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Your experience in the first example is due to the wing needing to fly
within a certain L/D for efficiency and your cooling drag... As your speed goes up so does your cooling drag... As your speed goes down, the airfoil L/D ratio deteriorates with increasing angle of attack... A simple look at the manufacturers range curves for fast aircraft shows that there a peak in the range plot at some point on the power curve... Since the curve is a mountain (or valley, depending on how the ordinate and abcissa are set up) there will be two points down from the peak, one at a higher power setting and one at a lower power setting where the range is exactly the same, and that is likely what happened to your high power / low power example... As far as fuel burn between a fast airplane and a slow one, that is apples and oranges.... Now range for fast aircraft is strongly affected by the airfoil characteristics... Slippery airfoils have a sharp rise in the drag as the AOA is increased to compensate for lower airspeeds and lower lift... Fatter airfoils have a lower rise in their drag with increasing AOA... My Apache is a case in point... The lower the power setting the longer the range, mostly because it's fat airfoil just loves high angles of attack... - and because cooling drag , goes down rapidly with decreasing speed. and vice versa - Example at sea level: 75% = 940 miles 65% = 1040 miles 55% = 1130 miles 45% = 1220 miles While I don't have a handbook for a Lancair IVP, or a Glasair III, I'm willing to bet that there is a range peak with decreasing power between roughly 68% and 63% and then it goes downhill from there because these laminar flow wings have to fly inside the L/D bucket or the drag goes sky high...... denny "Stealth Pilot" wrote in message bob my experience doesnt support that. I fly a Wittman W8 tailwind with an O-200. flying between Ceduna and Forrest via Nullabor Homestead is about 297 nautical miles. I have made the flight with two settings. -at reduced rpm (about 1800rpm) and about 70 knots. (in company with a piper cub) -at cruise rpm (2500 rpm) and 114 knots. weight and aircraft trim was just about the same. believe it or not the fuel consumed was the same. |
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