The first question is - How much does the aircraft weigh with full onboard compliments? Next, if your planning on utilizing 4 turbines you'll divide your weight factor by 4 to determine the thrust needed for your aircraft. Remember that the AMA rules dictate a 1:1 thrust ratio. Simply put, if the aircraft's total weight is say, 20lbs, your turbine should not have a higher thrust value than 20 lbs. So, say your aircraft weighs 48lbs, you can go with 4
12 lb thrust engines, and so on. Hope this helps. Say, I'd love to see some pics of these babies - I'm sure they are quite impressive! Let me know if I can be of further help.

Todd