What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Switching Tanks Technique. How do you do it?

Vlad

Well Known Member
It looks like a very simple operation to switch fuel tanks in flight. But since Paul Dye landed his RV-3 on a road I am always thinking twice before touching that selector knob. Especially when I am flying over inhospitable terrain or on top of a layer. Would be interesting to learn how others are performing this simple operation. RVs or not, VFR or IMC, please share your technique. What's your methodology long haulers? How would you manage your fuel for 5+ hours non stop?
 
First off, I have an Andair valve, so I have very little to no worries about my valve sticking.

To answer your question, I switch them every half hour by first turning on the electric fuel pump, switching tanks, and turning the pump off.
 
I switch every 30 min without the boost pump regardless of whether I'm VFR or IFR using the tank alarm function on my EFIS. I have a fuel data log I print up for my kneeborad that fill out enroute so immediately after I switch tanks I dial my fuel totalizer page on my MFD and copy down the consumption figures and manually do the math on the total remaining. I have absolute faith in my red cube which has been dead on accurate to the tenth of a gallon.
 
I just switch them (approximately) every half hour based on the timer on my Dynon. I also have the Andair valve. I then monitor the tank float gauges to make sure fuel is actually coming out of the other tank (so far has worked every time:D). I try to do the swap over some sort of reasonable landing area if possible, but don't really worry about it too much. I don't bother turning on the second fuel pump.

Greg
 
I use the minute hand of my watch. From 00-29 minutes I'm on the right tank and from 30-59 I'm on the left.

When I get distracted it's easy to look at the watch and confirm I'm on the correct tank. Much easier than writing it down and logging the changes.
 
I switch tanks each hour and always land with at least one hour of fuel in the tanks.
 
I don't switch my tanks that regularly and don't see a big problem with med size fuel differences in my tanks. I never switch tanks unless I'm somewhere I'm ok with loosing a motor. It's a risk. Everytime.
 
30 minutes at the first switch; every hour after that. If I'm looking to land at VFR minimums I'll run one tank dry, then land with all remaining fuel in one tank.

I try to make sure the switch happens near an airport or at least a safe place to land. Because I generally expect the handle to come off in my hand every time, I'll really avoid making ANY configuration changes over hostile territory.
 
Last edited:
I believe that switch tanks as few times as necessary reduces risk....

So I fly the first 30 minutes (including takeoff and climb) on one tank (doesn't matter which).
After switching to the second tank, I use it for one hour (the first 30 minutes on the second tank brings them back to being approx even in fuel level... the second 30 minutes makes the second tank go lower by 30 minutes).

I then make each tank switch at 1 hr intervals after that....
The fuel imbalance is then never more than 4-5 gallons (30 minutes of fuel burn), and a typical cross country leg will usually only require three switches at the most... sometimes only two.

I make exceptions to this based on the availability of suitable forced landing sites... I only switch if a have a decent forced landing site available (preferably a runway, paved road, dry lake bed, etc.)
Not following an exact time pattern doesn't matter to me because I keep notes of how many minutes I burn on each tank.

BTW I think there is some level of inherent risk regardless of what brand fuel valve you have..... anything can break.... and it will always happen at the most inopportune time.
 
I believe that switch tanks as few times as necessary reduces risk....

So I fly the first 30 minutes (including takeoff and climb) on one tank (doesn't matter which).
After switching to the second tank, I use it for one hour (the first 30 minutes on the second tank brings them back to being approx even in fuel level... the second 30 minutes makes the second tank go lower by 30 minutes).

I then make each tank switch at 1 hr intervals after that....
The fuel imbalance is then never more than 4-5 gallons (30 minutes of fuel burn), and a typical cross country leg will usually only require three switches at the most... sometimes only two.

I make exceptions to this based on the availability of suitable forced landing sites... I only switch if a have a decent forced landing site available (preferably a runway, paved road, dry lake bed, etc.)
Not following an exact time pattern doesn't matter to me because I keep notes of how many minutes I burn on each tank.

BTW I think there is some level of inherent risk regardless of what brand fuel valve you have..... anything can break.... and it will always happen at the most inopportune time.

