RCU Review: Flyzone L-39

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    Contributed by: Laurent Caekebeke | Published: July 2015 | Views: 20418 | email icon Email this Article | PDFpdf icon
    L39 on RCU

    • the L39 is fast. This machine screeeaaams!
    • very good looking plane
    • snap-out tip tanks - save the wing tips when landing on tall grass

    • battery location could be made clearer
    • elevator servo attachment becomes lose with time.
    Flyzone's new release is bound to raising interest within the RC pilot community. The parkflier branch of Hobbico is coming out with a 1.5 pound EDF jet capable of 90+mph right out of the box. This is an incredible feature on its own, but Flyzone didn't stop there: they made it scale, and nicely so. The airplane is a scale model of the L-39 Albatross - In fact, Flyzone likes the look of their latest release so much that they even include a stand to go with it.

    The real L39 is an east European sub-sonic jet aircraft, and although it has been lightly armed, its main purpose is for training. It was introduced in the late 60s, and has been a commercial success. It is used both for military application and in the civil world. The Breitling precision jet team, among others, uses the L-39 for their performance in aerobatic maneuvers.

    The Flyzone L-39 comes in only one level of completion: Receiver Ready (Rx-R). That means that the only things to add are the receiver and the battery.

    Product Details

    manufacturer picture
    Manufacturer's description:
      The high-viz trim scheme is already applied. A power system, most onboard gear, and all hardware are ready to go, installed at the factory. And the only assembly that remains is easy and over with in about 15 minutes. Add a receiver and a charged 4S pack and your departure time is minutes after you get to the field. Give it a hand launch, and it settles down into smooth, easy-handling flight almost immediately. Blip the throttle and it's suddenly downfield and disappearing fast. Line up for a low pass, push the throttle to the firewall ? and feel the rush that you've been waiting for.
    Manufacturer: Flyzone
    Wingspan: 25 in (635 mm)
    Length: 31 in (780 mm)
    Wing Area:  141 in² (9.1dm²)
    Weight Range: 24-25 oz (680-710 g)
    Wing Loading:  24.5-25.5 oz/ft² (75-78 g/dm²)
    Battery 4S 2200mAh LiPo battery pack
    Requires:  4-channel radio
    Price: $180 (as of time of review)

    First Look

    Only one version of the L-39 exists: the receiver ready Rx-R. So only one box variant ? there is no mistake possible when picking up the L-39 at the local hobby shop.

    The plane comes with a stand so you can have it as a desk or shelf decoration when it is not screaming at the local airfield. It is made of painted extruded polystyrene (XPS). The jet?s name is cut on side, which add to the cool factor.

    Used for the review

    The L-39 only requires a 4-channel receiver, and the smaller size the better. However, the range cannot be compromised. The model is fast and might quickly be out of range if using an indoor/parkflier receiver. We selected the R6106HFC for its mid-range capability while keeping a compact size.
    We used the recommended battery: ElectriFly 4S 2200mAh 30C. The battery is 105mm x 34mm x 32mm (from measurement, not including the wires) and fits just right in the cockpit. The inside of the fuselage looks bigger than it really is: the canopy takes some space, and the battery has to be rightfully placed for the canopy to close properly.


    Flyzone did most of the work for us, and there is not much left to the user to do. All the servos, linkage, ESC, motor, fan and other accessories are already installed. The assembly consists in gluing all the main elements together. Let's put it this way: the overall building time is about equal to the time it takes for the epoxy to cure.

    A thin layer of epoxy is spread on the wing saddle and the mating surface of the wing. It is good practice to poke a few holes on both of this surface. The epoxy doesn't bound very well on Aerocell, but it is still mechanically strong. The epoxy will spread in the holes and cavities before setting. The stabilizer and the vertical fin are attached in the same manner to the fuselage.
    Make sure to align the stabilizer with the fuselage before the epoxy cures.  
    The L-39 takes shape in no time. We are really within the proper definition of an Almost Ready to Fly: the plane is nearly complete out of the box, but still needs some workshop time before heading to the field.

    A side note on the benefits of using tip tanks

    The tip tanks have very peculiar effects on airplanes, which can be somewhat conter-intuitive. What could be the benefit of adding this large tank to the tip of the wing rather than slightly enlarging the fuselage to have the extra-fuel imbedded in the most flow-efficient way?
    There are many benefits in adding the tanks to the wing tips:
    • they reduce the bending moment on the wings by deporting a fraction of the mass to the wing tips. The overall weight of the aircraft stays the same (or maybe slightly increased),  but it is better spread on the wing spar. 
    • Well designed, they reduce the overall drag by acting as a winglet and prevent the formation of the wing tip swirl. This is specially true at low speed when the induced drag increase is prevalent to the parasite drag. A plane design for high speed is better off without using tip tanks, as exemplified by "Pipsqueak", an L-39 modified for racing with no tip tank.
    • On some airframe, they can be retrofitted later. Many companies offer tip tank upgrade kits for commercial airplanes to increase their autonomy.
    Designing tip tanks is a balancing exercise between several parameters, among which drag plays an important role. They do have many pros, but not all planes will benefit from storing fuel at their wing tips. 
    Pipsqueak While the L39 was designed with tip tanks Pipsqueal, the L39 modified for racing, had her tip tanks replaced by winglet to optimize the airflow at high speed.


