Electrical System, CDU, VOR/LOC remarks

[ken_v]

First of all let me just say, wow... what a great simulation is this! For starters, the look and feel of the 737 has been captured to an unbelievable extent.. Makes me feel right at home.  Then there's the depth of system simulation, that makes me want to experiment with the plane in such a way that it's rather fortunate that this is a sim!

I have been out of computer sims for a long time and I re-installed X-Plane especially for this long-awaited add-on (I had been lurking on the former ixeg.net blog and forum for quite some years..).  
As a result, my X-plane install is very clean and uncluttered by other add-ons (for now).  
I don't know if one thing has anything to do with the other, but I must say that I have been spared of most of the soft/hard/tough-to-troubleshoot crashes and unpredicted sim behaviour that has occasionally been reported by others especially a few weeks ago.

Therefore, please consider the following remarks not bug reports (they do not impact in any way the usability of the simulation nor the pleasure of operating it) as much as well-meant vetting, scrutinizing (well.. you've asked for it repeatedly in countless forum treads ;-)), mostly nit-picky matters brought up for discussion etc.  It's pretty great to be able to (maybe) assist in the finetuning of a wonderful product to become even better, more accurate and more robust.

CDU

1/ CDU legs page.  Between-point distances of over 9.9nm should have their format without decimal point, i.e. to the nearest NM. Is this rounded up or down..? I have no idea.

2/ CDU PERF INIT page during preflight: when entering a T/C OAT after entering a CRZ ALT, the resulting ISA DEV is erroneous.  eg. Enter FL310, then -50°C T/C OAT --> this results in ISA DEV displaying 25°C, while -50C at FL310 is in fact around -5°C ISA.  
Interestingly, if you do it the other way round eg. start by filling in the ISA DEV value, the T/C OAT is filled in correctly.

3/ When pushing the +/- key on the CDU keypad, 'minus' should be displayed first, then 'plus', rather than the way it is now.

 

ELECTRICAL SYSTEM

I have played around a lot with the electrical system and the electrical failures. Great to see little details having been put in.  These are some things I noticed, that could maybe be of use if it would later be decided to further enhance the simulation accuracy:

4/ TR1 and TR2 indicate slightly less amps than TR3. I would not expect to see this, rather the opposite (TR3 indicating about half needle deflection of what TR1 and TR2 have).  In fact, if I would see TR3 indicating more than either TR1 or TR2, and TR1/2 being at around zero amps, I would probably suspect a TR1/2 failure with TR3 having taken over the load. In any case, I would think twice before going somewhere CAT 3 ;-)

5/ with Transfer Bus 1 failed/unpowered, TR1 indicates zero amps and zero volt. This is partially correct: underlying TR1 is unpowered and this is correctly shown as TR1 amps at zero. However, the TR1 voltage indication should actually display underlying DC BUS 1 voltage, which is still powered by TR2/3 and therefore should still read normal and not zero.

6/ with Transfer Bus 2 failed/unpowered, TR2 seems unaffected in amps while it should be dead. Same remark for the voltage indication: it should still read normal.

7/ when airborne without any AC generators online, on battery power only (a bad day at the simulated office), I have noticed this:
    * GPWS should be dead (it is powered off a bus below XFER BUS 1), but aural alerts are still produced (no PULL UP annunciator though)
    * the opposite: with a cabin altitude above 10.000ft there is no cabin altitude warning sounding while there should be one. I don't know on which specific bus it is wired, but it's listed in the "significant equipment that operates with all generators inoperative" in the books (and I remember hearing it in the real sim :s)
    * also, Radio Altimeter 1 seems to be still working.  That is normally also on AC Electronic 1 and though I know that there are a lot of wiring differences as to what is powered by standby power, I really don't know whether it should be powered along with the rest of the CAPT flight instruments - it isn't included on the significant operating equipment list. But maybe on the LH fleet that was used as a reference they decided it was a negligible consumer and wired it up to the standby power anyway.
    * the TE Flap Position indicator still works, while it is on Transfer Bus 2 and therefore should not be powered

8/ when Air Data Computers are not powered or their source bus has failed, the Main Electric altimeters are (correctly) unfunctional, however the red ALT flag on the left part of the numbers readout is missing.

 

AFDS

8/ in VOR/LOC mode, the AFDS ignores the Bank Angle Selector, happily banking to 30° instead.  In HDG SEL it works fine.
9/ VOR/LOC outbound radial capture: the aircraft keeps turning and increasing the intercept angle until the radial is fully centered, obviously overshooting and then doing the same on the other side. The attached movie clip illustrates better what I mean.

 

Thanks again for a great product and such a great rendition of the 737 classic.

