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How quicky does fuel selector affect engine?

K

kirkbauer

Well Known Member
I'm trying to get an estimate on how quickly the fuel selector works on a typical RV10 (with standard fuel injectors. Less than a second? Ten seconds?

In other words, if you are in cruise and switch from a full tank to an empty tank, how long until the engine would start to lose power?
 
kirkbauer said:
I'm trying to get an estimate on how quickly the fuel selector works on a typical RV10 (with standard fuel injectors. Less than a second? Ten seconds?

In other words, if you are in cruise and switch from a full tank to an empty tank, how long until the engine would start to lose power?
Click to expand...

Rough estimate: About 10 seconds. Why do you ask?
 
There is old flying advice that says one should only switch tanks when overflying or somewhere very near an airport. If the valve malfunctions or gets stuck while switching, you only have a few seconds before the engine quits. My old school Van's fuel selector started acting up and getting a little jammed and hard to turn - very scary while airborne. I opened it up and overhauled it, and the issue never came back. But it did teach me a valuable lesson.
 
71459 said:
There is old flying advice that says one should only switch tanks when overflying or somewhere very near an airport. If the valve malfunctions or gets stuck while switching, you only have a few seconds before the engine quits. My old school Van's fuel selector started acting up and getting a little jammed and hard to turn - very scary while airborne. I opened it up and overhauled it, and the issue never came back. But it did teach me a valuable lesson.
Click to expand...
Yup. Change tanks when and where you can afford to lose an engine.
 
Depends on your fuel flow at the time.. on takeoff, it'll be much quicker than in cruise.. I would think 10 seconds or so in cruise.
 
Might take longer than you expect, and obviously depends on flow rate. Consider a that carbed 360 required a minute for the effects of a tank change to be noticed (100LL v. 10% ethanol). Flow was 9 gph.

It's one reason I never followed handbook rules of switching to the fullest tank for landing.
 
Thanks everyone! I ask because I was coming in low under a Charlie to land yesterday. I was down to about 10gal of fuel. I was trying to run the right tank low so I could use the left tank for landing. About one mile out, before crossing overhead for a left downwind entry, I switched to the left tank. At the time the right tank read 3gal and I have safely run it down to 2gal in the past.

Right when I switched tanks, the engine started sputtering. Without really thinking I quickly switched back to right. The sputtering continued. I decided to enter a right base instead of crossing over and made an immediate landing.

I did some limited troubleshooting but figured it was best to land asap. At this point I had pulled back to idle. The fuel pump seemed to help. I must have ended on the left tank but can't remember for sure.

I shut down and checked the tanks. Left tank had visible fuel. I suspected that the engine fuel pump might have failed right when I switched tanks. I tested on the ground with the left tank and no electric pump and the engine ran fine.

Filling the tanks was enlightening. 30.2 gal into the right tank and 20 into the left. So my theory now is that the right tank ran dry right as I was switching to the left, but the engine didn't start running rough until after I switched. Then immediately switching back to the right put more air into the fuel system.

Then I started wondering exactly how quickly the fuel valve takes effect. It was natural to undo what I just did when the engine started sputtering but in hindsight it couldn't have had an effect that quickly.

No ill effect other than some adrenaline for me and more brake wear than a normal landing. But perhaps I don't need to get every last ounce of fuel out of one tank next time.
 
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kirkbauer said:
Thanks everyone! I ask because I was coming in low under a Charlie to land yesterday. I was down to about 10gal of fuel. I was trying to run the right tank low so I could use the left tank for landing. About one mile out, before crossing overhead for a left downwind entry, I switched to the left tank. At the time the right tank read 3gal and I have safely run it down to 2gal in the past.

Right when I switched tanks, the engine started sputtering. Without really thinking I quickly switched back to right. The sputtering continued. I decided to enter a right base instead of crossing over and made an immediate landing.

I did some limited troubleshooting but figured it was best to land asap. At this point I had pulled back to idle. The fuel pump seemed to help. I must have ended on the left tank but can't remember for sure.

I shut down and checked the tanks. Left tank had visible fuel. I suspected that the engine fuel pump might have failed right when I switched tanks. I tested on the ground with the left tank and no electric pump and the engine ran fine.

