Engine Failure yesterday

68 posts in this topic

Posted

Uh... We just talked about this in another string... Were you using a header tank with open vent?

I had forgotten how small the original "behind the seat" header tanks were... If that is what you had (with an open vent) an additional pump would not have helped as with reduced, or no, flow from the main tank the header tank would have filled up with air from the vent anyway. Never leave the header tank vent open!

Please explain "never leave the header tank vent open".  

I just built a mk iv and trying to learn all i can about operations.

I ran both tanks to a tee and then to the header tank.

Then I ran a vent line up and out of the aircraft.

Thanks in advance.

James MIller

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Posted

Never leave the vent open as it pisses fuel everywhere once it has finished venting.............

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Posted (edited)

James,

there are, as you can read in this string, 2 schools... "Always open vent" or "Open vent only to vent out the excess air, then close it", pros and cons (based on sometimes conflicting theories) has been discussed at length.

I suggest you read all the mails (i.e. not only my mails and theory - that might be in minority...) . The way I see it is that an open vent is is a way for air not only to escape (that is what we want) but also to enter (and we do not want that). The comment from Gfry is also correct, fuel can get succeed out through the vent line (this is normally easy to detect as your canopy get white and crack almost instantly...)...

And I do have some thoughts about "both tanks to a tee"... 

Edited by FredStork

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Posted

I am a "closed vent" guy. My vent is a short one with a valve, and stays closed in flight. I open it on preflight and watch fuel pee out to assure that the header has no air. This design has successfully flown for about 700 hours over 22 years without a problem.

BTW I think Fred has a pretty good handle on what happened here.

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Posted

Same here,

I have a header tank with a closed vent. This vent is only opened when /if I empty fuel from that header tank so as to refill it...I also aded a infra red low fuel warning system on my header tank which will also tell me if there is any air in it.....

P.s I only have one main tank going into my header

 

My 2 cents

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Posted (edited)

"I also aded a infra red low fuel warning system on my header tank which will also tell me if there is any air in it....."

Hi FlyWise,

please tell us more about the infra red fuel level detector... like a link to wherever you got it from...

I have found that the system I have, an inclosed breaker triggered by a tube shaped magnet in somekind of floating plastic, tend to sometimes get stuck in the low position. 

Edited by FredStork
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Posted

Hey Fred, the sensor and indicator/test switch is from these guys    http://www.pillarpointelectronics.com/sensors.html

Very easy to install, no moving part....it can also be fitted inline of a supply line instead of the tank....

you can see it on the left , left of the trim switch

 

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Posted

Thanks! 

I like the inline version - but why did someone tell them this is used by people that are so rich they have their own aircrafts? I find the standard version for 1/4 of the cost on other sites but unfortunately not the inline version... 

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Posted

Hey Fred, I do agree it's expensive....where did you find cheap ones working in fuel? Back when i searched I didn't find any specifically built to withstand permanent immersion in fuel..

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Posted

James,

there are, as you can read in this string, 2 schools... "Always open vent" or "Open vent only to vent out the excess air, then close it", pros and cons (based on sometimes conflicting theories) has been discussed at length.

I suggest you read all the mails (i.e. not only my mails and theory - that might be in minority...) . The way I see it is that an open vent is is a way for air not only to escape (that is what we want) but also to enter (and we do not want that). The comment from Gfry is also correct, fuel can get succeed out through the vent line (this is normally easy to detect as your canopy get white and crack almost instantly...)...

And I do have some thoughts about "both tanks to a tee"... 

Thanks for your answer.  I flew today with the vent closed. Had no problems and no fuel vented and sprayed out.  

Would like to hear your thoughts about both tanks to a tee.

Thanks Again

Jim

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Posted

I got an OLS-10 Optitrol level switch. Same type as mentioned above. I see one now on Ebay for $15. 

1CFDD835-D0A1-469B-BE63-9286D62155C8.jpeg

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Posted (edited)

I have been flying my Avid close to 22 years and just about 1200 hrs. I have a inlet to the tank and a bleed valve. It is closed all the time unless I have drained the fuel system, then I open it to fill the header tank until it flows out of the valve. Making a big deal out of nothing.

