Two-blade or three-blade prop for I-550

Submitted by Anonymous on

Forums: 

From: frederickemoreno [at] gmail.com <frederickemoreno [at] gmail.com>
Sender: <marv [at] lancaironline.net>
Subject: Two-blade or three-blade prop for I-550
Date: Sun, 29 Jun 2014 09:01:58 -0400
To: <lml [at] lancaironline.net>
I have a chart somewhere from Hartzell which shows the theoretical projection of prop efficiency vs speed for two vs three blade, and the three blade is the winner by a small tweak, a per cent or two at the higher speed.   Several years old, but I do not think the part numbers have changed for the recommended Lancair props.
 
Fred Moreno

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Charles Brown <browncc1 [at] verizon.net>
Sender: <marv [at] lancaironline.net>
Subject: Re: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 07:38:05 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
I've enclosed the spreadsheet provided to me by Les Doud of Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He believes that the 3-blade is more effiicient than the two blade even in cruise.  I have a hard time believing that, and my airplane with 3 blades has not lived up to the prototype Legacy's performance with the 2-blade as documented in the CAFE report; and the 3-blade is heavier and more expensive to buy and overhaul.  Of course, my airplane is probably not as clean as the prototype.

But the 3-blade prop sure looks cool. 






From: "frederickemoreno [at] gmail.com

" <frederickemoreno [at] gmail.com

>
Date: June 29, 2014 8:01:58 AM CDT
Subject: Two-blade or three-blade prop for I-550



I have a chart somewhere from Hartzell which shows the theoretical projection of prop efficiency vs speed for two vs three blade, and the three blade is the winner by a small tweak, a per cent or two at the higher speed.   Several years old, but I do not think the part numbers have changed for the recommended Lancair props.
 
Fred Moreno



Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Chris Zavatston <chris_zavatson [at] yahoo.com>
Sender: <marv [at] lancaironline.net>
Subject: Re: [LML] Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 10:38:42 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
Fred,
Please post if you ever find it.  I would love to see the assumptions (power levels, etc) vs. results.
Chris

Sent from my spiffy iPhone

On Jun 29, 2014, at 6:01 AM, "frederickemoreno [at] gmail.com

" <frederickemoreno [at] gmail.com

> wrote:

I have a chart somewhere from Hartzell which shows the theoretical projection of prop efficiency vs speed for two vs three blade, and the three blade is the winner by a small tweak, a per cent or two at the higher speed.   Several years old, but I do not think the part numbers have changed for the recommended Lancair props.
 
Fred Moreno

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Stevens Family <stevens5 [at] swiftdsl.com.au>
Sender: <marv [at] lancaironline.net>
Subject: RE: [LML] Re: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 10:39:09 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

I am interested in this subject, because I purchased a partly built kit some years ago, (which I am still building!) which came with an MT 3 bladed constant speed prop. In my conversation with a builder in South Australia recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2 blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs which indicate the 3 blades are more efficient! It was my understanding that because a 3 bladed prop generates 3 tip vortices against only two on a 2 bladed prop, it is less efficient.

 

 

Rob Stevens

Perth, Western Australia.

 

 

From: Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud of Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He believes that the 3-blade is more effiicient than the two blade even in cruise.  I have a hard time believing that, and my airplane with 3 blades has not lived up to the prototype Legacy's performance with the 2-blade as documented in the CAFE report; and the 3-blade is heavier and more expensive to buy and overhaul.  Of course, my airplane is probably not as clean as the prototype.

 

But the 3-blade prop sure looks cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: <Sky2high [at] aol.com>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 11:13:30 -0400 (EDT)
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

 
Here is more to think about (rather than just efficiency).
 
Blades > 2 = better climb performance - consider the relative air
(AOA) to the prop chord for both the ascending and descending blade
for a 2 blade versus longer arcs, better bites for more than 2
blades.  Don't confuse  this with level flight where all blades
see the same AOA.
 
Blades > 2 can produce the same thrust as Blades = 2 but the prop
diameter for more blades can be smaller, thus allowing for higher rpm whilst
still avoiding the tips going supersonic.  I.E. The further the tip from
the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the 320 -
an 84 inch diameter prop cut down to 70 inches.  Most props deliver
max thrust about 2/3 out from the hub.  What did that mean for the enormous
chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its
path separation (interference) based on airspeed.  You'll be
surprised - odds are the bird will hit the windshield and not a prop blade at
cruise speed.
 
Hmmmm.....
 
