How to increase rotation speed?


so i am trying to increase the rotation speed of my flying character via a timeline. I am not talking about increasing the play rate (although it is in my Screenshot).
I want to gradually increase the rotation speed depending on how long a button is held down.
So basically this means that i want the y value of the timeline function to increase.
Or is there another way to do such a thing?
It is also important that the impulse doesn’t fade away as i release the button.

So i managed to set the rotation rate on key time down. Now it is spinning faster and faster when i hold the key down.
However there is still the problem that the movement stops when i release the button. That should not be. It should hold its impulse.
Looping doesnt make that better.
I need somehow to hold the value of the spinning rate once i release the button. HOw would i do that?
Any help appreciated.