Peter Gray/Los Angeles
Wildfires are a growing problem worldwide, as 1998 proved. Authorities usually use fixed wing tankers and light helicopters to fight fires, but the use of medium and heavylift helicopters has proved more cost effective, says Sikorsky.
The US manufacturer has developed a firefighting version of its S-70A, the international variant of the US Army's UH-60L Black Hawk. Flight International was invited to evaluate this specialised version, the Firehawk, while it was under evaluation by the Los Angeles County Fire Department during last year's fire season (August to November).
With twin General Electric T700-701C turboshafts, a maximum gross weight of 10,670kg (23,500lb) and a cruise speed of 155kt (287km/h), the S-70 was developed to operate in demanding environments and, with its 4,090kg underslung load capability, to lift bulky cargo and equipment.
When fighting fires, an aircraft's effectiveness is dependent on its direct operating costs, its speed and the distances to be flown, how much water and foam can be dropped and with what accuracy, the time to refill the water tank or bucket, and the time taken to refuel. Sikorsky says the Firehawk can be refuelled, foam replenished, windscreen cleaned and 3,790 litres (1,000USgal) of water loaded in 3.5min. When on the job, the helicopter can carry 1.5h-worth of fuel.
Most firefighting helicopters use a bucket, carried on the external load hook. This is simple and cost effective, but the aircraft is not allowed to overfly any buildings or carry any passengers, and its speed is restricted by the underslung load. A cockpit-controlled camera is usually required to allow the crew to view the bucket, suspended some way beneath the aircraft's belly. A big bucket requires a deep water source to allow the whole bucket to be submerged. Crews need regular training to keep current.
Instead, the Firehawk uses a belly tank. This allows a faster dash speed, as I was to find out during my test flights. A 3.6m-long "snorkel" with a powerful pump at the end is used to suck up the water, so only a shallow water source is required - about 45cm depth will suffice. The pump will suck up 3,790litres in about 1min. There are plans to investigate the possibility of filling from shallow water by laying the snorkel down horizontally. If there is no nearby water source, the aircraft can be replenished from tankers. Ground filling also takes about 1min.
Because there is no underslung load, the Fire-hawk can be flown straight to the water source and then on to the scene of the fire. Los Angeles' fire department puts great emphasis on getting to the fire quickly and hitting it hard. With no bucket dangling around underneath, the operation is safer. With all firefighting equipment installed, the aircraft can be used to fly up to 15 people to the scene of the fire. Conversely, it can be used to pull them out of danger. Less crew training is required - I felt comfortable after 1h 40min aircraft handling time and 40min firefighting practice.
Extra Equipment
The Firehawk is a standard UH-60 equipped with a few extras - landing gear extension fittings (standard gear is used), four belly tank and four landing gear attachment lugs and electrical wiring associated with the cockpit control panel and civilian radios. The 3,790 litre tank can then be fitted (or removed) in about 4h. The tank also contains a 115 litre foam reservoir. Foam can be mixed with the water during flight at whatever concentration is required.
The tank has two hydraulically actuated doors which open at a rate selected by the pilot, including an emergency dump which gets rid of the 3,790 litres in 2s, as I was to find out. The helicopter is then 3,800kg (8,370lb) lighter. The tank has its own computer to manage this, and the system uses its own internal hydraulic systems. No major modifications are required to convert a standard S-70.
I had three flights in the Firehawk, one for pure handling, one observing the experts and one for my own firefighting practice.
My pilot was Sikorsky engineering test pilot Chip Washington. He and a technician showed me round the aircraft. The maximum take-off weight is 10,670kg and landing weight 9,990kg. A standard UH-60L with crew of two would weigh about 5,720kg, so picking up 4,540kg on the external load hook (its maximum design load) still leaves 680kg for fuel - enough for 1.5h flying with no reserve. The aircraft can hover outside ground effect (OGE) up to about 3,000ft (900m) density altitude.
Fitting the water tank and other equipment increases the empty weight by 680kg, although Sikorsky is aiming to reduce this to 500kg for production units. Even though maximum take-off weight is reduced to 10,670kg, the Firehawk can pick up 3,790 litres of water, plus a crew of three and fuel for 1h, with a 30min reserve. At this weight, OGE hover ceiling goes to 3,500ft (1,000m) and the helicopter can hover at ground level up to 50 íC.
