comfortcat

comfortcat

Well Known Member
Friend
Greetings!

I'm building an RV-9A and may have a chance to buy a Cessna O-320 engine (no mechanical fuel pump):D

What is the general consensus on Electric only fuel systems?:eek:

Anyone flying one?
Anyone Sorry?

I know I can update to mechanical but why? Just extra expense or really extra safety? Electronic Ignition folks can dive in here. :cool:

Dkb
:confused:
 
Redundancy is key...

...in my opinion, David. The certificated airplanes use two mags, two fuel pumps and two sparkplugs per cylinder. Why would you want to limit yourself to one electric pump? Would it not be the same to have just one ignition system? No way out if it goes TU.

Figure your risk and safety factor first and I think you'll answer your own question reasonably.

The best,
 
I'm not sure he's asking about using only one fuel pump. I think he's asking about 'electric only', ie. two electric pumps. I think that is a great idea and may be more reliable, considering documented problems with mechanical engine driven pumps. If my engine driven pump fails, I'll definitely consider installing a second electric pump and getting rid of the mechanical one all together. Plumb them in parallel, turn both on for takeoff and landing, use one (alternately) for normal cruise, and make sure you check them both on every preflight. No problem as far as I can see.

Scott
RV-8FB (carbureted)
 
172N H2AD

I'm betting that your O-320-H2AD HAS a fuel pump pad (Mine did) and the cam has the drive lobe (mine did) that it's no problem to mount the fully available LW-15399, and loads of people have done it.

BUT, if you're doing it because it looks like a bargain, think again. The cylinders are roughly $1300 new, vs less than $1000 new for a 'typical' 320. The REQUIRED TO REPLACE AT O/H parts include things you inspect/yellow tag in other engines - like lifters, rockers and rocker pivots.

In the end, I built a 100% genuine Lycoming sourced H2, new cam, new Lyc cylinders, new fuel pump, all required parts replaced(and then some others I just didn't feel good about), crank, rods, case, etc, all inspected, O/H and yellow tagged but reputable shops, new alt, new starter, INCLUDING CORE, for $17,600. But it sits new on my stand, never run. It will run for the first time on the airframe.

If I had to do it all over again, I would be a lemming and buy a new 320 from Vans. But it was educational like no other part of the project. I am a moderately experienced engine builder, this was #6, and there are NO mysteries inside the crankcase, especially since half my engine builds were T3 VW race engines (how may jokes in that statement? Spend $8K on a motor that MIGHT, just maybe, make 130hp?)

Rick 90432
 
My original engine was , like yours, a 600 hr cessna (gravity fed carb) o-320. I planned on install in rv-9 with (2) electric fuel pumps in series. If the primary failed, the secondary was always avail. Both flowed fuel even when off. As for electrical failure, I have 8 amp aux alternator. I see no problem with this set-up. Shoot, you could even put in a third:rolleyes:pump if it gave you peace of mind.
 
There are a few people here on this site who have done it, and others (like myself) who are planning it. Frankh is flying the same setup I'm planning, with one electric pump in each wing root, drawing directly from the tank and supplying pressurized fuel forward. Our goals were to eliminate vapor lock potential, but the solution is the same. Both pumps on for TO/L, single pump operation the rest of the time. Switching tanks becomes a matter of turning on the left pump and turning off the right, or vice versa - no fuel valve needed.

This does, of course, make your aircraft electrically dependent - so a secondary alternator should be considered minimum equipment, and a secondary battery would be a strong consideration.
 
pierre smith said:
...in my opinion, David. The certificated airplanes use two mags, two fuel pumps and two sparkplugs per cylinder. Why would you want to limit yourself to one electric pump? Would it not be the same to have just one ignition system? No way out if it goes TU.

Figure your risk and safety factor first and I think you'll answer your own question reasonably.

The best,
Click to expand...

+10

Matt
 
Total Electrical Failures are not rare

I have had a significant number of total electrical failures in flight and the idea of having my fuel supply totally dependent on available electrical power when it is not necessary is unimaginable.

Bob Axsom
 
Yes

On two airplanes (one carbed this one FI'd) with about a thousand hours between them.

