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  #1  
Old 05-17-2022, 02:30 PM
ssturges ssturges is offline
 
Join Date: Oct 2014
Location: Portland, Oregon
Posts: 68
Default Rapid loss of fuel

Plane: RV9A IO320 stock per plans, Stock vans boost pump installed per Vans instructions. Number of hours on plane 102. No issues with fuel flow to engine during this incident or at any other time. Stock vent line and sniffle drain

A few weeks ago I had my tanks top off buy the fuel truck before flight. Unfortunately he over filled them to the point where when cap was installed fuel flood the wing, No big deal I cleaned it off.

Did run up, turned boost pump on for take off. After takeoff the tower had me do a series of 3 sharp 45 degree plus turns 1 right and 2 left for traffic avoidance. My fuel pressure with or without the boost pump runs about 37-40psi. I have the squawk limit to 40 so, I did here one squawk that indicated it got to 40 psi for a short moment and then dropped back down to 37 psi. I turned the boost pump off and I flew for 10 min or so to a near by airport and did 1 touch and go.

On departing this airport I look down and saw that I only 9 gallons in my right tank which was the active tank. I thought stuck fuel gauge lever. Rocked the wings and saw the fuel level bounce up and down. Ran for a bit on that tank and did not see further rapid fuel loss on the gauge. I switched tanks and proceeded on to my destination. On arriving I sticked the tank and I had indeed lost a bunch of fuel. Further operation of the plane has showed no further fuel loss.

So: what happened? Did the fuel siphon out the vent line on the steep turns after takeoff, because fuel was compressed into the top of the vent lines lines due to the overfill and start a siphon on the steep turns, this really seems like a physical possibility? Or does a IO320 fuel pump dump consider 40PSI an over pressure and dump the fuel?
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  #2  
Old 05-17-2022, 02:36 PM
airguy's Avatar
airguy airguy is offline
 
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The fuel pump does not have a mechanism to dump fuel, except for a failure of the fuel pump diaphragm which would show up as low fuel pressure, not high.

What fuel levels did you measure during the preflight, and what showed on the gauges during startup and taxi?
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  #3  
Old 05-17-2022, 02:41 PM
N427EF N427EF is offline
 
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First, I don't know why you run 37 PSI on an IO-320 ?
That alone does not explain the loss of fuel and I am curious as to what the cause may be.
Since your tanks where overfilled, it is possible that your fuel cap was not properly seated and low pressure on top of the wing sucked out a good amount of fuel without you noticing it.
Steep turns and other maneuvers should not cause you to loose fuel or else a serious flaw needs to be corrected.
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  #4  
Old 05-17-2022, 03:16 PM
Roadjunkie1's Avatar
Roadjunkie1 Roadjunkie1 is offline
 
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Location: Erie, Colorado
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Default Fuel issues.......

Quote:
Originally Posted by ssturges View Post

A few weeks ago I had my tanks top off buy the fuel truck before flight. Unfortunately he over filled them to the point where when cap was installed fuel flood the wing, No big deal I cleaned it off.
Several issues I see here. NOT to be critical but instructive; I was not there at the time.......

1) NO ONE has ever fueled any airplane that I have flown. I have been told the line person HAS to fuel the airplane and I tell them I'll be on my way without buying their fuel, which usually changes their mind, with occasional glances back to the office. Most of the time it isn't an issue and the line person doesn't mind not doing anything for a little while. It's a personal thing with me and my airplanes....not to mention Jet-A has never come near my fuel tanks and they have never been overfilled. And a fuel nozzle has never banged the inside of my fuel tank and no nozzle cap has ever banged into the wing.

2) For some reason, preflight has taken a back seat to just jumping in and going flying. I am NOT saying this happened here; just in general. Any time my airplane is on the ground having just arrived somewhere, I do a brief walk-around including pulling the tank lids and taking a peek inside before departure. If I have refueled, I tap the quickdrains to make sure water was not introduced into the tanks. Yeah, I know the water probably wouldn't get there that quickly but it makes me feel better. Again: Communing with my airplanes. SO: my airplane was on the ramp while I was in having breakfast with people walking up and looking at it. My abbreviated inspection tells me no one pushed on anything they shouldn't have, banged into a flap or other things people do. (I have had people push on my NO PUSH placard "just to see what it did" while I am standing there at fly-ins!) I have a very good friend, CFI/ATR etc with tens of thousands of hours who once left our fuel stop with the fuel caps of his Cub still on the ground. Or somewhere.

3) sounds like the fuel was sucked out somewhere. It may not have been from the turns but from the tanks priming the vents and sucking air/fuel out. Just a guess but it had to go SOMEwhere......

IMHO...YMMV......
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  #5  
Old 05-17-2022, 03:26 PM
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Walt Walt is online now
 
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Are you sure they were “topped off”, if you pump fuel in fast enough it can’t displace the air quick enough and will “appear” full and spit fuel out the filler. You have to fuel an RV much slower than most aircraft to truly get the tanks full.
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  #6  
Old 05-17-2022, 03:43 PM
PilotjohnS PilotjohnS is offline
 
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Location: Southwest
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Quote:
Originally Posted by Walt View Post
Are you sure they were “topped off”, if you pump fuel in fast enough it can’t displace the air quick enough and will “appear” full and spit fuel out the filler. You have to fuel an RV much slower than most aircraft to truly get the tanks full.
In the 9A that I am building, earlier builders complained that the holes in the ribs inside the fuel tank are sometimes too small and the fuel will burble out before the tank is filled. The vent cant release air fast enough either and the holes are too small to release air with fuel flowing past. I enlarged the holes in the ribs during tank assembly to help this situation

It sounds to me the fueler went too fast, the fuel burbled out and you thought it was full but it wasnt.

