Loiter Flight

Many military missions require the helicopter to loiter while observing or waiting for some specific action. For these mission legs, the optimum speed is at the bottom of the fuel flow curve of Figure 4.42, and the endurance at any speed is a function of the specific endurance, S. E., whose units are hr/lb:

1 1 hr

Fuel flow ’ lb/hr ’ lb

Figure 4.47 shows the calculated specific endurance curves for the example helicopter. Here again, the advantage of flying on one engine is evident. This might become important to a pilot who is forced to wait for a change in the weather or for a landing site to be prepared. The time spent in loiter flight while burning a given amount of fuel can be found by integrating under the specific endurance curves of Figure 4.47, since:

This equation can be used to generate payload-endurance curves similar to payload-range curves. /

Gross Weight, lb

FIGURE 4.47 Maximum Endurance Conditions, Example Helicopter