Particle accordian effect

I have a scene where Vipers are shooting out of Galactica’s launch tubes. To do this quickly, I created a single line with a vertex at the exit point of each launch tube, loaded the VIper Mark CVII low ploy model and used dupliverts and some wind.

The problem I get is that the objects are not constant, they move like an inch worm or according speeding up, slowing down, speeding up again.

Is there some easy fix for this?