Using the Airspeed Indicator as a Fuel Flow Meter?

Wolfgang Langewiesche tells us how.

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If you're looking for a staunch advocate of attitude flying, you'll find none better or more evangelical than Wolfgang Langewiesche in his classic Stick and Rudder. His sermonizing on the importance of angle of attack (and his practical explanations of what the heck it actually IS) guided many a future Air Corps pilot through the early stages of flight training during the latter stages of World War II. On page 371, he makes an interesting observation on high altitude flight, and how to select the optimum altitude for maximum efficiency in cruise. His first ballpark rule is, an airplane's most efficient altitude is likely in the range of two thirds its service ceiling. But he goes on to narrow it down further, and all without the benefit of a digital fuel flow meter:

"You know what your particular air-speed indicator reads in a normal glide. Add 5 mph or so; that is the Speed of Best Distance, power on — the flight condition in which your airplane will make the most miles per gallon. And that is the mark at which you want to keep your air-speed indicator. If at any given throttle setting, your air-speed indicator in level flight indicates higher, you are not yet at your best altitude for that throttle setting, you can still gain in miles per gallon by going higher. If at any given throttle setting your air-speed indictor indicates lower, you have too much altitude for that throttle setting …"

Quaint how he hyphenates "air-speed" isn't it? It had not yet become one word in 1944. One wonders how many combat pilots, armed with this fundamental knowledge, were able to extend their aircraft's range to the maximum and return to base after a long mission.

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