Fuel planning and use - Cherokee 6

[k9medic]

i took my first long trip in our new to us Cherokee 6/260 and have some interesting new fuel utilization questions for those who may have gone through something similar.

For the entire trip, I used 84 gallons in 5.8 hours in the tach.

My main tanks showed almost empty but when I fueled up I only put 19 gallons in per side. That means I had 6 gallons per side left in the mains.

Obviously I don’t trust the fuel gauges but my fuel totalizer matches what I put in.

Here is the major question - the POH says that all but one quart per tank is useable.

I have NEVER ran an aircraft that low and don’t plan on doing it so how do I maximize my range with the amount of fuel remaining?


FWIW I landed with almost 20 gallons total remaining.

 

[Salty]

In my mooney I run one side dry so I know all the usable fuel is in the other for the rest of the flight.

 

[k9medic]

When you say you run it dry, what are your indications? Do you run it until it stumbles or until the gauge reads zero?

 

[Salty]

When you say you run it dry, what are your indications? Do you run it until it stumbles or until the gauge reads zero?

I run until it shuts off. When it starts to stumble I switch, but I usually pull back the throttle too because it takes me longer to switch than there is fuel left. Then I push the throttle back in.

 

[James331]

I just use burn and time, fltplan is pretty damn good too at good burn numbers once you set it up.

I also always land with at least 1hr of fuel in the plane.

 

[tawood]

i took my first long trip in our new to us Cherokee 6/260 and have some interesting new fuel utilization questions for those who may have gone through something similar.

For the entire trip, I used 84 gallons in 5.8 hours in the tach.

My main tanks showed almost empty but when I fueled up I only put 19 gallons in per side. That means I had 6 gallons per side left in the mains.

Obviously I don’t trust the fuel gauges but my fuel totalizer matches what I put in.

Here is the major question - the POH says that all but one quart per tank is useable.

I have NEVER ran an aircraft that low and don’t plan on doing it so how do I maximize my range with the amount of fuel remaining?


FWIW I landed with almost 20 gallons total remaining.

Careful...just because your POH says your tank will hold X number of gallons, doesn't mean that it will. Over time, due to damage, bladders, etc, tanks sometimes hold much less.

 

[bradg33]

In my mooney I run one side dry so I know all the usable fuel is in the other for the rest of the flight.

I'm also a proponent of running tanks dry. If I'm landing with a 1 hour reserve, which is roughly 14 gallons, I'd rather have that all in one place rather than spread among several tanks (one of my airplanes has 4 tanks, the other 5).

In most (though not all) airplanes, running a tank dry really is a non-event. Engine stumbles or quits, select a tank with fuel in it, hit the boost pump (depending on airplane), engine comes right back. Certification requirements are, I believe, that a restart occur in no more than 30 seconds, though most are much, much quicker than that. 2-3 seconds in my airplanes and all the ones I've flown.

 

[drjcustis]

Do you have the 4 tanks?


Sent from my iPad using Tapatalk

 

[Fearless Tower]

When you say you run it dry, what are your indications? Do you run it until it stumbles or until the gauge reads zero?

In most airplanes, you switch at the first indication that it is losing suction. Usually, you will notice the fuel pressure needle start to bounce and dip before you notice any change in the engine. Then you can switch before your passengers get concerned.

Some airplanes will have a warning light that will give you a couple second heads up to switch before the engine falters.

 

[k9medic]

Yes I have the 4 tank set up. It’s a metal tank so no bladders to fall or compact.


I just cannot fathom running an engine to fuel starvation. I darn sure am not going to test the restart theory either.

 

[bradg33]

In most airplanes, you switch at the first indication that it is losing suction. Usually, you will notice the fuel pressure needle start to bounce and dip before you notice any change in the engine. Then you can switch before your passengers get concerned.

Some airplanes will have a warning light that will give you a couple second heads up to switch before the engine falters.

Those are the friendly airplanes. The less-friendly airplanes, like my Super Viking, go from full pressure to zero pressure in an instant with no warning.

 

[bradg33]

Yes I have the 4 tank set up. It’s a metal tank so no bladders to fall or compact.


I just cannot fathom running an engine to fuel starvation. I darn sure am not going to test the restart theory either.

