Croatian CL-415 in action

[Retired AF Guy]

Some amazing imagery of a Croatian CL-415 dropping water on a fire near Rijeka, Croatia. Originally posted on You tube in 2019.

 

[Dana381]

I'm not a pilot but putting that plane so close to the cliff, those guys have balls of steel!

 

[lenaitch]

I'd be checking the underside for twigs.

 

[Weinie]

I'd be checking the underside for twigs.

and bird's nests.

 

[lenaitch]

I was a passenger in a float plane taking off (perhaps a tad heavy) from a small lake and we later found a twig lodged in an elevator. Good times.

 

[Good2Golf]

I'm not a pilot but putting that plane so close to the cliff, those guys have balls of steel!

Not as close as it looks, actually. The long telephoto lens foreshortens the perspective significantly.

Let’s break down this picture (measuration techniques):


Because the plane is essentially perpendicular to the camera, the length is not distorted (like the banked wings are), so that is a good linear scale reference. So too with apparent altitude of picture elements: plane; terrain elements, etc., so a small-angle approximation at distance supports linear height comparisons as well.

So, let’s start by measuring the apparent height difference between the upper wingtip of the plane and the related upper wingtip shadow…and compare that to the aircraft length, based on both axes being linearly undistorted. I see the height difference between plane and shadow to be very similar to the length of the plane a CL-415 is 20m/66’ long, so I say the plane is vertically 20m/66’ above the shadow.

Now some assumptions about the terrain. It looks steep but we get some hints from a similarity of angle between the banked wings and the shadow of the wings on the terrain. The wing and its shadow appear to slant at the same angle (top behind the bottom, respectively) which tells me that the terrain is actually inclined at a slope similar to the bank of the wings.

A CL-415’s wingspan is 28m/92’. Comparing the wing’s apparent length visually to the plane’s length…I say the banked wings look about 3/4 (0.75) high as the plane in long, so it’s apparent height difference between upper and lower wingtip is 20m X 0.75 = 15m. Some quick trigonometry for a 15m height (upper tip above lower tip) and a 28m hypotenuse (the undistorted wingspan) sin-1(15/28) = 33° bank angle. That’s not an extreme bank angle, close to what we call a Standard Rate 2 turn (heading change of 6°/sec) although a Rate 1 Turn (3°/sec and bank angles in the 18-22° range) is what is often used in IFR flight. I’ll also interpret the ground slope to be similar, since the apparent layback of the wing shadow on the ground is close to parallel to the actual wings. If the ground was sloped much different than the banked wings, the shadow would not be so parallel to the wings…it would slant forward or aft (for steeper or shallower terrain respectively).

[EDIT: to correct a flow through error from using wrong height of aircraft above shadow below, should have originally used 20m, not 15m which was banked wingtipndifference]

So, we know (well, we assume/approximate) that the terrain is similar to the wing’s bank angle at 33°…or a 63% gradient (fairly steep, definitely hiking territory), so we use that to assess the distance the aircraft is out from the terrain. We figured the aircraft was 15 20m higher than where it’s shadow hit the ground. Using the 63% gradient (which has a 1 unit rise over a 1.57 unit run, from gradient tables) a 15 20m height yields a lateral 23.5 31.3m setback of the shadow horizontally from the aircraft. Assuming the terrain is consistently sloped (definitely an assumption), to determine the aircraft’s true outset horizontally from the terrain at the SAME altitude, we consider how ouch further back the terrain sets back as we come up from the shadow’s altitude to be level with the aircraft. We use the terrain’s ‘consistent slope’ and apply the same horizontal setback from shadow back up to the plane, but rearwards up the hill, not forward through the air to the plane itself. Total horizontal separation of the plane to the ground behind it at the same altitude? 23.5 31.3m + 23.5 31.3m = 47 62.6m (155 207’).

So how about the vertical heigh of the plane above the ground immediately below it? We use the same theory that height down to the shadow can then continue down the same distance following the terrain down and forward to be right under the plane, so we’re going to double that to relative to the plane’s height above its shadow. 15 20m + 15 20m = 30 40m (99 132’)

So, all things considered (and approximated) the crew is flying their plane 100 132’ directly about the ground, is 155 207’ forward of the ground at the same altitude, and the closest distance perpendicular from the ground directly to the plane is 25 33m (84 112’) (30 40m height X cosine33°), or slightly higher than an 8 11-story building.

That said, there are a whole bunch of factors that make such flying very demanding and not without significant risk, and visually very impressive, for sure.

 

[dapaterson]

That said, there are a whole bunch of factors that make such flying very demanding and not without significant risk, and visually very impressive, for sure.

Especially if you're an Eastern European pilot with a cigarette in one hand and a blood alcohol level near blackout...

