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**schu** · 06-23-2023, 11:54 AM

probably move my previous post as well

**Nev** · 06-23-2023, 12:45 PM

I think there are some significant distinctions between EI/mechanical injection and EFI

That's an excellent post schu

Your point (1) about returning fuel to a tank and not having a BOTH position on the fuel selector is a very important one. My own observation is that if not using the BOTH position, when the fuel quantities are lower, the aircraft must be flown with full attention on coordinated flight (ball centered) to prevent unporting and subsequent engine failure.

Due to the low yaw stability of my own Bearhawk I found this very demanding. I wondered if N22GM had an electrical issue, or an imbalance/unporting issue. Also with MattS engine failure HERE over the Amazon in PR-ZJO, I thought anecdotal evidence put a high probability on unporting of a tank with only one tank selected at the end of a 4 hour flight. We were very fortunate to have Matt share details of this with us for the benefit of the wider BH community.

**svyolo** · 06-23-2023, 06:19 PM

I was always biased towards EFI/EI, both are fully installed but not run yet (but soon). The biggest drawback is it is a big wiring job, and if you don't understand how it all works, it is a "black box". For me, I understand it and MFI is a "black box". If your wiring isn't spot on, it won't be reliable.

It should have all the benefits of Bendix style if Bendix is running perfect. But Bendix has 3 "black boxes" that I can't fix, are wear items, and are expensive to rebuild. The same goes for PMAG's vs standalone EI. The standalone is a wiring job, the PMAG easier to install. But the PMAG is a wear item.

For EFI/EI, the ECU and Hall Effect sensor have to be replaced by the manufacturer. Everything else can be sourced locally, and cheaply. The only wear items are the spark plugs and fuel pumps ($100). So more work to install, less maintenance, and hopefully cheaper to own. Hopefully.

Fuel system discussions are in older threads. I copied the system layout that Cessna did on later 180 series with Conti FI. I used a small 2L "collector" tank under the right front seat and returned fuel to that. It is tucked into the strongest part of the fuselage. I am pretty content with it, although the local DAR isn't in love with my choice of where to put the fuel valve (Newton).

**schu** · 06-23-2023, 09:39 PM

I’m pretty curious to see where you put the valve. Pictures? Mine is under the pilot seat in the frame right behind the stick.

**Utah-Jay** · 06-23-2023, 09:53 PM

You guys are too complicated for my taste
Carbed engine
Basic mags
GA Prop

But I should be light and simple, which was my main plan all along.

I do like reading this stuff, but only understand a bit of it

**FFTravism** · 06-23-2023, 10:14 PM

Why can't you have a both fuel valve? Is it to do with EFI/MFI or the actual fuel valve?
Travis

**kestrel** · 06-23-2023, 10:46 PM

Originally posted by FFTravism View Post

Why can't you have a both fuel valve? Is it to do with EFI/MFI or the actual fuel valve?
Travis

If you aren't using a header tank, you need to return excess flow to the tanks. If running off the left, return it to the left. If running of the right, return it to the right. This requires a duplex valve; two valves in a stack with one knob on top. The start of the problem is that it takes care to design a both with a high volume pump that won't "suck air" and the return needs to be balanced so that the tanks remain balanced. I would expect that if the system is built balanced, the tanks will balance themselves. The end of the problem is that the just mentioned problems result in a very tiny market for duplex valves with "both" so they are mostly unavailable. Andair doesn't make one. Newton makes one but it is for small engines with low flow rates.

**Ed.Meyer** · 06-23-2023, 11:41 PM

We have an SPRL duplex fuel valve in our EFII equipped Patrol. It has a both setting returning fuel to both tanks when selected. I fly with both selected nearly all the time. It has worked fine. There are times on a long flight that some imbalance occurs but i am not sure it is any more than a non return system with a both setting. When it does happen, I simply select the fuller tank for a while going back to both before landing.

