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
nallingtoon said
02:30 AM Feb 29, 2012
Hi All
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
PeterS said
02:58 AM Feb 29, 2012
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.
justcruisin01 said
04:23 AM Feb 29, 2012
nallingtoon wrote:
Hi All
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.
Ma said
05:55 AM Feb 29, 2012
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.
BobnBev said
12:42 AM Mar 1, 2012
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...
ken thomas said
01:57 AM Mar 1, 2012
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
old briney said
04:11 AM Mar 1, 2012
nallingtoon wrote:
Hi All
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 they are only to stop the roof rack whistle
justcruisin01 said
04:58 AM Mar 1, 2012
old briney wrote:
nallingtoon wrote:
Hi All
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 they are only to stop the roof rack whistle
Mate, you would have to be joking.
If its wind whistle you want to stop between roof rack bars ALL you have to do is connect a ocky srrap between the bars.
Same if a ratchet tiedown strap whistles put a half turn in the strap.
JC.
nallingtoon said
05:20 AM Mar 1, 2012
thanks all for the interesting response to my question might just try and find a cheapy on Ebay to give it a go will let you know how it goes
Dunco said
07:00 PM Mar 1, 2012
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 !!
justcruisin01 said
05:08 AM Mar 2, 2012
Dunco wrote:
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.
KMMA said
09:57 PM Nov 23, 2018
Neil,
Just wondering if ended up buying a wind deflector and if so, how did it preform?
Dickodownunder said
10:16 AM Nov 24, 2018
Ya dont really need a wind deflector when you have a boat.
Just mount the boat in the most strategic position to deflect the wind.
Oh and learn how to park close to the slab when in crowded caravan parks.
And one for the sparkies...check the power lead...
-- Edited by Dickodownunder on Saturday 24th of November 2018 10:26:31 AM
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
Hi All
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.
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.
Bob...
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
Neil they are only to stop the roof rack whistle
Mate, you would have to be joking.
If its wind whistle you want to stop between roof rack bars ALL you have to do is connect a ocky srrap between the bars.
Same if a ratchet tiedown strap whistles put a half turn in the strap.
JC.
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.
Just wondering if ended up buying a wind deflector and if so, how did it preform?
Ya dont really need a wind deflector when you have a boat.
Just mount the boat in the most strategic position to deflect the wind.
Oh and learn how to park close to the slab when in crowded caravan parks.
And one for the sparkies...check the power lead...
-- Edited by Dickodownunder on Saturday 24th of November 2018 10:26:31 AM