The R/C Universe review on this plane used an OS .91 Surpass w/o pump. The author said the performance was awesome. He used a 15x6 wooden prop. My UCD is almost ready for the flying field. I will be using an OS .91 Surpass w/o pump. I'm going to start out with a 14x6 APC prop, then graduate to an APC 15x6. Will let you know how it goes. From all the forums I have read, most flyers are using the OS .91 Surpass, or a Saito .91 or 100 with a 15x4 or 15x6 prop. Most flyers seem to love the plane. I'm sure I will too!