---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 02/26/26: 5 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:11 AM - Re: Fuel System Manager (wsimpso1) 2. 09:10 AM - Re: Fuel System Manager (user9253) 3. 11:08 AM - Re: Fuel System Manager (911pete) 4. 12:18 PM - Re: Fuel System Manager (Ceengland) 5. 04:46 PM - Re: Fuel System Manager (Eric Page) ________________________________ Message 1 _____________________________________ Time: 07:11:35 AM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "wsimpso1" Sorry I did not see this sooner. No lack of ambition in this project. Operational risk in this bird is higher than I am comfortable with, but the OP and I are different folks... Before we get into details, I have run through many schemes for a similar system (and only running fuel for a 200 hp engine) so I appreciate the issues you face. We had quite a conversation on the topic here: https://homebuiltairplanes.com/threads/transfer-pumps-and-fuel-system-configuration.30820/ There were other discussions of what makes sense and how to manage failures that will happen. Failure Modes and Effects Analysis is a good idea for review of each design option. Perhaps it is in the background and we have just not seen it here. I emphasize that every failure mode of every element of the system should be tracked down, then consequences (effects) at system mode must be chased through. To really do it right, you will need severity of consequences and some idea of the frequency of each failure mode. This gives you a look at the relative riskiness of each set of options, and usually will drive the designer towards managing failure modes. Now to details shown in the thread. The shown systems are all complicated, and complicated makes for more failure modes all competing to see which fails first. A drive for less failures will drive simpler systems. That being said, I love jet pumps. As long as your engine pump runs, you have transfer pump power. You must then have plumbing runs to each tank and those runs do have their failure modes and frequencies too... Solenoid valves take power. If they take power to shut off, that means loss of power to the valve OR stuck open will immediately attempt to transfer all fuel in that wing to the main tank, likely with much of it going out the main vent. If you lose ship's power entirely, both wing tanks will dump to the main, with most of it likely going out the vent. That may quickly leave you with just the main tank, so a runway had better be well within reach. Your solenoid valves are 3000 psi lines with 1/2" pipe connections, but the jet pumps will provide far far lower pressures to shove fuel to the main. Your flows for this thirsty engine may be inadequate with 1/2" plumbing and a jet pump. Total kinetic energy of the output is unavoidably less than the kinetic energy of the jet. Know what your jet pump output pressure vs flow curve look like, then figure out how much head loss you will have between wing and main tank to make sure you can flow roughly 2x engine burn rate to the main tank. I suggest that having more than one power source for running all this stuff is wise as you are becoming at least partial electrically dependent just to run the engine. I also suggest that you may want to have more than one independent way to power your fuel selectors. One of the fundamental teachings is that removing a failure mode completely is often way better than counter measures. Another fundamental teaching is the huge value in selective redundancy. More than one way to do something is really smart if you NEED that something done... Perhaps a manual valve would be way smarter? In my system, I considered jet pumps and all sorts of plumbing options. Instead I have two simple check valve equipped transfer pumps in parallel and a duplex manual valve to select tanks. The main tank vents to the source tank through the manual valve for no overboard fuel flow and no need for switching pumps on and off automatically. At max cruise, my main tank is over 100 miles of fuel, at best range I have more like 160 miles to get on the ground. That may not be good for a trip to Hawaii, but is way comfortable in the lower 48. I do have high and low switches in my main tank. They only run alarms, and I selected solid state industrial types - no float switches. When fuel drops below the high limit, I am warned to switch pumps OR switch tanks OR both. When the low level level light comes on, I am warned that I am about to land on something close by. By the time I got done doing my FMEA (several designs, and then updates meant more passes) I found that good switchology with independent wiring/powering and redundant elements was the way to keeping powered things powered. So, I have two always hot buses (each circuit fused) and two loads and two double pole double throw switches for each major function. S700-2-10 from B&C switches. Where I need power to get a function, I have four different ways to power each needed function. Since you need the no-power function to also be available, you would be wise to noodle on that. Perhaps a pullable breaker for each valve? All of this avoids logic circuits, diodes, AND/NAND gates, and Arduinos. The only extra wiring and connectors are the redundant circuits. Yeah, this long experienced ME is leaning away from complicated electricals and towards Bob Nuckolls' fundamentals of making it require very little in the way of intervention on any single failure while aloft. Fix it on the ground. Billski Read this topic online here: http://forums.matronics.com/viewtopic.php?p=516891#516891 ________________________________ Message 2 _____________________________________ Time: 09:10:03 AM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "user9253" Billski, Thanks