Easier way to write an array(Uint8)

It seems like it should be straight forward to write Bytes to a File.

outy = Array(UInt8).new
File.open("abc", "w").write(outy)

But it yields this:

Error: expected argument #1 to 'File#write' to be Slice(UInt8), not Array(UInt8)

Apparently requiring some extra work (and magic) to use. There is also a write_bytes method but it also yields Error: undefined method 'to_io' for Array(UInt8)

Might be nice to make this easier. Cheers!