VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #21  
Old 04-04-2018, 07:09 PM
DanH's Avatar
DanH DanH is online now
 
Join Date: Oct 2005
Location: 08A
Posts: 7,736
Default

Quote:
Originally Posted by rmartingt View Post
Can I please get some useful, constructive feedback on what I've presented...
Sure.

Note this popular maxim, from Saint-Exupery:

..perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away...

Now consider these two sketches. What is the reliability difference between the one on the left (your original) and the one on the right?



BTW, I am not suggesting that the one on the right is optimum. It's just an example, an illustration of a point.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #22  
Old 04-04-2018, 07:59 PM
rmartingt's Avatar
rmartingt rmartingt is offline
 
Join Date: Nov 2006
Location: Savannah, GA
Posts: 756
Default

Ok, thanks guys...

Quote:
Originally Posted by Carl Froehlich View Post
I did. Looking at that and your previous diagrams I assume the entire engine is running off the one engine buss, is that correct? Is it not possible to have half of the engine on each battery with separate feeds?
Unfortunately, no. The kicker is the injectors; each one is powered individually (rather than by the ECU driving it) and there's only one per cylinder, so one way or another power needs to be able to get to them from both "sides". Running on two of four injectors is not good. So at that point, if I need to feed power from both sides to make the injectors work, why not do it for all of the engine components? That's how I went from the original plan down to these later concepts, trying to address that issue.

Also, as I was playing with wire diagrams and got better details on the EFI system I discovered some failure modes with that approach that would have had me throwing switches after one failure, or even just losing a bit of power (like losing one mag). Running everything off one bus with multiple feeds means everything keeps working even after a hypothetical complete bus failure.

Quote:
Originally Posted by DanH View Post
Sure.

Note this popular maxim, from Saint-Exupery:

..perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away...

Now consider these two sketches. What is the reliability difference between the one on the left (your original) and the one on the right?

http://i67.tinypic.com/1263d5g.jpg

BTW, I am not suggesting that the one on the right is optimum. It's just an example, an illustration of a point.
The one on the right is essentially my "Mod 2" from July, just with switches shown on the feeds from the batteries. But it is a good point. Each has its advantages and disadvantages. Both will keep the engine running without a hiccup after a single electrical power failure and both allow that failure to be dealt with in a calm and unhurried manner. Mod 3 (left) offers a little more redundancy on engine power supply at the expense of an extra wire or two and another pair of diodes. Mod 2 (right) is a little simpler to build and wire. Both would probably be operated in exactly the same way in practice, and even for most failure cases until you got into multiple failures (going past two independent failures is definitely overkill here, amd even two is probably stretching it some...).

I know the devil can lurk in the details of the design and in the execution of the wiring, but from an overall view every other approach I start with leads me back to 2 and 3. And making the one into the other is something that could easily be done in an afternoon even after it's flying.
__________________
RV-7ER - fuselage structure in work
There are two kinds of fool in the world. The first says "this is old, and therefore good"; the second says "this is new, and therefore better".
Reply With Quote
  #23  
Old 04-04-2018, 08:25 PM
Zuldarin's Avatar
Zuldarin Zuldarin is offline
 
Join Date: Mar 2013
Location: Snoqualmie, wa
Posts: 297
Default

I've been considering this as well and this is the basics of what I feel has the most simplicity with adequate redundancy. Normal operation has the master switch and the engine bus feed on. In this scenario power is normally fed to the engine bus via the primary alternator/battery and in the event of a main alternator failure or master failure the backup battery/alternator will take up the load (backup regulator is set to lower voltage to prevent it from taking the load during normal ops). Engine bus is fed directly from the master solenoid (via a fuse) with a diode to prevent back feed.

__________________
Darin
Snoqualmie WA
RV-9A Flying as of 03/2015
RV-10 Building - Wings - Flaps/Ailerons
www.DarinAnderson.com
2018 donation sent!
Reply With Quote
  #24  
Old 04-05-2018, 05:15 AM
DanH's Avatar
DanH DanH is online now
 
Join Date: Oct 2005
Location: 08A
Posts: 7,736
Default

Quote:
Originally Posted by rmartingt View Post
Both will keep the engine running without a hiccup after a single electrical power failure and both allow that failure to be dealt with in a calm and unhurried manner.
The example on the right requires no pilot intervention, no in-flight switch flipping to maintain a turning prop. Smoke in the cockpit, for example, requires only killing the master switch(es), a classic response for any pilot. After all, you won't know which of your two busses (master or aux) is the smoke source.

Think about it. Although 90% of pilots consider themselves above average, Paul just told you that even NASA went to systems requiring limited human intervention...and their machines are flown by some very good pilots.

Quote:
Mod 3 (left) offers a little more redundancy on engine power supply at the expense of an extra wire or two and another pair of diodes.
No, it doesn't. It only compensates for a need to turn off the masters. When master OFF doesn't affect engine operation, it becomes unnecessary. Flip side, if the system never requires a master OFF, the extra power wire is simply riding around as a liability. Parts not on the vehicle never fail.

As before, an example. The best system is often the least system.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #25  
Old 04-05-2018, 12:26 PM
unitink72 unitink72 is offline
 
Join Date: Oct 2014
Location: Cedar Rapids, IA
Posts: 147
Default

Quote:
Originally Posted by Zuldarin View Post
I've been considering this as well
Same here. I think you have an elegant solution.

