Fuel Management

[Skeletool]

Hello All,

I've been thinking about getting a Maule, so I'm doing all my research to make sure it fits my needs. I've been flying a Piper J3 for a while now which has one 12 gallon tank. Not much to think about when it comes to fuel. I used to own a Cessna 140 with two tanks and no "Both" position on the fuel valve, so I kept track of each tank with a cooking timer. It didn't work real well for me. I guess what I want to know is, how do you all keep track of your fuel?

[Island Flyer]

The in-panel fuel gauges are there but I never trust them all the way. The first place to start is to know how much fuel your plane holds. I added two new main tanks on Island Flyer and even though they were suppose to be 21.5 gallons each, at one inch below the fill cap neck they are 23 gallons each. With the mains and the aux tanks I now can carry 76 gallons, but the vast majority of time I am just using the main tanks. I just ordered three new fuel gauge sending units because only two of them are working correctly and one of those (in one of the main tanks) was replaced before we put the tanks back in. We tested the units before we put them back in but in the last 14 hours of flying, the old main sending unit goes crazy at about 1/2 tank and one of the aux tanks will read full when it's empty unless you physically lift the float slightly then it reads empty. The problem with both is inside the contacts of the units. When we filled the tanks the first time we made a custom dip stick for fuel at 5 gallon increments. So I always 'stick' the tanks before every flight and figure a rate of 12 gph (Lycoming IO-540 235 hp) to be conservative. It's actual rate at sea level to about 5,000 feet seems to be averaging around 11 gph. With the JPI fuel flow option and slowly tweaking in the finagle factor (I think they call it the K factor), if you remember the set the fuel quantity when refilling, it seems to be fairly accurate. But even with all of the fancy gadgets, I will always stick the tanks. I only believe it when I see it.

[Kirk]

Like most airplanes with a 'Both' position, Maules don't always feed evenly in both. That's no big deal if you aren't going to go anywhere near empty tanks. Pattern work, local flying etc I go for both.

Cross country flying or if I will run the fuel down low, I stick the tanks before takeoff and run 30 minutes each side. I keep track of the times on a notepad and try to time it so that I have the most full tank selected when approaching destination.

Both position for takeoff and landing.

Kirk

[Ernie]

I've owned and flown a MX-7 160 for the past six years or so, and I learned early on that, in my plane at least, utilizing the both setting will cross feed fuel, causing fuel to vent overboard when tanks are full.

Once I have burned off some fuel, the both setting is okay, but mine will still cross feed some even then, as a result of turns etc., but not enough to vent overboard.

On a cross country, I use a stopwatch to remind me to switch tanks every hour, and that has worked out well for me.

The Maule is a great A/C, and you won't be sorry if you make the purchase.

Ernie

[Skeletool]

Ok, so you all pretty much time your fuel burn.
I did some looking last night to see if anyone made anything better than a cooking timer for timing your tanks. I started out looking for electronic devices, but then it dawned on me that perhaps someone makes a fuel timer app for iPodsPadsPhones. So I looked in iTunes, and sure enough there is one! It's called Fuel Timer and it was only $10, which was cheaper than the cooking timers I found, so I down loaded it. It's pretty cool. You can set fuel burn for your aircraft for Taxi, Climb, and Cruise. On the main screen are two big tanks, and buttons with the different modes of flight. Once you play around with it its pretty simple. You can select tanks by touching and holding the tank for like 2 seconds. If you want to switch tanks you just touch and hold the active tank. As you burn fuel, the tank on the screen gets emptier. You can set up Warnings to warn you when you have low fuel quantity, or when you are running out of time. You can also set up alarms that will tell you when to switch tanks.
The only thing I don't reall like about it is that you can only set up two tanks. You can name them what ever you want, but there is a max of two. I don't suppose that's a problem for most Maule pilots though. I've only played around with it at home, so I'm interested to se how it works in the air. I'm going to try and use it in my friend's 172 this weekend. I'd be curious to see if any of you think it is any good.

[nd_rice]

My 196 has a fuel timer option. You can select how many minutes between reminders. It will appear as a box on the bottom of the screen. I still use a kitchen timer too.

My PA 22 has NO both position and I do not miss it.

[Lowflybye]

Depending on the avionics in your aircraft you have plenty of options. I am most familiar with Garmin equipment so I will limit the answer to their options. I am sure the competitors have similar options as well.

I typically burn out of BOTH, but on a long trip where I plan to transfer fuel inboard I use the following procedure which keeps the maximum amount of usable fuel for the longest time. Remember that you cannot burn from the outboards so it should not be considered usable until it transfers inboard...if the transfer pump goes INOP you have only what is inboard.

