X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from omr-d01.mx.aol.com ([205.188.252.208] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6960515 for lml@lancaironline.net; Wed, 02 Jul 2014 07:28:04 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.252.208; envelope-from=Sky2high@aol.com Received: from mtaomg-aaf02.mx.aol.com (mtaomg-aaf02.mx.aol.com [172.26.127.100]) by omr-d01.mx.aol.com (Outbound Mail Relay) with ESMTP id 7A9A4700567CB for ; Wed, 2 Jul 2014 07:27:29 -0400 (EDT) Received: from core-mlc003b.r1000.mail.aol.com (core-mlc003.r1000.mail.aol.com [172.29.188.209]) by mtaomg-aaf02.mx.aol.com (OMAG/Core Interface) with ESMTP id 5364038000081 for ; Wed, 2 Jul 2014 07:27:29 -0400 (EDT) From: Sky2high@aol.com Full-name: Sky2high Message-ID: <88b90.409c6576.40e5469f@aol.com> Date: Wed, 2 Jul 2014 07:27:27 -0400 (EDT) Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550 To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_88b90.409c6576.40e5469f_boundary" X-Mailer: AOL 9.6 sub 168 X-Originating-IP: [24.14.166.87] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1404300449; bh=uq8x/BcynWlbchC71TT5RLEaY5ZMOVd9QgWA1QLKFS4=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=gBwUfStHmeJExyFekV5S0pW6gD0Hstbu3aK/EsjNOBpiNKdbpYXOETDeS/6589iyy rx0revDpTNRsYNimGwMhlefuHKeTs1rXeSKgyVnqZ8859xlOSaQl3uERKMz/CGcHD9 KlDaYyA7FwIpyWI7HvgJUDhyToK9ReIkx9bCVvJ8= x-aol-sid: 3039ac1a7f6453b3eca13133 --part1_88b90.409c6576.40e5469f_boundary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Oops... It is the ascending blade that has a lower AOA. =20 Grayhawk =20 =20 In a message dated 7/1/2014 11:12:11 P.M. Central Daylight Time, =20 colyncase@earthlink.net writes: Thanks Grayhawk. I do think about more cylinders. It doesn't seem =20 fair that the old pistons made thousands of HP and we are stuck at 350. = A=20 500hp turbo-charged piston would cruise in turbine territory but have much = =20 better range. ...and if it used some of the exotic metallurgy current i= n=20 turbines it could be lighter than what we have today I expect. =20 On Jul 1, 2014, at 5:00 PM, _Sky2high@aol.com_ (mailto:Sky2high@aol.com) = =20 wrote: Colyn, =20 As the 2 blade prop reaches horizontal, the descending blade has a higher= =20 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 high= er=20 AOA creates more lift - that is why you hold right rudder in the climb wit= h a=20 clockwise prop rotation. =20 With a three blade prop and when one blade is descending through the =20 horizontal, the other two are ascending, not at the opposing horizontal mi= nimum=20 AOA. Thus, the thrust is more even, the blades are usually shorter and th= e=20 tip vortice induced drag may be less because of reduced tip speed. When a= =20 blade is ascending and at the horizontal, the other two are descending,=20 but not at max lift AOA. =20 =20 It seems that 3 blades are smoother and a good match for 6 cylinder =20 engines when the prop is properly indexed. That is the engine power pulse= s are=20 more even and the three blade lift curve is also smoother - even in cruise= . =20 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= =20 cylinders or even two rows of 9 cylinders in a radial. =20 Grayhawk =20 =20 In a message dated 6/30/2014 5:34:25 P.M. Central Daylight Time,=20 _colyncase@earthlink.net_ (mailto:colyncase@earthlink.net) writes: Grayhawk, could you please expand on that climb performance argument a=20 little? =20 On Jun 30, 2014, at 11:13 AM, _Sky2high@aol.com_ (mailto:Sky2high@aol.com) = =20 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=20 the prop chord for both the ascending and descending blade for a 2 blade= =20 versus longer arcs, better bites for more than 2 blades. Don't confuse = =20 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 diamet= er=20 for more blades can be smaller, thus allowing for higher rpm whilst still= =20 avoiding the tips going supersonic. I.E. The further the tip from the hub= =20 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= =20 84 inch diameter prop cut down to 70 inches. Most props deliver max thrus= t=20 about 2/3 out from the hub. What did that mean for the enormous chord and= =20 pitch for that prop? =20 Finally, consider the corkscrew path of each blade tip and its path=20 separation (interference) based on airspeed. You'll be surprised - odds a= re the=20 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 =20 In a message dated 6/30/2014 9:39:14 A.M. Central Daylight Time,=20 _stevens5@swiftdsl.com.au_ (mailto:stevens5@swiftdsl.com.au) writes: =20 I am interested in this subject, because I purchased a partly built kit=20 some years ago, (which I am still building!) which came with an MT 3 blade= d =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=E2=80=99t 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=20 that because a 3 bladed prop generates 3 tip vortices against only two on = a 2=20 bladed prop, it is less efficient.=20 Rob Stevens=20 Perth, Western Australia.=20 =20 =20 From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of =20 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= =20 2009 his phone number was Phone: 937-778-4262 . He believes that the=20 3-blade is more effiicient than the two blade even in cruise. I have a ha= rd=20 time 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. = Of=20 course, my airplane is probably not as clean as the prototype. =20 =20 But the 3-blade prop sure looks cool.=20 =20 =3D =3D --part1_88b90.409c6576.40e5469f_boundary Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
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,=20 colyncase@earthlink.net writes:
= Thanks=20 Grayhawk.   I do think about more cylinders.    It doesn't= seem=20 fair that the old pistons made thousands of HP and we are stuck at 350. &= nbsp;=20 A 500hp turbo-charged piston would cruise in turbine territory but have m= uch=20 better range.    ...and if it used some of the exotic metallurg= y=20 current in turbines it could be lighter than what we have today I expect.= =20

