I have a scratch built (my design) 1/2A.....so I call it that !

Wing is 37-1/2" long with a chord of about 8",,,,,307 or so sq. inches. I flew this plane on a .09 Hornet and was a bit over powered. i am not real sure of the whgt...... what size eletric motor and or gear unit, battery should I use ? Pic is attached when it was glow.

There are many choices available today for replacing a glow engine with an electric motor. Often, the choice is based upon cost and desired performance.

Until you gain some comfort with electric conversions and electric flight, it is best to go with a sure thing.

A middle ground solution would be the Astro Flight Cobalt 05 motor which has the same power as a MAX 10. You can view them here.

You can swing an 8x4" prop on 8-cells at 14,250 RPMs.

If you have enough ground clearance for an 11" to 12" prop then a geared version of the Cobalt 05 motor, shown here, can give you 6000-8000 RPMs on 8-10 cell flight packs.

Typically, a geared Cobalt motor is more efficient but it is not necessary.

To supply the 30-40 amps max. that the power system needs, a CP2400 NiCd pack would make a good choice.

Good luck!