What's new
Van's Air Force

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

How Often To Switch Tanks?

D

David Paule

Well Known Member
I'm used to an airplane that runs happily on the "both" tanks selector position, so I'm building a timer for my RV-3B to remind me to change tanks every once in a while. The time won't be cockpit-adjustable, though, I'll have to program it in.

How often do you change tanks?

Thanks!

Dave
RV-3B
 
30 minutes

I change every 30 minutes, it helps keep the tanks balanced and prevent to much aileron trim usage. Timer set on the GRT EIS & EFIS incase I miss one.
 
I use the fuel used amount on the totalizer as the gauge. 5 gallons, then every ten thereafter. After all it is balancing the weight we are concerned with....
 
Used to change every 30 mins but then I learned my Andair valve can draw from both tanks when placed between R and L. Who Knew!!!
 
Initially, run one tank for 15 minutes then switch tanks every 30 minutes. That way the balance will be more equal.
 
Andirons Valve?

Jeff, do the Andair folks stand behind your conclusion to fly between L and R ??
If so, that's a big plus for Andair and I still have time to install one. I assumed what is good for Van is plenty good for me, but Andair sounds very good.
 
Caution! Will Robinson!!!

It's not a good idea to feed from both tanks on a low wing aircraft. If one tank runs low and unports the pickup, air will be introduced into the system and the fuel pump will not pump air.
 
Jeff Vaughan said:
Used to change every 30 mins but then I learned my Andair valve can draw from both tanks when placed between R and L. Who Knew!!!
Click to expand...

Hopefully you remember which tank still has fuel in it when you start sucking air on "both". Be careful and know the limitations of doing so!
 
I too was worried about remembering since I was used to a high wing. I set mine to 20 minutes but it seems I remember on my own now and the timer is just to remind me to look. I change on my own about every 15 just to keep things balanced.
 
Keeping the math simple, with a -7, I run 6 gallons, 6 gal, then swap every 5 gallons so I'm swapping on generally nice round totalizer numbers. (36/30/25/20/15/10). I manually track fuel during long cross countries, so it's just easier on the brain.
 
I switch every 5 gallons. You burn a lot more on takeoff and climb, so timed is not as accurate.
 
I set up my totalizer for 35 gallons. This gives me a 3 gal pad to start with, then I switch every 5 gals.
Starting on the left tank at 35, right tank at 30, left tank at 25..........etc.
This also is a double check for forgetting. For example if I have 23 gals remaining, I know I should be on the left tank. If I have 16 gals, I should be on the right tank.

If I have the ER tanks full, I set up 45 gals. This gives me a 2 gal pad.
5 gals out of the left tank, 5 gals out of the right tank. Then transfer ER tanks to mains and continue to switch every 5 gals.

It's much simpler than it sounds.
 
Last edited:
I fly for 30 minutes on the first tank then 1 hour thereafter. That leaves about a 4? to 5 gallon imbalance at any one time and keeps from switching tanks so often.
 
Back to the OP's question...

30 minutes here. The SkyView has a user setable tank timmer so you can set it to any value you desire.
 
Larry DeCamp said:
Jeff, do the Andair folks stand behind your conclusion to fly between L and R ??
If so, that's a big plus for Andair and I still have time to install one. I assumed what is good for Van is plenty good for me, but Andair sounds very good.
Click to expand...
Get the Andair valve but only because it is a top quality valve.
 
Jeff Vaughan said:
Used to change every 30 mins but then I learned my Andair valve can draw from both tanks when placed between R and L. Who Knew!!!
Click to expand...

I always understood a low wing aircraft should not be fed out of both tanks. If either tank goes dry you will lose all fuel flow.
 
I fly for a half hour on one tank, then switch tanks every hour afterwards. The airplane is never more than 30 minutes out of balance that way.
 
N941WR said:
30 minutes here. The SkyView has a user setable tank timmer so you can set it to any value you desire.
Click to expand...

I have a SkyView with fuel flow so I have it set up to remind me to switch every 5 gallons used. I switch at 5 gallons after take off then every 10 gallons after that. Keeps the airplane nice and balanced.

:cool:
 
GalinHdz said:
I have a SkyView with fuel flow so I have it set up to remind me to switch every 5 gallons used. I switch at 5 gallons after take off then every 10 gallons after that. Keeps the airplane nice and balanced.

:cool:
Click to expand...

Great idea. I'll give that a try.
 
I only change tanks in high cruise over an actual airport. As someone else said. It's just another chance for something to go wrong and if you plan on it going wrong it won't ever bite. Also I think it's bad to switch tanks when at low throttle settings.
 
Hi Dave,

I fly the -3 on one-hour change intervals. The IO-320 LOP at 10.5K is burning a little less than 7 gph, so that gives a little more than two hours per tank (to dry). One hour imbalance is hardly perceptible, and doesn't have me constantly changing tanks. I start on the left, go to right at an hour, back to left at an hour, and then I am looking for a place to land with the remaining hour in the right!

YMMV (literally)

Paul
 
Last edited:
Starting topped off, I too start with 30 minutes then 1 hour intervals. Not sure why folks do 30 minute intervals.... There is no difference and you use the selector less taking less risks.
 
