Aerodynamic...but not aircraft

3/4 ton extended cab pickup towing a 24 foot travel trailer. Fuel
mileage is effected much more by wind than weight.

I want to build a camper shell that will be cab high at the front and
direct the airflow smoothly over the trailer.

There is about 4 feet between the front of the trailer and the rear of
the proposed camper. For some reason, I believe the camper should be
higher than the trailer. But how much higher? Should the angle be
constant? Convex? Concave? A different exit angle?

About a foot from the top of the trailer, the front slopes back at a
45 degree angle. All opinions are welcome but educated calculations
will be given more weight.

--Andy Asberry--
------Texas-----

Andy Asberry wrote:
3/4 ton extended cab pickup towing a 24 foot travel trailer. Fuel
mileage is effected much more by wind than weight.

I want to build a camper shell that will be cab high at the front and
direct the airflow smoothly over the trailer.

There is about 4 feet between the front of the trailer and the rear of
the proposed camper. For some reason, I believe the camper should be
higher than the trailer. But how much higher? Should the angle be
constant? Convex? Concave? A different exit angle?

About a foot from the top of the trailer, the front slopes back at a
45 degree angle. All opinions are welcome but educated calculations
will be given more weight.

--Andy Asberry--
------Texas-----

I'd be betting against making the camper higher than the trailer. At
least on a/c, drag is reduced if the trailing body is slightly larger
than the object ahead of it. Ailerons with leading edges that are
slightly fatter than the wing trailing edge come to mind. If you can't
make a smoothly faired transition to a smaller cross section, the drag
will go up a lot. Think round gear leg vs one with a teardrop shaped
fairing.

Take a look at big tractor-trailer rigs. the air dams on the tractors
aren't higher than the trailers.

Charlie
I'm not an aerodynamicist, but I do know one. :-)

Back in the 70's, the Univ of MD did a real great study of that sort of
thing. They determined that if you could eliminate the gap altogether, you
would have a MUCH better efficiency.

They had a system of complex levers and springs and stuff on moveable panels
that eliminated the gap on top and sides, right down to the road almost.

Try that on your pickiup and your wickiup. - NOT!

Really, if you can get as close to eliminating the gap as you can, the only
problem will be the sides. The top can be a piece with a concaved-shaped
edge on the truck, a convex-sort of sheet on the trailer, with the *center*
of the arc approximately over the hitch-point.

The OTR trucks have side-fairings on the cabs that are sometimes two feet in
length, but they work that way because the pivot of the fifth wheel is over
the axles, about 4 or 5 feet behind the front of the trailer. When the
trailer turns, the corner of the trailer is up between the fairings.

Really, just eliminate as much open distance as you can. If you had a "fifth
wheel" trailer, you'd be further ahead.

Flash





"Andy Asberry" wrote in message
...
3/4 ton extended cab pickup towing a 24 foot travel trailer. Fuel
mileage is effected much more by wind than weight.

I want to build a camper shell that will be cab high at the front and
direct the airflow smoothly over the trailer.

There is about 4 feet between the front of the trailer and the rear of
the proposed camper. For some reason, I believe the camper should be
higher than the trailer. But how much higher? Should the angle be
constant? Convex? Concave? A different exit angle?

About a foot from the top of the trailer, the front slopes back at a
45 degree angle. All opinions are welcome but educated calculations
will be given more weight.

--Andy Asberry--
------Texas-----

On Wed, 16 Jul 2008 19:58:06 -0500, Charlie
wrote:



I'd be betting against making the camper higher than the trailer. At
least on a/c, drag is reduced if the trailing body is slightly larger
than the object ahead of it. Ailerons with leading edges that are
slightly fatter than the wing trailing edge come to mind. If you can't
make a smoothly faired transition to a smaller cross section, the drag
will go up a lot. Think round gear leg vs one with a teardrop shaped
fairing.

I'm aware of the stabilizer/control surface intersection but they
aren't four feet apart.

Take a look at big tractor-trailer rigs. the air dams on the tractors
aren't higher than the trailers.

I suspect this due more to height restriction. They are several feet
apart also. I might have to look into this some more.

