Geoff Roberts air tests Aero’s latest Albatros variant, the L 139.
MY FIRST HIDDEN reactions to an invitation to fly in the Aero L 39 Albatros could never be described as being fired with wild enthusiasm. After all, since 1974, over 2,800 of them have been produced and operated in 16 countries throughout Europe, Asia, Africa, and Latin America — hardly a new aircraft. Secondly, I admit to being influenced by badly informed sources regarding what I could expect at Famborough ’94. «L 39? An airborne Skoda isn’t it?» «Built by Emmett, I think.» How wrong they and I were.
Looking around the static park on Sunday prior to Famborough week, I stopped and admired the Aero L 139, not the L 39 which I had been expecting. Things were looking up. Sure enough, when I was introduced to Dobroslav Rak the Aero Chief Designer, he confirmed that I would be flying in the L 139 with test pilot Lodislav Snydr. I hod previously taken the trouble to have some facts and figures regarding the L 39 and it therefore became apparent that what little information I had digested was going to be about as useful as mammaries on a frog.
My Service instincts now surfaced and I rapidly ‘acquired’ a quantity of technical data on the aircraft with the express intention of reading the same that evening after a pint of cider. It never ceases to amaze me just how much the brain can absorb from reading at the breakfast table.
The L 139, a modernised derivative of the tandem-seat L 39, is being developed to meet the requirements of new generation jet trainers. It is being produced by Aero Vodochody in the Czech Republic. Although it will be used mainly for basic and advanced training it is also capable of fulfilling the ground attack role when fitted with hard points and under-fuselage gun pod.
The aircraft is powered by a Garrett TFE731 -4-IT engine. This is a two-spool medium bypass lurbofan engine with a modular design. The two main shafts are concentric with the low-pressure (LP) shaft passing through the high-pressure (HP) shaft. A single-stage axial fan is driven by the LP spool througn a reduction gearbox. The LP spool also includes a four-stage axial compressor driven by a three-stage axial turbine. The HP spool consists of a single-stage centrifugal compressor and a single-axial turbine engine and aircraft accessories are driven by the HP spool through a transfer and accessory gearbox. Engine functions are controlled and monitored by a digital electronic control system. Basic weight of the engine is 8221b (373kg).
Fuel is contained in five rubber fuselage tanks (290.6 gal/1,100 lit) and two wingtip tanks, each holding 26.4 gal/100 lit. Four under-wing drop tanks may be carried each of which can contain either 39.6 or 92.5 gals (150 or 350 lit). Fuel from the wing tanks is transferred to the fuselage tanks by air pressure bled from the engine. Fuselage fuel is fed to the engine by means of an electric pump. A negative g-trap ensures 20 seconds of inverted flight.
The hydraulic system, operating at 2,175psi, provides power to operate the undercarriage, flaps, air brakes and wheel brakes. An emergency system provides the hydraulic pressure to lower the landing gear and flaps and also to operate the wheel brakes.
A pneumatic system provides air to the hoses which form the canopy seals. This operates at 26psi.
Air for the Air Conditioning System is taken from the engine high pressure compressor. This is cooled and dried before entering the cockpits. The system may be controlled from either cockpit and the temperature adjusted between 10C and 25:C.
The primary flight controls (ailerons, elevator and rudder) are moved by a system of rods and levers while the secondary flight controls (trim tabs) are controlled electro-mechanically. Longitudinal trim position is shown on an indicator in the cockpit. A green light indicator illuminates to show when the lateral trim is in the neutral position.
A de-icing system, which takes air from the HP compressor, provides hot air to the leading edge of the engine air intakes and to the windshield.
DC electrical power is supplied from a 28V 12kW Lucas starter-generator or from a 28V 6kW Lucas auxiliary generator in the event of a main generator failure. A 24V 43Ah battery is an emergency source.
The aircraft is equipped with an On Board Oxygen Generating System (OBOGS). The quality of oxygen is automatically monitored and air for this system is taken from the anti-g air output of the HP compressor. OBOGS is also used on F-14, F-15, F-16, AV-8 and T-45 aircraft.
