There was a good comment for another UKposts video. The crux is don't let the tail (trailer) wag the dog (car/truck). This means the dog needs to be substantially heavier and bigger than the trailer. Don't tow at the limit of your vehicle as it assumes normal operation. A big wind gusts will take the towing dynamics exponentially out of the norm. Have that extra margin with a big heavy (dog) to dampen the initial swaying force.

As far as i know most caravans leave the frame at the underbody open. Which produces surprisingly much drag. There is great potential by just simply covering the framing.

Thanks to Kyle for helping the Mercedes F1 team. It's a pleasure to see a person from behind the scenes. Most caravans are sloped at the front opposed to the diagram being used here. So this fact could change Kyle's thinking and choose B over A. He did talk about rounding off the front edge of the van in B. By the way, the car diagram looked like a 76 series which doesn't have the sloped windscreen as a lot of other vehicles. So possibly C is the best option with most vehicles and vans with the front sloped as they commonly are. Very interesting video, thanks.

You nearly always want the centre of pressure and the centre of mass to be very close together, or the centre of mass slightly ahead. If you add a rounded nose cone, you would need to move the centre of mass further forwards.

Interested discussion. I hadn't thought in terms of Centre of Pressure before.

Option B, quite often we see cars with a tinnie upside down on its roof

Still thinking about this overall information. Thank you for the food for thought.

Thanks for the informative video. I'm just wondering whether the effects of the passing B double would be reduced if the driver of the car reduced their speed before the B double passes the van. Thanks for sharing

So i think what he is saying is, if you tow a caravan, put a dinghy on your roof...

Pop tops tend to have a square leading edge where as non pop top have some streamlining.

Good information. Air flow is like water flowing over a surface. The boundary layer of air/fluid flow over the surface is difficult to visualize.

Thanks Robert and thanks Kyle, that was quite insightful. The bottom line, it seems is: slow down for safety, stability and fuel economy and speed up to keep others happy. Is the answer to this contradiction to be found in road design; dual carriageways, frequent overtaking lanes etc. to allow caravans etc. to drive at a slower speed without creating as much angst in other drivers?

Good discussion…. Caravan aerodynamics are hugely important for fuel efficiency. Our van is brilliant- a 2005 Future System. I has a terrific smooth rounded fibreglass front end. It is definitely better on drag than our previous pop-top with a relatively squared off front end. People don’t believe the fuel efficiency that I get- however that’s their problem, not mine LOL :-). Most caravans have horrible aerodynamic properties. And yes- overtaking (truck overtaking van OR van overtaking truck) is far more critical with sway than opposite direction- which has virtually no sway potential normally.

Thanks for a thought provoking and worthwhile presentation with a well informed aerodynamicist. I have thought quite a bit about it as a pilot having scratched the surface in my professional endeavours. What the expert says is true; an oncoming passing B Train is a high frequency event that is over quickly while and overtake/Pass is a much lower frequency event BUT THERE IS MORE GOING ON HERE THAN MEETS THE EYE. It is just as he says so as you approach a B Train to pass there is a “suck” at the back of the B train that pulls you in then you put in a small steering correction to counter and keep your lane then as you approach the front of the B train there is a push at which time your small steering input works against you! So you need to put in an opposite correction! It is an unstabilizing event that can be unnerving. This matter can be made worse if there is play in your steering box! I had an old Chevrolet astro van (Basically a cube)with lots of play in the steering and this made it a handful while passing a truck. I later put a commercial product called “air tabs” all across the very back and top of the van. What they are supposed to do is create voticies off the van and create a virtual tail cone that extends a long way back off the vehicle …. This is the afore mentioned “off body aerodynamics”When I put them on the van it dramatically quietened down the oscillating left right stall that naturally happened on the back of the van causing an annoying back and forth sway even when not passing which had to be constantly countered with steering inputs. After the mod the van would track beautifully straight with one hand and was no longer a white knuckle affair. These devices are touted by the company to improve fuel efficiency by 1-2% ,I’m not sure I saw that but I certainly didn’t go backwards in terms of fuel economy, the handling characteristics improvement sold me alone and I said if I bought a caravan I’d buy a mess of them to place on the back of my caravan and perhaps even on the back of tow vehicle to improve sway control. They dramatically reduced the push and suck effect while passing a large truck. They are just a little sticky wedgie thing that can be stuck onto the body work of your vehicle. They look like a NACA duct when viewed from above and are supposed to create contra rotating vorticie pairs coming off the tab. They in a small way remind me of vortex generators sometimes placed on tops of wings to “reenergize the boundary layer” and delay airflow separation approaching high AOA’s.

