X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.122] verified) by logan.com (CommuniGate Pro SMTP 5.3.2) with ESMTP id 4118590 for flyrotary@lancaironline.net; Tue, 09 Feb 2010 20:57:46 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.122; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.0 c=1 a=75uvWrxZo1UA:10 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=Ia-xEzejAAAA:8 a=nUuTZ29dAAAA:8 a=gL5x3YSPyEibu_5VEl4A:9 a=YnsXE-YbZNooIbHWt5MA:7 a=59gZVW7AmQF9vPGFq4zqL-Zjx5oA:4 a=1vhyWl4Y8LcA:10 a=EzXvWhQp4_cA:10 a=iGwzO2iaxv5pHs8M:21 a=nYcg3Rm-dodSQD5v:21 a=SSmOFEACAAAA:8 a=RbcRTH-UKctMmOcVRg0A:9 a=JX6HuC7VzKqw9WQmYeAA:7 a=jI1F3yD2brG71G-br8wEWp56kt0A:4 a=Ns4E0fOTkqbZdxqw:21 a=9tmUHPKuKwSHFtUH:21 a=tC6YKQLvsyiDG588E-sA:9 a=sNVqgiWbfm6gx21eht5QA4Equm4A:4 a=1Vq_FK4TplAA:10 a=rK7_Snnp8w1mzslLtbcA:9 a=tY9SOkmA9sggeAwJ54AA:9 a=OZJGW_Z213-B3NEgXKdzjVFaZkcA:4 a=q6PCrga3cWlUD47UAaQA:9 a=CzjJBf81rvx4PltPpKAA:9 a=Cw0yJJRF8uhkOVBUJO4Zf-kaV7wA:4 a=e2n4KQ7JTmKbnDR3ovAA:9 a=Yblhoe6ZdYcz7Y2O:18 a=i6GYtFeWOMyvAXi3:18 a=Uvyq_eEvy86UaCuJ:18 X-Cloudmark-Score: 0 X-Originating-IP: 75.191.186.236 Received: from [75.191.186.236] ([75.191.186.236:4590] helo=computername) by cdptpa-oedge04.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 50/DF-04431-672127B4; Wed, 10 Feb 2010 01:57:11 +0000 From: "Ed Anderson" Message-ID: <50.DF.04431.672127B4@cdptpa-omtalb.mail.rr.com> To: "'Rotary motors in aircraft'" Subject: Where's the Speed?? was RPM vs Power Date: Tue, 9 Feb 2010 20:58:04 -0500 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_0070_01CAA9CA.930337B0" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Thread-Index: Acqp9HuKvpps1chzRJ+mI0YyjPYPfw== This is a multi-part message in MIME format. ------=_NextPart_000_0070_01CAA9CA.930337B0 Content-Type: multipart/alternative; boundary="----=_NextPart_001_0071_01CAA9CA.930337B0" ------=_NextPart_001_0071_01CAA9CA.930337B0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Actually, Al my top speed did increased with the larger prop about 4 mph (but not what I would consider significant). =20 But, to your point -- trying to get theory to answer real performance is hard thing to get at calculations wise, but here is my take on it. =20 =20 OK; Ed =96 given your expertise on technical explanations, I=92d like = your take on why your increased hp resulting from the increased RPM is not giving = you higher top end speed. Is it exhaust back pressure or less than optimum prop, or other? =20 Al First, as you suggested , there are many factors relative to aircraft performance and the prop is only one =96 a somewhat important one, but = its performance can be also affected by these other factors. That being = said, I am going to see if I can address your point focusing on the prop factor = - understanding that I am certainly not a propeller expert. =20 But I think using this equation for thrust address what happens =20 Here is an equation for calculating thrust, you can find others, but = this one is fairly straight forward. T being the thrust and D being the = diameter of the prop. Dv being the additional acceleration given to the air by = the prop=92s rotation. So all things considered Dv is principally a = product of engine RPM and propeller pitch =96 but pitch is fixed in this case, so = does not change. Therefore the dominate factor in accelerating the air in = this case is the engine rpm. =20 =20 T thrust [N] D propeller diameter [m] v velocity of incoming flow [m/s] additional velocity, acceleration by propeller [m/s] density of fluid [kg/m=B3] =20 =20 =09 So why if I am producing more power with the 