I know it's counter-intuitive, but if you want to get max range out of your airplane, you're gonna have to learn. With a 4 tank setup, you're potentially leaving a LOT of essentially unusable gas spread among multiple tanks. If you plan a max range flight with a 45min - 1 hour reserve, you could easily have that full hour of fuel spread among 4 tanks, or only have only 15 minutes of fuel in any given tank. That's just not smart. It's not a big deal if you're only flying short legs with lots and lots of extra fuel, but for max range flights, you should get comfortable with running them dry. It's honestly a non-event. Leave one of your tanks low, take off on a full tank, circle over an airport, switch to the low tank, let it run dry and see what happens and how quick it restarts (esp. with the help of the boost pump). Once you do it a couple times, it'll seem like second nature.

 

[drjcustis]

I know it's counter-intuitive, but if you want to get max range out of your airplane, you're gonna have to learn. With a 4 tank setup, you're potentially leaving a LOT of essentially unusable gas spread among multiple tanks. If you plan a max range flight with a 45min - 1 hour reserve, you could easily have that full hour of fuel spread among 4 tanks, or only have only 15 minutes of fuel in any given tank. That's just not smart. It's not a big deal if you're only flying short legs with lots and lots of extra fuel, but for max range flights, you should get comfortable with running them dry. It's honestly a non-event. Leave one of your tanks low, take off on a full tank, circle over an airport, switch to the low tank, let it run dry and see what happens and how quick it restarts (esp. with the help of the boost pump). Once you do it a couple times, it'll seem like second nature.

I absolutely agree with the idea that you can leave A LOT of fuel spread out. However, I don’t like to run a tank dry and my wife absolutely, positively, without a doubt hates it. In our Cherokee, the restart takes about 10 seconds and is filled with lots of surges. Not pleasant.

With my JPI fuel totalizer, I can get fuel in the tips down to <1 gallon. That leaves the mains with fuel for the final segment and about 2 gallons of unusable fuel.

I use the JPI’s fuel to destination feature for this kind of long range flying. Once set up in cruise, I look at fuel remaining and fuel to destination. As long as there’s more than 12 gallons difference, I’m good. If there’s less, I adjust power settings.


Sent from my iPad using Tapatalk

 

[bradg33]

I absolutely agree with the idea that you can leave A LOT of fuel spread out. However, I don’t like to run a tank dry and my wife absolutely, positively, without a doubt hates it. In our Cherokee, the restart takes about 10 seconds and is filled with lots of surges. Not pleasant.

With my JPI fuel totalizer, I can get fuel in the tips down to <1 gallon. That leaves the mains with fuel for the final segment and about 2 gallons of unusable fuel.

I use the JPI’s fuel to destination feature for this kind of long range flying. Once set up in cruise, I look at fuel remaining and fuel to destination. As long as there’s more than 12 gallons difference, I’m good. If there’s less, I adjust power settings.


Sent from my iPad using Tapatalk

That's kind of the one exception, if you've got a well setup fuel totalizer with a correct K-Factor, you can get the tanks down to half a gallon or less (assuming you're willing to, on occasion, inadvertently run it dry because the tank didn't contain exactly x gallons). If I have pax in my Super Viking that haven't flown with me before, I do try to remember to switch the tanks when they get down to .2 gallons or so.

 

[TommyG]

I have no need to run tanks that close to empty. Also no way in hell I’m flying more than 3 hours without stopping somewhere. But even with a JPI totalizer, I still plan my 182 for 14 gal/hr. I’m always gonna land with more than I planned for. I don’t gamble with that 30 or 45 minutes reserve.

 

[Pilawt]

Certification requirements are, I believe, that a restart occur in no more than 30 seconds, though most are much, much quicker than that. 2-3 seconds in my airplanes and all the ones I've flown.

FAR §23.955 ("Fuel flow"):

(e) Multiple fuel tanks. For reciprocating engines that are supplied with fuel from more than one tank, if engine power loss becomes apparent due to fuel depletion from the tank selected, it must be possible after switching to any full tank, in level flight, to obtain 75 percent maximum continuous power on that engine in not more than—

(1) 10 seconds for naturally aspirated single-engine airplanes;

(2) 20 seconds for turbocharged single-engine airplanes, provided that 75 percent maximum continuous naturally aspirated power is regained within 10 seconds; or

(3) 20 seconds for multiengine airplanes.

