1965 M20C....what is this?

[piperpainter]

I always forget to ask my mechanic what this hole is for and now im deployed so there is no asking still! Any ideas would be great, if not i'll find out in a few weeks! haha Thanks!

[Piloto]

The small hole is for the generator ventilation. A small duct hose is routed to the back side of the generator where a band with a hose nipple is attached for cooling of the commutator brushes.

José

 

[mjc]

Yep, and on planes made after they switched to alternators, the duct is routed to the cooling shroud on the back of the alternator!

[piperpainter]

ohhh i see!! So maybe you will know this question. I just got the alternator mod. Will that require the duct still or no? I know you said the factory one did require the duct, but maybe the mod is different!

[Piloto]

Alternators do not have commutators but slip rings for the rotor. So there is no need for cooling on the back. However the stator winding can get hot during load. This is why at the front pulley there is a fan attached to it. Just make sure the forward section of the alternator is getting some airflow.

José

 

[piperpainter]

Thanks for the info. I'll see what the new Alternator requires when I get home! Otherwise I wonder if that can be closed or redirected!

[mjc]

I think it depends on the alternator. When I bought the airplane, it had a Prestolite alternator with a fan in front and the duct connected to a flange on the back. I later installed a Plane Power alternator, with no fan in front, but there was a flange in back for the duct, an instructions to connect it.