Maryland. The information regarding V-22 ext and CH-53E ext is estimated in accordance with the following methodology.
An aircraft carrying an external load would go out at external-load cruise speed and return at internal cruise speed. Thus, the mission time for the out and in legs is
The effective round-trip cruise speed, then, is round-trip distance divided by mission time:
As discussed above, the rotary-wing aircraft no-load distance for internal loads is the maximum round-trip distance. A "no-load distance for external loads" can be defined as the extrapolation, to zero load, of a linear fit to data for finite loads. These data and extrapolations can vary for different types of external loads, but this is ignored here. An approximate value of an "external no-load distance" can be obtained by assuming that the hourly fuel consumption rates, and so the times of flight for internal and external loads, are about the same.2 Then the
"external no-load distance" = (external no-load time of flight ≈ internal no-load time of flight) x (effective external cruise speed).
The fuel consumption rate (tons/hour) depends on power settings which in turn, depend on the nature of the load. Heavy, high-drag loads demand extra power and higher fuel consumption. However, because fuel flow with external loads is probably slightly less than fuel flow with internal loads, the flight time with external loads may be slightly higher. Thus, the "external no-load distance" estimated here may be conservative.