by mezmo » Mon Dec 17, 2012 2:39 am
Hi Bonnie,
Does the BUB still have the front 'cowling' that Coal Burner' put on the
front of the top section ? If I recall right, he said that helped immensely
with mpg. Reason being, I believe, is that it thus made the front of the
trailer shape/area coincide/equal to the cross-sectional shape/area
of his tow vehicle, a VW Golf then I believe, when he did that. Do that again,
as that is still close enough for your Nissan Sedan's cross-sectional shape/area.
If you cut that off when you trimmed the top, and still have the pieces,
just put them back on, cutting them to fit/allow for the moving top and static
bottom, but looking and acting like one piece when the top is down in
the travel position. If you don't have the pieces yet, just make some new
ones your self. The car has already 'punched the hole' through the air
for it and the trailer, Trying to keep the airflow around the car go smoothly
onto the trailer is the objective. No gap between Tow Vehicle and trailer
is the ideal [see angib's posts at the pottom of page 3 of this thread], but
practical considerations like them not touching when backing up or going
over dips and up rises have to be dealt with too. So closing the distance
between the two is worthwhile but within reason and practicality and
necessity.
Another thing to try, would be to make a fairing/spoiler for the back of
the car, it starting out level/even with the roof and the sides and gradually
flaring out to the width and height of BUB's cross-section [especially with the
front narrowing and lowering cowling]. That would aid the air flow in
straight-line travel. But It'd probably be more work than major aero
results, although every little bit helps.
The dead or turbulent air between the tow vehicle and trailer will more-or-less
stay 'in place' if contained within the smoothed airflow between the tow vehicle
and trailer if you can get them lined up and flowing together, generally speaking
of course. Details matter, and one of the most important is smooth, i.e. smoothly
'radiused', edges and gradual change in planes/surfaces [within 15 degrees or
less it's said].
[This is all from what I've read or seen on the topic - no personal experience
yet though.]
Cheers,
Norm/mezmo
If you have a house - you have a hobby.