feedpro wrote:"running a tank dry" did me in.

Interesting, we have had this same discussion on a Beechlist. What was the general feeling on this?

I ran both tanks and do not recomend it.

Tim

On a long trip when I really want to know exactly how much fuel I have left, I burn one hour out of one tank, then run the other tank dry. After subtracting the hour, I know exactly how much time I have left. I am an old, long time pilot and this comes from flying a Piper that does not have the ability to draw from both tanks. Plus the bouncing fuel gages just added gray hair. I didn't have the accurate fuel flow computers we have now. In the many dozen times that I have run a tank dry, I never had a problem, outside of waking my wife. I highly recommend it for really long cross country flights. I have done it and will continue to do it. End of discussion. I will not respond to those who do not agree, thus keeping things happy here. This is the same type of discussion as "lean of peak" discussions. There are those who will and those who wouldn't and that is fine.

That's the same attitude we have over on the Beech list. 95% of the guys have no problem running a tank dry. The other 5% are horrified.

feedpro wrote:I am an old, long time pilot

Bonanza Man wrote:The other 5% are horrified.

I'm a young(er) short time pilot, and I'll admit it horrifies me. Not running one tank dry so much as using that method for a estimate of fuel endurance. Do you guys dip your tanks? Or just fill up and go?

I rarely see people dipping tanks at the airport, yet in my 170 I rarely ran full, trying to eek a little more performance out of it. I had a calibrated dowel with 5 gallon ticks on it that I used to check the level of each tank, and they were often different even though I ran the fuel selector on BOTH.

I'm not arguing so much as trying to understand if I'm missing something with this running a tank dry business. Run one hour on LEFT, then run RIGHT dry, and you can assume that you have Endurance of RIGHT tank minus 1 hour? Doesn't that assume that you started full, or with known equal quantities in each tank?

If you're going to truly know the capacity of your fuel tanks, you have to run them dry while in level flight to see how many gallons it takes to fill them.

Unless I'm just out for a short hop, I take off one one tank, run for about 15 minutes just to make sure that tank is feeding OK, then switch tanks over "hospitable" territory, and run the other tank for an hour. That way I know the fuel selector works, and both tanks feed properly while still close to home. Then it's managing fuel based on trip length and how heavy a wing I feel like holding up with aileron.

More engines, more tanks, I do more of the same. I rode a buddy's Cub to the ground south of Barrow one time (as a passenger) when the fuel selector broke, and he couldn't switch tanks. No biggie, but could have been avoided easy enough.

Gump

I run a tank out quite often expecially in the cubs on long trips. the problem is it always takes longer than i expect so in the mean time my ADD kicks in and it comes as a complete shock when the engine quits.

Zane wrote:I'm a young(er) short time pilot, and I'll admit it horrifies me. Not running one tank dry so much as using that method for a estimate of fuel endurance. Do you guys dip your tanks? Or just fill up and go?

Can't dip tanks in the Bo. I can have 20 gallons in each of my 40 gallon tanks and never see a drop due to the shape of the tank and wing dihedral. Unlike in the 182 where you could measure even 5 gallons. I made my own dipstick for the 182 but not for the Bo. I have a tab sticking down that shows 30 and 35 gallons. Ido have a fuel flow from Electronics Int'l and it works very well. It was .3 gallons off over about 50 gallons, never bothered to adjust it.

Bonanza Man wrote:


Can't dip tanks in the Bo. I can have 20 gallons in each of my 40 gallon tanks and never see a drop due to the shape of the tank and wing dihedral. Unlike in the 182 where you could measure even 5 gallons. I made my own dipstick for the 182 but not for the Bo. I have a tab sticking down that shows 30 and 35 gallons. Ido have a fuel flow from Electronics Int'l and it works very well. It was .3 gallons off over about 50 gallons, never bothered to adjust it.

I cant dip the Commander either I have a 730 that is never more than .5 gallon off. If you can dip then dip. Commanders are known for cross feeding while sitting so its easy to think you have more in one tank than the other. The fuel gauges are very accurate at low fuel levels, but I always look in the tanks because if it did cross-feed then there may be enough in one tank to see,

Did I mention how much I like the 730 it always seems to know how much fuel I have.

The point is I answered a question from Zane.

I don't know why anyone would be "horrified" of running a tank dry, unless they did so inadvertently.

