The International Cessna^® 170 Association

I’m thinking they want to cool the diodes doing the energy conversion.

Yeah, it seems that Cessna is taking a page from the oil screen blast tube blueprint, trying to blast cooler air on the rear of the housing in the area of the rectifier. There are actually three iterations of how Cessna attached the blast tube on these C-172's. I had assumed that the shroud was the final version but the IPC shows that it was actually the first. It was only used on 33 planes on the 1966 C-172G and the serial numbers are non-contiguous. My guess is that a customer could choose the tried and true generator or opt for the new-fangled alternator. The second version mounted directly to one of the three thru bolts that hold the alternator case halves together. Most of the 1967 C-172H models (404 units) used this mounting method. Before Cessna switched to the Lycoming engine in 1968 they mounted the last 22 alternator blast tube ducts in 1967 using half clamps around a through bolt. This is the method shown in SK172-22M.If this were an experimental I would consider adding vent holes around the circumference of the rear housing. That way air coming from the front fan or the rear ducting would have an exit.

c170b53 wrote: ↑Sun Jul 14, 2024 2:26 pm I’m thinking they want to cool the diodes doing the energy conversion.

I agree that the diodes and brushes are the most-needful of cooling…(and is why the original generators route cooling air aft-to-fwd…to cool the brushes/commutator)…Why would the fan-blades appear to be designed so-as to take air IN…moving air toward the rear? There must be something missing in our interpretation or appearance of the fan design.
Although it appears this fan (by rotating CCW) would draw air IN… I wonder if the inner-portion of those fan blades don’t “scoop” air from within the core and expel the hot air. If it could be spun on the bench and air-flow checked… it may provide the answer.