Filling the tanks was enlightening. 30.2 gal into the right tank and 20 into the left. So my theory now is that the right tank ran dry right as I was switching to the left, but the engine didn't start running rough until after I switched. Then immediately switching back to the right put more air into the fuel system.

Then I started wondering exactly how quickly the fuel valve takes effect. If was natural to undo what I just did when the engine started sputtering but in hindsight it couldn't have had an effect that quickly.

No ill effect other than some adrenaline for me and more brake wear than a normal landing. But perhaps I don't need to get every last ounce of fuel out of one tank next time.
Click to expand...
Good to know how your particular airplane reacts when it runs out of fuel and exactly how much useable fuel each tank holds. My IO-360 takes around 10 seconds to catch again after running a tank dry . . . can seem like a very long time on final.
 
71459 said:
My old school Van's fuel selector started acting up and getting a little jammed and hard to turn - very scary while airborne. I opened it up and overhauled it, and the issue never came back. But it did teach me a valuable lesson.
Click to expand...
This has happened to me as well but read somewhere here on VAF that if you lift up on the valve handle it will make it easy to turn again.

Fuel Selector Valve

I'm starting to run my fuel lines beginning with the fuel selector valve. I want to mount the valve, but I cannot get the handle off the valve stem (yes, I removed the screw :D). Is there a trick to this? Thanks, Tom
www.vansairforce.net
 
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I am running IO-540 with fuel return system for SDS fuel injection system. I run at 42 psi in cruise., with fuel flows around 10 - 11 gph, I can answer 1/2 your question. When changing fuel tanks (Andair valve) if I do not turn it quickly, I will see a fuel pressure drop as I move the valve from one side to another. When I am draining fuel tanks in the hangar, upon refilling, with fuel lines purged, it takes < 15 seconds to reestablish 42 psi. I have not done this in flight.
 
plehrke said:
This has happened to me as well but read somewhere here on VAF that if you lift up on the valve handle it will make it easy to turn again.

Fuel Selector Valve

I'm starting to run my fuel lines beginning with the fuel selector valve. I want to mount the valve, but I cannot get the handle off the valve stem (yes, I removed the screw :D). Is there a trick to this? Thanks, Tom
www.vansairforce.net
Click to expand...
That's good to know. I wouldn't want to have to do that every time though - I can just imagine the handle breaking off!
 
kirkbauer said:
I shut down and checked the tanks. Left tank had visible fuel. I suspected that the engine fuel pump might have failed right when I switched tanks. I tested on the ground with the left tank and no electric pump and the engine ran fine.
Click to expand...
This is exactly what I thought happened when reading your description of events. You got "lucky" that you unported the fuel pickup in the right tank just before you decided to switch, then switching made you think the full tank was the problem. That's a situation that can easily lock your brain into thinking you mixed up which tank is empty, or that the problem isn't the tanks, and diagnosing the issue into the ground when the solution is to go back to the known full tank (left) and wait for the pump to prime. Good on you for flying the plane first and getting on the ground safely.

And in future, maybe consider draining the tank on the ground if you want it empty... :)
 
kirkbauer said:
Thanks everyone! I ask because I was coming in low under a Charlie to land yesterday. I was down to about 10gal of fuel. I was trying to run the right tank low so I could use the left tank for landing. About one mile out, before crossing overhead for a left downwind entry, I switched to the left tank. At the time the right tank read 3gal and I have safely run it down to 2gal in the past.

Right when I switched tanks, the engine started sputtering. Without really thinking I quickly switched back to right. The sputtering continued. I decided to enter a right base instead of crossing over and made an immediate landing.

I did some limited troubleshooting but figured it was best to land asap. At this point I had pulled back to idle. The fuel pump seemed to help. I must have ended on the left tank but can't remember for sure.

I shut down and checked the tanks. Left tank had visible fuel. I suspected that the engine fuel pump might have failed right when I switched tanks. I tested on the ground with the left tank and no electric pump and the engine ran fine.

Filling the tanks was enlightening. 30.2 gal into the right tank and 20 into the left. So my theory now is that the right tank ran dry right as I was switching to the left, but the engine didn't start running rough until after I switched. Then immediately switching back to the right put more air into the fuel system.

