7,200 gallons of water x 7 lbs/gal = 50,400 lbs.
50,400 lbs = 25.2 tons
It just “scoops down” to pick up 25 tons? Holy cow!
Too fast and they rip the scoop plumbing out of the bottom.
Too slow and they simply get too heavy, stop flying and must land.
But wait, there;s more!
From Pistolshot's link at reply #7
http://www.martinmars.com/
The most frequently asked question regarding the Mars is "How do they pick up their water?".
This part of the flying operation is, perhaps, the most demanding in terms of teamwork among the crew.
The Captain executes a normal landing, keeps the the aircraft "on the step" and allows the speed to decrease to 70 knots.
He then passes engine power to the Flight Engineer and selects the scoops to the "down" position.
The ram pressure for injecting the water into the tanks is such that the aircraft is taking on water at a rate in excess of a ton per second.
To account for this added weight, the Flight Engineer must advance the throttles to maintain a skimming speed of 60-70 knots to ensure the aircraft remains on the step.
Pickup time is, on average, 25 seconds.
When the tanks are full, the Captain will have the scoops raised, call for takeoff power from the Flight Engineer and carry out a normal loaded takeoff.
Once airborne, the foam concentrate is injected into the water load (normally, 30 US gallons of concentrate into the 7,200 US gallon water load) where it is dispersed and remains inert until the load is dropped.
Once dropped, the tumbling action causes expansion which converts the water load into a foam load.
This process is repeated for each drop.
In other words, this vital team work is carried out, on average, every 15 minutes per aircraft.
For a Gel drop , the concentrate is injected during the scooping process to allow even mixing.