Count the parts in an Andair valve........ Then open up the stock valve and count the parts. Then check the price.
After removing the detente plate, the valve works smooth as silk with one finger and stays where I place it. Very easy to install and maintain.

Can be rebuilt for less than 50 cents of "O" rings from your local auto parts store....... and that may not be needed for 20 years, and it does not need to be removed from the system to rebuild or inspect the inside.
 
Kyle Boatright said:
I fly for a half hour on one tank, then switch tanks every hour afterwards. The airplane is never more than 30 minutes out of balance that way.
Click to expand...

If you fly solo in a side-by-side you could make the first selection for 1 hour on the left tank, and then every 30 minutes. This would probably be better balanced for a solo flight..
 
Thanks, Everyone!

This has been helpful.

Paul, I especially appreciate your comments on the imbalance and landing in the final hour.

Thanks to all,
Dave
 
David Paule said:
I'm used to an airplane that runs happily on the "both" tanks selector position, so I'm building a timer for my RV-3B to remind me to change tanks every once in a while. The time won't be cockpit-adjustable, though, I'll have to program it in.

How often do you change tanks?

Thanks!

Dave
RV-3B
Click to expand...

Only after Lead gives me the kiss off and the tank immediately runs dry. :eek:
 
Jeff Vaughan said:
Used to change every 30 mins but then I learned my Andair valve can draw from both tanks when placed between R and L. Who Knew!!!
Click to expand...

Not a good idea, as noted by others.

Besides...why would you do this, knowing the valve was not designed for it? (Just because it might work most of the time doesn't mean it should be used that way).

This is the 2nd or 3rd time in the last few months we've seen people trying to use Left-Right fuel valves in some "middle" "both" position.

On the Andair valve, there's not even a detent in the "middle"...the valve could possibly move to one side or the other, either restricting flow or running solely on one tank while you think you're using both (thus running it dry) without you being aware of it.

Bottom line...this is NOT how to use this valve (or any similar valve) on a low-wing aircraft.
 
Switching fuel tanks

One day I was flying along thinking I was getting great fuel milage as the needle was not even moving. Yes I had the valve on the other tank and it was almost dry when I figured it out and quickly switched tanks. I was thinking that I needed to work on that heavy wing some more when it dawned on me, "Fuel"..!!!!!?????...
I'm a truck driver by trade and our fuel tanks self level by a simple line from one tank to another. So I made such a set up in my RV3 and it works great. I did however have to over come some problems. There has to be a shut off valve in that line in case a bird punches a hole in one of the fuel tanks so you won't loose all your fuel. Also the fuel line must be very close to the floor so that it will flow from one tank to another easy. To get the air out of the line so it will self siphon and level the fuel all you have to do is have one of the tanks empty and fill the other and open the valve.
Flying is sure easy when both fuel tanks have equal amounts in them.:)
 
Last edited:
I was commenting more on the (mis-)use of a fuel valve with only L and R (and OFF) in some "middle" "position" than the wisdom of connecting the tanks together (there are many, many other threads on this issue).

But since you mention it...I wonder why Piper, Beech, Mooney, VAN'S, etc., didn't think of such a simple solution? :)

Mine? SkyView tells me to switch tanks every 5 gallons. I reach down and operate a valve. Pretty simple, eh?
 
"Jeff, do the Andair folks stand behind your conclusion to fly between L and R ??
If so, that's a big plus for Andair and I still have time to install one. I assumed what is good for Van is plenty good for me, but Andair sounds very good "

Larry,

They are the ones that educated me on this!!!
 
Hmmm...I seem to recall that on a previous thread, someone got info from them that said that the valve would not *completely* cut off the flow at any intermediate position between L and R. I don't know that that's the same thing as saying "go ahead use it that way as a normal thing". Did they tell you something else?
 
They told me if you position it in the center it will flow from both tanks.
I learned this at their booth at Oshkosh last year.
 
Jeff Vaughan said:
"Jeff, do the Andair folks stand behind your conclusion to fly between L and R ??
If so, that's a big plus for Andair and I still have time to install one. I assumed what is good for Van is plenty good for me, but Andair sounds very good "

Larry,

They are the ones that educated me on this!!!
Click to expand...

I don't think they will recommend that. The reason it works is They do not want a failure mode where the valve could stop stick in a position that would not flow fuel. It's a good feature but not intended for running both tanks.

George
 
Jeff Vaughan said:
They told me if you position it in the center it will flow from both tanks.
I learned this at their booth at Oshkosh last year.
Click to expand...

But be honest...does this *sound* like the right thing to do? Does it *seem* like it's a good way to operate equipment, even simple equipment like a valve?

It's basically relying on the fail-safe design of the valve and operating it in a kind of "failed" manner all the time.

I won't debate the whole thing about designing a low-wing fuel system with check valves and L-B-R selector valves and pumps in both tanks and all that...I'm merely suggesting that using a two-position valve for the fuel system (nothing critical about that, eh?) in some half-way, in-between, not-marked mode designed to prevent a complete blockage as a *normal* way of operating it is ill-advised.
 
