X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml Date: Mon, 25 Sep 2006 11:46:32 -0400 Message-ID: X-Original-Return-Path: Received: from mxsf31.cluster1.charter.net ([209.225.28.130] verified) by logan.com (CommuniGate Pro SMTP 5.1c.4) with ESMTP id 1419225 for lml@lancaironline.net; Mon, 25 Sep 2006 08:45:11 -0400 Received-SPF: pass receiver=logan.com; client-ip=209.225.28.130; envelope-from=troneill@charter.net Received: from mxip16a.cluster1.charter.net (mxip16a.cluster1.charter.net [209.225.28.146]) by mxsf31.cluster1.charter.net (8.12.11.20060308/8.12.11) with ESMTP id k8PCiF0c032608 for ; Mon, 25 Sep 2006 08:44:20 -0400 Received: from 68-184-229-22.dhcp.stls.mo.charter.com (HELO axs) ([68.184.229.22]) by mxip16a.cluster1.charter.net with SMTP; 25 Sep 2006 08:44:15 -0400 X-IronPort-AV: i="4.09,213,1157342400"; d="scan'208,217"; a="904417794:sNHT50456894" X-Original-Message-ID: <006601c6e0a0$4fbcf2d0$6401a8c0@axs> From: "terrence o'neill" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Boost pump switching X-Original-Date: Mon, 25 Sep 2006 07:44:15 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0063_01C6E076.6695E4A0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2905 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.2962 This is a multi-part message in MIME format. ------=_NextPart_000_0063_01C6E076.6695E4A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Gary, Thanks for the info on fuel congrollers, which I've filed for my Bendix, = which I hope to finally be using this year. =20 I have a zero-time LyCon 0320 B2B which I've converted to an IO. The = B2B is probably from a Tripacer fixed-pitch prop. Would you happen to = know if I can convert the engine to a constant speed -- ilke MT or = Hartzell, or will I have to find a prop with electric pitch control? =20 Terrence --- O riginal Message -----=20 From: Gary Casey=20 To: Lancair Mailing List=20 Sent: Sunday, September 24, 2006 10:07 PM Subject: [LML] Re: Boost pump switching There are at least 3 fundamental types of fuel injection systems in = production, whether for automotive applications or aircraft. A = "Speed-Density" essentially multiplies engine speed times manifold air = density to get a desired fuel flow. A "Speed-Theta" system multiplies = engine speed times a function of throttle position. And finally a "Mass = Air Flow" system measure air flow directly. In present-day automotive = applications air-flow systems are most common, but there are a lot of = speed-density systems used, primarily by Honda and Chrysler. The = Continental system is a speed-theta system, also used by Harley Davidson = and some Italian cars. (hmm....) The speed function is provided by the = constant-displacement gear pump and the "theta" function is provided by = the barrel valve linked to the throttle. Note that there is nothing in = the system that is related in any way to air flow - the assumption is = that an engine of a given displacement running at a given throttle = opening will want a given amount of fuel. Maybe, but a lot of = conditions affect it and that is why there are so many final adjustments = and tweaking required. And since fuel flow is the result of a balance = of flow through various orifices operation of the boost pump can upset = the system, since it essentially bypasses the engine-driven pump. The = engine-driven pump is not just a fuel supply - it is an essential = metering element in the system. The "Bendix" Precision Airmotive system used by Lycoming is an air = flow system. It uses a venturi to measure air flow and controls fuel = flow in proportion. It does this by regulating fuel flow so that the = pressure drop across the metering orifice is the same as the venturi = throat vacuum. Idle air flow is too low to accurately measure so there = is a separate "theta" control system for idle and that is the only = normal adjustment in the system. The system is completely insensitive = to supply pressure as long as the pressure is within an acceptable range = of typically 15 to 40 psi. One big advantage of this type of system is = that the system can be accurately calibrated on the bench. If you order = a replacement system you can just bolt it on and go. Another advantage = is that the orifice size of the injectors doesn't affect the fuel flow = (orifice balance does affect the fuel distribution, though). These = advantages are the main reason I went to the trouble to put a Lycoming = engine in my ES. The only other option in my mind was to adapt a = Precision Airmotive fuel system to a Continental engine - probably less = work. What are the disadvantages of the "Bendix" system? One is that = the venturi causes and unavoidable pressure drop in the system and = therefore the engine will produce slightly less power. Another is that = there is no return path that can separate vapor, notwithstanding the = "purge" valve that Air Flow Performance sells. The comment about altitude compensation is partly true. Some = Continental systems have an aneroid bellows that adjusts for altitude, = but I have no idea as to whether it works well. A standard Precision = system has not altitude compensation, but there are units available that = have altitude compensation. Even without it the Precision system has an = advantage since the venturi system inherently compensates by the square = root of air density - it essentially takes out half of the altitude = effect. I've suggested to Various Lancair people the possibility of offering a = Lycoming option, but I don't think there is much interest in doing so. Gary Casey "The TCM System varies greatly from its Lycoming counterpart, the = Bendix Fuel Servo. Perhaps most noticeable is the absence of a venturi = to schedule fuel flow proportionate to air flow. The Bendix system = regulates fuel flow by means of a delta pressure across an air = diaphragm. Comparatively, the Continental System has no way to sense = airflow. It does not compensate for altitude or density changes, nor = does it correct for MAP unless turbocharged. " = http://www.kellyaerospace.com/articles/ContinuousFlow.pdf#search=3D%22io5= 50%20fuel%20pump%22 Bob Belshe ------=_NextPart_000_0063_01C6E076.6695E4A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Gary,
Thanks for the info = on fuel=20 congrollers, which I've filed for my Bendix, which I hope to finally be = using=20 this year. 
I have a zero-time = LyCon 0320=20 B2B which I've converted to an IO.  The B2B is probably from a = Tripacer=20 fixed-pitch prop.  Would you happen to know if I can = convert the=20 engine to a constant speed --  ilke MT or Hartzell, or will I = have to=20 find a prop with electric pitch control?  
Terrence
 
