Ok, the takeaway for this thread at least is to stop being a pussy and learn to love the fuel selector valve. It's not a big deal to switch in flight, especially if you want to fly Beavers

I think you're on the right track, Z.

I have a "both" and found myself switching tanks L and R manually in order to better control the fuel balance. I'm not sure the exact time between switches, I just watched the levels and kept them about even. Maybe 30 min per tank?

I do like the idea of a duplex valve, so you're not going to run into overfilling your L or R tank while feeding from the opposite in a full-fuel situation. Where you forgot to swap tanks. For a while. Yeah... that might be a longshot, but it might happen?

I'm going to use a duplex valve and don't plan to run on both. Luscombe didn't have both and I was one of those guys that ran on left tank for 1 hour, switch to right till dry then back to left. Don't know how that will work with FI but I plan to find out.

Did all my learnin in a Cherokee (L/R tank only). When one wing starts to hang lower for no "apparent" reason, it means you need to swith to the high wing tank.

But seriously, like MTV said, it becomes part of the routine and its no big deal, and like Cam said, about every thirty minutes seemed to work pretty well.

Don't Maules that have the extra outboard tanks have a transfer pump for each wing?

In my opinion running wing tanks in either left or right instead of both is dangerous. I know someone who flew a C172 and missed some points on the checklist on run-up. Took off with the fuel sector in left and flew until he ran out of fuel in the left tank and the engine quit. Selected the fuel selector to both, engine did not restart, ditched into a lake and unfortunately drowned. Personally I like a fuel plumbing design where two wing tanks are connected directly via a fuel line, balance with gravity and then each have an additional fuel line going to the fuel selector valve. The reason why the fuel selector is switched between left and right on run-up is to check if the fuel pick-up of the associate tank is obstructed or plugged. There is absolutely no reason to run on one wing tank only.

KISS is certainly a good principle. In 25-years of flying, I've had several engine outs caused by running on just one tank. Two of those scared the living f--k out me. One was with the wife and over Hells Canyon; those kinds of close calls are due to human error of course. KISS helps a lot to minimize the risk, but it's still there when something like a fuel valve is involved. You can be dam sure I triple check now. And when the fan stops, that's the first thing I touch.

Z,

Check the pressures downstream of those EFII pumps, I remember it being high enough that I personally wouldn't place the pumps or pressurized lines in the cabin (like 60 psi?). FW forward would be more manageable from a risk standpoint.

Pusher wrote:In my opinion running wing tanks in either left or right instead of both is dangerous. I know someone who flew a C172 and missed some points on the checklist on run-up. Took off with the fuel sector in left and flew until he ran out of fuel in the left tank and the engine quit. Selected the fuel selector to both, engine did not restart, ditched into a lake and unfortunately drowned. Personally I like a fuel plumbing design where two wing tanks are connected directly via a fuel line, balance with gravity and then each have an additional fuel line going to the fuel selector valve. The reason why the fuel selector is switched between left and right on run-up is to check if the fuel pick-up of the associate tank is obstructed or plugged. There is absolutely no reason to run on one wing tank only.

I've never heard of a Cessna that wouldn't run with the selector on Both, assuming he was high enough for the fuel to fill the lines, gascolator, etc.....

And, there are indeed lots of good reasons to run on one tank only....one of which has already been noted: There are some Cessnas I've met that feed fuel faster from one tank than the other, and you wind up with a heavy wing....time to feed off that tank till you're balanced.

My Cessna 170 had Flint tip tanks. The procedure REQUIRED by Flint for those tanks is to burn fuel from one main tank till you have enough space to pump tip fuel into that main. Switch to the other main tank to feed the engine, and pump fuel from the other tip into the half full tank. You aren't supposed to run off the tank you're pumping into because you could conceivably flood the engine by pressurizing the fuel line. In the Flint tanks, the tip fuel line is Teed into the fuel outlet of the main tank, and you actually force fuel from the tip into the main tank outlet, and back into the tank, hence the concern over pressurizing the system.

The Maule has similar tanks, but the fuel system is different. Tip tanks feed directly into the main tank outboard. Then fuel runs from the inboard outlet of the main into the fuel system.

The Maules approve pumping from either or both tip tanks into the mains at once, though I think that's a very bad idea, and know of a fatal accident that suggested that it's not a good idea.

So, at least in the Flint system, you are required to operate from one tank at a time. And, there is nothing unsafe about that, assuming you have gas in that tank. And, there are lots of other airplanes that don't have a "Both" position on their fuel selector.

