Switching tanks on the ground

[RightPedal]

I set to the fullest tank after start up. If going long distance I try to change tanks at 30 min after departure and each hour after that. In a low wing a/c I turn the bust pump on and change to the fullest tank when entering the pattern for landing. In high wing a/c, or low wing injected motor just switch tanks without the boost pump.
Thats how I was taught and it's always stayed with me.
If you have trouble remembering to switch tanks, sooner or later you'll have an engine quit and you'll never have trouble remembering again. That silence taught me this lesson one night between Miami and Naples.

 

[User546]

The main reason to not switch on the ground is that if there is a problem with the feed from the new tank, and you switched just before takeoff, there may be just enough fuel in the line to get airborne and then quit.

That's why it's critical to switch the tanks either right after engine start, or during your taxi. That way you have the time it takes for your remaining taxi, as well as your runup to make sure it's going to run fine on the new tank.

I agree the engine can run suprisingly long with just the fuel in the lines, but unless your doing a fast taxi, and abbreviated runup, chances are it will die on your before you can get to the hold short line in case of blockage or failure.

 

[User546]

In a low wing a/c I turn the bust pump on and change to the fullest tank when entering the pattern for landing. In high wing a/c, or low wing injected motor just switch tanks without the boost pump.

I second that, my procedure when ready to switch tanks is this: Fuel Pump On, Switch Tanks, Fuel Pump Off, Fuel Pressure Check.

I also find it useful to label "F" on my sectional at the appropriate distance/time to change fuel tanks, that way I never forget to switch tanks - especially on those boring, long-legged flights.

 

[Cardinal]

Make sure both tanks contain a suitable amount of contaminant free avgas. Let the Gods sort it out from there.

 

[Lead Sled]

I agree with Bugchaser, I switch tanks just after the engine start check list and before taxi. It is not in the check list and is my personal practice.

Good advice. As others said, you do want to make sure that you've got good, accessable fuel; but NEVER do it just before takeoff. It seems that every year there are a few guys who forget that and find out that there's usually just enough fuel in the lines to get airborne.

Bugchaser gave some good advice. I always checked the amount of time it took for the engine to run the fuel out of the lines while at idle. Knowing that figure, it was a simple matter to switch tanks sometime right after start - you just had to make sure the the elapsed time from switching tanks, taxi, run up, etc. was greater than the time required to run the fuel lines dry.

For what it's worth, back in the old days when we flew the Cubs or Champs with the "armstrong" starters, we would alway hand prop them with the fuel shut off - just in case it were to try to get away from you. After starting the engine, you'd have just enough time to run around to the back of the airplane, untie the tail and run back around and climb in and turn the fuel on before the engine would quit. Then you just pulled the ropes to get the chocks out from the main gear. One of my buddies had a glider tow hitch on his J-3. He'd hook a tiedown line to it and when he was ready to taxi he'd simply pull the release from the cockpit. Electric starters, what a neat idea.

'Sled

 

[Tired Soul]

I switch before the run-up so I know both tanks are feeding without a problem.
A student questioned me one time so we timed it; Piper Arrow 40 sec before engine died at idle, might be an idea for every plane you fly, next time before shut down turn selector off and time how long it takes at idle.
Obviously at any other higher power setting it will take less, but you have an indication now.
I don't like switching tanks at low altitude or in the pattern, bad idea.
Or maybe I'm just scared after 4 years of instructing...

 

[bugchaser]

Hey Led Slead, thats a cool pic there. Nothing like a little water skiiing to pass the time.

 

[DrewBlows]

My thoughts on the subject...

If the POH says switch the tanks on the ground switch them, if not don't. Always take off with the fullest tank selected. Once in the air, look at your watch, if the minute hand is between 12 and 6 (the right side) use the right tank, if the minute hand is between 6 and 12 (the left side) use the left tank. If your watch is digital get a new watch, you look like a dork. For god's sake man have some pride.

As far as timeing how long it takes for an engine to quit, you might not want to do this. Any time you do something that is not specifically spelled out in the POH there may be unintended consequences. I have been told that fuel is used to lubricate the fuel pump. Is this true for every airplane? I don't know. Is this true for any airplane? Again, I don't know, but I would rather not find out. Think about it. In a typical training airplane there are many, many strudents who fly the airplane in a typical year. If an instructor shows this to every student once, that's a lot of time without lubrication. Then several years down the road a fuel pump fails in flight (or on takeoff) and it's attributed to a bad fuel pump. The mecanics likely wouldn't know this practice of shuting the engine down with the fuel selector is happening, and the cycle continues.

 

[bugchaser]

Settle down there. While following the POH is generally the best deal, there are many things that are not in the POH. As for the fuel pump, you wouldn't want to have the electric boost pump on, but the engine driven pump should be ok. The point that we were making is that it is possible for there to be enough fuel in the line to keep the engine running just long enough to get you into trouble.

 

[JAFI]

My thoughts on the subject...
If your watch is digital get a new watch, you look like a dork. For god's sake man have some pride.

Really, I have found that a digital watch (with a light) is much easier to read after a couple years of 16 hour work days, at night, when you start wearing bi-focals, or when you really could care less but have to fill out the log book. I do not buy expensive watches. You only need to bang them once, the wrong way and you just have expensive jewelery. And (as far as I know) no one was ever mugged for a cheep timex. But what ever floats your boat...

JAFI