---------------------------------------------------------- Zenith-List Digest Archive --- Total Messages Posted Sun 12/07/03: 9 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 10:58 AM - CH 701/912S Fuel System Questions (Walt Cannon) 2. 11:29 AM - Final inspection scheduled for Dec 17th (Rick Pitcher) 3. 03:33 PM - Re: Final inspection scheduled for Dec 17th (Al Young) 4. 04:53 PM - Re: CH 701/912S Fuel System Questions (Thomas F Marson) 5. 06:29 PM - Re: CH 701/912S Fuel System Questions (Phil & Michele Miller) 6. 07:29 PM - Re: CH 701/912S Fuel System Questions (Thomas F Marson) 7. 08:05 PM - Re: CH 701/912S Fuel System Questions (Rico Voss) 8. 08:14 PM - Re: CH 701/912S Fuel System Questions (Thomas F Marson) 9. 09:56 PM - Re: CH 701/912S Fuel System Questions (Dave Alberti) ________________________________ Message 1 _____________________________________ Time: 10:58:53 AM PST US From: "Walt Cannon" Subject: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Walt Cannon" All, I have recently contacted some of you directly with questions on this topic...the responses just made me want to open the issue up to wider input. I am nearing the completion of my 701/912S (without the fuselage tank) and still have some degree of unease about the redundancy and failure mode of the fuel supply system. I contacted Zenith to understand their philosophy and basically got the following: They do not have an auxiliary electric boost pump shown on their plans or installed on their demonstrator airplane. They did do a fuel flow test from wing tanks to the engine and were convinced that the flow was enough, but apparently didn't actually verify that the engine would run given the head pressure from the tanks. When I raise the nose to a climb attitude, it looks like the gravity feed head is maybe only 12 inches or so. They didn't seem to know if the 912 carbs required a certain feed pressure to operate. So here are my questions for this group: Have you run fuel flow tests from the gravity feed wing tanks to the engine in a climb attitude and was their enough flow? Has anybody actually tried to test the gravity flow by bypassing the engine driven pump and going straight to the carbs? Would the engine operate that way if the mechanical pump failed? Would it operate in a climb attitude? Does anyone have any information about failure modes on the mechanical pumps? When they do fail, do they fail open so a boost pump in series could push fuel through, or does the pump need to be in parallel? I would be glad to hear of specific solutions that people may have come up with. I understand from anecdotal information that I have received that the engine driven pumps are quite reliable. Never the less, a backup system seems to be fairly standard in Type Certified airplanes that won't run on strictly a gravity feed system. Thanks in advance, Walt Cannon Seattle, WA ________________________________ Message 2 _____________________________________ Time: 11:29:41 AM PST US From: Rick Pitcher Subject: Zenith-List: Final inspection scheduled for Dec 17th --> Zenith-List message posted by: Rick Pitcher Well, I finished building the Zodiac. It's sitting out behind the barn with the wings on and the gas tanks filled. Weighed in at 650 pounds empty... not much more than my old Quicksilver trainer :) The Jabiru starts so easy and runs so smooth... SWEET!!! Tomorrow it goes out to my hangar space at WJF for reassembly and final inspection. The EAA guys are slated for Saturday, Dec 13th, and the DAR is gonna have a look at it too. I'll have 4 days to work back the squawks and take care of any stray paperwork, then the DAR comes back Wednesday look it over one last time and sign the airwothiness certificate. It'll be cool if I can get Decemeber 17th as the date of birth on that Centennial Dataplate http://www.eaa.org/homebuilders/centennial.asp Fingers Crossed, Rick P. ________________________________ Message 3 _____________________________________ Time: 03:33:01 PM PST US From: "Al Young" Subject: Re: Zenith-List: Final inspection scheduled for Dec 17th --> Zenith-List message posted by: "Al Young" Congrats Rick- Hope you make it on the 17th, but hope also that you have a safe first flight, no matter if it doesn't come til Feb 17th. Get ready, get confident, and get going! Best of luck! Al Young 601XL (60% done) ________________________________ Message 4 _____________________________________ Time: 04:53:30 PM PST US From: "Thomas F Marson" Subject: Re: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Thomas F Marson" Walt, I can see your nervous about that fuel situation. Here is what