I am also building a Liberty Sport bi-plane, it has a 94" top wing, it says that it should weigh 22lbs. the plans mention nothing about a engine size. One guy told me a 50cc but I think that there is no way a 50cc engine could pull this monster straight up. I really like to fly at half throttle and have the option of going straight up . I 've only know the regular glow size planes aand have been flying them for a long time. The gas plane size is great, but I have little knowlege about the engine sizes. I have dozens of plans of giant scale planes and am starting to bulid a few of them. Any of you guys that can give me some bench marks would really be helpful.