The method for elevator use as descibed by your instructor works well for a tail dragger. Trike gear airplanes are very different. The LT40 is very stable because of the placement of the landing gear and the width between the wheels. With a rough grass field, the first thing you need to do is to have proper size wheels. Too small wheels try to push through the grass rather than ride on top of it it. This keeps the plane from gaining proper speed. On an LT40 you will need 3" wheels for the mains and 2 3/4" for the front steering wheel. I would get Dubro Lite Weights. For the take try this: elevator at neautral, throttle up to full and steer straight down the runway. When you have reached the 1/2 way point on the runway start to add in up elevator. The plane should leave the ground nicely followed by a smooth climbout. Holding in up elevator right away keeps the plane from gaining proper takeoff speed and the plane may also take off before its ready making control sluggish until it gains speed. Hope this helps, Fast!