I did on a Dakota Hawk, High wing with a Continental engine and gravity flow fuel feeding a carb. FUEL FLOW TESTS: I parked the plane in an attitude of 22 degrees nose up to measure fuel flow by gravity with only 5 gallons of fuel in the cowl tank. Cowl has head with 5 gallons of fuel and 22degrees up (plane stalls at 16 degrees) of only 10 inches. disconnect fuel line at carb and measured fuel flow of more than 150 percent of full throttle demand. Actual flow was rate was 14 gallons perhour. I have all 3/8 aluminum aero fuel line and AN 6 fittings. This passed normal requirements of 150 percent of maximum engine demand. Next to be sure of what would happen in real world. I parked the plane in the taildown position and had the tail tied to my tractor and put only 2 gallons of fuel in the fuel tank and had the boost pumps off. (we will talk about boost pumps later). With the boost pumps off I ran the engine at full throttle for a timed two minutes. It ran fine and developed full power static. I then shut the engine off and let it heat soak for 10 minutes. Next I restarted it and again ran it full throttle for 90 seconds, again boost pumps off. In both cases the engine ran flawlessly. This proved it would run with only 2 gallons of fuel in a steep climb, this is very low head of maybe 12 inches. It was 87 octane auto fuel, and a summer day of about 80 degrees. This told me that in the worst case of a missed approach and a go around in a steep angle of climb with very low fuel the engine would function normally. Now about boost pumps: As you probably have heard the majority of forced landings in homebuilt aircraft are from faults in the fuel delivery system. Auto Fuel vaporizes more easily than 100LL and has a bad history of vapor lock in aircraft applications but av gas can do it too. When it gets hot as in the engine compartment especially with a hot engine and an engine mounted fuel pump at low flow such as idling on a hot day it may vaporize and the pump will not pump vapor. . One of he systems used to reduce this situation is to plumb in a by pass system so unused fuel (that not needed by the engine at the moment) is piped back to the fuel tank. This will insure a continuous flow of cooler fuel in the lines and pump so in effect the hot pump is partially cooled by a inflow cool fuel. . That is the system recommended for RV aircraft where fuel is pumped up from the wing tanks. (low wing plane). In the RVs there is also a 12 volt boost pump installed at the root of the wing tank. The main source of pumping here is the engine mounted pump ( the one subject to getting hot). Even here with the boost pump in the wing root it is recommended to make the bypass system discussed above. NOW BACK TO MY DAKOTA HAWK WITH THE GRAVITY FEED SYSTEM: For a cost of 32 dollars each I purchase 2 Facet 12 volt pumps and installed them in parallel with each other with their output combined and then on to the gascolater and then to the engine. These pumps each have a built in check valve so fuel can only flow in one direction. Why two in parallel? I tested to find that a single pump would pass enough fuel by gravity (not operating) to run my engine at full power. Remember I have these fuel pumps installed in a gravity flow system). I installed two so that in the rare case where the internal check valve might stick closed and block flow the remaining pump would have to also have the check valve fail closed at the same time for my engine not to operate. I also installed individual panel switches and a full pressure gage so I can see when they are pumping. WHY ALL THIS EXTRA STUFF IN A GRAVITY FEED SYSTEM, CUBS AND CHAMPS MOST CESSNAS DONT HAVE THIS?? Two reasons: These planes were never designed to use auto fuel--------- though many do use it with an STC. And the nature of auto fuel is such that vapor lock is more likely than aviation gasoline. Secondly they all have a greater head (distance of fuel above the carb than my plane). What did all this cost? Not counting the head scratching time and testing time it added about 6 lbs and 150 dollars of cost, pumps, fuel pressure gage and circuit breakers and just a little more fuel tubing and fittings. I added a lot of redundancy to my planes fuel system. Was it worth it-- maybe not--------- if I never need it. But it may some day be worth my plane or maybe my life. The only real drawback was the added weight. The redundancy I believe is more than adequate, as neither pump needs to operate for my engine to work perfectly and both electric pumps must have their check valves stick and stick closed at the same time for fuel starvation