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Fuel Pumps and Decel points

 
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efpg0708



Joined: 21 Jan 2015
Posts: 151

PostPosted: Fri Feb 22, 2019 11:15 pm    Post subject: Fuel Pumps and Decel points Reply with quote

Hi guys.

First of all, I’d like to congratulate Mark for the constant work developing and improving the avionics suite. I have used another well known 737 avionics suite and I can say that when it comes to the avionics itself and the handling of VNAV/LNAV capabilities, Sim-A leads by a mile.

I’ve had some headaches in the past for wanting the sim to be the exact same thing as the real NG, which is impossible to achieve. On the other hand, I believe that some of our nitpicking really helps Mark to keep improving Sim-A. Here are some things that I have noticed (version 1.93):

1) The LOW PRESSURE lights illuminate when the fuel pumps are at the OFF position. Also, when there is less than 950 kgs in the center tanks, the procedure described in the manual is to open the CROSSFEED valve and turn off either one of the center pumps until the LOW PRESSURE light on the other pump illuminate (which happens around 350 kgs). After this, the scavanger pumps usually transfer the remaining 350 kgs from the center tanks to the wing tank, which doesn’t happen here (IIRC, it worked this way on version 1.7).

2) When flying VNAV/LNAV approaches, most of the time the decceleration points are not created when there is either a speed restriction or speed reduction. The target speed decreases as it should, but the aircraft doesn’t decrease the vertical speed in order to capture it. I can work around this by using the speedbrake, but I remember not having to do this on past versions.

3) When I select a STAR and transition, a route discontinuity point is created.

4) When using COROUTES that have more than one DCT fix in a row, the route is loaded correctly but on the RTE page, only the “last” fix is shown. For example:

DCT DHP DCT OMN DCT JAX will be show as DCT JAX only in the RTE page.

5) When first entering the PERF page on the FMC, the EXEC light illuminates.

6) The POS page is not accepting most of the gates entries.

Here’s a suggestion Mark: as I can see, the trim setting indicator is shown on the lower display only after pressurizing the electric hydraulic systems. However, for those who don’t have motorized throttles with trim indicators, it becomes impossible to set the takeoff trim correctly during the preflight procedures.

Please correct me if I’m wrong on any of what I have said above. As I said, my goal is to contribute to the improvement of this already great product.

Cheers

Eduardo
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MarkHastings



Joined: 18 Jan 2006
Posts: 893
Location: UK

PostPosted: Mon Feb 25, 2019 8:11 am    Post subject: Reply with quote

Hi

Thank you for your kind comments... and feedback is always appreciated. Wink

1) Fuel
An NGS system was fitted which reduces the risk of fuel ignition in the empty tanks. This allows the scavenger pumps to use all of the fuel in the centre tank.
The NGS can be enabled on the Server > Aircraft Details > Aircraft Options.

Quote:
Centre Fuel Tank Inerting

To date, two 737's, 737-400 HS-TDC of Thai Airways on 3 Mar 2001 and 737-300 EI-BZG operated by Philippine Airlines on 5 Nov 1990 have been destroyed on the ground due to explosions in the empty centre fuel tank. The common factor in both accidents was that the centre tank fuel pumps were running in high ambient temperatures with empty or almost empty centre fuel tanks.

Even an empty tank has some unusable fuel which in hot conditions will evaporate and create an explosive mixture with the oxygen in the air. These incidents, and 15 more on other types since 1959, caused the FAA to issue SFAR88 in June 2001 which mandates improvements to the design and maintenance of fuel tanks to reduce the chances of such explosions in the future. These improvements include the redesign of fuel pumps, FQIS, any wiring in tanks, proximity to hot air-conditioning or pneumatic systems, etc.

737s delivered since May 2004 have had centre tank fuel pumps which automatically shut off when they detect a low output pressure and there have been many other improvements to wiring and FQIS. But the biggest improvement will be centre fuel tank inerting. This is universally considered to be the safest way forward, but is very expensive and possibly impractical. The NTSB recommended many years ago to the FAA that a fuel tank inerting system be made mandatory, but the FAA have repeatedly rejected it on cost grounds.

