Particles - how do I make helicopter wind?

Trying to make a particle system that sends particles away from the center point out and away, but at the same speed. Currently the closest I can get is giving an initial velocity within a range, but that makes many particles go too slow for a convincing effect. I just now tried to give an initial velocity a high value in only one direction and add an initial rotation of 0-360. That didn’t work, and makes me think the initial rotation is more about the plane that the particle material is applied to.

Anyone able to clue me in to the right way? Thanks much.

You can try to use velocity cone module with settings like this:

140043-2017-06-01_1741.jpg

It will move particles inside a cone, oriented to -Z, with constant velocity.