to occur. These are very common pumps (you can buy them in NAPA or other auto parts store. ) have no history of sticking check valves. In 7 years of operation neither of my have failed to operate and of course never stick closed. I switch the pumps on for take off and landings. Oh I failed to mention, during taxi testing with very low levels of fuel in the tank (before I installed the pumps) on a moderately rough field the low levels of fuel unported the tank occasionally and a little air would enter the fuel line to the engine. It would quit. Then it would take 10 minutes before I could get engine to start again. This was in warm summer and the engine compartment was warm too. It was auto fuel. I was never completely sure it was only unporting or if it was vapor lock. In a sense it may have been one in the same. A bubble of air in a gravity system with very little head above it and the engine would not start again ten minutes. This repeated on 3 or four different days. I did note that later when I had more fuel in the tank it never happened. I continued more taxi testing on the same field several more days before first flight. Bottom line of all of this is that I bought redundancy and confidence with the dual boost pumps. When I switch them on and see the gage indicate 6 psi I have assurance of pressure at the carb. Tom Marson ----- Original Message ----- From: "Walt Cannon" Subject: Zenith-List: CH 701/912S Fuel System Questions > --> Zenith-List message posted by: "Walt Cannon" > > All, > > I have recently contacted some of you directly with questions on this > topic...the responses just made me want to open the issue up to wider input. > I am nearing the completion of my 701/912S (without the fuselage tank) and > still have some degree of unease about the redundancy and failure mode of > the fuel supply system. I contacted Zenith to understand their philosophy > and basically got the following: > > They do not have an auxiliary electric boost pump shown on their plans or > installed on their demonstrator airplane. > They did do a fuel flow test from wing tanks to the engine and were > convinced that the flow was enough, but apparently didn't actually verify > that the engine would run given the head pressure from the tanks. When I > raise the nose to a climb attitude, it looks like the gravity feed head is > maybe only 12 inches or so. > They didn't seem to know if the 912 carbs required a certain feed pressure > to operate. > > So here are my questions for this group: > > Have you run fuel flow tests from the gravity feed wing tanks to the engine > in a climb attitude and was their enough flow? > Has anybody actually tried to test the gravity flow by bypassing the engine > driven pump and going straight to the carbs? > Would the engine operate that way if the mechanical pump failed? Would it > operate in a climb attitude? > Does anyone have any information about failure modes on the mechanical > pumps? When they do fail, do they fail open so a boost pump in series could > push fuel through, or does the pump need to be in parallel? > I would be glad to hear of specific solutions that people may have come up > with. I understand from anecdotal information that I have received that the > engine driven pumps are quite reliable. Never the less, a backup system > seems to be fairly standard in Type Certified airplanes that won't run on > strictly a gravity feed system. > > Thanks in advance, > > Walt Cannon > Seattle, WA > > ________________________________ Message 5 _____________________________________ Time: 06:29:08 PM PST US From: "Phil & Michele Miller" Subject: RE: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Phil & Michele Miller" Walt, This is all good advice from Tom. I have a word of caution and a couple of comments: Take care when selecting your boost pump. The Rotax manual recommends a normal operating fuel pressure range of 2.2 to 4.4psi and a maximum of 5.8psi. Any more and you run the risk of flooding and engine stoppage due to fuel pushing past the carby float valves. Tom is right in saying that auto gas is more likely to vapour lock than avgas. Vapour locking will also occur sooner if the pressure is lowered as is the case when the engine pump sucks fuel up from a low wing fuel tank. Less likely with a high wing tank due to the pressure head from the tank. Heat protection sleeving for under-cowl fuel lines is a wise precaution. The bottom of the 701 wing tank is about 14 inches above the carbies in level flight. At 40 degrees nose up (Rotax maximum recommended) the fuel head reduces to about 10.6 inches. At 10.6 inches the