The extended undercarriage can withstand a 22g impact; at 10g, fire extinguisher bottles will release automatically into both engine bays to prevent a conflagration. With the extended gear comes a long step on both sides for easier access to the cabin.
The GE engines each deliver 1,410kW (1,890shp) for take-off, 1,240kW maximum continuous and have a single engine contingency rating of 1,445kW. Average fuel consumption is a remarkably low 454kg/h. An engine change takes just over 1h, Sikorsky says.
The anti-vibration bifilars, dampers and BIM indicators on the main rotor head are reminiscent of Sikorsky's S-61 helicopter. The flapping, lead and lag bearings are elastomeric, eliminating the need for lubrication. The main rotor blades have swept tips to help suppress the aerodynamic problems which beset rotors at high speed, and also to reduce noise.
Uniquely in my experience, the cockpit controls are dual redundant for most of their run - the co-pilot's take a separate route from the pilot's and meet at the jacks. If one set is damaged, the aircraft is still flyable.
The moveable horizontal stabilator is computer controlled with airspeed to keep the fuselage substantially level from the hover up to maximum forward speed - and even at high backwards speed, as I was to explore. The remarkable tailrotor is cranked over at an angle of 20í to help provide extra lift. Each pair of composite "paddle" blades are one continuous unit; flapping and pitch changes are achieved by deflecting the spar, so there are no bearings to lubricate. The blades are of a distinctive shape which gives plenty of power but reduces noise, and they are anti-iced, as is the main rotor. The aircraft has a full icing clearance and if the system is in automatic, the anti-ice systems will come on by themselves. All gearboxes have a 30min dry-run capability.
Inside the cabin, all passenger seats have a shoulder harness and are crashworthy. Other safety features include the crashworthy fuel system. The floor will take twice the stress of a civil aircraft - 1,460kg/m2. Two sideways facing seats opposite a retractable window allow the observer to lean out to see the snorkel while relying on his harness for restraint.
Washington showed me how to climb up and install myself in the comfortable, crashworthy pilot's seat. I adjusted the five-point harness, seat and pedals. Everything was well within reach. Both pilots have a full set of conventional analogue instruments, but some authorities operate the S-70 with a single pilot. Included in the pilot's scan is an instrument showing the position of the horizontal stabiliser and its limits - if it gets stuck or runs away, the pilot could run out of forward/aft cyclic pitch control. There is an audio warning to alert the pilot of this condition and Washington briefed me on what to do if I heard it. There are audio warnings also for engine failure and low rotor RPM.
Colour Changes
Presentation of engine and rotor parameters is by easy-to-interpret vertical strip displays with colour changes when approaching limits, so no need to memorise the limits. There are also digital readouts of the engine and rotor parameters. I liked the radar altimeter presentation in both analogue and digital formats- this was to prove useful when I did some firefighting runs.
Above the instruments are the warning lights for engine failure, low rotor RPM and engine fire. The pilot is allowed to exceed temperature, torque and RPM limits during single-engine operations, but there are warning lights and the exceedances are recorded. Visibility all round was good, although the pilot cannot see the external power connection; there is a warning light to advise that it is still plugged in.
The well-designed throttles are overhead, but since their function and use is semi-automatic single pilot operation is not a problem. The engine starter motors are air driven so the Firehawk has a compact but efficient auxiliary power unit which, once started, takes care of itself and shuts itself down in the event of a malfunction. It supplies air, power and heating.
There is a long checklist for start-up in the flight manual, but we dispensed with this and, instead, Washington showed me a route system where you start at the top and follow a route through the overhead console, instrument panel and centre console using an abbreviated "through-flight" checklist. We arrived at the first engine start quickly. I pressed the number one engine starter button, moved the throttle/speed-select lever to ground idle and sat back and watched. In a hurry, both engines can be started simultaneously.
The weather was good with a light wind. We were at 1,400ft pressure altitude, 3,500ft density altitude and were to go to 7,000ft density altitude at times, a good test for any helicopter where rotors and engines can be hard pressed to perform satisfactorily. With a Sikorsky flight engineer completing the crew, we were 3,630kg short of maximum take-off weight. All-up weight flying was to come later when we took on 3,790 litres of water.
