Introduction
The screaming sound of an EDF along with a jet scale shape in the sky makes every RC addict turn his head and imagine himself in the cockpit performing maneuvers alongside Maverick in Top Gun
The Aero L-39 Albatros is a high-performance jet trainer aircraft developed in Czechoslovakia. It was the first of the second-generation jet trainers, and the first turbofan-powered trainer produced, and was later updated as the L-59 Super Albatros and as the L-139 (prototype L-39 with engine Garrett TFE731). The design is still produced in an evolved state as the L-159 ALCA, while more than 2,800 L-39s still serve with over 30 air forces around the world. The Albatros – the most widely used jet trainer in the world – is versatile, seeing duty in light-attack missions as well as in basic and advanced pilot training
Kit Contents
The packaging was very good as expected from HobbyKing
In The Box
Fuselage
Wing and tail surfaces
EDF 64 mm – installed
Motor (3900kv Brushless Outrunner) – installed
30A ESC
4 9gr/ servos, installed
Pre cut canopy
Factory hinged ailerons
(Hardware (Push rods, horns, clevis, tires and nose wheel assembly
Decals and markings already installed
Y-connector for ailerons
Epoxy glue
Allen key
Picture assembly guide and text instructions
Required for Completion
Battery 1300mah 11.1V 3S 25C
4CH receiver
Servo extension for the ailerons
Included for Review
Optima 6 receiver
Aurora 9
3S 1300 mAh 20C and 3S 2200mAh 25C lipo
Assembly
The Hobbyking L-39 will require some assembly work to have it complete. This ARF was ready with about 3 hours of work
Done by the factory
Ailerons hinged and glued
Motor installed
All servos installed
Paint and markings
The builder needs to
Glue the tail and elevator stabilizers
Install the wings to the fuselage
Install radio system
Install the nose of the plane
Fuselage
You need to glue the elevator and vertical stabilizer to the fuselage which match perfectly
The vertical stabilizer does not have functioning rudder
To ensure that the clevis will not open I have used simple shrinks
Power system
The fan and motor were installed at the factory but the ESC was not connected to the motor and to my good surprise there is a hatch to the motor (locked with 2 screws) in case you would replace the motor in the future
Landing gear
The main gear has this nice “clips” to simply lock them in
The nose gear was assembled using the supplied key. It is steerable for better ground handling
Wing
The wings have molded pockets that fit the installed 9gr servos perfectly. This allows for short linkages that go directly from the exposed servos to the aileron control surface horns. Each aileron uses a separate servo
You need to glue the “fuel tanks” to the main wing
When testing the aileron servos I realized that one of the servos was defective and will not operate as it should. I then decided to replace both servos (to have the same speed and torque) to the HXT900
Amp draws
When tested this 3900kv motor on ground it draws around 23-24 Ampere and provides ~240w, though in the air it seems to draw more current as the batteries dried out rather quickly
Battery
I fly the L-39 with this base recommended power system (3S 1300mAh) and with 3S 2200 mAh, and it provides nice sport power. It is not the fastest EDF in the sky but it flies well on the stock system. Next I will try a higher C rate than 25C to check of any difference to the watts number
Flying
With the 3s battery pack placed in the tray the model was significantly nose heavy. Make sure that you check your CG (75mm from the leading edge where it connect with the fuse). I placed the pack in the nose area the most backward position I could, to achieve the recommended CG
I used my trusted Aurora 9 transmitter for this plane. Rates were set as to maximum with the horns for high rates. I found the high rates on elevator and ailerons to be much too high so setup 80% dual rates. I used 50% expo for all the primary flight controls. I should note while I liked these rates control surface throws are a very personal preference
I set the flight timer to count down from 4 minutes of mixed flying and used the telemetry which warned me even before (after less than 4 minutes with the 1300mAh I got ~3.7v per cell)
The quite large L-39 Albatros is very attractive and an impressive model both on the ground and in the air
Takeoff and Landing
The L-39 with the stock power system required about 30 meters of ground roll out on a hard surface to reach flying speed. It was very manageable and stable in pitch and roll authority on take-off
Landings were also very easy as this model with the quite large fuselage slows down very well. With most EDFs you will need to keep some power on but this one glides pretty well when shutting down the motor, and then it touches the ground very nice and soft
Special Flight Characteristics
The L-39 is actually quite simple to fly. It is not overly responsive in pitch, thus loops are not so easy require full power (you can see in the video that I almost stall when I reached the end of the loop). The model stalls very predictably for a light model with this size fuselage. When pushed to a stall (common phenomenon on turns if not flying hard on the throttle) the model slows down considerably and then drops the nose. I noted very little wing tip drop if at all but when turning on slow speeds it needs to be under control
Rolls are picture perfect with the high rate aileron throws
Video
http://www.youtube.com/watch?v=Z-zIJ3m1i9s
http://www.youtube.com/watch?v=neMbispStCA
Recommended power system
The stock power system provides nice sport power but do not expect a rocket ship. I would go for 4S to achieve high speeds and vertical climbs
?Is this plane for a beginner
Although not terribly difficult to fly EDF models are not where beginners need to start. This L-39 was very well mannered and will not cause any surprises to a pilot with just a bit of experience, however the long run for take offs, “nearly stalls” on turns and coming quite hot for landings is something you need to know. This is not a trainer obviously
Conclusion
This HobbyKing L-39 seems to be great flying EPS foam model and has no bad habits noted. EDF pilots will love its looks and behavior
Assembly of this ARF was straightforward and could be less than 2 hours if the aileron servo was not defective and required extra gentle work
CG was not achieved with the dedicated battery tray even when using the 1300mAh recommended lipo
It seems this motor is not the strongest while it draws high current and provides 3-4 minutes flying with 1300mAh battery and 4-5 minutes with 2200mAh
For those who want a power up, note the 4s power systems that will make this model a stunning performer and real attention getter
Pluses
Excellent looks
Flight stable performance
Lightweight
Minuses
No functional rudder
Motor could be more powerful to my taste
Considerably low flight times with recommended battery
