First you will need these tools.

Bill Potvin's Setscale(w) (Setscalew.zip) here
Bill Roth's AirEd here
Yusaku Homma's DPED. Latest version V 1.10 here
Jaesen Jones' Quick Combat Editor..Latest Version 2.2.0 here

Step 1. Create the drone in a separate folder

Note: AI drones should preferably be created from aircraft which already have their own accurate DP files.

• Copy/paste the flyable version of the aircraft from the CFS\Aircraft folder to your desktop.
• Rename the folder with an AI suffix so it's recogniseable as a drone. (e.g. Myplane_AI or Myplaneai)
• Paste the renamed folder back into the CFS1\Aircraft folder.
• Open Aircraft.cfg in Notepad & type AI after the title= name. (Myplane AI) Save changes.
• Delete the CDP file in the drone main folder.
  A new rescaled CDP will be created when the drone is selected in CFS.

AI drones still need panel & sound folders to work but the actual files are not used & waste HD space.
To reduce the file size, open the panel & sound folders & delete all the files including CFG files.

Step 2. Rescale the visual model

• Start Setscale(w) & select the MDL file of your drone. Scale 7 is x1 or normal scale for flyable aircraft.
• Type 8 in the New Scale box to rescale it to size 8. Click Update (then Quit to exit).
  (Scale 8 is x2. I think this is about right. Some people prefer Scale 9 or x3)

Step 3. Rescale the DP.

• Start DPED & open the DP file of your drone.
• Check out the Blueprint to make sure the damage boxes are accurate.
• Click Edit/Scale. Click the up arrow until it shows x 2.0 (x 3.0 for Scale 9)
  

• Click OK & save the DP. Exit DPED

Now start CFS & select the drone from the Free Flight menu. Remember it's named Myplane AI
Check out the DP by firing the guns. If the gun positions look OK exit CFS & open the AIR file in AirEd.
Change the Aircraft Type from 0 to 2 to remove it from the Free Flight menu.

Finally add the drone to the QC database with the QC Editor.
Check it out as an Enemy aircraft in QC before using it in your missions.