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#21
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"Mike Rapoport" wrote in message ink.net... Of course this is basically true for any two aircraft, the larger one will get more passenger miles per gallon. A 777 gets a lot more than a 737 for instance. The same is true for car vs bus. There are two numbers that tell the story: the weight of the vehicle per passenger carried, and the speed at which the vehicle travels. All other things being equal, it takes more power (and thus fuel) to carry more weight, and more power to carry a given amount of weight faster. If I throttled my 172 back to highway speeds I suspect the fuel consumption would rival many cars', though the same could not be said for payload. One interesting result of this is that many more modern passenger jets consume less fuel per passenger-mile than high-speed trains, because the trains carry a lot more dead weight per passenger. It is thus quite likely that the BOS-LGA shuttle operates at a higher fuel efficiency than the high-speed Amtrak train making the same trip. Best, -cwk. |
#22
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"John Galban" wrote in message om... "C J Campbell" wrote in message ... snip Some small single piston engine planes can easily exceed thirty miles per gallon, while others are doing well to get a third of that. I'm curious, CJ. Can you provide an example of a light single that easily exceeds 30 mpg? Most of the more common ones (172, PA28, etc..) tend to average around 15 to 18 mpg, depending on the power setting. I know a guy who claims to get that in his Long-EZ, and my brother says he will probably get that or better in his Celerity Mirage if he ever finishes it. |
#23
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John Galban wrote:
I'm curious, CJ. Can you provide an example of a light single that easily exceeds 30 mpg? Most of the more common ones (172, PA28, etc..) tend to average around 15 to 18 mpg, depending on the power setting. The Van's Aircraft RVs get right around 25 mpg -- Chris W Not getting the gifts you want? The Wish Zone can help. http://thewishzone.com "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -- Benjamin Franklin, 1759 Historical Review of Pennsylvania |
#24
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"Mike Rapoport" wrote in message
ink.net... Of course this is basically true for any two aircraft, the larger one will get more passenger miles per gallon. A 777 gets a lot more than a 737 for instance. The same is true for car vs bus. Not always the case. From the SAS website, the efficiencies of their various aircraft: Family: DH-Q400 (turboprop) Q400, 58-72 seats, 0.039 liters per seat / km Family: MD-80 series MD87, 110-125 seats, 0.048 liters per seat / km (JT8D) MD81/82, 141-145 seats, 0.043 liters per seat / km (JT8D) MD90, 147 seats, 0.039 liters per seat / km (V2500) Family: 737 (all CFM-56) 737-600, 123 seats, 0.044 liters/seat km 737-700, 131 seats, 0.042liters/seat km 737-800, 179 seats, 0.034 liters/seat km Family: A320 A321-200, 184 seats, 0.031 liters / seat km (V2500) Family: A330/A340 A330-300, 261 seats, 0.035 liter / seat km (Trent 700) A340-300, 261 seats, 0.039 liters / seat km (CFM-56) The bigger planes or those with more efficient engines in each family do better but it's not necessarily the case that the bigger planes are more efficient. However you can't compare these exactly as the short haul are probably more densely packed with seats than long haul. Paul |
#25
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On Fri, 22 Oct 2004 at 23:50:36 in message
. net, C Kingsbury wrote: One interesting result of this is that many more modern passenger jets consume less fuel per passenger-mile than high-speed trains, because the trains carry a lot more dead weight per passenger. It is thus quite likely that the BOS-LGA shuttle operates at a higher fuel efficiency than the high-speed Amtrak train making the same trip. What matters is drag. On the level a train may be heavy but its friction is very low. Rolling friction is roughly 10lb per ton or a bit less. So a train on level ground has a 'Lift' to drag ratio of 224. Air drag is a tiny part of a train's drag but let's say assume it easily achieves 200 to 1. For a 747-400 let's assume that it has a lift drag of 20 to 1. In cruise at say 705,000 lb. the 747 drag is therefore around 35,250 lb.. A train with about the same drag could therefore weigh around 3,250 tons. They both need a lot of energy to climb and the weight of train may be against it but they don't have to climb above 30,000 ft! :-) Let me know the AUW weight of the high speed Amtrak train and I can do it bit better. Incidentally the drag of an aircraft flying at its maximum Lift/Drag ratio is the same at all heights. But at altitude it flies much faster for the same drag. So some questions for you. Do modern jet airliners use less fuel per mile by flying higher or do they just get there quicker? Or perhaps the engine efficiency is much higher at altitude? Better specific thrust perhaps? -- David CL Francis |
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