My hot air balloon flies^^

My final project for eas140 is to make a hot air balloon and then write a 4 pages essay on problems related to my choice of engineering which is aerospace engineering. We did the whole plan and went on to buy the materials. We did all calculations and the hot air balloon was suppose to float. We made 3 balloons and all 3 sink instead of floating. So we gave up and go to sch to hand in the project. But a miracle happened. When it was our turn to show the balloon, it floated. We were damn lucky. Was wondering why it didn't float when we tryout in my dorm ^^ out of 10 teams only 3 floated ^^

Previous Projects:

Flight.

Portable shelter.

Electric case studies.

Making of bio diesel.