Fuel Management - Reserve in one tank or two ?

blimpy

blimpy

New member
Back ground:

1 Half of general aviation accidents and off field landings are due to running out of gas.

2. After more than 100 hours of dual flight instruction, I have basically zip background in Right/Left
fuel tank management.

I admit I grew up with no more fuel management required than an on/off valve, an oscillating mechanical float guage strategically aimed at the back of my head, and a pocket watch ( Luscombe with single tank).

In the Cessnas I got licensed in the selector got set to both, the watch got strapped to my wrist,
and I did the calcs usuing the POH. But R/L why bother ?

Now I am in the world of low wing airplanes ( cruisaire) where R/L management is mandatory.

Planning for 8.5 gph keeps me on the safe side for local flying calcs.

BUT....using a conservative 1 Hour reserve figure ( 8-10 gallons) the big question is

Where to keep it ?

All in one tank... or split between two ??

I sure dont feel comfortable with the idea of flying a landing pattern and maybe going around
on the bitter end of the fuel burn and only having ~ 4 gallons in the selected tank. (Also it's damn hard to be sure you have 4 gallons and not 3 or 6 without a dip stick... which I havent mastered in-flight.

I think the tank connections are on the inboard end of the tanks... picture where the fuel goes in the tank in turns if you are using the wing low tank.

Despite being told that " all the fuel is usable" in my bellanca ... I dont believe in the tooth fairy.

Splitting the reserve amount in two seems to double the amount ( what ever it might be) that is
not usable . That is inevitable.. while the "maybe one tank will fail" argument is
possible, the thing to makes that kind of failure likely is sucking the tank down to fumes and lurking crud.

So, I'm opting for almost all my reserve fuel eggs in one tank.. unless there are reasons otherwise. ??

---

All this begs the usual old questions about fuel management

When to change tanks ? Back and forth to balance the load side to side ??
Use all you can safely take from one tank, and then move on the other ??
Some combination of both.

With my single count up timer... it is easier to use one tank for
a set length of time ( leaving the reserve) then start on the other tank with a zeroed counter. Low work load, and visible reminder with no math. Hour and a half on the Left side, then change tanks.

Reset the timer. Fly another Hour and a Half... and it's probably time to land anyway.
If you have a brain fart and forget or actaully need to go two full hours you can ( 17 gallons) it's ok.

You've got that nice fat hour reserve waiting where you left it in the Left tank, and still a few gallons
in the right ( that half hour you didnt want to count on)... as the reserve-reserve.

What am I missing ?

( all this assumes gas guages are useless, they lie, cheat, and steal )

Comments ?
 
Good discussion, I like the idea of landing with all reserves in the tank I'm using at landing. My thought process is if you plan on landing on a long x-c with 8 gallons reserve, but make a 4 gallon planning error, if all your fuel is in one tank, your engine will run. If the tank selected is where that error is and you meant to have the 4 gallons in each tank, stuff gets more iffy. Since we're prone to error, I'd rather have a plan that allows for it.

It will be interesting to see the take other members have.
 
I would agree with Glen. If you were to keep the reserves in both tanks, then you would have to completely run out in the first tank to get the full amount of reserve before switching to the other tank.
 
I think Glenn's idea is correct. I fly for one hour on a main tank, then switch to aux or the other main. Use what it takes from the other tank(s) to get to your destination. Your first tank is always your reserve.
Dan
 
Another thought, when doing a long trip, I found I can burn most un-useable fuel out of a main tank in cruise. This has the effect of increasing your useable fuel in the remaining tank when you get to destination. I don't recommend running a tank dry, or landing with less than an hour reserve, but it is still good to stack the deck in your favor.
 
My take: I want ALL my reserve fuel in one tank and I NEED to know which tank.
Read NTSB reports for fuel starvation (different than fuel exhaustion) for post 68 (I think ) to pre mid-73 Vikings (7 tanks, 2 levers, 1 fuel gage) and you'll know what I mean.
More about this below...

