Need help with Aerocap for 05 Dodge Ram.

[Vajra]

Greetings everyone! I am new to the forum, joined out of pure frustration! I have read and checked out many, many, many of the threads on here about Aerodynamic lids for trucks. I saved templates of various types. My issue is no matter what I have done, the tail end of the template shows only a couple inches off the tailgate. I have a 2005 Dodge Ram 2500 Regular cab, long box. The wheel base is 140 inches. The back of the cab starts to decline just above the back edge of the door. I have spent about a dozen hours with the template but it comes out wrong. The truck sits tail end up a bit. If I use the template, I got almost nothing at the tailgate. If I do it with the bed of the truck dead horizontal I only get what appears to be a few inches about the tailgate, which is past the 13.5 mark, maybe almost 14. I think if the truck was done this way, the nose sitting lower would give about 12.5 in the end. I thought in reading somewhere, it is suppose to be 5" or 7" taller than the tailgate. Any help would be appreciated. In advance, thank you all for the sharing of information. The builds, information, as well as inspiration by Bondo, Swede, Aerohead, ChazInMT and others makes my hopes of just 1.5MPG more seem very reasonable. - Vajra

[Hersbird]

I think all of the aerocaps I have seen have been on short beds or small trucks. I would think that extra length of a full size, long bed would put it that much closer to the tailgate.
I also think the full size Ford has a taller cab then the Ram but maybe that's an illusion.

[freebeard]

Welcome to EcoModder

I have spent about a dozen hours with the template but it comes out wrong. The truck sits tail end up a bit. If I use the template, I got almost nothing at the tailgate. If I do it with the bed of the truck dead horizontal I only get what appears to be a few inches about the tailgate, which is past the 13.5 mark, maybe almost 14. I think if the truck was done this way, the nose sitting lower would give about 12.5 in the end.

It is what it is.

Can you show your work? 12.5, 13.5, 14 what? Inches, feet or degrees?

[aerohead]

Are you using the Streamlining Template tool at the top of the Aero Forum page?
If so,when your truck is properly aligned under the profile,as Freebeard has said,it is what it is.
It will terminate where it terminates.Just go with it and you'll be fine.

[Fat Charlie]

Instead of letting it terminate where it terminates, maybe slide it back to the tailgate and let it begin where it begins?

[Vajra]

Thanks all for the replies. I had tried the template tool on here with a few different attempts. I also did my own use Paintshop Pro X4 using the AST-2 drawings as well as one of the templates on here by ChazInMT. I changed the photo I used originally, pulled one from the net as I wasn't able to get as good of clean side shot currently. I reused the streamlining template my roof peaks right about the rear of the door. Again, same thing only this time past 16 degrees I believe but still just a inch or two above the tailgate. The bed of my truck is 8.2' I think the issue of the way the truck sits is causing me the most trouble. If it does make it back to 16+ degrees, isn't that a bad thing for the aerodynamic effects when it comes into calculation for reduction? I thought 12 degrees or about was optimal, or is my understand all wrong? If it terminates early, will it have a negative impact on reducing drag and increasing MPG? I seem to remember others saying the tail should be 5 to 7 inches tall at the tailgate, but can't find what threads it was in. Thanks - Vajra

[Hersbird]

Sort of off topic but I wonder if the SRT10 short spoiler on the longbed would help aero by giving a landing pad for the air coming off the roof right there. It's about right where the template line is at the tailgate in your drawing. Same thing with the taller Daytona spoiler on the short bed, about 8" high at the tailgate would be about right. If nothing else might be a good platform to build the rear of an aerocap on.


The short one might even turn around backwards and mount.

PS, the 2002-2005 Ram is the best looking truck they ever made IMO.

[Hersbird]

Here is maybe a better picture to work with although a 1500. Is yours 2wd or 4wd? I think the 2wd has a little more "rake" then the 4wd although both could be leveled if you wanted.

Although now that I look at your pic it looks good too, I thought it was a 4door but see that extra handle is on the template not the picture.

[freebeard]

The bed of my truck is 8.2' I think the issue of the way the truck sits is causing me the most trouble.

From an article linked in aerohead's Model A in a wind tunnel thread:

Test 9: Attitude:Most hot rods like to run a little forward rake because they look cooler that way. Again, this was something that had not been considered on the roadster. Peter, however, immediately picked up that more rake means more frontal area and therefore more drag, so it was time for an attitude change. We began by dropping the front 111/42 inches from our baseline and that resulted in a staggering 10hp increase in drag and an increase in front lift of 42 pounds. The more rake we put into the car, the more we increased the drag. Consequently, we put the front back to baseline and lowered the rear of the car 11/42 inch. Eureka! A reduction in drag of 10 hp and a slight reduction in lift in both front (4 pounds) and rear (2 pounds).

Ignoring the bogus numbers, level is better. Self-leveling would be best.

If it does make it back to 16+ degrees, isn't that a bad thing for the aerodynamic effects when it comes into calculation for reduction? I thought 12 degrees or about was optimal, or is my understand all wrong?

The degrees-of-angle-at-each-station way of defining things is confusing. It's really a parabolic curve that's defined by a quadratic equation. See https://en.wikipedia.org/wiki/Parabo...an_coordinates. Most of us aren't up for that. If you draw a circular arc, you'll see that the curve relaxes as it proceeds to the rear. So the curve is greatest at the beginning, but accumulating angle at each successive station makes it look like the curve is greater, not less.

If it terminates early, will it have a negative impact on reducing drag and increasing MPG?

Ending at the tailgate is terminating early. Probably 6-8ft early.


The problem here is the 2" gap should be sealed and you lose the early start to the taper.



The suggestion to turn this around is a good one. There is precedent, aerohead did a half-tonneau that followed the template, but it's not in his Pickup Images album. Maybe he can point to it.

A half-tonneau is 2nd best and less work. The lack of plan taper below the beltline is problematic. Thee Template is half-circular in section.

[Vajra]

My truck is a 4x4, sits a bit higher than either of the pictures. Not much, but a little bit. The 2500 has a beefier suspension. I seem to get inconsistent results with level or non level pictures. Not complaining, I love the way my truck looks, minus some rust issues. I very much like the body style, interior. I just wish it wasn't so bad on gas. New plugs, fuel pump, fuel filter, fuel rails. Everything and a tune-up. I know with 4.10 gears fuel economy wasn't going to be the strong point of the truck. But it was what I could afford for a HD, one that meets my needs in towing or hauling. If I can squeeze just a little MPG out of it, it would be worth it. I was going to be building a camper. Thought truck camper. Then streamlined tow behind.. now maybe a aerodynamic aerocap-camper sounds all the better, that is when it isn't being used. I seen bigger trucks with a more of a long slope aerocaps with a 8 inch or more tail-end of the lid tapering off above the tailgate. A Toyota Tacoma if not mistaken. I guess what I wonder most, is which is better to do, carry the curve to the end of the tailgate just above it, or past the tailgate and above it by 5-8 inches or so? I am no aerodynamic engineer, but I have build RC planes, jets, model rockets and understand rounding edges, blending surfaces. I just wonder which would be the most efficient. I guess I might have to make some mock ups and just go with things, changing as I go until I am happy. I am just surprised to see more short bed aerocaps verses long bed aerocaps it seems... I would think long beds have the most to gain from aaerocap/lid. I know a wallet that would love to save on fuel costs! Maybe a spoiler at the end of a well blended tail curve would help? - Vajra