 

[Colin Parkinson]

I was a passenger in a float plane taking off (perhaps a tad heavy) from a small lake and we later found a twig lodged in an elevator. Good times.

Flying out of Bull harbour in a float equipped Beaver. Goes to the end of the lagoon, powers up, goes on step, continues on step, trees at the end of the lagoon get closer, I ask on the intercomm: "Does it always take you this long to get airborne?" The Pilot; "No" , the distinct feeling of sphincter squeezing and everyone staring quietly at the trees.....

 

[RedFive]

Not as close as it looks, actually. The long telephoto lens foreshortens the perspective significantly.

Let’s break down this picture (measuration techniques):
View attachment 68651

Because the plane is essentially perpendicular to the camera, the length is not distorted (like the banked wings are), so that is a good linear scale reference. So too with apparent altitude of picture elements: plane; terrain elements, etc., so a small-angle approximation at distance supports linear height comparisons as well.

So, let’s start by measuring the apparent height difference between the upper wingtip of the plane and the related upper wingtip shadow…and compare that to the aircraft length, based on both axes being linearly undistorted. I see the height difference between plane and shadow to be very similar to the length of the plane a CL-415 is 20m/66’ long, so I say the plane is vertically 20m/66’ above the shadow.

Now some assumptions about the terrain. It looks steep but we get some hints from a similarity of angle between the banked wings and the shadow of the wings on the terrain. The wing and its shadow appear to slant at the same angle (top behind the bottom, respectively) which tells me that the terrain is actually inclined at a slope similar to the bank of the wings.

A CL-415’s wingspan is 28m/92’. Comparing the wing’s apparent length visually to the plane’s length…I say the banked wings look about 3/4 (0.75) high as the plane in long, so it’s apparent height difference between upper and lower wingtip is 20m X 0.75 = 15m. Some quick trigonometry for a 15m height (upper tip above lower tip) and a 28m hypotenuse (the undistorted wingspan) sin-1(15/28) = 33° bank angle. That’s not an extreme bank angle, close to what we call a Standard Rate 2 turn (heading change of 6°/sec) although a Rate 1 Turn (3°/sec and bank angles in the 18-22° range) is what is often used in IFR flight. I’ll also interpret the ground slope to be similar, since the apparent layback of the wing shadow on the ground is close to parallel to the actual wings. If the ground was sloped much different than the banked wings, the shadow would not be so parallel to the wings…it would slant forward or aft (for steeper or shallower terrain respectively).

So, we know (well, we assume/approximate) that the terrain is similar to the wing’s bank angle at 33°…or a 63% gradient (fairly steep, definitely hiking territory), so we use that to assess the distance the aircraft is out from the terrain. We figured the aircraft was 15m higher than where it’s shadow hit the ground. Using the 63% gradient (which has a 1 unit rise over a 1.57 unit run, from gradient tables) a 15m height yields a lateral 23.5m setback of the shadow horizontally from the aircraft. Assuming the terrain is consistently sloped (definitely an assumption), to determine the aircraft’s true outset horizontally from the terrain at the SAME altitude, we consider how ouch further back the terrain sets back as we come up from the shadow’s altitude to be level with the aircraft. We use the terrain’s ‘consistent slope’ and apply the same horizontal setback from shadow back up to the plane, but rearwards up the hill, not forward through the air to the plane itself. Total horizontal separation of the plane to the ground behind it at the same altitude? 23.5m + 23.5m = 47m (155’).

So how about the vertical heigh of the plane above the ground immediately below it? We use the same theory that height down to the shadow can then continue down the same distance following the terrain down and forward to be right under the plane, so we’re going to double that to relative to the plane’s height above its shadow. 15m + 15m = 30m (99’…let’s call it 100’)

So, all things considered (and approximated) the crew is flying their plane 100’ directly about the ground, is 155’ forward of the ground at the same altitude, and the closest distance perpendicular from the ground directly to the plane is 25m (84’) (30m height X cosine33°), or slightly higher than an 8-story building.

That said, there are a whole bunch of factors that make such flying very demanding and not without significant risk, and visually very impressive, for sure.

Man, you probably could have just said "because of the direction of the camera and based on my experience, I believe this aircraft to be about 100 feet off the ground" and I suspect most of us would have taken that at face value...

Thanks for the explanation though, that was interesting to work my way through.

 

[Weinie]

Not as close as it looks, actually. The long telephoto lens foreshortens the perspective significantly.

Let’s break down this picture (measuration techniques):
View attachment 68651

Because the plane is essentially perpendicular to the camera, the length is not distorted (like the banked wings are), so that is a good linear scale reference. So too with apparent altitude of picture elements: plane; terrain elements, etc., so a small-angle approximation at distance supports linear height comparisons as well.

