X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from omr-m02.mx.aol.com ([64.12.143.76] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6959815 for lml@lancaironline.net; Tue, 01 Jul 2014 17:00:52 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.143.76; envelope-from=Sky2high@aol.com Received: from mtaomg-mce01.mx.aol.com (mtaomg-mce01.mx.aol.com [172.29.27.207]) by omr-m02.mx.aol.com (Outbound Mail Relay) with ESMTP id BE9E0702A794E for ; Tue, 1 Jul 2014 17:00:17 -0400 (EDT) Received: from core-mld003b.r1000.mail.aol.com (core-mld003.r1000.mail.aol.com [172.29.122.81]) by mtaomg-mce01.mx.aol.com (OMAG/Core Interface) with ESMTP id 9870238000081 for ; Tue, 1 Jul 2014 17:00:17 -0400 (EDT) From: Sky2high@aol.com Full-name: Sky2high Message-ID: <7a5eb.7ec72515.40e47b61@aol.com> Date: Tue, 1 Jul 2014 17:00:17 -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_7a5eb.7ec72515.40e47b61_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=1404248417; bh=/L9vnEPHgvnpTLojZlbq5qSdz2k2IisVJQxbz4tR+ec=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=Knb+T7xjhA8f2oynOyPsnJ4RU24QmzeRLLiDRJu9/1vpVBzaWWKLNBQGA7l8XZ0rU iSL5/H+zoSa3IWeFj9T7v19JNw/SQ73a34TXdoVTQT6ye98lPhRf/OfgUUu6fGo2fx IvyowqwggXb311PsrU+cOsRgjjwz4Kb+a+kK+PCk= x-aol-sid: 3039ac1d1bcf53b321616b2e --part1_7a5eb.7ec72515.40e47b61_boundary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en 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 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 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 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 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 =3D --part1_7a5eb.7ec72515.40e47b61_boundary Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
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 rel= ative=20 airflow.  In climb there are two airflow vectors to consider - vertica= l=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 cli= mb=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 blade= s are=20 usually shorter and the tip vortice induced drag may be less because of red= uced=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 en= gines=20 when the prop is properly indexed.  That is the engine power pulses ar= e=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 tw= elve=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 perfor= mance=20 argument a little?  =20

On Jun 30, 2014, at 11:13 AM, Sky2high@aol.com wrote:
Hmmmm.......  See http://en.wi= kipedia.org/wiki/Single-blade_propeller
 
Here is more to think about (rather than just efficiency).
 
Blades > 2 =3D better climb performance - consider the relative a= ir=20 (AOA) to the prop chord for both the ascending and descending b= lade=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 b= lades=20 see the same AOA.
 
Blades > 2 can produce the same thrust as Blades =3D 2 but the pr= op=20 diameter for more blades can be smaller, thus allowing for higher rpm whi= lst=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 f= or=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 blad= e 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 s= ome=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 Austral= ia=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 re= call if that=20 was 7 Kts indicated, or 7 Kts TAS.) Not sure how this fits with the gra= phs=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-bl= ade=20 prop for I-550

 

I've enclosed the spreadsheet provided to me by Le= s 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 CA= FE=20 report; and the 3-blade is heavier and more expensive to buy and overha= ul.=20  Of course, my airplane is probably not as clean as the=20 prototype.

 

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

 


=3D
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