What about vortex generators on rear for stability and or drag

Thank you for getting the expert in to share in this discussion. It's a shame he didn't have the example picture of a current caravan front to work with. I'm thinking no caravans have been on the market in Australia for about 20 years that look like a freight carrying box trailer, they're all angled at the front to aid aerodynamics.

interesting topic, thanks. while talking about sway, do you know if vehicles that have trailer sway control and vehicle stability control (equiped as standard) have their brake lights come on, when these systems operate? if so ( given the trailer brake controllers 'mostly' derives the input from the brake lights) then how does this affect caravan ESC. if both vehicle and caravan are swaying?

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thank you I have been looking at the drag behind my van and have been looking at using rectangle pvc down pipe to bring air from one side and channeling it to the centre of the van to virtually pull air into the vortex behind the van would this remove the vortex drag thank you

Very interesting topic as the discussion (regarding trailer sway) seems to be counter intuitive. I would have thought that ideally you would want you centre of pressure (when talking about cross winds influencing sway) between your centre of gravity and the tow hitch. Thinking of the system as a set of levers, you want the stability the "lever" of COG gives you to always be greater than the "lever" the COP can exert sideways on the van, always keeping the van stable. Another analogy is as per you van loading/trailer sway videos where you talked about too much rearward weight adversely effecting stability. I guess we know why no van manufacturers dig too deep into the science of aero...its such a dark art!

I've been thinking about "V" nose enclosed trailers. I never see a travel trailer designed that way. Why not? I would think it's much more aerodynamic.

The drag factor is a good argument for the people who whinge about us only doing 80 kmh

Hi Robert, I currently tow a 19ft full height van with a Triton twin cab. I don't have a canopy but have ladder racks, the rear tub is fairly empty when towing as I take my ladders off the racks for trips. I was thinking about getting a roof top tinnie. Looking at this vid it should improve my towing yeah? I do currently have a tandem kayak but have not carried it while towing yest, I assume this will also help to a lesser degree. BTW what effects would be noticeable, is it just less fuel usage or would you actually notice any increased stability when towing?

So, increasing speed from 80km/h to 100km/ would double power required?

When you pass some trucks, its like hitting a brick wall. They must get poor fuel ecconomy.

I truely think that not many manufacturers don’t really invest into drag on the caravans looking at most of their factories here in Australia, it’s just about pumping them out and taking your money. After all they are just a brick behind your vehicle, could imagine the cost they would put on top of the already over priced box on wheels.

I think the Ultimate Off Road Camper would be very aerodynamic based on the discussion. Your thoughts?

what, no formulae? Aero drag is a force resisting forward motion, and so consumes fuel to overcome. Drag is function of coefficient x frontal area x velocity cubed. The coef is specific to the rig: change the shape and area of the rig, and you change the coef. Not much a driver can do about coef and frontal area. To reduce fuel, reduce the velocity. Drag is reduced also by laminar flow: ie reduced turbulence. The turbulence from the tow vehicle is enormous as the airstream leaves the rear. Every single appendage increases turbulence; mirrors, mud flaps, gap twixt truck and trailer, aircon on trailer roof, rollup shades, etc, etc. No trailer ever designed can magically restore laminar flow from the truck's turbulent stream. Also, at the low speeds of 75mph, improvements from laminar flow are hardly noticeable. If the goal is to reduce fuel consumption, the only practical means is to reduce velocity.