I've read all the various comments about the Saito and YS , "91 to 180" but what I haven't found is someone that has a OS 91 4 stroke in the ucd. How does it fly with the OS. The video that GP has and the instructions indicate the 91 should do well but that certainly isn't the impression I get from reading the various threads. I have a almost new OS and my intention is to use it but if the results are going to be terrible I might want to re-think this. Comments?

I am in a very similar boat as you... only with the Y.S. 91. I've tried to read all the threads and it's still hard to come to a conclusion at the end due to there being so many different pilots, flying conditions, etc. Just when I think I'm seeing a pattern... bam, it changes.

My choices were either the Y.S. 91AC which I already have (through a trade) but have not used or a Saito 100 which I would buy new. I decided on the 100 simply due to the fact that if I will be buying, I will buy the 100 over any of the 91s and from what I've seen both the Saitos and O.S. models perform very well in other planes. I persoanally own a Saito .72 and love it. I've owned O.S. 2-strokes and would almost buy nothing else for 2-strokes. I've not owned a 4-stroke O.S. but see many at our field that also perform very well. In fact, the only UCD that I've actually seen fly in person is at our field with an O.S. 91 non-pumped and it seems to perform very well - but that's only observation - not being the pilot. It seems to hover well and pull out well but I've never witnessed any throttle positions. Definitely sounds smooth. That's for sure!

Although my Y.S. is heavier, one reason I'm leaning toward it is that it's pumped. I'm not much interested in always making sure that the low needle is beyond human perfection for inverted running without loading up. I've seen people experience that at the field with various brands and also saw UCD posts that were similar.

Soooo.... I'm still on the fence a little but think I will indeed try the engine I already have. Are you looking for 3D out of that O.S.?

Oh, and my UCD just arrived today and looks great!

-s

I have an OS .91FS in my UCD and have been very Pleased.It is not a rocket out of a hover but it is not scary either.Has plenty power to keep you out of trouble.I run an APC 15x4W and 30% CoolPower.If you already have the OS I would definitely use it,you won't be sorry.JMO,
Mike.

I too use the SurpassII non pumped on my UCD, and I agree the performance is great. I've tried everything from a 14x6 thru a 16x4, and I felt the 15x4 (all APCs) provided the best static thrust for 3d flight. The plane flew regular aerobatics better on a 15x6 though. Plenty of power to hover and pull out as mentioned above. Not a rocket, but confident enough for low level stuff. I use Wildcat 10% in mine.

Thx, I'm going to bolt on the OS and let it rip.

Don't bother with the factory CG either, go right to 6" for improved 3D and hovering, does not effect slow speed handling at all. I have my battery mounted in a hatch halfway between the trailing edge of the wing and leading edge of the stab to get to 6" w/o adding weight.

I have the pumped version of the O.S. .91 FS in my UCD3D. I have been extremely pleased with the performance. It is easy to set up, reliable, and hovers great. It does not rocket out of hover, but it does pull out of a hover. Engine has never missed a beat. I love doing low and slow fly bys and pull into a "wall" then 1/4 turn into a hover about 25' off the ground. I am buy no means an expert 3D flier. The UCD3D has really helped me to learn some basic 3D stuff though. If ya got it...bolt it on!