X-Virus-Scanned: clean according to Sophos on Logan.com From: "Christamarmc" Received: from mail-pd0-f170.google.com ([209.85.192.170] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6999822 for flyrotary@lancaironline.net; Fri, 25 Jul 2014 19:51:00 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.85.192.170; envelope-from=christamarmc@gmail.com Received: by mail-pd0-f170.google.com with SMTP id g10so6503387pdj.1 for ; Fri, 25 Jul 2014 16:50:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:references:from:content-type:in-reply-to:message-id:date:to :content-transfer-encoding:mime-version; bh=6o2FBHl1mMOQAvyDyCO41VvGLZNLmZaIACEn4cowI5Q=; b=iIX+H94/zmBMxIvHFaRgAEbbzZcJZeQpHr7SMEV2QCNa1KCJx1/aibNWva4IyAf6oW zpFrr3x3/2hK7D080+1IzgczKsCR7wAUHT1whSTXQGgEV7+8L9SplKKl9QgpL6sr80Gh QY/Cb/qewMhfFfLzsKIn8I4Qaca1/gmboNAOhw/gsBuyVH637vLmUQSQ8PaRIXNjUmac 0NFXHrqJbE6tesviiUGJ3ahZV7SOmvoS0t/4rTkTpQ25K5MjQ2iD7WyGWel8THe0D1Zk hJKZetGAInLL3rH+lfmlWGATOQ3N5lsHpMYgQ4cLD+yAbK/llB82lwNxJUTt2Ng4t6xa m03w== X-Received: by 10.70.0.48 with SMTP id 16mr22299380pdb.8.1406332225745; Fri, 25 Jul 2014 16:50:25 -0700 (PDT) Return-Path: Received: from [192.168.0.3] (210.88.215.218.dyn.commander.net.au. [218.215.88.210]) by mx.google.com with ESMTPSA id ix7sm10023532pbd.36.2014.07.25.16.50.22 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 25 Jul 2014 16:50:24 -0700 (PDT) Subject: Re: [FlyRotary] Re: Rv7 renises p port References: Content-Type: multipart/alternative; boundary=Apple-Mail-FCA6E19A-0A62-4C13-87E2-DB8F23547AEE X-Mailer: iPad Mail (11D201) In-Reply-To: Message-Id: Date: Sat, 26 Jul 2014 09:50:22 +1000 To: Rotary motors in aircraft Content-Transfer-Encoding: 7bit Mime-Version: 1.0 (1.0) --Apple-Mail-FCA6E19A-0A62-4C13-87E2-DB8F23547AEE Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable I understand a bit more about the prop design now, theoretically speaking it= would be nice in a perfect world for all to use the same pitch measurement l= ike inches from the hub etc, but I guess it's not a perfect ideah as there a= re many differing designs of blades and tips etc Also we are never quite sure where the manufacturer has measured there pitch= on all there differing props so I guess it is a starting point for which pr= op to start with and then trial and error after that. Thanks all for your input Cheers Christian Sent from my iPad > On 26 Jul 2014, at 5:48 am, "Jeff Whaley" wr= ote: >=20 > We have had this discussion before =E2=80=A6 I=E2=80=99ll go out on a limb= here and agree with both James and Charlie. That is to say the prop pitch i= s not the same from one end to the other; therefore the =E2=80=9Ceffective p= itch=E2=80=9D is an estimation; and that doing better than theoretical is si= mply an error in the pitch estimation. It is impossible for any propeller t= o work at 100% or greater efficiency. Considering Tracy=E2=80=99s example o= f 217 mph Vs 212 mph is an error of only 2.5% (not accounting for the takeof= f and climb), possibly as much as 5-10% if takeoff and climb considered =E2=80= =A6 is that too hard to believe? You need a pretty slippery ship to get nea= r the =E2=80=9Ceffective pitch=E2=80=9D performance; here=E2=80=99s another e= xample. My Tri-Pacer has a 57=E2=80=9D pitch propeller that cruises at 2300= rpm =E2=80=93 theoretically this is 124 mph, exactly what the owner=E2=80=99= s manual says; however, I can tell you that the airplane hasn=E2=80=99t seen= 124 mph since the last time it was dove in a loop-entry =E2=80=93 it cruise= s at 90 knots (104 mph) or 20% off the theoretical prop pitch =E2=80=93 it i= s not a slippery ship =E2=80=A6 Jeff > =20 > From: > "Tracy" > Subject: > Re: [FlyRotary] Re: Rv7 renises p port > Date: > Thu, 24 Jul 2014 12:09:11 -0400 > To: > Rotary motors