Return-Path: Received: from wb2-a.mail.utexas.edu ([128.83.126.136] verified) by logan.com (CommuniGate Pro SMTP 4.2b5) with ESMTP-TLS id 165089 for flyrotary@lancaironline.net; Wed, 16 Jun 2004 12:53:27 -0400 Received: (qmail 73493 invoked from network); 16 Jun 2004 16:52:55 -0000 Received: from dhcp-191-101.per.utexas.edu (HELO benefits3.mail.utexas.edu) (146.6.191.101) by wb2.mail.utexas.edu with RC4-SHA encrypted SMTP; 16 Jun 2004 16:52:55 -0000 Message-Id: <5.1.1.5.2.20040616113505.01013680@localhost> X-Sender: msteitle@mail.utexas.edu@localhost X-Mailer: QUALCOMM Windows Eudora Version 5.1.1 Date: Wed, 16 Jun 2004 11:51:19 -0500 To: "Rotary motors in aircraft" From: Mark Steitle Subject: Fuel Delivery - Vapor Lock In-Reply-To: Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="=====================_69817968==.ALT" --=====================_69817968==.ALT Content-Type: text/plain; charset="us-ascii"; format=flowed Not to beat a dead horse here, but I still have some concerns/problems with the fuel delivery issue. The Eggenfelder Subaru group has had a second forced landing (controlled crash) due to what is believed to be vapor lock. They have identified a couple of problems that I think may cross over to rotary installations and would like someone smarter than myself to comment. First, it appears that at least one of the incidents resulted from the fuel pumps/gas collator/lines getting hot enough to cause vapor lock at the inlet of the pump(s). The a/c was running mogas at the time of the engine stoppage. One solution appears to be to shield and cool the pumps and related plumbing with fresh air. Once this happened, it led to the second shortcoming (I have experienced this with my 20B installation during ground runs). Once the system had vapor downstream of the pump(s), the efi pump couldn't force it past the pressure regulator. This can be the result of either vapor lock or running a tank dry. Their recommendation here is to install a bleed orifice (approx. .020") around the pressure regulator. Now, the Subie guys are contemplating a re-design of their fuel systems. I'm wondering now if I should make any changes to my fuel system (2 wing tanks, 6-port Andair valve, dual EFI pumps mounted on f/w)? Comments would be welcome, especially from those that have been flying for a while. Mark S. At 07:42 AM 5/26/2004 -0500, you wrote: >Tracy, >Do you have any pictures or can you sketch a diagram of your system. How >many high pressure pumps do you have in your system. As I understand it, >you have a facet pump and one or two high pressure efi pumps. What will >you change (if anything) for your RV-8? > >Perry -- How is your sump supplied... gravity? > >Mark > > >At 05:20 AM 5/26/2004 -0700, you wrote: >>Very good to bring this up Mark. I think this is not an issue with the >>fuel pumps inside a sump tank, the arrangement I have. If the sump tank >>runs dry, switching to the other tank refills it. The sump tank must have >>it's own vent line. >> >>Tracy Crook wrote: >>>Good point Mark. This sounds like another good argument for the >>>arrangement that I use. >>> >>>Always draw & return to the same tank. Refill from the other tank when >>>necessary using a low pressure facet fuel pump. This eliminates the >>>need to ever run the tank in use low and risk running dry (unless you >>>are really OUT of gas). No fuel selector needed. Simple >>>plumbing. Only requires a single return port. Eliminates that nervous >>>moment when you wonder "Should I switch tanks now or use that last >>>gallon of fuel in the tank & risk running dry". >>> >>>Tracy >>> >>>>----- Original Message ----- >>>>From: Mark Steitle >>>>Sent: Tuesday, May 25, 2004 4:12 PM >>>>To: Rotary motors in aircraft >>>>Subject: [FlyRotary] Fuel Pump Design >>>> >>>>Fuel system design hasn't come up in quite a while. But since a large >>>>portion of accidents are fuel related, I thought this would be worthy >>>>of discussion. >>>> >>>>I have experienced a failure mode during ground runs on my Lancair ES >>>>with 20B that seems to be a problem with other types of installations >>>>as well. I recently read a first flight report by a professional test >>>>pilot, David Allen, that almost had to set a Lancair ES, N711RG, down >>>>on I-70 due to the inability to restart the engine after running a tank >>>>dry. (See >>>>www.geocities.com/daveandjj for the >>>>full story.) This was a certified fuel-injected engine >>>>installation. Also, the Subaru guys (I have been lurking on the >>>>Eggenfelder Subie site today) had a similar situation, resulting in >>>>some glider time and a dead-stick landing. >>>> >>>>The problem is that after exhausting the fuel in one tank an airlock >>>>forms between the fuel pump(s) and the fuel pressure regulator that the >>>>efi pump cannot overcome due to lack of fuel in the supply line. This >>>>is what I have experienced with my installation on ground runs. I >>>>can't get the efi pumps to re-prime unless I momentarily break a line >>>>loose between the pump outlet and the pressure regulator. As soon as I >>>>do that the pump will re-prime and all is well. >>>> >>>>For the record, I have two of Tracy's efi pumps, with two efi filters, >>>>hooked in parallel. They are mounted low on the fire wall. Upstream >>>>is a gascolator and an Andair 6-port selector valve. Downstream of the >>>>pumps/filters is a map sensing pressure regulator. There is a -6AN >>>>going to the fuel rail, and a -4 return line back to the Andair valve/tank. >>>> >>>>I was curious if anyone else has had this happen and what they did to >>>>resolve the issue. I have come up with two possible solutions. >>>> >>>>1. Tee off the pump output and put an electric solenoid valve in the >>>>line and tee the outlet of the solenoid to the fuel return line, past >>>>the regulator. Push-button switch on panel would activate the >>>>solenoid. If needed, a second or two of activation should relieve the >>>>air-lock and allow the pumps to re-prime. >>>> >>>>2. Install a bleed line around the pressure regulator with a small >>>>metering orifice (.020-.030") that would bleed off any air that might >>>>get trapped. (This appears to be the solution the Subaru group is >>>>focusing on). This would be a full time bypass. This seems to be the >>>>simpler solution. >>>> >>>>3. Install a low pressure, high volume fuel pump in one, or both, of >>>>the wing tanks. Procedure would be to always keep reserve fuel in this tank. >>>> >>>>Any comments from seasoned flyers would be welcomed. >>>> >>>>Mark S. --=====================_69817968==.ALT Content-Type: text/html; charset="us-ascii" Not to beat a dead horse here, but I still have some concerns/problems with the fuel delivery issue.  The Eggenfelder Subaru group has had a second forced landing (controlled crash) due to what is believed to be vapor lock.  They have identified a couple of problems that I think may cross over to rotary installations and would like someone smarter than myself to comment. 

