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Posted (edited)

Most fuel flow gauges I have used were pressure gauges calibrated in fuel flow. Don’t know about the latest electronic stuff but I “suspect” they would be similar. It is of interest to know what a gauge is actually reading e.g. a fuel blockage can indicate a high fuel flow when using pressure as its source.

The location of the gauge in the delivery system is important.

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Dynon and other can have real flow through flow meter, impeller, and fuel pressure too, not all equipped as flow sensor costly.

It is technically quite hard to get sensors read the low pressures used in carb engines, often around 1-3 psi, variation is sometimes more than the desired reading

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There is an excellent reason to turn the electric pump off after starting and again after the take off. If you have a failure of your engine driven pump and you keep the electric pump on, you will not know about the failure until the electric pump also fails. You then have two failed pumps.

Electric pump on to start as it gets fuel up quicker, then turn off and do all your checks, warm up, taxying and if your engine driven pump is not working, you will know about it. Turn on electric for the take off, just in case the engine driven pump can't keep up. Electric off after the take off and if the engine driven pump fails, it is there to keep you going.

I am surprised that your instructor could not explain why he did what he did. Good that you question it.

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Posted (edited)

interesting,

I'm currently learning in a J160,

use the pump to prime for 5s before start, then turn on before takeoff after making the call.

it stays on until after landing. where it is shut down "to stop the buzzing noise it makes"

before any landing checks are done

 

then again I'm learning - the school probably built the standard practices around preparation for any recovery from all manner of mistakes

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I'm fairly sure there isn't a fuel pressure gauge in the injected C172 I have flown. Fuel flow definitely, but not fuel pressure.

You’re probably right. As Frank mentioned many fuel flow gauges are actually pressure gauges calibrated to show flow. There’s a requirement in FAR 23 (again from memory) to give info as to whether pumps are working or not.

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I just love a debate where we argue of what should be a "no brainer" - Turn ON your auxiliary fuel pump BEFORE EVERY stage of flight where, even momentary, fuel starvation could be a danger to continued safe flight and turn off only AFTER that stage is no longer applicable - if you dont know what the stages are - take off - landing - low level and any other situation where continued noise up front/behind must be assured for life to do the same.

 

Secondary considerations are just that - burning out the pump - over supply, - pressure & how its measured (as long as it actually delivers sufficient fuel for continued flight)

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Turn ON your auxiliary fuel pump BEFORE EVERY stage of flight where, even momentary, fuel starvation could be a danger

 

YEp - agree with that SD. I went for a fly with an instructor - high wing plane / tanks (who shall remain anonymous - not in queensland). Instructor was adamant that fuel pump (for whole flight and at least 5 landings) did not need to be turned on because mechanical fuel pump pressure was OK

 

I did not agree ............ but of course instructors rule (PIC) prevailed

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What did the AFM state?

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To my recollection C152 did not have an electric fuel pump, not even sure they had a mechanical fuel pump on the C150 just high wing, gravity feed. I have mechanical and electric fuel pumps on my high wing CH701 but only use the electric pump for pre-start prime. Other than that it is there for emergency use only. I know (I built the aeroplane!) that the gravity supply is ample under normal conditions.

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.......................................................................................... the gravity supply is ample under normal conditions.

Said the actress to the bishop !

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It seems like no clear out come whether to leave pump on or off other than what the flight manual says, so let’s say nothing mentioned regarding pump on or off as with many home built experimentals and also the Tecnam p92 Australian Flight Manual which I read cover to cover.

So how is this for an idea if unsure what is required.

1: Pump on prime engine, check pressure, pump off, 2: start engine and do run ups, check pressure and if no gauge and engine continues running, engine pump considered serviceable for flight, 3: before take off pump on check pressure and have 2 pumps on for duration of flight, the same as what we do with running both magnetos, we don’t run 1 mag and if the engine stops at 200’ we turn the other mag on. 4: should the engine stop and we have a forced landing we do what some flight manuals emergency procedures say and that is open doors, fuel off, master switch off and that will eliminate the problem of an electric fuel pump squirting fuel out should something rupture. 5: after landing we do clean up, flaps up, lights off, txp standby, fuel pump off, trim set neutral.

This procedure should check both the electric and mechanical pump for serviceability before each flight, just like doing a mag check.

I checked the 1.5 - 4 psi Facet fuel pumps on eBay, cost A $62.96 draw 1.6 amps and says lasts 4-5 times longer than many other rotary type pumps, so I don’t care about wearing out a $63.00 fuel pump for safety sake.

What’s everybody’s thoughts ?

Pump ON or pump OFF ?

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Looks fine to me but I still think it best to turn the electric pump off once you have sufficient height to get back to the field. The facet cube electronic pumps are very reliable and wear is negligible. But, you are still adding stress to the electrical system unnecessarily. It all depends on what other electrical items are running and how much your alternator can deliver constantly without getting too hot.