Grayhawk
 
PS Computations left to the reader and EXCEL. 
 
In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time,
stevens5 [at] swiftdsl.com.au writes:

I
am interested in this subject, because I purchased a partly built kit some
years ago, (which I am still building!) which came with an MT 3 bladed
constant speed prop. In my conversation with a builder in South Australia
recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2
blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that
was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs
which indicate the 3 blades are more efficient! It was my understanding that
because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.

 

 

Rob
Stevens

Perth,
Western Australia.

 

 

From:
Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To:
Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade
prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud of
Hartzell.  In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: John Barrett <jbarrett [at] carbinge.com>
Sender: <marv [at] lancaironline.net>
Subject: RE: [LML] Re: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 16:10:22 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

I understood from conversations with some prop designers a few years ago (can’t recall who) that the fewest number of blades to get the job done is most efficient.  One blade would be best except for obvious balance issues.  So the remaining factors include how much HP one blade can absorb.  I seem to remember that three was the minimum for an engine that goes much over 300 HP at least for the hubs and props we were looking at for the IVP.  This info may have come from MT because I was looking at the five blade MT vs four.  My understanding at that time was that more blades result in  quieter smoother ops but give up small amounts of efficiency.

 

Don’t believe anything I say here.  The memories are about 10 years old.

 

John Barrett

 

From: Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Stevens Family
Sent: Monday, June 30, 2014 7:39 AM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for I-550

 

I am interested in this subject, because I purchased a partly built kit some years ago, (which I am still building!) which came with an MT 3 bladed constant speed prop. In my conversation with a builder in South Australia recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2 blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs which indicate the 3 blades are more efficient! It was my understanding that because a 3 bladed prop generates 3 tip vortices against only two on a 2 bladed prop, it is less efficient.

 

 

Rob Stevens

Perth, Western Australia.

 

 

From: Lancair Mailing List [lml [at] lancaironline.net (mailto:)

] On Behalf Of Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud of Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He believes that the 3-blade is more effiicient than the two blade even in cruise.  I have a hard time believing that, and my airplane with 3 blades has not lived up to the prototype Legacy's performance with the 2-blade as documented in the CAFE report; and the 3-blade is heavier and more expensive to buy and overhaul.  Of course, my airplane is probably not as clean as the prototype.

 

But the 3-blade prop sure looks cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Jim Nordin <panelmaker [at] earthlink.net>
Sender: <marv [at] lancaironline.net>
Subject: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 16:11:28 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Hummmm … when I see the military
planes with props like the E2C Hawkeye with more than 7 blades I have to think
more is better for some. When the hp is high and clearance is tight, more
blades is obviously good. Same for our lawndarts – so why not an 8 blade
for the LNC2? It’d be short likely - $$$$. No need to be that short.

The Navy’s stuff:



“In 2004, the E-2C's
propeller system was changed; a new eight-bladed propeller system named NP2000
was developed by the Hamilton-Sundstrand company to replace the old
four-bladed design. Improvements included better
fuel economy as a result of increased efficiency, reduced vibrations
and better maintainability as a result of the ability to remove prop blades individually
instead of having to remove the entire prop and hub assembly.”

http://en.wikipedia.org/wiki/E-2_Hawkeye

 

Increased efficiency? Who needs that?
Petrol is only $7/gallon. Cheap if you say it fast.

 

Now what to believe is best for your
rocketship or which is most efficient, effective, I dunno cause I ain’t
no aerodynamicist or “cool” appraiser. Over my pea head. I paddle
when things get tough, flap and other stuff.

Jim

 

From: Lancair Mailing
List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf
Of Sky2high [at] aol.com

Sent: Monday, June 30, 2014 10:14
AM

To: Lancair Mailing List

Subject: [LML] Re: Two-blade or
three-blade prop for I-550

 

 

Here is more to think about (rather than
just efficiency).

 

Blades > 2 = better climb performance
- consider the relative air (AOA) to the prop chord for both
the ascending and descending blade for a 2 blade versus longer
arcs, better bites for more than 2 blades.  Don't confuse 
this with level flight where all blades see the same AOA.

 

Blades > 2 can produce the same thrust
as Blades = 2 but the prop diameter for more blades can be smaller, thus
allowing for higher rpm whilst still avoiding the tips going supersonic. 
I.E. The further the tip from the hub the faster the tip is moving at a fixed
rpm. 

