Thread: impeller sizes
03-28-2008, 10:21 PM #1
I have a question about the sizes on impellers. I have heard about many different sizes, but what do they really mean? ex. 12/20, 13/19, 14/20, 15/22. what does the first and second number mean?
03-28-2008, 11:08 PM #2
- Join Date
- Jan 2007
- Lakeland, FL
A regular prop has its blades positioned to push water at a given angle, say 20 degrees. Our props are varible-pitched, meaning that instead of each blade being 20 degrees, a 15/22 will start off with the leading edge (biting the water) of each blade at 15 degrees, and down the blade, the pitch will progessively bend until it is 22 degrees at the trailing end (pushing the water). The idea is to get some of the benefits of a lower geared prop (15, good bite or holeshot), and some of the benefits of a higher geared prop (22, good top speed). Unfortunately, there is no hard and fast rule of what should work best in each application. There's give and take with any variable prop, and it is a process of experimentation (or learning what worked well for someone else) to find a prop that is perfect for your jet. The trailing edge number is especially important because that needs to be matched with the power of your engine. You want the edge pushing water to be aggressive enough to give you the fastest top speed, without hitting the rev-limiter of the engine, but also not so aggressive that the engine doesn't have the power to spin it in that sweet spot under the rev-limiter.
03-29-2008, 01:00 PM #3
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