I think Aerosplat & Can 773 has it right. You need prop blast & lots of it. Fly close to stall speed

Some hints... Fly left to right (when you add power an airplane it should yaw to the left) Enter slowly at less than 1/4 power, as soon as the plane is KE...full rudder & full power. That should get you vertical. With enough power you will be on the up line. When you get to the top you will need opposite rudder to keep the loop round. About the 45-degree down line hammer the full rudder and full throttle again. That's the point you will find out if you plane will really KE loop