Grass field brakes optional will not roll on idle.
SAFETY REGULATIONS FOR MODEL AIRCRAFT
POWERED BY GAS TURBINES
6 - For RC fixed wing aircraft: With the exception of hand-launched aircraft which have no undercarriage
and with a flight weight under 7.5 pounds wet, the model shall be able to come to a controlled stop on
command with the engine at idle on a level hard surface.
How can you meet this requirement without brakes?
I've flown turbines off grass for 10 years. No way I would fly one without brakes.