The most useful advice I got before the one doors-off photo flight I took - probably 30 years ago, to get overall photographs of a large civic event (several hundred thousand in the area we were covering) from the air - was to bring some duct tape. Explanation: use it to tape the seatbelt buckle closed once you're strapped in, because there's a risk of your camera strap catching on it and pulling it open while you move around to get a shot. I thought you'd have to be pretty careless to let that happen, but I brought the tape anyway and used it as directed. And yep - my strap caught on the buckle at one point during the flight. Made a believer out of me.

As for equipment - it was long enough ago that I was using Nikons and Ektachrome (provided by the event) and almost certainly a mid-range Nikon zoom as they were interested in the overall crowd, not small details from above. It was a sunny day and I had polarizers, but even with one my recollection of the slides is that everything looked hazy, compared to the shots I took on the ground during the rest of the event. Perhaps not surprising given it was St. Louis in the summer, next to the Mississippi River.

...even BITD and using film I got pretty good results (and, yes, I'm flying the aircraft all trimmed up with the collective held with my left knee). I'm in a four-blade OH-6A "Loach" which didn't have a whole lot of vibrations (unless something was really wrong like blades shot up) and I'll wager tour aircraft are very much like that. That said, even back then I tried to get as much shutter as possible (I'm around a 250th for this one) so with today's equipment if I went up I'd use an 18-400 or somesuch and push the shutter over 1/1000th anyway...I'm pretty sure vibration effects would be minimized. Check that front seat guy, he likes me. ;0)

As a helicopter pilot, I can tell you that long lenses and helicopters aren’t a good mix. There are vibrations you don’t experience with an airplane, no matter how smooth the helicopter is. Also, there is limited room in the helicopter, and likely there will be others in there with you. I would recommend either a 50mm lens or something along the lines of a 24-70. Longer lenses can reward you with blurry images due to the vibrations a helicopter makes. And a whole array of lenses will be difficult to work with. If you have the ship all to yourself, that would be a different story.