When flying an RV other than the 12 I use this same procedure.
 
Start, taxi and takeoff on the fullest tank. I won't change to the other tank just prior to takeoff as I think it's important to sample the fuel for a period of time prior to takeoff. After that, using the Dynon timer each 30 minutes, electric fuel pump on, switch tanks, reset Dynon timer, fuel pump off and monitor fuel pressure and usage. Modify the switch when flying over less than desirable terrain. The last switch to the fullest tank should occur several minutes prior to top of decent.
 
Depends

For me when I feel my Depends are wet..switch; then when they are sticky...switch again.

OK...lame attempt at humor.

When alone I do 1 hour on the right for balance. After that I do the "top" and "bottom" half of the hours top = right.
 
Startup and taxi out on one tank; runup and takeoff on the other. Thereafter, switch tanks every 5 gallons per the Dynon Skyview message. When doing so, boost pump on and watch for slight pressure rise for 5-10 seconds, switch tanks, do nothing for 10 seconds or so while watching fuel pressure, then boost pump off and monitor pressure for another 5-10 seconds.

Andair fuel valve and boost pump; not worried about the valve sticking, either.

Always anticipating a failure, the procedure in case of a sustained loss of fuel pressure or flow would be boost pump on, mixture full rich, switch tanks.
 
Switching tanks with Andair

My process is to takeoff on left tank, get to altitude, then fly 30 min. Then I switch to right tank till I get close to destination then I switch back to left tank for landing. Boost pump always on when switching. If the destination is longer, I will run the right tank dry or almost dry, then switch to left tank for remainder of leg. Its kinda spooky seeing the fan stop but there is a little comfort in knowing that you got all the fuel you could out of that right tank.
cj
 
I do every thirty minute or so, but I will try to be over a runway or close by when I do it.

Bob burns
Rv-4 n82rb
 
+1
I do the same.

First off, I have an Andair valve, so I have very little to no worries about my valve sticking.

To answer your question, I switch them every half hour by first turning on the electric fuel pump, switching tanks, and turning the pump off.
 
Start, taxi and takeoff on the fullest tank. I won't change to the other tank just prior to takeoff as I think it's important to sample the fuel for a period of time prior to takeoff. After that, using the Dynon timer each 30 minutes, electric fuel pump on, switch tanks, reset Dynon timer, fuel pump off and monitor fuel pressure and usage. Modify the switch when flying over less than desirable terrain. The last switch to the fullest tank should occur several minutes prior to top of decent.

Same process for me. After two hours of continuous flight, I have to get out and walk around some and usually top the tanks off when doing so.
 
Well I guess I do it a bit differently...when on shorter than hour or so flights, I just fly there on one tank and land and use the other tank for the return flight. On longer cross country flights I burn 10 gallons at a time and then switch, but I've usually filled my tip tanks to some level before the longer flights.

Is the process of using timing rather than consumption a hold over from the days when we didn't really have a direct way of accurately measuring consumption other than via the proxy of time?
 
Is the process of using timing rather than consumption a hold over from the days when we didn't really have a direct way of accurately measuring consumption other than via the proxy of time?

Probably YES I'm thinking. And since I did my primary in Cherokee it's drilled into my brain and double riveted. Lisa says "where's BOTH?" and I tell her that's on the high wing she's training in.
 
Skyvew can provide "change fuel tank" messages based on fuel used since start up, which is what really matters for fuel balance. I have mine set for 5 gal on my -6A. Works great.
 
We put a vapor return line on ours which returns some fuel to the left tank.

So when using the right tank, some fuel is going back to the left. With full tanks I always plan to start on the left.

To switch the fewest times, 45 minutes or an hour on the left, depending on my trip length of course. Then one hour, or even 1:15 on the right. Then back to the left for landing. I always switch at altitude over safe as possible terrain. I do not feel that it gets too badly out of balance. Fuel pump always on to switch.

Land on the fullest tank. I always take off on the same tank I last landed on unless I am doing an extended run up or taxi. I would never make a habit of changing tanks on the ground right before takeoff. Every time I even have the thought I slap my hand a couple of times. If it doesn't switch right for some reason then you get to find out at low altitude.

