Hey Joe (Isn't that a song?)
For the life of me I have never been able to sleep on a plane regardless of how tired or are long I have gone without sleep. Same for in a car which is good, especially if you are the driver!
When I travel to a foreign country I always bring a sleep aide with me which I never use at home. After traveling 5,000 miles from the US and being awake for 30 hours or so one would think falling a sleep would be easy. Not for me! The adrenaline is still pumping, you are in a new country, in a hotel bed and you lay there wondering why you can't sleep. I pop a pill and before you know it I'm fast asleep.
I only use a sleep aide when I have an exceptionally early hour to get up to ensure I get enough sleep the night before which will be the case this October for my 6 a.m. flight back to the US. I'll take a pill before going to bed around 9 p.m. and get at least 6 hours of sleep and will be woken up by a wake-up call.
I'm not an advocate of using drugs for no reason but a sleep aide does come in handy when traveling overseas.