Fox Air Pty Ltd

07
Apr

2007

WELCOME TO THE JET AGE!

At some point in the careers of most professional pilots, be they fixed or rotary wing, a turbine endorsement will be the key to moving onward and upward through the industry. Whilst the turbine engine is a sophisticated and finely tuned piece of hardware, its operation and management from a pilot’s perspective is a fairly straightforward exercise as Martin Bass discovered.

Whilst piston powered aircraft may be more prevalent in numbers than their turbine siblings across the local aviation industry, their concentration is in areas such as training, charter, tourism and private ownership. Once the passenger or payload requirement becomes greater and aircraft get larger in size, the turbine outstrips the piston engine for high power to weight ratio and overall efficiency. Hence they tend to be the standard on many modern aircraft.

I had often been told about the joys and challenges of flying turbines. Whilst I had flown a handful of turbine-powered aircraft over the years, I had little knowledge of the engine management side of things and only a limited understanding of all those new and different instruments. Cylinder Head Temperature and Manifold Pressure had become straightforward indicators of engine function and available power. By comparison, Turbine Outlet Temperature (TOT) and Torque were strange new concepts and made little sense to me beyond the green yellow and red arcs on each instrument.

Enter the Enstrom 480B, a light, single-engine helicopter with turbine power, five seats and minimal complexity to bamboozle me during or after my training. I had flown the Enstrom a year earlier and had found it very pilot-friendly and straightforward to fly. Having sampled its general handling qualities on that occasion, I couldn’t imagine a better helicopter to nurse me through my first turbine endorsement. The regulations stipulate that the first endorsement on a new engine type requires five hours of flight instruction and three hours on each type thereafter, as long as there’s only one engine. I had already flown the Enstrom for one hour so I would need to complete another four this time around.

I had heard plenty of intimidating things about turbines for years – about how easy it could be to kill the engine with one ‘hot start’ or how simple an exercise it is to render the battery lifeless by running the engine through too many start cycles or even how I could over-torque the whole system by pulling too much power and murder the entire aircraft. I was hoping the endorsement exercise was going to demystify the whole business for me and give me a sound understanding of how to handle this beast without doing it irreparable damage.

Hugh Fox is a man with plenty of experience around turbine engines as a former captain on Ansett’s 727s and later, on the airline’s giant Sikorsky S61 helicopters that operated between the mainland and islands in the Great Barrier Reef. Hugh has flown Enstroms for many years and his company, Fox Air, has the distributorship for the Enstrom range throughout Australia.

I caught up with Hugh at his property in a picturesque part of Victoria south of Geelong. Situated in the semi-rural landscape of the Bellarine Peninsula, Hugh’s property is surrounded by open farmland and incorporates hangar facilities and a helicopter landing area behind the house. For our purposes this would be our base and, just a few minutes away by air, the Barwon Heads airfield and surrounding airspace would be the venue for most of the training.

With a coffee in hand the first order of the day was to spend some time talking through the mechanics of turbine engine operation. As an experienced flying instructor, Hugh knew instinctively how most pilots approach their first foray into turbine power and set about allaying my fears and putting a few myths to rest. “People tend to make far too much of turbine engines in terms of their complexity and management. In many ways the turbine is a lot easier to work with than the piston engine,” he said in conversation. “Turbines are very simple and reliable but many pilots who are making the transition from piston engines tend to regard them with a mixture of awe and apprehension. This is just another type of engine and its operation is straightforward,” he emphasised. Once it’s running there’s a minimal amount of work to do other than monitor the engine instruments like you would in any other aircraft and know how to respond should there be any indications out of the ordinary.”

That said we turned our attention to the Enstrom and its powerplant, the Rolls Royce 250-C20W. This engine, formerly produced by US manufacturer Allison, is one of the most proven and reliable turbines on the market with variants installed in aircraft such as the Bell 206 JetRanger, the MD (Hughes) 500 series, the AS 355 Twin Squirrel and our own fixed wing GAF Nomad. Its total operating hours run into the millions but little has changed in this engine since it first flew in the mid 1960s.

