Do you shut your electric fuel pump off on a lycoming?

[cgeyman]

My painful two cents

https://docs.google.com/presentation/d/1hBMikFdqinAP9IPx25YXEJbTahC_AxD8b9fyFrgK2iQ/edit

(My crash debrief about getting an airlock after unporting a fuel tank). Agree with Sam’s recommendations.
Cal

 

[Desert Rat]

I think that whether it's a Lycoming or not doesn't factor into my decision. On a high wing Cessna, no, I don't leave the fuel pump on. In fact I never turn it on except for priming and/or to make sure it works, per the POH.

A low wing airplane, especially a fuel injected one, is a whole different can of worms. In that case I also just follow whatever is says in the POH.

For my RV, since I'm the mfg, I get to decide, and I've decided that I want that assurance that I'm going to get fuel flow in close to the ground situations no matter what, so I'll be turning it on for takeoff and landing. Haven't decided yet about switching tanks at altitude, but I'm inclined to say yeah sure, it's not like it hurts anything.

Hope to be flying in a few months so I can put this into practice!

 

[Pilot135pd]

On a high wing Cessna, no, I don't leave the fuel pump on. In fact I never turn it on except for priming and/or to make sure it works, per the POH.

A low wing airplane, especially a fuel injected one, is a whole different can of worms.

So what you're saying is that a high wing fuel system creates enough pressure in the system to keep a fuel injected engine running if the mechanical engine pump dies.

 

[rv8ch]

https://docs.google.com/presentation/d/1hBMikFdqinAP9IPx25YXEJbTahC_AxD8b9fyFrgK2iQ/edit

(My crash debrief about getting an airlock after unporting a fuel tank). Agree with Sam’s recommendations.
Cal

Hi Cal, thanks for sharing the presentation. One question - no idea if it would have had any impact on the incident - why did you use an intersection takeoff? Looks like it was even a longer taxi to where you got on the runway.

Back to the topic of the thread, I also use my boost pump near the ground - takeoff and landing - and I use it when switching tanks. During my pre-first-flight testing I ran both tanks dry on the ground without the engine running and the Andair pump did re-prime, but I don't feel the need to try this in flight.

I have a Red Cube and GRT Avionics EIS4000/EFIS Sport EX which includes a totalizer that's really accurate (assuming I enter the correct amount of fuel added when I fill up) and I have the floats in each tank. Even if my totalizer says 19 gallons, seeing single-digit gallons on the fuel tank makes me very uncomfortable.

I have everything in Freedom Units, but I buy fuel in liters - which did cause me to run very low on fuel once. I added 40 liters with my 2 jerrycans, and told the totalizer I had added 20 gallons. Duh! Getting within 10 minutes of my destination with both tanks saying "low on fuel" was very uncomfortable. I still had almost 90 minutes of fuel, but gosh I was puckered up.

Your slide 48 which talks about the causes of engine failure should be something we all take to heart. Such an avoidable reason to crash.

 

[jrs14855]

Pump

A high wing Cessna with fuel injection requires use of the electric boost pump if the engine driven pump fails.
High wing airplanes with float carburetors do not require fuel pumps with rare exceptions such as the very early 170's that had an engine driven pump.

 

[Desert Rat]

So what you're saying is that a high wing fuel system creates enough pressure in the system to keep a fuel injected engine running if the mechanical engine pump dies.

I don't honestly know without looking it up, But I kind of doubt it.

However, I'm reasonably confident that there's enough head pressure so that if the engine driven pump fails or you get an interruption when switching tanks that you're not going to vapor lock the darn thing in the couple of seconds it takes to flip the boost pump on.

The fuel injected 172's came out 25 years ago so if that were a potential, then Cessna engineering and legal folks would have slipped a boost pumps on line into the takeoff and landing checklists years ago and that hasn't happened.

 

[jrs14855]

172

The current Cessna 172's have engine driven fuel pump and electric boost pump.
A Bendix style fuel injection cannot operate on gravity feed alone.
There are many Lycoming 172's with carburetors that operate on gravity feed.

 

[Fred.Stucklen]

Automate the Aux Fuel pump function

So the lycoming requirement for assured engine performance is to guarantee fuel flow to the engine at the proper pressure. In certified aircraft (and conventional implementation in the experimental domain) the aux pump if manually cycled to cover any possible mechanical pump failures during critical flight periods.

In the auto industry manual operation of fuel pressure is not available to the operator. Why should it not be the same in our EXPERIMENTAL aircraft? Why can't that function be automated?
With an independent fuel pressure sensing system coupled with a simple timer circuit controlled by a pilot operated switch (OFF-AUTO-ON) you'll never have to worry WHEN to turn ON the AUX pump (just like in your car). With the switch in the AUTO position, the pump turns ON when the fuel pressure falls below a setpoint, and stays on for some period after the setpoint is again reached. The engine is never without the needed fuel flow.

One argument is that this would be electrically dependent. But haven't we already designed our electrical systems with a secondary power source (secondary battery, or single battery assured bus) that could drive the automated aux pump?

I posted exactly this exact solution many moons ago, and have been successfully used it on my RV-7A for over 2000 Hrs. Something for the fleet to consider....
https://vansairforce.net/community/showthread.php?t=195197 Post #10....

 

[rvbuilder2002]

. But haven't we already designed our electrical systems with a secondary power source (secondary battery, or single battery assured bus) that could drive the automated aux pump?

Some have but my estimate would be that a large majority of the currently flying RV fleet do not have a secondary electrical system.

Count me as one that has zero interest in having, or promoting the use of, an automatic system that takes away the ultimate simplicity and reliability of the traditional back-up system and all of the benefits it provides to the pilot to evaluate the current heath of the fuel delivery system.

 

[BobTurner]

I fail to see the issue of redundant power. The aux pump is itself electric. Most aircraft rely on the odds of the mechanical pump and the electrical system both failing being very small. I would say, though, that a careful analysis would need to be done to check on the law of unintended consequences. In the event of a fuel line failure, would the system automatically react to the falling pressure and turn on the electric pump, pushing more gas out? etc. We need to be careful that the cure isn’t worse than the disease.

 

[rv8ch]

I fail to see the issue of redundant power. The aux pump is itself electric. Most aircraft rely on the odds of the mechanical pump and the electrical system both failing being very small. I would say, though, that a careful analysis would need to be done to check on the law of unintended consequences. In the event of a fuel line failure, would the system automatically react to the falling pressure and turn on the electric pump, pushing more gas out? etc. We need to be careful that the cure isn’t worse than the disease.

Very good point. I've seen many cases in the IT world where attempts to make things more reliable ironically has the opposite effect. I can imagine in mechanical systems it's even harder to predict all the possible failure modes and consequences.

 

[rvbuilder2002]

. We need to be careful that the cure isn’t worse than the disease.

I wasn’t meaning to imply that an automatic system should have redundant power, just that if the thought was that it was needed, that it wasn’t common.

My main point is that statistics show that the majority of engine stoppages in E-AB Aircraft are fuel related and generally fuel system design (often modifications away from standard) comes into play in some way.