Technical When was the radial fan shape in clutch friction faces first appear

Is it to reduce shudder?
I.e they have to go in the correct way around

 

I remember them on cars in the mid 60's so they probably showed up on a few somethings in the early 60's. (So, traditional?)
I bought a base model car to soup up and take to the quarter-mile on weekends. It came with the "base", solid fan. I traded a guy my fan plus a 6-pack for his clutch type fan. Reason? To free up some additional horsepower from the parasitic drag of the solid fan resistance. The question of "shudder" never entered my pea brain. I checked the clutch function numerous times, in the staging lane and back in the pits, enough to convince myself it worked as advertised.
The fan hub with the clutch internals was aluminum with those radial fins to shed heat quickly so it could free-wheel better and more often.

 

Think we are talking 2 different things?



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Maybe more ?
1. Clutch ?
2. Clutch fan ?
3. Fan ?
4. Fan faces ?
5. Appearance ?
6. Beer ?
7. Parasites ?
...

 

clutch driven disc, the friction material has a fan shaped pattern on it.



I think that's what he's talking about. when did they start using this pattern?

 

Are there some scimitar shape fan blades (like on a boat propeller) that I don't know about?

 

Yes, been looking at manual clutches all day, I apologise for the viscous coupling confusion.
I never noticed any difference before between clutch friction surfaces, so asked the question, I am thinking the grooves are for something

 

Doh! Now I get it. Excuse me all the way to Tulsa. My bad.

 

Did I mentioned Beer ?

 

To sling the clutch dust off the clutch face....

 

Maybe some cooling also as some air will pas through at all times..

 

Yep! That too.....

 

Maybe not having to do with "shudder" specifically but it does produce an overlap. I can see how it could smooth things out as well as aid venting and adding strength to the individual pads. It's like a possible refinement with a dose of "it couldn't hurt".