AERO VODOCHODY L159 - CONTINUED

Advanced Cockpit Configuration

AeroVodochody
AeroVodochody
L159 cockpitThe area of the aircraft that has had the most design time spent on it is the cockpit. The result has been an excellent pilot environment that is simple and user-friendly. The centre of the coaming has a Flight Vision's FV-3000 HUD fitted, that combines with the two colour multifunction HDDs to present tactical, navigation and weapons system information. The whole cockpit works on the Hands-On-Throttle-And-Stick (HOTAS) concept, allowing the majority of major 'fighting' functions to be controlled from the throttle and stick. The cockpit displays and lighting are night vision goggles compatible. The multi-mission requirements have necessitated the fitting of a good airborne radar. The one selected for the aircraft was the FIAR Grifo L Multi-mode pulse Doppler radar. This is capable of 8 air-to-air search or track-while-scan modes, 4 air combat modes, 10 air-to-surface and navigation modes. The aircraft is fitted with a stores management system and modern communication and navigation equipment, including a Honeywell state of the art inertial navigation system, with embedded GPS. To further aid autonomy the aircraft produces its own oxygen through an onboard generator.

The aircraft monitoring system can be used to aid in mission debriefing as well as a dual video system fitted in the cockpit. This can be used to record the HUD and one HDD as well as all voice communications. With these systems it is possible to rerun the flight on a PC workstation.

 

BUT WHAT IS THE AIRCRAFT REALLY LIKE?  (back to top)

The aircraft that I flight tested was a prototype two-seat L159 B and as such was not totally representative of the production aircraft. For example, the colour multifunction HDDs were not there, nor was the radar. This limited my assessment to the aircraft handling qualities and a static review of a production standard single-seater. However, I was given an excellent briefing by one of the Company's test pilots (Ladislav Snýdr) while sitting in the single seater with power on. The first thing that struck me was how at home I was and how familiar it all felt. Displays and procedures were similar to any Western modern fighter aircraft I had been in. The cockpit was laid out in a logical ergonomic fashion. The multifunction displays were easy to use and see, with a set of standby instruments between the two screens. Flap selection followed the family history by incorporating push-buttons for the three settings (up, take-off and fully down). The leg restraint system for the ejection seat was still of Eastern design, which I prefer and find much simpler. Instead of putting on leg garters, that are then connected to the seat, the 'garter' is fitted to the aircraft, running around each of the foot openings for the rudder pedals. With this system as long as your feet are on the rudder pedals when you eject the garter will be ripped off the foot-well wall, thereby grabbing your leg in the same way as a standard Western leg restraint - very simple and clever. Another great feature for strapping in was that once all the straps were connected and adjusted, there was a lever on the right-hand side of the seat that could be used as a ratchet to tighten the lap straps still further. This ensures that these straps are tight preventing any body movement off the seat base during combat manœuvring or emergency ejection. The central stick had a strange design in that it pivoted half way down for the roll control function of the stick. I thought that this might be rather clumsy in the air but to my astonishment, once airborne, it was not noticed at all; indeed, the controls were very well harmonized in the roll and pitch axes.

 

Flight Preparation  (back to top)

After the briefings on the emergency escape systems there was very little other preparation required; flying kit was made simple with the use of standard American-style helmets. Ladislav gave me all the 'numbers' required to fly the aircraft and a rundown of general flying techniques. From this information I produced my usual knee-pad brief, to give me a helping hand when airborne. Even the process for flying from Farnborough was easy this year!

Once at the aircraft I followed Ladislav on a walk-round of the aircraft. There was nothing unusual, just the standard check of tyres, brakes, control surfaces freedom of movement, jet pipe, and so on. Once in the cockpit, strapping in was conventional (apart from the lap straps ratchet) and the seat was very comfortable. Pre-start checks were extremely simple and few in number. Indeed, it was possible to jump in the aircraft and be ready to taxy within minutes.

 

Simplicity Itself  (back to top)

The engine starting was incredibly simple, so simple in fact that I would want to be able to lock the canopy to be sure nobody could steal the jet when I was not looking! Once power was selected only two actions were needed to start the engine:  firstly, the APU was started by pressing a small red button on the left-hand side of the cockpit. This lit a green light on the Master Warning Panel (MWP) to tell you that the APU was going through its start cycle. After 23 seconds the neighbouring green light illuminated to say that the APU was up and running. The second action was to move the throttle to idle - that's all. At this point the FADEC took over and started the engine fully automatically; this took a further 25 seconds. After-start checks were equally brief, waiting mainly for the inertial navigation system to align (2-3 minutes), before being able to taxy.

