LANCER wrote on 12/07/12 at 13:56:35:60 mph=60mpg
I think it's more like 50-53mpg but for simplicity I will go with 60mpg
Which gives 1gal/hr
Good running engine @ WOT=11hp/gal/hr ???
Is it the same for our 650 single as for a 650 sport bike ??? Hmmm.
Maintaining 60mph on our bike only requires about 1/3 throttle yet you only decrease the 11hp by 1hp. If the throttle setting is decreased by 2/3 why is the power not decreased by 2/3 ? Or even just 1/2 ?
Seems to me you are dealing with apples and oranges.
If instead of the assumed 10hp it is only 5-6 hp then your numbers change considerably which reduces the % of effective aerodynamic drag a corresponding amount.
Does it not ? ?
The figure of 11 hp-hr/gal comes from the Nebraska Tractor Test Lab, among other places. They tested gasoline tractors at maximum power for hours on end. That is an approximate median of some several hundred tests. Some tractors did better, but few exceeded 12 hp-hr/gal while many did considerably worse. This figure, by the way, means 11 hp for one hour while burning one gallon of fuel. A tractor producing more horsepower burns correspondingly more fuel. Typically, low-revving engines with few big cylinders (two cylinder John Deere) are more efficient than many cylinders turning very fast (sport-bike type engines, optimized not for efficiency but for maximum power). Gasoline engines are typically most efficient at WOT, because they do not have to inhale fuel and air past a partially-closed throttle plate. I reduced the 11 hp-hr/gal to only 10, to allow for at least part of the loss of efficiency caused by running the engine at half or less throttle. It might actually be worse, but I don't have any way to know. Remember that the LS650 is usually given credit for anywhere from 25 to 35 hp, depending on the source, so the 10 hp I use is much less than its maximum. I based my thrust calculation on the horsepower actually being developed based on fuel useage, not the max. If the true horsepower is different, then the thrust is different and so is the relative percentage of rolling resistance and aerodynamic drag.
My estimate of rolling resistance includes not only the rolling resistance of the tires, but also the frictional resistance of bearings, belt, and any other moving parts. In fact, we can measure this resistance directly by the relatively simple expedient of tying a rope to the bike, tying a spring scale to the rope, and having someone pull you along while reading the scale. At the low speed of a person pulling a small vehicle, it is safe to ignore aerodynamic drag. I'd welcome such real-world measurements as a check on my estimate. Since we are dealing with a land vehicle, we do not need to consider form drag, which is involved with production of lift in aircraft. Even if we did, form drag is part of aerodynamic drag. If we allow for non-level ground, we do have to consider the power required to literally lift the vehicle up a hill.
Please do not misunderstand me - I welcome your questions. I admit to a brief post with relatively few explanations, and I am often guilty of incomplete explanations. Incidentally, I probably should have said something more along the lines of "well-designed engine" instead of "good running engine." A poorly designed engine can run well, and a well designed one can run poorly.
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