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Old 17-12-2012, 14:28   #16
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Re: Maxprop issues

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Originally Posted by btrayfors View Post
If you were to turn the shaft slowly in free air with the blades feathered (as when the boat is hauled), the blades would stay feathered.
Yes, and if you were to turn the shaft quickly, the blades would rotate into position, because of centrifigal force.
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Old 17-12-2012, 14:34   #17
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Re: Maxprop issues

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Originally Posted by fstbttms View Post
Yes, and if you were to turn the shaft quickly, the blades would rotate into position, because of centrifugal force.
Clearly, you and I have a different understanding of the meaning of "centrifugal force".

Folding propellers work by centrifigal force.

Feathering propellers like the MaxProp do not.

Bill
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Old 17-12-2012, 14:35   #18
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Re: Maxprop issues

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Originally Posted by fstbttms View Post
Yes, and if you were to turn the shaft quickly, the blades would rotate into position, because of centrifigal force.
Don't think that is correct, fstbttms... Btrayf is right. Centrifugal force is directed radially outwards and has nothing to do with the rotation of the blades around their axis.

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Old 17-12-2012, 14:41   #19
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Re: Maxprop issues

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Originally Posted by Jim Cate View Post
Don't think that is correct, fstbttms... Btrayf is right. Centrifugal force is directed radially outwards and has nothing to do with the rotation of the blades around their axis.
OK, perhaps my grasp of physics isn't all it could be but the point is that the energy of a wave will not cause the Max Prop blades to feather while under way under power.
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Old 17-12-2012, 14:53   #20
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Re: Maxprop issues

The maxprop is designed so that each blade pivots around a shaft projecting laterally from the central hub. The area of the blade aft of the shaft is greater than the area forward of the shaft. When the hub is rotated the blade encounters more resistance from the water in the rear portion of the blade than in the forward portion. This difference in force on the blade causes it to rotate on the hub. The leading edge of the blade faces into the flow and trailing edge trails. This affect occurs whether the hub is rotating slowly or quickly.

There are stops in the hub to keep the blades from rotating past the preset pitch.

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Old 17-12-2012, 15:42   #21
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Re: Maxprop issues

My previous post applies to the feathering action of the blade only. The blades do provide resistance to the hub, but it is the gearing between the prop shaft and the hub that actually rotates the blades. Sorry for the confusion.
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Old 17-12-2012, 15:50   #22
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Re: Maxprop issues

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...it is the gearing between the prop shaft and the hub that actually rotates the blades.
Wha, wha, what?!!?

There is no gearing between the shaft and hub. The hub is secured to the shft by a standard key in a keyway of course, but the only gearing in a Max Prop is the cone gear mounted in the spinner halves and on the blade stems and is used to determine and maintain pitch.
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Old 17-12-2012, 15:55   #23
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Re: Maxprop issues

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Originally Posted by fstbttms View Post
Wha, wha, what?!!?

There is no gearing between the shaft and hub. The hub is secured to the shft by a standard key in a keyway of course, but the only gearing in a Max Prop is the cone gear mounted in the spinner halves and on the blade stems and is used to determine and maintain pitch.
OK substitute spinner halves for hub. When the spinner halves are rotated relative to the prop shaft the blades are rotated by the internal gears.
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Old 17-12-2012, 15:59   #24
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Re: Maxprop issues

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OK substitute spinner halves for hub.
Your post makes it sound like the blades are moved into position by shaft-driven gears, which is not the case.
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Old 17-12-2012, 16:03   #25
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Re: Maxprop issues

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Originally Posted by fstbttms View Post
Your post makes it sound like the blades are moved into position by shaft-driven gears, which is not the case.

When the spinner halves are rotated with a fixed prop shaft the blades rotate. How does that happen?
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Old 17-12-2012, 16:11   #26
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Re: Maxprop issues

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When the spinner halves are rotated with a fixed prop shaft the blades rotate. How does that happen?
The gearing of course. The blades can be forced to move through their range of motion with the shaft fixed. But again, it sounded like you were saying that there was a geared drive between shaft and prop. I'll assume I simply misunderstood you.
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Old 17-12-2012, 16:24   #27
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Re: Maxprop issues

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Originally Posted by fstbttms View Post
The gearing of course. The blades can be forced to move through their range of motion with the shaft fixed. But again, it sounded like you were saying that there was a geared drive between shaft and prop. I'll assume I simply misunderstood you.

Let's start with a fully feathered prop that is not turning. When the prop shaft starts to turn, the water resistance will hold the prop back. For a short period the prop shaft turns while the prop does not. It is this difference in rotation that drives the gears that rotate the prop blades.
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Old 17-12-2012, 16:26   #28
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Re: Maxprop issues

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Originally Posted by ChuckSK View Post
Let's start with a fully feathered prop that is not turning. When the prop shaft starts to turn, the water resistance will hold the prop back. For a short period the prop shaft turns while the prop does not. It is this difference in rotation that drives the gears that rotate the prop blades.
Understood. But there is no gearing connecting the shaft and prop, which again, is what it sounded like you were describing.
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Old 17-12-2012, 16:33   #29
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Fstbttms: it's not centrifugal force that deploys a MaxProp. It is as the others describe. Check one out next time you dive a boat If the engine is at low speed while sailing the prop will definitely partially feather when the torque becomes low due to sailing speed. And then un-feather when the shaft must apply torque to the hub.
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Old 17-12-2012, 16:39   #30
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Re: Maxprop issues

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