Fifth wheel trailer hurricane in truck bed
 

What to make of the fact that when towing a fifth wheel travel trailer, with the tailgate installed, anything in the truck bed that is light enough to be picked up by a person can be picked up by the air flow in the bed? Most fifth wheel owners find this out the hard way on their first trip. :)

This must be a bad thing aero-wise?

Some people pull fivers with no tailgate, and some with a vented tailgate. I haven't tried either. If I do, and the hurricane disappears, does this mean anything from an aero point of view?

What if the hitch could just emerge from a bed cover, would the bed cover reduce drag? For instance, imagine a modified gooseneck hitch arrangement, in place of a fifth wheel hitch, where the ball is at the top of a bed cover. If it could be mechanically sound, do you think it would reduce drag?

Something I like to believe, and your post makes a good opportunity to put it out there. I consider the amount of energy it would take to create the amount of turbulence you speak of, like a big fan, how much power would it take to run the fan? This applies to the vortex generation behind a car as well, the amount of power used to "spin" the air is just wasted. The energy required to move the air is an extra load placed on the engine of the vehicle and knocks the heck out of fuel efficiency.

I think a simple straight deflector from the cab roof back a couple of feet would kill it. I will have the opportunity to test that out this year.

The trailer is not a gooseneck? Either way, I'd make a bed cover out of some plywood or an aero topper with coroplast or fiberglass.

5th wheel = gooseneck

A 5th wheel and a goose-neck are technically very different. A 5th wheel has a much larger overhang that doesn't extend to the bed of the truck. A goose-neck has far less surface/frontal area, and the hitch extends all the way to the bed of the truck. If not properly accounted for, I have to imagine that the 5th wheel would have a far higher aero penalty than a goose-neck.

Given the design of the 5th wheel and its hitch attachment, you might be able to make a partial bed cover, which extends -- at least -- to the hitch point.

Right- the hitch mechanisms are different. But they both go to the center of the pickup box and they'd both be dealt with in identical or at least similar fashion from the standpoint of bedcovers and tailgates or whatever.

Anyway, back to OP's question, seems to me a lot of interaction there and I wouldn't want to make any bold predictions, but I'm pretty sure the "rolling wave" thing that naked pickups have going in the box wouldn't be the case here at all. Seems intuitive that a bed cover would help...

I've seen guys with older hitches that have hatches in their tonneau covers.
I would be afraid with the newer full floating hitches the side movement would crush a hard tonneau.
The big boys use cab deflectors top and sides.
My dad and I have found a properly angled, full width, roof deflector to help at highway speeds.
It may be keeping air from the top from going into the bed.
The air coming from the sides needs to be addressed as well.

Thanks for the comments. I asked something similar on an RV forum which I frequent. Someone pointed out this hitch.
http://www.youtube.com/watch?v=exQGJx_9C3s

It is similar to what I was imagining. Mine would have been taller. However towards the end of the video we can see the problem with a bed cover is really the hardware on the trailer side. The pinbox and pin are too far down below the trailer. In conventional use, the flush lower surface of the trailer in the hitch area is about 6-7" above the pickup bed rails. My idea would require that the existing pinbox be reengineered from the frame down, not just replaced with a short gooseneck hitch.

Interesting. I would think that would help too. It's a sore subject on the RV forum, because 99% of those who have experience or opinion on deflectors say they did/do not help. I look forward to Skyking's test too.

Here is the way one maker attacked the issue of fiver aerodyamics. They extended the upper body in a second step, almost above the cab of the truck. The company went out of business during the economic bust, though.
http://www.rv.net/SharedContent/cfb/...6%20(Copy).jpg

And here is my rig.

http://www.rv.net/SharedContent/cfb/...etSigPhoto.jpg

Nice rig, Snowman. I have some very hefty stake pockets in my bed system, 2x2x0.250 wall steel. I will build a headache rack off of those that will stay in the truck permanently.
The top horizontal member will be right at the top window gasket a couple of inches below cab top, so it won't obscure the 3rd brake light. It will have fittings on top of that to bolt on my aero cap, and any trailer fairings I make.

With this one, I'd dare say that you'd still want one of those deflector top hats that are used on many semis.

http://www.transportation-expert.com..._Deflector.jpg

Heck, might even work on your current setup if extended.

As far as tailgates: either stock tailgate up or no gate at all. Airgates = high drag.

A 5'er tends to be quite wide. That's a wall pushing aside a lot of air. In a head-on view these things can just dwarf the truck (big fish pursuing little fish, mouth wide open).

There have been some custom hauler beds which appear to take advantage of the "gap" for storage and best clearances. But the cost is prohibitive and the simple utility of the pickup is lost.

Aerohead's archaeology diggings brought up a trailer nose from 1982: fabric, inflatable (Fibrelock; search Pop Sci 1982). Something like that could both fill the gap and ideally not damage either vehicle if it had a little give (for the rare times interference occurred with an otherwise optimized design).

hitch
 

I'm not knowledgeable enough to properly address your drag question but my instinct would be to run with the gate up,to allow for the locked-vortex inside the bed.
Comparing a conventional,non-sleeper tractor to a C.O.E. tractor,the C.O.E.tractor has 15% lower drag simply because it's height is equal to the trailer height.
For both types of tractors,a 31.25" gap between tractor/trailer adds another 19% drag.
So anything which can fill in and blend these interfaces should show at the pump.
As far as raising the hitch point in order to run a bed cover.I think that it would negatively impact the center of gravity and how the rig would handle in emergency maneuvers when dodging Ken and Barbie.