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  #211  
Old 05-27-2018, 07:34 AM
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Quote:
Originally Posted by Toobuilder View Post
With all due respect, I'd rather shove bamboo shoots under my fingernails.
Chicken

Actually Mike hasn't proposed anything very radical between the EFI bus and the EFI components. As compared to the standard SDS diagram, he has eliminated only three switches...two coil, one pump. Here's the reworked version:



Personally I would not eliminate those three switches, as they add only benign failure modes, not critical failure modes, the point of analysis before philosophy.

In return, coil switches allow clear runup pad checks of coil and ECU function (in dual ECU setups, each coil is driven by a different ECU).

An unswitched primary pump is workable. However, IF it is desirable to alternate pump usage so they build operating hours equally, it's a whole lot easier to do it with switches. Again, the additional switch, if failed, is a benign result. The required pilot recovery (close a pump switch) is the same.

Power supply TO the bus? Yeah, single wire/single switch architecture is, ummm, radical. Mike, you're an engineer. Ditch the crank gear philosophy. With respect, it's trash talk. Is there an accepted industry method, numerical or logical, which would demonstrate that the single wire/switch power supply is somehow superior?

My opinion? It fails the most basic analysis. Either an open or a short in that segment results in a critical failure....the big fan stops, and there is no recovery.
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  #212  
Old 05-27-2018, 09:31 AM
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Toobuilder Toobuilder is offline
 
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The idea that additional switches for required (redundant) components adding a benign failure mode works on paper, but ignores the much more difficult to address PVI perspective. Knowing how pilots react in an emergency (personal experience here), removing "nice to have for maintenance troubleshooting" choices from the normal cockpit flow increases the chances of a successful outcome. That said, my coils are controlled by resettable CB's, labeled and easily accessable. I can pull them if I need to test something, but they are NOT part of the normal engine operation sequence. Your comment about balancing the fuel pump hours has merit, but again, I'm moving that out of the pilot workflow and transferring that responsibility to the maintainer. One less thing for the stressed out pilot to get wrong. And despite the fact that a single switch failure (short) can take down a traditional magneto equipped aircraft, the very remote possibility of my ENGINE control switch failing in flight can be overcome with the addition of a separate circuit and a "Hail Mary" switch pretty easily. This will be a guarded, but easily accessed switch that is still outside my normal PVI flow. My EP for engine out goes from one step (BOOST PUMP ON) to two (EMER POWER ON). So thanks for the reality check on that.
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying

Last edited by Toobuilder : 05-27-2018 at 09:33 AM.
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  #213  
Old 05-27-2018, 11:12 AM
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Originally Posted by Toobuilder View Post
The idea that additional switches for required (redundant) components adding a benign failure mode works on paper, but ignores the much more difficult to address PVI perspective.
Uhh, what's a PVI?

Quote:
....my coils are controlled by resettable CB's, labeled and easily accessable. I can pull them if I need to test something, but they are NOT part of the normal engine operation sequence.
Yeah, that was the point. Other than studying EGTs or pulling breakers, there is no available preflight check of dual ignition function...a normal (and highly accepted) operation.

Quote:
And despite the fact that a single switch failure (short) can take down a traditional magneto equipped aircraft....
With separate toggles, a switch failure takes down one magneto, a benign failure. The fan keeps turning.

Quote:
....the very remote possibility of my ENGINE control switch failing in flight can be overcome with the addition of a separate circuit and a "Hail Mary" switch pretty easily. This will be a guarded, but easily accessed switch that is still outside my normal PVI flow. My EP for engine out goes from one step (BOOST PUMP ON) to two (EMER POWER ON). So thanks for the reality check on that.
Ok, so now you have dual power supply to the EFI bus. Assuming you supply your EMER PWR switch from different battery, the architecture is straight from the standard SDS diagram.
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  #214  
Old 05-27-2018, 11:38 AM
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Quote:
Originally Posted by Toobuilder View Post
... My EP for engine out goes from one step (BOOST PUMP ON) to two (EMER POWER ON)...
Don't forget the Injector ECU Select switch.
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  #215  
Old 05-27-2018, 01:41 PM
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Quote:
Originally Posted by DanH View Post
Uhh, what's a PVI?.
Pilot Vehicle Interface... A human factors issue that has become its own engineering sub specialty in recent years.


