motorhome aerodyamics

[freebeard]

The difusser will want to start early, as close to the rear axle as possible and be 2-12° from horizontal. The back bumper may be problematic. Consider D in the diagram above. The bumper could be replaced by two vertical nerf bars in the skegs (inverted tailfins) on either side.

[chefdave]

Hi freebeard
steel bumper on back is used to carry waste pipes for toilet and sinks. would rather not have them inside. was going to use bumper as a mounting point then fix other end over axle. other things i have to consider are the water tanks just in front of bumper. will draw a simple diagram of layout and my thpughts on smoothing out rear belly. on rear body thinking of adding a cut off boat tail running parallel with rear bumper. no not large but should have some benefit even it makes it more stable in crosswinds or when passing trucks.
Would like to thank everyone for their contributions so far. all mods so far have increased my mpg by 70%. which is a big success. ulimate goal is 110% increase this is a theroical limit due to engine gearing and drag.

[chefdave]

Hi
thinking of doing a short version of picture F on page of this discussion. have room for 3" half rounds tp fit ay rear of front doors. off on to internet to see if i can find some 6" pipe or 3" half rounds.

[chefdave]

Hi freebeard
have found 4 1/2 inch half rounds by accident had a piece of guttering lieing in garage and fits perfectly by front doors. best bit is buying new is so cheap. off this weekend so hope to get guttering and run trial.

[freebeard]

Cool. Looking forward to the result. ...and the 'bellyplan'.