What does 国产地效船双船 mean? Apparently it means "domestically produced fixed-wing amphibian aircraft" but I can't find this on any dictionary.  Can you break it down for me?
first, it is not 国产地效船双船+试飞. It should be 国产地效船+双船试飞.

Second, if you want to add 双船 to 国产地效船 as a phrase, you should go with 国产地效双（体）船.