RCU Forums - View Single Post - Remove fly wheel and go from 3-blade prop to 2-blade prop will it increase power?
Old 05-07-2016 | 09:26 AM
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jester_s1
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Also, there isn't a particular brand of prop that works best, is most efficient, or "best" in any other category. When you get down into the details of maximizing the performance of any given plane, you'll find that props in the same size from different manufacturers give you different performance in different ways. In very general terms, the APC props are harder for your engine to swing through the air than the same size MAS "S" series props or just about anything else. So we say they load your engine more. If your engine is at its torque sweet spot in flight with the APC prop, then that prop will probably give you the most top speed and since it's a wide bladed prop will probably also accelerate your plane better. But going to the other extreme, the MAS "Scimitar" series props are very narrow and thin, so they load your engine a lot less. So if you're choosing props on the big side of what's acceptable, you will often find that the Scimitar lets the engine get into its happy RPM range in flight and so therefore gives you more top speed and more vertical pull. Getting deeper into it, you may find that experimenting with different brands or even different styles within a single brand becomes a trade off. One prop may accelerate your plane better and pull vertical better while the other gives you more top end speed. Then there are noise considerations, cost, idling characteristics, deceleration, and landing performance to consider as well.
So I'll share a personal anecdote that hopefully makes this all make sense. I fly a Kaos in SPA competitions. I flew it for a long time with a MAS "S" series prop, 10x6 size. I had tried a 10x7, but the performance was horrible because the engine didn't have the torque to get into its peak power RPM in flight. Then a know it all came along and told me I should be flying with an APC prop. So I tried a 10x6 APC and found that the engine RPM was lower in flight, top speed felt very close to the same, but the plane wouldn't pull vertical as well. So I concluded that the APC was loading the engine too much, and I didn't want to go down to a 10x5. So then I tried a MAS Scimitar prop, also in a 10x6. The engine was absolutely screaming in flight, had a bit less top speed and about the same vertical performance as the S series prop did. So I decided to try a Scimitar 10x7. That got the engine RPM back down into its happy place, the plane had better top end speed, and vertical performance was every bit as good as it had been with the 10x6 S series. I then tried an 11x5 Scimitar prop. Top speed was way down but the vertical performance was amazing. The engine RPM was down a bit from the 10x7, but it wasn't lugging like it has with the APC. But then we had a contest on a windy day, and I didn't do well because I didn't have the top speed to power through the wind. So now I'm back to the 10x7 Scimitar. Maybe there's a prop out there that would do better than it does, but I'm happy with what I have and I'm used to the way the plane flies with it.

So all that is to say that prop selection is dependent on a lot of factors including your flying style, what you want out of your plane, your plane's amount of drag, and the torque/horsepower curves of your particular engine. To give you a simple answer to your question, chances are you can get an improvement in top speed if you change your prop as that engine's recommended beginner propeller is on the big side and probably isn't letting the engine turn fast enough to make maximum power. It's a pulling prop which is great for a trainer to be used by beginner pilots, but you can definitely change the flying characteristics of the plane by going to a different prop.