 

Momentarily consider the weird
2-blade Hartzell CS prop for the 320 - an 84 inch diameter prop cut
down to 70 inches.  Most props deliver max thrust about 2/3 out from the
hub.  What did that mean for the enormous chord and pitch for that prop?

 

Finally, consider the corkscrew path of
each blade tip and its path separation (interference) based on
airspeed.  You'll be surprised - odds are the bird will hit the windshield
and not a prop blade at cruise speed.

 

Hmmmm.....

 

Grayhawk

 

PS Computations left to the reader and
EXCEL. 

 

In a message dated 6/30/2014 9:39:14 A.M.
Central Daylight Time, stevens5 [at] swiftdsl.com.au writes:

I am interested in
this subject, because I purchased a partly built kit some years ago, (which I
am still building!) which came with an MT 3 bladed constant speed prop. In my
conversation with a builder in South Australia recently, he mentioned that he
had swapped out his 3 Blade MT prop for a 2 blade prop, and increase his cruise
speed by 7 knots. (Can’t recall if that was 7 Kts indicated, or 7 Kts
TAS.) Not sure how this fits with the graphs which indicate the 3 blades are
more efficient! It was my understanding that because a 3 bladed prop generates
3 tip vortices against only two on a 2 bladed prop, it is less efficient.

Rob Stevens

Perth, Western
Australia.

From: Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Charles Brown

Sent: Monday, 30 June 2014 7:38 PM

To: Lancair Mailing List

Subject: [LML] Re: Two-blade or
three-blade prop for I-550

I've enclosed the spreadsheet provided to
me by Les Doud of Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the prototype
Legacy's performance with the 2-blade as documented in the CAFE report; and the
3-blade is heavier and more expensive to buy and overhaul.  Of course, my
airplane is probably not as clean as the prototype.

But the 3-blade prop sure looks
cool. 


Image


image001.jpg

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Colyn Case <colyncase [at] earthlink.net>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Mon, 30 Jun 2014 18:33:34 -0400
To: Lancair Mailing List <lml [at] lancaironline.net>
Message Header


Undecoded Message

Grayhawk,  could you please expand on that climb performance argument a little?  


On Jun 30, 2014, at 11:13 AM, Sky2high [at] aol.com

wrote:


 
Here is more to think about (rather than just efficiency).
 
Blades > 2 = better climb performance - consider the relative air
(AOA) to the prop chord for both the ascending and descending blade
for a 2 blade versus longer arcs, better bites for more than 2
blades.  Don't confuse  this with level flight where all blades
see the same AOA.
 
Blades > 2 can produce the same thrust as Blades = 2 but the prop
diameter for more blades can be smaller, thus allowing for higher rpm whilst
still avoiding the tips going supersonic.  I.E. The further the tip from
the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the 320 -
an 84 inch diameter prop cut down to 70 inches.  Most props deliver
max thrust about 2/3 out from the hub.  What did that mean for the enormous
chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its
path separation (interference) based on airspeed.  You'll be
surprised - odds are the bird will hit the windshield and not a prop blade at
cruise speed.
 
Hmmmm.....
 
Grayhawk
 
PS Computations left to the reader and EXCEL. 
 
In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time,
stevens5 [at] swiftdsl.com.au

writes:

I
am interested in this subject, because I purchased a partly built kit some
years ago, (which I am still building!) which came with an MT 3 bladed
constant speed prop. In my conversation with a builder in South Australia
recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2
blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that
was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs
which indicate the 3 blades are more efficient! It was my understanding that
because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.

 

 

Rob
Stevens

Perth,
Western Australia.

 

 

From:
Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To:
Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade
prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud of
Hartzell.  In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Kyrilian Dyer <kyrilian_av [at] yahoo.com>
Sender: <marv [at] lancaironline.net>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Tue, 01 Jul 2014 07:50:32 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
Rob,
I'd be careful about drawing conclusions from the Hartzell plots. I've spoken with Les Doud too and got the impression that the three blade Hartzell is more efficient not because it's three blade, but because the design is newer and thus benefits from improved analysis, manufacturing, etc. Performance also depends on the power and speed of the airplane. Constant speed props are better over a range of speeds and powers than fixed pitch, but they're still optimized around a design point. I may be all wet, but thought the three blade scimitar was designed for the Legacy (speed and power) while the two blade is an older design not specifically optimized for the Legacy/IO-550. Where MT's various offerings fit within this range is a whole separate set of variables.
Les, please correct me if I'm wrong on any of this.
- Kyrilian

Sent from my iPad

On Jun 30, 2014, at 10:39 AM, "Stevens Family" <stevens5 [at] swiftdsl.com.au

> wrote:

I am interested in this subject, because I purchased a partly built kit some years ago, (which I am still building!) which came with an MT 3 bladed constant speed prop. In my conversation with a builder in South Australia recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2 blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs which indicate the 3 blades are more efficient! It was my understanding that because a 3 bladed prop generates 3 tip vortices against only two on a 2 bladed prop, it is less efficient.