Ken

 

VORLOC.mp4

Edited May 20, 2016 by ken_v

[ixam500]

Maybe the FMC stuff is also software version related? Just a guess though.

[Morten]

9 hours ago, ken_v said:

8/ in VOR/LOC mode, the AFDS ignores the Bank Angle Selector, happily banking to 30° instead.  In HDG SEL it works fine.

Hi Ken, thanks for great report.

I'm not the systems expert, but think in LOC mode AFDS should ignore the limiter (not VOR)

Quote

 Localizer capture occurs at a variable point dependent on intercept angle, speed

and localizer deviation and rate, but never at less than ó dot. During localizer

capture, bank limit is 30 degrees regardless of bank limit selection

 

Edited May 21, 2016 by Morten

[Nils]

Ken, I'm looking into that VOR capture issue but it seems to work as intended here. What VOR were you tracking in the video?

[Litjan]

Hi Ken,

what a welcome and detailed report! Your remarks are well received, and very welcome in helping us push the boundary .

CDU:

1.) Checked my pics and you are right - three characters for distance, only (I guess the rounding is arithmetical?)

2.) it should work the way you describe it - will verify and add to list (never added any temps when flying, so had to look up myself how this works )

3.) this would make sense - not adding anything is a "+", anyway. Will add to list

Electrical:

4.) You are probably right - but this goes way beyond what we are trying to achieve. I have flown the 737 for 10 years, and I couldn´t tell you a thing about what each TR should approximately indicate...

5.) see 4

6.) see 4+5 (I will, however, keep all this in mind and maybe Tom has a professional itch to change these - I guess it depends on where the voltage is taken - over the TR itself or just at the exit point vs. mass. I have never checked in the real aircraft, it would mean putting the transfer bus switch to off, then unpowering a gen bus)

7.) All noted - some systems (EGPWS) are still "default X-Plane" - those are pain to simulate electrically (you need to "fail" them if unpowered). Some could be fixed, I add those to the list!

8.) Right! Will add this to the list!

AFDS:

8.) In VOR/LOC and in LNAV mode (at least in LOC) the limit selector is disregarded. The bank limit is 30 deg. After LOC on course guidance is established, bank limit is reduced to 8 degrees (iirc). I am not sure about the VOR capture mode, but I would think that the limiter is also disregarded or most captures might end in a disaster ;-)

9.) Yeah, I have seen some VOR quirkiness myself, sometimes. We have put this on a backburner during development, because the VOR mode is rarely used (or so I thought). Can you let us know which VOR you tried at (114.9 Mhz)? Also: Don´t fly with your centertank still filled and the wing-tanks not full - it is illegal .

 

Again, I am really happy to see that someone is exploring some of the detail we have added - especially the electrical system took a lot of work. I think it´s nice to be able to simulate some bus (or even total AC power) failure - and you are limited by battery capacity and can even "save power" by turning off some heavy users or electing not to try an APU start... However, this in not Level-D fully certified simulator and you will eventually reach some boundaries. That being said - the stuff you turn up will probably slip by 95% of all real 737 pilots. Except for maybe that one Check-Captain that everyone hated going into the sim with .

Jan

 

[tkyler]

yea, Tom does have a professional itch to get these a bit more refined at the proper time.  This post is noted   

-tkyler

[ken_v]

Thanks for all of your replies.

On 21/5/2016 at 1:20 PM, Litjan said:

4.) You are probably right - but this goes way beyond what we are trying to achieve. I have flown the 737 for 10 years, and I couldn´t tell you a thing about what each TR should approximately indicate...

I used to be the same ... until when a few years ago a mandatory check of the TR outputs became part of our procedures before any CAT2/3 approach (don't know if that was as a result of incorporating some updated Boeing procedure or just company-invented stuff).  That's why it sort of stood out to me when I saw it.

 

On 21/5/2016 at 1:20 PM, Litjan said:

6.) I guess it depends on where the voltage is taken - over the TR itself or just at the exit point vs. mass. I have never checked in the real aircraft, it would mean putting the transfer bus switch to off, then unpowering a gen bus)

In fact, looking at the system schematics I think it is quite impossible to determine the voltage pickup location like that, because while doing so will provoke an unpowered TR, it will also open the TR3 disconnect relay, preventing the backup of a DC BUS by its opposite side TR.  So the Volts readout would be zero anyway, because both TR and underlying DC BUS would be dead. 
Apart from that, let me just say that your (and Tom's) implementation of the electric system is sufficiently in-depth and well done (*) that it actually made me want to go through lots of old sim debriefing notes as well as a couple of well known and widely used reference sources - one of which is partially available online at http://www.b737.org.uk/ - just to make sure what I wrote wasn't total nonsense..