I startup and takeoff out of one tank with preference to the side of the aircraft that is the heaviest. After 1 hour I will switch to BOTH and begin transfering fuel from the side of the first tank. It will take about 30 minutes to transfer all the fuel from the outboard to the inboard as the transfer pump operates at 1/2 gal per minute. At this transfer rate vs fuel burn it should not vent any overboard. At the 1.5 hour mark you should still have (2) full main tanks (one will be about 3 gallons shy) and one full outboard. At this point I switch to the other fuel tank and burn a full hour from it. Halfway through this hour I will turn on the transfer pump as I now have approximately 10 gallons burned and should not vent any fuel overboard given the transfer / burn rate. At the end of the time period switch back to BOTH...you again have full main tanks with the outboards both empty and you are 2.5 hours into the flight having maintained maximum usable fuel the entire trip. By using this method the lowest usable fuel quanitiy should be no less than approximately 30 gallons at any point from startup to the 2.5 hour mark. This may be a bit more work, but unusable fuel is useless weight and on a long cross country I want the most usuable fuel possible at all times.

Back to the timer options with Garmin. Most of the Garmin transponders have a built in timer that will either count down from 2 minutes (for IFR holds) or it will count up for use as a trip timer.

00:00 - Select Tank
1:00 - Switch to BOTH / 1st transfer pump ON
1:30 - Select 2nd tank / 1st transfer pump OFF
2:00 - 2nd txfr pump ON
2:30 - Select BOTH / 2nd transfer tank OFF

If you have a 396 / 496 / 696 you can setup a Fuel Timer with given intervals that will display a message to remind you to switch tanks. There is also an option for User Defined timers on the same menu

If you have a panel mount model from the 400 series and up, you can setup multiple reminders for anything from switching fuel tanks at specified time intervals, to ELT / Transponder certification checks and Annual Inspections on a given date simply by using the Scheduler menu.

As I said, there are plenty of options already in the aircraft (depending on your equipment) so there is no need to add another gadget to fiddle with simply to remember to switch tanks.

Just my .02 worth.

[aero101]

LowFlyBy-

How come you select both while xfering from aux tank. I guess you realise you are also transfering fuel from the opposite full main to the one you just ran an hour on and this tranfer is at an unknown rate and amount?

If I'm running near limits on Mains, I run LH tank while my watch minute hand is between 6 and 12 (LH side of wristwatch) then switch to RH tank while watch minute hand between 12 and 6 (or RH side of wristwatch) and continue this cycle until I run the first tank dry. Although I recently added an EI fuel flow, so now generally run on both and have found the indicator to be accurate within a tenth gallon or so. If I start getting close to 75% of total fuel burned, I'll select either single tank, run dry and at that point I'll know almost exactly what I have left in other tank... And start looking for a lake or river to land in to add some more fuel if we're that close? If I'm on wheels, there's generally no reason to run into what I consider day VFR minimum fuel on board and I consider that to be 1hr up here due to lack of accurate WX info, and considerable diversion miles should WX change. On wheels fuel usually pretty easy to find, floats can be another story sometimes... I guess that's why they install storage hatches in floats, so you can carry some extra fuel in cans? And due to my aging, I've found the KISS principal to always work best.

[akloon]

I liked Jeremy's technique on a post a while back. Correct me if I'm wrong, Jeremy, but I think you advocated that for flights using the tip tanks, to avoid having a heavy/light wing, run from left and right mains for an hour each, then transfer at the same time while continuing to switch tanks as necessary until you're down below 20 gal or so when the fuel weight really won't affect lateral CG, then switch to both or run one dry and have your reserve in the other.
I have a Shadin totallizer that I have found pretty accurate, but I still stick the tanks as well.
Dave

[Lowflybye]

LowFlyBy-

How come you select both while xfering from aux tank. I guess you realise you are also transfering fuel from the opposite full main to the one you just ran an hour on and this tranfer is at an unknown rate and amount?

I select BOTH on the first fuel transfer simply because I have not burned enough fuel out of the first tank in the first hour to allow for enough room to transfer all of the aux tank without venting it overboard. By selecting BOTH for the next half hour I continue to burn enough fuel out of that tank to allow it to fill up without venting the excess. The same scenario works in reverse for the second tank.

With regards to the cross feed... here is my simplistic thoughts on it as I understand the setup of the fuel system. In order for the tanks to cross feed the fuel must transfer from one tank to the other through the fuel selector. This is why we can prevent the cross feed by selecting one tank or the other as it closes the connection between the tanks created by the OFF or BOTH selection. When the engine is not running there is no positive directional flow of fuel through the selector which allows for the fuel to cross feed in the OFF or BOTH position until it reaches equilibrium between the tanks. However, when the engine is running, the tanks should not be able to cross feed as there is a positive directional flow of fuel to the engine. If you are using the BOTH selection then both tanks are feeding the engine simultaneously although possibly at slightly different rates. The fuel in both lines is flowing from the tank, through the selector and toward the engine therefore the fuel cannot cross feed from one tank to the other because fuel cannot flow opposite directions in one line at the same time.