I do not have glass, or digital fuel flow, so I use a kitchen timer, pen, and paper
 
I've had fuel flow in my -6 since it was first built in 1993. Back then, virtually no one had fuel flow except the "big boys".

I have always switched tanks every 5 gallons. I start on the left tank after fill-up. My EI fuel flow reminds me when to switch.

In addition, I have the H-W Aviation ER tanks. When using them, I start out on left tank for 5 gallons, switch to right tank for 5 gallons, switch to left tank and turn on transfer pumps for 18 minutes (by D10A timer). This does not alter my 5 gallon per side rule.
 
Last edited:
Since there are many variations in our fuel systems, what works for one may not be good for another. For any longer trips, you should have planned out what works in your airplane while on the ground. Then do that every long trip. Be consistent. Write down gallons used or time and update next switch. Doing the same thing over and over will help eliminate confusion as to where your fuel is and if there is enough.
Short trips, depart on the most full tank, arrive on the most full tank.
Switch tanks with the fuel pump on because that's what the instructions say:D
 
No set schedule

In the summer I tend to run autogas (no ethanol) in the left tank and 100LL in the right, I take off and land on the right tank to use the 100LL and cruise on the left. Landing on the right clears all the autogas out of the lines etc so no gumming up issues if the RV sits parked for a while. Use 100LL in the winter but generally fewer long distance flights.

I switch to the left when at cruise altitude and switch back to the right when entering the pattern at the destination airport (can make the runway if there is a problem).

Tanks do get somewhat unbalanced on a long X country but nothing that the trim or A/P cannot handle.

I chose the right tank for the 100LL as most patterns are left so no chance to unport the pickup even on low fuel.

Interested in what other people do who use a mix of mogas and 100LL do.
 
My procedure is to start and taxi on the lowest tank, and switch to fullest for run-up and takeoff. After that, switch every half hour.
 
Switching Tanks

I have a somewhat different procedure for switching tanks, especially on long cross country flights.

1. Generally try to minimize number of times I activate the fuel selector . Admittedly somewhat paranoid, but stuff wears out eventually.
2. Know - really know - how much fuel I have left. Err on having slightly more in the tanks than indicated. My red cube is calibrated tightly - 36 gallons pumped into the tanks usually shows 36.5 gal used on my AFS 4500. My float indicators aren't that accurate - but I know and understand those inaccuracies.
3. If I'm going to arrive at a destination with less than one hour of fuel remaining, I'll burn 20 gallons out of one of the tanks, then switch to the other. Don't want to worry about fuel management if I end up in an unplanned divert / holding situation.
4. For "normal" FACIT ("Fool" Around And Call It Training) flights I switch at 10 gallons used.
 
Couple of posters say they switch just before take off.

That's a very bad idea. Particularly if you've just added fuel.

I discovered two MINUTES at cruise power settings is required to consume fuel downstream of the valve in a -7 before fuel from a newly selected tank reaches the engine. At the trickle rate of consumption prior to take-off you may choose a tank with problem fuel that won't show up until you're a few feet off the ground.

Before start-up, select the tank you're going to use for the first 30 minutes of flight then don't mess with it until you're within a short distance of a suitable landing area. Thereafter, I keep a simple log on a scrap of paper showing the time and which tank when I switch on the quarter hours.

John Siebold
 
Engine out on take off.

Couple of posters say they switch just before take off.

That's a very bad idea. Particularly if you've just added fuel.

I discovered two MINUTES at cruise power settings is required to consume fuel downstream of the valve in a -7 before fuel from a newly selected tank reaches the engine. At the trickle rate of consumption prior to take-off you may choose a tank with problem fuel that won't show up until you're a few feet off the ground.

Before start-up, select the tank you're going to use for the first 30 minutes of flight then don't mess with it until you're within a short distance of a suitable landing area. Thereafter, I keep a simple log on a scrap of paper showing the time and which tank when I switch on the quarter hours.

