Switch Tanks Before Takeoff

[Fly Boomer]

Having breakfast with pilots this morning, we discussed (among many other topics) tank switching before takeoff.  It seems to me that a good idea might be starting and warming up on one tank, and then switching tanks before runup and takeoff.  My argument is that if there is a fuel delivery or contamination problem, I want to know about it while still on the ground.  Some said they always want to take off on the same tank they were on at start.  In other words, they were concerned that the runup might not burn enough fuel to assure that the "new" tank didn't have a problem. 

What do Mooney drivers do?

[231MJ]

Start on the tank when I shut down.  After start, switch to the fullest tank then taxi, run-up, etc.  Then I know there is no issue with fuel flow.  If I start on the fullest tank, I just keep it there.  Others will disagree with this...but in any case, switching right before take-off seems to come with some risk.  Let the debate begin.

[Boilermonkey]

8 minutes ago, Fly Boomer said:

Having breakfast with pilots this morning, we discussed (among many other topics) tank switching before takeoff.  It seems to me that a good idea might be starting and warming up on one tank, and then switching tanks before runup and takeoff.  My argument is that if there is a fuel delivery or contamination problem, I want to know about it while still on the ground.  Some said they always want to take off on the same tank they were on at start.  In other words, they were concerned that the runup might not burn enough fuel to assure that the "new" tank didn't have a problem. 

What do Mooney drivers do?

Exactly what I've done since flying Mooney's.  

[Vance Harral]

In low wing airplanes, I teach to prime and start on one tank, then switch to the other immediately after engine start.  The idea is to prove that you can feed fuel from both tanks. as you say.  But I want to do this immediately after engine start so it's several minutes between switching tanks, and takeoff, preferably with a runup inbetween.

The risk factor of switching tanks right before takeoff is a scenario where the system can't deliver any fuel from the newly selected tank, but the lines downstream from the fuel selector have just enough go juice in them to get you airborne before the engine quits.  I don't worry about that scenario much in a fuel-injected engine.  I worry about it a lot in a carbureted engine: the float bowl can hold quite a lot of fuel.

It's an interesting experiment in any airplane to turn the fuel selector to OFF on the ground, and see how long it takes the engine to die.  I once flew with a guy in a Champ, who regularly turned the fuel selector to the off position shortly after clearing the runway, and taxied all the way to his hangar on just the gas in the carburetor bowl.

[Rick Junkin]

9 minutes ago, Vance Harral said:

In low wing airplanes, I teach to prime and start on one tank, then switch to the other immediately after engine start.

My technique as well. Here's my Garmin checklist for Engine Start

Ok so probably not worthy of a WARNING, but it could be.

Cheers,
Rick

[Joshua Blackh4t]

I fly pretty regularly so I normally ignore it. I'll find out in an hour when I switch and with the low risk, thats fine.

If i've been outside in rain I might do a left and right check but I don't think it will prove much because it still will be on fuel in the line the whole way to take off.

I generally set it to left tank in case I start 2nd guessing if I changed. That way I can remember that I Left on the Left. 

[A64Pilot]

The C-85  engines if you have I think the Marvel carb you can’t kill with mixture, most have had the mixture either removed or disconnected anyway.

I starve mine as you say by turning off the fuel because many of the carbs leak and don’t want it leaking in the hangar.

So far as switching tanks before takeoff I think that silly, if you can’t feed from one tank for some reason switch back you should still have a lot of fuel left to find somewhere to land.

My only rule is don’t switch tanks unless at cruise altitude, only problem I’ve had was I had the lever come off on me, as I was up high I had plenty of time to slide my seat back so I could see and put it back on, if I had been in the pattern maybe, maybe not.

I’ve always wondered why switch tanks anyway. The Thrush crop duster always feeds from both tanks, only fuel selection you have is on or off, makes sense to me.

[0TreeLemur]

I land on my fullest tank.   Next takeoff is on the fullest tank.

If parked outside and it rained use extra vigilance when sumping tanks using gats jar, and let the gascolator drain for a good 10 seconds.

[GeeBee]

Actually the M20R POH requires you to verify feed from both tanks prior to take off. I checked and the engine will quit in 30 seconds with the fuel valve off. So I start and taxi out on one tank. Change tank to perform a run up then take off.

 

[McMooney]

start and first hour is on 1 tank then switch, if i have issues, switch back

[Fly Boomer]

1 hour ago, Vance Harral said:

It's an interesting experiment in any airplane to turn the fuel selector to OFF on the ground, and see how long it takes the engine to die.

This exact experiment is one I thought of this morning to get some idea how long it will run on what's in the fuel lines.  I'll have to try it.

[Fly Boomer]

39 minutes ago, GeeBee said:

Actually the M20R POH requires you to verify feed from both tanks prior to take off. I checked and the engine will quit in 30 seconds with the fuel valve off. So I start and taxi out on one tank. Change tank to perform a run up then take off.

 

That 30-second number is one of the things I wondered about.  I'll have to try it.  If it's only thirty seconds, the switch before runup or maybe switch before taxi would feel comfortable.  Thanks.

[Fly Boomer]

52 minutes ago, A64Pilot said:

My only rule is don’t switch tanks unless at cruise altitude, only problem I’ve had was I had the lever come off on me, as I was up high I had plenty of time to slide my seat back so I could see and put it back on, if I had been in the pattern maybe, maybe not.

