X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 12 Jun 2007 22:47:21 -0400 Message-ID: X-Original-Return-Path: Received: from smtp0.av-mx.com ([137.118.16.56] verified) by logan.com (CommuniGate Pro SMTP 5.1.9) with ESMTP id 2099247 for lml@lancaironline.net; Tue, 12 Jun 2007 22:05:32 -0400 Received-SPF: pass receiver=logan.com; client-ip=137.118.16.56; envelope-from=pinetownd@volcano.net Received: from DennisDell (65-166-101-109.du.volcano.net [65.166.101.109]) (Authenticated sender: pinetownd@volcano.net) by smtp0.av-mx.com (Postfix) with ESMTP id 8F2111BF894 for ; Tue, 12 Jun 2007 22:04:56 -0400 (EDT) X-Original-Message-ID: <00c901c7ad5f$3c0b2450$6601a8c0@DennisDell> From: "Dennis Johnson" X-Original-To: "Lancair Mailing List" Subject: Boost Pump X-Original-Date: Tue, 12 Jun 2007 19:04:52 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00C6_01C7AD24.8EC520A0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_00C6_01C7AD24.8EC520A0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Hi Alan, You wrote,=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 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. ------=_NextPart_000_00C6_01C7AD24.8EC520A0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
Hi Alan,
 
You wrote,
 
*WITH=20 NO SPECIFIC KNOWLEDGE*, it does seem that because the Dukes pump is = *pre* the=20 engine, that too much fuel really can't happen, it's metered by the fuel = divider=20 and if the throttle body is not open, then the fuel is returned via the = return=20 line.  So in effect you are just pumping fuel back into the tanks = via the=20 return line....
 
I think that assumption is not = totally=20 correct.  I have an IO-550 and I have tried the "hot start" = technique of=20 running the boost pump on high with the mixture at cut-off and the = throttle=20 closed.  The idea is to circulate cool fuel through the mechanical = fuel=20 pump and then return it to the fuel tank.  I get a substantial = amount=20 of fuel coming out the cylinder drains when I do that.  So at least = in my=20 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=20 point is that shutting down my engine at the end of a flight by = pulling my=20 mixture control to cut-off won't work if the boost pump is on low; the = engine=20 keeps idling.
 
According to Flying = Magazine's=20 September 2004 Aftermath column, a Bonanza with a TCM TSIO-520 = crashed=20 shortly after takeoff probably because the pilot inadvertently had the = boost=20 pump in the high position.  According to the article, full power = operation=20 with the boost pump on high would not cause an appreciable loss of = power, but=20 (according to the NTSB) when manifold pressure is reduced below 24 = inches, the=20 engine will quit.
 
Fuel system problems are a common = cause of=20 experimental crashes.  I would be extraordinarily wary about making = any=20 change to my fuel system.
 
Best,
Dennis Johnson
Legacy, now flying
Major discovery:  Flying is = more fun=20 than building. 
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