|Wing Area:||141 sq. in.|
|Wing Loading:||17.9-18.9 oz/sq. ft.|
|Servos:||Futaba S3114 Micro HT Servos (3)|
|Receiver:||Futaba R156F FM 72MHz Micro Receiver|
|Battery:||Great Planes ElectriFly LiPo 11.1V 910mAh 20C Power|
|Motor:||Great Planes Ammo 20-40-3500 In-Runner Brushless Motor (Included with kit)|
|Fan:||Great Planes HyperFlow 370 EP Ducted Fan (Included with kit)|
|ESC:||Great Planes Silver Series 25A Brushless ESC 5V/2A BEC|
|Available From:||Great Planes distributors or your local hobby shop|
Great Planes has released a very nice looking sport scale EDF that includes the HyperFlow ducted fan unit and an Ammo in-runner brushless motor, all for under a hundred bucks. The plane is composed of a unique closed cell foam called Aerocell. It is not as brittle as more conventional forms of foam and can be glued with standard CA. This model comes out of the box pre-painted, but it is marketed as having a smooth, paintable surface, should you wish to alter the factory paint job. This low parts count kit comes from the factory with most of the work completed.
According to Wikipedia:
The Aero L-39 Albatros is a high-performance, jet trainer aircraft developed in Czechoslovakia to meet requirements for a "C-39" (C for CviãnØ - trainer) during the 1960s to replace the L-29 Delfín. It was the first of the second-generation jet trainers, and the very first turbofan-powered trainer produced, and was later updated as the L-59 Super Albatros and as the L-139. 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 is versatile, seeing duty in light attack missions as well as basic and advanced pilot training, and is the most widely used jet trainer in the world.
As I dug into the kit contents, I soon began to understand why this ARF may have been a little slow to arrive. It would appear the factory spent a little extra time on the kits, completing many of the steps normally handled by the customer. Control surface horns? Already mounted. Elevator push rod? Factory installed. It is not even necessary to hinge any of the control surfaces, nor to glue two wing halves together to make up the wing. All you must do is attach the wing and tail, insert your radio gear and power system, and fly it!
In the box:
Needed to complete:
Provided for this review:
For your convenience, ElectriFly makes a copy of the L-39 assembly manual available online HERE. Great Planes' assembly manuals are always very thorough, and this one is certainly no exception.
Make no mistake about it, this plane is one quick build. Almost all of the normal tasks have been completed for the builder by the factory. A few hours and a little epoxy, and you are ready to fly!
Electrifly Ammo 20-40-3500
|Number of cells:||Li-Po 2s-3s|
|Weight:||65g (2.3 0z.)|
|Motor Diameter:||20 mm|
|Shaft Diameter:||2.0 mm|
|Maximum Constant Current:||12 A|
|Maximum Surge Current:||25 A|
|Max Power(watts):||133 W|
The first order of business is to assemble the HyperFlow ducted fan and motor. An electronic copy of the assembly instructions can be found HERE.
The HyperFlow fan is designed to accept 370 sized brushed motors, as well as 20mm and 24mm brushless motors. The HyperFlow fan comes with three different fan rotor adapters, allowing it to mate up to several different motor shafts. The motor that comes with the L39 is the Ammo 20-40-3500, a 20mm diameter 3500Kv in-runner.
There is an adapter ring which must be mounted on this 20mm sized motor to center it in the HyperFlow fan housing. Use thread lock on all fasteners when assembling the EDF unit. At 35,000 RPM, you really do not want anything to work its way loose! This fan will also accept more powerful motors, and the performance you can expect from the larger 24mm brushless motors is well documented in the HyperFlow manual.
Once the fan is completely assembled, it gets glued into the fuselage and is accessible via a hatch that is tightly retained with magnets.
The one piece wing comes with a spar glued internally, and it is surprisingly rigid. The 3114 Futaba servos fit into the cutouts perfectly. A little hot glue, and they were locked into place. The aileron push rods are short and attach at the servo control horn with a z-bend. This technical note appends the procedure and tools for preparing the aileron servo arms for the push rods:
On page 6, step 1 of the manual, the drill bit size used to enlarge the outer holes of the aileron servo arms should be a #58 [1.06mm]. A 3/64" [1.2mm] drill bit could also be used but would result in a slightly loose fit of the aileron push rods in the servo arms.
The other end attaches to the aileron control horn by means of a quick link with an oversize thumb screw with a knurled perimeter.
Foam covers protect the servo control horns from impacting the ground on the belly landings that the L-39 will be undergoing. The wing gets glued to the fuselage with 30 minute epoxy, but only after the fan /motor assembly is mounted into it. This is because the three motor wires get passed into the forward part of the fuselage and become somewhat captive once the wing is attached.
Assembly of the tail involves little more than gluing the tail surfaces with epoxy after ensuring that you have them square and properly centered in relation to the fuselage and wing. The modular construction of the L-39 will assist you with the correct positioning of them, but use your eye and a tape measure to verify that they are perfect. Once the epoxy has cured, connect the preinstalled elevator push rod to the elevator control horn and move onto the next step.
All of the radio and power system gear is accessible through a pair of magnetically retained hatches. The canopy hatch covers a very roomy battery compartment, and the speed controller and receiver get mounted to the rear of this compartment. There is a foam box into which the elevator servo gets glued. You will need to bend a small offset into the elevator push rod to get it to cleanly connect to the elevator servo horn. This connection is made with an included quick link. I elected to not use servos extensions for the aileron servos, as they would just reach the receiver if I positioned it to the very rear of the canopy opening.