 

 

Rob Stevens

Perth, Western Australia.

 

 

From: Lancair Mailing List [lml [at] lancaironline.net (mailto:)

] On Behalf Of Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud of Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He believes that the 3-blade is more effiicient than the two blade even in cruise.  I have a hard time believing that, and my airplane with 3 blades has not lived up to the prototype Legacy's performance with the 2-blade as documented in the CAFE report; and the 3-blade is heavier and more expensive to buy and overhaul.  Of course, my airplane is probably not as clean as the prototype.

 

But the 3-blade prop sure looks cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Wolfgang <Wolfgang [at] MiCom.net>
Sender: <marv [at] lancaironline.net>
Subject: Re: Two-blade or three-blade prop for I-550
Date: Tue, 01 Jul 2014 16:35:57 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
Only a 1% difference ?
Given the costs involved . . . is it worth it
?
 
Wolfgang
 
----- Original Message -----
Sent: Monday, June 30, 2014 7:38 AM
Subject: Re: Two-blade or three-blade
prop for I-550

I've enclosed the spreadsheet provided to me by Les Doud of Hartzell.
 In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the prototype.

But the 3-blade prop sure looks cool. 





From: "frederickemoreno [at] gmail.com

"
<frederickemoreno [at] gmail.com

>
Date: June 29, 2014 8:01:58 AM
CDT
Subject:
Two-blade or
three-blade prop for I-550



I have a chart somewhere from Hartzell which shows the theoretical
projection of prop efficiency vs speed for two vs three blade, and the
three blade is the winner by a small tweak, a per cent or two at the
higher speed.   Several years old, but I do not think the part
numbers have changed for the recommended Lancair props.
 
Fred Moreno



I've enclosed the spreadsheet provided to me by Les Doud of
Hartzell.  In 2009 his phone number was Phone: 937-778-4262 .  He
believes that the 3-blade is more effiicient than the two blade even in
cruise.  I have a hard time believing that, and my airplane with 3 blades
has not lived up to the prototype Legacy's performance with the 2-blade as
documented in the CAFE report; and the 3-blade is heavier and more expensive
to buy and overhaul.  Of course, my airplane is probably not as clean as
the prototype.

But the 3-blade prop sure looks cool.







From: "frederickemoreno [at] gmail.com"
<frederickemoreno [at] gmail.com>
Date: June 29, 2014 8:01:58 AM
CDT
Subject: Two-blade or three-blade prop for I-550


I have a
chart somewhere from Hartzell which shows the theoretical projection of prop
efficiency vs speed for two vs three blade, and the three blade is the winner
by a small tweak, a per cent or two at the higher speed.   Several
years old, but I do not think the part numbers have changed for the
recommended Lancair props.
 
Fred
Moreno

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Wolfgang <Wolfgang [at] MiCom.net>
Sender: <marv [at] lancaironline.net>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Tue, 01 Jul 2014 16:36:15 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
"the fewest
number of blades to get the job done is most efficient"
The only reason for more than two blades is you
have too much HP.
More blades (more blade area) will let you convert
that extra HP to thrust.
You can produce only so much thrust for a given
blade area and speed before you get blade stall.
 
Wolfgang
 
----- Original Message -----
Sent: Monday, June 30, 2014 4:10 PM
Subject: RE: [LML] Re: Two-blade or
three-blade prop for I-550

I
understood from conversations with some prop designers a few years ago (can’t
recall who) that the fewest number of blades to get the job done is most
efficient.  One blade would be best except for obvious balance
issues.  So the remaining factors include how much HP one blade can
absorb.  I seem to remember that three was the minimum for an engine that
goes much over 300 HP at least for the hubs and props we were looking at for
the IVP.  This info may have come from MT because I was looking at the
five blade MT vs four.  My understanding at that time was that more
blades result in  quieter smoother ops but give up small amounts of
efficiency.

 

Don’t
believe anything I say here.  The memories are about 10 years old.

