, I can tell you from having driven with my not even closely optimized aerocap, that the way your truck will handle in slippery icey conditions with the CL optimized will really amaze you. My truck handled way better with the cap, it felt like an arrow going down the road.

So you get great handling, more storage, 95% of the aero efficiency gain, and I think it will just look better too. Winning.

[aardvarcus]

Vajra,

Past and angled back would be fine, a lot of my original concept drawings were like that for looks. I went through dozens (literally) of ideas on how to hinge, pivot, slide, or otherwise open my aeroshell, and I don’t really think there is a best method as they all have different complexities when you get into the details, especially if you are trying to keep it weather resistant.

I would like to add a camera to mine as well, so be sure and report any good models you find or anything you learn about them. Man, 14” drop hitch? Are you sure your truck isn’t lifted or on oversize tires?

Oh, and I took some new progress pictures of my V 2.0 aeroshell and bumped my thread with them, look for the Amocat-2005 Tacoma in the Aerodynamics sub forum and skip to the end to see where I ended up.

[Vajra]

ChazInMT, that sounds pretty good to me. After looking at the chart and trying to do a comparison of numbers not plotted. That would be a huge improvement. i go to worried about the side profile, had to remember later that I planned to narrow my sides down, tapering them. So I should see further reduction without adding CL. I have to wonder though why CL is such a issue. Can the lift generated really be that bad as to cause issues (other than flying aerocaps? )? I know how a airfoil works, but I would think on a nearly 6,000 lb truck that wouldn't be an issue. Oddly enough my trucks bed rail taper. I am going to use this to help reduce the width by a few inches per side, maybe a tad more.

So what do I do then to find this arc? I am thinking take a long board place in on the highspot on the cab, using a protractor, get the board to slope down 8 degrees. Measure the distance from the bottom of the board to tailgate. Then use PVC to make the gentle curve and take measurements at intervals?

Aardvarcus, my tires might add a inch over the normal tires, but her bumper sits pretty high up. I have a drop axle, on the cargo trailer. It is at about 12 inches off the ground of so. The hitch is at about my knee. Might not be quite 14, but close to it. I was just surprised at how far of a drop I needed to have, and it is still not quite level. Sometimes, I wish I had a elevator to get in and out of the bed. BTW, your V2.0 Aerocap is looking good. Can't wait to see it finished! How did V1 turn out, did you see positive gains?

Been a long day, and I am exhausted. Got lots of think about over the next couple days. I hope to make some starting checks this weekend so I can start planning. Thanks for all your responses and input. You guys are great! - Vajra

[aardvarcus]

Vajra,

Version 1.0 was only a half shell, and I did see gains (about 5% from my admittedly limited testing), but I ended up wanting the weather resistant bedcover that a half shell did not provide. I still am using it, except I have taken it off temporarily to be able to test fit Version 2.0.

[ChazInMT]

The lift on my 2000 GMC 1500 was enough to cause it to want to get "Loose" in icy windy conditions. It was really kinda tough to drive at highway speeds in the snow, particularly when passing a big rig. When the aerocap was on it never felt like skipping out. It is hard to describe the effect you'll have day to day, but I noticed my truck was quieter and smoother, and it just felt like it wanted to go straight down the road more.

Just get a 12 foot 2x4 and rip a 1x2 off it, put the back of your "Arc Stick" above your tail gate and add weight to the front and back, or tie it down somehow, till it droops to about 6" above your tailgate. Just be sure the transition from cab to cap is smooth, there should not be a drastic angle change anywhere.

About the sides, if you keep the aero cap a bit higher rather than try and follow the curve, I reason that you'll create less of a "Low" pressure zone on top of the cap, this will help reduce the amount of air that feels the need to go up along the sides of the cap to "fill the void". I noticed some pretty seriously upward angled water streaks on my cap even with a side taper and radiused edges. My cap was much too steep.

Do radius the edges! If you make square edges, it puts high & low pressure areas in very close proximity and will create Cd eating vortex generators on each side of your cap.

