[TCML] Why don't big Tesla coils use helical primaries?

[James Hutton <b-u-r-t-o-n-boy@xxxxxxxxxxx>]

Hello,
so I was just wondering why no one uses helical coils with insulated wire like this: http://www.johndyer.com/MakerFaireJD06.jpgwhen building big static gap tesla coils.
I have seen tons of small sgtc's with a primary like that, but it seems that with bigger sgtc's people always use copper tubing and carefully space them in a flat or conical spiral.
I don't understand this. Helical coils with insulated wire are so much easier to make, they cost less, their more durable, look better, and take up much less space.
Is it because helical coils are less efficient?
I need to build someone a nice looking tesla coil that is 900w (15/60nst) and makes ~4ft lightning. I dont want the base looking huge, and I can't spend a whole bunch of money on 50ft of copper tubing.
Should I still go with a pancake type primary using the usual copper tubing? or can I just get a pvc pipe wider then my secondary and wind an insulated wire around it/
and theres no way I'm air winding a copper tubing helical coil :P I dont know how people have the patience for that!
thanks for the help! 		 	   		  _______________________________________________
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