Tue Sep 06, 2022 6:55 pm
Each receiver aircraft has a flight envelope defined by available thrust, weight before and after refueling, altitude, and airspeed. In addition, the aircraft must have enough thrust margin to push on the boom or drogue with the required connection force.
Thus there is variability in the refueling condition, even for the same aircraft, depending on these factors. But I believe they are all determined & set in advance, so that both tanker and receiver know the correct conditions. This is part of the tanker certification for a given receiver aircraft.
The international standard for the boom connection force is 1400 lbs. The drogue system is probably lower, but there still is a minimum force required, just not sure what that value is.
Some examples from the KC-46, the A-10 cannot meet the 1400 lb requirement unless at low altitude and without a combat load. This was overlooked by USAF, and the boom is now being redesigned with a variable connection force, down to around 500 lbs.
This will also benefit some parts of the F-16 envelope, which pilots have said may require some afterburner to stay on the boom, in certain conditions with a heavy load.
For the B-1B, there is the variable sweep wing which would be effective at lower altitudes. I would think the envelope would be faster as you go higher, or with greater loads, which may be quite fast from the tanker's perspective. So maybe the two aircraft constraints (max vs min airspeed) would be meeting up in that regime, leaving not much margin for either.
There are some tanker guys here, so they may be able to provide a better answer.