Mount for the battery?
I just velcro mine to the fuselage.
I guess you could make a balsa crossmember and velcro the battery to that too.
But for me this would prevent me from installing my 2200mAh batteries.
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Prop selection depends in large part on your motor and ESC, or rather what they will draw.
You may want to use one of the on-line "motorcalcs" to figure out what you want to use that will not draw more current than the ESC can handle.
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Re: Struts
I haven't put mine together yet, but isn't it obvious?
Isn't there a hole already for the strut screws, although you may have to remove the covering over the hole?
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RE: Outrunner
NP recommends the 400T or 400XT which would make this plane haul.
When last I checked NP was sold out of both of them so I purchased one of these instead.
http://www.nitroplanes.com/a2oubrmow980.html