Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP id 150175 for flyrotary@lancaironline.net; Sat, 12 Jun 2004 15:28:20 -0400 Received: from EDWARD (clt25-78-058.carolina.rr.com [24.25.78.58]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i5CJRlfP021855 for ; Sat, 12 Jun 2004 15:27:49 -0400 (EDT) Message-ID: <002b01c450b3$5c0dc1b0$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Low fuel pressure Date: Sat, 12 Jun 2004 15:27:54 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0028_01C45091.D4B4B870" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0028_01C45091.D4B4B870 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable -----=20 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=20 > pressure. > Also replaced the fuel line to the pump. > On test flight last Sunday again had low fuel pressure, as low as 1 = psi,=20 > so I cut the flight short and headed home. >=20 > 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=20 > .5 then .1 psi, at which point the engine began to loose power.=20 > Fortunately I was ready for it and pulled back throttle to the two = outer=20 > carbs and was able to continue climbing and continue to a "normal" = landing. >=20 > It's nice to have redundant system and be overpowered for the = airplane,=20 > but I really need to solve the low fuel pressure problem to my outer=20 > 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. 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 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=20 > -> drain point -> split to two fuel pumps. >=20 > I've replaced the fuel filter in the last 3 months and 25 hours (cheap = > "G3" automotive paper filter). >=20 > Any ideas? >=20 > Finn >=20 >=20 >=20 > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html > ------=_NextPart_000_0028_01C45091.D4B4B870 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
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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=20 pressure

> I put a new Facet pump in place of = the old one=20 that had fluctuating fuel
> pressure.
> Also replaced the = fuel line=20 to the pump.
> On test flight last Sunday again had low fuel = pressure, as=20 low as 1 psi,
> so I cut the flight short and headed = home.
>=20
> This morning I put a vent tube in the fuel cap pointing into = the wind,=20
> to eliminate bad vent lines as a cause.
> Pressure to = outer carbs=20 normal (about 3.3 psi), dropped a bit on run-up.
> During take-off = I=20 noticed fuel pressure dropping more and more, down to
> .5 then = .1 psi,=20 at which point the engine began to loose power.
> Fortunately I = was ready=20 for it and pulled back throttle to the two outer
> carbs and was = able to=20 continue climbing and continue to a "normal" landing.
>
> = It's nice=20 to have redundant system and be overpowered for the airplane,
> = but I=20 really need to solve the low fuel pressure problem to my outer
> = carbs.=20 (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=20 increases.
> This would indicate a restriction on the pump inlet = side,=20 right?
 
Finn, why = not a=20 restriction on the outlet side of the pump- seems most likely to = me. =20 Scenario - there is a restriction between  the output of your pump = that=20 services your two outer carbs (why don't you go EFI? never mind!) and = your outer=20 two carbs.  While there is low fuel demand by your two outer carbs = the pump=20 is able to provide adequate fuel flow (and pressure) through the=20 restriction against the closed bowl plunger, but as the demand for = fuel=20 increases, the venture of your two outer carbs suck the fuel out of = their bowls=20 faster than your pump can pump fuel through the restriction to the bowls = and=20 since the bowl plungers are now full open (to allow fuel into the = bowl)=20  the pump can never build up pressure past the restriction (as it = could=20 when the bowl plunger was closed) to compensate.  So eventually the = bowls=20 are sucked dry and since the pump can't pump enough fuel through the = restriction=20 to meet the demand you loose pressure and power.
 
In effect the = line area past=20 the restriction is like pumping to open atmosphere and becomes more like = that as=20 the fuel level in the bowl decreases until when the bowl is nearly = empty, the=20 pump is pumping all the fuel it can through the restriction, but the = pressure=20 shows zero (which indicates your pressure gauge is on the carb side of = the=20 restriction - so the restriction should be between your pump and your = pressure=20 gauge)  and while there is fuel flowing its insufficient to fill = the bowl=20 or support the power demand.
 
Since the = restriction is on=20 the pump outlet side of the pump servicing your outer carbs, it does not = affect=20 your center pump or carb
 
Ed=20 Anderson
 
 
 
 

> But why is the other pump = apparently not=20 affected?
> If the outlet path were restricted the pressure would=20 increase, right?
> New hoses from common point to both pump=20 inlets.
> This is the path (that has been working for 100's of=20 hours):
> Fuselage tank -> Fuel selector valve -> Fuel flow = sensor=20 -> fuel filter
> -> drain point -> split to two fuel=20 pumps.
>
> I've replaced the fuel filter in the last 3 = months and=20 25 hours (cheap
> "G3" automotive paper filter).
>
> = Any=20 ideas?
>
> Finn
>
>
>
> = >> =20 Homepage:  http://www.flyrotary.com/
>=20 >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html>
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