X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao08.cox.net ([68.230.241.31] verified) by logan.com (CommuniGate Pro SMTP 4.3.2) with ESMTP id 965380 for flyrotary@lancaironline.net; Fri, 27 May 2005 10:52:25 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.31; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao08.cox.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with ESMTP id <20050527145139.FQSL16890.fed1rmmtao08.cox.net@BigAl> for ; Fri, 27 May 2005 10:51:39 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Sump tank - Velocity version Date: Fri, 27 May 2005 07:51:40 -0700 Message-ID: <000001c562cb$97b65800$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C56290.EB59F100" 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_01C56290.EB59F100 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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_01C56290.EB59F100 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

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.

=A0

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

engine out to=A0 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.=A0 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).=A0 Any small tank in a system that has to be fed by a pump, I’d call = a header tank.=A0 Header tanks are a different issue.

 <= /font>

Here is a = basic summary of my views on sump tanks. =A0I 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. =A0Assuming = 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.=A0 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. =A0It is also a reasonably large tank; about 2 =BD gal in the RG and I guess 4 = – 5 gallons on the FG.=A0 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. =A0

 

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.=A0 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. =A0When the = engine is running there is always a net flow from the main to the sump.=A0 There = is not an issue of the sump “overflowing”.=A0

 

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.=A0 Size the pumps so that one pump gives you = slightly more than the maximum burn you expect from the engine. =A0More 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.=A0 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.=A0

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.=A0 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.=A0 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.=A0 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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