in aircraft > >=20 > > Charlie is right. Consider that an airplane flying with the wing at 0 deg= . AOA does not fall out of the sky :-) > =20 > My average speed in the 2004 Sun 100 race was 217.58 mph which includes st= anding start takeoff and climbout. Prop was a 74 x 88, RPM was 7250 with a 2= .85 : 1 drive. If you calculate that out it comes to 212 mph with zero 'sli= ppage'. Draw your own conclusions! > =20 > Tracy >=20 > Sent from my iPad > =20 > From: > "Charlie England" > Subject: > Re: [FlyRotary] Re: Rv7 renises p port > Date: > Thu, 24 Jul 2014 17:49:27 -0500 > To: > Rotary motors in aircraft > >=20 > > The 'negative slippage' was a tongue in cheek verbal concoction intended t= o hint at the fact that 'slippage' is an artifact of old hangar tails based o= n lack of understanding, even among 'experts' of old, of how a prop actually= works.=20 >=20 > (insert pause here to parse that awful sentence....) >=20 > 'Pitch' implies that a prop is a screw. A prop isn't a screw. It's an airf= oil (properly made, a *twisted* airfoil) that rotates. If you put the flat b= lades from a ceiling fan on the nose of an airplane, then 'pitch' might have= some actual meaning (but I don't think so).=20 >=20 > Consider that 'pitch' is usually measured somewhere between 2/3 & 3/4 out f= rom the center to the tip of a blade. If you measure 'pitch' near the root, y= ou'd probably get something like 120-140 inches of pitch on a prop for RV's o= r EZ's, etc, and at the tip it would probably be something like 60", begging= the question, which part of the prop is actually screwing through the air a= t a particular 'pitch'. It doesn't mean that almost half the prop is 'slippi= ng' and almost to half the prop is actually dragging, with a couple of inche= s moving the plane. It just means that each 'station' of the prop blade must= be pitched to generate thrust at the relative speed it moves through the ai= r. The airfoil (BTW, I've never seen a symmetrical prop airfoil) is, or at l= east *can*, make the air move aft faster than the 'pitch' of the imagined sc= rew is moving through the air. Just like a sailing vessel, it's not moving d= irectly with the wind; it's moving at an angle. The relative wind for the pr= op is not aligned with the path of the plane.=20 >=20 > Depending on your religion, either Newton or Bernoulli makes the air go ba= ck when the prop spins. Polytheists like me believe in both.=20 >=20 > I love talking religion. Can we talk about politics next? >=20 > Charlie > ;-) >=20 > On 7/24/2014 12:18 PM, James Osborn wrote: > Charlie said: Ice sails, desert sails, and now, even unlimited class sail= boats can sail faster than the wind. 'Negative slippage'. :-) > =20 > I don't think the analogy quite applies here. For those types of crafts i= t is the wind that is doing the powering. While it is true these types of c= raft can sail faster than the wind, but not while pointing straight into it!= By definition to cruise in an airplane, the prop has to be generating some= kind of thrust and therefore could never go faster than "the wind" - the on= ly wind it sees is the relative wind that is generated due to its own thrust= (in cruise). In a descent, sure negative slippage is a fact. And slippage= has to increase greatly in a climb. I guess I am arguing that the only way= you could see zero or negative slippage in cruise is if either your blade c= ross section is asymmetrical (it usually is right?) or if the pitch number u= sed in the calculation is not really right based on the kinds of factors you= outlined Charlie. > =20 > Supposing that we have a typical non-symmetric blade cross section, an acc= urate pitch based on the chord line of the cross section, and I suppose a tw= ist that is correct for the cruise RPM. What then would be considered a goo= d or reasonable slippage in cruise? I saw 3% thrown out there. And if your= prop selection is good for all those conditions (in other words as efficien= t as possible), is this the slippage you expect? I am just wondering if you= can use a slippage calculation to judge efficiency (roughly). > =20 > -- James >=20 > On Wed, Jul 23, 2014 at 7:59 PM, Charlie England wrote: > Ice sails, desert sails, and now, even unlimited class sailboats can sail f= aster than the wind. 