Can it do it?

[PB666]

1 hour ago, mikegarrison said:

I don't recall whether they took off with "half-full" tanks or not. They did lose a lot of fuel during takeoff and climb due to the tanks not being sealed unless they were hot. So they had to tank up in the air almost immediately.

The tankers they used were not "specially designed". They were regular KC-135 tankers. But the fuel was special, so they couldn't use just any old tanker that happened to be in the air. They had to have their own dedicated fleet of tankers with their JP-7 fuel, plus tankers with regular fuel to tanker their tankers. Normally tankers can use their own tankered fuel as a reserve capacity, but not when the tanker flies on kerosene but the tank is full of JP-7. https://en.wikipedia.org/wiki/JP-7

SR-71s did not take off with a full load of fuel, the landing gear could not support it and as I understand it the engines produced terrible trust at sea level and wing loading would have been too high. Many accidents close to the ground for SR-71.

Another fun fact about SR-71, they use a buick v-8 engine to start its engines.

[sevenperforce]

11 hours ago, mikegarrison said:

I don't recall whether they took off with "half-full" tanks or not. They did lose a lot of fuel during takeoff and climb due to the tanks not being sealed unless they were hot. So they had to tank up in the air almost immediately.

The tankers they used were not "specially designed". They were regular KC-135 tankers. But the fuel was special, so they couldn't use just any old tanker that happened to be in the air. They had to have their own dedicated fleet of tankers with their JP-7 fuel, plus tankers with regular fuel to tanker their tankers. Normally tankers can use their own tankered fuel as a reserve capacity, but not when the tanker flies on kerosene but the tank is full of JP-7. https://en.wikipedia.org/wiki/JP-7

Tanks were definitely only partially full at takeoff. Lower liftoff mass meant lower takeoff speed.

The KC-135 did have to be physically modified (into the KC-135Q) to segregate the JP-7 from the JP-4. I also thought there were modifications to the tanker to allow higher cruise speed (usual refueling speed was below the Blackbird's stall v_min), but it may have just been a different flight profile rather than physical modifications.

10 hours ago, PB666 said:

SR-71s did not take off with a full load of fuel, the landing gear could not support it and as I understand it the engines produced terrible trust at sea level and wing loading would have been too high. Many accidents close to the ground for SR-71.

Another fun fact about SR-71, they use a buick v-8 engine to start its engines.

And the limiting factor on the SR-71's endurance was the amount of TEA-TEB carried onboard to fire the afterburners...which is the same stuff used to ignite Merlin 1D engines.

[mikegarrison]

6 hours ago, sevenperforce said:

The KC-135 did have to be physically modified (into the KC-135Q) to segregate the JP-7 from the JP-4.

Fair enough. I don't usually consider that kind of payload modification to be significant, but it did get its own Air Force model designation.

Edited December 19, 2017 by mikegarrison