As is the case with most turbines, the critical phases of the engine’s operations are startup and shutdown. This is where the operating temperatures vary most and it’s these quick changes in temperature, or excessively high temperatures that can do some serious damage if not managed correctly. Hugh had talked me through the start procedure earlier but now I was in the seat, staring at the relevant engine instruments and hoping that it would all fall into place.

I ran through it again in my mind – ‘throttle closed, depress the starter button on the collective, roll on throttle gently until the engine lights off, at 40% compressor (N1) RPM roll the throttle to the idle detent and allow time for the engine and transmission to spool up and temperatures to rise to within the safe operating range. Throughout this process, keep a close eye on the Turbine Outlet Temperature (TOT) and ensure that there are no temperature exceedences’.

For the initial start Hugh stood beside me, outside the aircraft, ready to act if things went wrong. In most other helicopters the command seat is on the right hand side, placing the main collective control in the centre. With the command seat on the left, the main collective control is between the command seat and the left side door making it impossible to reach by the instructor. Of course there is a second set of controls for the instructor, however the second collective lacks the starter switch and engine idle detent which means the instructor does not have control through startup.

I took a deep breath, stared at the N1 gauge and hit the starter. For a split second my senses were filled with that turbine magic – the whine of the compressor as it spooled up, the blast in the combustion chamber as the engine lit off and the whiff of kerosene as some of the exhaust fumes wafted through my open door. My split second of joy ended abruptly as I trained my mind back to the business at hand. I must have aged visibly, watching the TOT needle shoot up through the green arc and into the yellow as it raced towards the redline. Suddenly it stabilised and receded back into the green. As the N1 indication hit 58% RPM I released the starter and switched on the generator. Sure enough the engine continued to make its own noise. So far so good.

Hugh climbed aboard and after a minute of warm up time I checked the avionics and we were ready to fly. The start process had been straightforward as Hugh had assured me and the whole event was over in less than a minute. With his OK I wound the throttle up steadily until it hit the stop, taking the engine and rotor RPM into the green.

Remembering my earlier experience in the Enstrom I lifted into the hover, turned into wind and had the helicopter climbing on departure for Barwon Heads airfield. On the way Hugh outlined some of the problems I might encounter with engine starts on turbines in future. “During a hot start the TOT will race up, typically due to the introduction of too much fuel during startup. If this happens, chop the throttle and keep the starter engaged to ensure that plenty of cool air is coming through the engine to cool it down,” he explained. “You may also encounter a ‘hung start’ where the engine lights off but does not accelerate up to idle speed. This generally indicates battery problems so close the throttle again and shut the electrical system down.”

As we approached the airfield we turned our attention back to the flying. Barwon Heads was a small strip with just a few aircraft coming and going – perfect for our purposes. For a little over an hour Hugh guided me through a range of manoeuvres to get me reacquainted with the Enstrom and familiarise me with emergencies. After a couple of normal circuits we moved on to some hovering practice and slope landings. After demonstrating the Enstrom’s capabilities Hugh also took me through some running takeoffs and landings to simulate limited power situations. These manoeuvres required me to get the helicopter light on its skids and run it along the grass next to the strip, either to get the helicopter into the air with a little forward speed or to get it safely on the ground in circumstances where I have not got sufficient power to hover. After and hour of general handling we progressed to emergencies. Through several hovering autorotations, simulated jammed controls and autorotations from 1000 feet the Enstrom was docile and predictable. Our autorotations to the ground and running landings were made easy by the beefy landing gear which cushioned our arrival. The tall rugged skids are just one clue to the helicopter’s origins as a purpose-built trainer designed to military specifications.

Through the entire routine the Rolls Royce engine didn’t budge, the engine and rotor RPM needles seemingly glued into position at 100%. Several times I bottomed the collective to slow the helicopter down or initiate a steep descent. On each occasion the engine still didn’t falter, the only detectable indication being a soft transmission whine behind us.