Pulling up into my first hover, I was able to rest my cyclic pitch stick forearm on my right thigh, so I had good control - not that I needed much since the aircraft sat in an accurate hover with little input from me. We were light, so we had plenty of power in hand. I asked Washington to pull one engine back to ground idle, which he did quickly. We remained in the hover; there was a momentary 2% rotor RPM droop which quickly self-restored. The presentation of how much single engine power we were using (well below maximum continuous) and how much we had available was excellent.
The aircraft is cleared for high sideways and backward speeds, which is good news if the pilot has to hover out of wind to pick up water. We went to 50-55kt to the right and used full left pedal. At the same speed to the left we still had some right pedal available. Backwards at 45kt produced no surprises and we stayed fairly level, with no nose-down tucking - the stabilator was doing its job. Some fast spot turns revealed there are no nasty wind directions to avoid or be aware of in the hover.
We moved into forward flight and went to 5,000ft density altitude. Maximum continuous power gave us a healthy 142kt indicated airspeed, 152kt true. The aircraft will normally fly at 155kt indicated, but the tank produces extra drag. Our fuel flow was 545kg/h. The never- exceed speed at sea level is fast at 194kt, but with the tank and our altitude we reached 175kt. Vibration levels increased slightly, but were benign, and turns in both directions did not reveal any stresses.
Our pitch up and down limits with the tank and snorkel installed were 30í with no water, 20í with; maximum angle of bank was 60í with no water, 45í with. So I did some steep turns and pull-ups and pushovers. There was good, crisp handling all round due, no doubt, to the virtual offset hinges on the main rotor blades.
Straight And Level
We had settled down straight and level to a fast cruise when I asked Washington to reduce one engine quickly to ground idle. There was a momentary slight rotor RPM droop, which self-recovered, and no loss of airspeed, a satisfactory result.
We then explored vortex ring/settling with power. At low speed (less than about 20kt) and a rate of descent of about 300ft/min (1.5m/s), vortices around a helicopter's main rotor blades can destroy lift, causing blade stall, increased rate of descent and possible loss of control. Some helicopters enter the condition easily. Some will self recover. Most will not and need instant pilot response. Washington set up the conditions and we sat back and watched. Vibration increased and our rate of descent went from 300ft/min to 1,200ft/min - classic symptoms, which some experienced pilots ignore. They pull in collective pitch to reduce the rate of descent, but often it has the opposite effect and main rotor stall increases. We had enough cyclic pitch control to fly out of the condition, leaving the vortices causing it behind. The S-70 exhibits good warning signs and has enough control to recover.
An autorotation gave us a rate of descent of 2,500ft/min, about average for this size and configuration of helicopter. Control of rotor RPM was easy, though one had to be vigilant because of the rotor's low inertia.
To test the rotor RPM control provided by the engine fuel control units, I asked Washington to raise and lower the collective lever as fast as he dared. He was vicious, but we got little droop - a satisfactory result that gives the pilot confidence he can go up or down quickly without high or low RPM bells and lights coming on.
There are two stabilisation systems on the UH-60, so I asked Washington to take them both out to allow me fly the aircraft raw. I had to be slightly more vigilant to keep the aircraft stable, but not unnecessarily so. The mechanical mixing unit does a good job co-ordinating the controls. There was slight nose-down pitch with a right turn and nose-up pitch with a left, but easily spotted and corrected. I made an approach to the hover and landed without any fuss. There are two independent hydraulic systems to power the controls and absorb the feedback, plus a backup hydraulic pump. There are no speed penalties if one system fails and no difference in feel or aircraft handling restrictions.
Washington switched off a generator, which caused the master caution light and accompanying capsule to illuminate. There is plenty of electrical redundancy on this aircraft, so all services were still available.
Washington reached up and put one engine speed-select lever into manual throttle. In this condition, the engines still talk to each other and attempt to keep themselves matched, and it worked well. You have to be vigilant, however, as there is no engine temperature or overspeed protection. I made a circuit approach, hover and landing without any further adjustment to the manual throttle.
A steep approach to a target on the ground required me to kick the nose slightly left to keep the target in view all the way down. Vertical climbs and descents staying over the target were easily accomplished with the good visibility.
