Apprentice STS 1.5m Smart Trainer with SAFE RTF BasicOverview Back to Top ^ Introduction The E flite Apprentice STS 1. 5m is based on one of the best platforms ever designed for learning to fly radio controlled (RC) airplanesthe legendary Apprentice S 15e. That model's large size made it an ideal choice for better visibility and the ability to handle more wind while learning to fly at an RC club flying field, and its inherently stable design plus exclusive SAFE (Sensor Assisted Flight Envelope)