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“fuel management” techniques


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VFR: Run one tank to 10 gallons. Run the other tank dry. When the engine quits, I know I have an hour of fuel left.

 

IFR: Run one tank to 15 gallons, run the other till it indicates zero on the fuel guage.

 

 

I always start with known quantity and I have a fuel totalizer so this makes it easy.

 

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It depends on how long the flight is. My goal is to always land with 10+ gallons in the tank I am landing on.

If it is a short flight I will take off on the full tank and land on that same tank. If my planning is such that I will be coming in with 10+ gallons I see no reason to switch to the other tank when the one I am flying on has been working just fine.

If it is a long flight I will do something similar to what is listed in the POH. I have an EDM830 so I can see just about exactly what has been used. I will switch tanks when I have about 15 gallons left in the tank I took off with. I'll stay on the second tank until either A) The top of descent, or B) If I still have 10+ in the tank I switched to I will stay on it the rest of the flight. Again I don't see a reason to switch back if there is sufficient fuel in the tank I am on. 

That does go against the "Land on the fullest tank" mantra, but 10+ gallons is enough for more than one go-around so why switch tanks just to switch tanks.

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BD,

Expect procedures printed in 1965 to be woefully out of date in some areas...

1) Do you have a fuel flow indicator with a totalizer?

2) Do you have an engine monitor?

These two devices help change the way I monitor fuel usage in my plane.

In my C... with no fancy instruments...

1) Started with evenly filled tanks.

2) switched at top of climb.

3) Switched every hour after that.

4) Amount Of fuel used during the climb was a challenge to judge.  I kept the unknowns in one tank, the knowns in the other, if possible.

 

Try to get FF and totalizer in one good engine monitor, add carb temp to that... :)

Best regards,

-a-

 

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That's the same thing as in my 1970 C Owners Manual. I change tanks every hour, and know that I have 2:30 in each tank. I've gone 4:45 twice due to headwinds and diversions around weather, and I'm was on my toes for that last fuel change as close to top of descent as possible. Be sure to inform your passengers, as they will appreciate being included, especially if you cut it a little too close and the engine hiccups or quits. The engine going silent and pitching down with no warning is guaranteed to upset your passengers!  

If you know fuel will be close, plan a landing short of your destination, and see what your fuel situation looks like when you get there. Include your passengers in this discussion before leaving, too. Then you either make your planned fuel stop or continue on. If you are worried, then stop. 

My two long trips both ended with 11-12 gallons in the tanks, mostly in the one I landed on, as my wife is not a fan of running a tank dry. So I had the Golden Hour plus 15 minutes or so. But that's a long time in the cockpit, and we were both ready to stand up and walk around!

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In my F, with fuel totalizer(FS450), short range 3 hour flight,  filled  to the the tabs 52 gal, 1.5 hours(17 gal) on first tank then switch to other side for rest of flight 1.5 hours(15 gal). Leaving me an  hour in first tank if I need it but that’s my reserve.

Long range flight 4+ hours 64 gal, 2 hours (22 gal) on first tank then switch to other side for 2 hours or more(20gal) and have another 1hour+  in the second tank at cruise,  I then know I have another hour of fuel reserve in the first tank if something should happen to the second tank. 

Don’t switch tanks just prior to take off!!, I don’t run tanks dry, and I don’t see a reason to switch tanks every hour. I try never to get into my reserve fuel( I normally have to pee after 3 hours anyway) I climb WOT 2700, start lean above 5K in climb, burn 12 gal first hour, in cruise  run 64-65% ROP 10- 9.8 GPH every hour after. 

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BigD-

That’s a good basic idea, but the ringer is the line about cruise setting remaining unchanged.  Us turbo guys might take 40 minutes at basically a full power setting to climb to a cruise altitude of, say, FL210.  What I did, was to make sure my fuel totalizer (JPI930) was very accurate.  Then I make a little chart, its the only piece of paper I use in the cockpit.  I have an L and an R column, and I start with full fuel at the top of each column.  Then I will make the climb to altitude and after an hour or so I switch tanks and note the fuel used.  I then fly on the new tank for most of the flight.  I know exactly how much is left is the first tank for the descent and landing, I switch to that tank sometime during the descent.  On a flight of, say, 4 hours, I will have about 20 gallons left in that tank.  The totalizer is way more accurate than the gauges.

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Using my fuel totalizator  I fly 10 gallons on first tank now I know have at a minimum 1.8 hours at cruise remaining in that tank and I can stretch it a little longer if absolutely necessary but I do not plan on that.  I then fly the other tank until 15 to 30 minutes before my destination or when it is about to go dry and switch back to the first tank.   I try not to let the fan stop but not opposed to it if I'm alone.  Actually it is good engine out practice.  If I am flying that long I want all my usable fuel in one tank.

Shorter flights it will vary but 1.5 or less I usually stay on one tank.

 

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I think the original Mooney Idea was about as good as it gets. It is very simple and at the same time logical. It accomplishes quite a lot of things by approximation.

