I saw a couple of CL-415s near my lake house a few days ago, and it got me wondering, how do they pick up water? What method do they use to get water into the water tanks? How long does it take to fill up the water tanks? And do the tanks get filled up fully?
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7$\begingroup$ Not strictly on-topic, but there is a very interesting video showing the whole process and the skills required to perform the maneuver with an Air Tractor AT-802 Fire Boss. $\endgroup$– Ulli TCommented Aug 11, 2023 at 4:52
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2 Answers
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They scoop it up! Making contact with the water, a probe/scoop is extended, which allows water to gush into the internal tanks:
Image source: "Bombardier 415 Probe" by Wikimedia Commons user Aliano43 under CC BY-SA 4.0
The method is therefore simply a combination of aircraft forward speed and an adequately shaped metal duct. Here is another close-up good picture of the scoop, and a video showing the process from a good angle.
As for the duration, one source mentions that
“The water tanks can be filled in 12 seconds by the scoops.”
(which is what a large number of videos of this process seem to confirm).
answered Aug 10, 2023 at 19:01
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$\begingroup$ 12 seconds is 550 metres or a third of a land mile at 90 knots. That's not including lineup and departure lines so triple it and you need a lake that is 2 km long and wide enough. $\endgroup$– CriggieCommented Aug 11, 2023 at 21:35
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2$\begingroup$ @Criggie according to this aerialfirefighter.vikingair.com/firefighting/… the specs are: 6.5 feet deep, 300 feet wide, and a total distance of 1,340 meters, but a diagram below the table implies that the water surface may be shorter than that - likely if there are no trees/hills/obstructions around the water source. The minimum water surface for a full load would be 410 meters, in that context (I think they’re using slightly slower speeds than mentioned above) $\endgroup$ Commented Aug 12, 2023 at 15:49
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1$\begingroup$ It also says “If the designated water site doesn’t have the capacity for a full water load, a partial load will be used and the CL-415EAF aircraft will make multiple trips, returning to the fire.” which would imply to me that they can do partial loads if there’s not a sufficiently long water source $\endgroup$ Commented Aug 12, 2023 at 15:52
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2$\begingroup$ It's interesting to compare that with railway practice en.wikipedia.org/wiki/Water_trough where again the scoop depth was of the order of a couple of inches and the trough length around 500 metres with a bit less than 2,000 L picked up per run. $\endgroup$ Commented Aug 13, 2023 at 11:55
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$\begingroup$ For a quick calculation, the hydraulic head goes by H=v²/g. At 90kts=45m/s² this is over 100m of hydraulic head, or about 10 bar. No wonder it fills up fast. $\endgroup$ Commented Aug 14, 2023 at 9:56
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As stated above, either the flying boat superstructure, or the pontoon floats on the aircraft are fitted with “scoops” - ram intakes just fed of the step, which direct water up into a holding tank, mounted inside the aircraft. The aircraft makes an approach onto a lake or river with the scoops deployed, then maintains a high speed step taxi over about 10 to 20 seconds. The ram pressure of water hitting the scoops forces it up into the holding tank. Once filled, the aircraft will take off again and retract the scoops prior to heading out for another drop. Alternatively, the water tanks can be filled from trucks on the ground, or filled up with a mixture of water and chemical retardant prior to take off.
The TV series Ice Pilots: NWT featured a good segment in the episode below starting at time index @30:55, where Buffalo’s chief pilot Arnie trains Turkish Air Force pilots on how to scoop water and makes water drops in a CL-215.
When scooping up water in a high-speed step taxi, care must be taken to maintain a constant attitude with the appropriate increase in power to compensate for the quick increase in weight due to filling the water tanks. If you get it wrong, you can start causing the water to slosh around in the tanks, resulting in a pilot induced oscillations, and potential risk of an accident.
For both of CL215/415 and the Air Tractor Fire Boss, the scooping operation typically takes place in the neighborhood of 85 to 90 knots, depending on the air frame.
answered Aug 10, 2023 at 23:49