The Thunder Tiger Lazy Tiger is the perfect plane for the OS 40 LA. They recommend a .25 size, but the 40 gives it the power to do anything. I had the same delimma of what to do with the trainer engine. Trust me, you will have a blast with this plane and that engine. By the way, the OS LA series are some of the most dependable and durable engines there are. I have seen a lot of them smack the ground really hard and have no problem starting once you clean the dirt out of the carb. Happy flying!