**schu** · 06-28-2023, 10:05 AM

Originally posted by Nev View Post

Your point (1) about returning fuel to a tank and not having a BOTH position on the fuel selector is a very important one. My own observation is that if not using the BOTH position, when the fuel quantities are lower, the aircraft must be flown with full attention on coordinated flight (ball centered) to prevent unporting and subsequent engine failure.

Due to the low yaw stability of my own Bearhawk I found this very demanding. I wondered if N22GM had an electrical issue, or an imbalance/unporting issue. Also with MattS engine failure HERE over the Amazon in PR-ZJO, I thought anecdotal evidence put a high probability on unporting of a tank with only one tank selected at the end of a 4 hour flight. We were very fortunate to have Matt share details of this with us for the benefit of the wider BH community.

Nev

Frankly I don't see how the issue with MattS' airplane could have been caused by a coordination issue, and even if it was, how BOTH would solve it. Lets look at the data:

MattS' post is at https://bearhawkforums.com/forum/bea...2243#post52243 also https://bearhawkforums.com/forum/bea...2282#post52282

Here are the key take aways:

Airplane used a continental io-360 which returns to tank.
We don't know how the return to tank was plumbed
We know that he removed a L/R/OFF valve and installed L/R/Both/OFF.
The cross vent between tanks was not installed.
The pilot doesn't believe he unported a tank.
During 3 hour flight airplane was pulling more fuel from the left tank.
10:30AM Switched to right tank
11:00AM; Switched back to using both tanks, 5 minutes later began power-on descent
11:25AM; Descending then powered up to ~2200 RPM and began climbing for an extended downwind. About 2.5 miles from the runway entered a left base with power and a slow climb. Level wings in the left base the engine quit. No sputtering, no signal, suddenly dead. Switched to the right tank and started electric fuel pump. Engine surged once then quit again.
After the crash there was 10 liters in the left tank and 55.5 in the right.

With all of this data lets hypothesize that a tank was unported due to flying uncoordinated and consider these facts:

The airplane was in the BOTH position when the engine quit. This doesn't point to BOTH fixing the issue, whatever it was.
Turning left with 55.5L in the uphill wing, then level, then quit. If the airplane was flying uncoordinated it would probably be yawing to the right which would cause the fuel in the right tank to swing to the left, which would bring it towards the ports. Also the right tank had 14.5 gallons in it, which is more than half full, so you probably couldn't unport this tank as it was the fullest one.
The left tank is much more likely to be unported because it had less fuel, was on the downhill side (which wouldn't matter if coordinated) and any yaw to the right would move the fuel away from the port. If this tank did unport, then BOTH didn't help, rather it probably hurt.
Would unporting cause a very sudden power loss or would it sputter? I think it depends on if it stays unported, and the only way I can think for that to happen is for it to suck a bunch of air into the line which will cause the pump to loose its prime. That would be consistent with starting the electric pump and getting a sputter only to have that pump full of air too.

For these reasons I don't think this crash was due to uncoordinated flying that would have been fixed by a BOTH selector, I think that leaving the selector on the right would have avoided the fuel starvation because it seems like the airplane had air in the lines which would be less likely if runnning on the right tank and because there is no possibility that the left tank could draw fuel away form the the right tank before flooding the inlet of the pump which could happen if there was negative pressure in that tank.

In your post above you wrote:

Originally posted by Nev

My own observation is that if not using the BOTH position, when the fuel quantities are lower, the aircraft must be flown with full attention on coordinated flight (ball centered) to prevent unporting and subsequent engine failure.

I don't understand how using BOTH somehow solves unporting issues. If having any port unport creates a problem then using BOTH is a liability when low on fuel as you have more ports with less fuel over them. If all of the ports unporting creates the problem then how would selecting the fullest tank cause issues? If anything it's less likely to unport.

