Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-06-2006, 07:30 PM   #1
2 Rivet Member
 
ITowSilver's Avatar
 
Join Date: Jan 2004
Posts: 51
Does a truck cap help wind flow?

I intend to tow a 28' Classic with a 3/4t short-bed pickup. Would a bed cap (not a tonneau) increase towing efficiency by smoothing wind flow?

Thanks.

Sam
__________________

ITowSilver is offline   Reply With Quote
Old 03-06-2006, 07:33 PM   #2
Remember Burma Shave!
 
driftwood's Avatar
 
2006 19' Safari
2000 25' Safari
1985 25' Sovereign
Fort Myers , SW.Florida
Join Date: Sep 2003
Posts: 510
Images: 35
Yes!
__________________

__________________
NORM #3305

"... there is nothing you can't fix yourself ...
... if you're handy ...
... with a check book! ..."
driftwood is offline   Reply With Quote
Old 03-06-2006, 07:40 PM   #3
Rivet Master
 
overlander63's Avatar

 
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 21,096
If you can find one, get a fiberglass cap with a turn-up at the rear, this will help deflect the wind up and over the trailer.
__________________
Terry
overlander63 is offline   Reply With Quote
Old 03-06-2006, 07:41 PM   #4
4 Rivet Member
 
bill benton's Avatar
 
1991 34' Excella
Mansfield , Texas
Join Date: Jan 2004
Posts: 490
It would also give you more weatherproof storage. I would think anything that would decrease drag would be an improvement. Unfortunately I haven't seen any wind tunnel tests
bill benton is offline   Reply With Quote
Old 03-06-2006, 07:44 PM   #5
Rivet Master
 
JimGolden's Avatar
 
Vintage Kin Owner
1977 31' Excella 500
Berkeley Springs , West Virginia
Join Date: Sep 2005
Posts: 1,629
Images: 7
Oh man, I gotta chime in on this

Got a degree in Aerospace Engineering and used to work for Boeing. Now I build bridges...but I still love my airplanes!

If you're pulling a trailer, then a cap will most definitely help you. What will happen if you don't have one is that you will get vortices forming off the back of the cab that will then slam into the front of the trailer. That flow will then need to bend around the trailer again.

If you do have a cap, then the flow is pretty much smooth across the truck. When it gets to the rear, it will try to converge but...run into the front of your trailer and then stay relatively attached as it flows down the sides. Kind of like two NASCAR stockers drafting. An Airstream is better than a box SOB at allowing the flow to converge smoothly at the end, but it still will create turbulence as the air trys to come back together.

Now when you're not towing, it's just the opposite. The cap creates more drag than not having it. What you've basically got now is a giant brick and the air rolling off the back of the truck will really create some vortices.

Granted, we're not going 600mph here and it's not the same deal at 60 as it is at 600 (or even 150). But, the ideal would be to have an inflatable cone that comes off the back so that the air doesn't "slam" back together but converges smoothly. DOT would love it wouldn't they??!!

I've actually seen a device called the "Tailcone" on the backs of some semi truck box trailers. It would be next to useless, aerodynamically. But it looks cool.

Remember, the F-4 Phantom is proof positive that with enough engine, even a brick can fly!
__________________
- Jim
JimGolden is offline   Reply With Quote
Old 03-06-2006, 07:49 PM   #6
Rivet Master
 
overlander63's Avatar

 
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 21,096
Quote:
Originally Posted by JimGolden
Remember, the F-4 Phantom is proof positive that with enough engine, even a brick can fly!
I remember we used to call the Thunderchief "Thud" for the same reason, a 1:1 glide ratio. But I digress... Ideally, you chould remove the cap when you areen't planning to tow for a while. That brings up the question of where to store the thing when not in use. I suppose you could just leave it on the bed of the truck, if you don't have a place to store it, or slap together a pair of sawhorses in the back yard to hold it off the ground when you are not using it.
__________________
Terry
overlander63 is offline   Reply With Quote
Old 03-06-2006, 07:50 PM   #7
2 Rivet Member
 
ITowSilver's Avatar
 
Join Date: Jan 2004
Posts: 51
Thanks, guys.

How about an air deflector on top of the cab, like the 18 wheeler's use?

Sam
ITowSilver is offline   Reply With Quote
Old 03-06-2006, 07:51 PM   #8
Remember Burma Shave!
 
driftwood's Avatar
 
2006 19' Safari
2000 25' Safari
1985 25' Sovereign
Fort Myers , SW.Florida
Join Date: Sep 2003
Posts: 510
Images: 35
No!
__________________
NORM #3305

"... there is nothing you can't fix yourself ...
... if you're handy ...
... with a check book! ..."
driftwood is offline   Reply With Quote
Old 03-06-2006, 07:55 PM   #9
4 Rivet Member
 
bill benton's Avatar
 
1991 34' Excella
Mansfield , Texas
Join Date: Jan 2004
Posts: 490
No, too much drag. \Maybe for a SOB.
bill benton is offline   Reply With Quote
Old 03-06-2006, 07:55 PM   #10
Rivet Master
 
garry's Avatar
 
1969 31' Sovereign
Broken Arrow , Oklahoma
Join Date: Jan 2003
Posts: 1,448
Images: 7
Another downside to the cap is the weight impact.
Mine weights around 160 lbs but there is no way I could do without it.
Attached Thumbnails
Click image for larger version

Name:	airstream 002.jpg
Views:	123
Size:	89.6 KB
ID:	19053   Click image for larger version

Name:	airstream 003.jpg
Views:	145
Size:	108.2 KB
ID:	19054  

garry is offline   Reply With Quote
Old 03-06-2006, 07:56 PM   #11
2 Rivet Member
 
ITowSilver's Avatar
 
Join Date: Jan 2004
Posts: 51
Does a tonneau have a good, bad, or no effect when NOT towing? It would be nice to have lockable storage.

