The author posed with the flight-ready airplane.
|Wing Area:||299 sq. in.|
|Wing Loading:||11.5 oz/sq. ft.|
|Servos:||3 GWS "Naro", 1 Hitec HS-55|
|Transmitter:||GWS 4-channel Dream Starter|
|Receiver:||GWS Pico 6-Channel|
|Battery:||Electrifly 3-series 1500mAh LiPo|
|Available From:||Hobby Lobby|
This semi-scale foam ARF is a great-looking rendition of the Zlin Acro Turbo 137T, a serious European crop-duster which is driven by a 520hp turboprop engine. While the smaller version doesn't have quite that much power, when equipped as Hobby Lobby recommends, it has plenty of authority to do some serious dusting down at the local soccer field!
This kit is manufactured by Graupner in Germany, and is distributed in the US by Hobby Lobby. This review covers not only the airplane, but the brushless drivetrain that Hobby Lobby recommends.
Hobby Lobby provided me with the ARF kit, along with a radio and a brushless motor system to power it. Hobby Lobby recommends a PJS 550E motor spinning a 10X7 propeller, driven by a Jeti 18A brushless speed control. Also provided was a GWS 4-channel “Dream Starter” radio system, including a 6-channel receiver, charger, and 3 “Naro” servos. To complete the radio package for this airplane, which needs 4 servos, a Hitec HS-55 was also included.
Upon opening the box, I was presented with a lot of parts, some identifiable at first glance, and some not! Never fear, though – everything was clearly described in the instructions, and the kit was not missing any parts. The elevator had taken a bit of shipping damage, but was quickly patched up with some foam-safe CA.
The first thing I was struck by as I inventoried the parts was the quality of the foam and molding. The foam that Graupner uses seemed to have a much smaller bead than most foam used for expansion-molded models. This gave a very nice surface texture, and the foam also seemed a bit stiffer than most (though perhaps a bit more brittle as well). All in all, the foam parts were beautifully manufactured, with very few mold marks or seams.
The second thing that struck me was all the wood! For a “foamie” there sure were a lot of balsa and plywood parts! I’ll go into this in more detail as we go on, but Graupner made some very good choices in terms of materials for this airplane.
Cracking open the instructions, I initially spent some time searching for the English text. While I can stagger through technical German, I’d certainly rather work from my mother tongue. Fortunately, another look through the box located a separate stapled set of English text that matched up with the photos in the German section. It would have been nice to have both text and photos in one place, but this system worked service-ably.
Assembly started with the fuselage. According to the manual, you should mount the motor first. I skipped these steps, as I was installing a brushless upgrade, and knew that there were some modifications necessary. Moving on, the next section of instructions had me install some formers into the fuselage, along with the elevator and rudder servos.
One tricky step that I didn’t feel was adequately covered in the manual was the installation of the main spar. I was supplied with one piece of hardwood which I needed to cut into three lengths with long bevels on the ends. Here’s the technique I came up with, since the manual didn’t specify any lengths or angles:
Now we come to one of the real high points of the kit – the landing gear. Having ripped the undercarriage out of many a foamie, I was glad to see that Graupner really did their homework on setting up a beefy landing gear system for this plane. These landing gear aren’t going anywhere without taking a substantial portion of the airplane with them. They are effectively tied in to the main spar, as well as the plate that holds the wing bolts. Excellent load path design!
Time for radio setup. All the surfaces were driven by wire pushrods that mated to thin plywood control horns. The rudder and elevator used screw-lock pushrod connectors on the servo end for easy adjustment, but the ailerons were adjusted only by shifting the position of the horn in the aileron. It was important to be very sure of the servo center before performing this step.
Since this plane probably wouldn’t be a very good glider, I then turned back to the problem of motor installation. Neither Graupner or Hobby Lobby had provided me with any input or hardware to mount this little gem in the nose, but being an industrious fellow, I decided to work it out for myself. I installed a firewall into the foam of the nose, offset back far enough to allow the front face of the motor to be even with the nose. This involved cutting away enough foam that the larger-diameter PJS motor would rotate freely (it’s an outrunner), and cutting a slot for the firewall. I tried to maintain the thrust angles that had been molded in for the stock gearbox, which were small. All in all, the installation worked great.