Boeing has developed a Nitrogen Generating System (NGS) which decreases the flammability exposure of the center wing tank to a level equivalent to or less than the main wing tanks. The NGS is an onboard inert gas system that uses an air separation module (ASM) to separate oxygen and nitrogen from the air. After the two components of the air are separated, the nitrogenenriched air (NEA) is supplied to the center wing tank and the oxygenenriched air (OEA) is vented overboard. NEA is produced in sufficient quantities, during most conditions, to decrease the oxygen content to a level where the air volume (ullage) will not support combustion. The FAA Technical Center has determined that an oxygen level of 12% is sufficient to prevent ignition, this is achievable with one module on the 737 but will require up to six on the 747.


2) As you can imagine, VNAV can be a complicate beast.!
It will 'try' and create a decel point if it can, but it's not always possible based on the alt restrictions.
ie a decel segment will need to reduce the descent rate to around 1.2-1.8 degrees, but if there is a 9000ft then a 7000ft restriction and the descent angle between them is ~3 degrees (point to point) there is no opportunity to reduce the descent angle.
So a decel is really calculated on a case by case basis.
But by all means if you have a specific example that I can replicate where you think there should be a decel segment, please mail it to me and I'll make a test flight and figure out what it's doing.

3) Are you saying you're getting a disco between the STAR transition and the STAR ?
Please mail me an example. It might be the way it's loaded into the nav database. I think usually the transition end WPT would be the same as the first WPT of the STAR. In that case no disco would be created....
But if the WPT's are different this maybe causing the disco.

4) Ok I'll load a few CORoutes and see what's happening.

5) hmm It's not supposed to come on until you enter a CRZ Alt.. I'll check.

6) The Gate positions are validated against the Gate's found in the position.mdb.
By default these contain just P3D defaults.
If you have addon scenery you will want to rebuild the position database to match your actual scenery.
Run \Navigation_Data\Build_Position_Database.exe and follow the instructions.
Summary : you run Makerwys.exe in your P3D main folder to create r5.csv and g5.csv.
Copy these into the \Navigation folder and run Build_Position_Database.exe to rebuild the position.mdb with your current P3D data.

7) I don't think the stab trim would actually be set prior to the hyd pump being switched on ?
You have a couple of alternatives :
DISPLAY_EICAS_TRIM=1 in the EICAS CONFIG.INI.
This will place a trim msg on the EICAS display.

CTRL+F2 on any avionics to display the Stab Trim Graphic.

Regards
Mark
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Mark Hastings
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Sim-Avionics
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MarkHastings



Joined: 18 Jan 2006
Posts: 893
Location: UK

PostPosted: Tue Feb 26, 2019 12:56 pm    Post subject: Reply with quote

Regarding point 4 ) CO Routes
Can you mail me an example file ?

I've just saved and Reloaded, and it loaded correctly.

Do you have a problem loading a native SIMA file or a SimBrief generated file.?
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efpg0708



Joined: 21 Jan 2015
Posts: 151

PostPosted: Thu Feb 28, 2019 12:26 pm    Post subject: Reply with quote

Hi Mark, thanks for the answers.

1) Fuel: understood. So, what’s the correct procedure with the NGS ? The airline for which I have the manuals don’t have them installed. Do I keep both center pumps on until they are empty ?

I’m away on vacation, will email you the examples as soon as I get back.

Cheers

Eduardo
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efpg0708



Joined: 21 Jan 2015
Posts: 151

PostPosted: Thu Feb 28, 2019 1:05 pm    Post subject: Reply with quote

MarkHastings wrote:
Regarding point 4 ) CO Routes
Can you mail me an example file ?

I've just saved and Reloaded, and it loaded correctly.

Do you have a problem loading a native SIMA file or a SimBrief generated file.?


Simbrief
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