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Friendly Challenge, Fuel Pump Electrical Power

Freemasm

Well Known Member
A friendly challenge/request for help to Mr. Froelich, Mr. Stucklen, and others with an art for electrical/electronics.

I'm building an electrically dependent aircraft that will have redundant electric fuel pumps. Either is selectable as "primary" (no dedicated primary/boost/back-up) and my plan is to keep ~ equal run times. Of course, each will have a manual switch. I like Mr. Stucklen's automatic back-up power/timer but it appears to me (ME background) that this is intended for dedicated primary/boost config. I'd like to incorporate something similar.

How would you approach this? My initial thought would be a parallel power circuit that blindly energizes both pumps if the low pressure condition = true; warning light also, of course. What would you talented electrical types do?

What is not an option for me:
- Getting said functionality from any of the known power management systems. There appears to me to they would introduce single point failures for my liking.
- Introducing fluid system components like check valves, etc.

Any thoughts and ideas that could be shared would be appreciated. Sorry if this has been hashed our previously.
 
A friendly challenge/request for help to Mr. Froelich, Mr. Stucklen, and others with an art for electrical/electronics.

I'm building an electrically dependent aircraft that will have redundant electric fuel pumps. Either is selectable as "primary" (no dedicated primary/boost/back-up) and my plan is to keep ~ equal run times. Of course, each will have a manual switch. I like Mr. Stucklen's automatic back-up power/timer but it appears to me (ME background) that this is intended for dedicated primary/boost config. I'd like to incorporate something similar.

How would you approach this? My initial thought would be a parallel power circuit that blindly energizes both pumps if the low pressure condition = true; warning light also, of course. What would you talented electrical types do?

What is not an option for me:
- Getting said functionality from any of the known power management systems. There appears to me to they would introduce single point failures for my liking.
- Introducing fluid system components like check valves, etc.

Any thoughts and ideas that could be shared would be appreciated. Sorry if this has been hashed our previously.

I would need to know more about your fuel system configuration before making a recommendation. If your looking to put a fuel pump in each tank, or near the exit of each tank, and want automatic selection, it would require you to put an electrical switch on the panel that selects that tank when you physically select the fuel source (fuel valve). Once that electrical selection is performed, you could use the secondary low fuel pressure auto function to energize the selected tank AUX fuel pressure circuit for that particular tank. But this requires two inputs from the pilot : one to select which tank you draw fuel from, and which tank the auto low pressure sense curciut is enabled, which allows for pilot error if the two are conflicting. I know of no fuel selector valve that has an electronic selection output.

Let talk about this more...
 
A friendly challenge/request for help to Mr. Froelich, Mr. Stucklen, and others with an art for electrical/electronics.

I'm building an electrically dependent aircraft that will have redundant electric fuel pumps. Either is selectable as "primary" (no dedicated primary/boost/back-up) and my plan is to keep ~ equal run times. Of course, each will have a manual switch. I like Mr. Stucklen's automatic back-up power/timer but it appears to me (ME background) that this is intended for dedicated primary/boost config. I'd like to incorporate something similar.

How would you approach this? My initial thought would be a parallel power circuit that blindly energizes both pumps if the low pressure condition = true; warning light also, of course. What would you talented electrical types do?

What is not an option for me:
- Getting said functionality from any of the known power management systems. There appears to me to they would introduce single point failures for my liking.
- Introducing fluid system components like check valves, etc.

Any thoughts and ideas that could be shared would be appreciated. Sorry if this has been hashed our previously.

On page 6 of this document http://www.huvver.tech/wp-content/uploads/huVVer-AVI-V2C.pdf I show an automatic fuel pump controller that has a manual overide. The switch is OFF-AUTO-ON. The ON position is the most direct control. Hope this helps. It’s just an example.

VV
 
Interested as well with additional details

I also will have an electrically dependent engine with dual electric fuel pumps that can run in parallel but will normally only be used one at a time or on both for take-off and landing. There is no mechanical engine driven pump.

