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The B737 Classic Project

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I'm really glad you like it, that was exactly my purpose, to provide some insight and views through pre-flight operations and checks, as the 737 you guys are making is going to be operations heavy (ok the nostalgia factor as well, Olympic closed, classic 737's replaced etc). As for the rest, yes I know which period you mean. With our small Hellenicon airport by the sea, I was lucky enough as a kid to watch operations from the tower as well as fond memories from 737's cockpits of Olympic as pilots back then allowed enthusiastic kids to visit and watch a pilot in the work. However now the situation has dramatically changed in both the new Int airport and unfortunately cockpit visits.

Best wishes with the 737 project, it's anticipated with excitement.

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Couple of more, click on pic for higher resolution           A bit higher res.    

Hi all,   So a quick report here, since I am unable to post at the org.   As we have said, we are targeting a 2015 release still.  We know full well we have to stop developing at some point and just

We have put up a somewhat different kind of video.  This one is a more candid "over the shoulder" look at a developer testing the overall simulation experience during a crosswind landing.   These type

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Hi guys, just a little heads-up regarding development. Below a reply by Tom:

A user on our blog requested an update on the project and perhaps some regular postings to let users know what is transpiring. The team feels that is probably a good idea at this time.

Up until this point in time, we have been cautious about posting for a variety of reasons, but the primary reason is (and still is to some extent) our concern about whether or not we could do such a challenging project to the level that we envisioned when we began. A highly accurate airliner project of what has become known in flight sim lore as "PMDG Level" has always been somewhat of the "holy grail" of flight simming....and the team felt like X-Plane was long overdue for such a project. Of course like anything in life, these things can only happen once all the variables are just right....X-Plane technology, developer experience, willingness, timing, etc. The CRJ-200 by JRollon broke the ice for X-Plane in a big way. As much as we love it though, the 737 is more of the airliner standard and is why we chose to do one. We thought that perhaps starting with the classic instead of the NG would serve two purposes. 1.) It showed some deference to the x737 project and 2.) we BELIEVED it would be somewhat easier than the more complex 737ng. Well we were wrong. The NG is probably way easier than the classic. Why? Steam gauges..that's why! Now that we have steamrolled through most of the systems on the aircraft, they are really no different than the NG in complexity, only in their implementation. The steam gauges; however, are not just simple graphics, they're complex animations with rolling digits and wavering needles and flipping flags. We even went so far as to put in motion blur on the DME rolling digits on the ADF. I tell you that a LED readout or computer graphic would be much easier smile.png

What has transpired though as we have seen the cockpit and systems come together is that we very much have a fondness for the steam gauge elements. This particular variant of classic we are doing uses the modern glass EADI / EHSI and somewhat fancy ECAM and somehow delivers the best of both worlds, modern glass and steam gauge "complexity" and is really a feast for the eyes of cockpit fans. It definitely pushes our techo-geek buttons.

So about the state of the project. Given the experience of our team members, we decided early on to pursue systems programming first. It is always the most challenging part of a project and can stop a project dead in its tracks. The downside to this for anxious simmers is that is does not give us much to show. Code is not very exciting to look at, indeed I am finding it quite offensive to look at as of late. It is my guess that we probably have over 30,000 lines of code and counting daily. There is some good news though and that is we have just about every major system "over the hump". Just about every major system means just about every one except the FMS. Of course we have 'punchlist' items' on each of the other systems to do. The FMS framework is mostly implemented though. We have the CDU interface and pages mostly complete, we also have the autopilot mostly done and what remains is the calculation of VNAV and HNAV elements and the building of the flight plan. These elements will integrate with the ESHI display so we work on these elements simultaneously and these will come together at about the same time. We expect to begin this phase "next".

As far as the 3D work goes, we believe this is the easiest and quickest part, even though it is the most visible. We have a good portion of the fuselage done and textured but no wings/flaps yet. We do not have the main gear modeled yet either and the engines are about 30% modeled at this stage. The systems accuracy is the heart and soul of our project and to be honest, you probably will not see all the cool 3D screenshots until we are on the final stretch. We are also beginning our documentation process and getting ready to grow that element as the systems punchlist get completed.

