Yes, It does help to have some momentum but you don't have to be going too fast. I'm never real fast going downhill on my mountain bike anymore TOO OLD!

Anyway, shift your body weight way off the back of the saddle; you can rest your leg against the saddle to stabilize yourself; bend your elbows and your legs slightly so they will take up the impact when you hit the ground on the other side of the drop off. scrub off speed before you get to the drop off (not too much); then get OFF YOUR BRAKES, don't touch them, and especially your front brake. If you have to take your fingers off the front brake so you have no chance of grabbing it, do it. I do this some times cause that front brake after a drop off can put you over the handlebars.

Next thing is visualize this drop off when you are thinking about doing these, think about how smooth it can be just off the end and float on down. Think about relaxing with the bike, letting the bike just roll.

Wish I was closer to you and we could go out and practice. Hope this helps you.