N2 parameters at start

[CptIceman]

Hello.  I know that since LR changed a lot of things in their flight model, there have been a lot of adjustments here and there, particularly with the pneumatic system.

One issue with N2 at startup 7,340 ft.   It is not reaching 23-24%  it just gets to 18%.   The real airplane struggled at this altitude to reach 23.9 N2 at startup due to pressure altitude, but it reached it at some point.  The XP11 version was just on point of this struggle.   Now after not being able to reach more than 18% of N2 I just moved the start levers and the engines started very abruptly reaching 30% in a blink.

I hope you can fix this soon.

Cheers!

[CptIceman]

Another thing.  To break inertia and start taxing, I had to push the throttles to almost 46%N1  and keep them at 31%, while you would break inertia and start rolling typically at 32-35% and roll back to 26-29% to keep a smooth taxi.  

In these particular case, the XP11 version was right on point on this behavior.

Cheers!

[Litjan]

Hi and thanks for the feedback - I will doublecheck the starter power at high altitudes (MMMX), the move to XP12 created some headaches regarding starting. We have no control over the fuel scheduling and we might have to resort to some scripting to tame the spool up after fuel introduction.

I have also noticed that power requirements for taxiing were a bit high in our latest version, Laminar is changing wheel parameters a bit in the upcoming next version (less wheel weight, tiny increase of hub friction for the "stopped" case) and I will retune the rolling behavior when that drops.

I look forward to your further reports, it has been 11 years since I last released the parking brake of a 737-300 and memories fade fast...

Cheers, Jan

[CptIceman]

Hey Jan!  

Thx for the reply.

Yup, the parameters for the new aircraft model in LR changed really odd for some things.

For me also has been a bit a while the last time I flew the 300,  but since it was my first airliner (this one and the 200),  getting into the IXEG is just like riding a bike and all the muscle memory comes back to life.

So far this is the only thing that I caught, yesterday also could be a bit of the VOR/LOC capturing after heading the course to intercept the radial in a VOR/DME approach.  The flag turned green on the FMA annunciator at the EADI  but the plane did not turn to the bearing.  I will try another approach today and let you know.

I managed to configure a descent profile for the Honeycomb Bravo and Alpha to drive the MCP pretty decent.  Let me know if you will be interested in trying it... 

[Litjan]

10 minutes ago, CptIceman said:

I will try another approach today and let you know

Let me know how this works for you!

I agree, you never forget your first airliner, I get on my FO´s nerves by reciting the "Leaving airplane checklist" from memory when we shut down our 747-8´s

IRS mode selector - off
Fuel pumps - off
Galley power...

Edited September 16, 2023 by Litjan

[CptIceman]

Haha, indeed my mantra is the before-landing scan and check list.

Engine Start Switches - Cont.
Speed brake - ARM
Landing Gear - DN
Landing Flaps - 30

Landing checklist, complete...

[CptIceman]

Hey Jan.

A bit more info on this.  I tested at MSL and the start feels more like a JT8D series rather than a CFM 56 engine.  Even at sea level, it is hard to reach 24% N2 which is where you want these babies to be before pulling the start levers.  They only get 22% very hung start.

Also, I can corroborate that there is something odd with the VOR/LOC mode when it is armed.  Intercepting the bearing using heading as the lateral nav mode, it goes to active and turns green respectively on the FMA but it just continues straight without really anticipating the turn.  Not only does the aircraft overshoot it but it does not turn either.

This is in a VOR/DME approach.  I am going to try with an ILS and will communicate my findings.

Cheers!

[CptIceman]

Another issue in the FMC.

If I select an approach and then ERASE it.  I get this error.

[Litjan]

Thanks for those two reports - especially the lua error is a super high priority fix!

Keep `em coming!

[Litjan]

 

@CptIceman

Hmm, I just tried an engine spool up at sea level and I am getting 24.8% N2 even at +25C. See attached pic.

Also tried the "idle taxi" you reported and the plane will break free readily at 22% idle N1 and pick up speed briskly with a weight of 50t (110k lbs).

I am wondering if you maybe have some sort of plugin that interferes with our IXEG?

I also could not easily reproduce the lua error you got for the "erazing of approach", could you give me some further steps that helps me reproduce it?

Trying VOR interception next...

[Litjan]

Tried the VOR intercept and it worked fine for me - can you give me some repro steps on that, too, please?

(you DID remember to set the course on the MCP, right? I think the NG will do this automatically, Classics won´t and once in a while you will have to buy a beer for your colleague when the plane does the wrong turn on the ILS intercept because you forgot )

Edited September 17, 2023 by Litjan

[CptIceman]

I think I should change the title of the post.  To findings.

The FMC is not reading correctly the approaches from the xml files.   It only reads the FAF but not the transitions.   Instead of reading the transitions, it is reading the STARS.

In the following example.

for MMMD  Merida Airport.

ILS DME 2 or LOC Rwy 10 approach.

This is the char.