Then I started wondering exactly how quickly the fuel valve takes effect. It was natural to undo what I just did when the engine started sputtering but in hindsight it couldn't have had an effect that quickly.

No ill effect other than some adrenaline for me and more brake wear than a normal landing. But perhaps I don't need to get every last ounce of fuel out of one tank next time.
Click to expand...
Also good to remember that the fuel pickups are on the rear corner of the tanks, so descending nose low may unport a tank quicker than level flight. In some older Cessna manuals, they say you may restore fuel flow by raising the nose. In your case, sounds like you were empty (30.2 gallons) anyway.
 
steve murray said:
I am running IO-540 with fuel return system for SDS fuel injection system. I run at 42 psi in cruise., with fuel flows around 10 - 11 gph, I can answer 1/2 your question. When changing fuel tanks (Andair valve) if I do not turn it quickly, I will see a fuel pressure drop as I move the valve from one side to another. When I am draining fuel tanks in the hangar, upon refilling, with fuel lines purged, it takes < 15 seconds to reestablish 42 psi. I have not done this in flight.
Click to expand...
Which fuel selector? Vans standard?

In my 9A with IO360 and SDS, I'm running an Andair duplex valve, and even turning it slowly I don't see a drop. I think the "mid" range of the Andair opens both sides to flow, not sure about the Vans.
 
walkman said:
For even more fun, you can try running a tank dry when you're #2 in a flight of four for the overhead right when lead gives the pitchout signal. Bonus points when there's 50 RV pilots on the ground watching you and just itching to critique. It's great!
Click to expand...
You wanna get a new callsign? Cuz that's a good way to get a new callsign! (y)
 
71459 said:
There is old flying advice that says one should only switch tanks when overflying or somewhere very near an airport. If the valve malfunctions or gets stuck while switching, you only have a few seconds before the engine quits. My old school Van's fuel selector started acting up and getting a little jammed and hard to turn - very scary while airborne. I opened it up and overhauled it, and the issue never came back. But it did teach me a valuable lesson.
Click to expand...
If this ever happens, just reach under the lever with two fingers and lift about 1/4 inch and turn... The valve is a cone, so just lifting it a little will free the seat.
 
steve murray said:
When changing fuel tanks (Andair valve) if I do not turn it quickly, I will see a fuel pressure drop as I move the valve from one side to another.
Click to expand...

Interesting. When at OSH a while back the Andair folks told me that if you leave the handle between the Left and Right position you will receive fuel from both tanks (even though not labeled on valve). I sometimes do this when parking the plane after a flight to even out the fuel loads between tanks.

David
 
DCBrown198 said:
Interesting. When at OSH a while back the Andair folks told me that if you leave the handle between the Left and Right position you will receive fuel from both tanks (even though not labeled on valve). I sometimes do this when parking the plane after a flight to even out the fuel loads between tanks.

David
Click to expand...
Im not sure I follow this comment. I understand how a water level works but not sure how it would work to balance fuel in left and right tanks. Can you explain what you are doing a little more or it is just as simple as turning the valve to the top? I may give it a try and see what happens. Interesting idea for sure.
 
Even on Van's cheap brass valve if set up 1/4 turn L to R, the center will expose both inlets at the same time. But just a small amount.
Enough though that the fuel flow is never stopped.
 
rockwoodrv9 said:
Im not sure I follow this comment. I understand how a water level works but not sure how it would work to balance fuel in left and right tanks. Can you explain what you are doing a little more or it is just as simple as turning the valve to the top? I may give it a try and see what happens. Interesting idea for sure.
Click to expand...
The middle position effectively opens the fuel system between both tanks....like an open cross-feed valve.

When left in the position between L and R when parking, the fuel in the higher tank gravity-flows into the lower tank just like that water level. The fuel should level in your wing tanks (provided your parking spot is level).
 
swjohnsey said:
Is there a position that will turn the fuel completely off?
Click to expand...
Yes - there should be an OFF position (maybe two OFF positions on some valves). This is generally checked during phase 1, before you actually fly the plane with the engine running on the ground. You want to make sure that you can actually turn off the fuel flow.

The unporting of one inlet before shutting the other one off when switching from left to right for example, is pretty common. During training way back when, our instructors called those kind of valves “make before break” valves (self explanatory).
 
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