The pumps sit after the fuel selector (between the fuel selector and engine).

I would like a system to monitor the fuel pressure (35 PSI Nominal) and if it drops below, say 30 PSI, the system would automatically switch to both pumps and also alert me via a visual warning(digital input). The goal is to maintain fuel at 35 PSI to the engine automatically.

The alert would allow me to know about the issue and then possibly switch from both pumps back to pump 1 or pump 2 by switch or breaker and remove the bad pump from the electrical load, or worse fault.

Any ideas?
 
On page 6 of this document http://www.huvver.tech/wp-content/uploads/huVVer-AVI-V2C.pdf I show an automatic fuel pump controller that has a manual overide. The switch is OFF-AUTO-ON. The ON position is the most direct control. Hope this helps. It’s just an example.

VV

So what is you actual fuel source configuration? Do you have a single tank, or two tanks selected with a fuel source valve? Is the fuel selector valve BEFORE the dual pump configuration? Or are the pumps in each fuel source before the selector valve? What signal level is required for the annunciation function?

Is it necessary to turn BOTH pumps ON when a fault is detected? Or only the pump associated with the selected fuel source? Should the failure of one pump be automatically detected, allowing the second pump to take over?
 
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So what is you actual fuel source configuration? do you have a single tank, or two tanks selected with a fuel source valve?

It is basically a standard, low wing, no header tank config past the fuel selector. The typical boost pump is a dual/redundant electric pump assembly (no engine driven mechanical pump. As someone stated above, I’ll manually turn on the second, stand-by below ~2000AGL. To KISS it, I’m thinking my approach would be something akin to the original post; automatic back-up circuit to energizes both with a warning light. Am I on the right path?

Side note. I’m trying to keep suction losses as low as possible for Vapor pressure margin if 100LL has future issues. Will measure said suction losses once I’m further along. Pix = selector to gascolator to dual pump assembly.

Thx. Can be more thorough in the future when not thumb typing.
 

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Scott,

Just to level set, I do not see any advantage (specifically in engine efficiency) offered from an EFII airplane over a dual pMag, standard fuel injected engine, so I have not worked this issue.

But since you asked, off the top of my head:
- I first assume you have solved the power distribution problem. You can have a dozen fuel pumps but if you can’t get power to them you have the same problem, the fan stops. I’ve seen no single battery scheme that meets what I would consider bare minimum - regardless of number of alternators.
- You are looking at only one issue with EFII, keeping fuel pressure. I offer that while this is important there are many other things to work. As such a recommend a full system approach as the next step.
- For your specific question, back in my first career having two pumps for a single pump system was the norm. Here pump #1 would run on even days, pump #2 on odd. The pump control box (strictly analog) had the pump control switches - options for each pump was on, off or standby. For you this simple approach would be just fine - where the standby function had the pump off unless pressure dropped below a trip point. Then the standby pump would turn on. I also suggest that you add the feature that if the standby pump comes on it stays on until you turn it off (reset it). This will eliminate standby pump cycling if you have an intermittent issue.
- Taking this a step beyond simple pump electrical failure, I would incorporate check valves to preclude a failed pump providing a bypass back to the tank from the running fuel pump. Check valves are not a bad thing.

Carl
 
It is basically a standard, low wing, no header tank config past the fuel selector.

Photos suggest the system is sucking through a 50 micron Aerolab gascolator with both pumps, apparently while running a full time return line, probably for EFI. Can't tell if the fuel valve is duplex, or if the return simply tees in near the valve.

I’m trying to keep suction losses as low as possible for Vapor pressure margin if 100LL has future issues. Will measure said suction losses once I’m further along.

Please do post the loss at the pump inlet when you have it. Might want an operating temperature measurement too. I suspect you're stacking up a triple threat; very high flow rate, high restriction, and plenty of heat.
 
I would try to get pumps from 2 different manufacturers on the theory that they both won't fail at about the same time.........
 
