ORIGINAL: ameyam
The NGH 9cc weighs about the same a 46 size glow. Would it be a replacement for a 55ax?
Ameyam
That would depend on what your requirements are
If you are looking for a fishing weight - most likely it would work just as well (but that would be a waste of a 55AX).
If you are looking at placing it on a plane that you wish to fly - Consider the entire weight, engine, ignition, ignition power supply (Even an IBEC cables and switch adds some weight).
For 3D (which seems to be your preference) wing loading is pretty important.