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-   -   Suggested Engine Size for Bi-plane (https://www.rcuniverse.com/forum/questions-answers-154/4875173-suggested-engine-size-bi-plane.html)

ezurk1 10-16-2006 01:52 PM

Suggested Engine Size for Bi-plane
I have a Goldberg Ultimate Bi that has never been flown and it has a Super Tiger Gs-90 2-stroke installed. I have just "acquired" a new Magnum XL-91 4 stroke. I don't want to guess at which engine would be more appropriate for this plane, but my goal is to have better climbing power than speed. The Super Tiger instructions say to run a 13x8 prop. The Magnum recommends up to a 14x8. Any suggestions on which engine to use? Or should I forget both engines and step up to a 1.20 4-stroke.

hogflyer 10-16-2006 03:04 PM

RE: Suggested Engine Size for Bi-plane

Welcome to RCU. I guess the first thing is are you experienced in R/C aircraft, or did you intend on using the Ultimate for a trainer? The reason I ask is your first post is in the beginners forum and it's not uncommon for a beginner to get a plane that is not a trainer.

The Ultimate is more like a 3rd or 4th plane. If you have no experience I'd give it about a 5 second life span if you try to fly it on your own. Sorry if I'm bursting your bubble, but I'd hate to see you start off on the wrong plane. But you have landed in the right area to get all the info you need to get started in R/C aircraft.


Charlie P. 10-16-2006 03:30 PM

RE: Suggested Engine Size for Bi-plane

. . . but my goal is to have better climbing power than speed.
Speed (as in the kind that "is life") gives you momentum, which carries into climb. If you're doing "high alpha" or whatever they call the wing stalled, nose up maneuvers you would benefit from the 4-stroke turning the larger prop. To pull you up from a low inertia state.

campbec 10-16-2006 03:33 PM

RE: Suggested Engine Size for Bi-plane
Hi ezurk1,

Hogflyer has given you excellent advice if you are a beginner?

If not and you have posted in this forum by mistake I would recommend the ST from the two choices you have identified however IMHO a 125A Saito or similar light powerful four stroke would be my choice. I'm biased as I am very happy with the 125A Saito in my Ultimate built from a Cg kit.



daveopam 10-16-2006 06:03 PM

RE: Suggested Engine Size for Bi-plane
I have a ST 90 on my ULT built from a kit. It is a good combo unless you want to hover a lot. I run a 14x6 prop on mine. It needs 90% throttle to hover. I have heard a 15x4W is a better hovering prop for this engine. I just have not tried one. I have other 3D planes and don't use the ULT to 3D. Of the two engines you have the ST would be my pic. If I were starting from scratch the Saito 1.25 would be my choice.


ezurk1 10-17-2006 06:39 AM

RE: Suggested Engine Size for Bi-plane
Thank you all for your inputs. This was my first post on this forum and maybe I shouldn't have chose the "beginner" catagory for a question like this. I recently took up flying again after a 7 year break. Got back into it with a U-Can-Do .46 and have picked up where I left off. I wouldn't have dreamed to fly the Ultimate until I felt that the skills were back! Anyone know where I can get a good deal on a YS 1.25...? Thanks again

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