Hey Udi,

I hope this UCD is making up for your loss of Zero. I have flown my UCD 60 w/ a 2-stroke ASP 91 (same as Magnum). It will swing APC 15x4W @ close to 11k, which is a lot of thrust. The spool up and down response is however a sorry matter. You should give Pro Zinger 15x4 a try. This will give you a little higher rpm, maybe a little less thrust, but instant response.

Right now I have YS 110 w/ APC 16x6 on my UCD. It's such a joy to fly. I also tried a Zinger 16x5 w/ YS 110, swinging at about 9300 rpm. The Magnum 91 2-stroke should also spin it at least 9000 rpm, which is adequate power for UCD 60. With a 2-stroke 91, you are not hurting for thrust, but for response. So get a light, large, low pitch prop and you'll be fine.