Parkfly

Parkfly models are convenient. They are quicker to build and cheaper to fly. But most importantly, you can (generally) fly them at local parks.

My first foray into parkfliers was with a '10 size' glow engine. I bought an 'AP Hornet 09' engine. It is a nice looking engine, but it is a bit heavy for the amount of power it puts out. I would advise, if you are wanting to get a small throttled glow motor to factor its weight into the equation. In hindsight, I should have got an 'AP Wasp 061' (or better yet a 'Norvel BigMig 061') and made slightly smaller and lighter glow powered parkfly models.

Since I had just learnt how to fly, I wanted something quite docile and easy to rebuild if I crashed it. I ended up creating something that had its wings made out of flat polystrene sheets and its fuselage was made out of a yardstick. It flew quite well, and was gentle to fly because of its low wing loading (and thus a low stall speed). However, like my other glow planes, I had been sick of having to clean them from castor oil exhaust residue. I turned out an new aluminium muffler to make the exhaust come out at a convenient direction, then added an exhaust pipe that exited at the tail of the plane. This did reduce the mess, but the engine quit often in mid-flight - perhaps too much back pressure?

My second glow parkfly airplane used similar materials, but was of a more aerobatic design. Again, its wings were made out of polystrene. To strengthen and protect the foam from the fuel, I covered it with clear packing tape. It is amazing how much stronger this makes it. At the same time, it also makes it quite a bit heavier. This model also flew well, and the engine was now more reliable now that put on its original muffler and removed the exhaust pipe.

After building a couple more glow powered parkflyers, I decided to give electric a go. Although I did like the sound and the smell given off by glow engines, I really disliked how messy they make the airframe. I bought a speed controller and a speed 400 brushed motor. I made up a battery from oridinary 8x NiCad AA's. This budget battery yielded planes that did not fly well, mainly because the high internal resistance of the cells. The only way to get a plane flying with this battery was to build a really light airframe so that the motor did not have to work hard. As a result, many of these planes were built just strong enough.

Fortunately, cheap brushless motors and good batteries were becoming available. I took the plung and shelled out on a brushless motor and controller, along with a couple of LiPo battery packs and accessories. My first decent performing parkfly electric was based on a scaled up version of Tracer by Canterbury Sailplanes. This plane was very fun to fly, and the brushless gear was a drastic improvement over my previous setup. It did not quite have enough thrust-to-weight ratio to hover, but it was close to it. Again, I chose to make my Tracer out of polystrene. By this stage, I was adept at using this material, and knew how to create a decent looking model that did not weigh too much. For the control surfaces, I used dense foam cut from used fish boxes picked for free from a supermarket. For the fuselage and wings, I found some lighter density foam. Tape was added sparingly for added stiffness. The resulting airplane, which I was quite proud of and flew for a while:

There was nothing wrong with the performance of the Tracer, but for some reason I got the need for speed. I ordered some more brushless gear, and retro-fitted one of my old speed 400 planes (Tucano) with a speedy motor. The Tucano came to life with the brushless motor and LiPo battery. One day I was doing a high speed low pass, and soon after hitting a slight gust of wind, the wings 'clapped' together. The airplane spiralled as it came crashing down a few metres from where I was standing. The frame was mangled, the propeller broke, and the motor shaft bent, but fortunately the rest of the electronics survived. The broken model:

Continuing with my desire to fly fast aeroplanes I built a BAE Hawk from plans found off the internet. This model is in the pusher configuration, and since I put in a 500W system into a sleek 500g AUW frame, it would have gone pretty fast. Unfortunately, I never got around to flying my BAE Hawk. University assignments are partly to blame for this, along with my robot that I had just started work on. The BAE Hawk that never took flight:

Dave Blum's Jelly Bean was the first 'proper' balsa parkfly model I built, and as reported by others, it too proved to be a capable performer. Unlike my Sukhoi, I stuck mostly to the plans. Since I already had the electronics from another plane, and that they were too big and heavy for the original Jellybean, I scaled the plans up slightly. An gallery of my Jellybean is below. You will notice that there is no landing gear, which is common for lightweight and small electric airplanes. Instead, it is hand launched and is landed gently on its belly.

Initially I tried covering the model in clear lightweight laminating film. This material has similar properies to heatshrink film, but does not conforms as well on tight bends. It still turned out okay, and this is a cheap way of covering models. However, you will need to add colouring of some sort. I tried flying it as it was, and suffice to say, to keep track the orientation of the plane you had to fly it close. I plan to either add decals to my Jellybean, or add coloured covering film. The specifications for my Jellybean are:

  • 860mm wingspan.
  • 450g flying weight (with a 3 cell 1800mAh Lipo battery!).
  • 2215/25 850kv motor with a 10x4.7 propeller
  • Three 17g servos
  • A modified Hitec Feather receiver (smart PPM decoder)

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