I cannot stress to you how in-depth the systems will be and why the programming is taking so long. "Systems simulation" has always been a bit of a marketing buzzword by add-on developers but our consultant, a 737 captain of ridiculous attention detail will not let up. We read the real POH page for page, system descriptions word for word and if it says it in the POH, we try very hard to put it in. For example…did you you know that in the case of automatically deployed speedbrakes on landing, that you can advance the throttle levers a bit after landing to "auto-stow" the speedbrakes? Bump the throttles up a bit and watch the speedbrake lever go from "up" to "down" on the throttle quadrant. You cannot do this though if the speedbrakes were not deployed automatically from the armed position. If you move the speedbrake lever manually to deploy them on the ground, the 'throttle bump' will not work. Who uses that anyhow? Our consultant thats who! He lands and bumps the throttle instead of moving the speedbrake lever. So if he does it, we do it. He is really starting to bug us!

So to summarize this long-winded post for now, upcoming in the ensuing months is more 3D development of the cockpit / wings / flaps / gear, punchlist items on the major systems: hydraulics, electrics, pneumatics, IRS, etc. Development of hnav/vnav and the EHSI and the documentation. Final work will probably be the 3D cabin, eye candy and user-interface elements. That's the plan anyhow.

Tom Kyler

Laminar / IXEG

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Hi everyone,

we have another teeny little piece of news for you. Today I want to show you the work we have recently done on our EHSI.


On the attached picture you can see the EHSI as the lower of the two screens. While the possibilities of displaying data on the EHSI are numerous I would like to point out what you are seeing here.

The depicted mode is the "expanded map" mode, showing the area in front of the aircraft. The aircrafts position is the tip of the white triangle at the bottom of the screen. Look closely and you can see the "ground path prediction" lines extending from the tip of this triangle, they represent the path the airplane will take within the next 90 seconds (30s per segment) at current turn rate and ground speed. You can use this to make very smooth intercepts when using smaller map ranges. Comes in handy for the final turn from base during a strong head or tailwind...

The selected range is 40NM (you can see the 20 on the mid range ring), the map can be displayed in 6 steps from 10 to 320NM.

You can see the two tuned VOR´s show up in green - along with the bearing lines, the green dashed lines. These lines are selectable (tuned VOR´s always show), and a great way to check your map accuracy - since the lines bearings are directly taken from radio signal data (displaying radials) and the green navaid symbols positions are drawn from the map´s database. So if they don´t intersect - your map has probably shifted.

Also displayed are the airports within the selected map´s section. You can select to show airports, navaids, fixes, etc. on the map with the help of pushbuttons on the EFIS control panel.

The magenta dashed line is the heading bug - you can see the aircraft is turning towards that heading.

The white line with the little rhomb at the top is the current track - look how it is influenced by the crosswind from the left. This track line will make it very easy to establish the correct wind angle when tracking along the localizer, for example.

The wind is shown on the bottom left - but unlike default x-plane we don´t show the wind while on the ground. Why not? Well, the real airplane can´t do it either - the wind arrow is a result of vector calculation between IRS track and groundspeed versus heading and true airspeed. In other words, the plane needs to "sense" the drift before showing it. On the ground there is no drift - > no wind indication. Now you try explaining that to Austin :-) Of course we also don´t show the wind if its magnitude isn´t big enough - just like the real plane won´t.

The top line will show GS and TAS, and also the current magnetic heading.

Now if you really look at the bearing line of VOR 1 very closely, you can see another green line with the label "A1" overlay it. That is the bearing of the selected NDB - coincidentally pretty much the same bearing. NDB´s positions are not shown on the map, though.

The dashes in front of the NM at the very top are the placeholders for "distance to next route waypoint" - blank in this picture since no route is loaded in the FMS.