In the FMC if I select this approach, it only shows the transition MID, which is not correct.   This is transition will be only for the ILS DME 1



It is missing all the of the fixes for the transitions related to the approach from the chart above.

I check the xml file corresponding to this chart in the fmc_data/SidStar folder and it is correct.  It has the fixes but for some odd reason it is not reading them and just reads the VOR

This is happening with all the VOR / ILS approaches.   It is fun that you have to enter all the fixes for the approach with corresponding speed and altitude.  At least it keeps you busy in the cockpit.   But for short flights without a copilot...  It gets really busy.

Cheers 

PS.

I just check after adding the fixes to the approach manually in the FMC, and I noticed that there are three approaches selected in the picture only shows 2, but if you press the NEXT PAGE button it will show the third ILS10 approach available for MMMD as <SEL> also.

[CptIceman]

5 hours ago, Litjan said:

Tried the VOR intercept and it worked fine for me - can you give me some repro steps on that, too, please?

(you DID remember to set the course on the MCP, right? I think the NG will do this automatically, Classics won´t and once in a while you will have to buy a beer for your colleague when the plane does the wrong turn on the ILS intercept because you forgot )

Yes, of course, I selected the course in the MCP to intercept, flying with HDG mode, and the VOR tuned in the radio for a VOR/DME  approach.  At that time in Mexico we only had a few RNAV approaches and it was very seldom for us to use them.  Most of them were old school even for Mexico City.

On the other hand regarding the N2.  I see that your alt is NEG?   Try starting the engines at MMMX.  it is 7,340 ft ASL.

I don't have a bunch of plugins.  The basic ones I believe


I will record a video and post it.

Cheers

Edited September 17, 2023 by CptIceman

[Litjan]

Yes, I know that the N2 is not sufficient at Mexico City - I misunderstood you and thought you also reported too little N2 at sea level.

For the VOR interception I flew towards the radial with HDG SEL and VOR/LOC armed. When VOR captured (HDG green turns to VOR green) the plane banked to intercept the set radial. Is this not happening for you?

If you look at the approach chart for Merida that you posted you can see that all these different approach transitions have IAF´s that are ALL called "DXX.0 MID".  There are some with D17.0, some with D12.0 and some with D10.0 - that is why our FMS thinks that there are three different ILS approaches available, I bet. Separating approach transitions requires them to have unique names, if there are several that all start at "D12.0 MID" then our code can´t distinguish them.

[AngelOfAttack]

I heard from old guys some -300 do have problem getting to 25%N2 here at 6900'.

But just use 20% maximum rotation is good enough for almost every time.

[CptIceman]

39 minutes ago, AngelOfAttack said:

I heard from old guys some -300 do have problem getting to 25%N2 here at 6900'.

But just use 20% maximum rotation is good enough for almost every time.

What do you mean "Old guys"... We are still very young mate.

At these higher altitudes you will never get 25% but 23.8 to 24.0  You should not add fuel at lower N2% or you will flood the engine and it could cause a hot start, damaging the engine.   The lower limit you should get is 20% N2 but after max the motoring.

[CptIceman]

1 hour ago, Litjan said:

Yes, I know that the N2 is not sufficient at Mexico City - I misunderstood you and thought you also reported too little N2 at sea level.

For the VOR interception I flew towards the radial with HDG SEL and VOR/LOC armed. When VOR captured (HDG green turns to VOR green) the plane banked to intercept the set radial. Is this not happening for you?

If you look at the approach chart for Merida that you posted you can see that all these different approach transitions have IAF´s that are ALL called "DXX.0 MID".  There are some with D17.0, some with D12.0 and some with D10.0 - that is why our FMS thinks that there are three different ILS approaches available, I bet. Separating approach transitions requires them to have unique names, if there are several that all start at "D12.0 MID" then our code can´t distinguish them.

Ha, I was about to post a video of the starting at high altitudes.

There are 3 different ILS approaches for MMMD.


The problem is that the FMC just reads the data of the first one.

Selecting any of these approaches on the FMC results in only selecting the ILS DME 01
 

I am attaching the xml file for the sid/star so you can have a look.

Cheers

mmmd.xml

[Litjan]

Interesting... I will forward this to @tkyler he is the one that can see the Matrix  read the xml database and will be able to see what the problem is. Thanks for bringing this up!

I have already adjusted our starter strength to reach ca. 22%N2 on a hot day at Benito Juarez

[CptIceman]

1 minute ago, Litjan said:

Interesting... I will forward this to @tkyler he is the one that can see the Matrix  read the xml database and will be able to see what the problem is. Thanks for bringing this up!

I have already adjusted our starter strength to reach ca. 22%N2 on a hot day at Benito Juarez

Nice.  Can you also adjust the taxi lights.  They are very dim at night.  I have to turn on the landing light to see the yellow line... hahha

[Litjan]

1 minute ago, CptIceman said:

Can you also adjust the taxi lights.  They are very dim at night.

I remember them being very dim at nights...but I will see if we can bump them up a bit.