Genghis, Thank you for those few kind words.
Actually I've not had that many trip articles published, and those that have been accepted have been relatively unusual trips; it's a very competitive market. But I've been writing bits and pieces for all sorts of magazines for years, so I'll tell you what I know.
Pilot still pay on acceptance, at least in theory. For my last article I had to remind them several times, but I still got paid before publication, though since publication was nearly a year after I sent it.... Pay seems to have gone down a bit with the new editor, though I can't be sure of that. Flyer - and most other mags on any subject whatsoever - pay on publication, and it's normal to have to chase up payment.
I long ago gave up expecting to make much money out of magazine articles. It takes a lot of time to write to the standard they require - I edit and re-edit, because if I don't they will, and I probably won't like the result. As a result they rarely edit my stuff much...but that doesn't mean I get everything accepted. I'm more likely to phone and ask if they'd like an article than send in a proposal, but I've sent stuff on spec too - either way you can't be sure if it'll be accepted, but at least you'll find out if they have a year backlog of travel articles if you phone or write first.
One more thing...be very careful if anything you write could conceivably be construed as taking risks or bad airmanship or similar - someone is sure to write in and criticise you!
And after all that, good luck!