Return-Path: Received: from out007.verizon.net ([206.46.170.107] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 150383 for flyrotary@lancaironline.net; Sat, 12 Jun 2004 22:35:29 -0400 Received: from verizon.net ([4.12.145.173]) by out007.verizon.net (InterMail vM.5.01.06.06 201-253-122-130-106-20030910) with ESMTP id <20040613023457.DFDO28276.out007.verizon.net@verizon.net> for ; Sat, 12 Jun 2004 21:34:57 -0500 Message-ID: <40CBBD4A.4050604@verizon.net> Date: Sat, 12 Jun 2004 22:34:50 -0400 From: Finn Lassen User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax; PROMO) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Low fuel pressure References: In-Reply-To: Content-Type: multipart/alternative; boundary="------------070907090801030104070503" X-Authentication-Info: Submitted using SMTP AUTH at out007.verizon.net from [4.12.145.173] at Sat, 12 Jun 2004 21:34:57 -0500 This is a multi-part message in MIME format. --------------070907090801030104070503 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Ed Anderson wrote: > ----- > From: "Finn Lassen" > > To: "Rotary motors in aircraft" > > Sent: Saturday, June 12, 2004 2:57 PM > Subject: [FlyRotary] Low fuel pressure > > > 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? > > Finn, why not a restriction on the outlet side of the pump- seems most > likely to me. Scenario - there is a restriction between the output > of your pump that services your two outer carbs (why don't you go EFI? > never mind!) and your outer two carbs. While there is low fuel demand > by your two outer carbs the pump is able to provide adequate fuel flow > (and pressure) through the restriction against the closed bowl > plunger, but as the demand for fuel increases, the venture of your two > outer carbs suck the fuel out of their bowls faster than your pump can > pump fuel through the restriction to the bowls and since the bowl > plungers are now full open (to allow fuel into the bowl) the pump can > never build up pressure past the restriction (as it could when the > bowl plunger was closed) to compensate. So eventually the bowls are > sucked dry and since the pump can't pump enough fuel through the > restriction to meet the demand you loose pressure and power. Ok, I'll have to check the path between the pump and the pressure gauge. > In effect the line area past the restriction is like pumping to open > atmosphere and becomes more like that as the fuel level in the bowl > decreases until when the bowl is nearly empty, the pump is pumping all > the fuel it can through the restriction, but the pressure shows zero > (which indicates your pressure gauge is on the carb side of the > restriction - so the restriction should be between your pump and your > pressure gauge) and while there is fuel flowing its insufficient to > fill the bowl or support the power demand. > > Since the restriction is on the pump outlet side of the pump servicing > your outer carbs, it does not affect your center pump or carb Excellent point! > > Ed Anderson > > > > > > > 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 > > > > > > > > >> Homepage: http://www.flyrotary.com/ > > >> Archive: http://lancaironline.net/lists/flyrotary/List.html > > --------------070907090801030104070503 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Ed Anderson wrote:
 -----
From: "Finn Lassen" <finn.lassen@verizon.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, June 12, 2004 2:57 PM
Subject: [FlyRotary] Low fuel pressure

> 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?
 
Finn, why not a restriction on the outlet side of the pump- seems most likely to me.  Scenario - there is a restriction between  the output of your pump that services your two outer carbs (why don't you go EFI? never mind!) and your outer two carbs.  While there is low fuel demand by your two outer carbs the pump is able to provide adequate fuel flow (and pressure) through the restriction against the closed bowl plunger, but as the demand for fuel increases, the venture of your two outer carbs suck the fuel out of their bowls faster than your pump can pump fuel through the restriction to the bowls and since the bowl plungers are now full open (to allow fuel into the bowl)  the pump can never build up pressure past the restriction (as it could when the bowl plunger was closed) to compensate.  So eventually the bowls are sucked dry and since the pump can't pump enough fuel through the restriction to meet the demand you loose pressure and power.
Ok, I'll have to check the path between the pump and the pressure gauge.
In effect the line area past the restriction is like pumping to open atmosphere and becomes more like that as the fuel level in the bowl decreases until when the bowl is nearly empty, the pump is pumping all the fuel it can through the restriction, but the pressure shows zero (which indicates your pressure gauge is on the carb side of the restriction - so the restriction should be between your pump and your pressure gauge)  and while there is fuel flowing its insufficient to fill the bowl or support the power demand.
 
Since the restriction is on the pump outlet side of the pump servicing your outer carbs, it does not affect your center pump or carb
Excellent point!
 
Ed Anderson
 
 
 
 

> 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
>
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
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