Very happy I did it...I could not imagine using a hydraulically flawed mechanical fuel pump that may vapour lock at any moment....:)...Actually running mogas (with or without ethanol) is the only likely time this will happen.

Electrical redunadancy is the key...if I thought that I could not make the electrical system as reliable as a mechanical pump then I personally would never fly IFR either.

But yes I love the system I designed, no selector valve, bone smple to use.

Frank
 
I gotta go with Frank here.

One of our senior tech advisors used this engine in his -6A and put two of the little box pumps in each wing root. The MTBF was high enough that the risks of them both failing at the same time was about the same as having both the mechanical and electric pumps fail at the same time.

He would just turn on the pump to the tank he wanted to burn. For takeoff, he would flip on both pumps.

Somewhere I was looking at a thread on this site about a mechanical fuel pump that can be plugged into one of the accessory holes in the back of the engine, why not look into that prior to making your selection?
 
frankh said:
On two airplanes (one carbed this one FI'd) with about a thousand hours between them.

Very happy I did it...I could not imagine using a hydraulically flawed mechanical fuel pump that may vapour lock at any moment....:)...Actually running mogas (with or without ethanol) is the only likely time this will happen.

Electrical redunadancy is the key...if I thought that I could not make the electrical system as reliable as a mechanical pump then I personally would never fly IFR either.

But yes I love the system I designed, no selector valve, bone smple to use.
Click to expand...

I'd have to have a back up alternator to feel good about it. I've flown for over an hour with an alternator problem, and just using the battery for minimul purposes. Since the engine was running perfectly on it's own devices, and the battery "could" have been used for a fuel pump back up.........there was very little to worry about. Had I been required to use batteries only for a total electric pump system, I wouldn't feel near as comfortable. Would have to land somewhere & get it fixed, rather than getting back to home base.

L.Adamson --- RV6A
 
Yes I have a backup alternator..For me in going IFR this was not a problem as I would have built the same level of electrical redunancy in anyway.
For a VFR airplne I would probably biuld in a second battery instead, like I did on my first airplane..

Either way works

Frank
 
IF you think you'll ever consider resale, think about all us old farts out there who might be able to afford it but wouldn't be comfortable without a mechanical fuel pump in a low wing airplane.

The possibility of resale is the primary reason I prime alclad parts.;)
 
Indeed the H2"AD" engines are always cheap to acquire. There is a reason for that, in that they are an engine that is...well....seen as quite as good as the rest of the typical lycos for a number of reasons. They are quite different in design (having an integral accessory case for example) and a number other unique things about them. Not to say they are bad engines (once all the requisite AD's have been performed and the Tmod done), just to say they aren't quite as readily accepted by the mainstream. I personally am not a fan of those engines, but I wouldn't lump them as garbage either.

The discussion on fully electric fuel systems has been hashed over for many years. There are those here like Frank who are successful with their design and have proved that it works just fine. The fact of the matter is that the stock Van's fuel system works just fine, and is probably the best way to go. The electric way isn't wrong, but it is fixing a problem that statistically just doesn't exist in the many thousands of flying RV's that are out there.

I guess it's sort of like dual electronic ignition. If you have the redundant electrical supply to feed it, then you're headed the right direction. If you don't, then you gain little in the way of redundancy.

It's hard to beat the stock system as designed, and it's hard to beat a standard Lyco. The H2AD's are flying in many RV's so I'm not going to trash them to harshly, but if I had my druthers I'd pick a standard 320 or 360 with a stock fuel system for a myriad of reasons, but it's a personal decision you have to make.

My 2 cents as usual!

Cheers,
Stein
 
yup and if I was always going to run 100LL I would probably stick with the standard system.

Interestingly I only got to the electric only option because it was the only option I had on my sooby powered Zodiac. While I was designing that system well then it might as well be "hydraulically correct".

For me to switch to the STD system made me nervous...:)

It's actually. Pretty easy to convert to a standard setup using the parts I have plus a mech pump of course. So if my future buyer wants a STD system then it's not a huge deal to change.

Each to their own...:)

Frank
 
comfortcat said:
Greetings!

