X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao101.cox.net ([68.230.241.45] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4154154 for flyrotary@lancaironline.net; Sat, 06 Mar 2010 00:30:51 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.45; envelope-from=rv-4mike@cox.net Received: from fed1rmimpo02.cox.net ([70.169.32.72]) by fed1rmmtao101.cox.net (InterMail vM.8.00.01.00 201-2244-105-20090324) with ESMTP id <20100306053016.LBNH4995.fed1rmmtao101.cox.net@fed1rmimpo02.cox.net> for ; Sat, 6 Mar 2010 00:30:16 -0500 Received: from willsPC ([68.105.86.80]) by fed1rmimpo02.cox.net with bizsmtp id phWG1d0021k005Q04hWGe7; Sat, 06 Mar 2010 00:30:16 -0500 X-VR-Score: 0.00 X-Authority-Analysis: v=1.1 cv=KqzZVGv1/pIBe+XbL3gCBfL8vaFXECOST7Bs1vfp5Gs= c=1 sm=1 a=0h6B89VrGMoA:10 a=XruvlouZCDbGUgEaRUiNZQ==:17 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=HY4BztI7ipVzD43euoYA:9 a=xImCET9xT6XArw3FKAIA:7 a=MiRpkzBigIyl75Uofevcb--3TkIA:4 a=wPNLvfGTeEIA:10 a=1vhyWl4Y8LcA:10 a=SGHVjBXo3MNQ3Ned:21 a=5uNOQgDKo7uQ_vsz:21 a=Ia-xEzejAAAA:8 a=R0b6fOVdtoPMW1TZC8YA:9 a=MZaiqlDyVoNp5P4prtYA:7 a=GlysXhhGztXEed2LlPdOvryiyn0A:4 a=EzXvWhQp4_cA:10 a=XruvlouZCDbGUgEaRUiNZQ==:117 X-CM-Score: 0.00 Message-ID: <782D3569C3A944C98F05896BFE3A4886@willsPC> From: "Mike Wills" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] TB size, Travel and Power Date: Fri, 5 Mar 2010 21:30:14 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0030_01CABCAB.0B30AF90" X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8089.726 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8089.726 This is a multi-part message in MIME format. ------=_NextPart_000_0030_01CABCAB.0B30AF90 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, I hear what your saying (and I get it). Here's the thing, and I admit I = may have a misunderstanding here. Your explanation applies if you are = measuring manifold pressure essentially at the rotor face. If you = measure MP closer to the TB as I do unfortunately, it is possible to see = ambient at full throttle but have restrictions in the intake tract that = would result in less than ambient at the rotor face. Conversely (and = again theory - I'm open to being shown wrong here), a properly designed = DIE manifold would show ambient MP measured at the TB and greater than = ambient measured at the rotor face. I accept that by trimming the prop I can lighten the load and gain some = HP (though some here seem to think that HP will increase linearly with = RPM to infinity and I don't buy that either). But as you alluded to in = your previous, there's some potential for mistake in trimming any prop = until you are quite sure that you are not HP limited by something other = than load. And I'm not sure yet. Just a feeling based on the fact that = I'm using a cut down RX-7 TB that's maxed out about 1/3 short of fully = open. And honestly I still havent dug any deeper because the airplane is = flying well and has good performance. But sooner or later I'm going to = want to get more than the 5700RPM I'm currently getting - I want all the = performance that's there. Mike Wills From: Ed Anderson=20 Sent: Friday, March 05, 2010 6:36 PM To: Rotary motors in aircraft=20 Subject: [FlyRotary] TB size, Travel and Power I am apparently not doing a very good job making the point about the = relationship between throttle body size, throttle travel and engine = power clear. So here is another try at it - using extreme examples and = no math. Let's assume your volumetric efficiency is 100% (no losses). =20 IF you put a =BD " dia TB on you engine. You could have it wide open = and your engine (under normal prop load) probably wouldn't turn 4000 = rpm. That is because even wide open, the =BD" dia TB restricts airflow = sufficiently - that the manifold air density never approaches the = ambient air density. Since we know that the engine power is directly = proportional to the density of air in the combustion chamber - and this = density is limited in this case to less than ambient, you engine is not = going to produce much power, certainly not full power. So this bit of = information tells us "Bigger Lithium Crystals, Scotty!!" - i.e try a = larger throttle body.=20 =20 Now if you keep enlarging the diameter of the TB you would find that at = fully open -your engine would be producing more power than it was, but = perhaps still not the maximum power it is capable of. This is because = the air density in the manifold has increase due to the less restrictive = flow, but is still below ambient. This is due to the better, but still = restrictive effect of the TB size on the air flow. Now if you continued = enlarging the TB size, you would reach a point where with the TB just = reaching fully open - your manifold air density is exactly ambient and = your engine is producing all the power it is going to. =20 Now if you enlarge the TB even further, you will simply find that you = can cause the manifold pressure (air density) to reach ambient without = opening the TB fully. Its simply large enough that all the air the = engine can use (ambient air density point) is met at partial throttle = opening. In fact , you can certainly continue to advance the throttle = thereby opening the throttle plate even more - but, you are not going to = increase the air density in the manifold and therefore you will not = produce any additional power for that additional throttle travel. =20 Bigger Throttle body's result in more power only up to the point the = airflow they permit causes manifold air density to reach ambient. = Beyond that point, the only thing they do is provide frustration - by = having all that throttle travel remaining which does nothing to produce = more power {:>). =20 Now if you can somehow lighten the load on your engine, then engine can = turn faster providing more "suction" on the manifold volume reducing the = air density below ambient, now opening your "oversize" TB a bit more = will produce more power because you are increasing the airflow again to = the point where the equilibrium point between ambient air density in the = manifold and rpm is again reached. Lighten the load further and you can = again increase engine power by opening your TB more. Etc, etc. =20 =20 Ah, ain't this hobby wonderful {:>)=20 =20 =20 Ed =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 ------=_NextPart_000_0030_01CABCAB.0B30AF90 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ed,
 