The post above (right image) has two switches feeding the engine bus. What does that buy you when compared to this diagram? It removes a switch. Taking it one step farther by connecting both engine bus leads after the master would break the ability to throw the masters and still have everything work.
__________________
Josh T
RV-10 #1750
N67SC reserved
http://n67sc.blogspot.com/
2018 Dues Paid
Reply With Quote
  #26  
Old 04-05-2018, 03:22 PM
majuro15's Avatar
majuro15 majuro15 is offline
 
Join Date: Feb 2013
Location: Charlotte, NC
Posts: 434
Default

So what purpose does the switch between the batt bus and the engine bus serve?

Going back to your original post and evolution towards an engine bus instead of multiple feeds from separate batt buses, I'd think you could have diode isolated feeds from main, batt and aux batt bus all going to the engine bus. You're going to have to have multiple switches for SDS for normal function (ECU 1&2, Coil 1&2, Fuel Pump 1&2) anyway. Does this cover the failure for each of the batteries, alternators, wires (not all at once of course)?

I like the idea of diodes and have made some changes to my system based on feedback from Dan H. His feedback simply put was to try and make the engine bus a "or" system, ensuring only one of the power feeds is connected to the entire system at a time. That makes more sense to better isolate faults such as shorts in primary feeds. He mentioned using relays, but diodes would also work, allowing independent power in but limiting a fault's effect to the remaning power source.
__________________
www.N1017H.com
Tim Huneycutt, Capt, NCANG
RV-10 Fuselage under construction
N1017H Reserved
EAA #: 1106970
2018 VAF Dues Paid!
Reply With Quote
  #27  
Old 04-05-2018, 05:49 PM
DanH's Avatar
DanH DanH is online now
 
Join Date: Oct 2005
Location: 08A
Posts: 7,736
Default

Quote:
Originally Posted by unitink72 View Post
The post above (right image) has two switches feeding the engine bus. What does that buy you when compared to this diagram?
The two switches are turned on at start. Cycle them on the runup pad to confirm both power sources. There is never any in-flight diagnosis or switching to maintain engine power.

Zuldarin's: Architecture is functionally the same as Bob's. The difference is feeding aux power to the engine bus via the crossfeed, rather than via a dedicated wire. Given smoke in the cockpit, the pilot will need to find and flip the aux feed switch before opening the masters. Checking backup ignition power on the runup pad will require opening a master.
__________________
Dan Horton
RV-8 SS
Barrett IO-390

Last edited by DanH : 04-05-2018 at 05:51 PM.
Reply With Quote
  #28  
Old 04-06-2018, 09:14 AM
Zuldarin's Avatar
Zuldarin Zuldarin is offline
 
Join Date: Mar 2013
Location: Snoqualmie, wa
Posts: 297
Default

Quote:
Originally Posted by DanH View Post
Given smoke in the cockpit, the pilot will need to find and flip the aux feed switch before opening the masters. Checking backup ignition power on the runup pad will require opening a master.
I believe you are assuming that the aux bus switch is normally open? My thought was that normal operation has the aux feed switch closed so that power is available from both buses. If there is smoke in the cockpit I need only follow the normal procedure of turning off the master switch. The cross-feed switch is normally open.

Here is the actual diagram that I have been working on. Remember this is for an RV-10 which normally has the battery in the tail cone.

In this scenario I have a much smaller backup battery on the firewall. This allows me to have a reliable battery backup without having to run multiple long heavy power leads to the tailcone.

I added a relay in the main feed to the Engine bus but I want it to fail closed so I am planning on using a normally closed solenoid that is operated via a momentary switch. This allows me to test the backup power to the engine bus still have power in most failure modes.

__________________
Darin
Snoqualmie WA
RV-9A Flying as of 03/2015
RV-10 Building - Wings - Flaps/Ailerons
www.DarinAnderson.com
2018 donation sent!
Reply With Quote
  #29  
Old 04-06-2018, 09:36 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,541
Default

Darin,

Some thoughts:
- Both batteries available for engine start? If so, the rear battery need not be as big.
- Donít forget to do a W&B calculation. My guess is you will be nose heavy.
- Overlay the rest of your power to the panel plans to get the most out of having two batteries and a standby alternator.
- Consider a 70amp or so breaker on the output of the primary alternator. 60amp alternators have a nominal output of 60 amps. It is not uncommon for them to put out a little more if it is trying to bring up a depleted battery. A 70 amp breaker will help eliminate nuisance trips and still provide the protection you want.

Carl
Reply With Quote
  #30  
Old 04-06-2018, 10:48 AM
majuro15's Avatar
majuro15 majuro15 is offline
 
Join Date: Feb 2013
Location: Charlotte, NC
Posts: 434
Default

I like the idea of using a momentary open switch to test feeds. You could have a "push to test" button that is rated for whatever current going through that alternate power path that would then test the primary path. I would be an alternate to having multiple switches to power on the aircraft power.

Guess it depends on what works for you.

I think an important bit of advice is to make a comprehensive POH and checklists for the aircraft, no matter how you end up building it. Not only for you but for anyone else that ever flies the aircraft so that it is clear how to operate and what the failure modes / responses look like.
__________________
www.N1017H.com
Tim Huneycutt, Capt, NCANG
RV-10 Fuselage under construction
N1017H Reserved
EAA #: 1106970
2018 VAF Dues Paid!
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:03 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.