Re: Tenkan and Centrifugal Force
I think I agree with your line of thinking Mike. In my opinion and approach to practice of the initial tenkan movement as an entry prior to technique should be about getting off the line-of-attack and moving into a safer position while simulatneously making connection with your partner. Once you've turned your body and accomplished that, whether I throw them forward or lead them around in a circular path (which you can also call tenkan or kaiten at your discretion) is really beside the point because I should have made connection at that point and should be able to do whatever technique I want and/or comes naturally based on the dynamics of the situation. I have seen some people practice that initial tenkan movement with more of a focus on spinning their partner around them instead. However, my observation is they are depending on timing or upper-body strength and it doesn't seem like a particularly valuable practice approach to me, but to each his own.
Regarding using inertial force or centrifugal "force" to me I think that has some place in aikido practice but it may be overstated a bit. If you have a partner of some significant mass you have to have some pretty good angular velocity for the effect of that inertia to be significant on that mass which is at some given radius from the center of the rotational axis. I guess if the attack and the response is dynamic enough it may create enough inertial force or centrifugal "force" for the person to feel they are being thrown out of the rotational sphere by that momentum, but I don't think that happens all too oftern. Usually what I see is that the tenkan, or kaiten movement if you prefer, I think is used to put the uke in momentum that the nage controls (because he has connection with him) and then to put the uke in a kuzushi situation where he loses his balance at which point the nage can change direction (whether it be reversal like for irimi nage or towards the outside of that rotational sphere like kaiten nage) and then throw the uke with ease. To me that interaction is much more common in aikido but then again others may practice differently, so I don't put any absolutes on any of these observations.