Charlie
I'm not an aerodynamicist, but I do know one. :-)


--Andy Asberry--
------Texas-----

On Wed, 16 Jul 2008 23:18:56 -0400, "Flash"
wrote:

Back in the 70's, the Univ of MD did a real great study of that sort of
thing. They determined that if you could eliminate the gap altogether, you
would have a MUCH better efficiency.

They had a system of complex levers and springs and stuff on moveable panels
that eliminated the gap on top and sides, right down to the road almost.

Try that on your pickiup and your wickiup. - NOT!

Really, if you can get as close to eliminating the gap as you can, the only
problem will be the sides. The top can be a piece with a concaved-shaped
edge on the truck, a convex-sort of sheet on the trailer, with the *center*
of the arc approximately over the hitch-point.

The OTR trucks have side-fairings on the cabs that are sometimes two feet in
length, but they work that way because the pivot of the fifth wheel is over
the axles, about 4 or 5 feet behind the front of the trailer. When the
trailer turns, the corner of the trailer is up between the fairings.

Really, just eliminate as much open distance as you can. If you had a "fifth
wheel" trailer, you'd be further ahead.

Flash

About anything will be better than the open bed dragging an 8x8 flat
plate.

--Andy Asberry--
------Texas-----

Andy Asberry wrote:

3/4 ton extended cab pickup towing a 24 foot travel trailer. Fuel
mileage is effected much more by wind than weight.

I want to build a camper shell that will be cab high at the front and
direct the airflow smoothly over the trailer.

There is about 4 feet between the front of the trailer and the rear of
the proposed camper. For some reason, I believe the camper should be
higher than the trailer. But how much higher? Should the angle be
constant? Convex? Concave? A different exit angle?

About a foot from the top of the trailer, the front slopes back at a
45 degree angle. All opinions are welcome but educated calculations
will be given more weight.

--Andy Asberry--
------Texas-----


Best solution at lowest cost?

Slow down.

There is no induced drag here - only parasitic drag.

D = 1/2 Rho Cd S V^2

Also

Thrust Horsepower required = (D*V)/375
Which brings V up to a cube.

FWIW...

--

Richard

(remove the X to email)

America has become thouroughly convinced that the lunatics
are running the assylum and good idea or no, it will take
more that George W Bush at a press conference to reclaim
the public trust this administration has wantonly destroyed.

John R. Corroll

Flash wrote:
Back in the 70's, the Univ of MD did a real great study of that sort of
thing. They determined that if you could eliminate the gap altogether, you
would have a MUCH better efficiency.

They had a system of complex levers and springs and stuff on moveable panels
that eliminated the gap on top and sides, right down to the road almost.

Try that on your pickiup and your wickiup. - NOT!


It wouldn't be to hard if you were looking to build something.

Find some way to attach 3 rolls of heavy cloth to the truck, one to each side and one to the top. Spring return. A rod
with built in hooks down the pulled end. Put catches on the sides and top of the trailer. Might even add a zipper at
the top corners. A stiff canvas with a fairly stiff return spring should work.

On Thu, 17 Jul 2008 01:39:29 -0500, cavelamb himself
wrote:




Best solution at lowest cost?

Slow down.

There is no induced drag here - only parasitic drag.

D = 1/2 Rho Cd S V^2

Also

Thrust Horsepower required = (D*V)/375
Which brings V up to a cube.

FWIW...

I'm already that guy over in the right lane everyone is passing.
Coming from Nebraska last week, my 50 MPH ground speed was almost
overcome by my 100 MPH airspeed!

--Andy Asberry--
------Texas-----

On Jul 16, 11:42*pm, Andy Asberry wrote:
On Wed, 16 Jul 2008 19:58:06 -0500, Charlie
wrote:



I'd be betting against making the camper higher than the trailer. At
least on a/c, drag is reduced if the trailing body is slightly larger
than the object ahead of it. Ailerons with leading edges that are
slightly fatter than the wing trailing edge come to mind. If you can't
make a smoothly faired transition to a smaller cross section, the drag
will go up a lot. Think round gear leg vs one with a teardrop shaped
fairing.

I'm aware of the stabilizer/control surface intersection but they
aren't four feet apart.

Been many months since I looked for it (years?) ........... but down
load a copy of JavaFoil and make up some airfoils that look like a
truck and trailer, put them in and see what happens?
=================
Leon McAtee