Taxying was slightly unusual at first, because of a two-stage nose wheel steering (NWS) system. When the rudder pedals were deflected up to six degrees of NWS was available; however, if a button on the stick was pushed and held you could get the full 60 degrees of NWS capability, allowing tight turns to be performed. This took a little getting used to but by the time we were at the threshold, it was second nature. It is worth noting that the L159 is the first of the family to have a NWS system, the others had differential braking using a brake lever on the stick and different amounts of brake pressure applied to the wheels depending on how much the rudder bar was deflected (similar to the Spitfire!).

On the threshold, it was time to have a final check around the cockpit to make sure all was in order and that the 'take-off' flap light was on. I also re-briefed myself on the speeds for the take-off. The speed to start the rotation off the runway was very low at 70 knots, but I double checked it with Ladislav, who replied "it can take-off on very short runways"! I applied full power against the brakes to check the engine instruments and to get maximum acceleration down the runway. When the brakes were released the acceleration was good and 70 knots was reached very quickly. I lifted the nose wheel off with a reasonably heavy pull, before checking forward to prevent the aircraft lifting off too early. At about 110 knots the aircraft 'flew' itself off the ground. The take-off roll was approximately 2000 feet, using normal take-off techniques. Once airborne, with the gear and flaps up, the first thing that hit me was how quiet the cockpit was and how smooth the ride quality was - both excellent. There was no tendency to over-control and the stick forces were well balanced and reasonably light.

 

MULTI-ROLE ASSESSMENT  (back to top)

The first part of the sortie was clearing the Farnborough area, which gave me time to have a 'feel' of the aircraft and become comfortable in it before putting it through its paces. The first check was to see what its stability was like (typical test pilot - can't just have fun, had to get some numbers!). I put in some small inputs in the pitch and the roll axes to see how it behaved when the stick was released. In both of these axes any tendency to oscillate died down very quickly, which is a good trait for a multi-role aircraft: the last thing you want to be doing is fighting the aircraft's unwanted motions instead of your opponent. By the time I had played with the test pilot stuff, we had reached a suitable area for the main evaluation. The first on my list was to time a climb from 5,000 feet to 10,000 - this took 44 seconds at full power and 300 knots, or to put it another way a respectable climb rate of nearly 7000 feet per minute.

Next on the list was to look at the stalling and spinning qualities to ensure that they were sufficiently benign to allow the pilot to fly to the edges of the flight envelope without too much fear. The stalling was very docile, both in the clean configuration and the flaps and gear down configuration. For both stalls there was an initial light buffet with a gentle nose drop at 125 knots clean and 105 knots dirty. For the spinning I decided that more height was required even though Ladislav had assured my that it would be all right (some yellow streaks are worth having!). The spin entry was slightly unusual in that instead of applying full rudder and almost immediately full back stick, the technique was to apply the full rudder then wait until this had caused approximately 35 degrees of roll, then to apply full back stick. Ladislav explained that this technique was needed to get the aircraft into the spin - a good sign indicating that unintentional spinning might be difficult. Once in the spin the gyrations were unusual for a straight-wing aircraft and more characteristic of a swept-wing design. The spin was not stable at all with the nose pointing down between 45 and 60 degrees, with bucking gyrations rather than a smooth-turning spin. However, the gyrating motions were not so fast that they became disorienting. Recovery was almost instant when the controls were centralized. There was no need to use the usual full spin recovery technique (full opposite rudder followed by forward stick until the spin stops).

The stalling and spinning gave me a good level of confidence in the aircraft. The general handling was also very good; high-g manœuvring was excellent with the aircraft 'talking' to you with varying levels of buffet as the levels of aggression increased. The aircraft is stressed to plus 8 g and minus 4 g. Airframe buffet allowed you to manœuvre on the limits without having to look into the cockpit. An important quality for a fighting aircraft that is not protected by computers. Similarly, the engine behaved itself at all times, including idle to full power slams during the stalling and the high-g, high-buffet turning - a credit to the FADEC system. When turning at speeds between 250 and 350 knots very tight turns could be generated and at the lower speeds you felt as if you could turn around the wing-tip. If fitted with a heat seeking sidewinder missile this would be a potent capability. The quality is also very useful when fighting helicopters where speed is not as important as a small radius, turning capability. Add to this that the aircraft can be fitted with one, two or three 20 mm gun pods and you have a potent helicopter killer.

