If I'm picturing what you're explaining correctly, I think this would be difficult. Suddenly accelerating the arm from zero to hundreds of mph would put immense stress on the arm, not to mention whatever you're planning on using to transfer that energy (you kinda hand waved that bit).
I think your assessment is correct about the energy losses. I'm just not sure about the fix.
I think your assessment is correct about the energy losses. I'm just not sure about the fix.