Trends in bus aerodynamics

[Piwoslaw]

In recent years I've noticed how the shape of long distance busses has evolved. First, the side mirrors, which are no longer fixed to the front corner where they kill airflow down the whole side:

but now hang down farther away, looking like bug antennae:

Next, the rounded front:

and roof extension:

as shown on a Volvo (Elite?).

Finally, (partial) rear wheel skirts, as shown on a Neoplan Starliner:

and on a Man:

The skirts may be more to control spray than for aero reasons, like the front skirts on city busses.

Unfortunately, busses have been getting taller (=more frontal area) to provide more luggage space. A partial alternative would be a piggyback luggage holder, only shaped like a Kammback

Or an aerotrailer.

[instarx]

The hanging mirrors are mainly for safety. People standing on curbs kept getting smacked with the low mirrors.

And by the way, busses = kisses. Buses = more than one bus.

[Dawie]

Some buses from the 50's and early 60's were well rounded on the front corners. Unfortunately, most were rounded at the rear as well, not taking advantage of the Kamm effect.

Like the Setra S6, S10, some old Neoplans and others.

The GM PD 4104 is rounded as well, and the body/chassis is from aluminum, for lighter overall weight. They are a popular choice for conversion to a motorhome. The later PD 4106, also aluminum, may be a good choice as well. Think those old rounded-rear buses can benefit from a boat-tail conversion...

That "square-look" fashioned buses from the late seventies and 80's was probably a step backwards aerodynamically wise, at the time.

[Piwoslaw]

Originally Posted by instarx

And by the way, busses = kisses. Buses = more than one bus.

I wrote busses instead of buses because:

1. Both plural forms are correct. 'Buses' is more popular, especially in the US, but since most of the examples in my post are from Europe I used the older, less American form.
2. Today, June 6th, is Kissing Day here (one of three), as the media have been repeating over and over again. Hence, the 'buss'
3. The word 'buses' could be read, according to English rules, to rhyme with 'fuses', but not 'fusses'. On the other hand, the pronounciation of 'busses' is more or less unequivocal (if the pronounciation of anything in English can be unequivocal).

[Bill in Houston]

Originally Posted by instarx

The hanging mirrors are mainly for safety. People standing on curbs kept getting smacked with the low mirrors.

And by the way, busses = kisses. Buses = more than one bus.

I'm guessing that it REALLY bothers you that your title up under your name is spelled Dilatant?

[Bill in Houston]

I'm debating a roof extension like the Volvo's on my CR-V. The sides have a nice crisp break, but the top is curved. Worth the effort? Anyone?

[instarx]

Originally Posted by Bill in Houston

I'm guessing that it REALLY bothers you that your title up under your name is spelled Dilatant?

Never noticed it. But I'm guessing you'll have to talk to the person who created the ecomoddder titles to get it corrected.

And piwoslaw you are right - busses can mean more than one bus. I stand corrected. Interesting about it being kissing day, though. Should I plan my next trip to Europe for June 6?

[winkosmosis]

WTF is a dilatant?


Edit: Oh, it's a non newtonian fluid http://en.wikipedia.org/wiki/Dilatant

I've been wondering for a long time what the word for fluids like that is. Silly putty would be an example.

[Bill in Houston]

dilettante, i think, is what they were shooting for.

[KamperBob]

Originally Posted by Dawie

Some buses from the 50's and early 60's were well rounded on the front corners. Unfortunately, most were rounded at the rear as well, not taking advantage of the Kamm effect.

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).