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peterthomson
Joined: 18 Jul 2010
Posts: 41
Location: Thailand
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 Posted: Mon Jul 20, 2015 4:55 am Post subject: Vapor lock 914 |
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Friend has been having problems with "vapor lock" particularly at take off power.
Aircraft is Pelican, high wing, L and R wing tanks feeding through a L-Both-R-OFF selector to a gascolator, then through two Facet pumps in series to carburetors, with airbox. Return line is T-eed back to the gascolator. Most lines fire-sleeved.
Could the problem be fixed by taking the fuel return back to a wing tank ?
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davidjoyce(at)doctors.org
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| Posted: Mon Jul 20, 2015 5:34 am Post subject: Vapor lock 914 |
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For what it is worth, the LAA approved arrangement for the 914 in a Europa takes the return line back to the main tank situated in the fuselage. There is substantial return flow which means that you are getting rapid supply as far as the pressure relief valve of fuel at the (hopefully low) temperature of the main tank. In >1000hrs flying this arrangement in often very hot conditions, have never had serious vapour lock problems. Regards , David Joyce
On 2015-07-20 13:54, Peter Thomson wrote: [quote]
Friend has been having problems with "vapor lock" particularly at take off power.Aircraft is Pelican, high wing, L and R wing tanks feeding through a L-Both-R-OFF selector to a gascolator, then through two Facet pumps in series to carburetors, with airbox. Return line is T-eed back to the gascolator. Most lines fire-sleeved.Could the problem be fixed by taking the fuel return back to a wing tank ? | Quote: |
ist">http://www.matronics.com/Navigator?RotaxEngines-List
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Mon Jul 20, 2015 7:49 am Post subject: Re: Vapor lock 914 |
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Is the gascolator forward of the firewall (like cessnas) or in the fuselage (like old pipers or my Europa)? Location and temperature make a difference.
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Mon Jul 20, 2015 8:52 am Post subject: Re: Vapor lock 914 |
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Why does he think it is vapor lock? It could be something different especially at take off when things haven't had a good opportunity to get really hot.
Why couldn't it be fuel starvation?
All the Flight Design's have their recirculation line go back into the gascolator which is in the lower part of the engine compartment. None of them anywhere has ever had an issue. There is plenty of cool fuel moving through here to prevent vapor lock. If your gascolator were to be to near a heat source then it could be affected. Depending on which of his fuel lines are not fire sleeved then maybe this may contribute. You can plumb the recirculation line back to a header tank, the wing or the gascolator and all are acceptable.
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BARRY CHECK 6
Joined: 15 Mar 2011
Posts: 738
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| Posted: Tue Jul 21, 2015 1:42 pm Post subject: Vapor lock 914 |
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Peter,
That is not vapor lock!
That is IMPROPER part insulation.
1- Two boost pumps are not required.
2- The boost pump should be after the fuel selector.
3- What size lines are being used?
4- Gascolators... I hate them! They must be located at the very lowest point in the fuel system. They are a pain to maintain. Their are AD's concerning the safety wire procedure and the drain valve. They give a false sense of security. And, they don't work very well.
My guess is you are flooding the carb. Not starving it.
Do you have a fuel flow gauge? Check what the MAX fuel flow is from the engine manufacturer and comparing it to what you are seeing.
Since you are both a gravity feed and a boost pump feed flooding is more than likely your issue. So, to answer your question about a return line back to the tank! YES, that would be my suggestion also.
Next question: What FACET pump do you have? Some of their pumps stop fuel flow or have a high resistance to fuel flow once the pump is turned off.
Next question: Many builders think bigger and more is better. What fuel flow rate does your pump supply?
Next question: Did the designer say boost pump?
Prove to yourself that it is vapor lock. Bet you can't! IF you think it is vapor lock use AvGas and wrap aluminum foil crumpled around the hoses. You can also build a "COOL CAN"... A coil of copper tubing in a metal coffee can where you pack in Dry Ice. This will definitely eliminate vapor lock and increase the SG of the fuel and increase the HP.
But, my money is still on flooding.
Barry
On Monday, July 20, 2015, Peter Thomson <peterlthomson(at)gmail.com (peterlthomson(at)gmail.com)> wrote:
| Quote: | Friend has been having problems with "vapor lock" particularly at take off power.
Aircraft is Pelican, high wing, L and R wing tanks feeding through a L-Both-R-OFF selector to a gascolator, then through two Facet pumps in series to carburetors, with airbox. Return line is T-eed back to the gascolator. Most lines fire-sleeved.
Could the problem be fixed by taking the fuel return back to a wing tank ?
| Quote: |
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