How do I make roblox model move smoothly?

This is the script I used but some parts of the model moves and the other joins in within a couple tenths of a second causing some kind of lag effect. The script cannot move all the parts of the model at the same time but rather moves some part of it and then other part joins.

local flight = game.Workspace.FlightModel

while wait(.1)do
	flight:SetPrimaryPartCFrame(flight:GetPrimaryPartCFrame() * CFrame.new(0,0,0 + 	-5))
end