The foam's sort of a sickly yellow might make painting enticing, but the much wood on the plane made it required. Since the recommended Graupner paints weren’t readily available, I settled on Testor’s model paints, which I knew to be foam safe. However, even after several coats of the yellow base color, I couldn’t manage to achieve an even coloration I was entirely happy with. I’m not sure what effect was at work here, and the finish certainly looked OK, but I would only rate this paint’s performance on the Graupner foam as about a 6 out of 10. If you’re a real scale nut, you may want to see if you can find a paint that reacts better on this foam. The fuselage stand would make an excellent test piece.
With my less-than perfect results from the yellow in mind, I decided to simplify the red sections of the trim scheme a bit, just to avoid having too much color layering going on. In the end, I achieved a satisfactory, if not beautiful paint job.
I then cut out and applied the decals, which there are a lot of. These definitely enhanced the look of the airplane. The decals in this kit had a finish that was somewhere between flat and satin, rather than the normal glossy plastic look. I think these are probably the best looking decals I have ever applied!
Finally, I completed the trim scheme with a panel line pen and a straightedge. As more detail went on the plane, my dissatisfaction with the paint scheme faded – this thing was really looking nice!
Some quick checks of control throws and CG were all that remained before flight. With no battery installed, the plane balanced within the recommended CG range. This is an excellent characteristic, as it makes it possible to try different sizes of battery without having to shift weight around. The control throws were checked against the manual, and all matched except for the elevator, which ended up with a bit more throw than recommended. Since this plane was being controlled by a simple four channel radio, I decided to leave it as it was, and see how the plane responded. I often end up boosting recommended rates a bit anyway.
Looking back on the build, I really enjoyed it. This is a pretty complicated ARF, and requires a good bit of woodworking, but in the end, I enjoyed all of that – a lot of planes are so prefabricated that you don’t feel a lot of builder's pride. With this one, I had only invested about 25 hours in the model, but because of the woodworking and finish work, I really felt like I had built a plane, rather than simply assembling it.
With that, I was ready to go fly! Unfortunately, the weather didn’t cooperate, and the plane sat idle for over a month as I waited for a weekend with good weather. In central Illinois, January and February are not good months for flying…
Finally, the days got long enough that I could get some flying time in the afternoon after work, and I headed out to the local park. With an Electrifly 3S 1500mAh sitting on the CG, the motor system seemed to have plenty of pull and the balance was in the forward end of the recommended range – perfect! I attached the battery to the top of the wing using some industrial strength Velcro, connected it to the ESC, and bolted the wing on.
There it was – a complete airplane, sitting on the runway, ready to fly. It’s always hard not to just advance the throttle and fly, but preflights are still necessary, especially on maiden flights. I checked my control directions three times, walked out a range check, and was ready to go. The provided GWS radio system checked out fine on the ground, making about 75 feet of glitch-free range with the antenna down.
With all systems in the green, I decided to do some taxi testing to see how much yaw authority I would have on the ground with the fixed tailwheel. I needn’t have worried – she drove great. The rudder had a nice balance of authority and precision when rolling with the prop turning. I did notice the airplane getting very light on its wheels – this thing wanted to FLY!
The maiden takeoff went smoothly – I advanced the throttle gently, steering against the torque without any difficulty, and waited for the tail to come up. It never did – the plane rotated straight out of the three-point position and headed skyward on its own.
Down elevator got it back in line, and it required almost the full trim travel for level flight under power. Once trimmed, chopping the throttle resulted in a pretty substantial nose-down reaction – she needed more down thrust than I gave it. The reaction was very manageable, however, and once trimmed the airplane felt great! Level flight required about half throttle, but the cruising fell kicks in at around 2/3 throttle.
The recommended drivetrain performed really well in this airplane. This system offered a really good power balance – it had great thrust for quick takeoffs and authoritative climbs, but it wasn’t over the top on speed. All in all, the speed envelope was very scale-looking. I haven’t timed a flight yet, but the video flight was over eight minutes and the battery still had plenty of punch. Based on static current draw and the throttle settings used in flight, I’d guess that fifteen-minute flights would be easily possible.