unassisted pressure at the carbies is roughly 2.7psi which is a still within the normal operating pressure range. In level flight the unassisted fuel pressure will only be about 3.6psi. Note that these numbers are only approximate. You should do your own measurements and calculations. Failure modes for the Rotax fuel pump are stated in the manual as leaking valves or leaking diaphragm. A leaking diaphragm will cause fuel to leak out of the fuel pump housing at the vent hole and into the engine bay. This is not good and a boost pump will cause more fuel to be expelled. Leaking valves will cause partial or complete loss of pump pressure. I don't know how much pressure is required to bypass an inactive pump (I can see another test coming up on this one). Cheers, Phil Miller New Zealand 701/912S >>I can see your nervous about that fuel situation. Here is what I did on a Dakota Hawk, High wing with a Continental engine and gravity flow fuel feeding a carb. >>For a cost of 32 dollars each I purchase 2 Facet 12 volt pumps and installed them in parallel with each other with their output combined and then on to the gascolater and then to the engine. >>When I switch them on and see the gage indicate 6 psi I have assurance of pressure at the carb. Tom Marson ----- Original Message ----- From: "Walt Cannon" Subject: Zenith-List: CH 701/912S Fuel System Questions > --> Zenith-List message posted by: "Walt Cannon" > --> > > All, > > I have recently contacted some of you directly with questions on this > topic...the responses just made me want to open the issue up to wider input. > I am nearing the completion of my 701/912S (without the fuselage tank) > and still have some degree of unease about the redundancy and failure > mode of the fuel supply system. I contacted Zenith to understand their > philosophy and basically got the following: > > They do not have an auxiliary electric boost pump shown on their plans > or installed on their demonstrator airplane. They did do a fuel flow > test from wing tanks to the engine and were convinced that the flow > was enough, but apparently didn't actually verify that the engine > would run given the head pressure from the tanks. When I raise the > nose to a climb attitude, it looks like the gravity feed head is maybe > only 12 inches or so. They didn't seem to know if the 912 carbs > required a certain feed pressure to operate. > > So here are my questions for this group: > > Have you run fuel flow tests from the gravity feed wing tanks to the engine > in a climb attitude and was their enough flow? > Has anybody actually tried to test the gravity flow by bypassing the engine > driven pump and going straight to the carbs? > Would the engine operate that way if the mechanical pump failed? Would > it operate in a climb attitude? Does anyone have any information about > failure modes on the mechanical pumps? When they do fail, do they fail > open so a boost pump in series could > push fuel through, or does the pump need to be in parallel? > I would be glad to hear of specific solutions that people may have > come up with. I understand from anecdotal information that I have > received that the > engine driven pumps are quite reliable. Never the less, a backup > system seems to be fairly standard in Type Certified airplanes that > won't run on strictly a gravity feed system. > > Thanks in advance, > > Walt Cannon > Seattle, WA > > = == direct advertising on the Matronics Forums. == == == ________________________________ Message 6 _____________________________________ Time: 07:29:02 PM PST US From: "Thomas F Marson" Subject: Re: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Thomas F Marson" Hi Phil, thanks for the back up. I agree with most of your points except fuel pressure VS/head. I seem to remember 27 inches of water colum is 1 psi since gasoline is lighte than water 27 inches of water would be even less than 1 psi. Where am I wrong on this? Tom ----- Original Message ----- From: "Phil & Michele Miller" Subject: RE: Zenith-List: CH 701/912S Fuel System Questions > --> Zenith-List message posted by: "Phil & Michele Miller" > > Walt, > > This is all good advice from Tom. I have a word of caution and a couple > of comments: > > Take care when selecting your boost pump. The Rotax manual recommends a > normal operating fuel pressure range of 2.2 to 4.4psi and a maximum of > 5.8psi. Any more and you run the risk of flooding and engine stoppage > due to fuel pushing past the carby float valves. > > Tom is right in saying that auto gas is more likely to vapour lock than > avgas. Vapour locking will also occur sooner if the pressure