Two Czech built VS-2A ejection seats are installed, and command ejection, which ensures sequencing of ejections, is an option. Seats are rocket powered and will safely operate at 0 height and 0 airspeed.
As already mentioned the aeroplane could carry an under-fuselage gun pod. This is the GSh-23 twin-barrel gun. Ammunition is contained within a fuselage box and up to 150 rounds may be carried. Four wing-mounted pylons may also be fitted. These are capable of carrying a combination of bombs, rocket-pods or fuel. The load capacity of each outboard pylon is 5501b (250kg) and 1,1001b (500kg) may be carried by each inboard pylon.
Avionics include VHF/UHF radio, Global Positioning System, VOR, DME, ILS, Head-Up Display (HUD) in front cockpit, video camera and voice recorder and a Multi Function Display (MFD) in the rear cockpit on which can be displayed the HUD information. HUD symbology is similar to that on the F-16 and F-18.
Through the Central Mission Computer (CMC) weapons aiming solutions can be projected onto the HUD for air/air and air/ground gun attacks and for dive, level and toss bombing.
During the morning of September 5, Aero personnel, who were manning a stand in Hall 1, told me it looked very likely that my trip would be taking place the following evening and that I should present myself for briefing at about 4pm on the 6th. Great, I thought, I should be able to familiarise myself with the cockpit during the next 30 hours. Unfortunately, it is not that easy to obtain access to an aircraft which is participating in the flying display. As it transpired, any misgivings I might have had regarding not being afforded a cockpit preview were entirely unwarranted.
After arriving at the aircraft, although it certainly was not required of me, I had a good look at the airframe before climbing in. A very interesting design feature is apparent when inspecting the landing gear. The undercarriage doors are closed when the gear is down. This has obvious advantages when operating from grass or unprepared landing surfaces.
Loose articles could, obviously, be thrown into the undercarriage bays with the subsequent possibility of damage to hydraulic pipes and other unprotected areas.
The rear cockpit of the L 139 was quite uncluttered and acclimatisation took very little time. I was most concerned regarding the ejection seat, and heaven forbid, how it would function should it become necessary. All this was carefully explained by one of the groundcrew when he supervised my strapping in. Let us just say it was a different procedure than any other that I have experienced. The business handle was, as is normal on all later marks of ejection seat, between the legs. This one though, was a two-loop handle instead of the single which I have become used to in other aircraft.
Start-up, pre-taxiing drills, taxi out and ground operations were all performed by Lodislav since we were pushed to make our slot time for take-off. Once at the marshalling point I was given control of the aircraft and lined up on the runway when cleared by ATC.
«Lima One Three Nine you are clear to take-off» I released the brakes and opened up to full power. Any crosswind was negligible so I did not nave to work too hard to maintain the centreline and we were airborne at about lOOkts (185km/h) some l,650-2,000ft (500-600m) from brakes release. At this stage of the flight I was not conscious of any real restriction to the view forward since peripheral vision is good enough on the runway. When airborne and cleaned up we climbed to the west and entered cloud at about 1,500ft (457m) agl. Cloud was layered, with very few gaps, up to 10,000ft (3,050m) and even above 10 there was quite a build-up of cumulus-type clouds all around. The rate of climb was just over 4,000ft/min (20.3m/sec) which is quite acceptable for a trainer. I wonder what it would have been when loaded with ordnance and/or external fuel tanks?
I was impressed with the stability during the climb and concluded that it must be a fairly easy aircraft on which to take an Instrument Rating Test — particularly when so well equipped with navigational aids. Unfortunately, I was not going to have much time to become familiar with these ond their various displays as it was going to be a ‘turning and pulling’ sortie when clear of the weather.
Surveillance radar was positioning us in an operating area not too for from Boscombe Down — I’ll have to take their word for that, since all contact with the ground had been lost shortly after take-off. When in a reasonably clear area I first tried some steep turns. At about 11,000ft (3,250m) it appeared that the aeroplane could maintain a 3g turn. Again it was very stable within the turn and maintaining height was not difficult, even entering at 5½g.
