I used to fly quite a lot for business and found the vibrations of some airplanes would give me an erection, especially while sleeping. Being a free-baller my hard on would always be obvious enough to attract attention and I would do little to hide it. The cabin attendants (both male and female) would often smile approvingly and never gave me a look of disgust ... although I suppose that's just being professional.
I found that the planes with engines on the wings such as the Boeing 7xx series (other than the 727) and Airbus would cause the erection effect much more than the planes with engines in the back such as the 727, DC9 and MD80 series. I've had limited experience with L-1011 and DC10 aircraft and don't really remember how much they stimulated my genitals.
Once I was seated next to a young gal from back east on a flight to Las Vegas, she had purchased a first class passage and I had an upgrade to first class. While sharing conversation and adult beverages she put her hand on my leg and moved it up to my semi-erection. We wound up sharing a room in Vegas and she said that much of her motivation to shack up with me was simply to find out what the large lump in my trousers looked like.