Last year I built a pusher/puller plane w/ 48" wingspan and two 28 Magnum engines. I had a tough time getting off the ground and as a result ended up putting on winglets, as shown on the attached photo. I later found that my poor takeoff performance was due to improper engine tuning. A change in props also helped. I ended up liking the appearance of the winglets and decided to keep them anyway. I sometimes take off on one engine. Some days it is very difficult. I literally "jack" the plane off the ground with rapid movements of the elevator. It appears fully stalled at takeoff and then it is time to start a turn. It wallows a little but has never "snapped rolled" into the ground. It may be the winglets that make it so steady, but I'm not going to take them off to find out. They even serve a little as out riggers during poor landings or fast ground turns. The winglets are about 1-1/2 inch larger than the wing, top and bottom. I followed Ed Moorman's suggestions, as I recall. Thanks, Ed.