A dyno is very easy to make for aircraft engines, a simple bearing supported mount with an arm, scale, and tachometer will work. They are great for developing powerplants but tend to create more questions than answers and cause confusion for the end user. We already have a lot of people wasting time with tachometers and spring scales instead of going to the field and finding what actually flys best. Some of these guys will send their engines back or discard props before they ever fly them based on a potentially meaningless measurment. Ive found too many good flying engines and props that did not perform very well on a test stand. Maybe I could create a new sport by producing cheap dynos, engine MFGS would hate me.