X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao106.cox.net ([68.230.241.40] verified) by logan.com (CommuniGate Pro SMTP 5.2.16) with ESMTP id 3882348 for flyrotary@lancaironline.net; Sun, 11 Oct 2009 10:53:32 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.40; envelope-from=alventures@cox.net Received: from fed1rmimpo03.cox.net ([70.169.32.75]) by fed1rmmtao106.cox.net (InterMail vM.8.00.01.00 201-2244-105-20090324) with ESMTP id <20091011145256.XOYT21192.fed1rmmtao106.cox.net@fed1rmimpo03.cox.net> for ; Sun, 11 Oct 2009 10:52:56 -0400 Received: from BigAl ([72.192.133.78]) by fed1rmimpo03.cox.net with bizsmtp id rSsw1c0041hf1Cg04SswdR; Sun, 11 Oct 2009 10:52:56 -0400 X-VR-Score: 0.00 X-Authority-Analysis: v=1.0 c=1 a=vpsSGIOwZiAA:10 a=Ia-xEzejAAAA:8 a=83Ah4SaGiLcUht3N6VkA:9 a=QpIECTX6umLS2TlDjMkA:7 a=Eq965hHgKEp3kekjXgfX_Buzj7oA:4 a=EzXvWhQp4_cA:10 a=GsRxDq7KA5h9Ud8q:21 a=T4BLICYrcwkI4MrU:21 a=JlvEnsDjAhSxL2xC3dQA:9 a=jDX_CL69l-Ns75oRnfMA:7 a=XlnTP9TrlmOqAGe0tDZFOV5cxEAA:4 X-CM-Score: 0.00 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] where's the missing power? Date: Sun, 11 Oct 2009 07:53:23 -0800 Message-ID: <3D0DDE5114404DA692621F0567054560@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0027_01CA4A47.E85EF0B0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6838 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Importance: Normal In-Reply-To: Thread-Index: AcpKIuCKG85NzdoUT2mMlxkWS9V4NQAZkpUg This is a multi-part message in MIME format. ------=_NextPart_000_0027_01CA4A47.E85EF0B0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Mike; =20 As others have pointed out there are valid reasons for throttle position = not being proportional to engine power. The throttle plates are only one = factor in the over flow air. I'll just add that even if it were the only restriction, rotating a circular butterfly valve is not linear with flow = - the first part of the rotation increases flow much more than the last. Sizing of the TB is obviously a big factor. With a giant TB you may be = at full power with it just cracked open. And aside from other factors with = the induction system, at some point the restricting factor is the engine porting. So, if you are happy with the power you get, I wouldn't make = too much of it. OTOH; at some point you may want to look at ways improving = the system that might get you more power. =20 On mine I'd say the last 20 - 25% of throttle travel makes little difference. =20 Al G =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills Sent: Saturday, October 10, 2009 7:28 PM To: Rotary motors in aircraft Subject: [FlyRotary] where's the missing power? =20 I noticed quite a while ago and have mentioned several times here that = my engine does not have a linear response to throttle. It reaches its max = power before it reaches fully open throttle. I havent worried too much about = this up until now because the airplane has sufficient power as is, has = slightly better performance than my previous 160HP Lyc powered -6A, and my wood = prop is actually a pretty good match for the current power level. =20 But I would like to understand what's going on here and eventually = address it. I was flying yesterday, my usual boring holes in the sky directly = over the airport. Decided to investigate just a little so leveled at 5,000 = feet at full throttle. Started reducing throttle until I noticed a slight reduction in RPM and fuel flow. Then looked down at where the throttle = was actually set and was shocked to see it slightly below half open. I dont = have a regular manifold pressure gauge, just an industrial type vacuum gauge = ( I really gotta get an MP gauge). Anyway, the vacuum gauge was indicating = 4" of vacuum. =20 So I suspect I am giving up a substantial amount of HP. I think the most likely suspect is my throttle body. For a throttle body I copied Tracy's original design. Started with a stock late 80s Mazda TB and hacked off = the third port and all of the extra stuff. The cowl in this area is very = tight and I am unable to install any sort of air filter or any sort of bell = mouth on the TB. And I'm sure the cowl's close proximity to the TB influences airflow into it as well. =20 Any comments on this or ways to test it are welcome. =20 Mike Wills RV-4 N144MW ------=_NextPart_000_0027_01CA4A47.E85EF0B0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Mike;

 

As others have pointed out there = are valid reasons for throttle position not being proportional to engine power.  The throttle plates are only one factor in the over flow = air.  I’ll just add that even if it were the only restriction, rotating = a circular butterfly valve is not linear with flow – the first part = of the rotation increases flow much more than the last.  Sizing of the TB = is obviously a big factor.  With a giant TB you may be at full power with it = just cracked open.  And aside from other factors with the induction = system, at some point the restricting factor is the engine porting.  So, if = you are happy with the power you get, I wouldn’t make too much of = it.  OTOH; at some point you may want to look at ways improving the system that = might get you more power.

 

On mine I’d say the last 20 = – 25% of throttle travel makes little difference.

 

Al G

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike Wills
Sent: Saturday, October = 10, 2009 7:28 PM
To: Rotary motors in = aircraft
Subject: [FlyRotary] = where's the missing power?

 

I noticed quite a while ago = and have mentioned several times here that my engine does not have a linear = response to throttle. It reaches its max power before it reaches fully open = throttle. I havent worried too much about this up until now because the airplane has sufficient power as is, has slightly better performance than my previous = 160HP Lyc powered -6A, and my wood prop is actually a pretty good match for = the current power level.

 

But I would like to = understand what's going on here and eventually address it. I was flying yesterday, = my usual boring holes in the sky directly over the airport. Decided to = investigate just a little so leveled at 5,000 feet at full throttle. Started = reducing throttle until I noticed a slight reduction in RPM and fuel flow. Then = looked down at where the throttle was actually set and was shocked to see it = slightly below half open. I dont have a regular manifold pressure gauge, just an industrial type vacuum gauge ( I really gotta get an MP gauge). Anyway, = the vacuum gauge was indicating 4" of vacuum.

 

So I suspect I am giving up = a substantial amount of HP. I think the most likely suspect is my throttle = body. For a throttle body I copied Tracy's original design. Started with = a stock late 80s Mazda TB and hacked off the third port and all of the extra = stuff. The cowl in this area is very tight and I am unable to install any sort of = air filter or any sort of bell mouth on the TB. And I'm sure the cowl's = close proximity to the TB influences airflow into it as = well.

 

Any comments on this or = ways to test it are welcome.

 

Mike = Wills

RV-4 = N144MW

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