The Aerobird and the rest of the hobbyzone plans are designed to climb on full throttle.\

If you look you will see that hte motor is behind the CG and tipped down slightly. So, when you give it full power it pushes down behind the CG and pushes the nose up. That is the way the are designed. You can't really trim it out. You can give it some down elevator when you are flying at full power. That will level it out.