RE: I need help picking an engine
it depends on your flying style... a 52 is great for long spirited flying but nothing too crazy. a 70 will get you to a more aerobatic plane at speeds far exceeding scale. personally, i think a 52 is enough for something like a space walker but if you plan to get into aerobatics and will find yourself in the 40-size, the 70 will be a better choice as you'll be able to fit it into more aggressive planes. but if you're not on a budget, the O.S.52 is a gem of an engine.