So, let’s start by measuring the apparent height difference between the upper wingtip of the plane and the related upper wingtip shadow…and compare that to the aircraft length, based on both axes being linearly undistorted. I see the height difference between plane and shadow to be very similar to the length of the plane a CL-415 is 20m/66’ long, so I say the plane is vertically 20m/66’ above the shadow.

Now some assumptions about the terrain. It looks steep but we get some hints from a similarity of angle between the banked wings and the shadow of the wings on the terrain. The wing and its shadow appear to slant at the same angle (top behind the bottom, respectively) which tells me that the terrain is actually inclined at a slope similar to the bank of the wings.

A CL-415’s wingspan is 28m/92’. Comparing the wing’s apparent length visually to the plane’s length…I say the banked wings look about 3/4 (0.75) high as the plane in long, so it’s apparent height difference between upper and lower wingtip is 20m X 0.75 = 15m. Some quick trigonometry for a 15m height (upper tip above lower tip) and a 28m hypotenuse (the undistorted wingspan) sin-1(15/28) = 33° bank angle. That’s not an extreme bank angle, close to what we call a Standard Rate 2 turn (heading change of 6°/sec) although a Rate 1 Turn (3°/sec and bank angles in the 18-22° range) is what is often used in IFR flight. I’ll also interpret the ground slope to be similar, since the apparent layback of the wing shadow on the ground is close to parallel to the actual wings. If the ground was sloped much different than the banked wings, the shadow would not be so parallel to the wings…it would slant forward or aft (for steeper or shallower terrain respectively).

So, we know (well, we assume/approximate) that the terrain is similar to the wing’s bank angle at 33°…or a 63% gradient (fairly steep, definitely hiking territory), so we use that to assess the distance the aircraft is out from the terrain. We figured the aircraft was 15m higher than where it’s shadow hit the ground. Using the 63% gradient (which has a 1 unit rise over a 1.57 unit run, from gradient tables) a 15m height yields a lateral 23.5m setback of the shadow horizontally from the aircraft. Assuming the terrain is consistently sloped (definitely an assumption), to determine the aircraft’s true outset horizontally from the terrain at the SAME altitude, we consider how ouch further back the terrain sets back as we come up from the shadow’s altitude to be level with the aircraft. We use the terrain’s ‘consistent slope’ and apply the same horizontal setback from shadow back up to the plane, but rearwards up the hill, not forward through the air to the plane itself. Total horizontal separation of the plane to the ground behind it at the same altitude? 23.5m + 23.5m = 47m (155’).

So how about the vertical heigh of the plane above the ground immediately below it? We use the same theory that height down to the shadow can then continue down the same distance following the terrain down and forward to be right under the plane, so we’re going to double that to relative to the plane’s height above its shadow. 15m + 15m = 30m (99’…let’s call it 100’)

So, all things considered (and approximated) the crew is flying their plane 100’ directly about the ground, is 155’ forward of the ground at the same altitude, and the closest distance perpendicular from the ground directly to the plane is 25m (84’) (30m height X cosine33°), or slightly higher than an 8-story building.

That said, there are a whole bunch of factors that make such flying very demanding and not without significant risk, and visually very impressive, for sure.

So a birds nest from a tall tree?

 

[daftandbarmy]

Man, you probably could have just said "because of the direction of the camera and based on my experience, I believe this aircraft to be about 100 feet off the ground" and I suspect most of us would have taken that at face value...

Thanks for the explanation though, that was interesting to work my way through.

 

[Dana381]

Not as close as it looks, actually. The long telephoto lens foreshortens the perspective significantly.

So, all things considered (and approximated) the crew is flying their plane 100’ directly about the ground, is 155’ forward of the ground at the same altitude, and the closest distance perpendicular from the ground directly to the plane is 25m (84’) (30m height X cosine33°), or slightly higher than an 8-story building.

That said, there are a whole bunch of factors that make such flying very demanding and not without significant risk, and visually very impressive, for sure.

Very interesting post, I really appreciate you explaining how to determine distance from the video like that. I do understand how perspective works and I sort of came to a similar conclusion from previously watched videos of CL415's dropping water and how high they were from the ground. I could tell these ones were a similar height by the look of the water as it fell.

let me extrapolate from your post to explain my train of thought.

Estimated 84' from the ground to the plane while flying at a 33deg bank angle and performing maneuvers. Lets say your estimate is within +/-10% 84' -8.4'=75.6' Lets say 76'. CL415 wingspan you gave is 92', divide by 2 = 46' 76'-46'= 30'. So lets say the plane suddenly pitches right, maybe the right tank fails to deploy as commanded creating a weight bias. Or maybe something else causes the plane to level off or bank right. now the wing is only 30' from the ground or 1/3 the planes width. Damn close right. . Like I said I'm not a pilot but I would think if a GA or commercial plane got closer than 300' to anything, ground or another plane while flying (except landing of course) there would be an investigation.

