deflectors

philbe · Newbie

deflectors

Dougwe · Chief one feather

Welcome to the gang Phill, enjoy here and out in the playground.

If you mean the ones that sit on the roof of your car then I see why not as they direct the wind to go over the van.

Also and as well even, I hope you are a well behaved Phill cos we have a Phil C here and he spends most of his time in the naughty room. Say no more.

dogbox · Guru

it would depend on fast you travel an how far you go example if you spent $1000 dollars setting one up an you saved 1 cent per klm in fuel(speeds over 90 kph) you would have to drive 100,000 klm plus of highway driving to even come anywhere near covering the cost
they are effective on highway trucks because they travel at highway speeds 2-300,000 klm or more per year not really a good from an economical point if you tow your van 5-10000 klm per year an if it is not able to be removed or lowered when not towing it could cost you fuel because of the extra drag

someone maybe able to come up with some technical data to confirm or deny the above statement

how does doug know phil was in the naughty room so often is it because he sees him there????

-- Edited by dogbox on Tuesday 4th of August 2015 05:18:30 PM

rockylizard · Guru

Gday...

Firstly ...

Welcome 02.jpg

Have a gander at this review Philbe ... gives some indication.

http://www.caravancampingsales.com.au/content/news/2012/aeroplus-trims-fuel-costs-33975

Cheers - John

Woody n Sue · Guru

And it's welcome from us two 2 philbe don't know about these on cars but I remember a myth buster program that did a test on a "pickup Truck " in the states, two brand new trucks were filled and then run till they stopped one with the tail gate up one down.

And the winner was by a fair margin

Tailgate

UP

Yes I know the driver can make a fair difference to fuel consumption too.
Make of it what you will .

Woody

iana · Guru

Why is it that everybody likens traveling through air, to that of forcing a wedge to make a track through margarine? That the air will part away, allowing the vehicle to sail through, and achieving a 50% decrease in fuel consumption to-boot.
Unfortunately air does not behave like margarine, the air will be turbulent over protruding surfaces, and blunt ends, causing negative pressure areas and the result is drag.

Drag increases at the square of the speed, a body traveling very slowly will develop very little drag, For example a person going for a walk. If that person starts running the resultant drag will go up by the square of the speed increase.

This drag can be reduced, for example in the case of the runner with slippery suits, but the interesting thing is it not the front of the body which is the culprit but the back. Have a look at nature and we see some fish, whales and our parrots having blunt fronts, but they all have streamlined rear bodies.

We have the conception that by putting a point on something, then it will cut through the air, and while that may be true with high speed bodies, the main source of the problem is protrusions and poor streamlining at the rear.

Unfortunately your 4 x 4, Motor home and or caravan has the streamlining of a brick. About the only thing that may reduce drag as far as I am concerned is making the sides of the vehicles smooth, no protrusions. Aircraft do use protrusions; they deploy them as air brakes.

Protrusions may be TV aerials, satellite dishes, solar panels, air conditioners, awnings, vents, roof racks and deflectors. Well that was what I was taught early on in my career.

WobblyNut · Senior Member

got to agree with Ian A lot on this.

Plus if you have a look at the back doors of a semi , allways dirty,

more so between back of cab & front of trailer & some are so close to

each other , it makes you wonder how they turn . I noticed . There was

NO Cabover trucks on the highway in USA , they were All bonneted trucks.

Here we use mainly Cabover and as Ian said 'protrusions' - underneath , you

have - diffs , landing legs , tyre carrier , gate carrier & the 3 axles .

Philbe . I doubt , if by having one on your ute , will help. As you won't get it back far enough to assist.

I have found . If I drive smoothly . It Makes a Big difference . I am usually around a $ (100kph) .

I know what I use going to Siddely 20/8 I am going to th smoke , will try 90/95 , see what difference.

Ontos45 · Guru

This may be helpful in understanding drag.

https://en.wikipedia.org/wiki/Drag_(physics)

Shape and flow	Form Drag	Skin friction
	0%	100%
	~10%	~90%
	~90%	~10%
	100%	0%

Nomes · Senior Member

That was very well explained Iana, you explained that in a similar way to a yachtie friend who was teaching me how to sail his 42ft Jeanneau. Already I'm a better tower than a sailor.