On Jul 1, 2014, at 5:00 PM, Sky2high@aol.com wrote:
Colyn,
 
As the 2 blade prop reaches horizontal, the descending blade ha= s a=20 higher AOA and the descending blade has a lower AOA with respect to the= =20 relative airflow.  In climb there are two airflow vectors to conside= r -=20 vertical relative to climb rate and horizontal relative to forward=20 speed.  The higher AOA creates more lift - that is why you hold righ= t=20 rudder in the climb with a clockwise prop rotation.
 
With a three blade prop and when one blade is descending throug= h the=20 horizontal, the other two are ascending, not at the opposing=20 horizontal minimum AOA.  Thus, the thrust is more even, the bla= des=20 are usually shorter and the tip vortice induced drag may be less because = of=20 reduced tip speed.  When a blade is ascending and at the=20 horizontal, the other two are descending, but not at max lift=20 AOA.  
 
It seems that 3 blades are smoother and a good match for 6 cylinder= =20 engines when the prop is properly indexed.  That is the engine power= =20 pulses are more even and the three blade lift curve is also smoother - ev= en 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= =20 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@earthlink.net=20 writes:
Grayhawk,  could you please expand on that climb perf= ormance=20 argument a little?  =20

On Jun 30, 2014, at 11:13 AM, Sky2high@aol.com wrote:
<= FONT=20 color=3D#000000 size=3D2 face=3DArial>
Hmmmm.......  See http://en.= wikipedia.org/wiki/Single-blade_propeller
 
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= =20 blade for a 2 blade versus longer arcs, better bites for more than= 2=20 blades.  Don't confuse  this with level flight where all= =20 blades 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 w= hilst=20 still avoiding the tips going supersonic.  I.E. The further the ti= p=20 from the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for t= he=20 320 - an 84 inch diameter prop cut down to 70 inches.  Most p= rops=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'l= l be=20 surprised - odds are the bird will hit the windshield and not a prop bl= ade=20 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, <= A=20 title=3Dmailto:stevens5@swiftdsl.com.au=20 href=3D"mailto:stevens5@swiftdsl.com.au">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 blade= d=20 constant speed prop. In my conversation with a builder in South Austr= alia=20 recently, he mentioned that he had swapped out his 3 Blade MT prop fo= r a 2=20 blade prop, and increase his cruise speed by 7 knots. (Can=E2=80=99t = recall if=20 that was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with = the=20 graphs which indicate the 3 blades are more efficient! It was my=20 understanding that because a 3 bladed prop generates 3 tip vortices= =20 against only two on a 2 bladed prop, it is less=20 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=20 PM
To: Lancair Mailing List
Subject: [LML] Re:=20 Two-blade or three-blade prop for I-550

 

I've enclosed the spreadsheet provided to me by = Les=20 Doud 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 tim= e=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 over= haul.=20  Of course, my airplane is probably not as clean as the=20 prototype.

 

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

 

=

=3D

=3D
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