An example of a case where that's not a great idea is the Husky, which has an "On" and "Off" fuel selector, with two fuel tanks in the wings. Park a Husky with full tanks on even a tiny incline and it'll piss fuel out the vent, and port gas from one tank to the other. Pretty soon you've got a serious puddle of very expensive gas.

Every airplane is a bit different, and there may be reasons they were designed that way, but the certification rules for fuel systems are VERY specific and VERY strict. There's no way Cessna would have ever gotten their systems approved if what you claim were true.

MTV

MTV

The facts are when the aircraft was brought back to the surface:

- left tank was empty
- fuel selector in both
- right tank was full
- no obstruction in right pick up or fuel line
- engine started right up

That was the conclusion of the Investigator. Also there were 2 passengers on board who survived and stated that this was what happened.


Btw I was not talking about fuel tank systems with aux tanks.

I have left right off in the cub, I usually keep 5 gallons in the right for just in case, and then add 5 at a time to run out of the left when I'm just dicking around local. Still flys straight with the left full and right with 5. When I am traveling xc I would run the right dry and switch and know I had 18 gallons left. Guess it's not as important anymore now that I have a fuel flow. During the rebuild I will probably switch to left right both off, and ditch the header tanks. It's in my pa-18 btw

I don't like both...maybe it's more that I prefer L/R/off valves because that's mostly what I have experience with.

On my way to High Sierra 2013 I was cruising along at 10k MSL when the engine quite. I was running on both but when I checked the tanks the right was almost empty and the left was about half full; I really wasn't exactly sure how much fuel was in each thank. I switched to the left tank and turned toward the road that was behind me. After maybe a minute I switched to right tank and still got nothing. I ended up switching back to the left tank and left it there. After descending 5k feet the engine caught and we continued our trip. Obviously something was not right with that fuel system but the rest of the time I flew it I didn't use both and never had any more trouble.

Managing the fuel like I did in the Luscombe I knew how much fuel I had and which tank it was in.

It's probably not germane to the core philosophy of tank selection, but I will have 73 gallons aboard. The mains are 25 gal each, and the aux tanks are 11.5 each. The design intends no pump for the aux tanks like a Maule, at least as I understand it. Honestly I need to study that more.

So, each wing has 36.5 gallons, which is about what my 170 had total. Endurance won't be an issue, because like I said, the airplane easily outlasts my butt.

The main advantage to BOTH, with all this stuff in mind, is not so much that you have a larger volume of uninterrupted fuel in terms of endurance, rather it's a real time redundancy for blockage or interruption of one of the tanks.

Who is flying an injected Continental? How's that selector valve setup? Those have full return lines if I recall.

Pusher wrote:In my opinion running wing tanks in either left or right instead of both is dangerous. I know someone who flew a C172 and missed some points on the checklist on run-up. Took off with the fuel sector in left and flew until he ran out of fuel in the left tank and the engine quit. Selected the fuel selector to both, engine did not restart, ditched into a lake and unfortunately drowned. Personally I like a fuel plumbing design where two wing tanks are connected directly via a fuel line, balance with gravity and then each have an additional fuel line going to the fuel selector valve. The reason why the fuel selector is switched between left and right on run-up is to check if the fuel pick-up of the associate tank is obstructed or plugged. There is absolutely no reason to run on one wing tank only.

I'd have to disagree. For one thing, any 172 that has one tank full and the other empty, unless it's being run on an autopilot, will need a lot of opposite aileron to balance it out. That's such an obvious indication of a problem that it's hard to miss.

There is no requirement in any 172 checklist to switch between tanks during the run-up. In fact, most instructors will discourage switching tanks that late in the game. Much better to leave the fuel selector where it is, which should be "both" for both take off and landing. Unless you were to taxi a couple miles, you won't discover whether one or the other side is plugged during run-up--if one is, it won't show quickly. For the heckuvit, turn off the fuel sometime and see how far you can taxi before the engine quits--it's a long way.

Personally, I usually leave the selector on both for local flights, because I'm lazy. For longer flights, I start on both until it's time to level off in cruise. By then, I've usually burned out the first 5 gallons, and my fuel flow meter starts flashing. Then I switch to the left tank. Approximately half an hour later and another 5 gallons, I switch to the right tank, etc., when the fuel flow meter flashes again. Before I had the fuel flow meter, I leveled off at cruise, set cruise power and mixture, and then switched to the left tank. I switched every half hour. It's not difficult, and that way the fuel load is balanced, because many airplanes, with both selected, will nonetheless draw more from one tank than the other. When you're hand-flying, an unbalanced airplane isn't as pleasant to fly, especially long distances.

