A Small Field Duration Model for Electric Sport Free Flight
Following email exchanges with Brian Lever, a draft outline was muted for a free flight electric duration model capable of being flown at Ferry without getting your feet wet and without damaging 'other users ' of the facility. The half agreed draft specification was ..
Maximum span 20"
Motor tests :
Gasparin Bronco 12Watt with 1s ESC, 320mah Hyperion G3, GWS 4 x 4
3.27 amps , 3.71volts, 12.01 Watts
Wing : 3 x 1.5mm sq spars on a 95 mm chord with classic 3/10deg half angle dihedral. LE 3mm sq , TE 10 x 2.0mm. Esaki covered, 3 x 50/50 dope. Spencer Willis Sweet P20 airfoil
Stab : 0.8mm strip, top and bottom cap strips only, no ribs, 0.7 carbon TE, 2mm sq LE, 2 off 0.8 mm full length spars
Fuselage: Viscous DT, stab mount,
fin, pylon, motor mount, boom 10.3gms finished. 2 degs downthrust, 3 degs left
Total is : 10.3 + 10 + 2.3 + 13 + 6.5 +1.6 +1 = 44.7 gm
The GWS 12mm can motor supplied by G R Perkins as an EDF motor runs 2amps @ 7.4v on a 4.5 x 3 GWS and would be a prime contender. But I understand GRP has fallen out with GWS and they are hard to find. I have 4 off spares that can be sold to club members. I have not rig tested them but capable of 13-14Watts therefore as powerful as the Bronco. Weight is 13.6 gms but you have to use a 2s Hyperion G3 13.5gms RB 405624.
The kpaero KP01 with a 250mah is LiPo and 35sec kpaero controller is an obvious set up and there are many in the PMFC that have this power source. Suffice to say that I am not an aficionado of this motor and should you go this route you are on your own. I have no idea what the current draw might be.
Apart from the kP01 there are no obvious brushed motors that would provide a competitive power source without breaking the weight budget. A pair of 7mm geared pagers running GWS 5 x 3 would draw a total of 1.5 amps on 1s 250mah. Might be a start but none too competitive.
The PMFC FET timer might not be
suitable for use as a controller as there is a 3-5 sec run down tail on a
7-10sec motor run. This is too much of a handicap.
A good alternative to the Gasparin Bronco that I have used is the Robotbirds 5gm motor 409407 kv 3000 rev/min/volt. Suppliers data gives 4 amps at 13600 rev/min on a GWS 5 x 3. But you must use a 2 cell LiPo, a 25C capable 180mah battery would be recommended 405624. This will weigh 13.6gms and can be teamed with a 6gm 6 amp ESC 400210. The complete power unit with connectors, conductors , ESC, motor , mount and battery would top 30gms but would deliver 96gms of thrust allegedly. The only controller to use would be the kpaero.
Some pictures of the nearly completed model (as yet unflown)
Ian Middlemiss February 2013