    Flight Report

    There is always some apprehension on a first flight of a hand-launched racer. If the low speed capability is not there, it will be a battle until the aircraft gain some velocity. If, on top of that, something is not setup properly, the flight might take a wrong turn.

    So, here we are at the airfield with the newly built L-39 ready for take-off. A helpful hand is requested for this first launch. The Flyzone video shows that is perfectly doable for the pilot to launch the plane himself, but for now, I'd rather have both hands on the remote, just in case. The helper grabs the L-39 by the fuselage, from the top. Full throttle is applied, and small rotation of the shoulder later, the plane is airborne. It goes straight and out, and that is reassuring. The next few passes are used for trimming the plane, and the jet needs more than a few clicks to fly level and straight, but once set, it goes right on trajectory.

    The photograph already requests low passes for the camera, so the L-39 is brought a series of lazy-8 a few meters above the runway to get shot from every angles.

    The first impression is positive: the L39 is well-behaved at low speed, landing should be a breeze. The jet tends to oscillate a bit on the roll axis, but nothing severe. Despite not having a rudder, it remains perfectly controllable and docile.

    Alright, enough pictures, times to release the Watts! At full throttle, the trajectories are ballistic, and the tiny jet is very quickly out of the comfortable line of sight. No blinking allowed!

    The plane literally screams at maximum speed. The motor-fan unit is working hard at transforming the flow of electrons into airspeed. Some may want to have a quieter power unit, but that would come at a cost of efficiency. As a general rule, a fan efficiency increases with rotational speed and diameter. Well, the diameter is fixed by the size of the plane, so the designer had to work on something, and that something now screams through the sky, for the pleasure of my ears, and (probably) the discomfort of all animals around the runway.

    When it came to land, the jet was brought above the grass for a nice gliding finale on the short grass. This little screamer is easier to land that most trail draggers.

    This first very good experience with the L-39 was followed by many others. As mentioned earlier, the plane can fly relatively slow, but it is really at full throttle that it thrives. The speed is exhilarating. The L-39 can do all aerobatic maneuver in the book. Well, as long as the rudder is not needed, that is. With the power on hand, the only limit to the diameter of a loop is the eyesight of the pilot. The roll rate is fast and it is better to fly on low rate for long and clean trajectories.

    Not everything was beautiful and pretty during the course of the review. The hand launch is real easy with a true and tuned model, but if something goes wrong, it goes really wrong. The plane was obviously designed for performance, not strength. The L-39 is unlikely to survive an unplanned encounter with planet Earth.  It is a good thing that Towerhobbies is selling every pieces of the airframe as spare parts!
    So if you are building your new L-39, be careful and double check a few things. Here are a few problems that we had to deal with:
    •     A servo linkage for one aileron came off in flight. The little black snap-ring on the back of the linkage connection was lost in flight. The L-39 responses became very sluggish, yet controllable. We could land with no damage.

    •     The elevator servo developed some play in its pocket after several flights. That caused the trim to be completely off on one of the take-off. The L-39 went straight down, and the pilot had just enough throw to redress and skim the underneath of the plane on the runway and fly off. The canopy popped, and the battery moved. The rest of the flight would be best described as frantic.


    With the L39, Flyzone aimed at satisfying the speed addicted among us and they hit the target just right. The jet is a terrific bullet to fly. It is very enjoyable to look at, both on a ground and in flight, which add even more to the overall pleasure. The plane comes with an efficient and powerful power plant and is correctly priced.

    The L39 is designed for high performance and it shows when the plane is airborne. Overall, the plane is well-engineered, and the only place that would beneficiate from some improvement is the front of the fuselage, where the battery could be better secured, and the stabilizer servo less exposed and more firmly attached.

    Don't be fooled by the foam airframe, the flyzone L39 is a performance aircraft, which will bring joy to its pilot when properly maintained.


    References and links


    Tip tanks:
    Tip Tank Flight Tests by David F.Rogers
    Methods of reducing induced drag on Pilotfriend.com

    Pipsqueak - the racer
    L-39 on wikipedia

    Comments on RCU Review: Flyzone L-39

    Posted by: Jennifer Curtis on 07/13/2015
    Any idea why it becomes ballistic at full throttle? It seems like this should have been address before the plane was released. Jenny
    Posted by: Turnale on 07/13/2015
    By ballistic, I meant that the plane is fast and follows clean and straight trajectories, not that we lose control of the plane - The L39 stays very responsive, even at full throttle.
    Posted by: electric fly on 07/14/2015
    Good thing its ballistic, or else i would not buy it!
    Posted by: electric fly on 07/14/2015
    What is the flight times with a 2200 pack?
    Posted by: Turnale on 07/15/2015
    flight time is about 4 to 5 minutes, maybe 6 minutes with good throttle management.
    Posted by: Turnale on 08/22/2015
    Some additional data - we tested the L-39 with the Hobbico Big 5 GPS Logger, and the results are: - speed passes measured from 90 to 96mph - altitude: approx.850 ft before it was really too small to be seen.
    Posted by: electric fly on 04/11/2016
    Excellent flying EDF!! One of the best!!
    Page: 1
    The comments, observations and conclusions made in this review are solely with respect to the particular item the editor reviewed and may not apply generally to similar products by the manufacturer. We cannot be responsible for any manufacturer defects in workmanship or other deficiencies in products like the one featured in the review.

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