This could be simulated by connecting a half empty Sprite bottle to a full Coke bottle via a hose with a T connection in the middle. With the third line of the T plugged the liquid in the full bottle (Coke) will begin a positive flow through the tube, past the T connection, and into the bottle with a lesser quantity (Sprite) until equilibrium between the bottles is reached. This transfer will be very evident due to the dark vs light liquid. However, if we unplug the third line of the T we would create a positive flow out of the line and you will notice that both the Sprite and Coke will flow positively in this direction preventing the transfer between bottles.

Another thought...if the fuel could indeed cross feed with the engine running then we would not notice a difference in fuel burn rate between tanks when using the BOTH selection as they would remain in equilibrium resulting in the appearance of an equal burn rate for tanks.

Of course all of this is based on my understanding of the fuel system being correct. If my understanding of the system is incorrect then what I have said above could also be incorrect.

[Lowflybye]

I liked Jeremy's technique on a post a while back.

That post has a valid point, you do not want to find yourself with one tip tank full and one empty as you now have a large lateral weight difference on a long arm from the center of balance. This can create a "fun" scenario when landing.

I did not mention it in my post and should have...if I am going on a trip where I plan to use the aux tanks I make it a point to check them during the walk around. Just a quick flip ON and you should hear them pumping. However, if the first transfer pump decides to crap out in flight then I won't transfer from the second and use only the mains for the flight. If the first works, but the second craps out then the procedure is to use only the fuel in the second main leaving the first main full to help offset the weight that will remain in the second aux. It will not be an exact equal, but enough to significantly move the center of balance back towards the center of the fuselage.

There is more than one way to skin the cat and each has merit. Interesting to read all of the differences between us and why.

[aero101]

I'm not sure but think that the fullest bottle, if base at the same height, will flow more fuel due to it's pressure, but if it works on your aircraft for you, that's all that counts... Yes, it is interesting all the different ways of managing, and there are differences between individual aircraft of same models as to how they flow, xfeed, etc, etc, even though they're the same system. If I transfer from aux, I wait until second hour started and that tank selected, turn on the pumps... Yes, there is not enough room yet, but with the current burn coming out of tank and slow transfer rate, it will hold the fuel with no overflow.... or if running on both, I'll wait until 3rd hour starts and select both aux pumps on... The most important issue is know your system, your own airplane, and keep that gas flowing while the props turning!!

[kneel]

I use the same method as aero101. Although I usually transfer from my aux tank for 15 min on the start of the 2nd hour.
1:00 RH, trans 15min rh aux;
1:30 LH, trans 15min LH aux;
2:00 RH, trans 15 min RH aux;
2:30 LH, trans 15 min LH aux
The reason I like this method is it allows me to keep track of fuel and recovery from most failures of the fuel sytem. I can tell which tank I should be using by my analog timer, double check my fuel burn, easier identification of fuel venting or fuel loss, and never becoming too wing heavy. I have also found this method works good for all types of flights. So I can do this method without even thinking (habit). This is really important because I need all the brain power I can get when fly long x-countries.

my .02
Kneel

[Mountain Doctor]

Island Flyer wrote:

Even though they were suppose to be 21.5 gallons each, at one inch below the fill cap neck they are 23 gallons each.

I have found exactly the same thing on my plane when filling a main tank that was down to no useable fuel.

As far as fuel management goes, I just keep the tanks balanced by monitoring the fuel gauges. Sometimes if I'm heavy on a side (heavy passenger(s)) I will even the plane out by using that side's tank preferentially.

I run the transfer pumps when the mains are between 1/4 and 1/2 and I try to never run the auxillary tanks dry. I imagine that's bad for the pumps.

As long as I never run below 1/4-1/3 tank I find the factory gauges perfectly acceptable.

[andy]

I keep all my mains about 1" below the bottom of the filler neck to avoid siphoning out the vent tubes. I usually keep the aux tanks empty except on a long cross-country with one or two people and not much baggage. I never know when I'm going to get a call for a flight that includes four adults, so I don't want to have to deal with getting rid of fuel to reduce weight.

I use a wooden dowel with paint marks for full and half full to check the level during pre-flight. The dowel is too big to slip into the tank if I get fumble fingers in the winter. Don't ask me how I know about this.

I take off on left or right tank - whichever is fuller - to keep from cross-feeding on the ground or during banks. I have a JPI EDM-800 engine analyzer with a fuel flow sensor and I highly recommend using a fuel totalizer or something like it. You can determine exactly how much fuel you've used, but you still need to start out with a known quantity after you add fuel. It also gives you detailed knowledge of the airplane's fuel burn during climb, cruise at different power settings, and descent. No tables or guesswork.

After 30 minutes of cruise flight, I switch to the other tank and burn for 30 more minutes. Then I switch to the "both" fuel selector position for the remainder of the flight. The EDM-800 gives me the amount of fuel that I've burned from each side if I remember to look at it before switching tanks. My Maule is typical and burns more from one main (right) than the other.

I prefer landing with the fuel selector in the both position, especially if I'm low on fuel. I haven't looked at the plumbing on a Maule fuel tank, but I've heard others say that slips or banks can shift fuel away from the line to the fuel selector.