I'm building an RV-9A and may have a chance to buy a Cessna O-320 engine (no mechanical fuel pump):D
Click to expand...

I don't see where he ever said it was an H series engine. A lot of cessna's (prior to about 1978) were built with non H engines also, but they still had no fuel pump because of the gravity feed fuel system.

The main problem I have with two electric pumps is you are trading the benefits of the two electric pumps (lower likely hood of vapor lock, etc.) for I higher level of complexity in the electrical system. If you run two electric pumps you should also have a dual redundancy electrical system to make sure you can keep the engine running. This can be done without adding a lot more complexity; but it is more none the less.

Personal decision that a builder has to make.

Thousands of RV's are flying without ever having any hint of the problems associated with having a mechanical engine driven fuel pump. People who have concerns about it can implement some of the preventative measures ahead of time just to be sure. This is no different than choosing two electric pumps ahead of time...just to be sure, except it doesn't require a redundant electrical system also.
 
frankh said:
Yes I have a backup alternator..For me in going IFR this was not a problem as I would have built the same level of electrical redunancy in anyway.
For a VFR airplne I would probably biuld in a second battery instead, like I did on my first airplane..

Either way works

Frank
Click to expand...

Exactly correct. For me, I wanted to be able to go IFR at any time (which means redundant electrical is a requirement), and to be able to run mogas with possible EtOH, which raises the issue of increased vapor lock exposure AND mechanical pump diaphragm issues. Since I was already consigned to have redundant electrical for IFR nav, there is no longer a compelling reason to NOT consider full electrical for fuel supply. The only time you are exposed to a single fuel pump failure putting you in the dirt is in the case of burning a tank dry and not having that second pump available - simply don't do that.

My electrical plan right now is dual alternator, dual battery, independent busses with the ability to cross-tie.
 
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Dual Electric Pumps only...

Man! I LOVE this site. Everyone offers GREAT advice. But as everyone says, it is up to the builder to make the final choices. Putting certified anything on an experimental airframe does NOT make it a certified aircraft. More RVs have had in-flight break-ups than all the Cessna 172s.

Here are some additional thoughts:
=======================

1. The engine is not the H2AD engine (possible cam grief with that right?) It is out of a 1975 and I believe it is an O-320-E2D but no pump pad. The engine is low time and bolt-on, ready to run.

2. I never thought that one pump would do. The question was non mechanical pump, i.e. two electrics.

3. The single point of failure for dual pumps is still the electrical supply. Both IFR nervous folks and Electronic Ignition folks have the same worry.

4. 'Lectric Bob has TONS to say about critical bus electrics. Look at http://www.aeroelectric.com/ Simple and effective. I attended the seminar as well. Worth while. Get your local EAA chapter to offer it.

5. I never thought about dual pumps at each wing. What a cool idea. How about electronic switching so the plane switches tanks every five to ten minutes so the operator does not intervene? Great for us "Cessna Skyhawk" types that are used to the "Both" setting. Manual override of course.

6. Often, an 8 amp vacuum pad mount alternator is the second unit (No vacuum in my plane). For dual mags, and internal Dynon batteries, would 8 amps handle dual electric pumps? They only have to run until fuel exhaustion anyway.

7. Thanks all for the help.

Dkb
 
the SD8 alternator is what I run as a backup...I was amazed at what it would run without allowing the volts to drop below 12v. My guess is its really a 10A alternator at 12v.

I ran the GNS 430W, transponder and radio in recieve mode, plus the electric fuel pump (the fuel injection high pressure type) at lentgh and it never let the batt volts drop..that was at 2600RPM (engine)

Frank
 
as to auto switching..I guess you could but personally I like to be intimately involved in where the fuel is...Besides you would have to design the system so it does not violate the "no single point of failure" rule... May be more trouble than its worth

Frank
 
comfortcat said:
...
1. The engine is not the H2AD engine (possible cam grief with that right?) It is out of a 1975 and I believe it is an O-320-E2D but no pump pad. The engine is low time and bolt-on, ready to run....
Click to expand...
Check out the engine page on my web site for changing out your accessory case.

Although I did this to my old O-290, the process and parts are exactly the same. I think I paid $100 for the case, $80 for the cam gear, and $20 for the push rod. While I was at it, I replaced the oil screen with a 90 degree oil filter adapter.

