If you took an existing 3D model and added retracts, the laws of physics say that every ounce of added weight must be compensated for by an additional ounce of thrust in order to retain 3D qualities...
Add 8 ounces of retracts, servos, linkage, air tank, valving and hoses and you need to find another half pound of thrust... Hmm... maybe a JATO bottle???
Cheers!
Jim