[aerohead]

Originally Posted by Vajra

ChazInMT, that sounds pretty good to me. After looking at the chart and trying to do a comparison of numbers not plotted. That would be a huge improvement. i go to worried about the side profile, had to remember later that I planned to narrow my sides down, tapering them. So I should see further reduction without adding CL. I have to wonder though why CL is such a issue. Can the lift generated really be that bad as to cause issues (other than flying aerocaps? )? I know how a airfoil works, but I would think on a nearly 6,000 lb truck that wouldn't be an issue. Oddly enough my trucks bed rail taper. I am going to use this to help reduce the width by a few inches per side, maybe a tad more.

So what do I do then to find this arc? I am thinking take a long board place in on the highspot on the cab, using a protractor, get the board to slope down 8 degrees. Measure the distance from the bottom of the board to tailgate. Then use PVC to make the gentle curve and take measurements at intervals?

Aardvarcus, my tires might add a inch over the normal tires, but her bumper sits pretty high up. I have a drop axle, on the cargo trailer. It is at about 12 inches off the ground of so. The hitch is at about my knee. Might not be quite 14, but close to it. I was just surprised at how far of a drop I needed to have, and it is still not quite level. Sometimes, I wish I had a elevator to get in and out of the bed. BTW, your V2.0 Aerocap is looking good. Can't wait to see it finished! How did V1 turn out, did you see positive gains?

Been a long day, and I am exhausted. Got lots of think about over the next couple days. I hope to make some starting checks this weekend so I can start planning. Thanks for all your responses and input. You guys are great! - Vajra

Even though the bedcovers appear as an airfoil,their function is to regain static pressure which was formerly lost to separation-induced turbulence over the empty bed.
On the T-100,the rear mods reduced rear lift to 17-pounds,at 135-mph.Your truck should 'feel' like it's got 500-lbs in the bed,ride like a Cadillac,and be way less prone to aqua-planing,all without any appreciable weight gain.

[freebeard]

So what do I do then to find this arc? I am thinking take a long board place in on the highspot on the cab, using a protractor, get the board to slope down 8 degrees. Measure the distance from the bottom of the board to tailgate. Then use PVC to make the gentle curve and take measurements at intervals?

Referring to Permalink #16, that's what I did. Although I started well forward of the crown. The wood strip laid flat on the roof from the windshield header to the crown.

The PVC would be redundant, if you use knot-free wood. I would think it easier to take measurements off the rectangular section. But then I'm actively dislike PVC.

[Vajra]

Thanks for the replies! I started taking some measurements today. Going to be a project in the works till tax money comes back for the funds needed. I have some planning and thinking to do. I appreciate all the help, the knowledge base here is amazing.

Alright, hopefully soon, I'll pick up some wood to start the process. I do plan on radius for the edges, I'd like a smooth looking aerocap to match my truck!

My bed is 101.5" total from the front of the bed to the end of the tailgate. About 23.5" height for the cab to the crown, 73" wide at the front of the bed narrowing down to about 68". 1.25" gap between cab and bed. With that, bedtime for me, might get 6 or 7 hours of sleep instead of 4!! - Vajra

[Vajra]

Yesterday, I had the chance to put a 2x4x12 at about the crown of the cab, using a protractor and a couple coworkers. I also used phone app as a secondary observation. At 8 degrees down (slope) or whatever it would accurately be called, lands about 8" from the top of the tailgate. I asked another coworker whom is a engineer to see if he could could calculate where a 8 degree slope would end at using 23.5" for one side (height of the cab) and the length from the crown point to the end of the bed, which is about 112.5" When he came back with the paper he printed, it showed the line landing about 8" above the tailgate. I think I left the paper at work because I couldn't find it earlier so I assume that is where it is. Would you just go with this point of landing then for the Aerocap? - Vajra

[ChazInMT]

Here's a cool tool (COOL TOOL) to establish overall straight line angles if you're averse to the whole Trig thing. As I deduce from the Cal State paper by Feysal Adem, anything between 5° and 12° will yield a great Cd reduction, anything closer to 5° will yield a significant reduction in lift which will help make for a more drivable truck. So using the tool, it looks like 8° will be 8" off the tailgate.

You do plan on curving the top I trust. Just going with a straight flat top you may want to go with 10-12" off the gate.