Sam
ITowSilver is offline   Reply With Quote
Old 03-06-2006, 07:56 PM   #12
Rivet Master
 
overlander63's Avatar

 
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 21,096
The deflector will be too far away from the front of the trailer to help at all, and will only be a second source of drag.
__________________
Terry
overlander63 is offline   Reply With Quote
Old 03-06-2006, 07:59 PM   #13
Rivet Master
 
overlander63's Avatar

 
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 21,096
Quote:
Originally Posted by Sam Davis
Does a tonneau have a good, bad, or no effect when NOT towing? It would be nice to have lockable storage.

Sam
I had a tonneau cover on my Dakota, it seemed to make little difference in fuel consumption. I suppose if you wanted to have both, you could install a cover inside the bed rails of the truck, to use when not towing, and a cap on the top of the bed rails for towing, although it would be duplicative at best.
__________________
Terry
overlander63 is offline   Reply With Quote
Old 03-06-2006, 08:00 PM   #14
Rivet Master
 
overlander63's Avatar

 
1993 21' Sovereign
Colfax , North Carolina
Join Date: Jun 2003
Posts: 21,096
A cap like Garry's would be the type I would recommend if you were to purchase one. Note the upturn at the rear, to help move air over the top of the trailer.
__________________
Terry
overlander63 is offline   Reply With Quote
Old 03-06-2006, 08:03 PM   #15
2 Rivet Member
 
ITowSilver's Avatar
 
Join Date: Jan 2004
Posts: 51
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.
ITowSilver is offline   Reply With Quote
Old 03-07-2006, 08:13 AM   #16
Rivet Master
 
JimGolden's Avatar
 
Vintage Kin Owner
1977 31' Excella 500
Berkeley Springs , West Virginia
Join Date: Sep 2005
Posts: 1,629
Images: 7
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!!
__________________
- Jim
JimGolden is offline   Reply With Quote
Old 03-07-2006, 08:14 AM   #17
Rivet Master
 
JimGolden's Avatar
 
Vintage Kin Owner
1977 31' Excella 500
Berkeley Springs , West Virginia
Join Date: Sep 2005
Posts: 1,629
Images: 7
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!
__________________
- Jim
JimGolden is offline   Reply With Quote
Old 03-07-2006, 12:50 PM   #18
4 Rivet Member
 
Darol Ingalls's Avatar
 
Join Date: Mar 2004
Posts: 411
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
Darol Ingalls is offline   Reply With Quote
Old 03-07-2006, 01:10 PM   #19
Aluminut
 
Silvertwinkie's Avatar
 
2004 25' Safari
. , Illinois
Join Date: Feb 2003
Posts: 10,474
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.
__________________
Computers manufactured by companies such as IBM, Compaq and millions of others are by far the most popular with about 70 million machines in use worldwide. Macintosh fans note that cockroaches are far more numerous than humans and that numbers alone do not denote a higher life form. -NY Times 11/91
Silvertwinkie is offline   Reply With Quote
Old 03-07-2006, 03:43 PM   #20
Rivet Master
 
rseagle's Avatar
 
2004 22' International CCD
Spotsylvania , Virginia
Join Date: Mar 2004
Posts: 663
Images: 33
Some caps are more aerodynamic than others.
Attached Thumbnails
Click image for larger version

Name:	Airstream at Dam Neck CG_small.jpg
Views:	114
Size:	80.6 KB
ID:	19075   Click image for larger version

Name:	Airstream at Chippokes State Park_small.jpg
Views:	105
Size:	85.3 KB
ID:	19076  

__________________

__________________
Bob
---------------
"THE BAUXITE BUNGALOW"
2004 22' CCD
1997 F-150
TAC VA-12
AIR# 4749
ex WBCCI# 1430
rseagle is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
'59 Trade Wind flyfshr 1959-69 Tradewind 196 03-10-2013 09:42 PM
Flow Thru Exhaust and Muffler LKappenman Mechanics Corner - Engines, Transmission & More... 17 09-22-2009 11:29 AM
HELP PART NEEDED! Aluminum Termination Cap... InsideOut Waste Systems, Tanks & Totes 46 03-20-2006 06:08 AM
need to replace a radiator cap stuart1 Mechanics Corner - Engines, Transmission & More... 1 10-28-2002 02:12 PM
310 front cap Bfrank General Motorhome Topics 11 07-25-2002 08:36 PM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.



All times are GMT -6. The time now is 09:31 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.