roof airofoil for towing aid

[frank_374357141]

Hi folks, i am trying to locate an airofoil to fit on my Alhambra tow vehicle. they used to be made by a firm called Bumper to Bumper but seem to be out of fashion now.I find they are a good help when towing if only to keep the flies and such off the front of the ,van.thanks for reading this request Frank T

 

[GeorgeB]

Frank,

Yes I remember them, were'nt they called "Windslammers"?

Used to have one mounted on my MK1 Golf Diesel when tugging my Robin 12/4 way back in the early eighties.

Can't remember if they were of any benefit towing or fuel consumption wise but I seem to remember not having to clean the bugs off the front of the van so often though!

 

[Steve L]

I currently use a Wind Jammer aerofoil on my Laguna estate while towin our twenty foot twin axle van. As the vn was built in 1982, it has the aerodynamics of a brick wall. But using the aerofoil, not only improves stability as the wind is channeled down each side of the van, I also get better performance. I can get 7 miles per our faster and also upto 5 Mpg better fuel consumption.

I got my jammer from a local general sale auction for

 

[VonRyan]

Hi

Bumper to Bumper went out of business about 10 years ago. I was the U.K sales manager and left and they went out of business 18 months later.

The J.R group(Midlands and North) bought lots of these along with Homestead caravans in the South, A dealer in Ulverston, Cumbria who's name I can't remember at this time,along with a dealer in Gillingham. They were tested at UMIST(wind tunnel) in Manchester and they really did work when set up correctly. I used to have one but on one occassion I took it off the roof and put it behind the van while on site and it walked off never to be seen again.

You might find them at car boot sales and can be easily modified to fit gutterless vehicles.

Rob

 

[RogerL]

They were only beneficial on estate body shapes - in modern terms MPVs and 4x4s would also be included - even then it really needs a wind tunnel to set up the correct angle.

They can, and usually do, adversely affect stability by reducing the dynamic downforce on the front of the caravan.

Consider a front cover to keep the van clean while towing.

 

[Lutz]

Perhaps you may like to explain how an aerofoil near the rear of the roof of a boxy-shaped towcar (such as an estate or MPV) is going to reduce the dynamic downforce on the front of the caravan? I would have thought that anything which increases the size of the projected frontal area of the towcar (which an aerofoil would effectively do) is going to provide a larger shield against headwind acting against the caravan. As the heaadwind is responsible for the reduction in dynamic noseweight, anything that reduces frontal air pressure acting against the caravan is surely going to have less of an effect in reducing the noseweight. Or have I got something wrong?

 

[Reg]

Many years ago I used to tow a sprite alpine with a wolesey 16/60 and noticed a considerable improvement, i.e.less drag, when I had a mirror dinghy on the top of the car. A bit of a drastic measure and I'm not suggesting going out and buying a dinghy.

Having returned to caravaning after a 20 year break I have noticed a vast improvement in the drag. I believe it's the case with modern caravans that the drag is actually decreased by the shape of the back end of the van?

 

[Happy-Lappy]

Perhaps you may like to explain how an aerofoil near the rear of the roof of a boxy-shaped towcar (such as an estate or MPV) is going to reduce the dynamic downforce on the front of the caravan? I would have thought that anything which increases the size of the projected frontal area of the towcar (which an aerofoil would effectively do) is going to provide a larger shield against headwind acting against the caravan. As the heaadwind is responsible for the reduction in dynamic noseweight, anything that reduces frontal air pressure acting against the caravan is surely going to have less of an effect in reducing the noseweight. Or have I got something wrong?

Lutz,

I am assuming that the Windjammer/Airfiol works by deflecting the wind from the front of the caravan and I am in agreement with you, I don't see how this will effect the actual downforce applied to the towing hitch, therefore it is not going to become an issue with the noseweight,

best regards, Martin

 

[Lutz]

Perhaps you may like to explain how an aerofoil near the rear of the roof of a boxy-shaped towcar (such as an estate or MPV) is going to reduce the dynamic downforce on the front of the caravan? I would have thought that anything which increases the size of the projected frontal area of the towcar (which an aerofoil would effectively do) is going to provide a larger shield against headwind acting against the caravan. As the heaadwind is responsible for the reduction in dynamic noseweight, anything that reduces frontal air pressure acting against the caravan is surely going to have less of an effect in reducing the noseweight. Or have I got something wrong?

Actually, I'm saying that if anything it should have a positive effect because it reduces the amount of uplift of the front end of the caravan at speed.

 

[RogerL]

Lutz - the headwind acts in two places at the front of a caravan - the roof at the front is subject to high pressure causing downforce - the floor at the front is also subject to high pressure which causes upforce.

On a normal caravan the net effect of the two high pressure areas is upforce.

Using a windslammer increases that upforce by reducing the high pressure at roof level.

 

[vernon]

I seem to remember that the AA did some wind tunnel tests back in the '80s, which said gave some benefit, but concluded that the angle of the aerofoil did not matter and that a vertical 6 inch one had the same affect in deflecting the airflow over the caravan, as long as it was far enough back, hence they were better on estate cars.

