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Old 03-06-2006, 09:03 PM   #15
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Overlander63: I agree that having both on at the same time wouldn't be good. I was thinking of swapping if I have a place to store the unused piece, and could afford both.
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Old 03-07-2006, 09:13 AM   #16
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A tonneau would help the aerodynamics some when not towing. Many guys just drive with the tailgate down and that helps a little bit.

Think of a tear drop going down the road and that's the shape you want to copy. Bulbous front with a smooth taper to a point at the tail. The closer you get to that, the lower the drag.

It's not going to make that much difference at normal highway speeds, but it may get you a little bit. And at $2.50 a gallon for gas, every little bit helps!!
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Old 03-07-2006, 09:14 AM   #17
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F-105's are cool too. heaviest single seater we had.

My personal favorite is the F-104 Starfighter. The Missile with a Man in it. Stall speed of about 230mph; you have to go faster to take off than a Cessna goes wide open straight down. That's cool! Who needs wings...just put some directional vanes on there and light the burners!
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Old 03-07-2006, 01:50 PM   #18
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I have a canopy (cap) and a 11' boat (100 lbs) I put on top (pointy end forward, of course). The boat splits the wind for the trailer and helps prevent the build-up of bugs on the top front of the trailer. Gas milage is about the same with trailer and boat as it is with just the pickup. I always take the boat even if I don't plan to use it. Darol
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Old 03-07-2006, 02:10 PM   #19
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You know, I watched something similar to this on Mythbusters a few months back.

They had two identical trucks one with the tailgate down, and one with it up.

The one that had it up got better economy than the one that had it down.

I forget the term, but when it's closed, it makes the air shoot over the bed, but when open, that air pocket is gone.

Anyway, to answer your question, yes, having one would be better than not having one when towing. The problem is that some caps weigh a lot, so any economy gain you might get from the aerodynamics could be lost if you get a heavy cover.
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Old 03-07-2006, 04:43 PM   #20
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Some caps are more aerodynamic than others.
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Old 03-07-2006, 05:45 PM   #21
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Exactly....

Quote:
Originally Posted by Silvertwinkie
You know, I watched something similar to this on Mythbusters a few months back.

They had two identical trucks one with the tailgate down, and one with it up.

The one that had it up got better economy than the one that had it down.

I forget the term, but when it's closed, it makes the air shoot over the bed, but when open, that air pocket is gone.

Anyway, to answer your question, yes, having one would be better than not having one when towing. The problem is that some caps weigh a lot, so any economy gain you might get from the aerodynamics could be lost if you get a heavy cover.
Independent research has shown that there is no discernable difference to adding these to your vehicle.....
In fact, air drag is increased because more mass is introduced, regardless of the design.
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Old 03-07-2006, 06:24 PM   #22
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In regard to the Mythbusters episode:

The only way that could be true would be if the tailgate being up formed a "barrier" similar to a tonneau cover would. Essentially, it'd form a cushion of air inside the enclosed portion of the bed now. So essentially, you'd only have a vortex form from the depth of the top of the cab to the top of the bed. With the tailgate down, I'm assuming they're saying that the vortex would be larger because now the air is trying to converge from the top of the cab to the bottom of the bed. The larger the vortex, the greater the drag.

A perfect example is the '68 Dodge Charger. While the car was very sleek and racy looking, it had the flying buttress rear roof line where the C-pillars extended further back than did the rear glass. The rear glass was rather steep, actually. When they raced them in NASCAR, they said the suction formed by that vortex forming off that backlight would suck potato chip bags onto the track. In '69 Dodge lost to the Torino Talledega of Ford, which was a true fast back. Dodge responded with the Charger 500 where they made the rear glass flush with the C-pillars. That helped a lot. They then put a bullet nose on it and that made the car incredibly fast, only there was too much downforce at the front and it made the rear light, so they added the wing (not a spoiler but a real wing, a NACA 2412, mounted upside down to provide downward "lift) and that car was truly unbeatable. It was so that NASCAR outlawed them after one season. But I digress...

Again, think of a tear drop. That is nature's low drag shape and we've not been able to beat it.