Hey, this is fun, I'll pitch in... It completely depends on the mission circumstances. Yep, completely solo in a SxS, I probably have some extra to burn off on my side, thereafter, probably at 1hr intervals. Two up in weather, I'm probably going to run the first 2/3 at 1hr intervals again, but that might change to 30min for various reasons. Leading a flight long cross country, the 30min ops check is the rule. The first one will come at the top or bottom of the hour and thereafter. The tank change should be a whole lot more than just changing tanks, but all kinds of house cleaning tasks. Is the airplane configured as it should be and performing nominally. Are all the parts still attached? Is there a stream of blue coming out of one of the fuel caps. Are they both still there (after a fuel stop)? Do I know where "nearest" is... etc, etc. That is a tank change.
 
I would consider the Andair valve is designed to "flow both" when in between L and R so that it doesn't stop the flow of fuel at any point when switching between L and R tanks. It's just smart design work. Not quite the same as "running" on both, hence no detent, label, etc. in the mid position.
Bevan
 
Last edited:
Vote for 15/30

I vote for 15 min on left to start with after fill up then 30 min intervals. It minimizes aileron trim change and it gives me something to look forward too.:D "30 sec, got to catch it right on the number. Oh look at the pretty scenery, shoot missed the switch by 15 sec...".

I also want to put in my 2 cents on the tank cross feed. With this set up if you ever run out of fuel, you are out of fuel. By feeding from only one tank at a time even if you do make the BIG mistake you still can switch to the other tank and of course land immediately. I'm keeping it as designed.
 
Mogas in one tank

In an effort to make flying more affordable, I've been running mogas in my right tank and when doing so, I climb out on 100LL, then when I've reduced the power switch over to Mogas, and leave it there tell A-The tank runs dry (which I've done in testing) or B- I arrive at my destination, cause I make my landing run on 100LL. So realistically I'll have 20 gal in one tank and the other is near or at empty. It will require full aileron trim in this condition, but to save 12 bucks an hour I feel that moving the aileron trim more is worth it.

Randy
8A
 
This is how I manage my fuel. I have a Dynon skyview that displays gallons used. After I level off in cruise I see how much fuel it took. Most of my trips are around 2 hrs so I adjust the time to change tanks based on my ETA. I want to try and land with the same amount of fuel in both tanks.
 
Downwind

My RV 9 was written off last year. The pilot had been taught to change to the fullest tank downwind. It seems that this instruction was given regardless of whether there was only a marginal difference between tanks.

The engine cut out shortly after and a forced landing in field was made. The Pilot was fine even though it nosed over.

It seems there was contamination in the tank he changed to. Personally I would never change tanks down wind. You could have finger trouble and shut the fuel off, the valve could pick that exact moment to break, or you could go from a tank where everything was fine like ours, to a contaminated one.

The only time I would consider changing tanks before landing would be before I lost significant height and before entering the circuit.... possible 10 miles before, to ensure if I needed to side slip I would have the fullest tank supplying fuel on the lifted wing.
 
Interesting discussion. I fly solo in a 6A most of the time so I start off imbalanced because my lard butt is sitting on the left side. I taxi, run-up and depart on the right tank and when approx 1 gallon of fuel is burned off I switch to the left tank. I burn the first gallon out of the right tank just so I know it's flowing fuel and also to lower the fuel level so it does not puke fuel after landing on short breakfast runs.

Once I'm on the left tank I burn another 9 gallons (half tank) and switch to the right tank again. Now that I'm running on the right tank again I run it empty, or close to empty, before switching back to the left tank and planning my next fuel stop. I have 9 gallons left to plan that stop and usually end up with 4 to 5 in the left tank when I refuel.

I do it this way to keep my remaining fuel in one tank and not split between the two.

I don't do it any different when the wife is along on a long trip. It works, I remember it and it's never failed me yet. Well, one time Carolyn was monitoring the fuel pressure as we were getting close to running the right tank dry. She was checking the map/gps looking for the next fuel stop and forgot about the fuel pressure. It wobbled and soon after the engine quit. It scared the dickens out of her but I saw it coming and got it running again in a jiffy. She has never missed the right to left tank change since.
 
If it's a cross country starting with full tanks I simply use the 30 minute timer on the 396 - switch at the first 30 minutes, then one hour intervals from there on.
 
Steve,
A very sobering story indeed. I hate rote learning on the part of pilots.... that results from a low time CFI telling them what he heard... when getting his ratings. For example.... they almost all "deep cycle" a constant speed prop at least two or three times in runup. Or they pull carb heat, listen for the drop and then shove it in. Never noting what the rpm result was after turning off the heat. The list goes on and on.
I had a clueless Cessna 140 pilot blast my RV9A this week at the self serve pump on a cross country fuel stop. I had both caps off.... and ran for the tail to hold it... knowing what was coming. So, I may have dirt in my tanks now. Or, maybe not. Will be sumping for sure to watch closely.
Your story about a contaminated tank and low level failure.. is a lesson to all of us about real world operations... and what a CFI might repeat without thinking the whole situation through. Appreciate your post from across the "pond".
 
You must log in or register to reply here.
Back
Top