What you have in the Lake fuel system is standard in just about every low wing aircraft with a carburated engine, and also SOP on many Cessnas that have had larger engines installed without upgrading the supporting fuel system. The engine runs using a mechanical fuel pump for feed and has a standby electric fuel pump. Electric pump is turned on for take off and landing, and should be on any time you are low enough to preclude restoring fuel pressure and restarting should the mechanical pump fail and you empty the carb. Additionally, these are 100% duty cycle pumps, so if you feel safer with it on, it can be operated all the time. The idea, of course, is to ensure you always have fuel pressure during any critical phase of operation should the mechanical pump fail. That ensures a mechanical pump failure only happens either while on the ground or when you have sufficient altitude to deal with restoring pressure and restarting the engine. Issues with a draggy starter or failing sta rter bendix are another program and should be repaired. The electric pump should not be making enough fuel pressure to cause the carb to overflow and flood. If it does, that's another issue that should be repaired.
Before someone quotes me and says you can't run an electric pump all the time, this is in reference to carburated engines. Most fuel injected engines have a high pressure electric pump used for priming and only in case of mechanical pump failure. And yet others have a high/low output electric pump with the high output used for priming and emergency use and the low output used much like the electric pump with a carburetor. Personally, I like gravity feed fuel systems. I used a 9 gal header tank in my KR and typically refilled it from the wings on 30 minute intervals. That way if I had an electrical failure or for some reason was unable to pump fuel, it left me with 45 minutes to an hour to find an airport. Additionally, with that configuration, I had almost no CG shift during flight as I was always transferring fuel from the wing tanks forward to the header tank. If I took off with all the tanks full, and landed with them all empty, my CG was right where it started with them full. However, per the talk I did at the KR Gathering a few years ago, gravity feed systems aren't as simple as one may think. They can and do fail due to water or fuel trapped in a low spot in a vent line. I've seen it happen several times on different types of aircraft. There's nothing wrong with a well designed pumped fuel system. I'm not a big fan of building a system that requires a standby battery to stay in the air, but a lot of people are building that way. If flight is going to be dependent on electrical power, I'd rather use a standby alternator than a standby battery. For the same weight, it makes an emergency into a mere inconvenience. I'm not calling anyone's baby ugly here. Just sharing my thoughts of some 45 years of doing this stuff. -Jeff Scott Arkansas Ozarks > Sent: Friday, November 19, 2021 at 11:26 PM > From: "John Gotschall" <johngotsch...@gmail.com> > To: "KRnet" <krnet@list.krnet.org> > Subject: KR>Re: Header tank > > The plane in question is a Lake LA-4 amphibian. The engine mounted on a > pylon some three or 4 feet above the fuel tank. N1120L > > The fuel pump is engine driven. 4 ft lift. 100ll and it's ability to stay > liquid and not devolve in to vapor in a vacuum in an application such as > this at 13k ft. No car gas. > > I think I noted no header tank, don't recall saying single pump. However > if you follow the instructions you will be running a single pump. There is > an electric additional pump (backup?) for use only during approaches and > takeoffs. Might be useful in an emergency. > > So if you follow the instructions, in cruise your first sign of trouble is > a flameout. > > Unless your instrument scan habits are so fast you caught the 3 second > interval between pressure collapse and flameout. I cannot devote that kind > of time to checking a fuel pressure gauge while maintaining my other pilot > duties in flight. > > Gonna hope that while after flameout and while dropping like a lead balloon > (amphibs are after all flying bricks) that backup pump does something other > than hopelessly flooding the engine, and oh, btw how's that starter doing > right now?. Engine is hot, primer, no primer, wait for the carb to refill? > This plane has no primer! oops too much with the accellerator pump and now > it is flooded...... damn the sticky starter bendix! Try it again and > again whilst setting up for a landing between those cars on I-5. Well the > battery will be exhausted by the end so might not work to ignite the post > impact fire. Dang! Was I supposed to do something with prop pitch during > a flame out? No instructor said anything about that! Hey now's my chance > to find out! maybe I can "compression start" this thing.. where's the > clutch? > > ugh. > > > Better no flameout at all me thinks. Much preferable to have a half hour > flameout heads up by a header tank that refuses to top off. Better > scenario: > > Ho Hum, (yawn).. dang it won't top off. I guess I hafta land soon.. > Boring.... copilot is still asleep.. That's ok... I hope I can stay awake > that long. (yawn)** hmm nearby fields with fuel.?.... > > Seems like a better set of problems to me. > > jg > ________________________________ -Please see LIST RULES and KRnet info at http://www.krnet.org/info.html -Change list delivery options at https://list.krnet.org/list/krnet.list.krnet.org/ Affinity List Info Board -Search recent KRnet Archives at https://list.krnet.org/empathy/list/krnet.list.krnet.org/ -Search John Bouyea's decades of archive at https://www.mail-archive.com/krnet@list.krnet.org/