'Negative slippage'. :-) >=20 > A more significant point might be that pitch numbers are virtually meaning= less, unless you're comparing two props from the same prop maker with the sa= me blade plan form. Even then, it just tells you which has a finer pitch tha= n the other. >=20 > Variables can be: whether the pitch is measured on the back side of the bl= ade or through the chord line, where along the diameter the pitch angle is m= easured (due to blade twist), and no doubt others I'm not smart enough to th= ink of at the moment.=20 >=20 > Bottom line is that unless there's an identical airframe flying an identic= al prop, the pitch number isn't a reliable indicator of speed. >=20 > FWIW, >=20 > Charlie >=20 >=20 >=20 >=20 > On 7/23/2014 7:45 PM, James Osborn wrote: > I don't know jack about slippage, but I think it is the percentage differe= nce between actual distance traveled and theoretical distance traveled if yo= ur propeller corkscrewed through the air with no thrust. I found a prop sli= p calculator online and for 86 inch pitch, 2.85 gear ratio, 7000 rpm, 180 mp= h, I get 10% slip. Granted the calculator was for boat propellers, but I do= n't think it matters as long as the units are correct. There has to be some= slip because there would be no thrust otherwise. So what is considered a r= easonable or good amount of slip? Using Bill's numbers 86 inch pitch, 2.85 g= ear ratio, 7000 rpm, 200 mph, I get 0% slip. That can't be right! > =20 >=20 > On Fri, Jul 4, 2014 at 7:19 AM, Bill Bradburry wrote: > Christian, >=20 > It seems that you have a lot of prop slippage at cruise. I think that at > that prop rpm you should be getting 200mph if you had no slippage. >=20 > Bill >=20 > -----Original Message----- > From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] > Sent: Thursday, July 03, 2014 4:01 PM > To: Rotary motors in aircraft > Subject: [FlyRotary] Rv7 renises p port >=20 > Well hi all > Just thought I'd throw out there the mods I,ve done to the renises in an > rv7'. > Well the p ported engine is now back in the plane and running well, over t= he > standard short manifold that was originally in the plane I have gained > around 400 static rpm, same prop and gearbox combo, 2.85 ratio, this equat= es > to allot more hp at takeoff, just shy of 2300 prop rpm, I'm running a prin= ce > p tip prop at 68" x 86" pitch, > At 8000 ft it is turning 7000 at 180 mph tas which is an improvement of 25= > mph on previous tests, . So next plan is bigger prop and less pitch to let= > it rev to 7500 in strait and level. >=20 > Cheers > Christian > Rv7 renises Aus >=20 >=20 > Sent from my iPad > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html >=20 >=20 > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List= .html > =20 > This message, and the documents attached hereto, is intended only for the a= ddressee and may contain privileged or confidential information. Any unautho= rized disclosure is strictly prohibited. If you have received this message i= n error, please notify us immediately so that we may correct our internal re= cords. Please then delete the original message. Thank you. --Apple-Mail-FCA6E19A-0A62-4C13-87E2-DB8F23547AEE Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable

