You bought the manuals last December and you will get the 737NGX by this December. What can you say! JeffG

The solution to VNAV is 41. If 42 is the answer to the universe, 41 is a step down to VNAV programming.

That was a good line. So what would 40 be then? Calculating L4 and L5 points? I will be very disappointed if I won't be able to fly the NGX via Lagrangian points

Take your pick. :(

Forty is an octagonal number, and as the sum of the first four pentagonal numbers, it is a pentagonal pyramidal number. Adding up some subsets of its divisors (e.g., 1, 4, 5, 10 and 20) gives 40, hence 40 is a semiperfect number.Given 40, the Mertens function returns 0. 40 is the smallest number n with exactly 9 solutions to the equation φ(x) = n.Forty is the number of n-queens problem solutions for n = 7.Since 40 squared + 1 = 1601 is prime, 40 is a Størmer number.40 is a repdigit in base 3 (1111) and a Harshad number in base 10.

Can't we just go with pi? Everything works with pi...

Can't we just go with pi? Everything works with pi...

Custard doesn't always work with pie, although admittedly it depends on what type of pie it is, sometime gravy will be a better choice. A good general ratio is 3.14 pieces of pie for every jug of custard/gravy, and when it comes to dividing pieces of pie up, I'll take 22 over 7 any day of the week.Al

So, just out of curiosity, what's wrong with the existing Boeing sims of VNAV? The one in the 747 seems to work ok, if you have a programmed vertical nav profile. As I understand it, you set your alt bug and the plane climbs or descends as required on the profile up to (or down to) the limit in the bug. Is that not how its supposed to work?

So, just out of curiosity, what's wrong with the existing Boeing sims of VNAV? The one in the 747 seems to work ok, if you have a programmed vertical nav profile. As I understand it, you set your alt bug and the plane climbs or descends as required on the profile up to (or down to) the limit in the bug. Is that not how its supposed to work?

Actually, you didnt solve it so, 3²+4²=X² , 9+16=X², 27=X² , Take the Square root which gives you some retarded number so ill just say in radical form, 3√3

That's embarassing! 9+16 does not equal 27!! It equals 25. So x=5. VNAV - solved!

No offense, AAfan, but I'd just love to see some of your weight and balance, and fuel calculations. :(

So, just out of curiosity, what's wrong with the existing Boeing sims of VNAV? The one in the 747 seems to work ok, if you have a programmed vertical nav profile. As I understand it, you set your alt bug and the plane climbs or descends as required on the profile up to (or down to) the limit in the bug. Is that not how its supposed to work?

In theory yes, since even the default FS autopilot can drive up or down to a point in space at a certain speed, but in practice FMCs connected to an autopilot do a lot more than that. It's quite a complex problem to navigate an aeroplane accurately through three dimensions in a constantly-changing air mass whilst trying to maintain speed, flight path angle and ETA as well, so much so that even the real 737's FMC had difficulties with it a few years ago when the software was less sophisticated. Nowadays it is very accurate indeed, and since PMDG wanted to emulate that, then they obviously needed to emulate how good the real 737's FMC software and autopilot is at driving the aeroplane during a highly dynamic process.The main problem is that when trying to hit all those parameters - possibly based on several different predictions for wind and temperature - something generally has to give in order to keep the airplane doing more or less what is expected of it (so either speed, flight path angle, or descent rate might have to alter and average things out); that's why you'll see the estimated position of where your average FS airliner is going to hit its mark jumping around along the line of your flight plan track on the PFD, whereas the real thing is a crapload better at arriving where it says it will, when it says it will, by constantly assessing what it is doing with thrust and pitch in relation to the planned arrival point in space. As a consequence, it will do a better job of things without fluffing matters and moving the estimate about on the PFD like you presently see pretty much every FS airliner doing. On the real thing, that kind of capability is important for making crossing restrictions, RNAV, IAN and such, and is one of the reasons why a 737 costs millions of Dollars.To create an add-on that will do the same thing, yet probably come in at under 100 quid and run on a six year-old sim is no small problem to solve, so the truth is, most other FS airliner developers don't even try to properly solve the problem to the degree of accuracy that a real aeroplane's software and autopilot can manage, and instead live with it being 'close enough', but that kind of dedication to accuracy is why PMDG's NG wasn't released six months ago.Al

So, just out of curiosity, what's wrong with the existing Boeing sims of VNAV? The one in the 747 seems to work ok, if you have a programmed vertical nav profile. As I understand it, you set your alt bug and the plane climbs or descends as required on the profile up to (or down to) the limit in the bug. Is that not how its supposed to work?

For one up until the NGX nothing has simulated the Boeing FMC's speed prediction algorithm correctly - you'll see how this works soon enough, but it has the effect of making it a lot easier to slow down for approach and stuff. The real thing assumes a deceleration to Flaps 15 speed at the point of GS interception basically. The NGX does this and it does all the crazy math that figures out in reverse how to get the airplane to that condition at that point if possible based on the other constraints during the descent. I say "if possible" because if you have restrictions entered in earlier and there isn't enough space/time to both descend and slow down, it's going to tell you about it - there's a bunch of scratchpad messages this FMC will give you that have never really been simulated before in FS. Things like "DES PATH UNACHIEVABLE", "STEEP DESCENT AFTER XXXXX" etc...