You will have to move your oil pump over to the new accessory case. This is easy to do and will give you a chance to inspect it.

You can do this in a day, maybe less. Just buy the correct OH and parts manual from Lycoming. Don't get the manual from eBay as the Lycoming manual will have all the current updates.
 
Interesting...

So, If I use dual pumps instead of a valve, I assume a one-way valve is required to prevent fuel from being pumped back to another tank. Where do you place the one-way valves? Near pumps or near junction?

I guess Andair has these.

Are you planning dual fuel pressure gauges? Actually, for reduced cockpit workload, this makes no difference: "In case of suspected fuel problem, both pumps to "ON"

Also, pumps are pushers, not suckers. Specialty pumps?

(I still like the automatic fuel management idea. Should be easy. )

Dkb

airguy said:
There are a few people here on this site who have done it, and others (like myself) who are planning it. Frankh is flying the same setup I'm planning, with one electric pump in each wing root, drawing directly from the tank and supplying pressurized fuel forward. Our goals were to eliminate vapor lock potential, but the solution is the same. Both pumps on for TO/L, single pump operation the rest of the time. Switching tanks becomes a matter of turning on the left pump and turning off the right, or vice versa - no fuel valve needed.

This does, of course, make your aircraft electrically dependent - so a secondary alternator should be considered minimum equipment, and a secondary battery would be a strong consideration.
Click to expand...
 
All pumps are designed as pushers...no pump is designed specifically to suck. You can only suck on a fluid to the extent that the inlet pressure to the pump is equal to the valour pressure of the liquid..suck any harder and fuel boils and will valour lock. The higher the vapour pressure of the liquid the more likely this is to happen.

A check valve is required at the discharge of each pump as you describe

If you have a carbed engine you will simply use two of those 40106 facet cube pumps... There is a style that has a check valve built in. If you are going fuel injected the setup is similar but requires a different pump and more hardware... You can find the description of my system in the archives.

Frank
 
Interesting approach. I'd like to start using auto gas (with ethanol) in an IO-360 engine on an RV-7A. Everything in the fuel system has been designed to be able to use ethanol based gas, EXCEPT the engine mounted fuel pump. removing this item, and replacing it with two faucet high pressure pumps (with check valve) in the wing roots (and keeping the AUX electric fuel pump) would solve the problem. I already have a redundant electrical system (two batteries, two alternators).
Does anyone know if a ethanol tolerant diaphragm is available for the standard Lycolming high pressure fuel pump? This would be the simplest fix....

frankh said:
All pumps are designed as pushers...no pump is designed specifically to suck. You can only suck on a fluid to the extent that the inlet pressure to the pump is equal to the valour pressure of the liquid..suck any harder and fuel boils and will valour lock. The higher the vapour pressure of the liquid the more likely this is to happen.

A check valve is required at the discharge of each pump as you describe

If you have a carbed engine you will simply use two of those 40106 facet cube pumps... There is a style that has a check valve built in. If you are going fuel injected the setup is similar but requires a different pump and more hardware... You can find the description of my system in the archives.

Frank
Click to expand...
 
Fred.Stucklen said:
Does anyone know if a ethanol tolerant diaphragm is available for the standard Lycolming high pressure fuel pump? This would be the simplest fix....
Click to expand...

Except for the possibility of vapor lock - which is somewhat more likely with lower vapor-pressure fuels such as E10. The engine-driven fuel pump is bolted directly to the biggest heating element in your aircraft, and is heating the fuel flowing through it. Changing the diaphragm only solves half the problem.
 
What's been documented regarding mechanical fuel pump failures? In over 5000 hours of light plane flying I've never had one, nor have the pilots I asked about this. However, I have had 3 electric fuel pump failures. Bill
 
Bill- seems like your MTBF is over 1500 hours. Therefore, I don't fly any legs long enough to fail two electric fuel pumps on one leg. There are however, situations where vapor lock is a recognized risk, as opposed to a random failure. So from my perspective Frankh did his homework.

