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On Aug 13, 2022, at 3:46 PM, Cameron Garner via groups.io <500ks@...> wrote:
Aye, I'm not denying the testing & results.
However it would be nice to discover WHY this is the case; presumably there is no magic that 2 blades have that 3 do not. And why do our little birds sometimes perform better with fewer when the big boys are the other way around?
There are many variables here besides the number of blades.
-Cameron G
Building 44deg south
From memory, there was a theory that the airflow coming off the trailing edge of the wing/strakes just next to the cowl, is hit by both blades at the same time for a 2 blade prop, and not for a 3 blade. This contributes to the noise and vibration. It’s a theory at least. 3 blade props also tend to be shorter, so the tip speed would be less that the longer 2 blade for the same rpm, and might make more noise as a result. And I’m fairly certain there is some voodoo in prop making, but that’s also just a theory :)
------- Original Message -------
On Saturday, August 13th, 2022 at 14:58, skovbjerg <skovbjerg@...> wrote:
For the purpose of this group, the statement about 2 blades vs 3 is correct. Confirmed by race results…over and over
Jay
On Aug 11, 2022, at 20:54, Cameron Garner via groups.io 500ks@... wrote:
"The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop. "
This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around!
The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan.
-Cameron G
Building 44deg south
------- Original Message -------
On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io ken4zz@... wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote: Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
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Aye, I'm not denying the testing & results.
However it would be nice to discover WHY this is the case; presumably there is no magic that 2 blades have that 3 do not. And why do our little birds sometimes perform better with fewer when the big boys are the other way around?
There are many variables here besides the number of blades.
-Cameron G
Building 44deg south
toggle quoted message
Show quoted text
------- Original Message ------- On Saturday, August 13th, 2022 at 14:58, skovbjerg <skovbjerg@...> wrote:
For the purpose of this group, the statement about 2 blades vs 3 is correct. Confirmed by race results…over and over
Jay
On Aug 11, 2022, at 20:54, Cameron Garner via groups.io 500ks@... wrote:
"The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop. "
This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around!
The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan.
-Cameron G
Building 44deg south
------- Original Message -------
On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io ken4zz@... wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote:
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
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Hi Joe:
I have not forgotten you!
I will order a back-up 2-blade in the future from you.
I had paid Catto long ago for a 3-blade, and wanted to get any comments from all the flyers, before deciding.
Thanks to all!
Regards,
James
From: Joe Person
Date: Fri, 12 Aug 2022 07:59:50 PDT
James,
You can, optionally, get a new two-blade prop from a nearby manufacturer, and probably get it personally delivered to you.
-Joe Person
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For the purpose of this group, the statement about 2 blades vs 3 is correct. Confirmed by race results…over and over
Jay
toggle quoted message
Show quoted text
On Aug 11, 2022, at 20:54, Cameron Garner via groups.io <500ks@...> wrote: "The reason for the fewer blades is that the fewer the number, the greater the potential efficiency achievable by the prop. " This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around! The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan. -Cameron G Building 44deg south ------- Original Message ------- On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io <ken4zz@...> wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote:
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
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Joe Person
James,
You can, optionally, get a new two-blade prop from a nearby manufacturer, and probably get it personally delivered to you.
-Joe Person
toggle quoted message
Show quoted text
On Aug 12, 2022, at 7:27 AM, William Kastenholz <wkasty@...> wrote:
I have used both Catto 3 blade and a Hertzler 2 blade.
We are fortunate to have the services of both of these fine individuals/companies.
Noise, climb rate, top speed, etc… my comment is that the 3 blade will provide some amount of drag (much appreciated) on final approach to landing.
And I like to land after every flight.
Happy Canarding,
Bill Kastenholz
On Aug 11, 2022, at 9:52 PM, Cameron Garner via groups.io <500ks@...> wrote:
"The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop. "
This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around!
The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan.
-Cameron G
Building 44deg south
------- Original Message -------
On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io <ken4zz@...> wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote:
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
|
|
|
I have used both Catto 3 blade and a Hertzler 2 blade.
We are fortunate to have the services of both of these fine individuals/companies.
Noise, climb rate, top speed, etc… my comment is that the 3 blade will provide some amount of drag (much appreciated) on final approach to landing.
And I like to land after every flight.
Happy Canarding,
Bill Kastenholz
toggle quoted message
Show quoted text
On Aug 11, 2022, at 9:52 PM, Cameron Garner via groups.io <500ks@...> wrote:
"The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop. "
This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around!
The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan.
-Cameron G
Building 44deg south
------- Original Message -------
On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io <ken4zz@...> wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote:
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
|
|
|
"The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop. "
This explains why turboprop manufacturers are moving from 6-blade props to 3 or 4... wait, no... it's the other way around!
The rule of thumb is an oversimplification with limited application in the real world. Unless you are building a static cooling fan.
-Cameron G
Building 44deg south
toggle quoted message
Show quoted text
------- Original Message ------- On Friday, August 12th, 2022 at 15:44, KEN4ZZ via groups.io <ken4zz@...> wrote:
The basic rule of thumb I've seen in several places re # of blades is to
use the fewest that will satisfactorily absorb the engine's power
output. This acknowledges the physical situation that blades may have a
length limit in a given installation due to ground or structure
clearance. The reason for the fewer blades is that the fewer the
number, the greater the potential efficiency achievable by the prop.
I've actually seen pictures of a few experimental SINGLE blade prop
installations that had a counter weight on the other side of the prop
hub. I dunno how good an idea that would be for the real world long
term use though. I know 3 blades have potential to be smoother and
perhaps quieter, but given the higher cost of purchase and much higher
cost of shipping I'd opt for the 2 blade and spend some of the savings
on a top quality ANR headset.
Ken
On 8/11/2022 2:58 PM, James Russell wrote:
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
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KEN4ZZ
The basic rule of thumb I've seen in several places re # of blades is to use the fewest that will satisfactorily absorb the engine's power output. This acknowledges the physical situation that blades may have a length limit in a given installation due to ground or structure clearance. The reason for the fewer blades is that the fewer the number, the greater the potential efficiency achievable by the prop. I've actually seen pictures of a few experimental SINGLE blade prop installations that had a counter weight on the other side of the prop hub. I dunno how good an idea that would be for the real world long term use though. I know 3 blades have potential to be smoother and perhaps quieter, but given the higher cost of purchase and much higher cost of shipping I'd opt for the 2 blade and spend some of the savings on a top quality ANR headset.
Ken
toggle quoted message
Show quoted text
On 8/11/2022 2:58 PM, James Russell wrote: Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
|
|
|
Hi all:
I'm to the point of ordering my prop from Catto. My Cozy Mk IV will have a 180 hp O-360, eventually.
I need you flyers to please give feedback on props - 2 or 3 blade?
Nicole from Catto said:
1) Shipping: truck for 3 blade vs regular for 2 blade
2) 72 x 68 2 blade vs 72 x 66 3 blade
3) 3 blade 2777 rpm @ 7500' slightly slower @ 7500' 2 blade
4) 2 blade faster higher up
4) Accelerates & climbs slightly better - 3 blade
5) No nickel LEs - too much rework for pushers
6) Polyurethane LE tape - change 4-5 yrs for $90/kit
7) Much less noise 3 blade inside
My airplane will be a crusier, extra RoC never hurts, my main driver is noise inside: she said "3 blade is like putting on NC headphones"
Comments & feedback welcomed!
I have researched this topic...
Regards,
James
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