X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from elasmtp-banded.atl.sa.earthlink.net ([209.86.89.70] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTP id 6960227 for lml@lancaironline.net; Wed, 02 Jul 2014 00:11:54 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.70; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=PAV8cvGktKJv30NKfr/uOTbD3PH8vLnVrOantkqhsOWr/yAIEky1IYNnadhSEmwW; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [71.181.16.185] (helo=[192.168.1.24]) by elasmtp-banded.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1X2Bt3-0007Ni-GI for lml@lancaironline.net; Wed, 02 Jul 2014 00:11:13 -0400 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: multipart/alternative; boundary=Apple-Mail-52-765310738 Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550 Date: Wed, 2 Jul 2014 00:11:12 -0400 In-Reply-To: To: "Lancair Mailing List" References: Message-Id: <48B1A4D0-ED2D-487B-8292-E1B8FE51CB48@earthlink.net> X-Mailer: Apple Mail (2.1085) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da940c96db190ce89cfa6462d6c1682ddad97350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 71.181.16.185 --Apple-Mail-52-765310738 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 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@aol.com wrote: Colyn, =20 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. =20 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. =20 =20 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. =20 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. =20 Grayhawk =20 In a message dated 6/30/2014 5:34:25 P.M. Central Daylight Time, = colyncase@earthlink.net writes: Grayhawk, could you please expand on that climb performance argument a = little? =20 On Jun 30, 2014, at 11:13 AM, Sky2high@aol.com wrote: Hmmmm....... See http://en.wikipedia.org/wiki/Single-blade_propeller =20 Here is more to think about (rather than just efficiency). =20 Blades > 2 =3D 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. =20 Blades > 2 can produce the same thrust as Blades =3D 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.=20 =20 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? =20 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. =20 Hmmmm..... =20 Grayhawk =20 PS Computations left to the reader and EXCEL.=20 =20 In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time, = stevens5@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=92t 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. =20 =20 Rob Stevens Perth, Western Australia. =20 =20 From: Lancair Mailing List [mailto:lml@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 =20 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. =20 But the 3-blade prop sure looks cool.=20 =20 =3D --Apple-Mail-52-765310738 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 Sky2high@aol.com= wrote:
Colyn,
 
As the 2 blade prop reaches horizontal, the descending blade = has a=20 higher AOA and the descending blade has a lower AOA with respect to the = relative=20 airflow.  In climb there are two airflow vectors to consider - = vertical=20 relative to climb rate and horizontal relative to forward speed.  = The=20 higher AOA creates more lift - that is why you hold right rudder in the = climb=20 with a clockwise prop rotation.
 
With a three blade prop and when one blade is descending = through the=20 horizontal, the other two are ascending, not at the opposing=20 horizontal minimum AOA.  Thus, the thrust is more even, the = blades are=20 usually shorter and the tip vortice induced drag may be less because of = reduced=20 tip speed.  When a blade is ascending and at the = horizontal, the=20 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=20 when the prop is properly indexed.  That is the engine power pulses = are=20 more even and the three blade lift curve is also smoother - even in=20 cruise.  With modern prop airfoils, the loss in cruise may be very=20= small.
 
Now you can think about 4 or 5 blades in climb and perhaps eight or = twelve=20 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,=20 colyncase@earthlink.net = writes:
Grayhawk,  could you = please expand on that climb performance=20 argument a little?  =20

On Jun 30, 2014, at 11:13 AM, Sky2high@aol.com wrote:

 
Here is more to think about (rather than just efficiency).
 
Blades > 2 =3D better climb performance - consider the = relative air=20 (AOA) to the prop chord for both the ascending and = descending blade=20 for a 2 blade versus longer arcs, better bites for more than 2=20 blades.  Don't confuse  this with level flight where = all blades=20 see the same AOA.
 
Blades > 2 can produce the same thrust as Blades =3D 2 but the = prop=20 diameter for more blades can be smaller, thus allowing for higher rpm = whilst=20 still avoiding the tips going supersonic.  I.E. The further the = tip from=20 the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for = the 320=20 - an 84 inch diameter prop cut down to 70 inches.  Most = props=20 deliver max thrust about 2/3 out from the hub.  What did that = mean for=20 the enormous chord and pitch for that prop?
 
Finally, consider the corkscrew path of each blade tip and its=20 path separation (interference) based on airspeed.  = You'll be=20 surprised - odds are the bird will hit the windshield and not a prop = blade at=20 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@swiftdsl.com.au=20 writes:

I=20 am interested in this subject, because I purchased a partly built = kit some=20 years ago, (which I am still building!) which came with an MT 3 = bladed=20 constant speed prop. In my conversation with a builder in South = Australia=20 recently, he mentioned that he had swapped out his 3 Blade MT prop = for a 2=20 blade prop, and increase his cruise speed by 7 knots. (Can=92t = recall if that=20 was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the = graphs=20 which indicate the 3 blades are more efficient! It was my = understanding that=20 because a 3 bladed prop generates 3 tip vortices against only two on = a 2=20 bladed prop, it is less efficient.

 

 

Rob=20 Stevens

Perth,=20 Western Australia.

 

 

From:=20 Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of=20= Charles Brown
Sent: Monday, 30 June 2014 7:38 = PM
To:=20 Lancair Mailing List
Subject: [LML] Re: Two-blade or = three-blade=20 prop for I-550

 

I've enclosed the spreadsheet provided = to me by Les Doud=20 of Hartzell.  In 2009 his phone number was Phone:=20 937-778-4262 .  He believes that the 3-blade is = more=20 effiicient than the two blade even in cruise.  I have a hard = time=20 believing that, and my airplane with 3 blades has not lived up to = the=20 prototype Legacy's performance with the 2-blade as documented in the = CAFE=20 report; and the 3-blade is heavier and more expensive to buy and = overhaul.=20  Of course, my airplane is probably not as clean as the=20 prototype.

 

But the 3-blade prop sure looks=20 cool. 

 

<= /div>

=3D

= --Apple-Mail-52-765310738--