For one up until the NGX nothing has simulated the Boeing FMC's speed prediction algorithm correctly - you'll see how this works soon enough, but it has the effect of making it a lot easier to slow down for approach and stuff. The real thing assumes a deceleration to Flaps 15 speed at the point of GS interception basically. The NGX does this and it does all the crazy math that figures out in reverse how to get the airplane to that condition at that point if possible based on the other constraints during the descent. I say "if possible" because if you have restrictions entered in earlier and there isn't enough space/time to both descend and slow down, it's going to tell you about it - there's a bunch of scratchpad messages this FMC will give you that have never really been simulated before in FS. Things like "DES PATH UNACHIEVABLE", "STEEP DESCENT AFTER XXXXX" etc...

Is there anyway that you guys could demonstrate the capabilities of the VNAV and LNAV behavior before it is released in a video? Best Regards,

We'll see - we're still tweaking it, probably will be right up until release.

For one up until the NGX nothing has simulated the Boeing FMC's speed prediction algorithm correctly - you'll see how this works soon enough, but it has the effect of making it a lot easier to slow down for approach and stuff. The real thing assumes a deceleration to Flaps 15 speed at the point of GS interception basically. The NGX does this and it does all the crazy math that figures out in reverse how to get the airplane to that condition at that point if possible based on the other constraints during the descent. I say "if possible" because if you have restrictions entered in earlier and there isn't enough space/time to both descend and slow down, it's going to tell you about it - there's a bunch of scratchpad messages this FMC will give you that have never really been simulated before in FS. Things like "DES PATH UNACHIEVABLE", "STEEP DESCENT AFTER XXXXX" etc...

Thanks, Ryan. Interesting info. I've seen messages like XXXXX ALT UNABLE, (or something like that, its been awhile). so I'm very interested to see all the errors I can run up in this thing. By the way, love the options video on FB. Good looking stuff.

In theory yes, since even the default FS autopilot can drive up or down to a point in space at a certain speed, but in practice FMCs connected to an autopilot do a lot more than that. It's quite a complex problem to navigate an aeroplane accurately through three dimensions in a constantly-changing air mass whilst trying to maintain speed, flight path angle and ETA as well, so much so that even the real 737's FMC had difficulties with it a few years ago when the software was less sophisticated. Nowadays it is very accurate indeed, and since PMDG wanted to emulate that, then they obviously needed to emulate how good the real 737's FMC software and autopilot is at driving the aeroplane during a highly dynamic process.The main problem is that when trying to hit all those parameters - possibly based on several different predictions for wind and temperature - something generally has to give in order to keep the airplane doing more or less what is expected of it (so either speed, flight path angle, or descent rate might have to alter and average things out); that's why you'll see the estimated position of where your average FS airliner is going to hit its mark jumping around along the line of your flight plan track on the PFD, whereas the real thing is a crapload better at arriving where it says it will, when it says it will, by constantly assessing what it is doing with thrust and pitch in relation to the planned arrival point in space. As a consequence, it will do a better job of things without fluffing matters and moving the estimate about on the PFD like you presently see pretty much every FS airliner doing. On the real thing, that kind of capability is important for making crossing restrictions, RNAV, IAN and such, and is one of the reasons why a 737 costs millions of Dollars.To create an add-on that will do the same thing, yet probably come in at under 100 quid and run on a six year-old sim is no small problem to solve, so the truth is, most other FS airliner developers don't even try to properly solve the problem to the degree of accuracy that a real aeroplane's software and autopilot can manage, and instead live with it being 'close enough', but that kind of dedication to accuracy is why PMDG's NG wasn't released six months ago.Al

+1 Sir!VNAV and especially the descent phase is probably the hardest thing to achieve in the simulator. It requires both a good understanding of the logic of the system AND an in depth knowledge of some very advanced and complicated math. We're talking about a multiple variable dynamic system that needs to be described and solved. Our community is lucky that PMDG has one guy that knows the math like the back of his hand. Yes, it's this Dr. guy that everyone is talking about. The Dr. can also solve the math without ruining the frames because if he weren't using his magic math techniques we would end up with 5fps in an OCed [email protected]. Just to understand the complexity of the system, think how many times you read in various modern jet addon forums through the years, lines like:"We know our VNAV is not accurate but same happens with the real one", "Real pilots don't use VNAV. They don't trust it. They prefer V/S and FLCH", "The airline SOP we use, doesn't allow VNAV for descent. So you shouldn't use it, if you want to be realistic". Let me tell you something in a way that will save my post from deletion. This is nonsense, poppycock, sack of rubbish etc. Real aircraft FLY with VNAV and real pilots USE VNAV. And what I never understood is how easily simmers, including a lot of developers unfortunately , claim the opposite. It would be much more fair and honest to simply say: "Our developing abilities reached a dead end regarding VNAV calculations. We tried to simulate it in the best way we could but the result is not up to par. Thus the usage FLCH and V/S is recommended instead". IMHO, claims regarding the inaccuracy of modern navigation systems found in multimillion, last generation, passenger jets, especially in the era of RNP are only good for a laugh.