In the first hour after departure you will have climbed to cruise altitude and been running there for a while. In my C this means I will have burnt of about 10-12 USG climbing to 10'000 ft and running some 40 minutes there at 8-9 GPH, so there are some 15 USG left in that tank. The other will have 26 USG, which then with appropriate power setting will equalize in about 1.5 hours and then empty within 2.5 to 3 hours depending on fuel flow. The other thank will then have some 1.5 hours left itself, including a final reserve of 45' which corresponds to 6-7 USG, so landing should occur after the 2nd tank switch within about 45 minutes to an hour.

So in practice and using a 4 hour endurance (52 USG usable) with one hour reserve based on 10 GPH conservatively, it's a very easy way of doing fuel management which will not get you in any trouble. Switch tanks after 1 hours, then again when the other is empty or near empty and plan on landing within 1 hour of the last switch is a concept most of us can memorize without too many tech toys.

What this does is it keeps a reasonable balance between left and right tanks and it does it with a minimum of switching.

Of course totalizers and fuel flow gauges help with the above figures which are easy to remember as a backup. Using totalizers and exact fuel flow will do one thing primarily, it will optimize the range and use of your airplane and it will give you a much better idea about the way you run your engine and it will give you the possibility to achieve much larger range than simply running WOT and best power. Instead of just "knowing" that there will be fuel for "what the other tank had - 1 hour" you will have a clear indication of how long you actually have continuing on the same fuel flow. Or, e.g. with a GNS430 or similar GPS coupled to a fuel computer, get the expected fuel at destination. So all you really need to do is to keep the engine configured so that the fuel at destination never goes below the 45' final reserve or, if diversion is a real possibility, 45' plus the alternate fuel.

All in all, I think the Mooney offer on how to switch our tanks is easy and actually quite practicable. Seeing where most of our fuel valves are located, I do avoid switching in any situation but in cruise and on AP when you can do the acrobatics involved to get there without having to do much else. The Mooney suggestion pretty much takes care of that too.

 

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I installed Cies floats and a digital gauge so we know what we have in each tank.  No guess work based on time.  Assuming you are talking about a long flight...

I start on one tank and switch to the other tank prior to starting to taxi.  I do that to make sure both tanks feed.

I run that tank to level off or a value that is multiple of five, whichever comes later.  I then run the other tank until it is at the first multiple of five lower than the first tank.  I then switch every 10 gallons so that I never have more than a 5 gallon imbalance.  I'll continue until one tank has 10 gallons and then switch to the other tank.  I'll stay on that tank until I'm entering the pattern at which point I'll use whichever tank has the most fuel.  That will ensure I have at least 10 gallons in the tank I'm using during the pattern and landing.

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One thing that I notice, I think...

All Mooneys come with a variety of improvements...

1) Digital fuel level gauges. (Higher accuracy than the old mechanical devices)

2) Digital fuel flow. (Rate of fuel use)

3) Digital totalizer. (Fuel used)

4) Wing leveler/AP. (Otto lifts the heavy wing)

5) Depending on the strength of the pilot’s internal calculator and it’s associated memory bank... keeping track of tank changes every...

  • 10gallons works pretty well
  • 5gallons keeps things more balanced, but a lot more to remember or make note of.
  • TOC and hourly is really good at minimizing the memory challenge.
  • When you don’t have an operational wing level, you get a feel for how strong the weight imbalance actually is... do you lift the heavy wing or push down on the light wing?  :)
  • 100gallon tank or 52gallon tank, the challenges are similar.  Just, Otto can hide a really strong imbalance without letting you know... (use caution with this one)

Go Mooney!

-a-

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14 hours ago, BigD said:

Below is from my 1965 M20C manual regarding fuel management. Just curious what others might be doing? Thanks again!

Yep, this is exactly what I did with my C and now with my Turbo 252. There's no reason to keep switching tanks back and forth throughout the flight. There is too much opportunity for error, miscalculation, etc. Mooney's are easy to fly and even land with a huge fuel imbalance so keeping them balanced isn't an issue either.

With the 252 and larger tanks, I adjust this to depending on the flight. But I never switch tanks more than twice on any flight and most often only switch once. 

Take off, burn 20 gal off the right tank, switch to the left and run it until dry, then switch back. On shorter flights I might run 10 out of the left switch to right and leave it there for the remainder of the flight. 

I also always switch based on gal of fuel used or remaining and never on time. I think time was a useful number back when we didn't know the actual fuel used/remaining. But with modern gauges, we know volume and volume is a more accurate measurement. 

I can create more time while in flight. I can go from ROP to LOP and greatly increase my time until empty. But I can't increase the number of gallons in either tank. So I measure, and switch based on gallons. It's a better constant.

Just my $0.02

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There is a pretty Good read on this topic based on a fuel starvation NTSB incident in the April 2018 version of the Mooney Flyer, I have used a very similar approach no matter if I am flying my Mooney or renting a Cessna.

 

 

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I also do not switch until I am approaching an airport someplace within gliding distance.  Switch as you approach the airport, this gives you all the time to fly towards it and away from it to ensure it was a good switch......

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