motorhome aerodyamics

[freebeard]

my biggest problem is over hang at rear. estimate front to rear weight balance is 30% front and 70% rear. chassis was orginally designed for max gross weight of 2-2 1/2 tons. my motorhome weighs 2.8tons unladen

My weekly driver weighs 1980lb with 840lb on the front axle, that's more like 40/60, but similar. Pressing the limits like that, I'd want good brakes. Widen the rear track as much as possible, even a few inches with deeper offset wheels will help. Stiffen the rear in anti-roll and double up on the rear shocks. Fine tune by unbalancing the tire pressures.

I guess you can't extend the front any more than the rear. Your situation is similar to the box van (lorry?). You might take a look at: Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling and Safety of Heavy Vehicles

Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling and Safety of Heavy Vehicles

These experimental results show overall aerodynamic drag reductions on the Pneumatic Heavy Vehicle of 50% using only 1 psig blowing pressure in the plenums, and over 80% drag reductions if additional blowing air were available. Additionally, an increase in drag force for braking was confirmed by blowing different slots. Lift coefficient was increased for rolling resistance reduction by blowing only the top slot, while downforce was produced for traction increase by blowing only the bottom. Also, side force and yawing moment were generated on either side of the vehicle, and directional stability was restored by blowing the appropriate side slot. These experimental results and the predicted full-scale payoffs are presented in this paper, as is a discussion of additional applications to conventional commercial autos, buses, motor homes, and Sport Utility Vehicles.

I'm thinking elecic leaf blowers tucked behind the rear bumper. And there's lots of opportunity in the cab door and mirror area.

[renault_megane_dci]

Shame you can't use your exhaust gases in these area ...

[chefdave]

Hi
quick inital mpg figures show a 33% increase in mpg. not bad on an aerodyamic brick. still got more mods to carry out. am expecting much smaller increases. still looking to match a toyota 4runner mpg figures. so i need to find another 20% increase on latest mpg. now thats going to be a challenge.

[freebeard]

Congrats. I think there's another 20% to be had. Is the number from the pump and odometer, or do you have a Scanguage?

[chefdave]

Hi freebeard
calutions are done on tank and mileage. cannot fit a scanguage because i have an obd 1 port but mpgenio will fit and work.

[chefdave]

Hi
quick update on mpg % increase. from first tank which was 13 mpg (summer) now up to 19mpg (winter). This is almost 50% increase ??? Think a rear diffuser will pay divdends as reserach shows it helps to fill low pressure area left by vehicles. will take it from rear most edge of rear bumper curve it around water tank and up to floor above rear axle. exhuast measurements on diameter front to rear show at least 3 different diameters. narrowest is over axle with 1.5 inches outside on a crushed bend so internally more like 1 1/4 inches to 2 1/4 inches. best diameter for system is 2 1/4 inches so my engine is being sufforgated by exhaust. also this diameter has been quoted on several websites for toyotas as giving a 20% improvement in mpg. hopefully sort exhaust and tidy back up aerodyamically should see a consistant 20mpg +.

[renault_megane_dci]

Originally Posted by chefdave

exhuast measurements on diameter front to rear show at least 3 different diameterbecausesthe . narrowest is over axle with 1.5 inches outside on a crushed bend so internally more like 1 1/4 inches to 2 1/4 inches. best diameter for system is 2 1/4 inches so my engine is being sufforgated by exhaust. also this diameter has been quoted on several websites for toyotas as giving a 20% improvement in mpg. hopefully sort exhaust and tidy back up aerodyamically should see a consistant 20mpg +.

Congratulations on the good work

If your exhaust is a funky shape and variations of diameter, you'd better consider alternative routing because the current routing will probably not work with a bigger constant diameter : your motor home engineers did not waste time and money for the fun of pissing of owners ...

[chefdave]

Hi renault megane dci
exhaust has loads of space to move up to 2 1/4 inches. never seen so much space to run pipe work.

[trooper Tdiesel]

13mpg for a base line, it must be a gas engine, I-4?

auto trans?

[chefdave]

Hi trooper Tdiesel
its a 3.0 v6 petrol with 4 speed auto box