Waiting for the SkyBolts to come in, and gathering up the misc. stuff for the build, this is my first Bipe and I have a YS 91 that I will be using. Read close to all the post here and would like to narrow down the props to just maybe two that would fit the build. Since this is my first bipe, I am looking for something a little tame, predictiable and not a rocket to land. I'm more of a sport flier. from what I read the 91 surpass likes a 14-8 to a 15-6. i still use wood props but am open to APC. just want something that wont cause problems.
thanks
Tom

I've been using 14X6 props on my .91 Surpass.

I have the same plane with a Saito 91. Using a 14x6 APC

Hey TomH,

I'm a little confused about your post. In your first sentence, you say you have a YS 91 and near the end of the post you say you have a 91 Surpass. The difference between a YS91 and an "OS"91 Surpass are like trying to compare an apple to an orange. The power difference is incredible, especially if you have the YS 91 AC which has an air chamber on the rear if the motor between the carburetor and the cylinder that actually pressurizes the air / fuel mixture going into the engine which is similar to the way a supercharger works on a dragster. I had a kit built Sig Skybolt with an OS-91 Surpass on it and it was plenty of motor for the plane even though it was slightly on the heavy side since it was a kit. I also have a YS 91 AC on the front of a Great Planes Big Stick and it the only plane I've ever had that I would call overpowered and I rarely go over 1/2 throttle when I fly it. My YS has a 14x8 APC on it and I wouldn't use anything smaller that a 14 x 6. A YS 91 AC can turn a prop as big as a 14x10-14. A YS 91 in a Skybolt would be an AWESOME combination IMHO and I'm confident that you'd love it too.

A little trick that you may not be aware of if you have the YS is to wrap the fuel tank with reinforced packing tape BEFORE you put the foam around it so the pump doesn't split the tank. Now don't laugh at what I just typed. I have seen it happen with a YS 63 on a Mojo.

Good luck with your Skybolt and keep us posted on your airplane.................

Take care,
David

Ya your right, I got both motors, one is going on a Astro hog bipe, and the other is for the Skybolt, just got to choose which one goes on which plane. I guess there could be worse problems. I also just bought the Skybolt kit as well.

Hey Tom,

If it were me, I'd put your YS in the Skybolt since it would appreciate the increase in power and put the OS in your Astro Hog Bipe which is more of a docile flying airplane. Just my $0.02 cents

Take care,
David

With either engine, you will need to try different props which one works for the kind of flying you want to do. For example, I am using the OS FS 91SII on a Reactor 46 3D and a 14x6 MAS. I tried the 15x6 and 15x4 props and the engine would scream and the airplane wouldnt have any traction. I tried a 14x4 APC and the airplane wouldnt hover. I compromised to the 14x6 and if the engine is setup properly, I find it to be the best compromise.

Bipes are very draggy airframes, so I would err on a larger prop. Depending on which make and type you use your results will be different. If you have RF, you could try the Skybolt in it with the FS91 and different size props and use that as a startpoint

Ameyam

Tom, YS should spin a 15x8 (I like the APC). OS should use 14x6 as others have stated. The YS has the power of a 1.20 of other brands. I have the Skybolt ARF with an OS 91, spin 14x6 MAS, and it has plenty of power and balanced perfectly. The YS is a little heavier. If you build the Skybolt kit (not the ARF) it will be heavier than the ARF, and might make better use of the YS power.

use the YS and 15x6 maybe 16x6, maybe 7 and 8 pitches, try 3 or 4 different props of makes, pitch and wood.
Xoar makes some good props that could work well for you.
Ameyam, this bipe is not draggy at all, its quite quick and slick like a sport monowing.

I have the YS 91 AC in a 56" span scale acro sport bipe near similar spec to the Skybolt. I originally flew it with the OS 91 FS in and experimenting prop wise with the YS led me to larger finer pitch ie 15x8 and 16x6 especially as nitro wing suggested... 16x6 was a great combo for this size bipe. I found aileron flutter became a worry at the higher speeds with smaller higher pitched props. Slow it down and have fun with the great vertical and prop hanging on offer with bigger prop ;o)