(*) just try, for instance, failing a DC BUS and observe how it affects certain fuel pump controls. Not the fuel pumps themselves (they are on Transfer and Main buses), but the controlling circuit behind them - can't switch them on or off any more. Made me look it up in the books (and then smile ) when I noticed it.

 

On 21/5/2016 at 1:20 PM, Litjan said:

[...] but this goes way beyond what we are trying to achieve.

 

On 21/5/2016 at 1:20 PM, Litjan said:

[...] All noted - some systems (EGPWS) are still "default X-Plane" - those are pain to simulate electrically (you need to "fail" them if unpowered). Some could be fixed, I add those to the list!

 

On 21/5/2016 at 5:12 PM, tkyler said:

yea, Tom does have a professional itch to get these a bit more refined at the proper time.  This post is noted   

-tkyler

Got it!  Not holding my breath for it, but it's not entirely off the table, then.
The level of detail in there is already mind-boggling and it's of course totally up to you to decide if and when you want to refine it even further (push the boundary, as you say). 

It's pretty easy for me to just start abusing that inviting list of electrical bus failures and then make posts nagging about what I think should be slightly different, not knowing anything about how easy or hard something is to code in X-Plane (without breaking the rest of the simulation).  Just know that I'll be sitting in the "system fidelity before eye-candy" camp, ready with more scrutiny and input.

 

On 21/5/2016 at 10:39 AM, Morten said:

I'm not the systems expert, but think in LOC mode AFDS should ignore the limiter (not VOR)

 

On 21/5/2016 at 1:20 PM, Litjan said:

8.) In VOR/LOC and in LNAV mode (at least in LOC) the limit selector is disregarded. The bank limit is 30 deg

Indeed in LOC it should disregard the selector (which makes sense, really).  But in VOR mode it shouldn't :

Quote

Bank Angle Selector
Rotate –
• Sets maximum bank angle for AFDS operation in HDG SEL or VOR modes

 

On 21/5/2016 at 1:20 PM, Litjan said:

9.) Yeah, I have seen some VOR quirkiness myself, sometimes. We have put this on a backburner during development, because the VOR mode is rarely used (or so I thought). Can you let us know which VOR you tried at (114.9 Mhz)?

I think it was AFI near Brussels in that particular video.
I tried another setup yesterday (using Erlangen near NUE) in the same conditions (around 15000', high GS, outbound intercepts around 20-30nm from the station) and it worked fine, even taking out the intercept angle a bit too soon to my liking this time, slowly creeping from one dot towards a centered course deviation bar for minutes..  Strange.

Indeed I don't think I've ever used the VOR mode in reality for enroute-navigation. Before we were allowed to fly non-precision approaches in LNAV we did do VOR approaches in VOR/LOC, but as this is always low level, low speed and inbound, it's an entirely different case than what I brought up above (and it works great in IXEG, by the way)

 

On 21/5/2016 at 1:20 PM, Litjan said:

Also: Don´t fly with your centertank still filled and the wing-tanks not full - it is illegal .

Right.  Was just experimenting with the plane when I made the video. You should've seen the rest of the panel setup
 

 

[Litjan]

Hi Ken,

thanks for reporting back and following up!

Point 8 (VOR bank angle) is noted - I think it will be easy to implement this and you saved me the trouble of hunting through the manual, thanks!

And thanks again for the nice words - the no AC power case was a bit of an ugly stepchild - and implementing it was partially driven from the "equipment still available" list, my fuzzy simulator memory (while frantically finding a place to put her down) and assorted lists of electrical consumer & bus listings. Incidentially found out that there was also quite a bit of wiring difference between individual manufacturer numbers...

Please absolutey keep the scrutiny up, your feedback is invaluable!

Cheers, Jan

 

[papy.rabbit.08]

Hello,

just to add to this post, for n°9, I've seen a lot of problems with VOR and ILS, my last flight in 0 visibility ended 20 meter on the right of the runway with my autoland, because the plane turn too much and try each time to recapture the midline, but goes too far, and so on. It was in Portland, Maine, but I've seen that in other places.

[tkyler]

CDU items have been addressed for next hotfix....the LEGS distances and also the OAT entry ( addition is NOT subtraction Tom)...equation error    No work on the electrical yet...that is definitely last page stuff as it took a real pilot who actually gets into the electrics (cause Jan didn't) to catch it. ...but I will want to fix this up one day.

-tkyler

[judeb]

Hi Tom,

I continue to be impressed by your customer service and reaction to feedback. You deserve every cent!
Nice to see you've climbed to # 2 in the best-sellers list. (it's like "Top of the Pops", only better!)

 

Jude