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Another E20 using a Parkzone power unit

These notes continue the development of a small field 20" span E20 model based on designs that are appearing in the US. My previous attempt using a 12mm GWS can motor and 2 cells eventually weighed over 60gms and whilst providing exciting performance, I thought I could do better.

The link to US E20 activity is as below……….
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=14519.0
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The US designers are using an 8.5mm Parkzone motor with a 150-200mah single cell….see picture. This is the same power unit that Dave Shipton uses in a 4 ch lightweight RC RTF at Ferry. It might be a Sukhoi (?) and goes like stink? Surprisingly, the US are removing the gearbox and 140mm propeller from this power unit and run a direct drive 2.5 x 1 GWS or Tri-Turbo propeller. I have used the motor/gearbox/propeller intact, weighing 8.5gm . I have not measured current draw but estimate 1.2 -1.5amps. Power unit from Robotbirds part number 403375. Propeller 403356.

I am running a 200mah 1s LiPo , a FET timer and the complete power unit weighs in at
8.5 + 2.0 + 5.8 = 16.3gm. The fuselage uses an 18" length of 3mm CF tube (3gm) and the completed fuselage with stab (2.3gm) , rudder (0.4gm), DT, pylon, bands and motor mount weighs 16.3gm. With a Spencer Willis Sweet Pea wing (10gm), the complete model weighs in at 39.4gm. The cheapo Flitehook viscous DT timer is situated just behind the motor and uses a shirring elastic power source, stolen from the Domestic Controller, on the grounds that it does not deteriorate in UV.

The weight is a major improvement for me but is still heavier than the 30gm claim of some of the US models. I can see a saving on 3-4gm but 30gm is beyond my ability. Some of the discrepancy may be due to my use of the gearbox and larger (heavier) propeller. Flight testing this Tuesday 9th July, weather permitting.

Ian Middlemiss 7th July 2013
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