Quote:
Originally Posted by stcyrwm
In the next week I am planning on building a boattail on my 2004 GMC Savana 3500 Shortbus Camper. I am looking at doing something in the 2 to 4 foot range for length. I would like to keep it on the shorter side but could be swayed based on fuel savings. At the moment I am leaning toward a compromise of 3 feet or so.
I am currently getting 11.25 mpg. The engine is the Vortec 6L Short Block V8. Overall length of rig is 20'.
I guess my main question has to do with whether there is an ideal taper for roof, sides and base? My memory from reading through a lot here in the past is that maybe 10 or 12% would be ideal but I wanted to double check that number.
All other factors being equal I would lean toward a smaller taper for storage space reasons but that is definitely secondary to potential fuel savings.
Any help here would be greatly appreciated!
Thanks,
Bill
PS
I did read the "Aero RV (custom boat tail for '95 Ford E-350 Class C motorhome)" thread and noted that several folks thought his taper was too aggressive but I couldn't find what would have been better % taper in that thread.
|
If you were only dropping from the top,your best angle would be 9-degrees.
If you'll do a 10-degree side angle boat-tailing,plus a 10-degree upswept diffuser you can exaggerate the top slope to 25-degrees.Chamfering the edges will net you the drag minimum.It will be very much like the Aero RV.On a simple 'box' form,this tail delivers a 0.0934 drag reduction (delta-35.6%).This was all tested in 1984 by S.R.Ahmed et al.You'd find it in Hucho's text.