RE: 2 Blade VS. 3 Blade Prop  
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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 1:53:23 AM   
CafeenMan



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From: Spring Hill, FL, USA
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quote:

ORIGINAL: grandpa

Wow! That link is powerful! I'll be quite a while digesting my first read. I just hope the link stays active for a while, because I do not want to have to stor more paper around the house.

Again, thanks for the info.

Grandpa - Most decent web sites hang around for a while, but then you never know when one is going to disappear forever. Fortunately, you can save web pages on your computer.

If you use Internet Explorer, go to the File menu, click "Save As..." and then put it someplace where you'll remember where it is. Also, it's usually a good idea to save as "web page complete" so it looks right when you view it later.

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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 3:52:51 AM   
acropilot_ty



Posts: 122
Joined: 12/3/2002
From: Dana point, CA, USA
Status: offline 		I see how it is.... When I say multiple blades doesn't always mean less thrust everyone argues, but when Bolly says it, everyone instantly agrees... Don't worry I see this every day, I'm a flight instructor... I'll tell a student something a hundred times without them getting it.. then they'll read the same damn thing in a book and it must be true because it was published by "Someone Important" (ie. not me).

Ty

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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 3:57:49 AM   
CafeenMan



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From: Spring Hill, FL, USA
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quote:

ORIGINAL: acropilot_ty
Ty

That's 90% of the people in the world. When people don't know you, you're credible, but once they get to know you and realize you're not perfect, suddenly you don't know anything. People are strange.

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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 5:57:35 AM   
O2man



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From: Selah, WA, USA
Status: offline 		You obviously do not have any kids, or yours are not old enough to train yo! LOL

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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 9:42:09 AM   
Jimmbbo



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Joined: 10/1/2003
From: Fresno, CA, USA
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quote:

ORIGINAL: grandpa

Jimmbbo,

The Corsair and P51 got more blades as the horsepower increased because it was cheaper than redesigning taller landing gear for a longer prop blade. Ground clearance was the issue. The only thing horsepower had to do with it was the need for more prop and no place to put it without hitting the ground, which would have made the taxpayer unhappy.

That ought to to add enough logs to the fire to make some real heat!


Agreed... Coulda done it with one blade if they redesigned landing gear to be 40 feet high...

Jim

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RE: 2 Blade VS. 3 Blade Prop - 1/21/2004 9:46:24 AM   
Jimmbbo



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quote:

ORIGINAL: BruceDana

http://www.bolly.com.au/book/Book.jsp?Chapter=2&Section=2


Cool site... Thanks!!

Jim

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RE: 2 Blade VS. 3 Blade Prop - 1/24/2004 6:17:24 PM   
Crayon


 

Posts: 44
Joined: 11/28/2003
From: Suwanee, GA, USA
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quote:

ORIGINAL: acropilot_ty

I see how it is.... When I say multiple blades doesn't always mean less thrust everyone argues, but when Bolly says it, everyone instantly agrees... Don't worry I see this every day, I'm a flight instructor... I'll tell a student something a hundred times without them getting it.. then they'll read the same damn thing in a book and it must be true because it was published by !QUOT!Someone Important!QUOT! (ie. not me).


Don't sweat it, you've got my respect. People seem to always believe the written text. They need to start disbelieving!

The last place I worked, I had a cow-worker who wrote a Linux usage book on request of a publishing house. He didn't know the first thing about Linux or UNIX. I ended up answering almost all of his technical questions. His book went on to be a best selling Linux book. Damn publishing industry.

The place before that, we had a guy they hired as a Senior Network R&D engineer. His qualifications for the job were:
a) He wrote several books on the subject.
b) He had their respect because of this.
I've never met an networking engineer with less knowledge on the subject! Everyone ended up referring to him as wingnut. Damn publishing industry.

My personal library has over 5000 books in it. I've read most of them, and quite a few contain information that is just plain wrong. The really bad ones end up in the trash.

The publishing industry doesn't care about providing readers with accurate information or training. It's about making money.

I don't know enough about Bolly or his book to make a judgment about the accuracy of it's content.

Just because you read it, doesn't make it true. It especially doesn't mean the author is knowledgeable. Listen to the instructor, he's the one with REAL experience.

< Message edited by Crayon -- 1/24/2004 1:36:02 PM >

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RE: 2 Blade VS. 3 Blade Prop - 1/24/2004 7:52:34 PM   
FHHuber



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quote:

ORIGINAL: acropilot_ty
the perfect prop would start out as a 6 blade to decrease disc loading and increase static thrust for takeoff... sometime after takeoff exploding bolts would jettison 3 of the blades to optimize the prop for climb... once it levels off in cruise more exploding bolts would again jettison two of the remaining blades and a counter weight would pop out to ballance the one remaining blade. I just haven't figured out how to make it cost effective yet...

