I can't see how wind deflectors on a roof rack would not increase fuel consumption due to increased induced drag arising from turbulent airflow immediately behind the deflector.
They work on trucks only because they are located directly in front of and very close to the large box shaped trailer creating smoother (laminar) airflow around the trailer. Without the deflector there is significant turbulence created immediately in front of the trailer giving rise to increased drag.
Much of the arodynamic drag created by modern caravans comes from the large slab shape of the rear of the van. This applies to trucks too as every caravanner is reminded when being overtaken by a one.
Aerodyamic theory (and practice) suggests that the older teardrop rear ends of earlier caravan designs would be more aerodymanically efficient.The trade-off may be the possibility of less stability at higher speeds, it would require "real world" tests to establish if this were so however.
If caravan suppliers wish to dispute this ask them to produce the results of some wind tunnel tests.
Have a look at the design of an aeroplane's fuselage, it always tapers to a point.
-- Edited by jimricho on Tuesday 28th of February 2012 11:13:27 PM
Have never used one myself but a friend with a trucking company fitted the big ones to his trucks and saved up to 17% on fuel. not sure how they work on cars etc with caravans would expect would be almost as effective.
A question concerning wind deflectors (roof rack type) do they work has anyone on this site used one or uses one successfully appreciate any feed back
Regards
Neil
Neil. again dont have one but I think it should work ok.
Many talk about carring a boat on top & creating wind drag, I have a large boat & I honestly beleive this works the same as a deflector for the caravan, I dont notive any extra load drag from the boat & fuel seems to be the same.
I have a large bug/wind deflector on top of the bull bar & this works very well, very few bugs get tp the screen & you can see then diverting of to the side.
cheers;
JC.
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A pic of that bug deflector would be good if you have one Jim.
We have a kayak on the top of our tug and thought it would act as a wind deflector but I don't think it really does.
Our fuel consumption actually went UP after we decided to take the kayak along for the ride. Only marginally, probably about half a litre per 100ks so we aren't complaining.
I notice the differance when Ive got the boat on top, tows the van much easier. and when in a head wind its realy noticeable, for the better. its the side wind that kills me. I think they work, but need to be set up right.. Bob...
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Land Rover Discovery Chipped TD5 Manual ,Air Springs, Anti Sway. T.C. Auto level. Van, Roadstar 21.6 Voyager 4000 all sola powered.
Hello I am looking at getting a nosecone fitted to my van and they guarantee a 10% reduction in fuel use due to the aerodynamics Will see when it is fitted Ken
There was a few tests done some years back and they did nothing.
The problem is that the deflector is too far away from the van which causes the wind to "dip" after the deflector and hit the van, where the wind should be one flow over the deflector and over the van !!
There was a few tests done some years back and they did nothing.
The problem is that the deflector is too far away from the van which causes the wind to "dip" after the deflector and hit the van, where the wind should be one flow over the deflector and over the van !!
Thats posibily why a boat makes a good deflector, generely the boat is higher than the van & being so long it deflects very well , also is much closer to the van than a roof top deflector.
Our van being a poptop is much lower than the boat height.
JC.
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