Piper is an American cab-forward tank steam engine that first appeared in Season 3. She is the sixth trainee in the Series.
Fresh out of the "training yards", Piper is the most innocent out of the Crotoonians. A wide-eyed idealist, Piper sees every new day as magical and is always looking to learn new things from both young and old engines and crew mates. Working at one of Crotoonia's biggest stations may be a tough job, but Piper is always friendly and offering to help anyone who needs any assistance. Piper is also unique for being the only Crotoonian to burn vegetable oil, which makes her quite a standout from other engines, but relegates her work to mainly shunting. Piper is eager to see more of Crotoonia, but it'll take a lot of vegetable oil to do it!
Piper is based on the North Pacific Coast Railroad Cab-Forward 4-4-0 No. 21 "Thomas-Stetson", a rebuild of NPCRR #5 which had been wrecked in 1897. An innovative engine built by Bill Thomas, it is considered the first cab-forward locomotive and was one of the first oil burners, as well as the first locomotive to use a marine boiler. The engine had insufficient adhesion weight and its oil burners were prone to damage due their proximity to its water tubes, and was unpopular with crews, its unusual appearance earning it the nickname "The Freak". #21 was scrapped in 1905.
- Piper is the youngest steam engine in Chuggington.
- She is the only steam engine that hasn't lived in the old town of Chuggington.
- She is the only Trainee that doesn't have an Interactive Model so far.
- She's possibly an experimental electric-steam engine, considering the fact that she has an electric firebox and a monitor in her cab.
- Her siderods are often still, but her wheels are always moving.
- As of The Tootington Tunnel Piper still needs her training wheels.
- In German, she is called "Betty", in Polish "Pyza".
- She is cab-forward like Lexi from Thomas & Friends Journey Beyond Sodor.