Aero Efficiency of Motorhome/RV vs Car & Caravan

[cRiPpLe_rOoStEr]

Trailers might have some advantages, but I still believe a small motorhome might not turn into an exercise of gross excess all-year round. Assuming that you could get a pop-up roof to keep the overall height contained while driving, it would already decrease the overall drag. When it comes to interior arrangements, you could eventually attempt to make it easily reconfigured from campervan to cargo (even though some structures would require a more permanent or semi-permanent fitment such as the washroom and the kitchen).

[s_t]

Yes, I figure I can drive this to work each day, on electric power only. 2kW of panels on the roof is easily enough to fully recharge the batteries even if its cloudy - it is only a 50km round trip (25km each way).

Been a while since I posted here - I ended up looking at all those original plans/concepts I've drawn up, and realising that they were still all inferior to the Vixen, which is a 30 year old design. It had lower profile (1.8m high), good Cd, fairly low weight and good space/usability as a motorhome. Not available here in Australia though.

So I've been looking at ideas to actually advance/progress on past products/solutions. These include:

- a frame/body design that allows the floor of the motorhome to be very low to the ground (which means the roof profile can be correspondingly lower). The floor of most motorhomes is 0.8m or more above ground, which is very inefficient.

- A section of drop down flooring (rather than pop top roof). Just the main isle, which is also where you stand when at the kitchen. That way the solar panels on the roof are less affected, and I think sealing is easier too.

- adjustable height suspension, via airbags. Low for highway aerodynamics, medium for around town (sufficient clearance to ground) and high for offroad.

- all electric, very low Cd.

I've worked out a lot of the design concepts. The main problem is that this is now a completely custom vehicle- would have to be built as an ICV (Individually Constructed Vehicle). Which means an incredibly painful and expensive process to get approved and registered. Also a huge amount of design and construction work. I'm currently looking into those issues and considering if I want to take it on or not.

Originally Posted by cRiPpLe_rOoStEr

Trailers might have some advantages, but I still believe a small motorhome might not turn into an exercise of gross excess all-year round. Assuming that you could get a pop-up roof to keep the overall height contained while driving, it would already decrease the overall drag. When it comes to interior arrangements, you could eventually attempt to make it easily reconfigured from campervan to cargo (even though some structures would require a more permanent or semi-permanent fitment such as the washroom and the kitchen).

[cRiPpLe_rOoStEr]

Originally Posted by s_t

A section of drop down flooring (rather than pop top roof). Just the main isle, which is also where you stand when at the kitchen. That way the solar panels on the roof are less affected, and I think sealing is easier too

Not sure about it being easier to seal. But it actually sounds quite interesting to say the least, even though it might not be so easily doable without any compromise to the structural rigidity.

[s_t]

To provide a bit of an update, I ended up working on the motorhome option, as I think that suits our intended use better, and I want offroad capability (to get to many parts of Australia we haven't seen). Whilst starting from a donor vehicle would be preferable (and considerably easier), there is very little (nothing!) in the way of aerodynamic 4x4 motorhomes (or even suitable base 4x4 vehicles) in Australia. The 4x4 mercedes sprinter van is probably the closest. So I did a fair bit of looking at various concepts, and developed a preferred one.

But first, to skip to the conclusion, I've put this project on hold for 3-5 years. Decided that now isn't the right time to be putting a huge amount of effort and money into building a custom vehicle. Hopefully in several years time I'll be able to take this up again, though I think registration/roadworthy requirements (red tape) are only going to get more difficult as time goes on.

I designed a rigid centre tube (RHS) chassis to act as a structural backbone for the whole vehicle. Similar concept to Tatra trucks. Not fully detailed, but it checks out well in FEA analysis. Custom independent air bag suspension on all 4 corners. Approx 450mm of wheel travel (max for CV joints), and airbags make it height adjustable to optimise for road (low and aerodynamic) or offroad (lifted for clearance) driving.

Two electric motors, one for front, one for rear. Motors, gearboxes and diffs (two 'rear' diffs) are actually contained within the large RHS frame (flanged top surface). Gearbox are a small custom design, just to get low range for offroad use (ie. 2 speed, no clutch). A number of different motor options; Parker make some nice ones for example. Because of the offset middle part of the chassis, can get some cooling air flowing through the RHS pieces containing the motors and diffs.