is lowered > as is the case when the engine pump sucks fuel up from a low wing fuel > tank. Less likely with a high wing tank due to the pressure head from > the tank. Heat protection sleeving for under-cowl fuel lines is a wise > precaution. > > The bottom of the 701 wing tank is about 14 inches above the carbies in > level flight. At 40 degrees nose up (Rotax maximum recommended) the fuel > head reduces to about 10.6 inches. At 10.6 inches the unassisted > pressure at the carbies is roughly 2.7psi which is a still within the > normal operating pressure range. In level flight the unassisted fuel > pressure will only be about 3.6psi. Note that these numbers are only > approximate. You should do your own measurements and calculations. > > Failure modes for the Rotax fuel pump are stated in the manual as > leaking valves or leaking diaphragm. A leaking diaphragm will cause fuel > to leak out of the fuel pump housing at the vent hole and into the > engine bay. This is not good and a boost pump will cause more fuel to be > expelled. Leaking valves will cause partial or complete loss of pump > pressure. I don't know how much pressure is required to bypass an > inactive pump (I can see another test coming up on this one). > > Cheers, > Phil Miller > New Zealand > 701/912S > > >>I can see your nervous about that fuel situation. Here is what I did > on a Dakota Hawk, High wing with a Continental engine and gravity flow > fuel feeding a carb. > > >>For a cost of 32 dollars each I purchase 2 Facet 12 volt pumps and > installed them in parallel with each other with their output combined > and then on to the gascolater and then to the engine. > > >>When I switch them on and see the gage indicate 6 psi I have assurance > of pressure at the carb. > > Tom Marson > > > ----- Original Message ----- > From: "Walt Cannon" > To: > Subject: Zenith-List: CH 701/912S Fuel System Questions > > > > --> Zenith-List message posted by: "Walt Cannon" > > --> > > > > All, > > > > I have recently contacted some of you directly with questions on this > > topic...the responses just made me want to open the issue up to wider > input. > > I am nearing the completion of my 701/912S (without the fuselage tank) > > > and still have some degree of unease about the redundancy and failure > > mode of the fuel supply system. I contacted Zenith to understand their > > > philosophy and basically got the following: > > > > They do not have an auxiliary electric boost pump shown on their plans > > > or installed on their demonstrator airplane. They did do a fuel flow > > test from wing tanks to the engine and were convinced that the flow > > was enough, but apparently didn't actually verify that the engine > > would run given the head pressure from the tanks. When I raise the > > nose to a climb attitude, it looks like the gravity feed head is maybe > > > only 12 inches or so. They didn't seem to know if the 912 carbs > > required a certain feed pressure to operate. > > > > So here are my questions for this group: > > > > Have you run fuel flow tests from the gravity feed wing tanks to the > engine > > in a climb attitude and was their enough flow? > > Has anybody actually tried to test the gravity flow by bypassing the > engine > > driven pump and going straight to the carbs? > > Would the engine operate that way if the mechanical pump failed? Would > > > it operate in a climb attitude? Does anyone have any information about > > > failure modes on the mechanical pumps? When they do fail, do they fail > > > open so a boost pump in series > could > > push fuel through, or does the pump need to be in parallel? > > I would be glad to hear of specific solutions that people may have > > come up with. I understand from anecdotal information that I have > > received that > the > > engine driven pumps are quite reliable. Never the less, a backup > > system seems to be fairly standard in Type Certified airplanes that > > won't run on strictly a gravity feed system. > > > > Thanks in advance, > > > > Walt Cannon > > Seattle, WA > > > > > > > > == > direct advertising on the Matronics Forums. > == > == > == > > ________________________________ Message 7 _____________________________________ Time: 08:05:20 PM PST US From: Rico Voss Subject: Re: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: Rico Voss > I seem to remember 27 inches of water colum is 1 psi > since gasoline is > lighte than water 27 inches of water would be even > less than 1 psi. Where > am I wrong on this? Tom Good info, Phil, but I think Tom is right. Divers use the fact that one atmosphere (14.7 psi) occurs at water depth of 33 