i have a extra 300s with a OS YS90, basically it came with a hitek reciever from the guy i boght it from, which is not compatible with my jr radio, so i got a jr micro reciever 6 channel FM. works perfect, but i just read the instructions and it says to only put them in gliders, parkflyers, and 30 size nitros. how the heck does a reciever know the difference between a 30 and a 90?