Turns using aileron only resulted in the tail slipping to the inside quite a bit – there was some adverse yaw at work here, and the fin was pretty scale in size, which is often a bit undersized for models. This meant that flying a nice-looking coordinated turn required a continuous small input of rudder into the turn. Don’t worry though, the plane tolerated “yank-and-bank” aileron and elevator turns just fine – the tail just hung a bit low in them. Rudder alone only worked tolerably well for turning, but got the airplane to pretty hefty levels of sideslip – this should only be used at speed – do it too slow, and you may find yourself in a spin.
This airplane has a big wing that isn’t carrying very much weight, so I had to really work to get it down to stall speed. Coordinated, straight-ahead stalls in this airplane resulted in a gentle mush with minor altitude loss. However, the airplane got a very “disconnected” feel in yaw at and around stall, which made me suspicious about how it would handle uncoordinated stalls. Sure enough, holding any rudder at stall resulted in a pretty substantial wing drop in the direction of the rudder input. The plane flew out, even if the controls were held, and didn’t spin, but recovery happened in a nose-low, banked attitude that might be difficult to fly out of if the ground was too nearby. This wasn’t severe enough that I would consider it a “bad habit” on the part of the airplane, but it is something to be aware of.
Easy as pie! The light wing-loading lets this one come in at a crawl, especially in a headwind. It set down equally well on the mains or in a three-point, and transitions to rolling very well, without any tendency to bounce or nose over.
It’s no IMAC ship, but that doesn’t mean you can’t get it upside down! It’s got ailerons, right? The Agro Turbo did just fine with sport aerobatics – loops, stall turns, and rolls were all well within this planes capabilities, and are all on the acro video. And spins? Oh, yeah… This plane does really nice-looking spins and has an immediate recovery when the controls are neutralized. Check out the spin in the video and you’ll see what I mean – this is a fun one. I haven’t gotten it to flatten out yet, but it’s only a matter of time!
This is a model of a crop-duster, right? Flying it like one is a blast! Get it low, scrape across the field at low speed, then punch out for a climb and a wingover turn to make your pass the other way. I had a lot of fun pretending to distribute fertilizer over the local soccer field – now all I need are some challenging windbreak tree lines like the big ones get to fly over, and electric lines to slip under…
While this plane is a reasonably sedate flier, its stall behavior and the extensive building required keep me from recommending it to a beginner. Building this plane is not a bad experience (I enjoyed the build a lot), but it does take some time, and interpreting the instructions requires some previous modeling experience. In the air, it flies great, but you really need to be accomplished at using ailerons and rudder to be assured of flight success. All told, I’d say this would be a great third airplane. If you’ve mastered handling a 4-channel ship, then you’re ready to fly this one – just remember that that left stick moves…
Unfortunately, the batteries in the digital camera succumbed to the cold just after taking the ground photos, but we did manage to get a lot of video footage. I'd like to thank Mike Cross for his help with videography and flying for these videos - we had to tag-team it to keep our thumbs from freezing off!
The Zlin Agro Turbo 137 T from Graupner and Hobby-Lobby is a really great looking and flying plane. You get sport-scale looks and a great sport flyer out of a long weekend on the workbench, and the building style really makes you feel like it’s your plane. In the air, the recommended drivetrain has lots of authority without making the plane ridiculously overpowered, and it really does look like a crop-duster in the air. All in all, this plane is my current sport/scale favorite in my hangar. It’s handling in the air is a joy (I love the spins!) and it looks great to boot. I look forward to using it for “glow-flier attitude adjustment” this summer. With its balance of looks, performance, handling, and character, it should make some of them think twice about turning their noses up at electrics.
My only minor complaint with this kit is the instructions. They leave quite a bit to the modeler to figure out during construction, and the complete lack of instructions on mounting the recommended brushless motor could cause a lot of difficulty for a less-experienced modeler. I hope what I've provided here will help those who choose the same combination.
All in all, I’m really pleased. If you’re looking for something a little different, and enjoy working with an airplane on the bench without having to completely build a box of sticks, I urge you to consider the Zlin Agro Turbo 137T from Graupner and Hobby Lobby.
NOTE: I hope to put a smoke system on the plane and do some more crop dusting, so watch this spot for more flight footage and pictures!
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