 

[Reg]

I found this article by the caravan & camping club of S Australia

Its a bit long winded but worth a read:-

WIND DEFLECTORS

A wind deflector on a car can possible arouse more discussion than any other caravanning accessory. It is difficult to find someone who has tried a deflector to state other than that it is beneficial. Yet the simple truth is that some deflectors do more harm than good.

It should be remembered that anything which is attached to the roof of a vehicle, whether a pack rack or wind deflector, increases the fuel consumption. If, for example, a wind deflector increases the wind resistance created by a car by 10% then the corresponding resistance on the caravan must be reduced by at least 10% before any advantages can be expected.

Aerodynamics is a very complex science and the way that people think air behaves is reflected in the various deflector designs. Because of many different caravan and tow vehicle combinations there is unfortunately no readily available formula for calculating deflector dimensions.

Experience has shown, however, that if some basic requirements are met, wind deflectors do work.

Size: The effective frontal area of a deflector should be approximately 65-70% of the area of the front of the caravan which is above the roof of the area of the front of the caravan which is above the roof height of the car roof. It should be appreciated that the effective frontal area depends on the angle. A piece of material 1 m x 1 m has an effective frontal area of 1 ml when standing up straight but only 0.5m' if positioned at 45'.

Shape: A straight deflector will only lift the air that actually comes in contact with it. The air passing along each side will still flow back against the front of the caravan. To overcome this the shape must be such that it not only lifts the air but also spreads it so that it will flow either side of the caravan. This means it should be either curved or "V" shaped.

Angle: This should be at least 45' to supply enough lift for the air to flow over the top of the caravan roof. If the angle is obtained by the 'line of sight' method, then the air stream will not reach sufficient height to clear the roof.

Mounting Position: A deflector should be mounted as far back as possible on a vehicle roof. The greatest and most uncontrollable factor reducing efficiency of a deflector is the gap between the deflector and the caravan. The smaller this distance the more efficient a deflector is likely to be.

Method of Mounting: Because of the high wind pressures a deflector is subjected to, it must be securely positioned on at least four places on a vehicle roof. Any deflector mounted on only one bar or two mountings will place excessive loads on the mounting points.

From the previous points it can be appreciated that some deflectors are obviously more effective than others. One way that a deflector's effectiveness can be judged is to observe if it keeps the front of the caravan clear of insects. Besides a decrease in petrol consumption, a well designed and positioned deflector will also provide more stable towing, less buffeting from passing vehicle and lower engine operating temperatures.

 

[ShadySadie]

There clue may be in wind "deflector".

At 45 degrees a deflector will act partly as air brake and the wind will vortex spiral ;

 

[Reg]

Hi Shady Sadie,

Feel free to criticise it's not my article and my knowledge on the subject is zilch. I'm just curious about the subject really.

Does your husband have any information about the back of modern caravans which I believe is designed to create turbulance which causes a back pressure on the van and hence decreases the drag?

I have read about a similar technology used on car design.

My reason for asking is whether a deflector on the car would in fact change the airflow and might possibly alter and upset the caravan design.

 

[Lutz]

I appreciate that areodynamics is a complex subject and I specifically talked about having the deflector as far to the rear of the towcar as possible so as not to create the vortex between car and caravan, mentioned above. However, I still think that the exposed frontal area of the caravan, i.e. the area extending above the roof of the towcar, being so high and subjected to headwind, will result in a substantial moment about the axle (which is located much lower), causing an uplift at the front and thereby reducing the dynamic noseweight. If the exposed frontal area is reduced due to fitment of wind deflector, this should, in turn, reduce the uplift.

 

[vernon]

Surely the speed of the vehicle can very the effectiveness of the deflector.

What may be good at 60mph, may cause extra drag at 30mph. (Or visa-versa!)

 

[ShadySadie]

Giosg that was some years back , we had a Volvo estate when he first tried out the deflector experiments, I have always towed our caravans as he works away from home a lot. At the time our T/A caravan had what was described as an aerodynamic front, but I could feel the difference when towing with out the "wing" at the back.(better with the wing)

Moving to a new site about 40 or 50 miles along the coast I left the wing off and noticed the car kept changing down from top on the exposed autoroute, when moving on again I clamped the wing back on and found the car maintained speed better and held top gear in higher head winds and fuel consumption was always better with the wing.

Since we have used taller 4 x 4's the car is closer to the vans height and we found no benefit using the wing.

 

[JTQ]

I spoke a cross channel ferry to a fellow caravanner towing down to Spain who had a "Top box" on his Discovery3. He claimed it improved his long haul fuel consumption and that was his main reason for putting it on.

Anybody else info to add on this effect?

 

[Peter_374293316]

I spoke a cross channel ferry to a fellow caravanner towing down to Spain who had a "Top box" on his Discovery3. He claimed it improved his long haul fuel consumption and that was his main reason for putting it on.

Anybody else info to add on this effect?

