X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.2.16) with ESMTP id 3882570 for flyrotary@lancaironline.net; Sun, 11 Oct 2009 16:40:11 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (sv1-1.per.aanet.com.au [203.24.100.68]) by poplet2.per.eftel.com (Postfix) with ESMTP id 85E29173841 for ; Mon, 12 Oct 2009 04:39:35 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 28EECBEC003 for ; Mon, 12 Oct 2009 04:39:34 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: where's the missing power? Date: Mon, 12 Oct 2009 06:39:38 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0009_01CA4B06.C5107EC0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 091011-0, 10/11/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_0009_01CA4B06.C5107EC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Al, Interesting point you make ( on throttle openings) this is the same = for a slide throttle, depending upon the shape of the slide. For = instance a half round cut out in the slide is more linear that a flat = slide over a round opening. A piece of useless information for those who don't make carbies. George ( down under) 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 ------=_NextPart_000_0009_01CA4B06.C5107EC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
 Al,
 Interesting point you make ( on = throttle=20 openings) this is the same for a slide throttle, depending upon the = shape of=20 the slide. For instance a half round cut out in the slide is more = linear that=20 a flat slide over a round opening.
A piece of useless information for = those who=20 don't make carbies.
George ( down under)

Mike;

 

As others = have=20 pointed out there are valid reasons for throttle position not being=20 proportional to engine power.  The throttle plates are only one = factor in=20 the over flow air.  I=92ll just add that even if it were the only = restriction, rotating a circular butterfly valve is not linear with = flow =96 the=20 first part of the rotation increases flow much more than the = last. =20 Sizing of the TB is obviously a big factor.  With a giant TB you = may be=20 at full power with it just cracked open.  And aside from other = factors=20 with the induction system, at some point the restricting factor is the = engine=20 porting.  So, if you are happy with the power you get, I = wouldn=92t make=20 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=92d say the=20 last 20 =96 25% of throttle travel makes little = difference.

 

Al=20 G

 

-----Original=20 Message-----
From: = Rotary=20 motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Mike = Wills
Sent: Saturday, October 10, = 2009 7:28=20 PM
To: Rotary = motors in=20 aircraft
Subject: = [FlyRotary]=20 where's the missing power?

 

I noticed quite a while = ago and=20 have mentioned several times here that my engine does not have a = linear=20 response to throttle. It reaches its max power before it reaches fully = open=20 throttle. I havent worried too much about this up until now because = the=20 airplane has sufficient power as is, has slightly better performance = than my=20 previous 160HP Lyc powered -6A, and my wood prop is actually a pretty = good=20 match for the current power level.

 

But I would like to = understand=20 what's going on here and eventually address it. I was flying = yesterday, my=20 usual boring holes in the sky directly over the airport. Decided to=20 investigate just a little so leveled at 5,000 feet at full throttle. = Started=20 reducing throttle until I noticed a slight reduction in RPM and fuel = flow.=20 Then looked down at where the throttle was actually set and was = shocked to see=20 it slightly below half open. I dont have a regular manifold pressure = gauge,=20 just an industrial type vacuum gauge ( I really gotta get an MP = gauge).=20 Anyway, the vacuum gauge was indicating 4" of = vacuum.

 

So I suspect I am giving = up a=20 substantial amount of HP. I think the most likely suspect is my = throttle body.=20 For a throttle body I copied Tracy's original design. Started = with a=20 stock late 80s Mazda TB and hacked off the third port and all of the = extra=20 stuff. The cowl in this area is very tight and I am unable to install = any sort=20 of air filter or any sort of bell mouth on the TB. And I'm sure the = cowl's=20 close proximity to the TB influences airflow into it as=20 well.

 

Any comments on this or = ways to=20 test it are welcome.

 

Mike = Wills

RV-4=20 N144MW

------=_NextPart_000_0009_01CA4B06.C5107EC0--