Return-Path: Received: from imf25aec.mail.bellsouth.net ([205.152.59.73] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 150197 for flyrotary@lancaironline.net; Sat, 12 Jun 2004 16:18:46 -0400 Received: from bellsouth.net ([209.215.61.156]) by imf25aec.mail.bellsouth.net (InterMail vM.5.01.06.08 201-253-122-130-108-20031117) with ESMTP id <20040612201815.WDNL19385.imf25aec.mail.bellsouth.net@bellsouth.net> for ; Sat, 12 Jun 2004 16:18:15 -0400 Message-ID: <40CB650A.5050408@bellsouth.net> Date: Sat, 12 Jun 2004 15:18:18 -0500 From: Charlie England User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Low fuel pressure References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Finn Lassen wrote: > I put a new Facet pump in place of the old one that had fluctuating > fuel pressure. > Also replaced the fuel line to the pump. > On test flight last Sunday again had low fuel pressure, as low as 1 > psi, so I cut the flight short and headed home. > > This morning I put a vent tube in the fuel cap pointing into the wind, > to eliminate bad vent lines as a cause. > Pressure to outer carbs normal (about 3.3 psi), dropped a bit on run-up. > During take-off I noticed fuel pressure dropping more and more, down > to .5 then .1 psi, at which point the engine began to loose power. > Fortunately I was ready for it and pulled back throttle to the two > outer carbs and was able to continue climbing and continue to a > "normal" landing. > > It's nice to have redundant system and be overpowered for the > airplane, but I really need to solve the low fuel pressure problem to > my outer carbs. (Center carb is shared between rotors and has it's own > pump and throttle). > Pressure is OK at idle and apparently drops as fuel flow increases. > This would indicate a restriction on the pump inlet side, right? > But why is the other pump apparently not affected? > If the outlet path were restricted the pressure would increase, right? > New hoses from common point to both pump inlets. > This is the path (that has been working for 100's of hours): > Fuselage tank -> Fuel selector valve -> Fuel flow sensor -> fuel > filter -> drain point -> split to two fuel pumps. > > I've replaced the fuel filter in the last 3 months and 25 hours (cheap > "G3" automotive paper filter). > > Any ideas? > > Finn What would happen if the fuel were boiling between the pump & carb? Would pumping mostly vapor be easier (& result in less pressure) than pumping liquid fuel? Are the lines firesleeved & protected from exhaust heat by heat shields? What were Tracy's symptoms when he lost power on his carb setup? Charlie