 

Turn it on when you are low, or coming in to land or the engine falters. Otherwise the mechanical pump will just do its job.

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Just to add my limited experience here:

 

My Rotax 912 powered aircraft was equipped with a fuel pressure gauge and I noted that the Facet pump only raised the fuel delivery pressure by one psi. The pressure remained well below the Rotax recommended Max pressure.

 

So far, so good.

 

However my fuel flow gauge showed a significant increase in fuel flow when the Facet pump was on. This remained unchanged after replacement of the float valves.

 

I mention this for the benefit of pilots who may desire to run the Facet boost pump continuously, without pressure and flow monitoring. The increased fuel consumption could cause flight planning problems when the tanks go dry a bit early.

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Bald eagle,.... two pumps on for duration of flight like with the magneto's??? You turn a magneto off by shorting it out in the primary circuit . It's NORMAL to run on 2 mags ALL the time. The engine is timed ignition wise to allow for that situation. Running on one only is abnormal and not usually recommended. but the engine still runs.. You certainly don't PLAN to do it. It has the effect of retarding the ignition, which isn't good for it (it can run hotter, deliver reduced power and use more fuel).

Some gravity systems are quite perfect in how they work if they are designed and built properly. The flow rate meets the legal requirements in all normal phases of engine operation. Designed and test flow rate proven prior to first flight.. It's always better than relying on pumps. Pumps can fail in various ways and require stipulated refurbishing at defined intervals.

Planes differ as to how you operate Pumps. That's where the POH comes in. It IS the bible when it comes to how things are done as it's an approved document. Knowing WHY it's done a certain way is better than JUST doing it. This topic is quite straightforward, and pretty much all that needs to be said has been with the simple systems we operate. Don't make it harder than it really is. Nev

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Just looked at a J170 flight manual and it says leave pump on for flights 1000’ AGL or lower and landing with no engine power, master off, fuel off,

Simple enuff for u Nev ?

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Just to add my limited experience here:

 

My Rotax 912 powered aircraft was equipped with a fuel pressure gauge and I noted that the Facet pump only raised the fuel delivery pressure by one psi. The pressure remained well below the Rotax recommended Max pressure.

 

So far, so good.

 

However my fuel flow gauge showed a significant increase in fuel flow when the Facet pump was on. This remained unchanged after replacement of the float valves.

 

I mention this for the benefit of pilots who may desire to run the Facet boost pump continuously, without pressure and flow monitoring. The increased fuel consumption could cause flight planning problems when the tanks go dry a bit early.

 

 

Sounds like your pressure gauge is consistently reading low - non certified/calibrated gauges should only be interpreted as indicators and if readings are consistent (all other parameters OK) is probably fine.

 

I periodically record all my gauge readings (along with OAT & Alt - this gives a record that enables the pilot to make an informed decision's based on passed performance/indication.

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IF you Are using more fuel, after putting on the electric pump, were is that fuel going ?.

spacesailor

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facet style pumps running, messes with fuel flow meters, the pulses make them give false readings, often high

They cant make an engine use more fuel, unless somethings wrong with carb.

Jabiru need electric pump on because the std setup CANNOT deliver 1.5 x max fuel flow to the mechanical pump without electric one running

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Seems to cover it adequately, and that's the purpose of the Flight manual. I'm not against discussing things but his thread was starting to go around in circles where some clarity gets lost. Confusion is sometimes a result. Nev

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facet style pumps running, messes with fuel flow meters, the pulses make them give false readings, often high

They cant make an engine use more fuel, unless somethings wrong with carb.

Jabiru need electric pump on because the std setup CANNOT deliver 1.5 x max fuel flow to the mechanical pump without electric one running

 

Don't know where in your fuel circuit your Fuel Flow sensor/sender is located - mine is on the main supply hose, well before the mechanical pump - not effected by auxiliary pump on/off.

 

My Fuel Pressure sender is located on/in the fuel manifold, where the one supply line splits/divides for delivery to each carburettor - again other than a very slight increase in pressure no effect from turning auxiliary pump on /off.

 

You may have your sensor()s to close to the pump.

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Cant be any further apart, length of the fuse, also tried several orientations, same deal

Turbine meters are easily upset and they can be restrictive too

Very common to hear people comment electric pump increases fuel use

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As facthunter said we are going in circles, but to turn it into an oval and before anyone asks I will explain why one mag off gives the equivalent of an ignition retard. With one plug not working there is a time lag for the fuel on the far side of the cylinder to be ignited, due to the distance the flame front has to travel. This can be seen as a drop in rpm and also an increase in EGT, because there is more fuel burning when the exhaust valve opens. This is especially true as the size of the cylinder bore increases.

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my .01 $. Was told to turn off the fuel pump after landing (in a j160) because the ticking sound annoyed my instructor :)

 

(also turned off after takeoff because thats what I was taught *shrug* )

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