 

John
Barrett

 

From: Lancair Mailing
List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of Stevens
Family
Sent: Monday, June 30, 2014 7:39 AM
To: Lancair
Mailing List
Subject: [LML] Re: Two-blade or three-blade prop for
I-550

 

I am interested in this subject, because I purchased a partly built
kit some years ago, (which I am still building!) which came with an MT 3
bladed constant speed prop. In my conversation with a builder in South
Australia recently, he mentioned that he had swapped out his 3 Blade MT prop
for a 2 blade prop, and increase his cruise speed by 7 knots. (Can’t recall if
that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the
graphs which indicate the 3 blades are more efficient! It was my understanding
that because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.

 

 

Rob Stevens

Perth, Western Australia.

 

 

From: Lancair Mailing
List [lml [at] lancaironline.net (mailto:)

]
On Behalf Of Charles Brown
Sent: Monday, 30 June 2014 7:38
PM
To: Lancair Mailing List
Subject: [LML] Re: Two-blade
or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to
me by Les Doud of Hartzell.  In 2009 his phone number
was Phone:
937-778-4262 .  He believes that the 3-blade
is more effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: <Sky2high [at] aol.com>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Tue, 1 Jul 2014 17:00:17 -0400 (EDT)
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Colyn,
 
As the 2 blade prop reaches horizontal, the descending blade has a
higher AOA and the descending blade has a lower AOA with respect to the relative
airflow.  In climb there are two airflow vectors to consider - vertical
relative to climb rate and horizontal relative to forward speed.  The
higher AOA creates more lift - that is why you hold right rudder in the climb
with a clockwise prop rotation.
 
With a three blade prop and when one blade is descending through the
horizontal, the other two are ascending, not at the opposing
horizontal minimum AOA.  Thus, the thrust is more even, the blades are
usually shorter and the tip vortice induced drag may be less because of reduced
tip speed.  When a blade is ascending and at the horizontal, the
other two are descending, but not at max lift AOA.  
 
It seems that 3 blades are smoother and a good match for 6 cylinder engines
when the prop is properly indexed.  That is the engine power pulses are
more even and the three blade lift curve is also smoother - even in
cruise.  With modern prop airfoils, the loss in cruise may be very
small.
 
Now you can think about 4 or 5 blades in climb and perhaps eight or twelve
cylinders or even two rows of 9 cylinders in a radial.
 
Grayhawk
 
In a message dated 6/30/2014 5:34:25 P.M. Central Daylight Time,
colyncase [at] earthlink.net writes:

Grayhawk,  could you please expand on that climb performance
argument a little?  


On Jun 30, 2014, at 11:13 AM, Sky2high [at] aol.com

wrote:


 
Here is more to think about (rather than just efficiency).
 
Blades > 2 = better climb performance - consider the relative air
(AOA) to the prop chord for both the ascending and descending blade
for a 2 blade versus longer arcs, better bites for more than 2
blades.  Don't confuse  this with level flight where all blades
see the same AOA.
 
Blades > 2 can produce the same thrust as Blades = 2 but the prop
diameter for more blades can be smaller, thus allowing for higher rpm whilst
still avoiding the tips going supersonic.  I.E. The further the tip from
the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the 320
- an 84 inch diameter prop cut down to 70 inches.  Most props
deliver max thrust about 2/3 out from the hub.  What did that mean for
the enormous chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its
path separation (interference) based on airspeed.  You'll be
surprised - odds are the bird will hit the windshield and not a prop blade at
cruise speed.
 
Hmmmm.....
 
Grayhawk
 
PS Computations left to the reader and EXCEL. 
 
In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time, stevens5 [at] swiftdsl.com.au


writes:

I
am interested in this subject, because I purchased a partly built kit some
years ago, (which I am still building!) which came with an MT 3 bladed
constant speed prop. In my conversation with a builder in South Australia
recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2
blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that
was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs
which indicate the 3 blades are more efficient! It was my understanding that
because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.

 

 

Rob
Stevens

Perth,
Western Australia.

 

 

From:
Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To:
Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade
prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud
of Hartzell.  In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 


=

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Colyn Case <colyncase [at] earthlink.net>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Wed, 2 Jul 2014 00:11:12 -0400
To: Lancair Mailing List <lml [at] lancaironline.net>
Message Header


Undecoded Message

Thanks Grayhawk.   I do think about more cylinders.    It doesn't seem fair that the old pistons made thousands of HP and we are stuck at 350.   A 500hp turbo-charged piston would cruise in turbine territory but have much better range.    ...and if it used some of the exotic metallurgy current in turbines it could be lighter than what we have today I expect.