More to come soon,


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This is to much to take!!!!! A high system-simulated 737 classic in x-plane!!!! Im going nuts! :)

Incredible work!

Question about the glass of ehsi and other glass gauges:

It has an effect in this image that makes it really realistic with the shining of the glass, (kind of purple color). Is this made in studio render or is it inside sim? The reflections look great!!!

The navigation looks so good, really top class!!!

Excellent work!

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Hi meshboy,

the shot is taken in sim - shift-space to copy a screenshot as .png. I then resaved the .png as jpg to save size. No editing.

Thanks for your kind words - I will make a video showing of all the features of the EHSI in a little while when it is done completely. Currently chasing some nasty OpenGL bugs. But you really have to see it in motion. It is VERY realistic!


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Thanks for your answer.

looking forward to the video Jan!

I think it is a great topic for a new video.

I am so impressed with your project that you start with systems instead of graphics, think this is really smart and makes sucessrate much higher in a project like this.

Happy coding!

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  • 2 weeks later...

no screenshots yet (because we won't show them..not because they don't exist) , but we are well into the process of developing separate CDUs and also separately controllable ESHI displays. How that integrates in to future collaborative simming I'm not quite sure, but we do have an open design with the possibility in mind. The EHSI features are just wonderful....like nothing I've ever experienced in flight simming. Currently we see no surprises, stumbles or bugs and things just rolling right along :)

-Tom Kyler


P.S. Here's some fun for you cerebral types. See attached screenshot. Given the line segment from A to B....and with an aircraft position at point, C. What is the true course from north...to fly from point C....such that you will intercept the line segment A-B at an angle of 30 deg? Guesses no good....give us 3 decimal places! OK, maybe 2. Heck, I'll even take one. This is but one of the many relations we have to develop in order to provide real time flight path calculations.


Edited by tkyler
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So i guess it will be some app that can display PFD and EHSI on the iPad or Andraoid Tab maybe?

We're not even remotely there or thinking about that. The primary goal is to get the aircraft working as accurately as possible. Everything else on top of that related to "cool features" or convenience won't be addressed till well after the product is out, well - proven and stable.

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Hi everyone, back with a little update

We are currently pretty much finished up with the EHSI. I posted about this before, but I can not emphasize enough how much the completion of this part has gotten our 737 more complete. While you could navigate the 737 "old school" with just the RMI, I really missed the different modes of the EHSI for navigation. You spend the majority of your time staring at that screen - so it being there and looking exactly like the real one does is a big step.

Another thing we are working on is the FMS - we have just finished the FMS part of the autothrottle thrust limit computing. Let me explain for a bit - the 737-300 does not have a FADEC like more modern jets. It´s engines´ RPM is controlled by a hydromechanical unit (with fuel as transmitting liquid) and a power management computer. While the PMC helps a bit, it is still up to the pilot to control the engine. He does so with the thrust levers and the N1 indicators. N1 is the RPM of the outer fan - it gives you a very good indication of how much thrust the engine develops.

Controlling the engine seems straightforward - but there is a lot to keep in mind. The CFM56-3B1 engine we are modelling is rated at a thrust of 20.000lbs. This is the limit to which it is specified. On a standard day at sea level, this limit is achieved with about 91.5%N1. So if you would firewall the levers to the stops, you might get a lot more thrust - but possibly damaging the engines in the process. It´s up to the pilot to avoid "overpressuring" the engine! As it gets hotter, maximum N1 increases, because warm air is less dense and will output less thrust. But at +30C the hot air entering the engine is compressed and burned to reach the maximum EGT - so as it gets warmer the maximum N1 needs to decrease to stay under the EGT limit.

Booooring, I know. In ancient days, there was a flight-engineer on the deck to check the relevant N1 for the current conditions, and he would actually reach forward during take-off and adjust the levers to set correct power! On the 737 classic you have the FMS to help you out. It measures temperature, pressure, bleed air demand and pilot´s thrust derate input to calculate the current limit N1. This limit is sent to the autothrottle computer, which will then automatically set and maintain maximum thrust as specified.

