Aircraft Performance

Indicated airspeed (knots) 11-9 )teef( edutitla dradnatS 24,000 22,000 20,000 18,000 Absolute ceiling 16,000 Service ceiling 14,000 12,000 10,000 Best angle Best rate of climb (Vx) of climb (Vy) 8,000 6,000 4,000 2,000 Sea level 70 80 90 100 110 120 Figure 11-10. Absolute and service ceiling. )PH( deriuqer rewop/wolf leuF A common element for each of these operating problems is the specific range; that is, nautical miles (NM) of flying distance versus the amount of fuel consumed. Range must be clearly distinguished from the item of endurance. Range involves consideration of flying distance, while endurance involves consideration of flying time. Thus, it is appropriate to define a separate term, specific endurance. flight hours specific endurance = pounds of fuel or flight hours/hour specific endurance = pounds of fuel/hour or 1 specific endurance = fuel flow Fuel flow can be defined in either pounds or gallons. If speed. Blade loading is expressed in pounds per square foot maximum endurance is desired, the flight condition must and is obtained by dividing the total weight of a helicopter by provide a minimum fuel flow. In Figure 11-11 at point A, the area of the rotor blades. Blade loading is not to be confused the airspeed is low and fuel flow is high. This would occur with disk loading, which is the total weight of a helicopter during ground operations or when taking off and climbing. divided by the area of the disk swept by the rotor blades. As airspeed is increased, power requirements decrease due to aerodynamic factors, and fuel flow decreases to point B. Range Performance This is the point of maximum endurance. Beyond this point, The ability of an aircraft to convert fuel energy into flying increases in airspeed come at a cost. Airspeed increases distance is one of the most important items of aircraft require additional power and fuel flow increases with performance. In flying operations, the problem of efficient additional power. range operation of an aircraft appears in two general forms: 1. To extract the maximum flying distance from a given Cruise flight operations for maximum range should be fuel load conducted so that the aircraft obtains maximum specific range 2. To fly a specified distance with a minimum throughout the flight. The specific range can be defined by expenditure of fuel the following relationship. e d u altit At Reference line Maximum endurance at minimum power required Applicable for a particular A Weight Altitude B Maximum range at L/DMAX Configuration Speed Figure 11-11. Airspeed for maximum endurance.