Fred Weir, a former RCAF Neptune pilot, clarifies the the terms “endurance” and “range”.
"Endurance is the technical term for flying at the appropriate indicated airspeed resulting in maximum time in the air, and range is the term for flying at the indicated airspeed that will result in maximum distance covered. The range figure given in pilot’s operating manuals was the calculated distance that the aircraft could fly with maximum fuel load in still air. It was sensitive to wind and power failure so each trip had to be planned for existing conditions which were never textbook.
When the Neptune was equipped with jet engines, flight planning became so much more complicated that the whole concept of the range figure in the manual became far less meaningful. The maximum flight time with full tanks was about 12 hours chock to chock which would give us a practical range of about 2000 nautical miles in still air with a fuel reserve of 2000 pounds. I believe this to be a meaningful indication of the aircraft’s performance after the jets were installed.
The controlling limitation for time “on task” (or “on station”) in the Neptune with jets was the fuel reserve necessary for the transit home or to a suitable airport in case an engine failed. The aircraft was being operated at as much as 12,500 pounds above the weight at which it could maintain altitude on one engine. Losing an engine on task invariably meant one jet had to be fired up to maintain altitude. This configuration resulted in a very large increase in fuel consumption which had to be used for a large portion of the trip home. I remember computing a radius of action of 720 nautical miles for the Neptune with jets with full tanks with a reserve of 2000 pounds in still air. This means that a Neptune would require all remaining fuel except the reserve to transit home if an engine failed at that point. Time on task would be about 4 hours and 30 minutes with a transit distance of 500 nautical miles and about 8 hours with a transit distance of 250 nautical miles. These times on task would be sensitive to wind conditions being longer with tailwinds going home and shorter with headwinds going home".
Credits and References:
1) Fred Weir <fweir(at)live.com>
Nov 2/09