Largely, whether you do or don't, as Gump suggested, will depend largely on two things:

Length of trip, therefore fuel required to complete

And, number and size of tanks.

When I checked out in the Beaver (an airplane with five fuel tanks, but only three of which you can run the engine directly from) I was taught to run each tank dry as I drained it. My mentor's logic: That way, you know PRECISELY how much fuel is left in that tank, and you won't be tempted to go back to that tank and squeeze a few more minutes out of it. Also, in the Beaver, there is a very effective low fuel pressure indication system, so it's pretty easy to see when you are ABOUT to run a tank dry. Wait for the pressure to start dropping, and the annunciator light to illuminate, switch tanks, pump up a little pressure, and your passengers will never know you ran out of fuel.

On the other hand, consider the Cessna 170, with two fuel tanks and a right/left/both/off fuel selector. Most flights, I just use the EDM 700 to tell me how close I'm getting. I regularly see fuel quantities as close as .2 gallons in a fill up=close enough. On the other hand, consider that MINIMUM LEGAL fuel for that airplane is less than five gallons (30 minutes at normal cruise). Now, put three gallons of that gas in one tank, and two in the other, and things are spread pretty thin. I'd rather have all five remaining gallons in ONE tank, to prevent a tank from unporting.

BUT, I don't believe in 30 minutes fuel reserve, having been very nearly dissappointed once playing that game. I got away with it then, but never again. Nowadays, ONE HOUR fuel remaining is mandatory as far as I'm concerned.

If you have an airplane with multiple tanks, and/or a right/left fuel selector, running a tank dry is not a bad idea. Again, as Gump says, KNOWING PRECISELY how long it takes to run a tank dry, and how much fuel is remaining there when the fuel gauges say ZERO is very important for any airplane I fly.

Out Top Cub has Dakota Tanks and standard Univair Cub type glass sight gauges. The tanks hold a total of 50 gallons, but according to the POH, six gallons of that is unuseable (the "benefits" of a headerless fuel system). We ran the plane (in the pattern) down to the point where the gauges read zero in both three point and flight attitudes, and the indicator balls were GONE. Landed, fueled it up, and it took 36 gallons. So, with gauges at ZERO, that airplane still has 8 gallons USEABLE fuel and 6 gallons unuseable fuel.

That's good information to have if you're working an airplane, or if you're doing a long cross country in it.

MTV

Paxs are sleeping, fuel quantity gauge is bouncing off E, your hand next to the fuel selector and eyes on the fuel flow gauge. ATC calls traffic 5 o’clock, 5 miles, opposite direction, you look because you cant just ignore him. No traffic and you readjust yourself in your seat. Start thinking “That pretty girl at the FBO was smiling at me”. Vrrrrrrump! Your hand changes tanks so fast that it surprises you. Some airplanes the engine comes back instantly while others surge until the bubbles are all gone. The plane settles down and you breathe again, look over at the paxs, and wonder if the look on their face is a reflection of yours

The thing I have always wondered my 170B is plackcarded to use bolth tanks for takeoff and landing wich is kind of pointless if one tank has been run dry. I presume this is so you have max fuel flow in case of an overshoot but like MTV I would rather have 5gal in one tank than 2.5 in each. What do you 170-172 guys do in this situation?

I went out on a hot day and did simulated go arounds at a safe altitude on each tank with the boost pump on and off and couldent make it hickup so I dont worry about it too much but I still wonder somtimes.

ccurrie wrote:The thing I have always wondered my 170B is plackcarded to use bolth tanks for takeoff and landing wich is kind of pointless if one tank has been run dry.

I am trying to figure this out also.
The guy I bought my 182TW from said if you are low on fuel have it in one tank. With only one port in the back of the tank and pitched forward for landing it can unport. But than there is the cross wind to be considered. POH says both for takeoff and landing.
Although a little unsure I have been using left or right tanks and not both. First takeoff on left tank I discover that the engine wants 20GPH and it's only getting 12GPH. New o-rings in the fuel selector fixed that.

ccurrie wrote:The thing I have always wondered my 170B is plackcarded to use bolth tanks for takeoff and landing wich is kind of pointless if one tank has been run dry. I presume this is so you have max fuel flow in case of an overshoot but like MTV I would rather have 5gal in one tank than 2.5 in each. What do you 170-172 guys do in this situation?

