I think that 50% fuel is close to enough to fly across the map twice in the Lancaster. Take up 25%.
You have to take into accoutn that climbing to 30+ k takes
a lot of time. And you don't just want to get there, you want to make it to target and (hopefully back). And of course a smart buff driver would climb to alt before entering enemy airspace - so in case he's going to bomb strats, he will still have quite some way to go.
When you take 50%, you will have just about 35 mins of fuel left when reaching 30k.
Loadout: 50% fuel, 14x1000 lbs bombs
Time to climb to
- 10K: 15 minutes
- 15K: 21 minutes
- 20K: 30 minutes
- 25K: 42 minutes
- 30K: 61 minutes
- 34k: 75 minutes
When I crossed 34k, the autopilot couldn't climb anymore, the plane went into an oscillating movement.