 I hear what your saying (and I get=20 it). Here's the thing, and I admit I may have a misunderstanding=20 here. Your explanation applies if you are measuring manifold = pressure=20 essentially at the rotor face. If you measure MP closer to the TB = as I do=20 unfortunately, it is possible to see ambient at full throttle but have=20 restrictions in the intake tract that would result in less than ambient = at the=20 rotor face. Conversely (and again theory - I'm open to being shown wrong = here),=20 a properly designed DIE manifold would show ambient MP measured at the = TB and=20 greater than ambient measured at the rotor face.
 
I accept that by trimming the prop I can = lighten the=20 load and gain some HP (though some here seem to think that HP will = increase=20 linearly with RPM to infinity and I don=92t buy that either). But as you = alluded=20 to in your previous, there's some potential for mistake in trimming = any=20 prop until you are quite sure that you are not HP limited by something = other=20 than load. And I'm not sure yet. Just a feeling based on the fact that = I'm using=20 a cut down RX-7 TB that=92s maxed out about 1/3 short of fully open. And = honestly=20 I still havent dug any deeper because the airplane is flying well and=20 has good performance. But sooner or later I'm going to want to get = more=20 than the 5700RPM I'm currently getting - I want all the performance = that=92s=20 there.
 
Mike Wills

From: Ed Anderson
Sent: Friday, March 05, 2010 6:36 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] TB size, Travel and = Power

I am apparently not doing = a very=20 good job making the point about the relationship between throttle body = size,=20 throttle travel and engine power clear.  So here is another try at = it -=20 using extreme examples and no math.  Let=92s assume your volumetric = efficiency is 100% (no losses).

 

IF you put a =BD =94 dia = TB on you=20 engine.  You could have it wide open and your engine (under normal = prop=20 load) probably wouldn=92t turn 4000 rpm.  That is because even wide = open, the=20 =BD=94 dia TB restricts airflow sufficiently - that the manifold air = density never=20 approaches the ambient air density.  Since we know that the engine = power is=20 directly proportional to the density of air in the combustion chamber = =96 and this=20 density is limited in this case to less than ambient, you engine is not = going to=20 produce much power, certainly not full power.  So this bit of = information=20 tells us =93Bigger Lithium Crystals, Scotty!!=94 =96 i.e  try a = larger throttle=20 body.

 

Now if you keep enlarging = the=20 diameter of the TB you would find that at fully open -your engine would = be=20 producing more power than it was, but perhaps still not the maximum = power it is=20 capable of.  This is because the air density in the manifold has = increase=20 due to the less restrictive flow, but is still below ambient.  This = is due=20 to the better, but still restrictive effect of the TB size on the air=20 flow.  Now if you continued enlarging the TB size, you would reach = a point=20 where with the TB just reaching fully open - your manifold air density = is=20 exactly ambient and your engine is producing all the power it is going=20 to.

 

Now if you enlarge the TB = even=20 further, you will simply find that you can cause the manifold pressure = (air=20 density) to reach ambient without opening the TB fully.  Its simply = large=20 enough that all the air the engine can use (ambient air density point) =  is=20 met at partial throttle opening.  In fact , you can certainly = continue to=20 advance the throttle thereby opening the throttle plate even more =96 = but, you are=20 not going to increase the air density in the manifold and therefore you = will not=20 produce any additional power for that additional throttle=20 travel.

 

Bigger Throttle body=92s = result in=20 more power only up to the point the airflow they permit causes manifold = air=20 density to reach ambient.  Beyond that point, the only thing they = do is=20 provide frustration =96 by having all that throttle travel remaining = which does=20 nothing to produce more power {:>).

 

Now if you can somehow =  lighten=20 the load on your engine, then engine can turn faster providing more = =93suction=94 on=20 the manifold volume reducing the air density below ambient, now opening = your=20 =93oversize=94 TB a bit more will produce more power because you are = increasing the=20 airflow again to the point where the equilibrium point between ambient = air=20 density in the manifold and rpm is again reached.  Lighten the load = further=20 and you can again increase engine power by opening your TB more. Etc,=20 etc.

 

 

Ah, ain=92t this hobby = wonderful=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.r= otaryaviation.com/Rotorhead%20Truth.htm

 

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