https://www.youtube.com/watch?v=YwXLSNh9-cU https://www.youtube.com/watch?v=S1ke1xQ-rmY The first in my model aircraft compressed air powered engine series, "Model Aircraft Styled Air Engine, Experimental" was the result of yet another challenge; build a single cylinder compressed air engine using the fewest number of parts, and all 100% 3D printed. Weighing in at a mere .8 ounces (25 grams), this engine requires only 8 3D printed parts (only one more than my "3D Printed "Wobbler" Style Air Engine" design), no purchased parts, and incorporates a rotary valve (as I used before in my "Four Cylinder Air Engine, Experimental" design) with a difference. The rotary valve used in this design was inspired by the 1933 work of Joseph S. Ott (and no, I wasn't around then to see it) which utilizes the propeller axle as both an axle and a valve. The valve timing is determined by the angular offset between the flat surfaces on the axle and the pin on the journal. As an added bonus, the design provides a fairly decent exhaust system. I learned quite a lot during the design of this engine, and used that knowledge in subsequent engine designs for model aircraft use. While this early version will not necessarily propel an aircraft, it does make quite a conversation piece around my workshop. It will indeed test your 3D printer capabilities. You will need a 1/4" threaded compressor adapter and compressor to operate this model. If you do not wish to 3D print the propeller, a 6 by 5.5 E propeller with a 6.2mm center hole will work. As is usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make mistakes in plenty. Designed using Autodesk Fusion 360, sliced using Cura 3.0.4 and printed in PLA and PVA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.