John Siebold


It is also bad if the off position is selected by accident. :eek:

Some selector valves are quite easy to select off by accident. Especially if you fly multiple aircraft on the same day. Ask me how I know. Use a timer to see how long you can taxi around after the fuel valve is selected off. Just enough time for a run up and take off.

I personally do not touch any fuel valve before take off. Other than to make sure it is ON. I just make certain the tank selected has adequate fuel for the flight, with no water in the fuel.
 
Last edited:
In the summer I tend to run autogas (no ethanol) in the left tank and 100LL in the right, I take off and land on the right tank to use the 100LL and cruise on the left. Landing on the right clears all the autogas out of the lines etc so no gumming up issues if the RV sits parked for a while. Use 100LL in the winter but generally fewer long distance flights.

I switch to the left when at cruise altitude and switch back to the right when entering the pattern at the destination airport (can make the runway if there is a problem).

This is exactly what I do when on local flights. On XC I have the Skyview set at 8 gallons to notify me to switch tanks (5 was too frequent) and use 100LL in both tanks.
 
I chose the right tank for the 100LL as most patterns are left so no chance to unport the pickup even on low fuel.

If you fly coordinated turns the fuel will not unport on right turns, either. However, you might consider slips - like in a crosswind landing - in choosing which tank to use.
 
Some selector valves are quite easy to select off by accident.

This is one of those times when experimentals are well advised to do things the certified world does:

FAR 23.995
g) Fuel tank selector valves must?
(1) Require a separate and distinct action to place the selector in the ?OFF? position; and
(2) Have the tank selector positions located in such a manner that it is impossible for the selector to pass through the ?OFF? position when changing from one tank to another.

E.g., the Andair valves require lifting up on a central knob while simultaneously turning the valve...an action that cannot be done accidentally.
 
I switch every 30 minutes based on the reminder from GRT without turning the boost pump. If I am very close within 10 minutes of landing and the timer goes off, I will ignore it and will not switch.

For long trips, I follow the above procedure only will try to keep one tank a bit fuller than the other, so I may skip one time switching. As I get closer to my destination, I will switch to the tank that is a bit fuller. Also I will keep in mind left or right pattern so I am on the tank that the opposite side of my turn in the pattern in hopes of not to suck air if the fuel rushes to the other side of the tank in a sharp turn in the pattern. But generally I will avoid getting so low on the fuel. I believe my longest leg was just shy of 5 hours and when I landed I still had 11G (I added about 31G of fuel)
 
Tank Switching

If taking off with full fuel I fly 45 min on first tank and switch about every hour after that with interval adjusted so tank switch happens in gliding range of a airport or suitable landing spot. I flight plan to have last tank switch at top of descent. I really avoid switching tanks before takeoff or a low altitude. After landing I switch to tank that will be used on next takeoff and set takeoff trim at the same time.

Don B

RV 9 rebuild in progress
 
Couple of posters say they switch just before take off.

That's a very bad idea. Particularly if you've just added fuel.

I discovered two MINUTES at cruise power settings is required to consume fuel downstream of the valve in a -7 before fuel from a newly selected tank reaches the engine. At the trickle rate of consumption prior to take-off you may choose a tank with problem fuel that won't show up until you're a few feet off the ground.

Before start-up, select the tank you're going to use for the first 30 minutes of flight then don't mess with it until you're within a short distance of a suitable landing area. Thereafter, I keep a simple log on a scrap of paper showing the time and which tank when I switch on the quarter hours.

John Siebold

This is an interesting discussion. A couple of centuries ago, during my primary and instrument training, I was taught by several instructors and check pilots to start up and taxi out on one take, then switch to the other tank and do the run-up and take-off, thus ensuring good fuel flow on *both* tanks.

I can see the logic of not switching until after take-off, I guess...although it might be disconcerting to find out *in flight* that you can't get fuel from one tank. Out of curiousity, who does which method here? (N.B., I'm not likely to change what I've been doing for all these years, but just curious about the thinking).
 
When I'm flying certificated planes I taxi on the lower tank, switch to the fuller tank before runup and leave it there until the first switch (bottom of the hour)

For high wings I start up on left, switch to right while taxiing, and then go both before the runup and then I don't touch it again.

