teardrop cap for pickup truck?

[bennelson]

Hey Everyone,

I was wondering about designing a cap for a pickup truck loosely based a a teardrop back end.

The idea is that it would improve the aerodynamics of the truck and be more useful than a standard tonneau cover, because it would be hinged up higher.

Here is a custom made one similar to what I was thinking:
http://forum.ecomodder.com/showthread.php?t=583

and here is a thread on another forum talking about it:
http://forum.ecomodder.com/showthread.php?p=5277

[PaulC]

Not wishing to put your idea down but, why is it that a lot of people seem to think that the teardrop shape is one of the most aerodynamically best shapes?
A short course in aerodynamics will show that it's not.
Hey Andrew, where are you when we need you
If you want to improve the aerodynamics of your pick up,put a big pointy nose on it.

Cheers
Paul

[bennelson]

I know a teardrop is not an ideal aerodynamic shape.

I was more thinking that there are a lot of creative people on this web forum that are used to working with various materials, waterproofing them, and having the whole thing look really nice.

The shape I am imagining would be a little longer and pointier than a teardrop, but would hinge and latch in a similar way.

Something like this:

[PaulC]

Okay, that looks so cool
Cheers
Paul

[Nitetimes]

Okay, that looks so cool
Cheers
Paul

I was thinkin' that too. Enough so that I am considering building one!

[angib]

That aero-shell should work fine, but to do the job really well, it has to be quite complex:
- It has to either be joined to cab, or sit just proud of the surface of the cab as short a distance behind it (like less than an inch), so that the airflow coming off the cab "re-attaches" to the shell - without this half the benefit is lost.
- The same has to be done for the sides as well as the roof - if instead a typical rectangular-cross-section teardrop shape was used, it would probably create as much extra drag from the square sides as it saved on the tapering roof. I'm assuming pick-ups have curved side window glass, right? That makes it harder.
- The roof has to curve very gently into the 'fastback' - it's hard to be sure from that photo, but it certainly looks like that shell is curved way too tightly - again, half the benefit can be lost.
- Really the joint between the sides and the fastback need to be rounded, but then the construction gets really really hard!

That photo however is a good example of about the right amount of 'fastback-ing' - anything steeper than that (ie, every teardrop ever built) isn't aerodynamics, it's just styling. Our forefathers did not have some secret that we've forgotten (talking about fastbacks, here)!

An aero-shell could certainly be done in plywood, but it wouldn't be easy - sloping in the sides does make the build a fair bit harder than a 'simple' teardrop. But it would be good to try - I'd be happy to offer help on the design side.

Andrew

[Nitetimes]

An aero-shell could certainly be done in plywood, but it wouldn't be easy - sloping in the sides does make the build a fair bit harder than a 'simple' teardrop. But it would be good to try - I'd be happy to offer help on the design side.

Andrew

So speak up don't be bashful.....wadda ya got in mind???
I think I'lll give that a go closer towards spring, need the cap on right now, too much stuff to haul around in the snow. That would work good for spring/summer/early fall tho. Looks cool too!!

[brian_bp]

I agree that the teardrop shape is useful only for aesthetics, not aerodynamics. For the most useful cap, just buy a regular one, and get an aerodynamic improvement and lots of space. For side access, get one with side hatches.

One problem with truck caps is that they interfere with rear and rear quarter vision; the illustrated cap on the F-150 makes a Ferrari's rear vision seem good... it might as well be a panel van.


The guy who says (in the Ecomodder.com forum) that he built that aero cap talks about a patent; there's no hope that there's anything patentable about the general design, in my opinion.

He also says "A regular camper shell actually has a worse coefficient of drag than a truck with nothing over the bed at all", which conflicts with anecdotal evidence from other people I've met. Even a plain flat tonneau cover reduces drag... after all, a regular truck is kind of pulling a parachute.

