Why is bad!?

[CheiN]

  
local screenWidth, screenHeight = getScreenSize ( ) 
  
function copter (killer) 
local killer = getPlayerName 
   dxDrawText ( helid, 44, screenHeight - 43, screenWidth, screenHeight, tocolor ( 255, 255, 255, 255 ), 1, "pricedown" )  
end 
addEventHandler ("onClientPlayerHeliKilled", getRootElement(), copter) 

[Cadu12]

Please read wiki:

In order for the text to stay visible continuously, you need to call this function with the same parameters on each frame update (see onClientRender).

Your code is wrong at all.

[Jaysds1]

Cadu12 is right,

here's some functions/event that you need:

onClientRender

dxDrawText 
getPlayerName 
guiGetScreenSize 

[DNL291]

local screenWidth, screenHeight = guiGetScreenSize ( )  
local time = 8000 
  
function copter (killerHeli) 
local killedName = getPlayerName(source) 
   dxDrawText( killedName .." ".. killerHeli, 44, screenHeight - 43, screenWidth, screenHeight, tocolor ( 255, 255, 255, 255 ), 1, "pricedown" )  
end 
  
addEventHandler( "onClientPlayerHeliKilled", root,  
function () 
    addEventHandler( "onClientRender", root, copter) 
    setTimer( function() 
        removeEventHandler( "onClientRender", root, copter) 
    end, time, 1 
    ) 
end 
) 

[TAPL]

local screenWidth, screenHeight = guiGetScreenSize()  
local time = 8000 
local killedName = "" 
  
function copter () 
     dxDrawText(killedName, 44, screenHeight - 43, screenWidth, screenHeight, tocolor (255, 255, 255, 255), 1, "pricedown") 
end 
addEventHandler("onClientRender", root, copter) 
  
addEventHandler("onClientPlayerHeliKilled", root, 
function () 
     killedName = getPlayerName(source) 
     setTimer(function() 
          killedName = "" 
     end, time, 1) 
end)