I went out on a hot day and did simulated go arounds at a safe altitude on each tank with the boost pump on and off and couldent make it hickup so I dont worry about it too much but I still wonder somtimes.

Simple: Don't EVER get so low on fuel that you need to worry about that.

Did you do your tests with full fuel in each tank, or minimum fuel in each tank? Very different scenarios.

The engine driven pump and the electric boost pump required on the Avcon conversions are only there because of one length of fuel line (from the fuel selector to the gascolator) that is too small in diameter to gravity feed an adequate fuel supply to an O-360. So, Avcon had to install an engine driven pump to increase the fuel pressure, and that then requires an electric back up pump. The pumps are redundant.

I know a mechanic who replaced that section of fuel line in several 180 hp 170s and 172s and removed the pumps, and got that setup field approved. Lots of expense to save a few pounds, but it works.

You won't run the engine out of fuel if the pumps are off, but it may not make full power.

The admonition to land and takeoff on both is a result of SOME folks not flying coordinated. Fly uncoordinated a while, with min fuel in a tank, and running off that one tank, and the fuel will run to the outboard end of the tank, and voila----engine failure.

But, don't EVER fly the airplane that low on fuel. Trust me, a lot of folks have wrecked perfectly good airplanes simply because they were stupid about fuel.

MTV

I'm with MTV on this one ... it seems that running a tank deliberately dry violates the notion of safety through redundancy. It's always a good idea to have a backup available for any system (except maybe your wings! ... and in a single engine aircraft, your backup to an engine failure is altitude below you, and being prepared for a dead-stick landing). Running one tank completely dry in a two-tank aircraft means you have no more fuel redundancy, and any failure of the fuel system on the remaining tank means you're in emergency landing mode.

How is that? Let's suppose you run one tank dry, then on the other tank you've been bouncing along in turbulence and suddenly a piece of crud breaks loose inside the tank (it happens) and clogs the fuel port ... now you're in emergency landing mode.

I can see the argument that if you're down to a handful of gallons of gas, splitting it between two tanks is not as good as having it all in one tank ... but as MTV pointed out, intentionally getting down to just a couple of gallons of gas in the tank is a bad idea anyway. Always land with a minumum of one hour of reserve fuel at your alternate destination - a half hour in each tank is best. If your fuel tank ports are going to uncover in the landing pattern with just a half hour fuel in them, then you need more than an hour's reserve at the end of your flight.

Aux Tank and the Cessna

Years ago when I had a Cessna 172, it had an aux 18 gallon tank in the baggage area. To use the aux tank, you had to run the right wing tank mostly down, and then you turn on the aux tank pump and let it pump for 1 hour to get the aux tank empty.

In the mornings after topping off in my level hangar, my method was to take off on “both” wing tanks, then switch to the right tank for 1 hour, then to the left tank for the next hour. After that 2nd hour, I went back to the right tank and watched the time until the engine quit. I then knew how much time was left in the left. While running on the last part of that left tank, I would pump the aux tank up to the empty right tank. After the left tank went dry, I knew I had two more hours in the right side.

One time I was 5 miles from home when everything went quite while running on that last right tank and the left had already been used up. I set up for a crash landing in trees when I thought of that empty aux tank pump. I hit the switch and in a few moments it fired up and took me home on the electric pump. Thankfully the book was wrong on the 60 minutes to empty that tank.

Last week I was climbing out to make an open water crossing after running on both tanks low low level down a river for about 30 minutes. I had 12 gallons in the left tank and 10 gallons in the right tank. I reached over and shut off the right tank and about 5 minutes later was greeted by the sound of silence. Seems there was some ice in the line on the left tank. I switched the right tank back on and hit the electric backup pump and got her fired back up after loosing only a few hundred feet of altitude. The next 45 minutes over the open water had me a little tense just waiting for that right tank to ice up too. Had I run that tank dry before switching over, things would have been a bit more expensive getting the twisted up bird helicoptered out of the trees. Not to mention the - 20 temps would have really sucked to camp in, even though I was prepared with adequate survival gear.

akavidflyer, Was that on auto gas or av gas that you got the ice?

auto gas. It was my fault for not running the gas through my Mr. Funnel, but I figured that it was -20 and any water that may have been in the 5 gallon jug would have been frozen. Lesson learned. Once again, I will be faithful to run all the gas that goes in the plane through the Mr. funnel twice. Once going into the jug, once going into the plane!