There was an airplane brought out some years ago called the Questair Venture. I always thought it was ugly, but it was very fast. It looks like an egg. The better looking planes are more streamlined and elongated looking (like a Swearingen SX-300 for example), but that elongation actually increases drag. The ideal ratio for aerodynamic drag reduction is about 3 to 1. That is, the length of the body should be triple the diameter. When you get higher than that, you're increasing the surface area excessively, even though it looks a lot better.

A Venture will cruise at 300mph on a 300hp engine. The SX-300 is probably 15mph slower, but (in my opinion) looks a lot better.

Anyway, pickups and SUVs are bricks and there's not much of any aerodynamic aids that will really make a huge difference. The boat idea is a good one. You probably can't do a whole lot better than that.
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Old 03-07-2006, 06:46 PM   #23
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hi air flow, air foil, air head, airstreamers......

the tail gait up/down issues just won't die....
and like the myth busters demo, i've seen several demos/reports debunking the value of tail gait down suggestions.....

now as for the cap issue on a truck pulling an airstream....

clearly the cap lowers mpg on the truck sans trailer....more weight, more drag, blunt butt...

while towing.....
i'd like to think it helps.....but i'm not so sure....

1. i use a hensley...so the gap betweeen truck and trailer is way more than drafting cars/bikes and so on...

2. the trailer is much taller than my 4/4 superduty with is pretty tall...

3. during rain or bugs...the front on my trailer (rockguards, upper segments and lower panels still get hit by lots of stuff...water/bugs don't flow past the front end of the trailer....as expected in a draft....

4. ford, gm, dodge, and all of the other towing vehicle guides mention what FRONTAL AREA (in sq.ft.) size limitations exist....just like weight load/towing or hitch weight limits....with no mention of improvements using a shell

5. the van versions of ford/gmc do not get better mpg than the trucks while towing....at least i've not seen anyone report better mpgs...

6. bike racks mounted between the truck/cap and the trailer still get really dirty....air does not flow past this stuff but all around it....

utilimately the full caps let us carry more crap and keep our crap from flying out of the truck...... but i really don't thing sheels/caps help fuel economy while towing our silver bullets...

show me the data!

cheers
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Old 03-07-2006, 09:18 PM   #24
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Smile Here's the data!

Wow I put on my tin foil thinking cap and remembered that I saw something about this on tv, it was great, and it boiled down to something about Strouhal numbers and simplified flight waveforms. So the formula is that you take the airspeed velocity of an unladen swallow and…wow, Here’s the data!
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Old 03-08-2006, 07:06 AM   #25
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I can tell you this about air flow between my 91 F150 with camper shell and 68 trade wind: if the window on the shell isnt LOCKED the air pressure pulls it to an open position every time.
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Old 03-08-2006, 07:13 AM   #26
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Quote:
Originally Posted by JimGolden
In regard to the Mythbusters episode:

The only way that could be true would be if the tailgate being up formed a "barrier" similar to a tonneau cover would. Essentially, it'd form a cushion of air inside the enclosed portion of the bed now. So essentially, you'd only have a vortex form from the depth of the top of the cab to the top of the bed. With the tailgate down, I'm assuming they're saying that the vortex would be larger because now the air is trying to converge from the top of the cab to the bottom of the bed. The larger the vortex, the greater the drag.
I think thats what they were referrring to. It was one of the more interesting shows they've had.....most of them are kind of fluffy, but I really liked this one.
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Old 03-13-2006, 07:45 PM   #27
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Many thanks for the good advice.

Sam
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Old 09-25-2007, 05:10 PM   #28
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Pick Up with Cover for storage.

I purchased a ARE MX series with a lift rear door for my CC because my 30' SO trailer has such limited storage and weight restrictions. It was necessary for me also to get a canoe on top of the PU and bikes off the end of the cab. Too much stuff to travel without having that extra room that a camper back has to offer. When it's fully loaded, it handles great with Hensley managing my back side too. I use a cover for the bikes to keep them clean.


And for storage, it's fully lockable too!

Happy camping
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