A human-powered aircraft (HPA) is an aircraft powered by direct human energy and the force of gravity; the thrust provided by the human may be the only source; however a hang glider that is partially powered by pilot power is a human-powered aircraft where the flight path can be enhanced more than if the hang glider had not been assisted by human power. Likewise HPA inevitably experience assist from thermals or rising air currents. Pure HPA do not use hybrid flows of energy for thrust.