On Jul 1, 2014, at 5:00 PM, Sky2high [at] aol.com

wrote:


Colyn,
 
As the 2 blade prop reaches horizontal, the descending blade has a
higher AOA and the descending blade has a lower AOA with respect to the relative
airflow.  In climb there are two airflow vectors to consider - vertical
relative to climb rate and horizontal relative to forward speed.  The
higher AOA creates more lift - that is why you hold right rudder in the climb
with a clockwise prop rotation.
 
With a three blade prop and when one blade is descending through the
horizontal, the other two are ascending, not at the opposing
horizontal minimum AOA.  Thus, the thrust is more even, the blades are
usually shorter and the tip vortice induced drag may be less because of reduced
tip speed.  When a blade is ascending and at the horizontal, the
other two are descending, but not at max lift AOA.  
 
It seems that 3 blades are smoother and a good match for 6 cylinder engines
when the prop is properly indexed.  That is the engine power pulses are
more even and the three blade lift curve is also smoother - even in
cruise.  With modern prop airfoils, the loss in cruise may be very
small.
 
Now you can think about 4 or 5 blades in climb and perhaps eight or twelve
cylinders or even two rows of 9 cylinders in a radial.
 
Grayhawk
 
In a message dated 6/30/2014 5:34:25 P.M. Central Daylight Time,
colyncase [at] earthlink.net

writes:

Grayhawk,  could you please expand on that climb performance
argument a little?  


On Jun 30, 2014, at 11:13 AM, Sky2high [at] aol.com

wrote:


 
Here is more to think about (rather than just efficiency).
 
Blades > 2 = better climb performance - consider the relative air
(AOA) to the prop chord for both the ascending and descending blade
for a 2 blade versus longer arcs, better bites for more than 2
blades.  Don't confuse  this with level flight where all blades
see the same AOA.
 
Blades > 2 can produce the same thrust as Blades = 2 but the prop
diameter for more blades can be smaller, thus allowing for higher rpm whilst
still avoiding the tips going supersonic.  I.E. The further the tip from
the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the 320
- an 84 inch diameter prop cut down to 70 inches.  Most props
deliver max thrust about 2/3 out from the hub.  What did that mean for
the enormous chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its
path separation (interference) based on airspeed.  You'll be
surprised - odds are the bird will hit the windshield and not a prop blade at
cruise speed.
 
Hmmmm.....
 
Grayhawk
 
PS Computations left to the reader and EXCEL. 
 
In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time, stevens5 [at] swiftdsl.com.au


writes:

I
am interested in this subject, because I purchased a partly built kit some
years ago, (which I am still building!) which came with an MT 3 bladed
constant speed prop. In my conversation with a builder in South Australia
recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2
blade prop, and increase his cruise speed by 7 knots. (Can’t recall if that
was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graphs
which indicate the 3 blades are more efficient! It was my understanding that
because a 3 bladed prop generates 3 tip vortices against only two on a 2
bladed prop, it is less efficient.

 

 

Rob
Stevens

Perth,
Western Australia.

 

 

From:
Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Charles Brown
Sent: Monday, 30 June 2014 7:38 PM
To:
Lancair Mailing List
Subject: [LML] Re: Two-blade or three-blade
prop for I-550

 

I've enclosed the spreadsheet provided to me by Les Doud
of Hartzell.  In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 


=

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: <Sky2high [at] aol.com>
Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550
Date: Wed, 2 Jul 2014 07:27:27 -0400 (EDT)
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message

Oops...  It is the ascending blade that has a lower AOA.
 
Grayhawk
 
In a message dated 7/1/2014 11:12:11 P.M. Central Daylight Time,
colyncase [at] earthlink.net writes:

Thanks
Grayhawk.   I do think about more cylinders.    It doesn't seem
fair that the old pistons made thousands of HP and we are stuck at 350.  
A 500hp turbo-charged piston would cruise in turbine territory but have much
better range.    ...and if it used some of the exotic metallurgy
current in turbines it could be lighter than what we have today I expect.


On Jul 1, 2014, at 5:00 PM, Sky2high [at] aol.com

wrote:


Colyn,
 
As the 2 blade prop reaches horizontal, the descending blade has a
higher AOA and the descending blade has a lower AOA with respect to the
relative airflow.  In climb there are two airflow vectors to consider -
vertical relative to climb rate and horizontal relative to forward
speed.  The higher AOA creates more lift - that is why you hold right
rudder in the climb with a clockwise prop rotation.
 
