L-39 Albatros Pilot Report
by Buck Wyndham, L-39 Instructor Pilot
Photo by Leslie Hicks, Eclipse Aviation Photography
|The L-39 Albatros is, by all
estimates, the most popular jet warbird on the US market. Its sleek looks, reasonable
operating costs, and ease of operation explain much of the allure of this Czechoslovakian
beauty, but there are other factors which make it such a desirable airplane. Let's go
flying and see what everyone's so excited about.
The L-39 is a single-engine advanced trainer used by many of the world's air forces, and as such it has many of the design features and handling characteristics as the high-performance fighters that its students will one day fly. The cockpits are fully pressurized, heated and air-conditioned. Each of the tandem cockpits is equipped with enough flight controls, flight instruments, engine gauges, and system status indicators to allow either pilot to safely operate the airplane. As with most military jet trainers, the back seat was designed for instructors and, like many modern trainers, there is limited or no access to certain controls and switches in the rear "pit." In the L-39, these items include environmental controls, fuel pump switches, and the normal electrical controls. Also, the rear seat occupant cannot monitor the Exhaust Gas Temperature (EGT) simultaneously with the front-seater. In actual practice, none of these factors is a problem. There are duplicates of the really important controls in the back (and who really needs all that stuff, anyway?) The back seater does, however, have a few unique items to himself: a fiendish array of levers and switches which allow him to fail the front-seaters instruments at will -- a holdover from the airplanes days as a military trainer.
The L-39 features some relatively sophisticated systems, such as an automatic Ram Air Turbine (RAT) that pops out of the fuselage and powers the electrical buses in the event of a main generator failure or engine failure; a series of backup hydraulic accumulators and interconnect valves that allow you to extend the gear, flaps and speed brakes via emergency means; an emergency fuel control system; and even some backup controls for the environmental control system (ECS).
Preflight of the Albatros is very conventional. Starting at the cockpit, you make sure the control lock has been removed, check your parachute harness and personal gear, ensure that the cockpit controls and switches are in their proper positions, and check the fuel quantity gauges. It's standard practice in jet aircraft to always have full tanks prior to departure. If your airplane has active ejection seats (which most do not), the seat and canopy safety pins should be in place. These will be removed once you're ready to strap in.
You walk clockwise around the airplane. All critical preflight sight-gauges and fluid level indicators are located within easy reach while standing on the ground, so ladders or platforms are not needed. This is just a small example of the user-friendly design philosophy of the airplane. A reasonably fit person can easily get up on the wing unassisted to check fuel caps and inspect the topside of the airplane. Engine oil level is checked via a handy sight-gauge on the right rear flank of the fuselage, a vast improvement over many jets, which often require you to remove a very inconveniently-located dipstick. Several popular modifications make preflighting the airplane even easier, including a light to illuminate the engine oil sight glass, and a pair of hydraulic accumulator gauges.
The trailing-link landing gear design, utilized on all three gear, looks beefy and tough, and it is. These airplanes were designed to be operated from rough fields, and even grass strips. Most private owners, though, stick to hard surfaces to minimize the risk of foreign object ingestion.
As you inspect the tail section you notice that, unlike most airplanes, the elevators "fall" into the full-up position, rather than the down position. This is because of the way the flight controls are balanced, and because the L-39's pitch control system is fitted with a bungee assist device. As the airspeed builds on takeoff roll, the elevators -- and therefore the control stick -- will move to the neutral position. Until then, the stick will remain firmly against your lap unless you hold it elsewhere.
You climb up to the cockpit using a series of built-in steps, including a heavy-duty fold-out step at the bottom and another integral step above it. From the top step, it's a matter of throwing your right leg over the canopy rail, standing on the seat, then stepping down onto the floor and sitting down.
Depending on the particular set-up in the airplane you're flying, you either strap in to the L-39 using a conventional parachute harness and lap-belt/shoulder-harness configuration, or the original, slightly funky Russian system, which involves things like leg straps, pilot weight settings, oxygen mixture regulators and the like, plus a huge all-in-one comm/G-suit/oxygen connector near your left thigh. Most operators have converted to the Western system for ease of maintenance, and the vast majority of U.S. aircraft have had their ejection seats pinned and deactivated. This dictates a forced landing or a manual bailout in the event of a serious problem. There is very little apparent squeamishness in the L-39 community about a forced landing -- no maintenance-related engine failures have been recorded in civilian use, and the airplane is completely capable of a "flameout" touchdown at around 95 knots, slow enough to greatly minimize the possibility of such an event turning out badly. More and more L-39 owners are opting for live ejection seats, but this option is still a relative rarity.