An important parameter during any combat manœuvring is the ability to recover lost speed quickly. The L159 has more thrust than any other member of the family and so I was interested to see how it performed during a level acceleration. With the aircraft set up at 140 knots at 5000 feet, it accelerated level to 400 knots in a respectable time of just under 60 seconds. If allowed to use the height as well, speed could be added very quickly, giving more energy for the combat engagement. The top speed of the aircraft was 505 knots (936 kph) or 0.82 Mach. If these speeds were approached the aircraft protected the pilot from over-speeding by deploying the speedbrake automatically just as the limit speed was reached. This could come as quite a shock during combat and might come just at the wrong time; whilst it may be a good safety feature I am not sure I was totally convinced of the need for it.

The fuel consumption in the cruise varied from about 1800 pounds per hour, at low level and 300 knots, to 4000 pounds per hour at full power. I did not have a chance to look at the high level cruise but Ladislav said that maximum range was around 800 nautical miles (1,500 km) with internal fuel (3,519 pounds/1,596 kgs) and around 1,350 nautical miles (2,500 km) with four external drop tanks (6,554 pound/2,973 kg).

 

Time To Return  (back to top)

After about 50 minutes' of general handling is was time to go back to the circuit as I still wanted to perform a touch-and-go, as well as the full-stop landing. Back in the pattern the aircraft was very easy to fly, with 'downwind' started at approximately 200 knots, slowing to 160-170 knots as the first stage of flap and the gear were lowered. Engine handling was very easy throughout. Full flap was selected as I tipped into finals. Minimum speed now was 150 knots, with the power set at about 85 per cent. The aim then was to cross the 'hedge' at 130 knots to touchdown at about 120 knots (very similar to the BAe Hawk speeds). For the touch-and-go I held the nosewheel off the ground, pressed the take-off flap button and applied full power - very simple and easy to perform. Coming round finals for the full stop, Ladislav said that I should try out the short stop landing capability by applying full brakes as soon as the nosewheel was on the ground. This is the type of procedure that worries me as I always expect the automatics to fail where brakes are concerned. However, I thought, he is the company test pilot and he should know best! Just after putting the nosewheel down I applied full brake pressure to the wheels and was amazed by the severity of the braking and the incredibly short stopping distance - an excellent demonstration of the aircraft's short-field capabilities. After the landing the taxy back was relatively sedate!

 

A CAPABLE LIGHT ATTACK AIRCRAFT  (back to top)

This evaluation flight has demonstrated that Aero Vodochody has produced a serious contender for the Light Attack Combat Aircraft market. The aircraft was a good all round handling aircraft with very few vices seen but plenty of feedback when flying at its limits. The cockpit and operations were extremely simple and ergonomically sound. As a lead-in trainer for more sophisticated Western hardware, the aircraft was ideally suited, with its Western avionics and displays presentation. The weapons capability of the aircraft could not be assessed but, hopefully, this will be the subject of the next assessment of the aircraft!

 

Soon To Enter Service  (back to top)

The first five aircraft finished factory testing earlier this year and they are just about to finish their military testing phase (the equivalent of our Boscombe Down testing). Then these five aircraft and 16 others should be delivered, by the end of the year, to the first squadron at the Cáslav Air Force Base, 70 kilometres east of Prague. The Base presently operates MiG 21s and L39s. The Czech Air Force has ordered a total of 72 aircraft and it is anticipated that the remainder will be delivered by 2002. Originally, all 72 aircraft were to be single-seaters but it is now expected that the last 10 to 12 aircraft will be two-seat variants.

 

I would like to thank the whole Aero Team, especially Ladislav Snýdr and Jan Halub, for making the flight possible and for their excellent company.

 

BASIC DATA (L159 A)  (back to top)

Max speed  936 km/h  505 kt

Max rate of climb at sea level  62.1 m/s  12,210 ft/min

Service ceiling  13,200 m  43,300 ft

Take-off run  470 m  1540 ft

Empty weight  4,320 kg  9,525 lb

Max ramp weight  8,000 kg  17,640 lb

Max external stores  2,340 kg  5,160 lb

Wing span  9.54 m  31 ft 3 in

Length  12.72 m  41 ft 8 in

Height  4.77 m  15 ft 12 in

Max engine thrust  28.2 kN  6,330 lb

Structural load limit  +8g to -4g

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