First, it appears that at least one of the incidents resulted from the fuel pumps/gas collator/lines getting hot enough to cause vapor lock at the inlet of the pump(s).  The a/c was running mogas at the time of the engine stoppage.  One solution appears to be to shield and cool the pumps and related plumbing with fresh air. 

Once this happened, it led to the second shortcoming (I have experienced this with my 20B installation during ground runs).  Once the system had vapor downstream of the pump(s), the efi pump couldn't force it past the pressure regulator.  This can be the result of either vapor lock or running a tank dry.  Their recommendation here is to install a bleed orifice (approx. .020") around the pressure regulator. 

Now, the Subie guys are contemplating a re-design of their fuel systems.  I'm wondering now if I should make any changes to my fuel system (2 wing tanks, 6-port Andair valve, dual EFI pumps mounted on f/w)?  Comments would be welcome, especially from those that have been flying for a while.

Mark S.



 At 07:42 AM 5/26/2004 -0500, you wrote:
Tracy,
Do you have any pictures or can you sketch a diagram of your system.  How many high pressure pumps do you have in your system.  As I understand it, you have a facet pump and one or two high pressure efi pumps.  What will you change (if anything) for your RV-8?

Perry -- How is your sump supplied... gravity? 

Mark


At 05:20 AM 5/26/2004 -0700, you wrote:
Very good to bring this up Mark. I think this is not an issue with the fuel pumps inside a sump tank, the arrangement I have. If the sump tank runs dry, switching to the other tank refills it. The sump tank must have it's own vent line.

Tracy Crook wrote:
Good point Mark.  This sounds like another good argument for the arrangement that I use.
 
Always draw & return to the same tank.  Refill from the other tank when necessary using a low pressure facet fuel pump.  This eliminates the need to ever run the tank in use low and risk running dry (unless you are really OUT of gas).  No fuel selector needed.  Simple plumbing.  Only requires a single return port.  Eliminates that nervous moment when you wonder "Should I switch tanks now or use that last gallon of fuel in the tank & risk running dry". 
 
Tracy
 
----- Original Message -----
From: Mark Steitle
Sent: Tuesday, May 25, 2004 4:12 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fuel Pump Design
 
Fuel system design hasn't come up in quite a while.  But since a large portion of accidents are fuel related, I thought this would be worthy of discussion.

I have experienced a failure mode during ground runs on my Lancair ES with 20B that seems to be a problem with other types of installations as well.  I recently read a first flight report by a professional test pilot, David Allen, that almost had to set a Lancair ES, N711RG, down on I-70 due to the inability to restart the engine after running a tank dry.  (See www.geocities.com/daveandjj for the full story.)  This was a certified fuel-injected engine installation.  Also, the Subaru guys (I have been lurking on the Eggenfelder Subie site today) had a similar situation, resulting in some glider time and a dead-stick landing. 

The problem is that after exhausting the fuel in one tank an airlock forms between the fuel pump(s) and the fuel pressure regulator that the efi pump cannot overcome due to lack of fuel in the supply line.  This is what I have experienced with my installation on ground runs.  I can't get the efi pumps to re-prime unless I momentarily break a line loose between the pump outlet and the pressure regulator.  As soon as I do that the pump will re-prime and all is well. 

For the record, I have two of Tracy's efi pumps, with two efi filters, hooked in parallel.  They are mounted low on the fire wall.  Upstream is a gascolator and an Andair 6-port selector valve.  Downstream of the pumps/filters is a map sensing pressure regulator.  There is a -6AN going to the fuel rail, and a -4 return line back to the Andair valve/tank.

I was curious if anyone else has had this happen and what they did to resolve the issue.  I have come up with two possible solutions. 

1.  Tee off the pump output and put an electric solenoid valve in the line and tee the outlet of the solenoid to the fuel return line, past the regulator.  Push-button switch on panel would activate the solenoid.  If needed, a second or two of activation should relieve the air-lock and allow the pumps to re-prime.

2.  Install a bleed line around the pressure regulator with a small metering orifice (.020-.030") that would bleed off any air that might get trapped.  (This appears to be the solution the Subaru group is focusing on).  This would be a full time bypass.  This seems to be the simpler solution.

3.  Install a low pressure, high volume fuel pump in one, or both, of the wing tanks.  Procedure would be to always keep reserve fuel in this tank. 

Any comments from seasoned flyers would be welcomed.

Mark S.
--=====================_69817968==.ALT--