This thread has me questioning... are there fuel selector valves out there I should be avoiding (and making sure I don't already have installed)
 
Andair valve is different

The Andair valve is different in two cases:

1. as allready mentioned by RV7A Flyer
E.g., the Andair valves require lifting up on a central knob while simultaneously turning the valve...an action that cannot be done accidentally.

2. If you switch from LEFT to RIGHT: In the beginning of valve rotation, it opens the canel to the right tank. Then for a part of rotation, both tanks are feeding, then in the last moment of rotation, it closes the left and only the right is feeding.

So, if you are not absolutley dry on one tank, there should not happen anything bad, if you would rip of the handle or the shaft brake away. Which would be very very unlikely. The andair valves are so smooth. If it is going strong, as on many GA planes, you should investigate to find out why and maybe replace them, before something bad happen.

But if you are using the original, Vans brass vauchet, then it is a really different animal .... thats the reason Andair is selling so much of there valves! Paul got the lesson and had quit a bit of luck on his side. Veri kind he shared his experiance with us.
 
So, if you are not absolutley dry on one tank, there should not happen anything bad, if you would rip of the handle or the shaft brake away.

This is only true to a point.... Once one of the tanks ran dry the fuel pump would likely start sucking air into the system through the empty tank (that is why we do not use a fuel selector with a both position on a low wing airplane).
 
Paul got the lesson and had quit a bit of luck on his side. Veri kind he shared his experiance with us.

Always happy to share our "Lessons Learned" Dominik!

In this case, the lesson was not really about fuel valves - it was that we never rely on "Luck" - we rely on preparation so that WHEN a failure happens, it is no big deal. We had a good landing site under us for a reason and we used it when we needed it.



Oh, to the point of this thread- since we now live in a mountainous part of the country, I always take a look around before switching tanks - and if I can put myself in a better position with regards to a landing opportunity by delaying a switch, I do so. Why not set yourself up for an easy emergency case when you can?
Paul
 
Last edited:
In my 6, when taking off with both tanks full, since I'm most often solo I take off on the left tank and run for 15 minutes and begin switching tanks every 30 minutes thereafter. The takeoff and climb to cruise altitude burns fuel faster than level cruise and my technique helps to lessen having a heavy wing due to fuel level imbalance. I've been doing the same thing since the days of flying my old Cherokee 140 which had no autopilot to artificially keep the wings level for me :)

I always turn on the electric pump when switching tanks... and keep an eye on the fuel pressure gauge too, just like I did in the Cherokee. Old habits are hard to change.
 
I use a similar 1/2 hour for take off, followed by 1 hour switches to minimize the frequency of tank switches. This keeps the plane in reasonable balance, and minimizes the small risk of valve failure while switching. I don't use the auxiliary fuel pump if I have lots of altitude.

As part of testing, I purposely ran each tank dry while 5000' over the airport (separate flights) to check fuel gauge calibration and re-start performance. In level flight, my plane takes about 8 long seconds to recover from fuel starvation without using the auxillery pump, and about 3 seconds to recover with the pump. I can cruise about 8 minutes after the calibrated EFIS gauges read zero before it gets quiet, HOWEVER, I can starve the engine with 5 gallons in a slip. As a result, I like to keep a minimum of 10 gallons in my left (primary) tank for landing, and let my right tank run to the onset of starvation before the last enroute switch.

I run premium Mogas in my right tank, and avgas in the left, which is why I consider the left tank my "primary". Both tanks work the same, but I can get vapor lock on Mogas on warm days if the auxillery pump is not running. When away from home I run straight avgas, which lets me test the left tank to the onset of starvation. (Full starvation occurs several seconds after the onset)

I would encourage you to test each of your tanks to starvation under controlled conditions. The knowledge lets you make longer legs with peace of mind, may prevent an uneccesary precautionary landing, and avoids the dangerous situation of landing with two low tanks. I dont use this procedure to shave my fuel reserve, it just ensures I have a truly usable reserve when I land.
Jay
 
As part of testing, I purposely ran each tank dry while 5000' over the airport (separate flights) to check fuel gauge calibration and re-start performance. In level flight, my plane takes about 8 long seconds to recover from fuel starvation without using the auxillery pump, and about 3 seconds to recover with the pump.

