The adventure started when my son broke his wrist while skiing in Tahoe area. Having his right hand in a cast made him very uncomfortable piloting model planes. To ease that discomfort I decided to build him a model, which would be very easy to fly indoor. All model airplanes were to heavy at that time to be capable of flying at crawling slow speed and being able to turn in tight corners at the same time. However if model can be attached to lighter than air balloon it's weight would be reduced and what seemed to be impossible, became doable.
Then I made the first simple version of radio controlled blimp. I bought helium filled latex balloon from Party Store. Two micro servos powered elevator and rudder, and old servo with broken gear became an organ donor for the speed controller and the engine powering a propeller. To adjust the weight of the blimp I used syringe filled with water as a ballast.
The main problem with that blimp was that the latex balloon was leaking helium quite fast. Helium is a gas with very small molecules, what make it lighter than the air but difficult to keep in a thin wall container because these small molecules of helium can sip between particles of thin wall material. I have tried different materials for and finally I decided to use a ready made replacement bag for a toy blimp from local hobby shop.
Another problem I found was yaw control in my blimp. At slow flying speed the ruder was not efficient to turn the blimp around in tight spaces. I decided to use solution from helicopters and instead of ruder I used a tail rotor. Old broken servo had all parts required - motor and the speed controller. Vertical control was still provided by big elevators placed just behind the prop. This was quite effective even in the slow forward speed as big surfaces deflected prop-wash air up or down as required.
The blimp was fun to fly. We were running obstacle course through the house or racing around the room. Even it was not easy to transport (unless i want to refill it with gas) I took it to the office building and played in big open indoor space. It was a lot of fun.
Eventually my son's wrist healed, I got bored and I needed a space for other projects, so the blimp has been retired.