After a couple of hours in the air I had had enough adrenaline through my system and it was time for a break. “Let’s do a couple of confined area approaches on the way back,” Hugh suggested. He pointed to a small area of green between the trees in the middle distance. “That’ll do – it’s tight but you’ll make it in and out of there without any trouble.” Overhead the area I had no idea how I could get in without chopping down some foliage. Nevertheless I made my descent with caution, slowing the helicopter down to a manageable speed, the tension in my arms and legs taking me back to my early training days when I had less hours and experience in my logbook. Everything went just fine and we settled onto the ground with satisfactory clearance from surrounding trees.

On departure, the turbine engine came into its own. Getting out required a vertical ascent to around 50 feet to clear the trees, a stunt that would inevitably redline a piston engine with any reasonable load onboard. The Enstrom made an effortless climb vertically until I could lower the nose and pick up some forward airspeed. The torque gauge indicated a good amount of power in reserve but I kept the ascent slow to ensure we stayed well clear of obstacles.

Landing back at Hugh’s place I returned the throttle to the idle position to give the Allison its obligatory two minute cool-down. This done I shut the helicopter down and we retreated indoors to examine the ins and outs of turbines in more detail. Hugh started with a rundown of the design of the Allison engine and its parts, comprising the compressor or gas producer (N1), the ‘hot section’ or combustion chamber, the power turbine (N2) and the accessories gearbox. “The Allison 250-C20W develops 420 shaft horsepower (SHP) but the power available is limited by the transmission to 317 SHP. This is deliberate in the design so that there is some power in reserve for hot weather or high altitudes,” he outlined. “You can use all of this power for takeoff but maximum continuous power is limited to 289 SHP. The power indicator is the torque gauge and is measured in pounds per square inch (PSI). The redline is set at 72 PSI which gives you 317 SHP. The green arc goes to 65 PSI which indicates 289 SHP. The Enstrom has good power reserves but it’s important to observe the torque indicator on hot days or at high altitudes and do your calculations for weight and balance, just like piston aircraft.”

Over some lunch he discussed some of the issues to watch for with turbine engines in the air and on the ground. Erosion, as he explained is the main issue that causes problems with turbines. “Particle separators remove over 90% of solid materials before they go through the compressor, but there’s still some that makes it through into the engine,’ He said. “The main turbine is spinning at well over 30 000 RPM and at this speed, minute grains of dust can do significant damage to the turbine blades over time.” Hugh added that in flight, the main things to watch for are increases and decreases in temperatures and pressures as these will be the best indicators of impending trouble.

After another hour of talking turkey over turbines I called it a day. With 2.5 hours of flying completed on day one, I would be back the next day for the final 1.5 hours to finish the endorsement.

The next morning brought more of the same flying weather – cool and calm with a few knots of sea breeze in the air. Having completed the emergencies section of the training to a satisfactory standard I was in for more general handling. I had performed several engine starts on the first day and I felt comfortable with the process. Nevertheless I’d be lying if I didn’t admit that pushing that button still gave me an adrenaline rush.

In the air again we headed for a nearby property to visit a fellow pilot and Enstrom owner, giving me more valuable opportunities to practice my off-airport procedures, confined area techniques and engine startup and shutdown. After a brief stop we departed once more, heading for the mouth of Port Phillip Bay. Some straight and level flying gave me an opportunity to experience the Enstrom through a range of airspeeds from low speed up to Vne and I also put the Enstrom through some steep turns and a couple of simulated engine failures from 300 feet. I ate up an hour and a half of flight time without blinking and I greeted Hugh’s signal to head for home with a twinge of surprise and disappointment.

I ran the Allison through one last two minute cool-down and thought about what I’d done over the last couple of days – my turbine endorsement had been a challenge all round and I had gained a new level of understanding about this engine type. Most of all though, thanks to Hugh Fox, I no longer had those feelings of awe and apprehension about the turbine engine – just that adrenaline thing whenever I hit the button.