22 October, Thursday

After achieving straight flight with steering, our full focus was on pitching up and down. When we filled up the balloon this week, it could not lift as much mass as the last time. We realised that atmospheric air can enter our balloon over time, similar to how helium can escape. Thus, even after we filled our half-deflated balloon to its maximum limit, it is unable to lift all of our avionics and camera as air occupies some of the volume on the blimp. Due to time constraints and lack of access to a vacuum, we made a calculated decision to cut a small hole in our blimp to let out most of the air. Then we patched it up just like how we patched up our previous tear. This was an emergency decision and should not be used in standard cases of deflation.

After inflating it with helium again, we attempted flying it upwards by constantly pitching propellers down to push the blimp up.

 

 

As can be seen from the videos, the rotation of the servo motor was limiting the pitch. The vertical force is small and our blimp is unable to efficiently raise its altitude. Instead, its movements were more like a plane taking off.

More importantly, when the propellers are pitched, path deviation is prevalent even with steering. We attributed it to our misalignment of propeller once again, where propeller holder is not parallel to the horizon and the line of action of force on the blimp from thrust does not pass through the CG. Even after multiple manual adjustments were made to the propellers using trial and error, we were still unable to achieve straight flight while pitching.

Finally, we wanted to push our propellers to their limit and kept pitching up to see how high we we could reach and disregarded straight flight.

 

 

After several attempts, we made it to level 3 in the SPMS building. It took around 10 minutes to reach that height but that included time wasted from bumping into the narrow walls and trying to re-orientate the blimp. If it were in a larger open space, the estimated time could be around 4 minutes with respect to the first few seconds of rate of climb where there were no obstacles.

Conclusion

We chose to conclude our project on this prototype. Ultimately, flight performance is a complicated study. There are many factors that affect flight. The blimp was handmade and thus symmetry cannot be guaranteed. Due to this asymmetry, the centre line along the blimp was tough to locate. All components also had to be manually attached to a non-rigid surface. All these imprecisions accumulate which ultimately had a negative impact on flight performance. Even when striving to obtain a straight flight, there is a certain degree of human intervention in the form of steering. This already demonstrates the instability of the blimp, which is exacerbated during pitching as the propellers are running at full throttle. We could only do so much in terms of adjusting and repositioning, and we feel that accomplishing a straight flight with some steering and angled turns is quite a favourable outcome for us although we did not manage to do so during pitching.