Another main reason for the offset RHS tube in the middle is to limit vehicle height - the floor for the kitchen/walkway will be beside and lower than the top of the RHS chassis. With the floor of the standing part of the motorhome also forming the underside of the body, overall vehicle height can be kept at around 2.1m with standing room inside (when air bags fully lowered). Planned an almost flat underbody, just the centre RHS tube (but not cross beams) sticking down 50-100mm or so, and there will need to be cut-outs/slots for suspension arms to move up and down past floor pan. That centre part of the chassis will also act as a water tank.

Considered a monocoque frame, and yes it could probably be done a little lighter that way, but construction would be significantly more complicated and involved (especially considering I have very little practical experience in composites, and it would be critical to get that right). Also the state of the structure would be more difficult to assess, monitor and repair (remembering this is an offroad vehicle).

For the cab, plan to graft the front part of a Renault Trafic, or possible Ford Transit Custom, onto the frame (just the cab, not including drive, suspension, wheels etc). Using the already approved windscreen, doors, seats etc would help a lot in meeting local roadworthy/registration requirements.

There are lots of custom features in this, and whilst none of them are individually overly difficult, put together it is a huge amount of work. In the meantime I am going to improve the aero performance of my box shaped homebuilt camper/caravan! (some pics in here: From Here to There | Around Aus)

For now, hopefully this discussion helps trigger design ideas for other people. Thanks to those who contributed and provided advise in the thread. If all goes well I'll revive it in several years time

[kach22i]

Originally Posted by s_t

.......... The 4x4 mercedes sprinter van is probably the closest. So I did a fair bit of looking at various concepts, and developed a preferred one.

But first, to skip to the conclusion, I've put this project on hold for 3-5 years. Decided that now isn't the right time to be putting a huge amount of effort and money into building a custom vehicle./................

In the meantime I am going to improve the aero performance of my box shaped homebuilt camper/caravan!

1. Looks like a good van to start with.

2. I'm always shocked when some of the from scratch vehicle costs are listed.

3. Back to Ecomodding verses from scratch eco-design, the reason this forum exists.

Most of the sketches I've done on a similar topic is converting my 8'x12' flat snowmobile trailer into an aero-camper. The main feature is a pop-up roof like a VW van camper with the front edge hinged.

I have an alternate design with full height rear entry but it is very narrow at the tail end. Fewer moving parts and the simplicity makes me lean in that direction - sort of a Box Fish.

[aerostealth]

https://www.greencarreports.com/news...economy-record

Article about an attempt to set a cross country fuel efficiency record for a semi truck haul freight cross country.

[freebeard]

For now, hopefully this discussion helps trigger design ideas for other people. Thanks to those who contributed and provided advise in the thread. If all goes well I'll revive it in several years time

More like flashbacks, really.



Section your Forester at the top of the wheelwells and graft a Vanagon body on 6-8" above the original floor level. Put sliding drawers in the gap for jacks and wrenches.

Don't forget the Hello Kitty mascot.
________

I think kach22i is trying to steal my idea:



Good on him. More people need to do that.

[slowmover]

I’m late to the party.

I prefer (and forty-five years of experience tells me) that for lowest overall cost (as fuel is but one part; generally half) drivetrain separate from RV works best. Why? Majority of hours of use are ALWAYS when parked. The right trailer can last decades. The motive power can be changed as desired.

Building new looks great on paper. But years go by. Even an non- extensive renovation can be two plus years given a working man’s available hours.

Get something that will re-sell quickly. That should be focus (in my opinion) while your boys are still at home. (Can take six months or more to sell a nice RV at a fair price in USA). So whatever the choice of type, get the brand in demand. This removes the end of ownership pains.

Good luck!!

[cRiPpLe_rOoStEr]

Originally Posted by slowmover

I prefer (and forty-five years of experience tells me) that for lowest overall cost (as fuel is but one part; generally half) drivetrain separate from RV works best. Why? Majority of hours of use are ALWAYS when parked. The right trailer can last decades. The motive power can be changed as desired.

Sounds pretty accurate, but it's too hard (and expensive) to find a trailer suitable to tougher off-roading conditions, which looks like a top-tier priority in this project.

[slowmover]

Not in his country. They’ve plenty. Purpose-built.