With a three blade prop and when one blade is descending through the
horizontal, the other two are ascending, not at the opposing
horizontal minimum AOA.  Thus, the thrust is more even, the blades
are usually shorter and the tip vortice induced drag may be less because of
reduced tip speed.  When a blade is ascending and at the
horizontal, the other two are descending, but not at max lift
AOA.  
 
It seems that 3 blades are smoother and a good match for 6 cylinder
engines when the prop is properly indexed.  That is the engine power
pulses are more even and the three blade lift curve is also smoother - even in
cruise.  With modern prop airfoils, the loss in cruise may be very
small.
 
Now you can think about 4 or 5 blades in climb and perhaps eight or
twelve cylinders or even two rows of 9 cylinders in a radial.
 
Grayhawk
 
In a message dated 6/30/2014 5:34:25 P.M. Central Daylight Time, colyncase [at] earthlink.net


writes:

Grayhawk,  could you please expand on that climb performance
argument a little?  


On Jun 30, 2014, at 11:13 AM, Sky2high [at] aol.com

wrote:


 
Here is more to think about (rather than just efficiency).
 
Blades > 2 = better climb performance - consider the relative air
(AOA) to the prop chord for both the ascending and descending
blade for a 2 blade versus longer arcs, better bites for more than 2
blades.  Don't confuse  this with level flight where all
blades see the same AOA.
 
Blades > 2 can produce the same thrust as Blades = 2 but the prop
diameter for more blades can be smaller, thus allowing for higher rpm whilst
still avoiding the tips going supersonic.  I.E. The further the tip
from the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the
320 - an 84 inch diameter prop cut down to 70 inches.  Most props
deliver max thrust about 2/3 out from the hub.  What did that mean for
the enormous chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its
path separation (interference) based on airspeed.  You'll be
surprised - odds are the bird will hit the windshield and not a prop blade
at cruise speed.
 
Hmmmm.....
 
Grayhawk
 
PS Computations left to the reader and EXCEL. 
 
In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time, stevens5 [at] swiftdsl.com.au


writes:

I
am interested in this subject, because I purchased a partly built kit some
years ago, (which I am still building!) which came with an MT 3 bladed
constant speed prop. In my conversation with a builder in South Australia
recently, he mentioned that he had swapped out his 3 Blade MT prop for a 2
blade prop, and increase his cruise speed by 7 knots. (Can’t recall if
that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the
graphs which indicate the 3 blades are more efficient! It was my
understanding that because a 3 bladed prop generates 3 tip vortices
against only two on a 2 bladed prop, it is less
efficient.

 

 

Rob
Stevens

Perth,
Western Australia.

 

 

From:
Lancair Mailing List [lml [at] lancaironline.net]">mailto:lml [at] lancaironline.net] On Behalf Of
Charles Brown
Sent: Monday, 30 June 2014 7:38
PM
To: Lancair Mailing List
Subject: [LML] Re:
Two-blade or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to me by Les
Doud of Hartzell.  In 2009 his phone number was Phone:
937-778-4262 .  He believes that the 3-blade is more
effiicient than the two blade even in cruise.  I have a hard time
believing that, and my airplane with 3 blades has not lived up to the
prototype Legacy's performance with the 2-blade as documented in the CAFE
report; and the 3-blade is heavier and more expensive to buy and overhaul.
 Of course, my airplane is probably not as clean as the
prototype.

 

But the 3-blade prop sure looks
cool. 

 


=


=

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Charles Brown <browncc1 [at] verizon.net>
Sender: <marv [at] lancaironline.net>
Subject: Re: Two-blade or three-blade prop for I-550
Date: Wed, 02 Jul 2014 08:19:26 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
Les Doud asserted that there was a crossover around 300hp where you want to go with 3 blades -- but without offering a really good rationale.  I'll make the following observations:

1.  Tip Mach is probably only an issue at top speed.  A quick hack shows that at 2700 rpm and 250ktas forward speed (basically Legacy max airspeed), the 70-inch 3-blade has a tip Mach of 0.84, vs the 72-inch 2-blade at 0.86 Mach.  That difference between .84 and .86 undoubtedly costs wave drag penalties -- at max speed.  At 2300rpm and 210ktas, the tip Machs are 0.72 and 0.73 -- negligible diff in wave drag.  

2.  3 tip vortices vs 2 --- is somewhat offset by decreased blade angle of attack.  The 3blade has more area, and operates at lower angle of attack for a given load and speed.  So the vortex shed by each 2-blade tip will be stronger than at each 3-blade tip; assuming similar blade aspect ratios, twist, etc.  