Quote:
Originally Posted by DanH View Post
...With separate toggles, a switch failure takes down one magneto, a benign failure. The fan keeps turning..
But there are more than a few certified airplanes that funnel the two P leads into a single Bendix switch... In fact, its the industry norm. Sure, its a rare ocurrence in practice, but still will not survive your critical deconstruction on a schematic. An internal short of that single switch is critical and unrecoverable. Yes, an easy "fix" is to simply use two independant switches, but its funny how the industry adopted a single point failure as the norm... Is it because of PVI concerns?


Quote:
Originally Posted by DanH View Post
...Ok, so now you have dual power supply to the EFI bus. Assuming you supply your EMER PWR switch from different battery, the architecture is straight from the standard SDS diagram...
Yes, addition of a second switch and wire is easy. But so is the addition of a short length of fuel tube to bypass a clogged fuel filter or a broken fuel fitting...

See where this can go if you're not careful?
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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  #216  
Old 05-28-2018, 08:28 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by Toobuilder View Post
Pilot Vehicle Interface... A human factors issue that has become its own engineering sub specialty in recent years.
Ahhh. Good subject.

Here we have two diagrams. On the left (best I can tell from the description, circa post 212) is Mike's EFI bus supply architecture. On the right we have the same system, with the addition of two diodes located (specifically) at the EFI bus connections.



First, a partial wire-by-wire fault check.

Left diagram.

Conditions, leftmost switch closed, in flight:

1 open: no power to EFI bus. PVI: Close right switch

1 short: left fuse pops, no power to EFI bus. PVI: in order, open left switch, close right switch. (closing right switch first causes unrecoverable failure, CRITICAL)

2 open: no power to EFI bus. PVI: close right switch

2 short: left fuse pops, no power to EFI bus. PVI: UNRECOVERABLE closing right switch pops right fuse. CRITICAL

The above notes are the minimum PVI's specific to the circuit segment condition. Since the segment conditions are unknown to the pilot, the actual PVI for all failures would be (left switch off->right switch on->wait for a response->if no response, pump switch->ECU select switch)

Now the right diagram.

Conditions: BOTH power supply switches closed, in flight:

5 open: 7-8 supplies power. PVI: None

5 short: left fuse pops, 7-8 supplies power. PVI: None

6 open: 7-8 supplies power. PVI: None

6 short: left fuse pops, 7-8 supplies power. PVI: None

No power supply circuit problem results in power interruption; all failures are benign. The PVI following engine power failure would be (pump switch->ECU select switch). If the physical fuel system will allow both pumps to operate at the same time (aux pump ON for takeoff, the conventional PVI), the entire power interruption PVI becomes (flip ECU select switch).

When an additional component is necessary to design for fault tolerance, it is simply treated as a part of the circuit segment. In this example, an open diode is simply an open in segment 6 or 8. An internally shorted diode may be treated as a wire, which would negate its isolation benifit. In reality, if that isolation became necessary the diode will act like a fuse. For example, assume diode 6 will pass electrons both ways, and wire segment 6 shorts to ground. The diode will at as a fusible link, as shorted amps in either direction would exceed its current capacity. No change to the wire-by-wire check.

Quote:
Yes, addition of a second switch and wire is easy. But so is the addition of a short length of fuel tube to bypass a clogged fuel filter or a broken fuel fitting...

See where this can go if you're not careful?
Into a philosophy argument? I'd rather teach 'em how to fish.
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Last edited by DanH : 05-28-2018 at 09:40 AM.
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  #217  
Old 05-28-2018, 10:13 AM
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Default Rusty Crawford Photos



Here's a couple of photos of Rusty's ECU, relay and MAP sensor layout for those who may be interested.

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http://sdsefi.com/cpi.htm


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  #218  
Old 05-28-2018, 10:17 AM
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Quote:
Originally Posted by rv6ejguy View Post


Here's a couple of photos of Rusty's ECU, relay and MAP sensor layout for those who may be interested.