Here is a random failure that hasn't been discussed. When a mechanical fuel pump fails, it usually leaks fuel. In an RV, it will drip directly onto the hot exhaust. The failure of an electric fuel pump generally means it quits pumping - period.

LarryT
 
Heat problem is not a big issue.

airguy said:
Except for the possibility of vapor lock - which is somewhat more likely with lower vapor-pressure fuels such as E10. The engine-driven fuel pump is bolted directly to the biggest heating element in your aircraft, and is heating the fuel flowing through it. Changing the diaphragm only solves half the problem.
Click to expand...

I solved the heating problem by directing two blast tubes to the mechanical fuel pump. Eliminating 90-degree fuel line fittings also helps. Unfortunately my source for ethanol-free premium mogas just switched to E-10.:mad:
 
Nope...

LarryT said:
When a mechanical fuel pump fails, it usually leaks fuel. In an RV, it will drip directly onto the hot exhaust. The failure of an electric fuel pump generally means it quits pumping - period.

LarryT
Click to expand...

....not if you place a recommended drain line down to the lower edge of the firewall, for that reason,

Best,
 
Fuel stuff

I would not use the two fuel pumps in the wings without some type of transfer system. Otherwise if one pump fails then the only fuel available is what is left in the tank with the good pump. If you had allready used alot of that fuel ... you are in trouble. My preferance is to have a fuel system with a "both" setting. I have seen skilled - high time pilots, screw up and select an empty tank causing an engine stopage. The simple fact is, sooner or later, we all make mistakes. So design a mistake tolerant system. Russ
 
OK! Here's what I'm thinking (while my cat helps me type):

Two electric fuel pumps. One at each wing root.
Plumbing is:

1. Tank to pump
2. Pump to Electric pressure switch (Open with zero pressure, closed with 5 lbs pressure) Switch controls Green LED
3. Pressure switch to one-way valve
4. One-way valve to T-fitting (two tanks in, one line out)
5. one line out to EFIS flow/pressure switch
6. EFIS pressure/flow switch to Gascolator
7. Gascolator to Carb.

On engine start, both pumps on, and dual green indicators show pressure at both pumps. Green is go. No dual green, no go. Burned out LED? Tough. Broken wire? Tough. No green, No Go.

Dual pumps on at take off.

After level flight, turn off one pump.

At tank change time every 30 minutes, both on, see green, and turn off pump old tank

This will keep about the same amount of fuel in both tanks.

In flight emergency, both pumps to on.

*** OPTIONS / Questions:

What about adding an On-off valve (ala C-150)?

What if one-way valve failed AND a pump failed? Would fuel pump to opposite tank and not to the carb at all?

If I forgot to change tanks for a long time, then the Other pump failed, Would I need a transfer system?

Cons:
====
Electrical dependent (as is Electronic Ignition)
Extra complexity - One-way valve and LED pressure switches. Extra wiring.

Pros:
====
No fuel fittings or valves that might leak in the cockpit.
Low vapor lock risk
Easy pre-flight check of pumps.
No rubber parts to fail in flight.


Please feel free to add to list of pros and cons.

Cheers!

Dkb



comfortcat said:
Greetings!

I'm building an RV-9A and may have a chance to buy a Cessna O-320 engine (no mechanical fuel pump):D

What is the general consensus on Electric only fuel systems?:eek:

Anyone flying one?
Anyone Sorry?

I know I can update to mechanical but why? Just extra expense or really extra safety? Electronic Ignition folks can dive in here. :cool:

Dkb
:confused:
Click to expand...
 
filters

Don't forget a fuel filter (or gascolator) ahead of each pump. So pumps in wing roots means 2 filters/gascolators. Do-able...just sayin.

I seem to recall that some gigh pressure pumps have built in check valves so that may be a simpler way to go with fewer connections.

Bevan
 
The one-way valves are to verify that each pump is producing pressure. If one pump failed, and no one-way valves, the pressure back to the bad pump would make the green light come on.

Thanx!

Dkb


Bevan said:
Don't forget a fuel filter (or gascolator) ahead of each pump. So pumps in wing roots means 2 filters/gascolators. Do-able...just sayin.

I seem to recall that some gigh pressure pumps have built in check valves so that may be a simpler way to go with fewer connections.