@Carl F
Yes. It is a whole system integration/redundancy approach. We've spoken a little in the past and I'd like to again if you don't mind. I sent you a PM. I too am in favor or a "dumb" analog back-up system with an idiot lite to inform me it's activated. The delay circuit that Fred incorporated makes good sense. You don't want the back-up system cycling and also provide time for the operator (pilot) to perform any related manual operations. I've designed a lot of power generation systems. Resisting idiot's (my opinion) constant push to digitalize safing systems from stone simple, open to activate, back-ups and fail safes was a constant challenge.

@DanH
Yes/no/maybe? I don't plan on using anything but 100LL or a future FAA approved equivalent. There are 9.6:1 pistons in the lovely Feng Shui appurtenance in the back of the hangar. Fuel is the cheapest thing we put in our aircraft (different touchy subject). Just trying to design around any future availability issues. Potential different pistons aside or fuel additives, this is TBD obviously.

Suction losses?

- Parasitic. Speed kills but there's not much I can do there if I stick with a more modern full flow system. Run length and bends are kept low, elevation changes limited, etc.

- Heat. Not as bad as one might think. I did a flow velocity calc for someone else here. The returned fuel will spend fractions of a second forward of the firewall. Back calculating amp draw of the Walbros versus theoretic pumping HP from flow/head suggest a very high efficiency (some type of PD pump probably gear? couldn't verify) thus little heat introduced there.

- Component losses. I'll find out. Nothing is listed for the Andair valve but playing with it, it appears very low. You mentioned the Aerolab. I'm quite aware of the effects from media beta and know that higher (finer) doesn't mean better for an application. I rationalized to myself based on available surface area which is much better due to increased diameter. Reference attached graph below. I did a review on this here on VAF. You might have fun picking at it. The choice for me made for better packaging and a lot less tube work and length.

So after wading through the BS above (not blindly, mind anyone), I'll test the finished system config for total loss at condition when I can. I'm not one of those types who studies reports and such to determine conditions when I could open the blinds to see if it's raining.

Back to the main subject. Thanks for the input so far. I hope it keeps coming and in more detail. This is a great place, isn't it?

Cheers boys
 

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So after wading through the BS above (not blindly, mind anyone), I'll test the finished system config for total loss at condition when I can.

No BS Scott. Rate, restriction, and heat are not necessarily a problem when taken individually, but combined there is a potential for trouble. Please note you did mention your wish to design for vapor pressure margin in case 100LL has future issues...which I referenced.

I'd suggest a very practical test. Rather than attempting to measure pressure drop at the pump inlet, simply replace the the gascolator-to-pump line with a length of clear polyurethane tube. Raise the tank temperature to 100F and the gascolator temperature to 120F or so, then run the pumps with an open return and observe the poly line for bubbles.

I suggest 120F or so for the gascolator for a reason. Here the Aerolab body is mounted to the hottest skin surface on the whole airplane, the center of the belly, a foot or two aft of the cowl exit. The skin aft of the ramp is quite warm on my RV-8, and RV-10's are famous for a hot tunnel. What sort of belly temp is typical for a Rocket?
 
@DanH. You might have misunderstood my meaning. I was calling BS on myself. I’ve been through too many engineering/technical issues in my life to not respect the unknown variables that can creep in. You can calculate and analyze all day and the real world can still find a way to bite you (me) in the a$$. Been there, done that, got the tee shirt. The careful and fortunate ones of us don’t have any codes or professional standards written in our blood.

I don’t know the tunnel temps on a Rocket but expect them to be equally bad compared to RV world.

I’ll take your advise on the clear tube at the pump suction. I’ll still measure the static P with a manometer. If there are no bubbles, I’d like to be able to determine any margin (at those ambients/fluid temps/blend/one v two pumps running/etc. I’ll move the variables as much as I can.

Back to the original topic, had a good off-line convo with Carl F. Probably leaning to an automatic latching circuit/manual reset for back-up pump activation on low pressure supply pressure indication. This story ain’t over until it’s over.
 
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