I understand a bit more= about the prop design now, theoretically speaking it would be nice in a pe= rfect world for all to use the same pitch measurement like inches from the h= ub etc, but I guess it's not a perfect ideah as there are many differing des= igns of blades and tips etc
Also we are never quite sure where the= manufacturer has measured there pitch on all there differing props so I gue= ss it is a starting point for which prop to start with and then trial and er= ror after that.

Thanks all for your input
Cheers
Christian

Sent from my iPad

On 26 Jul= 2014, at 5:48 am, "Jeff Whaley" <flyrotary@lancaironline.net> wrote:

=

We have had this discussion before =E2=80=A6 I=E2=80=99= ll go out on a limb here and agree with both James and Charlie.  That i= s to say the prop pitch is not the same from one end to the other; therefore= the =E2=80=9Ceffective pitch=E2=80=9D is an estimation; and that doing better than theoretical is simply an error in the pitch estimation.&n= bsp; It is impossible for any propeller to work at 100% or greater efficienc= y.  Considering Tracy=E2=80=99s example of 217 mph Vs 212 mph is an err= or of only 2.5% (not accounting for the takeoff and climb), possibly as much as 5-10% if takeoff and climb considered =E2=80= =A6 is that too hard to believe?  You need a pretty slippery ship to ge= t near the =E2=80=9Ceffective pitch=E2=80=9D performance; here=E2=80=99s ano= ther example.  My Tri-Pacer has a 57=E2=80=9D pitch propeller that crui= ses at 2300 rpm =E2=80=93 theoretically this is 124 mph, exactly what the owner= =E2=80=99s manual says; however, I can tell you that the airplane hasn=E2=80= =99t seen 124 mph since the last time it was dove in a loop-entry =E2=80=93 i= t cruises at 90 knots (104 mph) or 20% off the theoretical prop pitch =E2=80=93 it is not a slippery ship =E2=80=A6  Jeff

 

From:

"Tracy" <flyrotary@lancaironline.net>

Subject:

Re: [FlyRotary] Re: Rv7 renises p port=

Date:

Thu, 24 Jul 2014 12:09:11 -0400

To:

Rotary motors in aircraft <flyrotary@lancaironline.net>

<image001.gif>

<ima= ge002.gif>

Charlie is right.  Consider that a= n airplane flying with the wing at 0 deg. AOA does not fall out of the sky := -)

 

My average speed in the 2004 Sun 100 r= ace was 217.58 mph which includes standing start takeoff and climbout.  = ;Prop was a 74 x 88, RPM was 7250 with a 2.85 : 1 drive.  If you calculate that out it comes to 212 mph with zero 'slippage'.   Dra= w your own conclusions!

 

Tracy

Sent from my iPad

 

From:

"Charlie England" <flyrotary@lancaironline.net>

Subject:<= /span>

Re: [FlyRotary] Re: Rv7 renises p port

Date:

Thu, 24 Jul 2014 17:49:27 -0500

To:

Rotary motors in aircraft <flyrotary@lancaironline.net>

<image001.gif>

<image002.= gif>

The 'negative slippage' was a tongue in cheek verbal c= oncoction intended to hint at the fact that 'slippage' is an artifact of old= hangar tails based on lack of understanding, even among 'experts' of old, o= f how a prop actually works.

(insert pause here to parse that awful sentence....)

'Pitch' implies that a prop is a screw. A prop isn't a screw. It's an airfoi= l (properly made, a *twisted* airfoil) that rotates. If you put the flat bla= des from a ceiling fan on the nose of an airplane, then 'pitch' might have s= ome actual meaning (but I don't think so).

Consider that 'pitch' is usually measured somewhere between 2/3 & 3/4 ou= t from the center to the tip of a blade. If you measure 'pitch' near the roo= t, you'd probably get something like 120-140 inches of pitch on a prop for R= V's or EZ's, etc, and at the tip it would probably be something like 60", begging the question, which part o= f the prop is actually screwing through the air at a particular 'pitch'. It d= oesn't mean that almost half the prop is 'slipping' and almost to half the p= rop is actually dragging, with a couple of inches moving the plane. It just means that each 'station' of t= he prop blade must be pitched to generate thrust at the relative speed it mo= ves through the air. The airfoil (BTW, I've never seen a symmetrical prop ai= rfoil) is, or at least *can*, make the air move aft faster than the 'pitch' of the imagined screw is movi= ng through the air. Just like a sailing vessel, it's not moving directly wit= h the wind; it's moving at an angle. The relative wind for the prop is not a= ligned with the path of the plane.

Depending on your religion, either Newton or Bernoulli makes the air go back= when the prop spins. Polytheists like me believe in both.

I love talking religion. Can we talk about politics next?

