Engine-out due to no fuel pressure

by Gottfried Thoma in General Tech Discussion 6 years ago

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Re: Engine-out due to no fuel pressure

by Garrett Wysocki » 6 years ago

Garrett Wysocki

1 572 1.45k

I used to have similar problems with the old style pump. When pressure started to drop I would put a few drops of engine oil in the top weep hole between the pump mounting flange and the pump diaphragm, this would always bring the fuel pressure back up. This meant that the shaft was sticking due to lack of lubrication and was pounding on the eccentric on the prop shaft. This in turn damaged the end of the shaft on my new style pump which was discovered during a gearbox inspection/cleaning after many hours of 100LL use. Ended up replacing the pump again the and eccentric. You should visually inspect the fuel pump eccentric after removing the old pump for eccentric damage.

Thank you said by: Gottfried Thoma

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Re: Engine-out due to no fuel pressure

by Bill Hertzel » 6 years ago

Bill Hertzel

13 1.95k 7.96k

... I had the engine-out at 7,500 feet. On my Dynon EFIS, OAT was 17 degrees C (~62 F) ...I'm using Auto-Gas 95.... vapor lock appears to be the most logical conclusion but I'm still baffled how this can happen at straight-and-level flight for 20 minutes at 7,500 feet PA (9,600 feet DA)...As you've pointed-out, high non-standard temperatures might be a key issue leading to vapor lock. At 7,500 feet, the standard temperature should be 0 degrees C (32 degrees F) but my OAT was 17 degrees C (~62 F).
Glad that I now have a workable auxiliary electric fuel pump as a back-up...

The OAT is irrelevant, The Temp of the actual fuel is all that matters.
Pressure Altitude, Not DA is the determining factor concering boiling.
Fuel in the tanks and sitting in the hot sun for a few hours before the flight may very well be hot soaked to a temperature above the ramp temperature. It will take a while for 20 gallons to cool down in flight.

Common U.S. Summer Grade E-10 AutoGas has a Reid Vapor Pressure (RVP)of 10psi.
This translates to a boiling point of ~40°C at 7500ft.
E-0 (RVP-9) fuel will allow ~45°C.
Less expensive Auto Gas (Winter Blend, RVP-14) will boil at ~30°C @ 7500ft.

If you have a fuel return line and it does not return the fuel to the fuel tank itself, consider that it will warm up a little each pass around the circuit.

If the AUX pump adds 4psi to fuel lines, that will move the vapor point to ~60°C or allow flights above 20,000ft.

RVPtoTVPChart.pdf (You do not have access to download this file.)

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Engine-out due to no fuel pressure

by Barrie Strachan » 6 years ago

Barrie Strachan

0 7 0

I had similar fuel pressure problems for years with a 912ULS in a StingSport, including an engine-out 5 seconds into the takeoff roll. It's endemic to low-wing Rotax powered airplanes and is (I believe) a result of locating the fuel manifold on top of the engine where it gets good and hot, leading to vapor lock. In my case the flow restrictor (actually a carburetor jet) in the fuel return line was plugged solid, with what I do not know. Anyway once I corrected that, I have had no more issues. If you think I'm making this up, check out this accident report. The pilot reported vapor lock right after t/o and attempted to return to the field with a crash as the outcome. http://www.kathrynsreport.com/2018/03/czech-sport-aircraft-pipersport-n422ps.html

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Re: Engine-out due to no fuel pressure

by Gottfried Thoma » 6 years ago

Gottfried Thoma

1 7 0

Thanks for taking the time and posting your comments, Bill. Appreciate it since it allows me to learn and become a better and safer pilot.

My following information is in reply to your comment that " The OAT is irrelevant, The Temp of the actual fuel is all that matters. Pressure Altitude, Not DA is the determining factor concerning boiling.
Fuel in the tanks and sitting in the hot sun for a few hours before the flight may very well be hot soaked to a temperature above the ramp temperature. It will take a while for 20 gallons to cool down in flight.
Common U.S. Summer Grade E-10 AutoGas has a Reid Vapor Pressure (RVP) of 10 psi.
This translates to a boiling point of ~40°C at 7500ft.
E-0 (RVP-9) fuel will allow ~45°C.
Less expensive Auto Gas (Winter Blend, RVP-14) will boil at ~30°C @ 7500ft.
If you have a fuel return line and it does not return the fuel to the fuel tank itself, consider that it will warm up a little each pass around the circuit. "

Additional information:

1. Before take-off for the x-country flight, my plane was hangared and not sitting in the hot sun. The temperature in my hangar was an estimated 30 degrees C (86 degrees F). After receiving clearance for start-up, I took the plane out of the hangar and took-off within 10 minutes. The sky was about 80% overcast so little direct sun exposure.

2. My x-country flight was for an estimated 250 NM -- lasting for about 2.5 hours -- and I flew between 3,500 feet and 7,500 feet. The OAT was between 25 degrees C and 17 degrees C (77 degrees F and 62 degrees F).

3. I was flying for more than 2 hours -- and the last 20 minutes straight-and-level with AP on at 7,500 feet -- when the engine-out due to no fuel pressure occurred. I would assume that the fuel in the tanks by that time -- due to cool ambient temperature for more than 2 hours -- was "cooled-down" to about 20 degrees C (68 degrees F). For obvious reasons, the fuel circulating the engine and going to the carburetors must have been warmer/hotter but still within safe parameters.

Based on the above, I'm still baffled about the unexpected engine-out at 7,500 feet PA with OAT at 17 degrees C (62 degrees F).

Unless there was something fundamentally wrong with the fuel pump, can you think of any other reasons why I had this incidence (besides possible problems with the fuel return line)? Would value your opinion. Thanks.

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Re: Engine-out due to no fuel pressure

by Norvel Swallie » 6 years ago

Norvel Swallie

23 37 73

I find this interesting. I fly here in Las Vegas at temps above 110 deg. F (even up to 115 - 118) using plain old Costco auto fuel (91 Octane) and I have never had a problem with vaporizing fuel. My fuel pressure runs about 4 # with engine fuel pump and 6 # with elect fuel pump. Low wing, fuel return to left tank. Rotax 912 ULS with carbs. What am I doing right?
Ernie

Thank you said by: Gottfried Thoma

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Engine-out due to no fuel pressure

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