3.  Better takeoff and climb -- if you're operating at high horsepower and slow speed, the reduced angle of attack of the 3-blade makes operate at a better L/D, so it's a better "low gear".  I integrated Les Doud's static thrust for the two props from 0 to 75ktas, at 2100 lb gross weight, and came up with a roll of 400ft for the 2-blade, 342 ft for the 3-blade.  The 3-blade is also a better airbrake on approach, if you cut back to idle power.  

4.  The 3-blade is 20 lb heavier.  Assuming that cruise L/D is around 8:1, that 20 lb weight translates into about 2lb of drag, just offseting Les Doud's claimed 2lb cruise thrust increment.  (purists note:  I've assumed that the CGs are in the same place for 2- and 3-blades, so trim drag is identical.)

5.  Noise -- is probably better with 3-blade even if the noise energy is identical -- because it's shifted to a 50% higher frequency that's probably better damped by the airframe.  

6.  Looks -- no contest.

I think the most significant differences between the two props are purchase price, overhaul cost, takeoff roll, and looks.  Also -- you might choose the prop that puts the CG where you want it, if everything else is done and you don't want to move anything.  That 20 lb way out front translates to something like a full inch of CG position at middling aircraft weight.  

Charley





From: "John Barrett" <jbarrett [at] carbinge.com

>
Date: June 30, 2014 3:10:22 PM CDT
Subject: RE: [LML] Re: Two-blade or three-blade prop for I-550



I understood from conversations with some prop designers a few years ago (can’t recall who) that the fewest number of blades to get the job done is most efficient.  One blade would be best except for obvious balance issues.  So the remaining factors include how much HP one blade can absorb.  I seem to remember that three was the minimum for an engine that goes much over 300 HP at least for the hubs and props we were looking at for the IVP.  This info may have come from MT because I was looking at the five blade MT vs four.  My understanding at that time was that more blades result in  quieter smoother ops but give up small amounts of efficiency.

 

Don’t believe anything I say here.  The memories are about 10 years old.

 

John Barrett

 

Two-blade or three-blade prop for I-550

Submitted by Anonymous on

From: Gary Casey <casey.gary [at] yahoo.com>
Sender: <marv [at] lancaironline.net>
Subject: Re: Two-blade or three-blade prop for I-550
Date: Tue, 08 Jul 2014 07:54:51 -0400
To: <lml [at] lancaironline.net>
Message Header


Undecoded Message
I got curious about the math so I did some calculations of the vectors in a climb.  Assuming the wing angle of attack during climb is 3 degrees higher than at cruise,  The "down" blade (right sided) has a 0.5 degree higher angle of attack than the left side blade.  Further, the right blade sees a 3% higher apparent wind.  Both effects will make the right blade produce more thrust.  So it is probably significant.  The total thrust is something less than 700 pounds at that (130 mph) speed, so what would the thrust difference be?  At the highest I would guess the difference is less than 10% and that calculates to a torque of 280 ft-lb trying to turn the airplane to the left.  But to some extent the prop
"makes" its own wind and that reduces the effects.  But there is also the sprial slipstream that is acting on the tail and turning the plane left.  Also, the engine torque itself is trying to roll the plane left (noticeable if you have a P-51).  But the question was, is there a difference between 2 and 3-blade propellers?  I say the difference is very, very minor.  If the 3-blade has a smaller diameter, the effects of asymmetrical thrust is a tiny bit less than with a 2-blade.  Other things being equal (they never are), the 3-blade will produce more static thrust because it has more blade area, but the smaller diameter is working against it - a rule of thumb is that the static thrust is proportional to the square of the diameter.  But the greater blade area of the 3-blade has necessarily higher drag, which makes itself felt at cruise.  And then if the diameter (of the 2-blade) is such that the tips go transonic,
the drag can go up a lot.  Thousands of detail compromises have to be made.  Each blade "flies" in the wake of the previous blade, so the closer it is the poorer the effiicency.  The thrust, and consequently the amplitude of the noise pulse of each blade is less with more blades, but the frequency is higher.  So you pays your money and you takes your choice.  To me, a lightweight, slippery plane tends to favor the 2-blade.  But most everyone puts a 3-blade prop on them.

Hopefully reading this dissertation didn't cost you more than it was worth :-)



Oops...  It is the ascending blade that has a lower AOA.
=20
Grayhawk