View Full Version : Another old dog needing new tricks

12-18-2005, 04:41 AM
After 30 years of RC I'm going to try electric. I've got a House Of Balsa "School yard scale" J3. 52.5 span, 350 sq inches and all up weight of less than 2 pounds. Any suggestions which GWS motor and gearbox and prop I need for this? I do NOT want the brushless stuff.


12-18-2005, 04:46 AM
That seems a bit heavy for a GWS power Plant. If I were to guess I'd say a Speed 400 with a gear ratio of at 5.33:1

Is this a glow plane you are converting to E-power? Also have to consider what batteries you plane to use.

Don Sims
12-18-2005, 10:38 AM
Welcome cigar, 2 lbs is a bit heavy for a GWS motor. You need to build as light as possible and there is no need to tank the plane with a lot of extra epoxy up front.

tim hooper
12-18-2005, 11:48 AM
I'm not familiar with the actual model, but 2lb AUW would put you in the middle of geared-S480 country, I reckon, for a floaty scale Cubby-thing.

Li-pos, Nimhs or Nicads?


12-21-2005, 07:53 AM
MotoCalc gave these results…

MotoWizard Results - HOB SYScale J3 Cub

Desired Full-throttle Performance: Trainer
Minimum Partial-throttle Flying Time: 9 minutes

Number of Motors: 1
Wing Span: 52.5 in
Wing Area: 350 sq.in
Empty Weight: 24 oz
Airfoil: Thin Flat Bottomed

Elevation: 2000 ft
Sea-level Pressure: 29.92 inHg
Air Temperature: 75°F

Drive System Types: Direct Drive or Geared
Motor Types: Brushed Only
Manufacturer: Any Manufacturer
Maximum Number of Cells: Any Number
Cell Types: Any Type

#1 choice

Motor - Astro Cobalt 020 9T #602; Battery - 7x1300SCR; Gear - 5:1; Prop - 12x11 Rating - 1.000

The same motor came up 2nd for direct drive..

Motor - Astro Cobalt 020 9T #602; Battery - 7x1300SCR; Prop - 5x2.5; Rating - 0.997

Highest rated GWS motor system

Motor - GWS EM400; Battery - 10x600AE; Gear - 5:1; Prop - 11x11; Rating - 0.885