2.85 ratio - why aren=92t I = going faster on the top end. =20 Well, the thrust factor Dv as produced by the turning prop accelerating = the air. But as incoming air flow V increases during flight Dv gets = smaller. Airspeed will increase with the inflow air V increasing until a point = is reach where the propeller is producing no additional thrust or where Dv = =3D 0. In other words, the velocity of air flow out of the prop disc is the = same velocity as the air flowing into it and there is no further acceleration = or thrust or Dv =3D 0. =20 As a results, a larger diameter (but slower turning prop) reaches the = point in flight where Dv =3D 0 sooner than a smaller diameter but faster = turning prop does. Reaching Dv sooner limits the velocity the aircraft can = achieve So in theory, that is why the racers want (in part) these short diameter high rpm props. So that is why all things else being equal a larger diameter, but slower turning prop, is not the best for top speed. =20 =20 But, as you know, there is more to it than just this. For example an aircraft with less drag (and/or more power) can spin a larger prop = faster than one with more drag or less power (all things else being equal). That is one reason I believe that Tracy=92s RV-4 gets a higher top speed = with the same prop than I do. He may or may not have a more powerful engine (probably does), but he certainly has less drag than my hefty RV-6A. = But, in both cases, I believe the reason the top speed increased was more = power was available as the torque load was loader on the engine permitting = higher rpm. Had the power being produced remained unchanged then of course my = top speed would have dropped. =20 =20 I once had one older gent who had raced in the Cassute? class that = stopped by and chatted with me a while at a fly in =96 told me if I wanted to go faster to trim some off the diameter of my prop. Well, I don=92t care = about top speed, I want the take off performance to get me off grass strips = and over tall trees off short runways. =20 So I have a larger diameter prop which helps in take off, but it turns slower so it=92s not the optimum for top speed. =20 That=92s about the best answer I can give you, Al. There are numerous = other factors such as advance factor, Coeffiences of Thrust and Power you find = in some thrust equations and on and on. But on the back of the envelope = that=92s the way it looks to me. =20 Ed Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm =20 _____ =20 From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Tuesday, February 09, 2010 1:10 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: rpm vs Power was : Throttle limits was Re: N.A. Renesis to turbo =20 Ed wrote: The new set up gave a noticeable benefit in take off performance (and I = do mean noticeable). However, the top end was relatively unaffected - = although I did measure an approx 4 mph increase in top aircraft speed. =20 OK; Ed =96 given your expertise on technical explanations, I=92d like = your take on why your increased hp resulting from the increased RPM is not giving = you higher top end speed. Is it exhaust back pressure or less than optimum prop, or other? =20 Al __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com =20 =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm =20 =20 =20 =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm =20 =20 ------=_NextPart_001_0071_01CAA9CA.930337B0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Actually, Al my top speed did = increased with the larger prop about 4 mph (but not what I would consider = significant).

