X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml Date: Wed, 25 Nov 2009 12:03:50 -0500 Message-ID: X-Original-Return-Path: Received: from smtp-auth-04.mx.pitdc1.expedient.net ([206.210.66.137] verified) by logan.com (CommuniGate Pro SMTP 5.3c3) with ESMTPS id 3990737 for lml@lancaironline.net; Wed, 25 Nov 2009 11:11:22 -0500 Received-SPF: none receiver=logan.com; client-ip=206.210.66.137; envelope-from=rpastusek@htii.com Received: from HTBOB001 (static-72-66-86-7.washdc.fios.verizon.net [72.66.86.7]) by smtp-auth-04.mx.pitdc1.expedient.net (Postfix) with ESMTPA id F33E5E48AB for ; Wed, 25 Nov 2009 11:10:45 -0500 (EST) From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Fuel Pressure question X-Original-Date: Wed, 25 Nov 2009 11:10:42 -0500 X-Original-Message-ID: <007b01ca6de9$d676adf0$836409d0$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_007C_01CA6DBF.EDA0A5F0" X-Mailer: Microsoft Office Outlook 12.0 thread-index: AcpsX5m1j/VFud78Te+IZTmif9rE/QBhkPlA Content-Language: en-us This is a multi-part message in MIME format. ------=_NextPart_000_007C_01CA6DBF.EDA0A5F0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Dan Ballin wrote: A few questions have come up regarding fuel pressure while flight testing Ralph Love's Legacy, N122PT. It has an IO-550 with MT prop. We've had indications of high fuel pressure when the throttle is retarded (38-40 psi) in the pattern which is accompanied by engine roughness. All gets better when the mixture is leaned. Testing has been done in Redmond - so patterns about 4-5000 ft. So is this "normal" and just explained by the overly rich state due to altitude and leaning is the solution or is something else going on? Where should the fuel pressure be measured from? The unmetered side of the fuel metering unit or the metered side? and why. And lastly, where have you mounted the fuel pressure transducer? EI suggests the firewall, but that leads to a long fuel line and ? does that make any difference in the readings, dampening etc. Can you mount it closer or are the vibrations going to cause failure of the fitting and fuel leaking over hot cylinders? Dan, I'll offer that engine roughness that accompanies the high fuel pressure you note at low power settings almost certainly indicates too rich a mixture. During testing/set up of my TSIO-550E, I once got the mixture so rich that the engine quit on takeoff. Easy fix after a couple of gulps, but makes one appreciate a good set up, and some attention to these details. I also have an MVP-50 and think it's one of the best/most reliable instruments in my airplane. I use it to monitor lots of stuff besides the basic engine and it's been flawless. Like you, I have seen high fuel pressures during rapid throttle movements during testing, but they were of very short duration, and slowing the throttle movement rate has completely eliminated them.after I got the boost and fuel flow dialed in as directed by Continental SIT 97-3E. I typically fly very lean (100+ LOP) in the high teens to low flight levels, and increase the fuel flow about 2 GPH when I start down from altitude. During testing, I tried descents to pattern altitude while remaining very lean, and had no problems at all, but I had a Cherokee engine quit momentarily on short final many years ago because I forgot to richen the mixture, so I'm being a bit conservative here. I don't go to full rich to descend because I'm typically 20+ minutes out and the fuel burn difference is significant. I'm not an instructor, and am reluctant to recommend this as a technique because you still need to get the engine set up for a go around (RPM up and mixture in) before landing...but it works well for me. The "book" says to measure the fuel pressure on the un-metered side, so that's what I did...although the Continental bulletin has you measure metered pressure during set up. Might be a question for a good Continental expert? I mounted my pressure transducer on the firewall with a long line. Since the flow through this line is effectively zero, the pressure is the same at the manifold as at the transducer end. A very long hose will provide some "dampening," but for the size and length, I doubt even a highly precise instrumentation package could measure it. For an analogy, you don't notice any "dampening" of the brakes, although the lines are the same diameter.or smaller. and the length is several times more. I did mount my flow transducer on top of the cylinders, just forward of the baffle that separates the cylinders from the accessory case and the back of the engine. I built a rubber shock mount to hold it, insulated it well from radiant heat from the cylinders below, and focused cooling air from the inlets over the top of the transducer. Has worked well for 400+ hours. Fuel leaking over a hot engine is always a problem; more so if you have a turbo. Best quality hoses, fire sleeved and replaced periodically, is good insurance. I also installed a "standard" EI temperature probe in the engine compartment exhaust tunnels (one on each side) and hooked them to the MVP-50 as "fire lights." The normal air temp in this area is 120-130 degrees, so I alarmed them at 150 degrees. Never a false alarm.so far.and I think this will give the first indication of anything flammable getting to one of the turbos. In flight these are red hot, and will combust almost anything.oil leak, fuel leak, etc. Hope this helps. Bob ------=_NextPart_000_007C_01CA6DBF.EDA0A5F0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Dan Ballin wrote:

