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

Question

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?

Answer 1

I have experience on seaplanes, although not flying boats, and used to teach float ratings. The techniques for flying boats and floatplanes are more or less the same except for the differences due to the tip floats.

When you fly floats, you learn to apply up elevator to compensate for a pitch down from the drag of the floats at water contact (not too aggressively, or you pop back into the air; just enough). In fact, when landing on glassy water, which is normally done with a special procedure where you fly on very gently because you don't know your precise height, the pitch over is the signal that you have touched down.

Same with a flying boat. When you have scoops sticking down, it just makes the pitch over and deceleration stronger, and you have to apply more up elevator to compensate, but the timing and application is exactly the same as a normal landing, just more. On some waterbombers the intake probes are extended after stabilizing on the step at touchdown, so there two separate pitch reactions, but again, you are just responding to an action you are expecting.

You normally land seaplanes with power on until you've settled on the step after water contact, so the procedure if you're scooping water is to check the pitch over and add more power, enough to keep the plane from decelerating too much, and just hold that until you retract the scoops. Whatever the pitching tendency is from the scoops going down and up, you just learn to counteract it with control inputs intuitively, and similarly with power.