X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from omr-d04.mx.aol.com ([205.188.109.201] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6957539 for lml@lancaironline.net; Mon, 30 Jun 2014 11:14:05 -0400 Received-SPF: pass receiver=logan.com; client-ip=205.188.109.201; envelope-from=Sky2high@aol.com Received: from mtaomg-mce02.mx.aol.com (mtaomg-mce02.mx.aol.com [172.29.27.208]) by omr-d04.mx.aol.com (Outbound Mail Relay) with ESMTP id DB19F70047DCF for ; Mon, 30 Jun 2014 11:13:30 -0400 (EDT) Received: from core-mla001b.r1000.mail.aol.com (core-mla001.r1000.mail.aol.com [172.29.186.79]) by mtaomg-mce02.mx.aol.com (OMAG/Core Interface) with ESMTP id AD60A38000084 for ; Mon, 30 Jun 2014 11:13:30 -0400 (EDT) From: Sky2high@aol.com Full-name: Sky2high Message-ID: <49b89.6ee2da7b.40e2d89a@aol.com> Date: Mon, 30 Jun 2014 11:13:30 -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_49b89.6ee2da7b.40e2d89a_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=1404141210; bh=bokmUuZRjRGoUi9qlG69wstuF7TDD+xdG+OX7k7v1Wo=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=VTzvkYfxBPf8TK7YwxGLeK3nUzU4E1o7wcsg0/uocKDBIkHoMEjLVmxEaDItfwGRj B6IQZOLBTqeaY9NG7guhTROdZMI9rfyWmjEHECy0w52XC6uUPP5OFGbf+V2i/i+xNM sPvCnO/go6tKgiO0Po/ZTBVFf9ji+nFUwNGjlw4g= x-aol-sid: 3039ac1d1bd053b17e9a37b9 --part1_49b89.6ee2da7b.40e2d89a_boundary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en 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 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 tha= t=20 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 --part1_49b89.6ee2da7b.40e2d89a_boundary Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Hmmmm.......  See http://en.wiki= pedia.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 bla= de=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 bla= des=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 whils= t=20 still avoiding the tips going supersonic.  I.E. The further the tip fr= om=20 the hub the faster the tip is moving at a fixed rpm. 
 
Momentarily consider the weird 2-blade Hartzell CS prop for the 3= 20 -=20 an 84 inch diameter prop cut down to 70 inches.  Most props deliv= er=20 max thrust about 2/3 out from the hub.  What did that mean for the eno= rmous=20 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,=20 stevens5@swiftdsl.com.au writes:
=

I=20 am interested in this subject, because I purchased a partly built kit som= e=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=E2=80=99t reca= ll if that=20 was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the graph= s=20 which indicate the 3 blades are more efficient! It was my understanding t= hat=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: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. 

 

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