Bevan
Click to expand...
 
The only thing I would question would be the need for the gascolator after the pumps. You'll certainly need fine filters on the inlet of each pump in the wing roots - after that point there's not much reason for a gascolator AFTER the pump.
 
Gravity Feed in case 2 DC Fuel Pumps lose power?

I'm very curious to hear the answer to this question. After looking at my 9A with a Lyc O-235, the carb appears to be 6 - 12 inches below the lowest part of the fuel tanks. Does this mean that if both electric fuel pumps lost DC power or the mechanical pump failed, would gravity take over and supply the carb with enough fuel to keep the engine running for a landing? What is the minimum fuel pressure required for adequate cruise and landing engine rpm. Or do I just need enough fuel flow for my engine to keep it running. My engine requires 5.2 gal/hr, which doesnt sound like very much of a flow rate. Will gravity keep the engine running or not?

Thanks for your time,
 
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Flow rate math

(5.2 x 128)/3600 = 0.185 oz./sec if it's not too early in the morning for my brain to work. Another way of looking at it: It would take just over 43 seconds to fill an 8 oz. cup

LarryT

mfshook62 said:
I'm very curious to hear the answer to this question. After looking at my 9A with a Lyc O-235, the carb appears to be 6 - 12 inches below the lowest part of the fuel tanks. Does this mean that if both electric fuel pumps lost DC power or the mechanical pump failed, would gravity take over and supply the carb with enough fuel to keep the engine running for a landing? What is the minimum fuel pressure required for adequate cruise and landing engine rpm. Or do I just need enough fuel flow for my engine to keep it running. My engine requires 5.2 gal/hr, which doesnt sound like very much of a flow rate.

Thanks for your time,
Click to expand...
 
Last edited:
LarryT said:
(5.2 x 128)/3600 = 0.185 oz./sec if it's not too early in the morning for my brain to work. Another way of looking at it: It would take just over 43 seconds to fill an 8 oz. cup

LarryT
Click to expand...

And if my math is correct, that's about 5.23 gallons/hour. Barely enough to sustain cruise flight for the most efficient RV's.
 
airguy said:
There are a few people here on this site who have done it, and others (like myself) who are planning it. Frankh is flying the same setup I'm planning, with one electric pump in each wing root, drawing directly from the tank and supplying pressurized fuel forward. Our goals were to eliminate vapor lock potential, but the solution is the same. Both pumps on for TO/L, single pump operation the rest of the time. Switching tanks becomes a matter of turning on the left pump and turning off the right, or vice versa - no fuel valve needed.

This does, of course, make your aircraft electrically dependent - so a secondary alternator should be considered minimum equipment, and a secondary battery would be a strong consideration.
Click to expand...

While the use of two electric fuel pumps that are plumbed in this way does offer a degree of redundancy, it doesn't match the redundancy of the conventional setup with two pumps in series. In the first case, loss of one pump also makes the remaining fuel in that tank inaccessable. In the second case, either of the pumps alone can draw from either of the tanks, and all of the fuel is accessible.

I also think that there is value in having an engine driven mechanical pump so that the fuel system is not electrically dependent.
 
Skyhawks with carbs have no fuel pump, so the flow rate would not be the issue.

With a mechanical pump, the pump is mounted on the front or back of the engine, above the tank level, so you'd be SOL with that. (Simply out of luck)

With the engine carb 6-12 inches below the bottom of the tanks, that would probably work in straight and level flight, but maybe not a climb (or flare)
(No Go-around for you!)

Dkb



mfshook62 said:
I'm very curious to hear the answer to this question. After looking at my 9A with a Lyc O-235, the carb appears to be 6 - 12 inches below the lowest part of the fuel tanks. Does this mean that if both electric fuel pumps lost DC power or the mechanical pump failed, would gravity take over and supply the carb with enough fuel to keep the engine running for a landing? What is the minimum fuel pressure required for adequate cruise and landing engine rpm. Or do I just need enough fuel flow for my engine to keep it running. My engine requires 5.2 gal/hr, which doesnt sound like very much of a flow rate.

Thanks for your time,
Click to expand...
 
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