In your post here: https://bearhawkforums.com/forum/bea...4509#post74509 you show a diagram (a really nice one I might add), but it seems to me that selecting the fullest tank would always keep at least one port covered, probably both. Also, if there was some air in the line, you have another tank to switch to that you really don't have when running on BOTH. In single tank operation you would in theory always have a column of fuel up to the fuel selector valve ready to feed the pump that you could switch to.

Also, you don't say if you have the cross vent installed or not. If not, there is more nuance here because you don't technically have two tanks acting as one, you have two independent tanks feeding through a y.

I understand the argument that BOTH makes fuel management easier, I also understand the argument that a single tank might not flow enough fuel, but I don't agree that BOTH could be a fix for uncoordinated flying and I for sure don't agree that BOTH would have saved MattS' day.

I have no way to confirm, but I theorize that BH fuel system problems come in three varieties: Pilot error and ran out of fuel, using a returning fuel system that moves fuel faster than the system can burp itself thus if unported sucks air, some pressure differential between tanks that causes one tank to feed the other instead of the inlet of the carb (or pump). If I am right, then only the first one might be fixed by using the BOTH position. If the other two, it probably make it worse. So far I haven't seen anything that leads me away from my theory. Every fuel starvation issue I'm aware of was running a return to tank system or lacked the cross vent to deal with any pressure differential.

NOTE I am discussing theory of operation and thinking through this while considering a non standard engine install. If you are building and aren't sure what all of this means, then build exactly like Bob planned it, with a carb and make sure you have 150% of required fuel at the carb in nose up attitude. Adding a cross vent couldn't hurt.

**svyolo** · 06-28-2023, 05:42 PM

I don't know how much excess return fuel Conti MFI has. SDS/EFII the pumps are pumping 35-40 gph, so at 8-12 gph burn rate you are returning a lot of fuel, and if returning to the main tanks, the tanks and plumbing must feed that much under gravity. If they don't do it under gravity, the pumps will be sucking. Sucking by itself is OK, but not if you have multiple fuel pickups. Suction fed pumps are fed by one fuel pickup, by convention. If you have more than one pickup, and one gets unported, you can suck air thru the pump.

Whee used 1/2" fuel lines on his Conti IO-360 fuel system, at least on the rear fuel pickups IIRC. If I returned to the tanks, I would have used 1/2" lines as well. I ended up using a 2L small tank under the right front seat, and returned fuel to it. The top of that tank vents to the main tanks. The main tanks and plumbing only have to feed engine burn.

**Nev** · 06-28-2023, 07:35 PM

For these reasons I don't think this crash was due to uncoordinated flying.....

schu This is a very well reasoned and very interesting discussion Schu. I'm keeping an open mind because I don't think we know the exact cause of the failure in the end. I don't have a tank cross vent on my own aircraft, and your knowledge of the Continental FI system is well beyond mine.

But I'm still scratching my head.

Matt said they found 55 litres in the right tank and 10 litres in the left. This has got me scratching my head because in the photo it clearly shows the left wing 30° low and Matt said the fuel selector was in BOTH. So the fuel should have ALL transferred under gravity to the left tank after the aircraft came to a stop. But it didn't.

Matt doesn't say whether they drained those quantities out of the respective tanks, or whether they determined the quantities from looking at the sight gauges. It makes a big difference. With the aircraft stationary and left wing 30° down, the fuel in the left tank is mostly outboard. So in order to read 10 litres on the sight gauge there is (I'm estimating) probably 50 litres in the left tank, and only a tiny amount of that is able to register on the sight gauge.

The fuel in the right tank is mostly inboard, so a very small quantity of fuel would have shown a very large reading in the right sight gauge. Perhaps as little as 5 litres resting on the inboard area of the tank would have filled the sight gauge. You can start to see the problem, because in flight before the engine stopped, if the ball was out to the left, the fuel conditions would have been very similar, causing the appearance of low fuel on the left tank and high fuel quantity on the right when actually it may have been the exact opposite.

