Engine surging on RV-10 on landing approach

[Wayne Hadath]

It has been my practice to enter the airport pattern on the right tank due to left hand circuits and in my experience mostly left hand crosswinds. This practice has served me well until recently.
I was coming back to Kitchener Ontario from Portsmouth NH just after hurricane Earl had moved up the US East coast and the winds were strong and gusting from the north west. The trip which usually takes 2.5 hrs took 3 hours and 40 minutes. Most of the trip I was grounding 120 to 125 kts but at times I was down to 107 kts.
As I approached my home airport I was cleared to a 4 mile final on runway 26 with reported winds 300 at 23 gusting 37 knots.
This gave me a 40 degree cross wind. I had 9 gals in the left and 7 gals in the right tank and had chosen the right tank for approach and landing. I was indicating 110 kts on approach but grounding 75. Runway 26 is 7500 feet and I had decided not to land at the threshold due to past experience with turbulence at the threshold of 26 due to some trees. I was planning to attempt touch down about ? way down the runway. The turbulence on approach was considerable and I need almost all of the left rudder to keep the right wing low and the aircraft lined up with the runway. As I came over the threshold the engine began to surge adding to the difficulty to keep the aircraft stable. I generally land power off so I decided rather than switch tanks I just pulled power to idle and continued with the landing. My major concern at the time was that this had now become a landing and not an attempt to land as I had no power to go around. As fortune would have it the turbulence subsided as I went into the flair and the landing was uneventful. I switched to left tank and taxied back to the hangar. My family was onboard and we talked about what had just happen and I said I would trouble shoot the problem as this was not a situation that I would like repeated.
I decided to drain the fuel tanks to confirm the gauges were accurate and yes they were and I had 9 gals in the left and 7 gals in the right. I pulled the gascolator and it was free of debris. I did a fuel flow test on each side and confirmed that the flows were good.
The weather was clear today so I decided to see if I could duplicate the surging but at 4000 feet.
The aircraft did not surge on either tank while taxiing or in cruise and in coordinated turns.
I turned on the boost pump put the selector on the right tank and was burning 13 gal/hr at 120 knots. I set the timer, dropped the right wing and put in full left rudder to hold a steady heading. 31 seconds later the engine began to surge. I switched to the left tank and seconds later the engine recovered and ran smoothly. I repeated this experiment 3 times on the right tank and the interval was 31 to 35 seconds. I switched to the left tank and did the same tests and the results were the same.
I believe the fuel pick up which is located at the lowest corner of the fuel tank is being unported when the fuel moves to the wing extremities in these uncoordinated maneuvers.
I intend to do this experiment with more fuel in the tank to see at what fuel levels the pick up can be unported. I will also test this on my F1 Rocket.
It looks like my pattern approach has to be rethought and cross winds considered when I select which tank to land on.
There does not seem to be an end to the stuff to learn in this endeavor.
Wayne Hadath
RV 10, 82 hrs
F1 Rocket, 435 hrs

[David Paule]

Does your airplane have a "Both" position for the fuel tank selector?

That might make a positive difference.

Right now you've got an operational restriction: you must use the fuel on the wing that's high during slips.

[Norman CYYJ]

Wayne, what was the fuel pressure doing?

[Wayne Hadath]

David
As far as I am aware we cannot use a both selector switch on low winged aircraft. We are restricted to left or right. Until I can test at what fuel level the pick up unports I will select the high tank on landings.
Thanks
Wayne

[Wayne Hadath]

Norman
I have run the fuel tanks dry on previous flights and just before the engine begins to really shake there is fluctuations in the fuel pressure with the boost pump on. I have never ran a tank dry without the boost pump running. If I can make the switch before the fuel pressure enters the red zone there is very little time before the engine runs smooth again. On this particular occasion I did not look at fuel pressure but did notice that the right tank read 0 and the left read 14. First thought was that I was pumping fuel across to the other tank but soon realise that was not possible.
Wayne

[Kyle Boatright]

Originally Posted by David Paule

Does your airplane have a "Both" position for the fuel tank selector?

That might make a positive difference.

Right now you've got an operational restriction: you must use the fuel on the wing that's high during slips.

A search will show many threads on "both" settings on our fuel selectors. The short story is that on low wingers, a both setting is a recipe for a fuel management related engine failure.

If the original poster's RV-10 was my plane, I'd check for obstructed fuel vents and/or induction leaks.

[Wayne Hadath]

Kyle
I will check the vent lines. What do you mean by induction leaks?
Thanks
Wayne

[Kyle Boatright]

Originally Posted by Wayne Hadath

Kyle
I will check the vent lines. What do you mean by induction leaks?
Thanks
Wayne

On a carbureted engine, you could have a leaking induction tube (cracked tube or loose clamp on the rubber hoses that connect the air intake and the induction tubes on the cylinder) or someone could have left a plug out of a port on a cylinder (maybe a primer port or manifold pressure port), leading to odd engine behavior.

A fuel injected engine could have the same plug/port issue, as could a throttle body type injector. I'm not sure what kind of induction leaks an engine with injectors on individual cylinders might have.

Good luck tracking this down.

[az_gila]

Originally Posted by Wayne Hadath

It has been my practice to enter the airport pattern on the right tank due to left hand circuits and in my experience mostly left hand crosswinds. This practice has served me well until recently.
....

...in most low wing certified aircraft specify "Switch to Fullest Tank" as part of the Landing Checklist?

Perhaps you need to modify your practice?

[Neal@F14]

Do you have an MT prop governor? I remember reading about an rpm surging issue with certain revisions of MT governors.