logo Heading














































































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"
Maximum weight 50gms
Permitted motor run 7-10secs
Motor and battery, whatever you can find.

Motor tests :

Gasparin Bronco 12Watt with 1s ESC, 320mah Hyperion G3, GWS 4 x 4

3.27 amps , 3.71volts, 12.01 Watts

Manufacturers data:
GWS 5 x 3 3.58amps 10037 rev/min 12.5 Watts 92gm thrust
GWS 4.5 x 3 3.48 amps 11337 rev/min 12.5 Watts 86gm thrust

Construction details

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

CG calculation

Wing span : 508mm 20”
Wing chord 95mm 3.74”
Stab span 230mm 9.05”
Stab chord 75mm 3.0”
Wing TE to stab LE 266.7mm 10”
For 15% static margin . CG is 62mm or 2.44" from LE


Fuselage: Viscous DT, stab mount, fin, pylon, motor mount, boom 10.3gms finished. 2 degs downthrust, 3 degs left thrust
Wings : 6.2 gms wood, 8.7gm Esaki covered, 10gm doped. 1.5 mm washout tips, 1.5mm wash in right inner panel.
Stab : 1.5 gms wood, 1.9 gms Esaki, 2.3gm doped
Motor, ESC, prop, connectors, conductors 13gm
Battery : 1s 240 mah Hyperion G3 LiPo 6.5gm
Controller: kpaero 1.6gm
Bands : 1gm

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 fallback position would be to allow FET users an extended motor run time to compensate for the lazy cutoff. This I would recommend as the 12mm motor is a very good option. I intend to make a spare fuselage with this system to see the potential.

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)

Model weight 45gm with intent 1s 240mah LiPo

Gasparin Bronco with 1 s 7amp ESC and GWS 4 x 4 Heat shrink not yet shrunk,
waiting to see if rotation is correct when battery arrives

Kpaero controller and viscous DT

Battery ordered not yet installed

Top view

Spare fuselage with next best motor option, GWS 12mm EDF controlled by a FET timer.
Likely model weight with intent 2s LiPo would be 52-53gm

Close up of the bits less battery

Ian Middlemiss February 2013