X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 13 Jun 2007 22:07:54 -0400 Message-ID: X-Original-Return-Path: Received: from [69.146.254.20] (HELO arilabs.net) by logan.com (CommuniGate Pro SMTP 5.1.9) with ESMTP id 2101026 for lml@lancaironline.net; Wed, 13 Jun 2007 20:38:04 -0400 Received-SPF: none receiver=logan.com; client-ip=69.146.254.20; envelope-from=Kevin@arilabs.net Subject: RE: [LML] Boost Pump MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C7AE1C.2EFDF6DB" X-Original-Date: Wed, 13 Jun 2007 18:37:26 -0600 Content-class: urn:content-classes:message X-MimeOLE: Produced By Microsoft Exchange V6.5 X-Original-Message-ID: <7141427652BB3049A7DBF1084B67805B0F8061@penumbra.arilabs.net> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [LML] Boost Pump Thread-Index: AcetZUGWK9/YfZDmRLGhFZT6TPSGQwAtnzAQ From: "Kevin Stallard" X-Original-To: "Lancair Mailing List" This is a multi-part message in MIME format. ------_=_NextPart_001_01C7AE1C.2EFDF6DB Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Is it safe to assume then that the fuel return line isn't able to return all the fuel that isn't being used? Maybe there are restrictions in the return line that prevents fuel from retuning at a flow rate that would prevent it from also bypassing the mechanical pump? =20 Or does the return line start after the bypass value for the mechanical pump? =20 Kevin =20 ________________________________ From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Dennis Johnson Sent: Tuesday, June 12, 2007 8:47 PM To: lml@lancaironline.net Subject: [LML] Boost Pump =20 Hi Alan, =20 You wrote,=20 =20 *WITH NO SPECIFIC KNOWLEDGE*, it does seem that because the Dukes pump is *pre* the engine, that too much fuel really can't happen, it's metered by the fuel divider and if the throttle body is not open, then the fuel is returned via the return line. So in effect you are just pumping fuel back into the tanks via the return line....=20 =20 I think that assumption is not totally correct. I have an IO-550 and I have tried the "hot start" technique of running the boost pump on high with the mixture at cut-off and the throttle closed. The idea is to circulate cool fuel through the mechanical fuel pump and then return it to the fuel tank. I get a substantial amount of fuel coming out the cylinder drains when I do that. So at least in my case, high boost has enough pressure to overcome the relief valve in the mechanical fuel pump and to provide fuel to the injectors. Another data point is that shutting down my engine at the end of a flight by pulling my mixture control to cut-off won't work if the boost pump is on low; the engine keeps idling. =20 According to Flying Magazine's September 2004 Aftermath column, a Bonanza with a TCM TSIO-520 crashed shortly after takeoff probably because the pilot inadvertently had the boost pump in the high position. According to the article, full power operation with the boost pump on high would not cause an appreciable loss of power, but (according to the NTSB) when manifold pressure is reduced below 24 inches, the engine will quit. =20 Fuel system problems are a common cause of experimental crashes. I would be extraordinarily wary about making any change to my fuel system. =20 Best, Dennis Johnson Legacy, now flying Major discovery: Flying is more fun than building. =20 ------_=_NextPart_001_01C7AE1C.2EFDF6DB Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Is it safe to assume then that the = fuel return line isn’t able to return all the fuel that isn’t = being used? Maybe there are restrictions in the return line that = prevents fuel from retuning at a flow rate that would prevent it from also bypassing = the mechanical pump?

Or does the return line start after = the bypass value for the mechanical pump?

Kevin

From: = Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Dennis Johnson
Sent: Tuesday, June 12, = 2007 8:47 PM
To: = lml@lancaironline.net
Subject: [LML] Boost = Pump

Hi Alan,

You wrote,

*WITH NO SPECIFIC KNOWLEDGE*, it = does seem that because the Dukes pump is *pre* the engine, that too much fuel = really can't happen, it's metered by the fuel divider and if the throttle body = is not open, then the fuel is returned via the return line. So in effect = you are just pumping fuel back into the tanks via the return line.... =

I think that assumption is not totally correct. I have an = IO-550 and I have tried the "hot start" technique of running the = boost pump on high with the mixture at cut-off and the throttle closed. The = idea is to circulate cool fuel through the mechanical fuel pump and then return = it to the fuel tank. I get a substantial amount of fuel coming out = the cylinder drains when I do that. So at least in my case, high boost = has enough pressure to overcome the relief valve in the mechanical fuel pump = and to provide fuel to the injectors. Another data point is that shutting down my engine at the end of a flight by pulling my mixture control = to cut-off won't work if the boost pump is on low; the engine keeps = idling.

According to Flying = Magazine's September 2004 Aftermath column, a Bonanza with a TCM TSIO-520 crashed shortly after takeoff = probably because the pilot inadvertently had the boost pump in the high position. According to the article, full power operation with the boost pump on = high would not cause an appreciable loss of power, but (according to the = NTSB) when manifold pressure is reduced below 24 inches, the engine will = quit.

Fuel system problems are a common cause of experimental = crashes. I would be extraordinarily wary about making any change to my fuel = system.

Best,

Dennis Johnson

Legacy, now flying

Major discovery: Flying is more fun than building. =

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