The design of the cooling fins of an air cooled engine is critical to getting the heat out of the engine cylinder and for ensuring that there are no hot spots. Therefore, I’ve been looking at some of the work that people have done in this field and then collating some of the fundamental principles:
- Increasing the number of cooling fins increases the cylinder cooling.
- However, the cooling may decrease with an increased number of fins and reduced spacing at stationary to low speeds. This is due to the fact that the air does not flow well between the fins at low flow speeds.
- At low speeds the temperature on the leeward side increases and this results in cylinder bore distortion.
- A. Biermann, H. Ellerbrock, “The design of fins for air-cooled cylinders“, Nasa Tech Reports, Jan 01, 1941 – this is one of the definitive reports.
- O. Schey, V. Rollin, “The Effect of Baffles on the Temperature Distribution and Heat-transfer Coefficients of Finned Cylinders“, Nasa Tech Reports, Jan 01, 1936 – this is a great paper with images of the test setup and data, great reading material for optimising an air-cooled engine design
Engine Design – a number of short articles discussing aspects of engine design and in particular model engine design.