***Meaning*** :: <u>L</u>ycoming O-360 180hp 4cyl, <u>H</u>orizontally opposed, <u>A</u>ir cooled, <u>N</u>ormally aspirated, <u>D</u>irect drive Used to remember info about the Piper Archer II or Cessna 172 #engine ### Meaning for O, I, etc If you'd like to learn more about the meaning of the letters in a Lycoming engine model, they have a guide here: [CERTIFICATED AIRCRAFT ENGINES](https://www.lycoming.com/sites/default/files/attachments/SSP-110-2%2520Certified%2520Engines.pdf) In particular, O=horizontally opposed and I=fuel injected. #acronym