What do helicopter size numbers mean?

[boomer23059]

I'm new to heli's - having a blast with a Blade CX. I'm doing a lot of reading and getting my bearings, but I don't understand the reference to 30, 50, 60, and 90 size helicopters. I get that the bigger number is a bigger heli, but what does the number correspond to?

[AaronS]

the numbers you are asking about refer to the motor size in cubic inches. for instance the 30 would be a 0.30 cubic inch displacement engine, and so on for the 50, 60 and 90. the other numbers that are thrown around are the 300, 400, 600 etc for electrics, and unfortunatly, they do not directly corrospond with each other, but to get you started, the 300 size could also be called "micro", and models like the Blade CP or Hummingbird would fit this class. An example of 400 size models would be the T-REX 450, MX 400 and could be called "mini" and the 600 size models like the T-REX 600 and Logo 10 to 14 would fall somewhere in between a 30 and 50 size nitro (fuel powered) model.