how did i make a good cargo plane in 1 attempt after 2-3 years of not being able to make one?

[DracoRen]

so, i made a good cargo plane, flies well, has good cargo entrance/exit stuff, (forgot to put cargo in though)

but for the last 2-3 YEARS they always either explode instantly or plummet into the sea,

what the heck?

(im actually confused)

[steuben]

 "I haven't failed -- I've just found 10,000 that won't work.", Thomas Edison. The man was jerk on the level of Steve Jobs. But, he was right. 
Sometimes it is just the one subtlety that you finally figure out reflexively after  all those attempts.

[Vanamonde]

You are discovering why real planes are designed by people with masters and doctorates in engineering.