I TOTALLY agree that fuel gauges are DECORATION, but they HAVE to be included in your fuel management strategy as a whole as you gain experience with a particular aircraft.
First time you fly it you watch (NOT trust!) how the fuel gages behave.
Repeat as necessary until you learn their behavior pattern for every step of the trip.
The day that the pattern changes is the day that you land and check for a fuel leak.

The blueprint for your fuel management is a long XC flight started with full tanks, and all other variations of fuel management are a direct consequence of how you manage this case.
The important thing is: YOU ALWAYS KNOW HOW MUCH FUEL YOU STARTED WITH AND WHERE YOU HAVE IT.
If you are unsure, do a gross misrepresentation of the fuel 'you have' and ALWAYS assume that you have less fuel than what you see.
And I stress here: the fuel that YOU HAVE is the fuel that YOU SEE.

I had an almost-checkride-ready student in Alaska (whom I was going to give the final brush up) to go preflight and brief me about the fuel situation.
The kid came back and merrily told me: 'we have full tanks! :)'
And how do you know?
And he said: 'I flipped the master ON and looked at the gauges'!
I felt like someone just gave me a back-rub massage with an ice cream and seriously wondered about the quality of his instruction (and instructors).
Please REMEMBER: you ONLY have the fuel that you SEE!

Post mid-73 SV have 3 'virtual' tanks. Virtual because Bellanca piped the old thanks together, made it a single point refueling system and made it look 'like one tank'. That brewed up a different problem. You have to refuel a SV in 'stages'. Once it is full, you wait.
And wait.
And wait some more...
Then you look.
Half of your fuel is gone because it went to fill the 'other parts' of the 'virtual tank'.
That created the problem of pilots asking the 'line boy' (<sarcasm>surely an expert aviator</sarcasm>) to 'top off the tanks' unsupervised.
And they did.
Or they thought they did...
And the pilot never bothered to recheck because he didn't know how much fuel he needed to begin with.
Then went flying on what he thought was a full tank...

Which brings me to another tidbit of advice:
1.- ALWAYS refuel (or at least supervise it) your own airplane.
2.- ALWAYS declare beforehand how many gallons you will take up on every tank.
You'll know if you were right...
I was always within a gallon in my Viking tanks.
That meant that I knew within 5 minutes when I was about to run out of gas.
And I 'un-proudly' put it once to the test and landed with half a gallon IN ALL TANKS!
One of those (shameful) stories along the lines of: why refuel here if I *KNOW* that I can make it there.

Finally (so I can put the soapbox away), here is how I did fuel management in my Super Viking and how I extrapolated it to the my 'new' Crusair:
SV: 13 Gal/hr, 3 tanks: Left (30 usable), Aux (15 all) and right (30 Usable).
Rule to respect: Do not switch tanks over an empty tank.
What that means is: I had to go 'over' the left tank to switch from aux to right (or vice-versa). So I ALWAYS kept fuel in the left tank for as long as there were fuel in the aux and the right.
With that said:
I started my flight on the left tank and taxied, climbed and flew the first whole hour. I assumed that as a customary 15 gals burned, which left me with 15 gals (1+ hour plus unusable) sitting in my left tank. Then I switched to the right tank an flew 1 hour. Then I switched to the aux tank and ran it dry (that's another topic). Then I switched to the left tank and ran it dry. Whatever time the left tank gave me was what I assumed I had left in the right tank (regularly some 1.3-1.4 hours) and I knew that I was landing within the next half-an-hour (assuming VFR, I didn't run tanks dry IFR and I was more conservative)

I have flown my Crusair twice across the continent in the 5 months I've owned it (gearing up to fly North now). My Crusair has 2 20-gallons tanks and I have not yet ran it dry. When a Continental equipped SV quits because you run a tank dry, you depend solely on the electrical fuel pump to restart it. The engine doesn't quit if you do it 'right', but there are not guaranties. I have read that the Crusair pumps air into the fuel lines when you run a tank dry, and that may make the restarting pretty exciting (again, read NTSB reports). I'm planning to climb some 10000 ft over KTHA (uncontrolled, 'un-busy', 3 fighter-jet runways to choose from) and run a tank dry to see what happens. I'll report the outcome.

