An aircraft designed to take off nearly vertically, transition to fixed wing flight, and land nearly vertically.
Search and rescue wants an aircraft that launches without a runway and still cruises efficiently. A tailsitter is a way to achieve both objectives, but is difficult to design and fly because the aircraft must transition between distinct flight modes.
I built and tested four prototypes of these types of aircraft, iterating on the design each time. While I learned a lot about the design of these aircraft through iterative prototyping, I wasn't able to get transition working before I went off to college, sticking with hand launches. Now that I've completed a mechanical engineering degree, I aim to come back to this project soon.
I was still in high school when I first attempted this, so I would change pretty much everything about my approach knowing what I know now. First of all, I would define a thrust to weight ratio that gives more than enough margin for vertical flight, and then I would focus on building a stiff frame with oversized control surfaces and a CG slightly in front of the quarter chord. I would stick with a moderate sweep back and a Clark-Y airfoil for the first prototypes, and focus on making something durable so that I can nail down the parameters of transition like transition time and minimum airspeed.
The first airframe existed to fly the electronics rather than the mission. Its wing was far too small to sustain forward flight, so hovering was all it was ever going to do.
The second airframe took off vertically and rotated into forward flight, and shortly afterwards nose-dived. It stalled; the control surfaces were too small to bring it back; and the centre of gravity sat too far forward.
The third airframe changed the sweep angle and enlarged the control surfaces. It failed the same way, for the reason neither change touched: not enough airspeed to sustain forward flight.
The fourth airframe reduced the sweep again and grew the control surfaces again, and went up by hand. The point of it was to measure the airspeed forward flight actually needs rather than keep guessing at it.