Cone Cluch problem

[Workx 17]

I was trying to work out a problem from Shingley's book. The problem is below. I calculated cone angle from the length. My answers are not correct. 

I am wondering if I calculated cone angle correctly.  Sin alpha = .5/2.25 = .22 is this correct?

A cone clutch has D = 12 in, d = 11 in, a cone length of 2.25 in, and a coefficient of friction
of 0.28. A torque of 1.8 kip ? in is to be transmitted. For this requirement, estimate the actuating
force and maximum pressure by both models

Edited January 28 by Workx

[monty01 34]

I'm trying to visualize this in my head, but I'm thinking the angle would be arctan(.5/2.25).  Try that and see if you get the correct answer.

[Ramnares P.E. 1,960]

Agree with @monty01

 

[Workx 17]

Got it. Thank you.