Thanks! Would love to see power circuit diagram.
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  #219  
Old 05-30-2018, 01:21 AM
444TX 444TX is offline
 
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Ross and group

I work on cars from near new to very old age, just out of warranty to worn out. We have replaced relays with as little as 40,000 miles and I personally have cars with 400,000 miles that have everything original except the water pump, brakes, and maintenance. What happens while under manufacturers warranty is not usually experienced by me, but plenty does goes wrong. I hear the stories. Mileage and age are not the only factors.

1. We have replaced more than a few Bosch type alarm relays where the normally closed contacts are bad and the starter will not engage. As stated on a previous post, we have replaced hundreds of relays with problems with the normally open section. A relay is just another switch. Again, I feel they are becoming over used in circuit design.

2. Has anyone here ever had a Honeywell TL switch failure? I have seen several Carlin switches fail at the rivets (Can send pictures). Only Honeywell with screw terminals on my planes. Same for B&C alternators and starters.

3. I have seen strobe and fuel pump switch fast-on connections with heat damage, along with Bus brand fuse boxes with heat damaged fuses and melted plastic (can send pictures). All crimps and terminals appeared to be OK. Fast-On's are OK in general, but I feel EFI requires higher quality where possible. Redundancy can make up for the risks. Two EFI bus power sources, two independent fuel pump circuits, one independent backup ignition source, backup fuel system (see: Dave Anders install information, Cessna 185 missionary backup fuel system).

4. We have been running fuel injection on mechanical fuel pumps, with the electric pump only used for starting and TO/Landing. Now they will be necessary, not a backup. I have concerns and would want two independent pump circuits, not on one switch or relay, and carefully check electrical connections at every annual. Time will tell.

5. I see strange electrical failures with low mileage older aged vehicles. My RV8 is 16 years old. What will we do with old EFI computers, injectors, sensors. I have witnessed EI pickups, LS ignition modules, ignition coils fail and have witnessed intermittent problems. These planes will not be new forever. What are the plans here? Run until failure?

6. Terminal quality and crimps are important. A Daniels sub-D, environmental splice, Thomas Betts Sta-Kon WT145A style crimpers along with tefzel strippers are a good start, can be purchased on E-bay, and will provide high quality connections. Here is not the place to be cheap, there is a difference. Larger cable ends can be done with an inexpensive hydraulic crimper purchased on E-bay. They do a great job and are easy to use. An RV10 crashed with fatalities because of an improper crimp and Van's has a Service Letter for improper cable crimps.

7. Quality relays only. The ones on post #101 spec well and one can double up the contacts for load sharing. Same goes for switches.

8. Some of these diagrams have no redundancy and lack pilot control. I would have two battery power sources that could be used simultaneously or isolated, along with EFIS monitor/aural warning of both sources. I would want independent control of the fuel pumps allowing both for takeoff and landing. Both on the Battery EFI Bus, maybe one on a breaker or relay controlled by the ECU and the other on a stick grip controlled relay or panel switch by the throttle for takeoff, landing, emergency. I would run the coils and ECU from a dedicated EFI breaker panel, fewer switches and still maintain control.

I woke up this morning thinking I could find no good reason to install an EFI system on a Lycoming equipped airplane. Any benefits would be minimal at best and the complexity and chance of a dangerous fuel system failure is far greater. I like modern technology, but not for the sake of technology. Some will make the decision and install EFI, some will pursue (like alternate engines) and go back to the old tried and true Bendix style injection. Just go in, realizing the risk and responsibility, with eyes wide open. Sorry, but I will still continue to try and help to the best of my ability.

George Meketa
ASE master tech, A&P mechanic
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  #220  
Old 05-30-2018, 06:09 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by 444TX View Post
7. Quality relays only. The ones on post #101 spec well and one can double up the contacts for load sharing. Same goes for switches.
Carl's original link:

https://www.alliedelec.com/schneider...d-12/70185034/

I pulled up the data sheet, and there is a spec detail I'm curious about. Take a look at the NC rating:

https://www.alliedelec.com/m/d/fdee0...a90d4f03ff.pdf

Are they saying the NC contacts are only good for 3 amps at 28V?
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