Trends in bus aerodynamics

[aerohead]

Originally Posted by KamperBob

In Hucho 4th Ed 1998 page 204 is figure 4.101 showing the corner radius effect work of D.M. Waters 1969. The same figure in German appears in Peschke & Mankau 1982 which is available as a Google Book.



Waters' work was based on a (camper) trailer (my area of interest) towed behind a car so the flow field conditions are not quite the same as a bus but I see a feature worth noting. The solid curve shows marginal diminishing return from nose rounding. The dashed curve shows much more dramatic improvement for a rectangular block with all corners radiused not just the front. I'd love to sink my teeth into Water's original paper.

Meanwhile, the rounded rump of a vintage bus seems pretty beneficial. A lot of Airstream trailers and other brands benefit from a similar shape by all accounts I have found (mostly owner reports comparing rounded to boxy units).

SAE Transactions,Volume 70,1962: General Motor's Chevrolet Truck Division did similar research.
*The 'oval',a 56-inch radius on a semi-trailer COE tractor had lowest drag,@ ---------------------------------Cd 0.547.
* 18-inch radius on same tractor= Cd 0.562
* 12-inch radius ---------------- Cd 0.562
* 6-inch radius------------------ Cd 0.725
* 45-degree chamfer------------ Cd 0.74
* square leading edges---------- Cd 0.88

[skyking]

I've got a large travel trailer design in my head keeping me awake at night
I have 12" radii on the side/top joint to maximize volume and facilitate the pop up system, but the aft part will be able to follow the "template" perfectly. Thanks for this.

[aerohead]

Originally Posted by skyking

I've got a large travel trailer design in my head keeping me awake at night
I have 12" radii on the side/top joint to maximize volume and facilitate the pop up system, but the aft part will be able to follow the "template" perfectly. Thanks for this.

The $50,000 Bowlus 'Papoose' will have some company!

[aerohead]

This is worth checking out if you haven't seen it.

[skyking]

Thanks! My design has 5'9" headroom at the outside corners with the top lowered, and an 18" screw jack lift for the whole trailer roof. That makes for some nice headroom but keeps the highest point at 7'6" high when collapsed. You can still go in and use it when the roof is down, just a little crouched. I'll pick up the template station 0 at about 15' from the aft end, and the trailer would end at station 60. It scales off a ~35" drop over those stations, so outside height would go from 90" to ~55".
The trailer lower edges would go from 12" to 20" above the ground, and the sides would taper in from 8' to 6'.
Imagine a 3' by 6' oval spaceship arse end!