Frank

We used a homemade wind deflector in the 1990's made from a sheet of aluminium (based on the windslammer design) which was fixed to 2 roof bars and clamped to the the roof guttering on cars that had them (gutters)in those days. I tried towing with and without on occasion to see if it really made any difference. The angle of the deflector was crucial. I found that the best result was when it was angled so that the deflected air hit the front of the caravan just below the roofline. It certainly kept the front of the van cleaner and while it may not have noticeably reduced fuel consumption, I got up to cruising speed (ie 60mph where permitted) noticeably quicker. I think the temptation was to drive a little faster which nullified the fuel consumption benefit. I think that one deflector design used a large inflateable bag strapped to the front of the caravan though I never saw one on the road! What I noted again recently is that HGV tractor units have sculpted cab roofs or plastic "deflectors". I'm sure the cab/artic manufacturers wouldn't do this without good reason. It seems to me there is a gap in the market here. I may even get my welding kit out and try to recreate the old design and try it on my (very slippery) C4 Picasso. I realise that modern car designs are streets ahead of those in the 90's but what the heck, if no one is making them these days let's give them a try.

 

[Peter_374293316]

Apologies - I had meant to reply to topic here.

Frank

We used a homemade wind deflector in the 1990's made from a sheet of aluminium (based on the windslammer design) which was fixed to 2 roof bars and clamped to the the roof guttering on cars that had them (gutters)in those days. I tried towing with and without on occasion to see if it really made any difference. The angle of the deflector was crucial. I found that the best result was when it was angled so that the deflected air hit the front of the caravan just below the roofline. It certainly kept the front of the van cleaner and while it may not have noticeably reduced fuel consumption, I got up to cruising speed (ie 60mph where permitted) noticeably quicker. I think the temptation was to drive a little faster which nullified the fuel consumption benefit. I think that one deflector design used a large inflateable bag strapped to the front of the caravan though I never saw one on the road! What I noted again recently is that HGV tractor units have sculpted cab roofs or plastic "deflectors". I'm sure the cab/artic manufacturers wouldn't do this without good reason. It seems to me there is a gap in the market here. I may even get my welding kit out and try to recreate the old design and try it on my (very slippery) C4 Picasso. I realise that modern car designs are streets ahead of those in the 90's but what the heck, if no one is making them these days let's give them a try.

 

[frank_374357141]

Apologies - I had meant to reply to topic here.

Frank

We used a homemade wind deflector in the 1990's made from a sheet of aluminium (based on the windslammer design) which was fixed to 2 roof bars and clamped to the the roof guttering on cars that had them (gutters)in those days. I tried towing with and without on occasion to see if it really made any difference. The angle of the deflector was crucial. I found that the best result was when it was angled so that the deflected air hit the front of the caravan just below the roofline. It certainly kept the front of the van cleaner and while it may not have noticeably reduced fuel consumption, I got up to cruising speed (ie 60mph where permitted) noticeably quicker. I think the temptation was to drive a little faster which nullified the fuel consumption benefit. I think that one deflector design used a large inflateable bag strapped to the front of the caravan though I never saw one on the road! What I noted again recently is that HGV tractor units have sculpted cab roofs or plastic "deflectors". I'm sure the cab/artic manufacturers wouldn't do this without good reason. It seems to me there is a gap in the market here. I may even get my welding kit out and try to recreate the old design and try it on my (very slippery) C4 Picasso. I realise that modern car designs are streets ahead of those in the 90's but what the heck, if no one is making them these days let's give them a try.

Hi everybody, thanks for all your comments on the airofoil question that i posted.heck i didnt expect such a flood of interest in the subject.I am still of the opinion that they help to protect the front of the caravan when towing,roof position being the critical factor. I still have my original windslammer which fitted cars with gutters(age now showing)but as yet have not fathomed out how to fix it to the roof bars on the alhambra considering it will have to be secure. Many thangs to you all for the discussion on the subject,this caravanning is a great hobby. frank T

 

[gary]

It amused me to read that it was 'difficult to find' anyone that had used one not to say it worked, as a passed user I'd say thats most probably because they do work.

All I would say is much depended on it's design/distance from van and had little noticeable effect under 50mph

 

[Sedo]

Without getting involved in the shapes etc. of deflectors, I remember years ago when fairings were first fitted to motor bikes (pre- Japanese invasion) I was told that aerodynamics had very little effect under 50 m.p.h.

Tomo

 

[Lutz]

It depends what sort of aerodynamic effect you are talking about. An aerofoil on a solo vehicle travelling at low speed may only provide a few kilos of downward thrust that is not going to have much of an effect on its handling, but the same change to noseweight may have a significant influence on the stability of a caravan.

 

[Bezzer]

A fairing is effective from lowish speeds upwards always giving better aerodynamics so aiding stability,weather protection, mpg and higher top speed not to mention rider comfort.

Think you'll find the 50mph mark with bikes is for the buffeting you get on a "naked" one, once you get over 50-60 it starts to become uncomfortable to average the higher speeds and a fairing comes into it's own for that reason