# How do water bomber pilots deal with the changing forces and mass when scooping water?

How does a pilot flying the scooping maneuver in a CL415 firefighting plane deal with the changing forces from taking on such a large mass of water (nearly 50% of the plane's own mass) as quickly as these planes do?

Some basic math indicates that the scooping maneuver would generate $$F=\dot{m}v = 18.4\ \mathrm{kN}$$ of additional backwards force just from accelerating the $$\dot{m} = \frac{\Delta m}{\Delta t} = \frac{6140\ \mathrm{kg}}{12\ \mathrm{s}} = 512\ \mathrm{kg/s}$$ of scooped water up to the plane's $$v = 36\ \mathrm{m/s}$$ scooping speed.

Or using a different calculation, with no additional thrust added to compensate, the plane would slow from 70 to about 50 knots from taking on the water. Plus, there's other forces generated here too — a downward force from accelerating the water vertically to lift it into the plane's tank, probably a pitch-down torque from the scoop placement, the additional weight from the changing mass, and also just the hydrodynamic drag forces that seaplanes also deal with landing or taking off.

Some of the control inputs seem clear, like needing to throttle up and probably pitch up slightly, but how does the pilot determine the adjustments to make here, and how do they coordinate the timing for making these adjustments?

Also, how does adjusting trim for the empty vs full states work? I'm imagining that there'd be some way to mark down separate trim settings for empty vs full and then use that to quickly switch to the appropriate trim after scooping or dumping the load, but is this done manually or is this automated in some way?

• I don't know how to fly a water bomber, but I can put your numbers in perspective: 18.4kN at 36m/s is 'only' about 900hp, which is less than 20% of the total installed power of the CL415. Nov 8, 2021 at 15:31
• The 13,500 lbs of water that is scooped is very near the center of gravity, and is is only about 1/3 of the 47,000 lbs total weight of the aircraft. The trim changes are handled by “seat of the pants” manual adjustments. Nov 8, 2021 at 15:55
• @Sanchises Sure, and I have no doubt that the plane has enough power to handle it. This is more about how the pilot coordinates applying that power while transitioning from the scoop approach to making contact with the water. Nov 8, 2021 at 17:02