In Cessnas, only the 150/152 has only a both position plus off. 172s and 182s have left, both, right, and off. 200 series Cessnas have left, right, and off--no both. Yeah, sometimes Cessna pilots screw up and forget to switch, but that doesn't make it dangerous to switch--what makes it dangerous is not flying like one is taught.

But all that's FWIW. As someone said, it's your airplane, Z. Design it the way you want, build it the way you want, fly it the way you want. Just be safe!

Cary

I've already learned so much about aircraft design from this project that it's amazing how much I didn't know I didn't know. I think this is one of the neatest things about homebuilding-- the intimate knowledge of your aircraft when you're finished. Dreaming about building and actually doing it are miles apart and I would be lying if I said I've not been intimidated at times. But that is my favorite part-- dig in, learn, evaluate, commit, execute. If you're lucky you'll only do it twice.

This fuel system stuff is fun. I enjoy bending the lines and playing with the fittings. It's a heck of a lot easier than cutting and shaping aluminum sheet.

When we did Bearhawk #357 with the Land Rover engine we did the standard piping to the duplex fuel valve which was left/right both and off. The return lines did the same. We mounted the dual electric high pressure pumps on the motor side of the firewall, put a little box around them and brought in cold air for cooling. The nice thing about the return lines back to the tanks is that when you turn the pumps on, any fuel that has been heated up during the shut down gets pumped through the system and into the tanks to cool down. Also when you are running about 15% to 30% of the fuel is returned to the tank and this gets rid of any heat the fuel may have picked up on it's way through the motor compartment. The new GM systems have no return from the motor area so I guess that they do not get boiling because they are running just about 60psi head pressure and their pump which is mounted in the tank has an internal relief to keep the pump from overheating. We ran dual SDS systems and coil splitters. The backup system was not as complete as the main system as it did not require a throttle position sensor. The TPS is only used to activate the digital version of the old accelerator pump and not required for our type of operation.
If you really want back up take a look at the guy that runs a fully operational carb/magneto system on his 150 and runs normally on the SDS system. This is a situation where you can have your cake and eat it too.
KenW

The term "fuel management" to me means putting some in from time to time, other then that I have NO managing to do. No selector valve, both wing tanks feed the header tank, the header feeds the engine, both wing tanks AND the 3 gallon header have sight gauges. The S-7 will empty one tank out before the other, always has and always will, and it makes no difference whatsoever in engine operation or how the plane handles, a total non issue. Obsessing over keeping both wing tanks somewhat even is busy work.

courierguy wrote:Obsessing over keeping both wing tanks somewhat even is busy work.

You probably intended this statement in reference to the S-7, but here's another perspective:

My plane flies significantly different with one tank full and the other anywhere below 1/4. But that's with 30 gal per side.

Each model aircraft have their own unique quirks. Cool to hear the S-7 is so benign!

Pusher wrote:MTV

The facts are when the aircraft was brought back to the surface:

- left tank was empty
- fuel selector in both
- right tank was full
- no obstruction in right pick up or fuel line
- engine started right up

That was the conclusion of the Investigator. Also there were 2 passengers on board who survived and stated that this was what happened.


Btw I was not talking about fuel tank systems with aux tanks.

I don't doubt that it happened. As I noted, if you run a tank dry in one of these, it takes a bit for the (very low) head pressure to refill the lines and gascolator downstream of the selector. If you're at a relatively low altitude when this happens, good luck.

My point with the Flint aux tank system was simply that running a Cessna on one tank was thoroughly tested for certification.

Look, focus and determination can make ANYthing "unsafe". We humans can find all sorts of ways to hurt ourselves. Airplanes are not perfectly safe contrivances....they require that the pilot participate. Running out of gas on one tank shouldn't kill you IF you were high enough when it happened to get fuel to the engine from the full tank.

And, as noted, a 172 with one tank full and the other empty will give the pilot all sorts of feedback that all is not well.

MTV

Binary logic: ON or OFF. Something so simple it's hard for even me to mess it up.

After running (6) tanks in a long range Navajo, the simplicity of the Scout's fuel is welcome. Only caveat, in my opinion, is crossing feeding fuel if aircraft is not kept level. Always keep the ship level (as possible) on ground, water and air. Crossing feeding is dangerous if not kept in check.

The schematic of 8GCBC fuel system without the auxiliaries (+35gals). Binary logic, on/off only.

MTV

Maybe I should rephrase my previous comment to "potentially dangerous". A fuel system should be designed so it is easy to manage. Like courier said, put fuel in the tanks and forget about it. I always liked the C152 system with the tanks plumbed together for gravity balancing and a simple ON/OFF fuel shut-off valve.