Dispersal systems for firefighting aircraft?

bflynn

bflynn

Final Approach
Joined
Apr 24, 2012
Messages
9,594
Location
KTTA
Display Name
Display name:
Brian Flynn
How do firefight aircraft drop water? I've heard that it's like an agricultural sprayer, but also that it's just dropped as a mass and lands like a bomb on the ground. My firefighting background comes from the Navy and I learned that water puts a fire out by cooling it below the ignition point and to a lesser point, by smothering it. A stream of water is not as effective as a spray. Because of that, I'd expect a sprayer to be effective but a a "drop" to be largely ineffective.

Please avoid the obvious political extension, I'm just trying to figure out how aircraft drop water.
 
bflynn said:
I'm just trying to figure out how aircraft drop water.
Click to expand...
Some of big jets like a 747 have huge pumps that deliver the water. Everything else pretty much uses gravity to disperse the water/slurry. Some helicopters have onboard pumps that suck water from rivers or swimming pools for a drop. And others using a Bambi bucket dip the bucket into the water source. There are some fixed wing that can scoop the water as they glide across the water surface.

But the effectiveness of the drop is more on the skill of the pilot in placing the drop than the type of equipment that delivers it. More water is definitely better. And from what I was told a forest fire is a much different animal than a structure fire. I've seen 2,000 gallons dropped on the edge of a grass fire where it died with a hiss then literally roared back into life a minute later to 30 foot flames and jumped the road in front. It's a sight to been seen and heard. There are a number of videos out there.
 
Most fixed-wing firefighting aircraft drop retardant. They build barriers to contain the fire, while helos drop water on specific spots. The relatively few amphibs can scoop and drop water and directly extinguish it.
 
ateamer said:
Most fixed-wing firefighting aircraft drop retardant. They build barriers to contain the fire, while helos drop water on specific spots. The relatively few amphibs can scoop and drop water and directly extinguish it.
Click to expand...
That's about it. Water alone needs to go onto the burning material to do much good. The retardant is intended to be spread ahead of the flames to slow the fire to give ground firefighters a chance to stop it. That retardant is mixed to various strengths as ordered by the fire control officer in the bird dog airplane, and it has retardants and fertilizer (to aid in regrowth) and thickeners to make it hang in the trees and on the brush.

The big bombers mostly have tanks with computer-hydraulically-controlled gates (long doors) to release the retardant at rates specified by the FCO. The computer opens the gates further as the head pressure in the tank decreases, to make the spread consistent.

I worked on Lockheed Electra fire bombers for a bit more than a year.

handley.jpg
 
Bell206 said:
Some of big jets like a 747 have huge pumps that deliver the water. Everything else pretty much uses gravity to disperse the water/slurry. Some helicopters have onboard pumps that suck water from rivers or swimming pools for a drop. And others using a Bambi bucket dip the bucket into the water source. There are some fixed wing that can scoop the water as they glide across the water surface.

But the effectiveness of the drop is more on the skill of the pilot in placing the drop than the type of equipment that delivers it. More water is definitely better. And from what I was told a forest fire is a much different animal than a structure fire. I've seen 2,000 gallons dropped on the edge of a grass fire where it died with a hiss then literally roared back into life a minute later to 30 foot flames and jumped the road in front. It's a sight to been seen and heard. There are a number of videos out there.
Click to expand...

Yes, fire takes work to put out. Water will reduce the heat, but unless it gets it below the threshold for combustion, its going to come back.
 
With the 10,000 Liter Bambi Bucket, the most effective method was to make a high, misting spray over the area, followed by a targeted heavy application on the hot spot.

Hitting the fire directly with a big dump just scatters the embers and makes things worse...
 
I’ve always wondered, fire fighting planes, or bombers dropping their loads, how it is for the pilot with that sudden change of weight and CG, what they do to keep balanced, etc.
What that experience is like, and if they have to anticipate and know how much adjustment will be needed at the moment the conditions change when they drop.
 
Much faster flows than ag sprayers.

The CG change and coming out of the dive they're usually in (water drops are made from low levels) is a learned skill for sure. When the guys started flying the Global Super Tanker (747 water bomber), they had to develop new skils as the ones designed for the heavy prop bombers didn't work well with the jet engine spool up on the 747. The GST holds 19000 gallons which is probably a bit over half of the usable load in the plane.
 
LongRoadBob said:
I’ve always wondered, fire fighting planes, or bombers dropping their loads, how it is for the pilot with that sudden change of weight and CG, what they do to keep balanced, etc.
What that experience is like, and if they have to anticipate and know how much adjustment will be needed at the moment the conditions change when they drop.
Click to expand...

The tank is close to the CG. It's full of baffles to prevent fore-aft surging when less than full. And even when the gates slam full-open in an emergency dump, it doesn't happen instantaneously. Takes a few seconds.
 
Most of the water bombers meet a requirement that they drop the full load in 9 seconds I think. The GST takes just slightly longer than that (like 11).
 
You must log in or register to reply here.
Back
Top