Switching tanks on the ground

[TrafficInSight]

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.

With the caveat that if you are operating outside the POH you wont have a leg to stand on if something happens.

 

[DrewBlows]

My point is simply to be careful when taking advice from an internet message board, or just taking advice from anyone that's contrary to the POH (or not addressed in the POH). While I'm sure many people have some really good techniques, there are some pretty crazy ideas floating around out there.

I think the worst example I have ever heard was "I bet the Mooney can do a barrel roll (wink, wink), ha, ha, ha." It really pisses me off when people do stupid things in airplanes that I fly, and brag about it. One of Kershner's books describes the senario where one pilot loops an airplane not approved to do so, then brags about it. The next guy goes out and does the same thing, then brags that "the wings flexed, like, a foot!" At this point the airplane is damaged but it doesn't show so this behavior continues until one day a strudent is out practicing stalls, and pulls out of a stall aggressively (well within design limitations) and a wing falls off. It's been a while since I've read the book so I'm sure the details are off but the point is don't do things that are contrary to the POH.

I'm sure it is a slippery slope to go from turning the fuel selector to off on the ground to looping an airplane, but hopefully I've illustrated my point.

I'll get off my soapbox now.

 

[Propsync]

If it starts on the tank, run on it. If you switch during taxi or even right before takeoff, how much fuel would you have left in the line before you takeoff if the system is bad? I don't think I ever changed tanks on an Arrow I once flew. If you have problems inflight, just switch back to the good tank. Just because the POH says you can or should do it doesn't mean you have to. If you're going out for a one hour lesson, would you ever switch the tanks? I guess I'd rather find out how the system is working or not at 6000 feet rather than 600.

 

[Lead Sled]

If the POH says switch the tanks on the ground switch them, if not don't. Always take off with the fullest tank selected...

And what it the selector doesn't happen to be on the fullest tank? Then what?

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...

There are few folks on this forum that have been more vocal about following the POH /AFM as me. That being said, Bugchaser hit the nail square on the head - "there are many things that are not in the POH". The POH is perhaps best considered as the minimum standard. In a fully equipped high performance piston aircraft there are several things that it would be appropriate to check that are probably not listed in the POH.

I have been told that fuel is used to lubricate the fuel pump. Is this true for every airplane?...Again, I don't know, but I would rather not find out.

It's true for some and not true for others. As a pilot, I would think that you'd want to know those types of things. It could be very important knowledge to have. If you burn up a pump because you didn't properly understand the system it could cause you problems - there are few thing more useless than fuel on your airplane that can't be transferred and aircraft fuel pumps can be quite spendy. As for using that as an excuse not to find out how long it takes for the fuel to burn out of the fuel lines... Just how do you shut down a piston engine after the flight? With the mixture control right? What are you doing when you pull it back to idle cutoff? It sounds to me like you need to spend some quality time with a knowledgable aircraft mechanic. Ask a few questions then sit back and listen. You will learn a lot.

'Sled

 

[DrewBlows]

And what it the selector doesn't happen to be on the fullest tank? Then what?

Switch it before you start the engine.

It's true for some and not true for others. As a pilot, I would think that you'd want to know those types of things. It could be very important knowledge to have. If you burn up a pump because you didn't properly understand the system it could cause you problems - there are few thing more useless than fuel on your airplane that can't be transferred and aircraft fuel pumps can be quite spendy. As for using that as an excuse not to find out how long it takes for the fuel to burn out of the fuel lines... Just how do you shut down a piston engine after the flight? With the mixture control right? What are you doing when you pull it back to idle cutoff? It sounds to me like you need to spend some quality time with a knowledgable aircraft mechanic. Ask a few questions then sit back and listen. You will learn a lot.

'Sled

Take a look at your fuel diagram, the mixture is after the fuel pump (in every possible senario), therefore the fuel pump keeps fuel in it as long as you don't run a tank dry. I ask a mechanic anytime I have a systems quesiton that isn't clear and have called the manufacturer at time or two. That said, thank you for educating me on the fuel system of a piston aircraft. I am now smarter knowing that when I pull the mixture it majically stops the fuel at a point before the fuel pump.

 

[DrewBlows]

Disregaurd the last post. I may have been inebreiated when posting.

 

[TrafficInSight]

Disregaurd the last post. I may have been inebreiated when posting.

hahahahaha

In all cases the mixture cuts the fuel flow either in the carburetor or the fuel servo, the fuel pump never runs dry, I think that's what you were trying to say right?

 

[DrewBlows]

Yeah, thanks.

 

[mtrv]

hahahahaha

In all cases the mixture cuts the fuel flow either in the carburetor or the fuel servo, the fuel pump never runs dry, I think that's what you were trying to say right?

He was correct the first time around. Pump will run dry if fuel selector is on an empty tank, or at least the pickup tube is above the fuel level (banking, aerobatics). And mixture is what both of you said.

 

[TrafficInSight]

He was correct the first time around. Pump will run dry if fuel selector is on an empty tank, or at least the pickup tube is above the fuel level (banking, aerobatics). And mixture is what both of you said.

I was only talking about the mixture part, he was right about the pump part

 

[Lead Sled]

Sorry guys, I'm in the middle of a move and got things a bit twisted. What you said about the fuel pump is correct, however there are fuel pumps (transfer pumps) in various locations in the fuel systems of many aircraft - some are fuel lubricated and some aren't.

As a general statement, in most piston-powered light aircraft, you're not going to damage an engine-driven pump if you run it out of fuel. Electrical powered transfer pumps are a different animal - many of them are fuel lubricated and you can damage those if you allow them to keep running with out fuel.

The whole point of this thread isn't about fuel pumps - it's about the wisdom of making sure you can access the fuel in all of your tanks before takeoff and how to safely do it. Knowing how long it take to run a fuel line dry at idle power is about the only method you have to know how long an eninge will run if its fuel is interrupted. You only have to do it once per tank - not every flight. If the number happens to be 40 seconds and it's been 3 minutes since you switched tanks you're in fat city. If the number is 40 seconds and you just switched tanks 10 seconds ago and now you're applying takeoff power - well, you could have a real problem in about a half a minute.

The same advise goes for checking that you can actually draw fuel from the opposite tank via the crossfeed lines when you're flying your light-twin.

Checking the fuel continuity is a pretty big deal. I seem to remember that about 20-25 years ago there was a problem with the fuel selector valves that Piper had installed in several different single-engine models. It was part of the taxi checklist to switch tanks and verify fuel flow.

'Sled