Trends in bus aerodynamics
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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: http://ecomodder.com/forum/attachmen...1&d=1307348424 The skirts may be more to control spray than for aero reasons, like the front skirts on city busses.http://ecomodder.com/forum/attachmen...1&d=1307348424 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. |
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. :) |
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. |
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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?
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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? |
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. |
dilettante, i think, is what they were shooting for.
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http://ecomodder.com/forum/attachmen...1&d=1307454152 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
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*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 |
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. |
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GOOGLE IMAGES: Civis bus
This is worth checking out if you haven't seen it.:)
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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! :D |
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