Talk:Economies of scale/Archives/2013
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Unsourced claim needs attention
Currently, the article states: "Operating crew size for ships, airplanes, trains, etc., does not increase in proportion to capacity." Wikipedia's own article about Yacht charter states: "a 35-foot boat with a husband-and-wife team serving as captain and chef to a 300-foot boat with a squad of 30 or more crew members". That sounds like a proportional increase. A Cessna 172 has a cockpit crew of one. A Boeing 717 has a cockpit crew of two. A Boeing 747-300 has a cockpit crew of three. It seems to me that operating crew size for at least ships and airplanes does in fact increase in proportion to capacity. Thoughts, comments? EdumaGator (talk) 13:12, 19 February 2013 (UTC)
- Capacity of shipping is rated in tons, not ship length. For airlines it would be number of passengers. There is no way a small plane has a crew to passenger ratio lower than a jumbo jet.Phmoreno (talk) 18:33, 1 March 2013 (UTC)
- Somewhere in my library I have reference about shipping and crew size, but I did not find it in my notes.Phmoreno (talk) 18:55, 1 March 2013 (UTC)
- An aeroplane for 70 passengers may have 2 flight attendants, one for 350 10. Gets close to proportionality when most of the crew is dealing with the passengers and not with the vehicle. On cruise ships with a crew so large that an additional layer of managers is needed between the crew members directly interacting with the passengers and the captain, crew size increases faster than lineair growth. Seems to me the statement only properly applies to cargo transport. PiusImpavidus (talk) 12:15, 12 September 2013 (UTC)
- OK, operating crew, fair enough. Still, for passenger vehicles this effect cannot be very important as operating crew is often only a small fraction of total crew. Never mind. PiusImpavidus (talk) 18:40, 12 September 2013 (UTC)
But now that I'm at it, the article also states
- Friction loss of trains, ships and airplanes is proportional to cross sectional area, so making these longer results in less friction per unit of cargo volume, speed and other drag factors being equal.
I don't know too much about economics, but I do know something about physics. This is really about drag, not friction, which results from the contact of solid surfaces. This statement is reasonable for buses and lorries, for aeroplanes somewhat less so (dynamic drag depends mostly on weight; stretching an aeroplane negatively affects the aerodynamics but is done because it's cheaper than complete redesign), for ships things get really complicated (see wave-making resistance) and in trains, or any other vehicle that's more than a hundred times as long as it is wide, drag is nearly proportional to length as it is dominated by the sides, not the front and rear of the vehicle. In other words, the drag coefficient changes when making the vehicle longer (having reached a minimum at the length/width ratio of the average aeroplane fuselage) or (alternative interpretation) other drag factors cannot remain equal when making the vehicle longer. A better statement may be something like:
- Drag losses of trucks, airplanes and ships generally increase less than proportionally with cargo volume, although the exact mathematics can be complicated. With the speed taken equal, increasing the size of a vehicle usually decreases drag per unit of cargo volume.
PiusImpavidus (talk) 18:40, 12 September 2013 (UTC) (Just passing by)
- It's more specific to say drag than friction; drag just being a form of friction. Thermodynamically all drag ends up as random molecular motion, which is heat. With trucks and trains, rolling resistance does not increase in proportion to weight. This was important with the switch to steel rails in the 19th century. Steel rails allowed heavier locomotives and longer rail cars. Longer rail cars allowed the freight to rail car weight to increase from 1:1 to 2:1. All of this gets too complicated for an encyclopedia article that's about economies of scale. At one time I had an article with the formulas for energy consumption versus speed for trains, planes ships and trucks. I think the title was something like "The price of Speed". I have not been able to relocate it. See also: http://www.lafn.org/~dave/trans/energy/rail_vs_truckEE.html#ss6.2Phmoreno (talk) 20:35, 12 September 2013 (UTC)
- In which case it's probably best to remain intentionally vague and refer people to drag (physics) for details. In fact, the current statement isn't entirely true either, as each vehicle has an optimum length-to-width ratio. As the article is about size, not length, this doesn't matter. PiusImpavidus (talk) 12:07, 14 September 2013 (UTC)
- It's more specific to say drag than friction; drag just being a form of friction. Thermodynamically all drag ends up as random molecular motion, which is heat. With trucks and trains, rolling resistance does not increase in proportion to weight. This was important with the switch to steel rails in the 19th century. Steel rails allowed heavier locomotives and longer rail cars. Longer rail cars allowed the freight to rail car weight to increase from 1:1 to 2:1. All of this gets too complicated for an encyclopedia article that's about economies of scale. At one time I had an article with the formulas for energy consumption versus speed for trains, planes ships and trucks. I think the title was something like "The price of Speed". I have not been able to relocate it. See also: http://www.lafn.org/~dave/trans/energy/rail_vs_truckEE.html#ss6.2Phmoreno (talk) 20:35, 12 September 2013 (UTC)