X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao107.cox.net ([68.230.241.39] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4155076 for flyrotary@lancaironline.net; Sat, 06 Mar 2010 22:13:38 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.39; envelope-from=rv-4mike@cox.net Received: from fed1rmimpo02.cox.net ([70.169.32.72]) by fed1rmmtao107.cox.net (InterMail vM.8.00.01.00 201-2244-105-20090324) with ESMTP id <20100307031301.OWMB20722.fed1rmmtao107.cox.net@fed1rmimpo02.cox.net> for ; Sat, 6 Mar 2010 22:13:01 -0500 Received: from willsPC ([68.105.86.80]) by fed1rmimpo02.cox.net with bizsmtp id q3D11d00L1k005Q043D1o1; Sat, 06 Mar 2010 22:13:02 -0500 X-VR-Score: -130.00 X-Authority-Analysis: v=1.1 cv=KqzZVGv1/pIBe+XbL3gCBfL8vaFXECOST7Bs1vfp5Gs= c=1 sm=1 a=hCNxu-qUHAUA:10 a=XruvlouZCDbGUgEaRUiNZQ==:17 a=kviXuzpPAAAA:8 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=cAosuDRoBCfyOVlC-5wA:9 a=2u1GP2SAFRkwDvszbFcA:7 a=bB3a13qu5hczYLE7_MuZUdDboJgA:4 a=pILNOxqGKmIA:10 a=1vhyWl4Y8LcA:10 a=4vB-4DCPJfMA:10 a=nhxoarLNfuinYjeK:21 a=Yiq3UL_HONcAJxVX:21 a=Ia-xEzejAAAA:8 a=dZUd7FplAse7V40J96gA:9 a=1RoOGhr54_TaLBglf1YA:7 a=axa0AmndHOLziTyf_QUrBE6BvtsA:4 a=iVkDmfvjeKcA:10 a=EzXvWhQp4_cA:10 a=XruvlouZCDbGUgEaRUiNZQ==:117 X-CM-Score: 0.00 Message-ID: <186AAF5BDB244886B59121F55B4C7AA7@willsPC> From: "Mike Wills" To: "Rotary motors in aircraft" References: In-Reply-To: Subject: Re: [FlyRotary] Re: TB size, Travel and Power Date: Sat, 6 Mar 2010 19:13:00 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00C7_01CABD61.09B86FC0" 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_00C7_01CABD61.09B86FC0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Tracy, Yes I have confirmed that I get full ambient pressure at 2/3 (roughly) = throttle near sea level. And yes I still have the POS vacuum gauge. I = know it needs replaced - just havent had the opportunity yet. My point in bringing this up yet again was to emphasize the point Ed = made a couple of posts back - that this whole thing is a complex problem = with a lot of variables. And to not dive in and start whacking on the = prop until certain that is where the problem is. In my case I'm not sure = it is. Full ambient MP at the TB doesn=92t indicate how well the intake = is flowing and it is entirely possible to have full MP but a very poor = performing manifold. Guys in racing make lots of $ porting and flow = testing manifolds. I need to make some changes to the intake anyway for other reasons so = I'm going to focus on that first. And once that's done, if I'm still = giving up some RPMs then I'll take a look at the prop. Unless of course = I can do it the easy way as Al suggested and borrow a prop. On that = note, are there any of you RV guys that have upgraded from the 2.17 gear = ratio to the 2.85 that have a "wrong way" prop you'd be willing to lend = for a test? Meanwhile I havent been able to fly for the past 3 weeks due to this = crappy weather. Why's it always have to rain on the weekends? Its not = supposed to rain in SoCal at all. Mike Wills From: Tracy Crook=20 Sent: Saturday, March 06, 2010 7:06 AM To: Rotary motors in aircraft=20 Subject: [FlyRotary] Re: TB size, Travel and Power Mike, you are measuring the MP exactly where you should, You can't do it = properly anywhere else, at least not with a simple instrument. But are you at last confirming that you DO have full ambient MP at 2/3 = throttle setting? That IS an important question if you want to know = the right answer to your question. BTW, ditch the vacuum gauge (if = that's what you are using) and get a proper MP gauge. Tracy On Fri, Mar 5, 2010 at 9:30 PM, Mike Wills wrote: 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=92t 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=92s 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=92s 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=92s assume your volumetric efficiency is 100% (no losses). IF you put a =BD =94 dia TB on you engine. You could have it wide = open and your engine (under normal prop load) probably wouldn=92t turn = 4000 rpm. That is because even wide open, the =BD=94 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 = =96 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 =93Bigger Lithium Crystals, Scotty!!=94 = =96 i.e try a larger throttle body.=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. 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 =96 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. Bigger Throttle body=92s 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 =96 by = having all that throttle travel remaining which does nothing to produce = more power {:>). Now if you can somehow lighten the load on your engine, then engine = can turn faster providing more =93suction=94 on the manifold volume = reducing the air density below ambient, now opening your =93oversize=94 = 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. 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.rotaryaviation.com/Rotorhead%20Truth.htm ------=_NextPart_000_00C7_01CABD61.09B86FC0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Tracy,
 