Once you've gotten strapped in, you put on your helmet and plug in your comm cord. Oxygen is not needed for flights below approximately 20,000 feet, since the cabin is at or below 12,500 feet at those altitudes. Your feet slide onto the rudder pedals, which are fitted with retaining stirrups designed to keep your feet in place during extended negative-G maneuvering. We don't plan to be doing much of that today. You attention turns to the checklist.
Like many Soviet-bloc jets -- even the modern ones -- the L-39's main electrical switch panels are composed of grids of toggle switches, separated by metal guard-rods. There are a lot of switches -- a 5 x 3 pattern of them on the main panel, and an 8 x 3 grid of switch-breakers on the sidewall-mounted secondary panel, to be exact -- and they all look the same, so it's important to identify and verify exactly what you are turning on or off. Most L-39 owners have retained the original positioning of most of the switches, a most helpful practice for those of us who fly numerous individual airplanes.
After turning on the battery, powering up the intercom and avionics, setting up the com/nav radios and GPS, obtaining a clearance and transponder code, and testing the fire detection system and caution light panel, the canopies are closed before starting the engine. The L-39's canopies, hinged on the right side, are completely manually operated, and they are a bit heavy. It's important to lower them carefully and gently. Your triceps (and some other muscles you didn't even know you had) will get a nice workout. Opening the canopy is even more critical. If you just push it open and let it slam against the stop, one day you'll have the thrill of seeing it fall off the airplane and crash onto the ground.
Time to make some noise. Under normal circumstances, the L-39 is completely self-sufficient for start. Starting air is provided by a built-in auxiliary power unit called a Saphir, which is one of the neatest, most reliable little devices you'll ever see. Nestled under the engine, this nifty little unit contains a turbine engine, starter, computer modules for automated RPM and EGT control, automated bleed valves, and various solenoids -- all of which are designed to work together to provide automatic pneumatic power for starting the engine. The system works great, and operation is a snap. You start the Saphir merely by pushing a button. It starts with a pleasant whine, and about 20 seconds later it has reached idle speed. A light on the panel indicates it's ready.
Starting the engine is equally straightforward. You momentarily push the engine start button and move the throttle into the start position, then you simply sit there and monitor the start parameters while the engine winds up. The RPMs for the High Pressure Compressor and Low Pressure Compressor are shown by two different needles on the same gauge, so it's easy to monitor how things are going. Once the engine has whistled up to a stable idle condition, the Sapphire's job is complete, and it shuts off automatically.
Taxiing is one of the more quirky aspects of operating the L-39. It's definitely a skill which can only be learned by doing -- no amount of mental preparation or studying can fully prepare you for it. After some practice it's not a big deal. Like the vintage MiG fighters and the Yak-52 and Nanchang CJ-6 trainers, the L-39 utilizes a stick-mounted wheel brake lever. There is no nosewheel steering -- the front wheel assembly castors freely. A selector valve sends hydraulic pressure to the left and right main wheel brakes in proportion to the rudder pedal deflection, and in proportion to how hard you squeeze on the handle. This means that if you need to make a left turn, no matter how small or large, you push the left pedal ALL the way down, then modulate the turn by squeezing either lightly (for a gentle turn) or more forcefully (to crank the nose around in a tight spot.) To stop a turn (again, no matter how small or large), you'll need full opposite pedal and some more carefully-modulated squeezing of the brake lever. You can actually do a 180-degree turn in the width of a narrow taxiway like this, but it takes a bit of momentum to do it. Careful speed management and anticipation are the keys to avoiding looking like a rank amateur, or worse, when maneuvering an L-39 on the ground. You can always spot a pilot who's trying it for the first time: They're the one who has decided to steer it like a "normal" airplane by holding down the brake lever a bit and simply steer using the pedals. This invariably results not only in prematurely-worn brakes, but a Pilot-Induced Oscillation and a lot of cussing.
Before the first takeoff of the day, the flight manual calls for a full-power engine run-up to check the throttle response, spool-up/spool-down time, fuel pressure and maximum power output. The maximum RPM is noted, so it can be monitored on takeoff. This number changes based on the ambient temperature and pressure altitude, and is usually nearly 107% RPM on a standard day.
The takeoff roll is very conventional for a jet -- slow at first, and more exciting as it goes faster. The rudder does not begin to take much effect until about 40 knots, so it's important to start the takeoff with the nosewheel straight. (Remember that any low-speed steering involves using the brakes, which lengthens the takeoff roll.) The average takeoff roll on a standard day at sea level is about 1700 feet, and an L-39 can usually safely operate out of a 5,000-foot strip at most lower elevations.