I can appreciate that it can be good to have a separation between cab and cargo, but if that is not needed than a van (instead of pickup) is the obvious answer for space and aerodynamics, with much easier side access. I asked a guy selling truck caps why anyone would get the Honda Ridgeline and cap he had on display, when they could just buy the Honda van from which it was derived; he said the setup was what they called a "man van"... a minivan for the guy who wouldn't admit to driving one. As a minivan owner (real men drive... whatever they want), I thought that was hilarious.

[Nitetimes]

One problem with truck caps is that they interfere with rear and rear quarter vision; the illustrated cap on the F-150 makes a Ferrari's rear vision seem good... it might as well be a panel van.

That's what they make mirrors for! I've driven a truck most of my life and never had a problem with a cap or side boards obstructing my vision. If you're gonna drive em ya learn to adjust and use the mirrors!!

[madjack]

One problem with truck caps is that they interfere with rear and rear quarter vision; the illustrated cap on the F-150 makes a Ferrari's rear vision seem good... it might as well be a panel van.

That's what they make mirrors for! I've driven a truck most of my life and never had a problem with a cap or side boards obstructing my vision. If you're gonna drive em ya learn to adjust and use the mirrors!!

...yep, near 2 million miles in an 18 wheeler and I still use the side mirrors to back up a car...go figure...and the only time I ever ran over somebody on that side was when a guy drove up under me in his little Datsun "Z" car (boy was he suprised)
madjack

[Nitetimes]

One problem with truck caps is that they interfere with rear and rear quarter vision; the illustrated cap on the F-150 makes a Ferrari's rear vision seem good... it might as well be a panel van.

That's what they make mirrors for! I've driven a truck most of my life and never had a problem with a cap or side boards obstructing my vision. If you're gonna drive em ya learn to adjust and use the mirrors!!

...yep, near 2 million miles in an 18 wheeler and I still use the side mirrors to back up a car...go figure...and the only time I ever ran over somebody on that side was when a guy drove up under me in his little Datsun "Z" car (boy was he suprised)
madjack

Can you say, "speed bump"!

Never felt a thing did ya???

I use the mirrors in a car too....I hate driving anything that doesn't have mirrors on both sides. I kinda feel blind I guess, but it's a habit that's hard to break. I don't even look back to back up a car...mirrors, mirrors fix my mirrors!!!

[angib]

First shot, based on a Dakota, because I had one drawn already (and thank you again Dodge for publishing your drawings). Have they changed the basic body since I drew this or just restyled the front end?





So it looks similar to the photo, but the small differences could be important. Rounded front edges on the top and side - probably easiest done in solid wood - to 'collect' the airflow coming off the cab.

The red spots show the cross-section area of the shell that sticks out beyond the truck body - not ideal, but bearable. Building a roof that's curved in two dimensions is way too hard, so matching the camber of the cab roof isn't possible.

There's a very gentle curve (11ft radius) into a simple flat fastback - the angle is 17.5 degrees which is more than the 15 degrees that is my 'rule of thumb' maximum. Raising the trailing edge 1.5" would solve that.

Clearly the easiest way to build this is as a one-piece shell. Opening the shell at the back isn't easy, but it probably is possible by building a false front that carries some hinges up near roof level. Easier would be to make it open to one side.

Andrew

[bennelson]

Hey Andrew,

Thanks for the drawing. That's the sort of thing that I am thinking.

Also, it would look great done up in the same style exterior as a teardrop.

There is a local nursery that has some greenhouse glazing material I could get. That might make good stuff for a lightweight cap.

I will keep you up to date here if I do that.

-Ben

[Nitetimes]

Thought I'd resurrect this old thread because I decided to give building one of these a shot to see how it performs.

Frame glued up and front angle fitted to truck cab. (hopefully!) The wires were holding it in place.

Framed sides, not much huh.

First side on.

From front.

Most of top done.


Tomorrow I'll finish the top and frame and cover the hatch. Then the gap between the sides and top ply will get blue foam glued in so I can sand the roll on the corners for a nice rounded edge then it'll get glassed and painted to match the truck.

[Elumia]

plexi hatch so you can see out? would look like a big Honda CR-X

Mark