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Side Rack Instead of Yakima Rack

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#11 Vic Harder

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Posted 04 March 2021 - 12:26 AM

The drag UNDER the vehicle is really important too.  Those lower lips you see under the bumper on trucks make a significant difference.  They also interfere with approach angles, and can get ripped off.


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#12 DavidGraves

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Posted 04 March 2021 - 01:15 AM

The other obvious MPG mod I daydream about is to make some sort of fairing for the front corners of the camper main box.

 

On my Chevy these are perhaps a foot wider than the truck cabin and cry out for some sort of slipstreaming.

 

But then , I do a lot of day dreaming. : )

 

DG


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#13 steve whiteside

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Posted 05 March 2021 - 02:52 AM

Very cool!  Im a mechanical engineer but by no means an expert on the subject of fluid mechanics.  A couple things stick with me though- you guys probs already know this.  Amount of the drag force is related to velocity squared.  So as you go quicker it really works against you.  The other thing is that frontal area is multiplied by the coefficient of drag.  I would guess that your roof top rack probably increased your frontal area more than your side rack- but you know this.  I would also guess that the rack up top compared to the rack on the side didn't really change your overall vehicle coefficient of drag much.  Both additions are going to be draggy.

 

So, you are thinking that your gas mileage will improve and I agree with you.  This would be based on your frontal area being less.  I also like your idea to measure drag with the repeatable hill.  Neat idea to give you a quick look.

 

--------

I just went through a design/build on a rack to carry my ski's.  If I had seen your post I probably would have done as you suggested vs what I built.  Im happy with my thing but it grew beyond just carrying my skis and now needs a place in my garage for storage and it is not small.  In my case the frontal area of my truck did not grow but the coefficient of drag may have changed.  Good or bad I dont know.    https://www.wanderth...unted-ski-rack/

 

 

Steve


Edited by steve whiteside, 05 March 2021 - 03:04 AM.

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#14 ntsqd

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Posted 05 March 2021 - 02:35 PM

Consider the shape that a falling water drop is always drawn as, or even pictured with high speed photography. The bottom or front is hemispherical because that shape offers the greatest volume for the least frontal area or the least drag. Look at the tail, water wouldn't form that way by itself, something else is doing that. Drag, air drag in this case. The surface tension of water is high so the air drag from the laminar boundary layer stretches out the tail in an effort to stay attached to the surface.

 

Those little fins are properly called "Vortex Generators". https://en.wikipedia...ortex_generator Aircraft pioneered their use. Then they showed up on rally cars at the top of the rear window and on the underside of F1 rear wings. Shortly thereafter they showed up on the rear of under-belly trays, and the street scene glomed onto them.

 

If you can see the chair bags ruffling in the wind while going down the highway it would probably benefit from having a smooth outer surface. A 'door' or fairing of some sort. Could be as simple as a piece of plastic sheet covering the whole that is attached with high strength velcro.


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Thom

Where does that road go?

#15 DavidGraves

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Posted 05 March 2021 - 04:04 PM

So my Chevy 3/4 ton with camper would have to reach at least 45 MPH for the little fins to impart any effect on fuel consumption ?

 

Dang, the kid down the street with the 335 HP Subaru said they were all the rage.....

 

What is a chair bag ?

 

David Graves


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#16 UmkaAndHawk

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Posted 09 March 2021 - 07:54 PM

Tell me more about the box on the front of the camper between it and the truck back window!

I too think that could be valuable space!


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#17 ntsqd

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Posted 10 March 2021 - 12:59 AM

So my Chevy 3/4 ton with camper would have to reach at least 45 MPH for the little fins to impart any effect on fuel consumption ?

 

Dang, the kid down the street with the 335 HP Subaru said they were all the rage.....

 

What is a chair bag ?

 

David Graves

 

The bag that most camping chairs come with to store them in.
 


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Thom

Where does that road go?

#18 DavidGraves

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Posted 10 March 2021 - 03:56 AM

Oh sure, bags with folding chairs inside them.

 

Our chairs stow inside.

 

Is there anything simple that can be done to improve airflow and mileage for highway speeds with our campers ?

 

David Graves


Edited by DavidGraves, 10 March 2021 - 03:56 AM.

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#19 LuckyDan

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Posted 10 March 2021 - 09:14 AM

Is there anything simple that can be done to improve airflow and mileage for highway speeds with our campers ?
 
David Graves


If you dig WAY back through either the Truck Campers or Four Wheel Camper Discussion sections, there was fairly lengthy discussion on, and examples of adding a fairing in front of the cabover. From what I remember, those who had added one were getting a mile or two a gallon increase. It may have been part of the discussion on what to do with the space under the cabover with examples instead. The discussions happened around the same time.

Good Luck....
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#20 Vic Harder

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Posted 10 March 2021 - 10:46 PM

Punch this into Google - www.wanderthewest.com air deflector or just click this link: 

www.wanderthewest.com air deflector - Google Search

 

I added one once, and found that it cause the cab of my truck roof to "tin can"... super annoying.  Took it out.  


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2015 Silverado 3500 crew cab 8' bed Diesel

2012 ATC Puma Shell build - https://www.wanderth...012-puma-build/

Power considerations thread - https://www.wanderth...e-power-scotty/

Building out an electrical system - So, you want to setup a good electrical system in your camper? - Electrical, Charging, Solar, Batteries and Generators - Wander the West






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