IMAG0344.jpg

Edited by Bandit

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Posted

I noticed that when I did my flow testing of my fuel system on the new plane with tanks in both wings the header would not fill when it was empty with only one wing valve open. As soon as I opened the other side it took it big gulp of air and fuel started flowing quickly. Once the header was full you could see fuel shoot up into the other line even though that side was empty. Once the header is full it feeds pretty evenly from both tanks.

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Posted (edited)

C5Engineer,
it sounds like you have separate arrivals to the header tank from each of the wing tanks (i.e. the 2 wing tanks are not joint by a T prior to the header tank). If this is correct the noticed behavior is expected. The air in the header tank, with "no where to go" (no vent open and nothing being drained from the header tank) will block the arrival of fuel. The diameter of the fuel lines is too small to let air of any significance trickle back to the tank against the fuel. When you open the valve to the other tank the air will escape through that tank. Once the header tank is full fuel will flow from tank 1 to tank 2 until they reach the same (vertical) fuel level. With identical tanks, and the plane level, they will end up with the same volume.
If you open the vent on the header tank you can fill it up without opening the second wing tank valve. Either "always open" at a point higher than highest point of your wing tank or open on demand.

Jim,
it is not clear if you only have a T between the 2 tanks or if you have a T and 2 valves so you can select what tank to use. If the connection between the 2 tanks is always open fuel will flow between the tanks until they are at the same level (communicating vessels). This is normally not a problem and the advantage is that there are no valves to be set in the wrong positions. But if gives less choice.
Going back to the start of this string...  if you lose a fuel cap and have communicating wing tanks both tanks could be emptied through the lost cap with little or no fuel reaching the header tank at all (particularly with an open vent...).
If fuel flow (significantly) faster from one tank than the other (partially clogged fuel lime...), that tank could get drained before the other - ending up with the fast flowing tank working as a vent where air can get sucked into the header tank, rather than fuel, by the pump as discussed in the string. 

Also, while everyone loves flying most of the time we fly alone, and while we spend a lot of time flying for most of our flights the volume of one wing tank is sufficient. Our planes are light and you can feel the difference between empty and full tanks. Piloting from the left seat the fuel will be a counter weight if you use the right wing tank (single tanks are by default on the right side for this reason). We don't always know if there is ethanol in the fuel and what our tanks think about it, saving one tank from permanent exposure and only use it for long flights might pay back one day...  Same goes for any contamination of one tank, you can use the other. It is also easier to read  the fuel level when using only one tank. Gravity flow will benefit from one tank as the difference between tank fuel level and the outlet will be greater.

But none of this actually matter as we always fly with the knowledge that the engine can stop at any time and we therefore always know ahead where to land. Slow and light we glide to safety, fold our wings and have a friend pick us up with a trailer... Been there, done that... 

 

 

     
 

 

Edited by FredStork
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Posted

Hey Fred, I do agree it's expensive....where did you find cheap ones working in fuel? Back when i searched I didn't find any specifically built to withstand permanent immersion in fuel..

You probably have a point there. I even found one explicitly saying not to be used with flammable or explosive liquids... and no one  saying permanent immersion in fuel... I'll keep digging - but will probably end up with the expensive version as usual... Thanks for the link!  

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Posted (edited)

I had thought about buying the $pensive (float type, I think) from Kitfox to go with my $pensive plastic header tank, but after hearing about others, I am undecided to go with it, or some other, or change to the larger type aluminum Avid header tanks (2 of them) and find another sensor.  Guess now I will let the final builder make those decisions. 

I still like the Kitfox vent lines better than the Avid style - Kitfox vents back to the upper part of the wing tank from the header, and not into the open air stream, and can be used as a sight gage for the early tanks that don't have the sight gage lower fittings.  They don't need shutoff valves.   EDMO

Edited by EDMO

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Posted

Mikuni pump overhauled today.  It hasn't made a massive difference, its at least now a constant pressure and not flickering.  At 2500rpm it's 0.3 bar and full power is a tiny bit over 0.2bar.

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