Ty


LOL

You would have to have a cage on the thing to catch the blades as they popped off; don't want to plant one in the roof of the local cop's car. (or a lot of other places they wouldn't be wanted...)

And you'd want something to put the blades back on so you could have the 6 blade prop at landing approach... in case you had to go around.

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RE: RE: 2 Blade VS. 3 Blade Prop - 1/25/2004 3:20:46 AM   
acropilot_ty



Posts: 122
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From: Dana point, CA, USA
Status: offline 		Details....

Ty

PS, I'm writing a book on spins (full size airplanes), so I hope mine doesn't end up in your trash Crayon.

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RE: RE: 2 Blade VS. 3 Blade Prop - 1/25/2004 5:42:02 AM   
Crayon


 

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Joined: 11/28/2003
From: Suwanee, GA, USA
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quote:

ORIGINAL: acropilot_ty

Details....

Ty

PS, I'm writing a book on spins (full size airplanes), so I hope mine doesn't end up in your trash Crayon.


Trash...No, I assure you that it would have a place of honor and dis-STINK-tion in my bathroom, er, uhm library.

Seriously though, send me a copy, I'd love to read it.

Years ago I used to instruct. I remember getting pretty cheesed at students that didn't listen or thought troubleshooting the instructor was a good thing to do. People don't realize how much work is involved in preping for a class.

Erik

< Message edited by Crayon -- 1/25/2004 12:41:51 AM >

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RE: RE: 2 Blade VS. 3 Blade Prop - 1/25/2004 12:26:06 PM   
Flypaper 2



Posts: 4337
Joined: 3/29/2002
From: Kingston, ON, CANADA
Status: offline 		Was just questioning to myself where Bolly says " Diameter for diameter for diameter,a well designed four blade prop will, in the same circumstances, perform better than the equivalent two blade prop". Sounds incomplete to me. would need a lot more horse power or a lot less pitch to do it. Someone enlighten me.

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RE: RE: 2 Blade VS. 3 Blade Prop - 1/25/2004 8:54:41 PM   
FHHuber



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quote:

ORIGINAL: Flypaper 2

Was just questioning to myself where Bolly says " Diameter for diameter for diameter,a well designed four blade prop will, in the same circumstances, perform better than the equivalent two blade prop". Sounds incomplete to me. would need a lot more horse power or a lot less pitch to do it. Someone enlighten me.


Can keep same diameter and same pitch... gear the motor and reduce RPM. You can even go with a higher pitch

A slower swinging prop is more efficient. (less tip vortice at the blade end... less wasted power.) but I doubt that is what Bolly was refering to.


There is more blade area with the 4-blade than the 2-blade.. More blade area means that the prop CAN develop more thrust. (not that it always will... Static thrust may be the same but thats another complete subject)

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RE: 2 Blade VS. 3 Blade Prop - 1/30/2004 7:00:29 PM   
Mech_gadget



Posts: 64
Joined: 2/8/2003
From: Houston, TX, USA
Status: offline 		With all of this background information could any of you kind people make a recommendation for the following engines:


Saito 150 4s- three blade (future project)

Magnum 120 2S- 3 & 4 Blade (for P51)

Thanks,


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RE: 2 Blade VS. 3 Blade Prop - 2/7/2006 2:54:43 AM   
Jetison


 

Posts: 1
Joined: 2/7/2006
From: Tracy, CA, USA
Status: offline 		Would a four bladed prop give more thrust than a two or three bladed prop?

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RE: 2 Blade VS. 3 Blade Prop - 2/7/2006 3:15:32 AM   
BMatthews



Posts: 9001
Joined: 10/4/2002
From: Burnaby, BC, CANADA
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quote:

ORIGINAL: Jetison

Would a four bladed prop give more thrust than a two or three bladed prop?


Not without a larger engine to spin it...

The Reader's digest of the whole thread is that the less the number of blades the more efficient the prop is. The only reason we have other types is for various reasons why the engines can't use two blade props due to size and tip Mach speeds and such.

Any given engine will produce more thrust with a two blade prop than a multi bladed prop assuming the prop is sized to allow the engine to achieve the same peak power output. The same applies to electric motors. If the props draw the same current, and therefore the system is using the same number of watts, then the 2 bladed prop will be more efficient than a multiblade prop. The more blades the worse the thrust.


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