**schu** · 06-28-2023, 08:39 PM

Nev

Hmmm, MattS said:

Later when we began removing the wings we discovered that I had 10 litters in the left tank and 55.5 in the right. This does not included the limited quantity that was spilled during the removal process.

I take that to mean they measured it, but who knows.... If they didn't measure it, all bets are off. As far as the fuel equalizing after the crash I recall Matt saying that he switched back to the right tank"

Remembering I had more fuel in the right tank I switched to right and then hit the electric fuel pump.

I suspect he left it that way which is why it didn't drain out.

Anyway, I appreciate your willingness to think this all through with me, I like reasoned debate as we all learn something.

svyolo

Good call on the EFI related fuel system changes. Your comment about the crank position sensor so why not EFI started this entire train of thought. I knew you considered what would have to change with the fuel system, but I wasn't sure others reading knew about the challenges of a returning to tank fuel system. I also considered EFI, but I decided I didn't like the return to tank requirement and the electrons it took to make it work, even if it allowed me to pretty much run any fuel.

**Battson** · 06-29-2023, 12:48 AM

Really interesting original post Schu.

Originally posted by schu View Post

[referring to unbalanced flight] I don't understand how using BOTH somehow solves unporting issues. If having any port unport creates a problem then using BOTH is a liability when low on fuel as you have more ports with less fuel over them. If all of the ports unporting creates the problem then how would selecting the fullest tank cause issues? If anything it's less likely to unport.

At the risk of getting off topic... Not sure I understand the above correctly?

With some caveats below, and at the risk of oversimplifying things - if the plane is consistently flown out of balance, once fuel levels are low and with the fuel selector only drawing from the fullest tank, during uncoordinated flight the fuel could to 'slosh' to the outboard side, unporting both intakes. If the condition persists, the engine potentially quits.

If the same conditions occur with the selector in the "both" position (providing there is fuel in each tank) then at least one tank always has fuel 'sloshed' inboard against the intake ports. Hence fuel pressure is available at the fuel selector. So the engine keeps running.

To that end, running on both appears to nicely address the risk of unporting tanks when fuel levels are low.
Am I missing something?

Caveats:
I really doubt the commonly used fuel pumps want to suck air down from the tank. I think we've done that discussion.
Assuming neither of the tank vents have been blocked earlier in the flight.
We've kinda done the whole Both vs L/R tank discussion, and the running tanks dry discussion, let's not do that in this thread.

**schu** · 06-29-2023, 01:48 AM

Sure, I think I was trying to make a distinction between a system that only needs a single port covered in fuel (I suspect this is the case with carb or returnless FI) or a system that really needs all of the ports covered (I suspect this is the case with EFI because it draws a lot more fuel).

If all ports need to be covered: header tank.

If only one port needs to be covered (assuming 8 gallons which is roughly VFR reserve):

With BOTH: you might have 4 gallons in each tank which is only 16% full. In turbulent conditions or uncoordinated flying you are very likely to unport something, but as you say, other stuff is covered in fuel and things keep working.

With single tank: you might have 1 gallon in one tank (or less) and 7 in the other (assuming you burned it down to sputter) which is 28% full. In turbulent conditions or uncoordinated flying you may move fuel away from the port, but there is more than a 1/4 tank in there which is much harder to unport.

Point: I'm not sure that having less fuel above 4 ports is better than double the fuel above 2.

ECU (each)	.08-.13
Fuel Pump (each)	4-6
Injectors (each pair of 2)	2-4
Injectors (each bank of 3)	3-6
Injectors (each)	1-2
Coil Pack 4 cyl. (each)	1-4
Coil Pack 6 cyl. (each)	2-6
Check Engine Light	.1
Advance Switch Power	.1
RPM Switch Relay Power	.3

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EI vs EFI and the types of EFI

EI vs EFI and the types of EFI

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