Charlie
;-)

On 7/24/2014 12:18 PM, James Osborn wrote:

Charlie said:  Ice sails, desert sails, and now,= even unlimited class sailboats can sail faster than the wind. 'Negative sli= ppage'. :-)

 

I don't think the analogy quite applies here.  Fo= r those types of crafts it is the wind that is doing the powering.  Whi= le it is true these types of craft can sail faster than the wind, but not wh= ile pointing straight into it!  By definition to cruise in an airplane, the prop has to be generating some kind of thrust= and therefore could never go faster than "the wind" - the only wind it sees= is the relative wind that is generated due to its own thrust (in cruise). &= nbsp;In a descent, sure negative slippage is a fact.  And slippage has to increase greatly in a climb.  I g= uess I am arguing that the only way you could see zero or negative slippage i= n cruise is if either your blade cross section is asymmetrical (it usually i= s right?) or if the pitch number used in the calculation is not really right based on the kinds of factors you ou= tlined Charlie.

 

Supposing that we have a typical non-symmetric blade c= ross section, an accurate pitch based on the chord line of the cross section= , and I suppose a twist that is correct for the cruise RPM.  What then w= ould be considered a good or reasonable slippage in cruise?  I saw 3% thrown out there.  And if your prop= selection is good for all those conditions (in other words as efficient as p= ossible), is this the slippage you expect?  I am just wondering if you c= an use a slippage calculation to judge efficiency (roughly).

 

-- James

On Wed, Jul 23, 2014 at 7:59 PM, Charlie England <= flyrotary@l= ancaironline.net> wrote:

Ice sails, desert sails, and now, even unlimited clas= s sailboats can sail faster than the wind. 'Negative slippage'. :-)

A more significant point might be that pitch numbers are virtually meaningle= ss, unless you're comparing two props from the same prop maker with the same= blade plan form. Even then, it just tells you which has a finer pitch than t= he other.

Variables can be: whether the pitch is measured on the back side of the blad= e or through the chord line, where along the diameter the pitch angle is mea= sured (due to blade twist), and no doubt others I'm not smart enough to thin= k of at the moment.

Bottom line is that unless there's an identical airframe flying an identical= prop, the pitch number isn't a reliable indicator of speed.

FWIW,

Charlie





On 7/23/2014 7:45 PM, James Osborn wrote:

I don't know jack about slippage, but I think it is t= he percentage difference between actual distance traveled and theoretical di= stance traveled if your propeller corkscrewed through the air with no thrust= .  I found a prop slip calculator online and for 86 inch pitch, 2.85 gear ratio, 7000 rpm, 180 mph, I get 10%= slip.  Granted the calculator was for boat propellers, but I don't thi= nk it matters as long as the units are correct.  There has to be some s= lip because there would be no thrust otherwise.  So what is considered a reasonable or good amount of slip?  Usin= g Bill's numbers 86 inch pitch, 2.85 gear ratio, 7000 rpm, 200 mph, I get 0%= slip.  That can't be right!

 

On Fri, Jul 4, 2014 at 7:19 AM, Bill Bradburry <flyrotary@lan= caironline.net> wrote:

Christian,

It seems that you have a lot of prop slippage at cruise.  I think that a= t
that prop rpm you should be getting 200mph if you had no slippage.

Bill


-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
Sent: Thursday, July 03, 2014 4:01 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Rv7 renises p port

Well hi all
Just thought I'd throw out there the mods I,ve done to the renises in an
= rv7'.
Well the p ported engine is now back in the plane and running well, over the=
standard short manifold that was originally in the plane I have gained
around 400 static rpm, same prop and gearbox combo, 2.85 ratio, this equates=
to allot more hp at takeoff, just shy of 2300 prop rpm, I'm running a prince=
p tip prop at 68" x 86" pitch,
At 8000 ft it is turning 7000 at 180 mph tas which is an improvement of 25 mph on previous tests, . So next plan is bigger prop and less pitch to let it rev to 7500 in strait and level.

Cheers
Christian
Rv7 renises Aus


Sent from my iPad
--
Homepage:  http= ://www.flyrotary.com/
Archive and UnSub:
http://mail.lancaironline.net:81/lists/flyrotary/List.html<= br>

--
Homepage:  http= ://www.flyrotary.com/
Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html

 

This message, and the documents attached hereto, is intended only for the ad= dressee and may contain privileged or confidential information. Any unauthor= ized disclosure is strictly prohibited. If you have received this message in= error, please notify us immediately so that we may correct our internal records. Please then delete the origina= l message. Thank you.
= --Apple-Mail-FCA6E19A-0A62-4C13-87E2-DB8F23547AEE--