 

But, to your = point -- trying to get theory to answer real performance is hard thing to get at calculations wise, but here is my take on it.=A0 =  

 

OK; Ed – = given your expertise on technical explanations, I’d like your take on = why your increased hp resulting from the increased RPM is not giving you higher = top end speed.  Is it exhaust back pressure or less than optimum prop, or = other?

 

Al


First, as you suggested , there are many = factors relative to aircraft performance and the prop is only one – a = somewhat important one, but its performance can be also affected by these other factors.=A0 That being said, I am going to see if I can address your = point focusing on the prop factor - understanding that I am certainly not a propeller = expert.

 

But I think using this equation for = thrust address what happens

 

Here is an=A0 equation for calculating thrust, you = can find others, but this one is fairly straight forward.=A0 T being the thrust = and D being the diameter of the prop.=A0 Dv being = the additional acceleration given to the air by the prop’s = rotation.=A0 =A0So all things considered Dv is = principally =A0a product of engine RPM and propeller pitch – but pitch is fixed in = this case, so does not change.=A0 Therefore the dominate factor in accelerating the = air in this case is the engine rpm.

 

 

T

thrust

[N]

D

propeller = diameter

[m]

v

velocity of incoming = flow

[m/s]

additional velocity, acceleration by = propeller

[m/s]

density of = fluid

[kg/m=B3]

 

 

So why if I am producing more power = with the 2.85 ratio - why aren’t I going faster on the top = end.

 

Well, the thrust factor = =A0Dv as produced by = the turning prop accelerating the air. But as incoming air flow V increases = during flight =A0D<= font size=3D2 color=3Dnavy face=3DArial>v gets smaller.=A0 Airspeed will increase with the inflow = air V increasing =A0until a point is reach where the propeller is producing no additional thrust or where D<= font size=3D2 color=3Dnavy face=3DArial>v =3D 0.=A0 In other words, the velocity of =A0air flow out = of the prop disc is the same velocity as the air flowing into it and there is no = further acceleration or thrust or D<= font size=3D2 color=3Dnavy face=3DArial>v =3D 0.

=A0

As a results, =A0a larger diameter (but slower turning prop) reaches the = point in flight where = Dv =3D 0 sooner than a smaller diameter but faster turning prop = does. Reaching D<= font size=3D2 color=3Dnavy face=3DArial>v sooner limits the velocity the aircraft can achieve So in = theory, that is why the racers want (in part) these short diameter high rpm = props.=A0 So that is why all things else being equal a larger diameter, but slower = turning prop,=A0 is not the best for top speed.=A0

 

But, as you know, there is more to = it than just this.=A0 For example an aircraft with less drag (and/or more power) = can spin a larger prop faster than one with more drag or less power (all things = else being equal).

That is one reason I believe that = Tracy’s = RV-4 gets a higher top speed with the same prop than I do. He may or may not have a = more powerful engine (probably does), but he certainly has less drag than my = hefty RV-6A.=A0 But, in both cases, I believe the reason the top speed = increased was more power was available as the torque load was loader on the engine = permitting higher rpm.=A0 Had the power being produced remained unchanged then of = course my top speed would have dropped.=A0

 

I once had one older gent who had = raced in the Cassute? class that stopped by and chatted with me a while at a fly = in – told me if I wanted to go faster to trim some off the diameter = of my prop.=A0 Well, I don’t care about top speed, I want the take off performance to get me off grass strips and over tall trees off short = runways.

 

So I have a larger diameter prop = which helps in take off, but it turns slower so it’s not the optimum for = top speed.

 

That’s about the best answer = I can give you, Al.=A0 There are numerous other factors such as advance = factor, Coeffiences of Thrust and Power you find in some thrust equations and on = and on.=A0 But on the back of the envelope that’s the way it looks to = me.

 

Ed

Ed Anderson

Rv-6A N494BW Rotary = Powered

Matthews, NC

eanderson@carolina.rr.com=

http://www.andersonee.com

http://www.dmack.net/mazda/i= ndex.html

http://www.flyrotary.com/

http://members.cox.net/roger= sda/rotary/configs.htm#N494BW

http://www.rotaryaviation.co= m/Rotorhead%20Truth.htm

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Tuesday, February = 09, 2010 1:10 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = rpm vs Power was : Throttle limits was Re: N.A. Renesis to = turbo

 

Ed = wrote:

The new set up gave a noticeable benefit in take off performance (and I = do

mean noticeable).  However, the top end was relatively unaffected - = although

I did measure an approx 4 mph increase in top aircraft = speed.

 

OK; Ed – = given your expertise on technical explanations, I’d like your take on = why your increased hp resulting from the increased RPM is not giving you higher = top end speed.  Is it exhaust back pressure or less than optimum prop, or = other?

 

Al



__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com



__________ Information from ESET NOD32 Antivirus, version of virus = signature database 3267 (20080714) __________

The message was checked by ESET NOD32 Antivirus.

http://www.eset.com

 

 

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

 

 

 

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

 



__________ Information from ESET NOD32 Antivirus, version of = virus signature database 3267 (20080714) __________

The message = was checked by ESET NOD32 Antivirus.

http://www.eset.com
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