The L-39 is relatively small and this allows you to place it atop a table or desk with ease. It looks great sitting on top of my computer desk. Attach the removable missiles and drop tanks, and it looks quite menacing.
Now is a very good time to check the CG and set up the control throws. Stick to the recommendations in the assembly manual until you have a few flights under your belt.
The L-39 is engineered very well. I say this because inevitably folks want to go faster, and the L-39 is up to the task. In fact, Great Planes even recommends specific larger and more powerful propulsion systems if you feel the need for speed. In addition to speed modifications though, you need to look at the amazing canopy and pilot upgrade available from Keith Sparks. I really like the colors of the stock canopy, but if you want to change the canopy and add a few pilots, Sparky has you covered. In case you have not come across his work here on RCGroups, Keith is a master builder/designer and also is very adept at creating plastic pieces that are in themselves works of art. If you'd like more information, have a peek HERE. This is a sport scale plane, but with a little extra time and effort, you can really detail it up and make it look even more authentic.
This plane does not come with any options for installing landing gear since doing so would only add extra weight (which is not a good thing for a plane of this size). It is necessary to hand launch the L-39.
I have a confession to make: I am not very adept at hand launching EDFs, and my first effort to launch the L-39 ended up being more of a test of the durability of the Aerocell foam. One very short flight and one hard landing later, and the only damage was a small crack in the foam at the rear of the canopy opening. Impressive!
The manual gives pretty thorough instructions on how to launch the L-39 with an underhand toss. I have seen it done in this manner successfully, but I have had better success with an alternate method of launch: It involves holding the plane in much the same way you would hold a shot put and hoisting if forward and upward. The advantage may be related to the fact that it starts out with over six feet of altitude instead of the three feet of altitude that comes with the underhand toss method. Please watch the video below to get a better idea of my method.
There is no threat of a prop strike when hand launching an EDF powered plane. Unlike a pusher prop, the spinning element is completely contained within the fuselage. So go ahead and give it almost full throttle for the launches. Once launched, EDFs take a few seconds to "get on step". Resist the urge to feed in any up elevator at first, and instead concentrate on keeping the wings level and allowing the speed to build. Once you have a little momentum, feather in a some up elevator, and start the climb to altitude.
Alternately, you may enlist the assistance of one of your fellow flyers. Just make sure they do not heave it up at too steep of an angle. Straight and level, with perhaps just a slightly nose high orientation will work best.
The plane and power system provided for this review are undoubtedly the lightest possible combination, so the wing loading is extremely light. Landing this review plane was as easy as turning final and killing the throttle. The L-39 would glide in with no sign of any surprise. If I felt I was going to come up a little short, a little throttle would extend the glide. Check the landing in the video to see just how nicely it slows down for landing. Due to the exposed aileron linkages on the bottom of the wing, it is a good idea to get into the habit of checking the tightness of the linkages after each landing.
Going with a more powerful power system will add weight, increase the wing loading and require holding a higher speed on landing.
With elevator and ailerons, the L-39 is capable of loops and rolls. Watch your speed at the top of the loops: A slight diving entry will help you carry enough to get completely over the top. Rolls are slow and scale with the recommended throws. I increased my aileron throws a little to expedite the roll rate. With the light weight set up, the L-39 will slow down nicely. I was amazed at how slowly I could cruise by, especially with a little bit of a headwind. If you have not already heard the scream of an electric EDF jet as the throttle gets pushed to maximum in preparation for a high speed pass, you are missing a very exciting and addictive sound. The L-39 screams along at a very satisfying speed when running at full throttle. I really enjoyed racing along a few feet off the deck at full throttle and then aggressively pulling up and climbing heavenward.
EDFs can be a little difficult for a beginning pilot. The launches take a little bit of finesse, an EDF does not instantaneously respond to throttle changes, and there can be a bit of lag from the moment you initiate a throttle change to the time the aircraft actually responds. Once in the air and flying, the L-39 is certainly not a difficult plane for anyone used to flying with ailerons. It is a rather compact model at 25 inches of wingspan, and that, coupled with its relatively high speed, can mean it gets small fast.
I will emphatically answer YES to the proverbial question, “Was it worth the wait?” I am completely amazed at what Great Planes will give you in exchange for a one hundred dollar bill: a sturdy and sharp looking electric ducted fan ARF that includes the fan and motor. It is an incredible value.
Terry and I had a blast shooting video and photos of this one. Thanks for the assistance TR!
I am building another L-39 and should have it finished today. It has a slightly hotter set-up, as many guys have already found the L-39 will handle with no problems. This one comes out of the box strong enough to handle more power, with only minor modifications necessary.
I used some Blenderm, top and bottom, on the aileron hinges.
Last edited by Bajora; Jun 20, 2008 at 09:52 AM. Reason: typos!
Thanks for a great review! I was kinda on the fence over the GP L-39 but because of you, I will be $100 poorer. For me, the most striking aspect of this model is the undeniably excellent value considering the quality and completeness of the kit compared to the current crop of overpriced (IMO) and mediocre quality RR/ARF EDF jets coming out of China.
Great review. FastAlJr. and I had the same good experience with ours. Best $99 I spent at Toledo. We are also talking about buying a second to add a little more giddy-up to. Thanx goes to G_rod22 for this one. I did add an exhaust shroud to the fan and a battery cooling duct under the nose and out through the fan inlets, just as a precaustion from past experience with EDFS; otherwise ours was box stock.
A Mostek Sr.
George is batting 1000, eh?! Reactor Bipe and now this? I love 'em both!
My hotter L-39 has a JS with 5 blade Alfa fan and a 4S lipo. I am mointing the ESC right in front of the fan for optimum cooling.
May have video by end of day!!
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