It was about now that I began to take an interest in the forward vision. The front canopy support arch restricts the view from the rear cockpit between 15c and 20: above the horizon directly in front and between 25c and 35° left and right on the horizon. Of course this does not matter too much during a turn when heading is continuously changing but when straight and level does necessitate a constant movement of the head to avoid the blind spots. It was always thus, which is one of the reasons why flying instructors have thick necks!
Stalling was next on the agenda to be followed by aerobatics. Best carry out some HASELL (Hazel) checks! The RAF is very strong on these aide memoires for checks — there is a rather rude one for the downwind checks in a Chipmunk. HASELL checks are corned out before manoeuvring. I don’t know the Czech equivalent, but no doubt they carry out something similar.
H — Height. Yes we have plenty of that.
A — Airframe. Configured as appropriate. For us the gear and flaps will be up and airbrakes retracted.
S — Security. No loose articles Lying around the cockpit. Map stowed — that is a iough — I never had one! Pockets done up. Strops tight.
E —Engine. Seems to be turning OK.
L — Lookout. Clear of other idiots all round — particularly below. Away from clouds.
L — Location. Somewhere over southern England. Radar will advise on restricted airspace.
The aeroplane is very slippery and it seemed to take forever to slow down in level flight to practise stalling. Because It really did lake some time to slow down, I felt it necessary to turn the aircraft and clear the airspace ahead and below. At about 95-100kts (176-185km/h) there was a slight buzzing — that’s the best way I can describe the approach to the stall. The vertical speed indicator was showing level with the stick bock and the nose dropped below the horizon at 88kts (163km/h). There was no wing drop and recovery was immediate on applying power and moving the control stick forward. Although I didn’t do so, it is quite possible to slam the throttle from idle to full power and the engine will respond within 0.4 second. Must be very nice in formation.
Aerobatics were restricted to loops, Cubans, barrel rolls, slow rolls and Derry turns. All were undemanding with looping manoeuvres entered at 300-330kts |555-610km/h) and rolls started at 250-270kts (460-500km/h). Hod the Moch number approached 0.8, which it never did, the airbrakes would have automatically extended to restrict the speed to Mach 0.8.
I would have liked to have had a look at the weapons symbology but there is a limit to what can be accomplished in a short duration flight and it was now time to return to Famborough. Radar vectors were given and a descent started prior to a hand-over to Famborough radar. We were informed by ATC that a radar approach was mandatory and that this was to be followed by a full-stop landing due to the prevailing weather conditions.
The radar pattern was flown at about 200kts (370km/h) and when the glide-path was intercepted full flap was selected. Flaps can be Up, Mid (25°) or fully Down (44°). In this configuration the final approach was flown at 130kts(240km/h). I opted for a descent rate of 700ft/min to maintain the 3½° slope but this was obviously over-generous since talk-down told me I was straying lower than the ideal. A slight power adjustment and we were then correcting bock towards the dide-path. We broke doud at about 3 miles (4.8km) and I then look an interest in the HUD repeater. It was necessary to adjust the brilliance, but once that had been done, the picture was very good — so good that I continued the approach using this source of information solely.
Unless one is really ham-fisted it is almost impossible to land heavily since the soft undercarriage and low main-wheel tyre pressure of 87lb PSI are very forgiving.
We didn’t carry out a max braking landing, but using the toe-operated anti-skid brakes to maximum effect, it should be possible to stop within 1,970ft (600m).
Clearly I cannot comment on the operational performance of the aeroplane, but if this matches the daims mode for handing, which I can vouch for, then Aero have a very worthy basic, advanced, and weapons trainer, which is a natural lead-in to the modern generation operational aircraft. Debriefing of any sorties can be conducted accurately within minutes of down-time by utilising the video facility for the HUD.
Thank you all at Aero, particularly Dobroslov Rakand, of course, test pilot Lodislav Snydr, for the superb flight and for patiently answering all my questions. I really enjoyed myself and look forward to meeting you again away from the hectic airshow environment.