Is it possible to power an ultralight airplane with a single-cylinder weed-whacker engine?
There are methods of calculating the power required to fly a particular plane.  In your case, assuming that you'll also need to carry ~18 kg of fuel and a pilot (roundly 75 kg), the answer is NO.  A 2 hp (1.5 kw) power plant will be insufficient to give safe takeoff and climb performance -- with the possible exception of a high performance sailplane airframe (some self-launching sailplanes use ridiculously small engines).