JMHO.
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  #7  
Old 05-17-2022, 04:36 PM
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Carl Froehlich Carl Froehlich is online now
 
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Quote:
Originally Posted by PilotjohnS View Post
SNIP

It sounds to me the fueler went too fast, the fuel burbled out and you thought it was full but it wasnt.

JMHO.
The one time in 20 years I did not personally fill my plane - and I got shorted 5 gallons. The good news is the float gauges were well calibrated so I noted the error.

Always fill your own tanks.
Carl
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  #8  
Old 05-17-2022, 04:37 PM
YellowJacket RV9 YellowJacket RV9 is offline
 
Join Date: Oct 2012
Location: Clearwater, FL KCLW
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Quote:
Originally Posted by Walt View Post
Are you sure they were “topped off”, if you pump fuel in fast enough it can’t displace the air quick enough and will “appear” full and spit fuel out the filler. You have to fuel an RV much slower than most aircraft to truly get the tanks full.
This. It is common for me to need to wait for the fuel to settle for a minute or so and then add several more gallons, depending on how fast the fuel is being dispensed. Somebody who just topped them off and put the cap back on may not realize that after settling, there is room for several more gallons.
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  #9  
Old 05-17-2022, 04:43 PM
ssturges ssturges is offline
 
Join Date: Oct 2014
Location: Portland, Oregon
Posts: 68
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I checked the fuel after the fueler fueled the plane. I always install the caps or reinstall the caps after someone else fuels the plane. The caps were correctly installed.

I verified the caps were correctly installed when I landed. The second I noticed the fuel look I looked over at the cap to insure in was in place. In this case I installed the caps, hence I know the plane was fueled to the brim. I am very picky on fuel cap installation.

My tanks and caps are tight as when I pop the caps when someone over fuels the plane you get a small burst of fuel out the top from the vapor pressure. My tanks also vent fuel out the vent lines in case of an overfill when the plane rolls into the sun or has a temp increase. This was the case here I noted there was fuel dripping from the vents after the fueling and the caps had been installed.

I am based at large airport, you cannot self fuel your plane. I always supervise the fueling however, that does not mean they will not fill to the brim however in spit second. I agree that having someone fuel your plane or behind your back is not desirable.

Spec fuel pressure for an IO320 is between 12-45psi. I did not pick this fuel pressure everything is stock Vans/Lycoming. My fuel system runs at 36-40 both the engine pump and the boost pump.

The one thing I cannot remember is if I switched tanks during runup or taxi. I often do this on the case of an overfill to get a little bit of fuel out the tanks and vent tubes. In this case I might have start up on the left tank and switch to the right tank after runup and before taxi. In that case the right tank when have still been had fuel in the vent line which could have created a siphon on the steep turn.

My corrective action is don't let your plane be overfilled. If you are over fueled and have fuel dripping out the vent tubes don't do steep turns and burn some fuel out of each tank. Hard to believe I am the only person to have this happen. A lot of deep questions about how smart it to switch fuel tanks right before take off however :-)
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  #10  
Old 05-17-2022, 05:34 PM
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RV7A Flyer RV7A Flyer is online now
 
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Quote:
Originally Posted by ssturges View Post
My tanks and caps are tight as when I pop the caps when someone over fuels the plane you get a small burst of fuel out the top from the vapor pressure. My tanks also vent fuel out the vent lines in case of an overfill when the plane rolls into the sun or has a temp increase.
I get the exact same thing.

Quote:
I am based at large airport, you cannot self fuel your plane.
Never heard of anyplace with this as a regulation before, but maybe flipping the line guy a few bucks now and again might "persuade" him or her to let you handle the nozzle while he "supervises"? I'm with the previous poster...NOBODY fuels my plane but me. Only damage I've ever had was due to line guys.

Quote:
Spec fuel pressure for an IO320 is between 12-45psi. I did not pick this fuel pressure everything is stock Vans/Lycoming. My fuel system runs at 36-40 both the engine pump and the boost pump.
IMO, this is WAY too high. I have the stock IO-360, and with the boost pump on, it's around 26-27. 24-25 with it off. 40 may be in spec, but why is it so much higher than everyone else's?

Quote:
The one thing I cannot remember is if I switched tanks during runup or taxi. I often do this on the case of an overfill to get a little bit of fuel out the tanks and vent tubes. In this case I might have start up on the left tank and switch to the right tank after runup and before taxi. In that case the right tank when have still been had fuel in the vent line which could have created a siphon on the steep turn.
Plenty of people fill 'er up, taxi on one side, runup on the other, and take off without losing s**tloads of fuel. You have something else going on. Stuck drain valve? Leaking fitting somewhere? Running ungodly rich (not leaning the engine, or you *think* it's being leaned, but it's not)?

Vents shouldn't be creating a suction. If they're done right, they should be creating *higher* pressure in the vent line (open end facing forward).

Keep looking.

Quote:
My corrective action is don't let your plane be overfilled. If you are over fueled and have fuel dripping out the vent tubes don't do steep turns and burn some fuel out of each tank. Hard to believe I am the only person to have this happen. A lot of deep questions about how smart it to switch fuel tanks right before take off however :-)
I think you've jumped to a conclusion without adequate evidence. How would a (coordinated) steep turn offload any sizable amount of fuel?
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Last edited by RV7A Flyer : 05-17-2022 at 05:40 PM.
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