See Heath and Heath-Henderson. The 28 hp Henderson was used on the Johnson D-1 aircraft and the 24 hp Henderson on the Heath Hummingbird, both presented at the 1924 Lympne meeting.

-Henderson was the manufacturer of the famous motorcycles, and their engines were mainly adapted for aviation by Heath.

-They were air-cooled engines with four upright cylinders in line. The 28 hp engine was also mounted on the Driggs-Dart.

From Appendix 6: The engines that were adapted for aviation by Henderson (see Heath as well) were coming from the motorcycle of the same name.

“Logo”

“Henderson motorcycle”

-It is not surprising that the engine's four in-line, air-cooled cylinders, in addition to the direct output of the power shaft made it ideal for adapting and installing it on light and sport aircraft.