--- O    riginal Message -----
From:=20 Gary=20 Casey
Sent: Sunday, September 24, = 2006 10:07=20 PM
Subject: [LML] Re: Boost pump=20 switching

There are at least 3 fundamental types of fuel injection systems = in=20 production, whether for automotive applications or aircraft.  A=20 "Speed-Density" essentially multiplies engine speed times manifold air = density=20 to get a desired fuel flow.  A "Speed-Theta" system multiplies = engine=20 speed times a function of throttle position.  And finally a "Mass = Air=20 Flow" system measure air flow directly.  In present-day = automotive=20 applications air-flow systems are most common, but there are a lot of=20 speed-density systems used, primarily by Honda and Chrysler.  The = Continental system is a speed-theta system, also used by Harley = Davidson and=20 some Italian cars.  (hmm....)  The speed function is = provided=20 by the constant-displacement gear pump and the "theta" function is = provided by=20 the barrel valve linked to the throttle.  Note that there is = nothing in=20 the system that is related in any way to air flow - the assumption is = that an=20 engine of a given displacement running at a given throttle opening = will want a=20 given amount of fuel.  Maybe, but a lot of conditions affect it = and that=20 is why there are so many final adjustments and tweaking = required.  And=20 since fuel flow is the result of a balance of flow through various = orifices=20 operation of the boost pump can upset the system, since it essentially = bypasses the engine-driven pump.  The engine-driven pump is not = just a=20 fuel supply - it is an essential metering element in the system.

The "Bendix" Precision Airmotive system used by Lycoming is an = air flow=20 system.  It uses a venturi to measure air flow and controls fuel = flow in=20 proportion.  It does this by regulating fuel flow so that the = pressure=20 drop across the metering orifice is the same as the venturi throat = vacuum.=20  Idle air flow is too low to accurately measure so there is a = separate=20 "theta" control system for idle and that is the only normal adjustment = in the=20 system.  The system is completely insensitive to supply pressure = as long=20 as the pressure is within an acceptable range of typically 15 to 40 = psi. =20 One big advantage of this type of system is that the system can be = accurately=20 calibrated on the bench.  If you order a replacement system you = can just=20 bolt it on and go.  Another advantage is that the orifice size of = the=20 injectors doesn't affect the fuel flow (orifice balance does affect = the fuel=20 distribution, though).  These advantages are the main reason I = went to=20 the trouble to put a Lycoming engine in my ES.  The only other = option in=20 my mind was to adapt a Precision Airmotive  fuel system to a = Continental=20 engine - probably less work.  What are the disadvantages of the = "Bendix"=20 system?  One is that the venturi causes and unavoidable pressure = drop in=20 the system and therefore the engine will produce slightly less = power. =20 Another is that there is no return path that can separate vapor,=20 notwithstanding the "purge" valve that Air Flow Performance = sells.

The comment about altitude compensation is partly true.  = Some=20 Continental systems have an aneroid bellows that adjusts for altitude, = but I=20 have no idea as to whether it works well.  A standard Precision = system=20 has not altitude compensation, but there are units available that have = altitude compensation.  Even without it the Precision system has = an=20 advantage since the venturi system inherently compensates by the = square root=20 of air density - it essentially takes out half of the altitude = effect.

I've suggested to Various Lancair people the possibility of = offering a=20 Lycoming option, but I don't think there is much interest in doing = so.

Gary Casey

"The TCM System varies = greatly=20 from its Lycoming=20 counterpart, the Bendix Fuel Servo.  = Perhaps=20 most noticeable is the absence of a venturi=20 to schedule fuel flow proportionate to air flow.=20 The Bendix =20 system regulates = fuel flow by=20 means of a delta pressure across an air diaphragm. = Comparatively,=20 the  Continental System=20 has no way to sense airflow. It does not=20 compensate for altitude or density changes,=20 nor does it correct for MAP unless turbocharged.=20 "

http://www.kellyaerospace.com/articles/ContinuousFlow.pdf#sear= ch=3D%22io550%20fuel%20pump%22

 

Bob=20 = Belshe


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