3 May 15 - Scrapped

positron-01.gif (11780 bytes) positron-02.gif (10838 bytes) R.I.P.

N° of launches / Time 23 58 mins

Ü Includes all flights

Wingspan 20.5 in 0.51 m

Wing Area 168 in² 10.8 dm²

Flying Weight 14½ oz 410 kg 16.1 oz 457 g
Wing Loading 12.4 oz / ft² 38.1 g/dm² 13.8 oz / ft² 42.2 g/dm²
Wing Cube Loading 11.5 - Between Aerobatic and Scale groups 12.8 - Scale (Ouch, but there is a fair bit of power)
Motor Robbe 400/35 (equivalent to Graupner Speed 400 6v) Hacker B20-18L brushless with 4:1 gearbox
Propeller Graupner 6 x 3 folder Graupner 9" x 5" folder
Speed Controller Schulze slim-18be - 18/25A - 6 to 8 cells - BEC & Brake Hacker Master 18-3P - 18A - 6 to 10 cells - BEC & Brake
Batteries 7 Sanyo 500AR or 600AE cells or 8 GP 1200mAh NiMH cells. 3 series 15C Kokam 2000 mAh
Receiver Webra Nano S6 - 6ch - 35 MHz GWS GWR-4P/H - 4ch - PPM - 35 MHz
Servos Elevons - 2 x Ripmax Diamond SD200 Elevons - 2 x Union Micro UM9G
Static motor parameters  11,800 rpm @ 10A, estimated output 55 W/lb. after 30s 8000 RPM @ 8.25A and 11.0V, output power = 91W after 30s and power : weight = 90 W/lb. Having estimated the thrust : weight in my hand it is about 1:1
Flight performance Climb is about 20°. Roll rate on reduced control throws is approx. 360°/s and on full throw 1080°/s (3 rolls/s). It is necessary to build up speed to complete a loop and a lot of speed is lost during the manoeuvre. Better than the previous power system but still lacks real performance.

3 May 15 - I decided to retire this model as it never met my expectations and was never going to fly again.

28 Dec 04 - I decided that I should bring this model out of retirement (it had been in my loft for a couple years with no equipment in it).  Whilst doing so I decided that Li-Po batteries were essential as the increased capacity will give good flight times, which was always a problem before.  The only 3S pack I have that is good for this model is my 15C Kokam 2000mAh pack, which is a little heavy.  I will be ordering an 8C Kokam 1500mAh, which is considerably lighter and more suitable for this model.  The reduction in weight is around 60g which will put the model lighter than it's original flying weight and increase the power to weight to around 100W/lb - I can't wait.

25 Mar 01 - I came across a photograph of this model in an old copy of Electric Flight International and have added it above.

26 Aug 00 - I have experimented with a number of other propellers, including the Günther 125mm x 110mm (4.9" x 4.3"). Despite the model being nice to fly, I have decided to retire the airframe. This is primarily because I am fed up with 2½ minute flights and the inability to fly with the throttle anywhere but full. The receiver and motor will be fitted into the Contour, with the servos becoming spare (temporarily).

12 Aug 99 - Flight performance is not much changed when using a 6 x 3 folder, but flight times have increased.

26 May 99 - Fitted a Graupner CAM 5 x 5 propeller for the flights today as I thought it should give better performance than the 6 x 3 folder. The performance was good, the model flew well and the propeller survived. I think I'll try some more flights with the 6 x 3 folder and get a 6 x 3½ folder to how they fly.

22 May 99 - For some reason the motor suddenly stopped working. I think due to the motor being overloaded, the commutator was quite black and once cleaned it started working again. However, I decided to replace it with the Robbe Power 400/35 motor from the SkaT, and use the Schulze slim-18be controller already soldered to the back plate of the motor. This reduced the flying weight by 3½ oz.

27 Mar 99 - I managed to get a proper 1st flight in. It was obvious that the 6 x 6 folder was overloading the motor and performance was not as good as expected. I have fitted 3 different propellers to hubs to experiment with - they are a Graupner 6 x 3 folder bored out to a 3.2mm shaft, and 2 Graupner CAM propellers of 5½ x 5½ and 5 x 5.

 15 Mar 99 - I managed to get to the flying site after work and complete the 1st flight - well almost. I tested the model on the ground and then hand launched the model. It climbed extremely quickly and I started a few manoeuvres, including a roll. I then started to experience control problems with the model periodically not responding. I immediately throttled back and started a landing circuit which was interrupted twice by control loss. I eventually regained control about 50' up and 70° nose down. I managed to pull the nose up and achieved a heavy pancake landing in the slightly longer grass beyond the square (reminded me of a Space Shuttle landing). No damaged was done other than breaking the fuse - this was due to the landing shock as the motor was stopped. The receiver has been replaced as it appears to be the culprit.

Note the rubber band on the spinner to prevent the blades from folding back. If the blades fold they foul the wing and would stall the motor if a restart was attempted. The rubber band allows the blades to flick back on impact, e.g. with ground on landing, but keeps them forward in flight. An alternative I might try is to use a thin wire guide from one leading edge of the wing to the other over the top or bottom motor tube. This will stop the blades folding to the point of the motor being unable to start.

I have modified the model to allow the fitting of the Multiplex 450 Turbo instead of the normal Speed 400. The latter will turn the bigger propeller at a higher rpm than the Speed 400.

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