I'm in the "switch to fullest tank at top of descent" camp.

[ArtVandelay]

Like A64Pilot I switch during cruise AND if possible while within gliding distance of an airport. I only switch once at the halfway point.

[Fly Boomer]

2 minutes ago, ArtVandelay said:

Like A64Pilot I switch during cruise AND if possible while within gliding distance of an airport.

I especially like the phrase "within gliding distance of an airport".

[Pinecone]

12 hours ago, GeeBee said:

Actually the M20R POH requires you to verify feed from both tanks prior to take off. I checked and the engine will quit in 30 seconds with the fuel valve off. So I start and taxi out on one tank. Change tank to perform a run up then take off.

My 252 POH is the same.  Start and taxi on one tank, switch before the run up.

I was wondering how long it would run without fuel delivery.  I suspected with fuel injection it would not be long.

[M20F]

I am not a fan of changing anything that is working to something else 30 seconds prior to take off.  
 

If it ain’t broke, don’t fix it.  Pilots struggle mightily with this in terms of ownership and operation. 

[Shadrach]

I verify continuity for both tanks before takeoff.  I don’t go crazy worrying about which one has more fuel unless there’s a serious imbalance. If there is an issue, you’re likely to find out well ahead of being airborne.  At taxi power, my IO360 will starve about eight seconds after the selector is moved to the off position. However, Trying to pull fuel from a closed valve is not the same thing as pulling air from an unported tank.   One of my tanks is empty right now for sump valve replacement. I’ll try to get some data on how long it will run when switched from tank with gas to tank with no gas After I finish the annual.

[Fly Boomer]

17 minutes ago, Shadrach said:

At taxi power, my IO360 will starve about eight seconds after the selector is moved to the off position. However, Trying to pull fuel from a closed valve is not the same thing as pulling air from an unported tank.

I like the eight seconds, but had not thought of the difference between "off" and empty tank.  If you test it, let me know.  Thanks.

[PT20J]

I switch tanks every half hour. I like to keep the plane balanced and also those brass valves like to be exercised or they get stiff. 

I usually taxi out on one tank and switch before run up. This is primarily to make sure the valve turns freely - I’m really not much concerned that somehow fuel won’t flow through the lines. And, I sumped the tanks, so I know there is no water (BTW, in 6,000 hours of flying a lot of different make and model airplanes, I have found a significant amount of water in the fuel tanks exactly ONCE. But, I still sump the tanks. You never know when twice will occur.)

If you want to avoid the biggest risk, check the handle attachment. The only failure I personally know about was a friend in an Archer that had the screw attaching the handle back out and jam the handle in the trim around the selector in a position between tanks where no fuel flowed. In a slight panic, he tried to force it and jammed it worse. He finally got it unstuck. I could easily see the handle on my J coming loose and getting dropped and rolling under the seat. And then there are models with the valves that you cannot hardly reach without gorilla arms or an extension…

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[Hank]

I don't change tanks anywhere near takeoff. This is from my Owners Manual, note the WARNING:

If you want to check safely, switch tanks when you get in, then crank up. Once running smoothly, set for the fullest tank. I've done this sometimes, but never having an issue leads to complacency . . . .

[RLCarter]

Like others have said, it’s a good idea to verify fuel flow from each tank while on the ground and allow ample time running on the tank your going to takeoff on before attempting to get airborne 

[DCarlton]

Thought provoking thread.  I may modify my usual CONOPS.  Will likely start verifying flow from both tanks and proper valve operation before take-off (instead of just switching to fullest tank before engine start).  However, it will be done before taxi to run-up and long before take off.  

[Nokomis449]

1 hour ago, PT20J said:

(BTW, in 6,000 hours of flying a lot of different make and model airplanes, I have found a significant amount of water in the fuel tanks exactly ONCE. But, I still sump the tanks. You never know when twice will occur.)

Same here minus the 6k hours.  Once long ago, the Mooney was flown by someone else to Kansas City to visit family.  He had it topped on arrival.  Days of monsoon weather ensued and being VFR only, he elected to fly home commercially.  I hopped a ride to KC to pick it up, and during the preflight I found the fuel cap incorrectly installed (it was at an angle instead of flat) and got nothing but water from the sump.  After the 3rd cup, I asked for the FBO manager, who himself found the other tank in the same condition.  If memory serves, the lineman then sumped about a gallon from each wing.  When even slightly askew, the O-ring does not completely seal and water that collects on top of the fuel cap meanders into the tank.  So at the risk of being labeled "THAT pilot", I point out an incorrect cap position any time I find it, and why.

Point being that IF there was enough fuel in the carb and lines to make it through runup to takeoff, I most certainly would had encountered a fuel issue that switching tanks wouldn't fix.

[Utah20Gflyer]

I started my plane with the fuel selector on off and ran it until it died, maybe a minute at idle power.  So from my experience any quick switch from one tank to another doesn’t prove anything.  A full run up would prove it, but I don’t want to do two full run ups .  
 

So I start on the fuller tank, do my run up on that tank and takeoff on that tank.  I will switch tanks a half hour later at full power and some altitude.  Between this procedure and religiously sumping the tanks I feel this is a reasonably safe procedure.  Not perfect, but reasonable.