 

A few questions have come up regarding fuel = pressure while flight testing Ralph Love's Legacy, N122PT.  It has an IO-550 with = MT prop.  We've had indications of high fuel pressure when the = throttle is retarded (38-40 psi) in the pattern which is accompanied by engine roughness.  All gets better when the mixture is leaned.  = Testing has been done in Redmond - so patterns about 4-5000 ft.  So is this "normal" and just explained by the overly rich state due to = altitude and leaning is the solution or is something else going on?  Where = should the fuel pressure be measured from?  The unmetered side of the fuel metering unit or the metered side?  and why.    And = lastly, where have you mounted the fuel pressure transducer?  EI suggests = the firewall, but that leads to a long fuel line and ? does that make any difference in the readings, dampening etc.  Can you mount it closer = or are the vibrations going to cause failure of the fitting and fuel leaking = over hot cylinders?

Dan,

 

I’ll offer that engine roughness that accompanies = the high fuel pressure you note at low power settings almost certainly indicates = too rich a mixture. During testing/set up of my TSIO-550E, I once got the = mixture so rich that the engine quit on takeoff. Easy fix after a couple of = gulps, but makes one appreciate a good set up, and some attention to these = details.

 

I also have an MVP-50 and think it’s one of the = best/most reliable instruments in my airplane. I use it to monitor lots of stuff = besides the basic engine and it’s been flawless. Like you, I have seen = high fuel pressures during rapid throttle movements during testing, but they were = of very short duration, and slowing the throttle movement rate has completely = eliminated them…after I got the boost and fuel flow dialed in as directed by Continental SIT 97-3E.

 

I typically fly very lean (100+ LOP) in the high teens to = low flight levels, and increase the fuel flow about 2 GPH when I start down = from altitude. During testing, I tried descents to pattern altitude while = remaining very lean, and had no problems at all, but I had a Cherokee engine quit momentarily on short final many years ago because I forgot to richen the mixture, so I’m being a bit conservative here. I don’t go to = full rich to descend because I’m typically 20+ minutes out and the fuel = burn difference is significant. I’m not an instructor, and am reluctant to = recommend this as a technique because you still need to get the engine set up for a go = around (RPM up and mixture in) before landing...but it works well for = me.

 

The “book” says to measure the fuel pressure = on the un-metered side, so that’s what I did...although the Continental = bulletin has you measure metered pressure during set up. Might be a question for = a good Continental expert? I mounted my pressure transducer on the firewall with a long = line. Since the flow through this line is effectively zero, the pressure is = the same at the manifold as at the transducer end. A very long hose will provide = some “dampening,” but for the size and length, I doubt even a highly precise = instrumentation package could measure it. For an analogy, you don’t notice any = “dampening” of the brakes, although the lines are the same diameter…or = smaller… and the length is several times more.

 

I did mount my flow transducer on top of the cylinders, = just forward of the baffle that separates the cylinders from the accessory = case and the back of the engine. I built a rubber shock mount to hold it, insulated = it well from radiant heat from the cylinders below, and focused cooling air from = the inlets over the top of the transducer. Has worked well for 400+ hours. =

 

Fuel leaking over a hot engine is always a problem; more = so if you have a turbo. Best quality hoses, fire sleeved and replaced = periodically, is good insurance. I also installed a “standard” EI = temperature probe in the engine compartment exhaust tunnels (one on each side) and = hooked them to the MVP-50 as “fire lights.” The normal air temp in = this area is 120-130 degrees, so I alarmed them at 150 degrees. Never a false = alarm…so far…and I think this will give the first indication of anything = flammable getting to one of the turbos. In flight these are red hot, and will = combust almost anything…oil leak, fuel leak, etc.

 

Hope this helps.


Bob

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