 

[foresterab]

Appreciate the math on the flight height. From my experience watching them fly overhead I would have said 200' drop height (double tree height) was more common in part to allow for greater spread of the drop. This is part of the Air Attack Officers' call...do I want a slug of water to break through the forest canopy or a wider distributed spread due to lighter fuels (i.e. grass).

Drop location on the fire would also be a factor as you may have different thermals near the head of the fire than the flank/rear and approaches would be done to trying to minimize this impact.

Unfortunately winds are a big driver of fires and depending on the airframe can be flipped with unexpected gusts. It's partly why many agencies run a mix of airframes from larger planes good for longer drops (lower drop interval though) that are limited on how close they can fly to the ground (i.e. mountains) vs. smaller tankers like the Air Tractor 802 which can dance in tight quarters but are limited under high winds.

For refence off the top of the head Newfoundland, Quebec, Ontario, Manitoba and Saskatchewan fly CL-415's with Alberta flying CL-215T's and North West Territories flying CL-215's. There are also some flying in the US along with Malaysia, France, and Thailand (can't remember who has -215's vs -415's). Viking Air has started floating the CL-515 concept but it's still a theoretical aircraft at this time.

 

[daftandbarmy]

And Viking now has the 515... made in Sidney, BC:

Building on the pedigree of the CANADAIR CL-415, the CL-515 “First Responder” is the next generation of purpose-built aerial firefighter and multi-role amphibious aircraft. Through the incorporation of new technology and the integration of the state-of-the-art Collins Pro Line Fusion® digital avionics suite, the 515 provides operators with world class reliability, enhanced safety, and unrivaled situational awareness. The multi-mission Canadair 515 First Responder addresses obsolescence issues associated with the older CL-415 airframe and systems, while improving maintainability through its use of modernized materials and airframe systems enhancements. Its expanded tank capacity (7,000 L) and ability to refill in 14 seconds from water sources in close proximity to wildfires allows the CL-515 to drop enormous amounts of foam-injected fire retardant on a continuous basis, increasing productivity by up to 15 percent.

 

[Good2Golf]

Dana381, definitely something to think about, and your methodology is exactly the math to consider! It’s also why ASW aircraft at low altitude have to be careful when they crank and bank since a P-3/P-8 have a decent sized wingspan. Same applies for helicopters. Imagine flying a Chinook at the same speed that CL-415 is flying, but wheels just 3m/10’ over the ground and a rotor span of 18m/60’…three times wider on either side of the fuselage than the height of the wheels over the ground…definitely have to be careful banking at those low altitudes!

 

[Dana381]

Dana381, definitely something to think about, and your methodology is exactly the math to consider! It’s also why ASW aircraft at low altitude have to be careful when they crank and bank since a P-3/P-8 have a decent sized wingspan. Same applies for helicopters. Imagine flying a Chinook at the same speed that CL-415 is flying, but wheels just 3m/10’ over the ground and a rotor span of 18m/60’…three times wider on either side of the fuselage than the height of the wheels over the ground…definitely have to be careful banking at those low altitudes!

The workload in the cockpit of a water bomber must be intense, I've driven long haul in most any weather and I know how tiring it is to be on edge while driving straight in low visibility conditions. The water bomber pilots need to fly the plane while watching the ground and making sure they don't fly into smoke that will kill the engines, monitor for other air traffic, deal with changing weight and balance, and in this case a 30deg ground slope that requires dumping while banked. WOW.

Military pilots flying helos while being shot at in busy airspace would have very similar workloads. My hats off to all these pilots working hard to keep us safe at home and at war.

 

[YZT580]

At any time you are operating in close proximity to the surface (even arrival and departure) leaves you very little time for recovery if anything goes awry.

 

[Good2Golf]

And this event in particular notes the impact of descent rates, even if initially at significantly higher altitudes.

I was there and saw this happen…I knew they were screwed well before they hit the water because the sink rate was outrageous.

 

[lenaitch]

Flying out of Bull harbour in a float equipped Beaver. Goes to the end of the lagoon, powers up, goes on step, continues on step, trees at the end of the lagoon get closer, I ask on the intercomm: "Does it always take you this long to get airborne?" The Pilot; "No" , the distinct feeling of sphincter squeezing and everyone staring quietly at the trees.....

Or the oft-seen doing laps around a lake trying to get up speed, sometimes getting one pontoon out of the water to reduce drag. A 185 on floats has limited money-making capacity. Bush pilots are a different breed.