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Author Topic: OS 46LA Three blade prop  (Read 853 times)

Offline Craig Beswick

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OS 46LA Three blade prop
« on: April 22, 2020, 09:07:52 PM »
Hello all,
I am completing a Bob Palmer Hurricane and for the sake of scale I would like to use a three blade prop.

I am putting an OS 46LA in it and have read most of the 46LA, "Set up", posts but couldn't find one with a three blade prop. Is it not the done thing? Are there draw backs in using a 3 blade prop?

I was thinking of a 10 x 5, if okay to do so, any other suggestions?
Thanks

Craig
Ps. Engine is brand new stock standard.
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Offline Avaiojet

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Re: OS 46LA Three blade prop
« Reply #1 on: April 22, 2020, 09:19:10 PM »
Quote from: Craig Beswick on April 22, 2020, 09:07:52 PM
Hello all,
I am completing a Bob Palmer Hurricane and for the sake of scale I would like to use a three blade prop.

I am putting an OS 46LA in it and have read most of the 46LA, "Set up", posts but couldn't find one with a three blade prop. Is it not the done thing? Are there draw backs in using a 3 blade prop?

I was thinking of a 10 x 5, if okay to do so, any other suggestions?
Thanks

Craig
Ps. Engine is brand new stock standard.

Craig,

I have many three bladed props purchased for an OS LA 46.

Some carbon fiber also.

PM or email if interested.

Charles
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Online Brett Buck

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Re: OS 46LA Three blade prop
« Reply #2 on: April 22, 2020, 11:30:24 PM »
Quote from: Craig Beswick on April 22, 2020, 09:07:52 PM
I was thinking of a 10 x 5, if okay to do so, any other suggestions?

   That sounds a little too small and a lot too much pitch. I would probably start with a 11-4 3-blade, and then work up to a 11.5-4 3-blade.

     Brett
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Offline Reptoid

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Re: OS 46LA Three blade prop
« Reply #3 on: April 23, 2020, 02:02:52 AM »
The general starting point rule of thumb when going from two blades to three is -1" in diameter and +1" in pitch. Less diameter to maintain rev range with additional prop area/drag and additional pitch to compensate for dirty air and slightly lower angle of attack to air flow behind leading blade.
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Offline Craig Beswick

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Re: OS 46LA Three blade prop
« Reply #4 on: April 23, 2020, 03:16:02 PM »
Thank you for the input.

So no real issues with going to a 3 blade just finding the right size.

Thanks again
Craig
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Offline Shorts,David

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Re: OS 46LA Three blade prop
« Reply #5 on: April 23, 2020, 03:24:47 PM »
Quote from: Reptoid on April 23, 2020, 02:02:52 AM
The general starting point rule of thumb when going from two blades to three is -1" in diameter and +1" in pitch. Less diameter to maintain rev range with additional prop area/drag and additional pitch to compensate for dirty air and slightly lower angle of attack to air flow behind leading blade.

To clarify, unless I am mistaken. A 10x5 three blade is about the equivalent of an 11x4 two blade. If I am off, please let me know.
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Online Brett Buck

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Re: OS 46LA Three blade prop
« Reply #6 on: April 23, 2020, 05:50:22 PM »
Quote from: Shorts,David on April 23, 2020, 03:24:47 PM
To clarify, unless I am mistaken. A 10x5 three blade is about the equivalent of an 11x4 two blade. If I am off, please let me know.

   No, pitch is pitch. What you want is something like a 11.5-4 3-blade if you have a flat-backed or semi-symmetrical airfoil, and  maybe 11.25-3.7 3-blade if  the airfoil has undercamber. If the 11.5 is too big, you can cut it down.

     Brett
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Offline Al Ferraro

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Re: OS 46LA Three blade prop
« Reply #7 on: April 23, 2020, 10:28:31 PM »
 I use a Master Airscrew 11x6 3 bladed prop that I cut to 10” or 9-7/8” on my LA 46 powered Vector, the full blade is to much load on the engine. This prop work really well except on windy days. In the loops the 3 blade really winds up a lot more than the APC 12.25 X 4. I tried the Master Airscrew 10x5 but it does not have the same holding, stability that the cut down 11X6 3 blade has. The 11X6 has wider blades and I think that is making the difference over the stock 10X5. MS does not make a 11X5. I really like the way the Vector fly’s with the cut down three blade, but I keep the  APC 12.25X4 in the flight box in case the wind goes over 10mph. I even cut the MS 11X6 down to 9-3/4 for my Brodak 40 powered Nobler and get the same results.
Al
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Offline Shorts,David

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Re: OS 46LA Three blade prop
« Reply #8 on: April 24, 2020, 10:53:11 AM »
Quote from: Al Ferraro on April 23, 2020, 10:28:31 PM
I use a Master Airscrew 11x6 3 bladed prop that I cut to 10” or 9-7/8” on my LA 46 powered Vector, the full blade is to much load on the engine. This prop work really well except on windy days. In the loops the 3 blade really winds up a lot more than the APC 12.25 X 4. I tried the Master Airscrew 10x5 but it does not have the same holding, stability that the cut down 11X6 3 blade has. The 11X6 has wider blades and I think that is making the difference over the stock 10X5. MS does not make a 11X5. I really like the way the Vector fly’s with the cut down three blade, but I keep the  APC 12.25X4 in the flight box in case the wind goes over 10mph. I even cut the MS 11X6 down to 9-3/4 for my Brodak 40 powered Nobler and get the same results.
Al

Thanks for that info Al. Until the money fairy, or the hand-me-down fairy blesses me with carbon fiber blades, modified MA props are something I've tinkered with but hadn't tried modifying them.
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