Page 193 - Understanding Flight

CH07_Anderson 7/25/01 9:00 AM Page 180

180 CHAPTER SEVEN

Mitchell Field in Milwaukee, WI, is the takeoff distance of a jet is increased by 20 percent over the
named after Gen. “Billy” Mitchell, sea-level distance. The altitude affects the acceleration of a
a strong advocate of military non-turbo-charged, piston-powered airplane, and thus its
aviation, who as a colonel faced takeoff distance is increased by about 40 percent at 6000 ft.
a court martial for being Small single-engine airplanes, like the Cessna 172, can take
outspoken about the military’s off in distances less than 1000 ft at sea level. The Cessna 172 has
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“incompetence” in aviation. a wing loading of only 13.5 lb/ft (66 kg/m ). The light wing
loading contributes to the short takeoff distance. Its available
power is moderate, and, as we saw in Chapter 5, the thrust available
decreases with speed, and so is a maximum during the takeoff run.
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A Boeing 777 has a high wing loading of about 100 lb/ft (490 kg/m ).
This is over seven times that of the Cessna 172. Its ground-roll takeoff
distance is on the order of 6000 ft (2 km). In order to comply with FAA
regulations for air transports, which require that the airplane be able to
fly safely with one engine inoperable, the thrust available for the Boeing
777 must be double what is necessary for a sustained climb. So the
thrust available compared to the weight of a Boeing 777 may be double
that of the Cessna 172. The thrust available compared to the weight is
called the thrust-to-weight ratio.
A Boeing 777 cannot take off from a 1500-ft (500-m) grass
runway. On the other hand, the Cessna 172 cannot cruise at
In 1919, Winston Churchill was
500 mi/h (800 km/h). Its top speed is only about 125 knots
named Britain’s air minister.
(225 km/h).

Climb

Up to this point, besides glides, only straight-and-level flight has been
discussed. You have probably thought about what happens in a climb
to increase altitude. A simplistic answer is that you need to generate
more lift, the logic being that as one increases the angle of attack, the
lift goes up, and the airplane climbs. When the pilot first pulls back on
the controls to start a climb, this is what happens, but only for a few
seconds while the airplane is slowing down. The airplane must slow
down because no power was added to create this lift. Then, at this
lower speed there will be less lift then there was initially. In a sus-
tained climb the lift of the wing is actually less than the weight of the