Yes I have confirmed that I get full ambient = pressure at=20 2/3 (roughly) throttle near sea level. And yes I still have the POS = vacuum=20 gauge. I know it needs replaced - just havent had the opportunity=20 yet.
 
My point in bringing this up yet again was to = emphasize=20 the point Ed made a couple of posts back - that this whole thing is a = complex=20 problem with a lot of variables. And to not dive in and start whacking = on the=20 prop until certain that is where the problem is. In my case I'm not sure = it is.=20 Full ambient MP at the TB doesn=92t indicate how well the intake is = flowing and it=20 is entirely possible to have full MP but a very poor performing = manifold. Guys=20 in racing make lots of $ porting and flow testing = manifolds.
 
I need to make some changes to the intake = anyway for=20 other reasons so I'm going to focus on that first. And once that's = done, if=20 I'm still giving up some RPMs then I'll take a look at the prop. Unless = of=20 course I can do it the easy way as Al suggested and borrow a = prop. On that=20 note, are there any of you RV guys that have upgraded from the 2.17 gear = ratio=20 to the 2.85 that have a "wrong way" prop you'd be willing to lend for a=20 test?
 
Meanwhile I havent been able to fly for the = past 3 weeks=20 due to this crappy weather. Why's it always have to rain on the = weekends? Its=20 not supposed to rain in SoCal at all.
 
Mike Wills

Sent: Saturday, March 06, 2010 7:06 AM
Subject: [FlyRotary] Re: TB size, Travel and = Power

Mike,
   you are measuring the MP exactly where you = should,  =20 You can't do it properly anywhere else, at least not with a simple=20 instrument.
 
But are you at last confirming that you DO have full ambient MP at = 2/3=20 throttle setting?   That IS an important question if you want = to know=20 the right answer to your question.    BTW, ditch the = vacuum gauge=20 (if that's what you are using) and get a proper MP gauge.
 
Tracy

On Fri, Mar 5, 2010 at 9:30 PM, Mike Wills = <rv-4mike@cox.net>=20 wrote:
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 essentially at the rotor face. If you measure MP closer = to the=20 TB as I do unfortunately, it is possible to see ambient at full = throttle but=20 have restrictions in the intake tract that would result in less than = ambient=20 at the rotor face. Conversely (and again theory - I'm open to being = shown=20 wrong here), a properly designed DIE manifold would show ambient MP = measured=20 at the TB and 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=20 using a cut down RX-7 TB that=92s maxed out about 1/3 short of fully = open. And=20 honestly 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=20 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=20 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,=20 the =BD=94 dia TB restricts airflow sufficiently - that the manifold = air density=20 never approaches the ambient air density.  Since we know that the = engine=20 power is directly proportional to the density of air in the combustion = chamber=20 =96 and this density is limited in this case to less than ambient, you = engine is=20 not going to produce much power, certainly not full power.  So = this bit=20 of information tells us =93Bigger Lithium Crystals, Scotty!!=94 =96 = i.e  try a=20 larger throttle 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=20 is capable of.  This is because the air density in the manifold = has=20 increase due to the less restrictive flow, but is still below = ambient. =20 This is due to the better, but still restrictive effect of the TB size = on the=20 air flow.  Now if you continued enlarging the TB size, you would = reach a=20 point where with the TB just reaching fully open - your manifold air = density=20 is 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 met at partial throttle opening.  In fact , you can = certainly=20 continue to advance the throttle thereby opening the throttle plate = even more=20 =96 but, you are not going to increase the air density in the manifold = and=20 therefore you will not produce any additional power for that = additional=20 throttle 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=20  lighten the load on your engine, then engine can turn faster = providing=20 more =93suction=94 on the manifold volume reducing the air density = below ambient,=20 now opening your =93oversize=94 TB a bit more will produce more power = because you=20 are increasing the airflow again to the point where the equilibrium = point=20 between ambient air density in the manifold and rpm is again = reached. =20 Lighten the load further and you can again increase engine power by = opening=20 your TB more. Etc, 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<= /P>

http://www.flyrotary.com/

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

http://www.rotaryaviation.com/Rotorhead%20Truth.htm

 

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