Caravan Aerodynamics - with an F1 engineer

[@apemaster6976]

Designing a trailer for an EV for work and a boat trailer. Trying to make them as aero as possible because aero is the main thing that kills EV range. Can’t tell you how enormously helpful this is 🙏

[@CocoNut2018]

There was a good comment for another KZbin 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.

[@Malc664]

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.

[@antonmaier2263]

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.

[@darrylday30]

I add sheet foam insulation under the floor. Smooths out the drag and keeps the floor warm too.

[@jonbradley4789]

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

[@L2SFBC]

Glad it was helpful! Please share!

[@BooBaddyBig]

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.

[@davexb6595]

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

[@geoffgeoff143]

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

[@FutureSystem738]

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.

[@MiniLuv-1984]

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?

[@L2SFBC]

Less speed = more safety & less fuel use, but you can take this too far and not get anywhere, and then introduce fatigue problems. Also, a caravan is difficult to overtake; it's long, and blocks the view ahead. Slow moving 'vans are a menance.

[@chainsawcharl1e677]

I hope the truck camper builders are paying attention, especially you, Total Composites, builder of the "zero thermotransfer" brick....

[@steveknight9254]

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.

[@L2SFBC]

Fantastic post, thank you! Yes there could be a lot of work done to improve caravan efficiency and stability I feel, an unexplored area.

[@stephenwade8093]

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

[@jonbradley4789]

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.

[@grantm1891]

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

[@L2SFBC]

😁

[@chrishockley5014]

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.

[@L2SFBC]

yes they are, but I don't think any put much effort into aero with the exception of Bruder.

[@chrishockley5014]

@@L2SFBC so why didn't you use the correct picture that related to the answers you wanted? You left out the big thing caravan manufacturers do do to help earodynamics and that is the angled front. That would have changed the experts answers when talking about the foils on the roof of the towing vehicle. The rest of the talk was very interesting and informative. What do you want the aerodynamics for? They won't help stability as the speed isn't high enough. In my opinion. The only way to stop sway is to move the wheels to the front and rear of the caravan but then nearly no one would buy one as they are a very different thing to tow. Fuel saving? It's a big box making a hole in the air at speed the has to have standing room and permanent fixtures so the shape can't change that much. To help drivers maintain higher speeds? Those people aren't going to go faster no matter what. In my opinion. The proof is on open speed limit roads, people still drive at the 'slow' speed they want to drive at. I've driven trucks in the UK and wondered why there isn't very much aerodynamics here in oz on the trucks. Apart from the trucks that run as single trailer on long distance - that isn't many - the weight of the combination and the energy needed to turn the wheels and tyres in a multi trailer combination is greater than the saving from aeronamic forces and costs.

[@L2SFBC]

the point of the discussion was to discuss changes in aero and I felt the shapes used best served that purpose. Speeds are high enough with vans for aero to be a problem, absolutely. And drag reduction is critical to fuel economy, every bit helps.

[@chrishockley5014]

@@L2SFBC a very good discussion it was, but you called the video 'caravan aerodynamics' and didn't use the shape of a caravan.

[@andyg9991]

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!

[@L2SFBC]

I see your point, but I think it's better to reduce the yawing movement (rotation in a vertical axis) on the van. With the CoP ahead of the CoG, you'll get a yaw and that'll put stress on the towcar rear axle. It is similar to CoG, where I recommend that should be just ahead of the axles..but with weight, weight distribution is critical - you can have 100kg TBM with vastly differeing weight distributions.

[@johnretallack3629]

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

[@L2SFBC]

Glad I could help

[@placestosea]

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?

[@L2SFBC]

ESC and TSC don't really slow the vehicle/rig down, they brake individual wheels, so no need for brake lights. Same for TSC on trailer. I don't know for sure, but I doubt the deceleration is enough to warrant brake lights.

[@simonthebroken9691]

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.

[@L2SFBC]

Best shape is teardrop

[@stephenwade8093]

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

[@L2SFBC]

Sadly yes

[@christurner68]

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.

[@L2SFBC]

well, to be fair, there's not too much they can do without compromising things like living space. But, it should be a consideration, yes.

[@ricmiller9624]

What about vortex generators on rear for stability and or drag

[@Sir-Dexter]

nice

[@craigclarke1628]

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

[@L2SFBC]

Not really...I think other considerations are more important but aero should be thought of

[@craigclarke1628]

@@L2SFBC So what's your opinion/analysis of the Ultimate Off Road Camper for aerodynamic design? Curious and wanting further discussion.

[@L2SFBC]

Sorry, didn't realise you were talking about THE Ultimate not an ultimate! Yes based on what Kyle said, that's pretty good; very rounded leading edges, lower roofline than towcar, same width. So I'd expect that to be way less draggy and more fuel efficient than a box on wheels.

[@geoffgeoff143]

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

[@L2SFBC]

depends how draggy the vehicle is

[@rienkhoek4169]

Drag would increase by 1.25*1.25, so not twice. Engine efficiency isn't the same across the rev range, so max power is probably not the value to go on.

[@geoffgeoff143]

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

[@squatch2461]

🍻

[@robgrune3284]

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.

[@L2SFBC]

Nothing a driver can do about drag other than slow down, but once stopped, you can change your trailer in ways which reduce drag. Laminar flow isn't quite simply reduced turbulence either; I would suspect that the main issue is form drag with all those appendages you mention, and of course the huge squared-off area at the back of the trailer. Also, 75mph is more than enough speed for aerodynamics to play a huge part in drag - at that speed it'd be a much bigger factor in energy use than rolling resistance or driveline friction.

[@michaelnugara1]

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

[@L2SFBC]

Yes slower speed less effect.