If Sam plays with any toy, it will be his remote controlled airplane.
Why can't we use would be instead of will be ?
Grammar rules for conditionals are some of the hardest to understand.
The sentence you provided is a real conditional, the outcome of which will happen in the future the moment Sam plays with a toy.
If you wanted to express an unreal conditional, one that did not come true, it might look like:
"If Sam had played with any toy, it would
have been his remote controlled airplane" (this did not happen - Sam did not play with a toy)
Will = real conditional
Would = unreal conditional
Check this out: gmat-grammar-book-modal-auxiliary-verbs-100606.html