Can you please provide me with information about the B747-400ER optimal glide ratio?
Looking through the web I came up with figures ranging from 1:9 to 1:22...
How much better is it compared to the B747-200 (I think it has 1:15)?
To the aviators, glide ratio information is generally not given or found in the Flight Manuals as the pilot usually flies the correct airspeed to get the optimal glide in the event of all engine failures. What is available to the pilots are the best gliding speed (best lift/drag ratio) at different weight and altitude.
However as a rule of thumb, most modern jets have an average glide ratio of around 1: 15 - meaning for every 15 feet forward, it drops one foot.
For instance, on an Airbus A330, assuming all engines failed at 40,000 feet, the recommended initial speed to fly at is 300 knots to achieve an auto restart. If all fails, the speed would be reduced to the best gliding speed (green dot speed) of approximately 210 knots at 180 tons. Just before touch down, speeds are further reduced as the landing gears and flaps are selected.
So the initial glide ratio is 1:18 (approximately 1300 feet per minute or covering 3 nm for every 1000 feet) reducing to a glide ratio of 1:9 (1.5 nm for every 1000 feet) on the landing approach.
Overall, at an average glide ratio of 1:15, the plane would glide a distance of around 100 nautical miles with nil wind from 40,000 feet.
Similarly, the Boeing 747-200 and 747-400ER should also be the same and have an average glide ratio of around 1:15.
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