The earlier CAR 3 3.4221(d) had an even stronger requirement for single-engine airplanes.

If an engine can be supplied with fuel from more than one tank, it shall be possible to regain the full power and fuel pressure of that engine in not more than 10 seconds (for single-engine airplanes) or 20 seconds (for multiengine airplanes) after switching to any full tank after engine malfunction becomes apparent due to the depletion of the fuel supply in any tank from which the engine can be fed. Compliance with this provision shall be demonstrated in level flight.

I used to own an older fuel-injected Bonanza with two main tanks and two aux tanks. The fuel injection system would draw fuel from the selected main tank at the rate of about double the normal cruise fuel flow, and return the excess to that same tank. But if you were running on the aux tanks -- left and right aux tanks fed simultaneously -- the excess was sent back to the left main (it was weird watching the left main fuel gauge go up in flight!). Fuel in the aux tanks could not be used for takeoff or landing. Therefore, for every minute I didn't use available fuel from the aux tanks, two minutes of fuel remained unusable for landing. So I wanted to completely drain the aux tanks and move as much fuel as possible to the mains where I could get to it if I needed it. From practice I knew that at normal cruise power, full aux tanks would go about 48 minutes before the fuel pressure needle started to twitch. 40 minutes after beginning to feed from the aux tanks I'd glue one eye to the needle, and when it started its shimmy, I switched back to one of the mains. Doing it this way there was no noticeable hesitation or sputtering from the engine.

Foolproof? No. Once the engine started to gag only about 20 minutes into using the aux tanks. On landing there was still plenty of fuel in the left aux tank. Turned out there was a bad O-ring on the left aux fuel cap, and suction on the top of the wing (and a big hello to you, Dr. Bernoulli) kept fuel from flowing through the checkvalve below a certain point.

 

[sarangan]

I never ran a tank dry, so this is just a question. Is there any chance the fuel pump sucking air might not properly resume when fuel tank is switched?

 

[Pilawt]

I never ran a tank dry, so this is just a question. Is there any chance the fuel pump sucking air might not properly resume when fuel tank is switched?

Maybe, but then the airplane would be in violation of the certification standard (CAR 3.4221(d) and/or FAR §23.955(e)).

 

[Sundancer]

A little contrarian here - I like to plan for what the burn really is, rather than an exagerrated higher number. I don't need to lie to myself, and I like to know what's really in the tanks. We have a JPI now, and it's been accurate. When traveling, I'm OK with going down to legal reserves.

 

[k9medic]

[QUOTE="TommyG, post: 2627919, member: 10334]...Also no way in hell I’m flying more than 3 hours without stopping somewhere. But even with a JPI totalizer, I still plan my 182 for 14 gal/hr. I’m always gonna land with more than I planned for. I don’t gamble with that 30 or 45 minutes reserve.[/QUOTE]


I have a saying that I have a 2 hour butt or a 2 hour bladder, whichever tells me to land first. The whole reason I bought this plane is to fly full loaded from my house to the Bahamas and then back to KFPR to clear customs.

On a no wind day, Leg 1 is about 2.5 hours. Leg 2 is about 1.5 hours. My most recent trip was 5.8 hours round trip due to winds.

 

[Hank S]

I have no need to run tanks that close to empty. Also no way in hell I’m flying more than 3 hours without stopping somewhere. But even with a JPI totalizer, I still plan my 182 for 14 gal/hr. I’m always gonna land with more than I planned for. I don’t gamble with that 30 or 45 minutes reserve.

I don't gamble with it either, by knowing how much fuel I start with and how much I burn. I've been 4:45 twice (yes, I was very happy to get out and stand up!), and had 11 gal once and 12 gal the second time. First time fuel was split between tanks, second time I ran almost to quit before switching and had 1-2 gal left in that tank. Still gave me an hour in the tank I landed on.

It's the only way to get all the range possible, with however much fuel you start with (doesn't have to be full tanks).