X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao03.cox.net ([68.230.241.36] verified) by logan.com (CommuniGate Pro SMTP 4.3.2) with ESMTP id 965583 for flyrotary@lancaironline.net; Fri, 27 May 2005 13:56:12 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.36; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao03.cox.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with ESMTP id <20050527175524.DNCO26972.fed1rmmtao03.cox.net@BigAl> for ; Fri, 27 May 2005 13:55:24 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Sump tank - Velocity version Date: Fri, 27 May 2005 10:55:26 -0700 Message-ID: <000001c562e5$436e92c0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C562AA.970FBAC0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C562AA.970FBAC0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable One other comment while it is on my mind. I have run my 20B at 5300 = WOT, gravity feeding from one main with about 2 gallons in it, through a 3/8=94line; and the low level warning near the top of the sump did not = come on. From that I infer that even with only about 3=94 head above the top = of the sump, I had adequate flow; maybe 18 -20 gph (EM2 flow flow not yet calibrated. Normal operation then, with both tanks connected, I would = have more than double the necessary gravity flow needed to feed from the = mains to the sump. =20 Al =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Friday, May 27, 2005 6:52 AM To: Rotary motors in aircraft Subject: [FlyRotary] Sump tank - Velocity version =20 How do we KNOW that the return to the sump is what caused the prob? Are=20 we talking his redesign or the original install? =20 We do NOT know that the return to the sump caused the engine out on = Paul=92s last flight. =20 My original plan was to return fuel to the sump, but after Paul's first=20 engine out to also have the sump vent be capable of overflowing into=20 one of the wing tanks (both of which gravity feed into the sump). =20 There are sump tanks and there are header tanks. I would define a sump = tank as one that is at or near the lowest point in the fuel system, and is gravity fed from the main(s). Any small tank in a system that has to be = fed by a pump, I=92d call a header tank. Header tanks are a different = issue. =20 Here is a basic summary of my views on sump tanks. I state them as = facts, but obviously it is my interpretation of the facts. =20 A sump tank has the advantage of eliminating the need for a pump from = the main tank; and eliminating the need for valves from one tank or the = other. Assuming it feeds from the lowest point in mains, it also gives you a = single point for collection of water and impurities that may get in the fuel, = and a single sample drain. These are desirable and important reliability and safety features. =20 The Velocity has a true sump tank which is full (or above) any time = there is fuel in the main tank. It is also a reasonably large tank; about 2 =BD = gal in the RG and I guess 4 =96 5 gallons on the FG. A fuel pump at or near = the exit from the sump tank; at a level at or below the level of the bottom of = the tank, with a reasonably sized line (3/8=94 or larger) from sump to pump = should never see less than at least 1 atmosphere of feed pressure, and = therefore be highly resistant to any vapor lock issues. =20 =20 With the fuel exit from the sump a bit up from the bottom (room for collection of a quart or more of water and impurities) there should be = no need for a filter between the sump and the pump that could result in = flow resistance. Put the filter (30 micron or less, I suppose) downstream = from the pump to catch anything you don=92t want going to the injectors. =20 I don=92t believe there is an issue with returning the bypass fuel from = the pressure regulator to the sump as long as the sump tank is a few gallons = or more. When the engine is running there is always a net flow from the = main to the sump. There is not an issue of the sump =93overflowing=94. =20 =20 If you have a smaller sump, or if it is reasonable and simple (reliable) = to do so; return the bypass to the main tanks (tanks, plural; for gravity = feed returning to one tank could result in level imbalance.)=20 =20 If you are pumping fuel at a rate that far exceeds that burned by the engine, there is a potential for heating of the fuel in the sump from = heat picked up in the fuel lines and rail in the engine compartment. Size = the pumps so that one pump gives you slightly more than the maximum burn you expect from the engine. More than that; or running both pumps more than just during takeoff, is just circulating a lot of fuel through the = engine compartment to no advantage, and causing heating of the fuel. Fire = sleeve on the fuel lines is a good idea, and provides some (probably not much, = but some) degree of heat insulation.=20 =20 Monitoring the fuel temp at the bottom of the sump could be a good idea = and provide useful information about the amount of heating of the fuel in = the sump. I=92d expect the worst case to be long periods on the taxiway with = a fully heated engine at low power. =20 Do a power run-up prior to takeoff. (This assumes your cooling system = design allows this.) =20 The reason for circulating fuel through the fuel rail rather than a = dead-end system is to keep the fuel temperature from rising in the rail, and to = force any air or vapor bubbles (mostly a possibility at or prior to startup) = back to the tank. I have found that some period after shutdown of the hot engine, I could hear bubbles feeding back to the sump for a second when turning the fuel pump back on. =20 In its simplest form (as in the Velocity) both mains and the sump are = vented to the atmosphere for air to exit upon fill-up, and for air to enter as = the fuel level goes down in the mains. The vents must of course be above = the highest fuel level and the lines not subject to filling with fuel that = must be drawn upward for air to enter. Keep in mind that the fuel level in = the sump will be the same as that of the main tank; meaning that the vent = line from the sump will have fuel in it up to the level of the of the fuel surface in the mains. =20 I realize that there have been or may be other anomalies in the vent = system (leaky fuel caps, or whatever) that can affect the function of the vent system (as in Jim=92s case); but that=92s a separate discussion. =20 FWIW, =20 Al =20 =20 =20 =20 ------=_NextPart_000_0001_01C562AA.970FBAC0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