Not to necessarily disagree with anything you said, but what part of this portion of your testing required you to do it in flight? Couldn't you have determined the same thing on the ground?
 
I start and taxi on one tank, then change tanks and do run ups and takeoff on the other. I stay on that second tank for 30 mins and switch, then I switch every 60 mins after that.

I have an EI fuel flow meter which flashes a blinking light at me as a reminder every half hour. If I've missed a change and actually need the reminder, I either have a good reason (e.g., unlandable terrain -- do it later) or I chide myself for my lack of discipline.

The actual change: Boost pump on, wait for pressure to increase, switch, count to ten, boost pump off, observe pressure reduce and stabilise. if anything bad happens, I'll switch back and full rich. Hasn't yet.

Andair valve.

I'm intimately aware of how long an aircraft can run on the fuel in the lines and carb bowl. Many years ago, I was in a Glasflugel Libelle, taking the first glider launch after the tow plane had refueled. The tow pilot's routine was to switch the fuel off during shutdown; for some reason he didn't turn it on again for start up.

He had enough fuel in the system to start, taxi from the fuel bunker to my glider, idle while I was being hooked on, and then run at takeoff power for JUST long enough for the glider to become "light" on its wheel... then the engine stopped, and the tug behaved roughly the way a car behaves when the driver jams on the handbrake, while I was 50 metres behind at 30knots with insufficient weight on the wheel for the brake to work.

Somehow I reacted quickly enough to hit full forward stick, full right rudder, and full right aileron while I was pulling the release handle, and initiated a ground loop to avoid ramming the back of the Pawnee. Skidded to a stop sideways about fifty feet starboard of the tow plane, in line with its cockpit.

I think the tow plane ran for over three minutes with the fuel off. Pretty sure I'd have broken both of my legs if my reactions had been just a split second slower.

- mark
 
Huge fuel imbalance flew fine

During phase 1 I flew one tank empty and the other near full with no problem It was a limited maneuvering flight but flew straight with enough trim. Not recommending it, but know that vans design is strong.
 
Not to necessarily disagree with anything you said, but what part of this portion of your testing required you to do it in flight? Couldn't you have determined the same thing on the ground?

In-flight restart is going to be completely different from an on-ground restart, this was a valid test point, at least in my opinion.
 
Other Considerations

I fly an RV4, generally agree with most comments but have a couple other considerations that I did not see mentioned.

First the aerobatic flop tube. Have one in the left tank, not in the right. Noticed a report of the flop tube hanging up on one individual who ran out of gas with some 3 gallons left in the flop tube tank. Consequently, whenever I'm pushing the fuel on a cross country I run the flop tube tank dry and continue with the right tank. (where I could dump it in somewhere) Even if the flop tube doesn't hang up, it might crack with age and be a problem.

Secondly, I use a 30 minute interval on the switch over. I don't have aileron trim, and the 30 minute interval is enough to let the wing with more fuel in it get heavy enough for me to notice.

Bye the Bye, I have changed out the Van's fuel valve once already - after awhile, when I'd wiggle the old fuel lever a few drops of fuel would appear around the top. Could probably have replaced the packing but easier to just replace.
 
I fly an RV4, generally agree with most comments but have a couple other considerations that I did not see mentioned.

First the aerobatic flop tube. Have one in the left tank, not in the right. Noticed a report of the flop tube hanging up on one individual who ran out of gas with some 3 gallons left in the flop tube tank. Consequently, whenever I'm pushing the fuel on a cross country I run the flop tube tank dry and continue with the right tank. (where I could dump it in somewhere) Even if the flop tube doesn't hang up, it might crack with age and be a problem...

Fuel level/flop tube uncertainty was the primary reason that I would run the aerobatic tank dry first on cross country flights with the Hiperbipe. Despite the highly reliable sight tube fuel level indicators, one could never really tell how much time I could get out of that tank. OTOH, the main tank was a hopper style with a bottom feed and would use every drop.
 
Back
Top