feet... or roughly 1/2 psi per foot of water. Would be interesting to see whether the 1/2 psi of head pressure would be enough to keep the engine running. Rico, 601XL, fuse, in KC do not archive __________________________________ http://companion.yahoo.com/ ________________________________ Message 8 _____________________________________ Time: 08:14:19 PM PST US From: "Thomas F Marson" Subject: Re: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Thomas F Marson" Fuel pressure /vs/ head of gasoline. I went to Machineries Handbook, twentieth edition. Page 2316 "one foot head of water will be 0.43 psi." Gasoline is only 72 percent the weight of water so that would mean, 12 inches head of gasoline will develop 0.309 psi. What I have experienced in the past is that carburetors that are stated to need X amount of minimum pressure, will operate with much less at least for Stromberg and Marvel Schebler. But the facts seem to be that it will take about a little over 36 inches to develop 1 psi. Of course if you have an airpressure tube putting blast air into your fuel tank that will raise the pressure of what ever column you have by the amount the tank is pressurized. You can buy these Facet pumps in several pressure ranges if you desire. I think as low as 2 psi and as high as 8 or more psi. ----- Original Message ----- From: "Phil & Michele Miller" e care when selecting your boost pump. The Rotax manual recommends a > normal operating fuel pressure range of 2.2 to 4.4psi and a maximum of > 5.8psi. Any more and you run the risk of flooding and engine stoppage > due to fuel pushing past the carby float valves. > > ________________________________ Message 9 _____________________________________ Time: 09:56:06 PM PST US From: "Dave Alberti" Subject: RE: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Dave Alberti" A system that requires no more than 3 psi (for example) will be unable to keep the proper fuel level in the float bowl at pressures above 3 psi. It will over fill and essentially flood because the float system will be overwhelmed. Although you may not notice the condition at wide open throttle except for excessive fuel consumption. What you need is fuel flow; excess capacity. This is governed by the smallest orifice in the lines from the tank to the carbs. Example...3/8" lines to the fuel pump, with a 1/4" inside diameter fitting at the fuel pump. Calculate or actually test the fuel flow at that small fitting and make sure you get the 150% flow in gal or liters per hour above the max consumption rate for the engine. A fuel pump will assist this and increase the flow rate but only if gravity can deliver enough fuel to the inlet side of the pump. What a static fuel pressure reading will give you is an indication of the systems integrity (leaks etc.) post fuel pump. If you have a system that is totally based on gravity feed to the carb (no pumps at all) fuel pressure is useless, because as indicated in earlier posts, you need multiple feet of head tube length to get a practical measurement of pressure. A sealed fuel tank system can use dynamic ram air pressure (like pitot) to build additional pressure in the system, but this is airspeed and air density dependant. And as a follow up to the electric pump as a backup to the Rotax mechanical pump, yes you can pump through the mechanical pump. I do it on every initial engine start to charge the system with the meager 3 psi. If the mechanical pump dies so will your engine for sure. Don't count on gravity pushing the fuel through the dead pump. My backup electric pump is located below the tank level but above the gascolator on the gascolator output side. Dave -----Original Message----- From: owner-zenith-list-server@matronics.com [mailto:owner-zenith-list-server@matronics.com]On Behalf Of Thomas F Marson Subject: Re: Zenith-List: CH 701/912S Fuel System Questions --> Zenith-List message posted by: "Thomas F Marson" Fuel pressure /vs/ head of gasoline. I went to Machineries Handbook, twentieth edition. Page 2316 "one foot head of water will be 0.43 psi." Gasoline is only 72 percent the weight of water so that would mean, 12 inches head of gasoline will develop 0.309 psi. What I have experienced in the past is that carburetors that are stated to need X amount of minimum pressure, will operate with much less at least for Stromberg and Marvel Schebler. But the facts seem to be that it will take about a little over 36 inches to develop 1 psi. Of course if you have an airpressure tube putting blast air into your fuel tank that will raise the pressure of what ever column you have by the amount the tank is pressurized.