for your input. I like your idea of venting the main tank back to the wing tanks. And I agree that Failure Modes and Effects Analysis is a good idea. It is my understanding that the original designer of the Viper Jet also designed the fuel system, not the current builder, Pete. Originally the main fuel tank level was controlled by a computer. Since that computer is no longer available, Pete asked for my assistance. I substituted a relay for the computer. If that relay fails, no big deal, the main tank level can be controlled manually with the toggle switches. As for float switches, there are none. I drew float switches on my schematic to make it easy to understand. But the level switches are actually industrial solid state switches. Pete posted the switch manufacturer's description in a previous post. I agree that the operational risk in this bird is higher than I am comfortable with. However, Pete flies Jets for a living. Each of the 3 fuel tanks also has independent capacitor type fuel level sensors. Assuming that those sensors are connected to an EFIS, the EFIS can be configured to alarm whenever a fuel tank level is either too high or too low. If something goes wrong with the fuel transfer system, the main tank holds more than 30 minutes of fuel. Hopefully that is enough to fly to an airport with a long runway. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=516892#516892 ________________________________ Message 3 _____________________________________ Time: 11:08:35 AM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "911pete" Billski As Joe said Im a builder, not a designer. Even though there arent many of these planes flying there are some and the fuel system has been proven to work with respect to the ability of the jet pump having enough capacity to keep the main tank full I read through your thread on HBA. As someone else noted in your thread this isnt really a fuel system but a transfer system meant to keep the main tank full. In the event of total electrical failure all three valves open and supply the main tank. Yes there will be fuel venting overboard. If it happens with anything in the wing tanks you will get a full main tank plus some of the wing tank fuel until they are dry. Should give you no less than 30 minutes until fuel exhaustion. Thats 30 minutes at 300+ knots. You mention the 3000psi solenoid valve. The original design used a 150 psi max valve from Dukes aerospace. They are no longer in business and Im having a hard time trying to contact the follow on company. The valve Im contemplating is good up to 3000psi, but there will be nowhere near that in actual use As far as pullable breakers to remove power I think the panel mounted switches do that As Joe and Eric have designed this it seems very simple, one relay and two switches. The level sensors also have no moving parts Pete Read this topic online here: http://forums.matronics.com/viewtopic.php?p=516893#516893 ________________________________ Message 4 _____________________________________ Time: 12:18:35 PM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "Ceengland" Hi, Late to the party (gmail has been sending Matronics stuff to spam), but one or two thoughts. The plumbing diagram shows L & R plumbed in parallel to the jet pump. Do be aware that many 2-tank systems, if (when) fuel feeds unevenly and one tank empties, will start to suck air instead of fuel. If there isn't significant source pressure from the remaining fuel, the pump will find it easier to pump air than fuel. This usually isn't an issue with high wing a/c and a low-mounted join/pump, but is pretty common with low wing a/c. Many low wing a/c prohibit operating with the tanks in 'both' for this reason. Might not be an issue with that particular airframe, but I'd want to know that it's been proven by emptying a tank in flight (and the other tank, on a different flight) to verify, before committing to the design. Just because it's flown doesn't mean that the empty tank issue has been thoroughly tested. The main tank vent issue has already been mentioned. There are certified a/c flying with systems like the one described, and some of those systems have caused crashes when the loss of fuel wasn't detected. There are venting plans that can avoid pumping fuel overboard (and, for that matter, possibly eliminate most of the switchology). Bilsky already mentioned FMEA. A stuck solenoid valve, or a stuck switch (unless there's access to that switch's power source) could cause loss of all fuel in the affected tank. Just a couple of FWIW thoughts... -------- Charlie Read this topic online here: http://forums.matronics.com/viewtopic.php?p=516894#516894 ________________________________ Message 5 _____________________________________ Time: 04:46:04 PM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "Eric Page" I haven't gotten back to working on this but I wanted to check progress here. It looks like Joe has the basic switching schematic pretty much licked. Except... As drawn, the HPFS is only under manual control by the switches, and the relay can't control it in AUTO mode. The HPFS will be open any time either switch is in any position other than OFF, even if both LPFS are closed by AUTO mode. Maybe that's not a problem. Pete, what say you? A relay with 3 or more normally open poles may be able to control the HPFS in parallel with each LPFS, but I haven't thought through the switchology... I have the bones of a low fuel light delay and flasher circuit, so I'll press ahead with that part. Pete, do you want an output to trigger an EFIS alarm or do your other fuel level senders have that covered? If so, does your planned EFIS system accept 24V inputs for alarm triggers, or would 12V be preferred? 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