One other comment while it is on = my mind. =A0I have run my 20B at 5300 WOT, gravity feeding from one main = with about 2 gallons in it, through a 3/8”line; and the low level warning = near the top of the sump did not come on.=A0 From that I infer that even with = only about 3” head above the top of the sump, I had adequate flow; maybe 18 -20 gph = (EM2 flow flow not yet calibrated.=A0 Normal operation then, with both tanks = connected, I would have more than double the necessary gravity flow needed to feed = from the mains to the sump.

 

Al

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Friday, May 27, = 2005 6:52 AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Sump = tank - Velocity version

 

How do we KNOW that the return to the sump is = what caused the prob? Are

we talking his redesign or the original = install?

 

We do NOT know that the return to the sump caused the engine out on = Paul’s last flight.

 

My original plan was to return fuel to the = sump, but after Paul's first

engine out to  also have the sump vent = be capable of overflowing into

one of the wing tanks (both of which gravity = feed into the sump).

 

There are sump tanks and there are header tanks.  I would define a sump = tank as one that is at or near the lowest point in the fuel system, and is = gravity fed from the main(s).  Any small tank in a system that has to be fed by = a pump, I’d call a header tank.  Header tanks are a different = issue.

 <= /font>

Here is a basic summary of my views on sump tanks.  I state them as = facts, but obviously it is my interpretation of the facts.

 

A sump tank has the advantage of eliminating the need for a pump from the = main tank; and eliminating the need for valves from one tank or the other.  Assuming it feeds from the lowest point in mains, it also gives = you a single point for collection of water and impurities that may get in the = fuel, and a single sample drain.  These are desirable and important = reliability and safety features.

 

The Velocity has a true sump tank which is full (or above) any time there is = fuel in the main tank.  It is also a reasonably large tank; about 2 =BD = gal in the RG and I guess 4 – 5 gallons on the FG.  A fuel pump at = or near the exit from the sump tank; at a level at or below the level of the = bottom of the tank, with a reasonably sized line (3/8” or larger) from sump = to pump should never see less than at least 1 atmosphere of feed pressure, and therefore be highly resistant to any vapor lock issues. =  

 

With the fuel exit from the sump a bit up from the bottom (room for = collection of a quart or more of water and impurities) there should be no need for a = filter between the sump and the pump that could result in flow = resistance.  Put the filter (30 micron or less, I suppose) downstream from the pump to = catch anything you don’t want going to the injectors.

 

I don’t believe there is an issue with returning the bypass fuel = from the pressure regulator to the sump as long as the sump tank is a few gallons = or more.  When the engine is running there is always a net flow from the = main to the sump.  There is not an issue of the sump “overflowing”. 

 

If you have a smaller sump, or if it is reasonable and simple (reliable) to = do so; return the bypass to the main tanks (tanks, plural; for gravity feed = returning to one tank could result in level imbalance.)

 

If you are pumping fuel at a rate that far exceeds that burned by the = engine, there is a potential for heating of the fuel in the sump from heat = picked up in the fuel lines and rail in the engine compartment.  Size the pumps = so that one pump gives you slightly more than the maximum burn you expect from = the engine.  More than that; or running both pumps more than just = during takeoff, is just circulating a lot of fuel through the engine = compartment to no advantage, and causing heating of the fuel.  Fire sleeve on the = fuel lines is a good idea, and provides some (probably not much, but some) degree = of heat insulation.

 

Monitoring the fuel temp at the bottom of the sump could be a good idea and provide = useful information about the amount of heating of the fuel in the sump. = I’d expect the worst case to be long periods on the taxiway with a fully = heated engine at low power. 

Do a power run-up prior to takeoff. (This assumes your cooling system design = allows this.)

 

The reason for circulating fuel through the fuel rail rather than a dead-end = system is to keep the fuel temperature from rising in the rail, and to force = any air or vapor bubbles (mostly a possibility at or prior to startup) back to = the tank.  I have found that some period after shutdown of the hot = engine, I could hear bubbles feeding back to the sump for a second when turning = the fuel pump back on.

 

In its simplest form (as in the Velocity) both mains and the sump are = vented to the atmosphere for air to exit upon fill-up, and for air to enter as the = fuel level goes down in the mains.  The vents must of course be above = the highest fuel level and the lines not subject to filling with fuel that = must be drawn upward for air to enter.  Keep in mind that the fuel level in = the sump will be the same as that of the main tank; meaning that the vent = line from the sump will have fuel in it up to the level of the of the fuel surface = in the mains.

 

I realize that there have been or may be other anomalies in the vent = system (leaky fuel caps, or whatever) that can affect the function of the vent = system (as in Jim’s case); but that’s a separate = discussion.

 

FWIW,

 

Al

 

 

 

 

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