X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from elasmtp-dupuy.atl.sa.earthlink.net ([209.86.89.62] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTP id 6958345 for lml@lancaironline.net; Mon, 30 Jun 2014 18:34:18 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.62; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=DBmfonEAxfeDZb8a3ypCbvwd/D3GNv2zEQPWJK+IZuj3f1B0EjljxbQtOxSMr5Fd; 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 [70.20.41.183] (helo=[192.168.1.24]) by elasmtp-dupuy.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1X1k8m-0003du-Bv for lml@lancaironline.net; Mon, 30 Jun 2014 18:33:37 -0400 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: multipart/alternative; boundary=Apple-Mail-131-658651917 Subject: Re: [LML] Re: Two-blade or three-blade prop for I-550 Date: Mon, 30 Jun 2014 18:33:34 -0400 In-Reply-To: To: "Lancair Mailing List" References: Message-Id: X-Mailer: Apple Mail (2.1085) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da94013d2cf294394c23bf848994fd8289e8f350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 70.20.41.183 --Apple-Mail-131-658651917 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 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 --Apple-Mail-131-658651917 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 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 = deliver=20 max thrust about 2/3 out from the hub.  What did that mean for the = enormous=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 = 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 of=20 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>

= --Apple-Mail-131-658651917--