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Old Oct 19, 2005, 08:34 PM
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Your right Jim. It does work very well. I don't know what formula Dave used to arrive at this configuration but it sure does work!

Steve
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Old Oct 19, 2005, 08:34 PM
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Mesa Falcon Fld, Arizona, United States
Joined Sep 2004
426 Posts
Jim,

The simple part does not scare me, I can eyeball another prop pretty easily, I just want to have some fun trying to do some engineering on it

Adam
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Old Oct 19, 2005, 08:52 PM
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Understood Adam.

Steve
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Old Oct 20, 2005, 09:57 AM
"Old 8140"
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Arizona Via NH
Joined Mar 2005
279 Posts
Adam,

For some reason I knew that is what you would say!!!

Just like "My" kids -- "I want to do it my self!!!!"

Don't blame you - learn by doing.

Jim
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Old Oct 20, 2005, 07:30 PM
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Wichita, Kansas
Joined Jan 2004
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Adam,

Impeller design is very complex and this is not the forum for a 4th year disertation on fluid dynamics. It is not simple, period. The Seawolf propulsor was designed using a mainframe computer and a $250,000 CFD software package. .01% accuracy, not even close. 25% maybe if you are lucky. The propeller flow dynamics go out the window and it becomes an extremely intricate flow reversal, control, and fluid impulse math problem.

Now, with that said, my suggestion is to scrap the technical approach at this point and go the the imperical methodology(trial and error). The biggest problem with very small propellers is the rules of similitude. Read up on that and it will clue you into 50% of the problem you are experiencing. You really need to profile the blades as Dave Merriman does. Get ahold of one of Dave's props and take a look at it. Cut one of the blades in half chordwise and you will see why Dave's props work so very well. Or, have Dave cast up a SSN21 impeller for you and send it to you. Scale it down, but thicken the blades up and reduce the pitch. Small props stall very easily, so you may want to reduce the # of blades as well to say 3 or 4.
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Old Mar 10, 2014, 06:05 PM
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after read info i am more desoriented that before read it, i am close to finish my first rc sub, and i dont know what propeller is best for my sub, the fat part (or the thickets diameter of the sub) is 30 cm, my power plant is 700watts at 12500 rpm, the total weight its about 10 kg, i already know how to build a propeller but i dont know whow many blades must had, the diameter and the pitch, and how the angle is measured from the hub, i dont wanna build a maximum perfomance propeller either, just the right propeller to move the sub and not overheat the motor
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Old Apr 05, 2014, 03:53 PM
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United States, MN, Brainerd
Joined Oct 2004
2,374 Posts
Whoa - a lot of approaches. Here's a simple, cheap one....
Qualifier: I have only one sub (about 30in/75cm long) and very little sub model experience.
On the Trumpeter 144 Seawolf conversion to RC, I used the fan blade assembly taken out of a computer fan. It's inside the Seawolf impeller shroud, so not even visible (who knows exactly what the real one looks like anyway). With a very small drive motor, it cranks the sub WAY more than scale speed.
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