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Fuel Pump missing


Ben Longden
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Just as I was hopping into Shepp Aero Clubs third tecnam, 5159, I was given the heads up on my checklists...

 

Forget about the fuel pump switch.

 

Cos there aint one.

 

Anyone else have the same?

 

For a pilot with only bloody limited stick experience, but shiploads of right seat time, I would have thought a switchable fuel pump was almost standard, especially on a 42 degree day when vapour locks on rotate come to mind.

 

Ben

 

 

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Even if the aircraft is built under 101.28, it is not mandatory to have an additional fuel pump if the fuel can flow to the carby(s) by gravity. You do have a fuel pump on the engine, so you do actually have a redundant system.

 

David.

 

 

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Guest pelorus32

G'day Ben,

 

that's only one of the things that are different about 5159. When I bought her home to Shepparton the other day I took a few minutes to master the new attitude picture because of the reclined seats. Don't know whether I like all of those rocker switches either. Unlike the last new Tecnam however this one seems to fly straight and not want to drag a wing. She also has a turn of speed and rolls more freely on taxi than the last one.

 

Like kids really....all different.

 

Regards

 

Mike

 

 

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The complete opposite here...if you're looking for comfort with a spare fuel pump or 2, the CT4 has 4 of them! 1 engine driven pump, 1 prime pump, 1 low boost pump and 1 emergency boost pump...just in case...

 

Cheers,

 

Matt.

 

 

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The Tecnam P92 SE is certainly gravity fed, as has been pointed out.. my only concern is when its 42 degrees and the engine is hot... what about force feeding the engine when a fuel vapour lock happens.

 

Sorry, but I come from the old school of "just in case"..:;)3:

 

Still, apart from that the new Tecnam at Shepp is a sweet ship... very sweet... no vices... EFIS and leather seats!!

 

Ben

 

 

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Fuel pumps will not pump vapour usually and can also be a source of additional heat.

 

 

 

The suction side of a pump could cause the fuel to boil (cavitation) reducing available fuel flow. Pumps if used need to be placed where they get the maximum available static pressure on their suction side after allowing for the losses in pressure that occur when the fuel is flowing.

 

 

 

So an engine mounted mechanical pump often has the lowest static pressure in the system on its suction side and it can be a source of heating for the fuel.

 

 

 

Regards

 

 

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The correct place for a fuel pump in my opinion is close to the tank, there it will not get vapour.

 

I have heard it recommended that the electric auxilliary fuel pump should be left on all the time when running. A bad idea in my opinion as if the engine driven pump fails, it's failure will be masked by the electric pump until that also fails.

 

 

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More useful? info about fuel pumps

 

As Subaru EA81 engines have never run mechanical fuel pumps (all car installations used electric pumps) I fitted an electric pump in series with the fuel line from the high wing tanks, and always use it when climbing out. Level flight is always on gravity feed alone

 

Before Easter, en route to Narromine, the fuel pump stopped (turned out to be a stuck piston, after buying a new pump!) In experimenting caused by necessity, I discovered that I could still pull 4000 revs and 500 fpm on climbout just on gravity feed alone when the wing tanks were less than 500mm above the carby.

 

Are we a bit hung up on the need for multiple fuel pumps on high wing aircraft?

 

 

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Ian, I was always taught to turn it on to start the engine, turn it off for taxi, then turn it on for takeoff. That way, I'll know if my mechanical one has failed whilst I am taxiing for take off.

 

 

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Fuel pump factors.

 

An engine mounted fuel pump would heat fuel up in two ways, the actual heat in the body of the pump (conveyed from the engine crankcase) and the fact that the fuel lines are routed over the hot parts of the engine to get to and from it. In a Gipsy major installation the failure of the diaphragm can allow fuel to enter the crankcase and mix with the lube oil. On an engine driven pump, IF the mechanical actuation fails, what pressure is required to bypass both valves in the fuel pump, to ensure that adequate fuel still gets to the carburettors?

 

With both pumps operating the pressure applied to the carbs. is the SUM of both pumps, if they are in series. (which is the usual case). This can sometimes result in excess pressure being supplied to the carbs. which can cause flooding. A gravity system with all the fuel lines heat insulated past the firewall, is pretty foolproof, if adequate head of fuel is available.Regards Nev...

 

 

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Guest Nelson Smith

With two pumps in series, it doesn't necessarily mean the pressure is the SUM of the two pumps.Most engine driven pumps have built in regulators.As the pump builds up pressure, then the diaphram is held clear of the operating HOOK.If the electric pump (in series) pumps greater than the designed pressure then the plunger (solenoid) stalls and won't pump any more.

 

Nelson Smith

 

 

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Fuel Pump performance.

 

You are correct with the diaphragm pump. I overlooked the fact that the spring alone determines the final pressure as, if the pressure entering the pump is instrumental in compressing the spring, the diaphragm will not stroke, and therefore not add to the pressure already available. My comments relate to centrifugal pumps, or unregulated pumps, which add to the input pressure. Thank you Nev....

 

 

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Mechanical pump by-pass pressure.

 

I would be indebted to someone who would be able to measure the head of fuel required flow through an engine mounted mechanical fuel pump which is not operating. This could be done on a bench or just with the cowl off & fuel lines removed. I havent been able to find this information out. A minimum head of fuel is specified in certain instances for gravity feed systems. I am trying to cover the situation where an engine driven mechanical pump is installed but has failed in the linkage so is not operating for that reason, Both the inlet and outlet one-way valves have to be bypassed so there has to be some back pressure. Nev..

 

 

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  • 2 months later...

Just curious on others starting techniques with fuel pumps.

 

My RAA instructor suggested using the electric pump to prime the Jab for a few seconds then switch off to as the Jab started easier using this technique.

 

Later there was a change in emphasis. Prime with the electric pump then switch pump off to start the engine as a possible engine fire at starting will be fed fuel by the electric pump which ain't good for the soul!

 

I thought this was an excellent reason to follow this starting procedure.

 

Switch pump on again for the T.O and initial climb after which the pump was only used again for the landing phase.

 

 

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