At 95 knots, you begin easing the stick back, and takeoff occurs at about 115-120 KIAS. You retract the gear immediately, and wait a few seconds until 140 KIAS to retract the flaps. There is a slight pitch down and settling sensation as the flaps retract, but this is easily countered with a slight back-stick pressure. Since the optimum climb speed is around 216 KIAS, it's a good idea to stay in a very shallow climb until reaching that speed, unless obstacles are a factor, of course. Once 216 is reached, the sea level climb rate is between 3000 and 4,000 feet per minute. At climb power settings and low altitude, the IA-25 turbofan burns about 330 gallons per hour (GPH), but this rapidly decreases to about 155 GPH in cruise at Flight Level 180.
Whats it like to fly the L-39? Its delightful. The flight control system is all-mechanical, with rod-actuated control surfaces, and the control feel is smooth and instantly responsive. Elevator forces are moderate during most inflight maneuvering, but close to heavy during takeoff and landing. Cockpit visibility is excellent in all directions. Aerobatics are easy and rewarding, and the L-39 is capable of all the basic positive-G jet maneuvers: aileron rolls, barrel rolls, loops, Cuban-8s, Immelmanns, cloverleafs, etc. Entry speed for most over-the-top maneuvers is 320-330 KIAS, and a 4-G loop takes approximately 4,000 feet of vertical space. Negative-Gs, for those so inclined, are limited to 10 seconds due to oil system limitations.
In the positive-G realm, the bungee-boosted elevator begins to apply its compensation at about 2 Gs (actually, 18 degrees of stick deflection), and its effect becomes very noticeable by the time you reach approximately 4 Gs. It feels like someone is helping you pull on the stick. Thus, the "stick force per G" curve is non-linear, which takes a few minutes to get used to.
Stalls are conventional for a jet aircraft of this type, with a stall break that is not sharply defined, and does not result in the nose dropping. Instead, the stall is preceded by an easily identified low-frequency rumble that feels about the same regardless of landing gear or flap position. Wings-level stall speed ranges from 88 to 103 KIAS, depending on flap setting. The slow spool-up time of the engine (nominally 9-12 seconds from idle to full power) means that the stall recovery must be a finesse exercise. Rushing the process will almost always result in a secondary stall and a further loss of altitude. This is a very important concept to grasp, especially in the traffic pattern, and its why L-39 pilots-in-training should spend a lot of time doing stalls and exploring the lower edge of the speed envelope. The aircraft is almost impossible to spin.
For pilots who want to have some serious fun in their L-39s, formation flying offers a chance to really enjoy the handling characteristics of the airplane. Since there are a lot of these airplanes out there, the chances of finding a formation partner based nearby are pretty high. As with all other aspects of high-performance flying, a thorough knowledge of the airplane and its limitations is imperative in order to fly formation well (and safely) in the L-39. The slow engine response time dictates a higher level of pilot anticipation and experience than in some other jets, but this is certainly well within the capabilities of a disciplined jet warbird pilot of average skill level.
Landings are usually set up from a 360-degree overhead traffic pattern. Initial is usually flown at 200-250 KIAS. In the pitchout to downwind, you pull the throttle back to 80-85% RPM and extend the speed brakes with the throttle-mounted button under your left thumb. Once below 180 KIAS on downwind, you extend the landing gear and retract the speed brakes if desired. Slowing further, the flaps can be extended to either the "Takeoff" or "Full" position when below 160 KIAS. The final turn is flown at 140 KIAS, slowing to 120 KIAS when on final. The final turn and final approach require strict attention to airspeed and power control. An undetected sink rate, steep glide path, or improper touchdown aim point, coupled with a too-low power setting, can get you in trouble because of that old bugaboo, engine spool-up time. Extending the speed brakes for the approach helps keep the RPMs up, and the spool-up times slightly shorter.
At about 15 feet AGL over the threshold, you smoothly pull the power off and flare gently, working for a smooth touchdown with no sideways drift. Once on the ground, you have a choice of stopping techniques. On shorter runways you should lower the nosewheel and carefully use the wheel brakes to minimize the rollout distance. On longer runways, you can aerobrake by holding the nose up until it falls by itself at about 80 knots.
The L-39 is a docile, fun, jet warbird. It requires very little additional support equipment or ground crew, can be operated from relatively short runways, is very mechanically reliable and robust, and can be operated for about the same overall per-hour cost as many piston-powered warbirds. Flying one is as close to being a fighter pilot as many people will ever get -- and you dont have to sign up for ten years of military service. Is this a great time to be alive, or what?
-- Buck Wyndham
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