So this is what I've been doing:
20 gallons at 8.5 Gal/hr (its really more like 8.3 Gal/hr, but fudge against it) is about an hour and 20 minutes of fuel.
So I taxi, TO and climb on the left and fly an hour and 20 minutes.
Switch to right and fly for another hour and 20 minutes.
Switch to left and fly an hour.
Switch to right and I know that the left tank is gone, my fuel is on the right, and I have to be on the ground within 20 minutes (preferably less).

If you know how much fuel you started with, and where it was (assuming that you time your flight and know your rate consumption), you'll always know what tank to switch to when you say 'landing gear down'.
YMMV...

PS: And yes, the kid mentioned above had serious deficiencies in his training.
Bad thing in Alaska... :-(
 
Keep in mind if you are making a coordinated turn the fuel will not migrate to the outboard of the fuel tank of the low wing. If the ball is centered on the inclinometer then the fuel (and everything in the airplane for that matter) will have no tendency to favor either side of the airplane.
 
Mine is a variation of most.
Taxi and take off on left tank. If someone REAL heavy is in the right seat I start off on the right and all the info below is switched to mean the opposite tank but for simplicity I will just refer to starting on the left.

Fly for :45 min on the left tank. Then fly for 2:20 on the right tank...or 'till empty if there is good landing spots under me. Then switch back to the left for the remainder of the flight.

I have flown to empty a tank...they do take 20 gal on refill. Only had a sphincter tightener once when I mistook the fuel shut off for the tank selector...stupid me, but that is a WONDERFUL example of piss poor human engineering. For those not familiar with the Cruisair's fuel valves, the tank selector is directly above the shut off. Neither is easily visible in flight, unless you almost stick your head up your a... They feel exactly the same, the difference is you turn the tank selector to the up position to feed on the right tank, and turn the shut off to the right to turn off the fuel...so when switching to the RIGHT tank, you want to remember to turn the TOP valve to the up position, otherwise if you turn the bottom valve to the right, it remains silent in the plane for WAY TOO LONG, until you figure our that you inserted your head into a dark body orifice!

To momentarily digress...I don't know how much unusable fuel is aboard, but since I have verified that I refilled them with 20 gal after running one dry (on different flight of course) I have just deducted 40 gal or 240 lbs from my W&B when I have calculated W&B after weighing with full tanks. BTW, I have made a calibrated dip stick for my tanks out of clear plastic tubing.

Back to fuel management - fly for an :45 on the left tank, switch tanks to the right tank and fly until empty or almost empty, and fly the rest of the flight with the left tank, assuming I have one hr less than it took to (almost) empty the right tank. I actually use 45 minutes, but assume I lost an additional 15 minutes in ground time and climb at full power. My fuel burn at altitude (6000-8000) is ~8.3-8.5 gph at 2550 rpm.

I almost always land with 8-10 gals left on a cross country, though there was one flight I'd didn't. Flew it way too long. No longer have the bladder for that though...I know - TMI. Sorry.

Boy, this thread has gotten the longest answers! Larry
 
I put new senders, gauge, and 3 position switch in the crate the gauge reads within a gallon so it is trusting. STILL you have to be careful to switch the tank and the gauge to read the same. Bellanca did a crap job on fuel and it continued in the Viking. Nothing gets your heart racing like an engine sputter >>>> BTDT. Lynn the crate :!:
 
Thanks everybody !

It's good to know my thinking runs in parallel with experienced hands.

When i first got the bird in September I made and calibrated a dip stick ( wooden paint stiring stick).
It is calibrated in 5 gallon intervals and I use it every time I fly or fuel up.

The longest term owner of N74360 used the log books as trip log books also, and recorded the same
8.3 to 8.5 gph fuel use. In the "training mode" I've been in ( thanks to the Ins Co.) it has been using considerably less.

It will be interesting to do some real "block to block" measurements now that I can cruise the cruisair.
 
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