|Dec 27, 2012, 10:32 AM|
Joined Nov 2009
generalhobby Sbach 55 inch wingspan
Some notes on a Steinbach that I bought from generalhobby, as an experiment.
Price: $179 (may be on sale now)
Weight: projected at under 5 pounds, but I am flying it around 6.5 lbs
Construction: laser cut plywood and balsa
Gear: tail dragger, carbon fiber main gear came with it
Power system: recommended was a 28mm electric, which is far too light to pull
this plane through vertical aerobatics.
Actual power system:
NTM PropDrive 50-65 2,000 watts, 15 x 8 electric prop.
hobbyking 190A opto speed controller
hobbyking 8-15A voltage regulator for servos and speed controller
6S 5,000 mAh main battery
Servos: Solar 109 analog from hobbypartz. Cheap, smooth, and fast enough.
This build was an experiment, and was not the recommended power system!
The goal of this build was to get a light weight, relatively cheap, aerobatic Steinbach. I have not seen reviews of the accessible 50 to 70 size Sbachs, and this plane has a lot of wing, so could potentially carry more weight.
Nose: there is a built in battery box (good), that was far too light (bad). I strengthened it with 1/8" plywood on the sides, and 1/4" sheet balsa on the floor. Strengthening goes almost all the way back to the wing tube.
Tail: servo boxes in the tail are very close to regular (40g) servos, although the Solar 109's just bump in the middle -- can still be screwed in. Makes a short control rod setup, with elevators up on the pull stroke.
Main gear: none of the supplied hardware seemed to fit the CF gear, so I scrambled to get axles. I cut strips of 1/8" plywood to go on top of the CF gear to fill the gear slot in the body, and bolted the strips over the CF gear into the body.
(I fly at a club with paved runway. Wouldn't recommend this for grass.)
Tail gear; I used a heavier tail wheel from a Seagull plane, screwed into a triangular 1/8" plywood base, epoxied to the bottom rear of the body. Steering is with the tail wheel wire going through a piece of plastic control rod tube, epoxied to the outer bottom of the rudder (epoxy will pop off on a hard landing, before the rudder is ripped apart).
CG: the manufacturer did a good job balancing this VERY LIGHT laser cut plane for a lighter power system. With the NTM propdrive 50-50 in the nose, and a 5,000 mAh 6S battery and a 1300mAh 3S backup battery, the plane is quite nose heavy. I balanced it about 25% chord with 3 AA batteries epoxied under the horizontal tail, in the fuselage (accessible via an electric vent hole cut in the bottom rear of the fuselage).
1. Used heavy exponential for the first flight. Futaba: depress ailerons by -75%, and aileron by -50%.
WARNING! Keep throttle down until the plane is trimmed. My first flight was less than 50% throttle.
2. Plane rolled right (needed noticeable aileron adjustment in the direction of torque).
3. Plane heavily lifted nose under power. Added heavy down thrust (1/8" shims on the top two aluminum pole mounts).
4. After above, trimmed to glide without power -- beautiful slow speed glide that reminds me of a Yak coming in to land.
5. Power: NTM Propdrive 50-50 has 580kv, or 12.876 rpms with 6S. Without air resistance, it will want to make turns for about 97 mph. With air resistance, it will probably pull the plane about 70 mph. Aerobatics probably need 40 mph or much less speed. So manage your throttle, to keep the speed down, or you will rip the plane apart.
This is a very interesting aerobatic experiment. Just trimming it to fly straight is a significant job. But the plane is light and maneuverable, and the power system is cheap and will accelerate straight up. I hear guys at the club asking "That's an electric?" I have only tried endurance for 6 minutes. Keep LiPo cells above 3.5 volts to avoid damage.
Bottom line: this is a nice plane ARF, and with a little strengthening and an unorthodox power system, is an aerobatic muscle plane that does not fly like a brick. (Don't use gas/glow power, as the build really is light.)
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