RE: Hobbico Twin Star conversion
Carlos,
I think John's approach of using a direct drive brushless motor is a good one. There are many to choose from and shape or size can be a determining factor in your decision as well as cost.
Let's look at the [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJPH0&P=7]Hobbico Twinstar ARF[/link] specs:
[ul][*] Wingspan: 56" (1420mm)[*] Wing Area: 560 sq in (36.1 sq dm)[*] Weight: 5 - 5.5 lb (2270g - 2490g)[*] Wing Loading: 21-23 oz/sq ft (64-70g/sq dm)[*] Length: 50" (1270mm)
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The key spec. here is the flying weight of 5lbs and the fact that it is a twin motor design. For great performance, we'll want 75-100 watts per pound or about 400-500 watts combined input power. This means that each motor should provide 200-250 watts.
The [link=http://www.hobby-lobby.com/brushless-axi2820.htm]AXI 2820/10[/link] is more than we need on a 10-cell NiCd or 3-cell Lithium pack with a 10x6 prop as it provides about 300 watts input power. A single 3-cell Kokam 3.2AH (20C) pack or 10-cell GP3300 NiMH pack could power the entire plane.
Keep in mind that this is just one example of many solutions.
Good luck!