We did some landings from all four directions on 6ísloping ground. You have to be careful with the tank installed, but test pilots have landed the Firehawk on 9í slopes. The basic Black Hawk will go to 15í.
Second Flight
For my second flight, I sat in one of the sideways-facing crew seats in the back and observed two pilots and their crewman, in the other sideways facing seat, go about their business of firefighting. Washington, in the co-pilot's seat, ran quickly through the start-up route, started both engines in quick succession and announced we were ready to go in about 2min. I was able to stand up and lean out, relying on my harness to restrain me. Communication with all crewmembers was through an intercom system.
They dropped me at a vantage point beside a lake while they went to fill the tank, then did a spray run alongside me. The water cover was massive and would surely suppress any fire, especially if mixed with the foam or retardant.
The Firehawk landed and I took the captain's seat. The 3.6m-long snorkel was now hanging free under the helicopter and snaked out over the ground, so the crewman hanging out of his window told me to pick up, move slightly sideways then up and away. I flew to the lake, and chose a spot close to the bank as a good visual reference while in a 10ft radar-altitude hover to pick up water. The crewman provided a running commentary on how far the pump on the end of the snorkel was from the water. Then it was in the water and he told me to hold my hover. I noted 10ft on the radalt.
To keep the controls simple and avoid complications when hovering a large helicopter 10ft above the water, in what could be in smoky conditions, Sikorsky has used existing buttons on the cyclic and collective to operate the water system. I pressed what is normally the go- around button on the cyclic and kept it pressed. This started the pump. Washington monitored the contents gauge on the small water/foam control panel. This provides all you need to know about the water/foam system - you can preselect how much to dump, or adjust the foam/water ratio. He announced we were full, I released pressure on the button and transferred my thumb on the collective to the dump button (normally the underslung emergency hook release). I pulled up on the collective, alternatiing between looking outside to maintain my position over the water and inside to monitor the torque meter. The crewman gave me a running commentary.
We were now at the maximum take-off weight of 10,670kg. The snorkel broke the surface; I pulled up a few extra feet to a highish hover and checked the torque. It wavered between 109 and 110%, which was satisfactory as I had 120% available at our density altitude. Washington talked me through a cautious departure, gently lowering the nose and building up forward speed. I felt the translational lift come in and I went into a confident climb, using no more power.
The aircraft still handled crisply. Although our angle of bank was now restricted to 45í, this was more than enough to position the UH-60 within the small bowl of the lake and line up for a spray run over a nearby winding road. The best combination for good spray cover is 60kt at 70ft. Again the good radalt presentation helped me achieve an accurate height. Once over the target, I pressed the button on the cyclic, normally reserved for the underslung cargo release, and out went the 3,790 litres. The aircraft remained stable, with no sudden jolts or tendency to climb. Remarkable.
I spent 40min spraying various locations, Washington picking more and more difficult places, which required agility from the aircraft and adequate handling from the pilot. On our final pickup, at the critical moment of moving off from the hover, he reached across and pressed the dump button on the lever. We lost 3,790 litres in about 2s and our weight suddenly reduced by 3,800kg, giving us an easy single engine hover and flyaway capability.
Washington says he can train an experienced Black Hawk pilot to operate the Firehawk in about 5-7h, and a pilot with experience, but not on the Black Hawk, in about 7-10h.
User Friendly
From the pilot's point of view, the Firehawk and its systems are user friendly. There is enough main and tail rotor and engine power and agility for the firefighting role, especially when at maximum weight and at higher altitudes and ambient temperatures.
The cockpit is comfortable, important for a long day at the controls in the event of a serious fire, although because of the high workloads involved in firefighting the pilot would benefit from a more modern cockpit.
Compared with other firefighting helicopters, the Firehawk offered the flexibility to move people and equipment quickly and to use shallow water sources or ground tankers. It is a safe aircraft with several crashproof systems, and provides the crew with good communications and well-designed tools for the job.
The Firehawk evaluated in this test was converted from a US Army National Guard UH-60L for evaluation purposes. Plans call for additional aircraft to be equipped with provisions for the firefighting kit, allowing more UH-60s to be used in this role.
Source: Flight International
