I am flying a plan in RC mode (without any flight controller) when I loss signal and it crashes the throttle is still high. Is there any way to make the throttle cut when it loses signal ? I am using FrSky X8R receiver and Taranis QX7 transmitter.
The receiver has failsafe functionally that can output predetermined signals in the event of signal loss.
Check out the receiver’s manual: https://www.frsky-rc.com/wp-content/uploads/2017/07/Manual/X8R.pdf
On my planes I set FS with the throttle down, slight up elevator and slight left or right aileron. That way it kind of circles around rather than floats off into the far end of the field 
Thank you very much for your help
For your TX and RX set them to “No pulses”.
When bench testing (turning off the transmitter) you’ll see an error in the MissionPlanner HUD for No RC receiver, as if you have completely disconnected it.