Now there are many different thrust limit. Take-off thrust, go-around thrust, maximum continous thrust, climb, cruise, reduced version of the above, and so on. Of course our model knows, computes, annunciates and sets these limits (flight-phase related and pilot-selectable) just like the real jet.

On the screenshot below you can see the N1 LIMIT page that controls thrust limits. It looks like this before take-off. Notice how one N1 value differs from the other one - it is because the left pack is off - so N1 can be higher without overstressing the engine (due to less airbleed extraction). You will notice the N1 change with packs on/off/hi, engine anti-ice, wing anti-ice and so on...


Just another example of a very complicated mechanism running behind the scenes that even most pilots take for granted tongue.png

The last few days I have also taken quite a few testflights to validate and sample climb performance - while we stay very close to the offcial numbers, there is just not enough data published to calculate climb performance through the whole envelope. We know you want your TOC prediction to be precise, so we have to account for different weights and different combination of climb speeds. An airplane climbs better at constant Mach, so a climb at 280/.74 will look quite different from one with 300/.72. You need to calculate the crossover point, calculate climb profile before and after that, and so on.

Yesterday I took her for a ride from Westerland in northern Germany to Rome, Italy - just over two hours. While we still don´t have an LNAV route to follow (working on it as we speak) it was nevertheless a joy to follow the VOR´s down to Frankfurt, Zuerich, Genoa and then to chop the throttles at 110NM out (FL370) and glide right onto the ILSof 16L without touching the levers or the speedbrake again cool.png .


Edited by Litjan
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Hi guys,

These last few days we have been busy with the FMS again. You might know that all modern airliners have one of these - and while you can theoretically fly without them, they are very much a centerpiece to a safe and efficient operation. They are quite complicated and highly sophisticated - and while that is great when actually using them on board, it is also the reason why a realistic FMS has been the domain of very few and selected add-on making companies so far.

Well, we are taking on that challenge. The quality and feel of our FMS is blowing me away every time our coders punch out a new page or feature. I have written about the thrust management before, today I will punch up a few more "preflight pictures" and point out what I think is special about them.


Above pic shows the two CDU´s - note that they are still "floating" in mid-air right now. Every CDU can operate independently of the other one - show a different page, accept input, etc.


Above pic shows the "PERF INIT" page, where you will input weights and other parameters of the flight. You can see that I am about to enter "FL240" as cruise altitude into the boxes on the top right. The FMS uses this data to compute various things - amongst them the takeoff speeds as you can see on the next picture:


Above pic shows the TAKEOFF REF page on the left CDU and the N1 LIMIT page on the right CDU. You can see on the right that I have entered a TASS of 45 degrees - the FMS has calculated a reduced take-off N1 of 87.5%. It has also automatically selected a reduced climb thrust - otherwise the N1 would increase at the thrust reduction altitude. Also note the thrust mode annunciator shows "R-TO" to alert the pilot that a reduced takeoff thrust will be set.

The left CDU shows the takeoff data - once you enter the takeoff flap setting (1 in this case) the FMS will calculate and suggest V-speeds, that you can accept with the click of a button or overwrite with your own speeds.


This last pic shows the effect of those inputs on the EADI. V1 and Vr are automatically shown on the speed tape. V2 must be set manually with the MCP speed selector. Ready for a reduced power take-off.


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Hi Jan,

would you mind to explain why/how the (additional) bleed air for packs etc. stresses the engine? I would have guessed that it would lower the stress because it will lower the pressure behind the bleed valves (right?). Or is it the bleed valve itself that might get damaged?

Thanks a lot and please keep the booooring stuff coming ;)


Edited by FloB
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Great pictures! Finnally a hardcore FMS in X-Plane!

If you have the time it is nice if these images goes to ixeg.net to have all the images in one place (i go there almost 1time/day to get my saliva production up to maximum!)

This plane will take X-Plane into a new kind of system-depth-simulation!

EXcellent work!

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Hi Flo,

The engine is only rated to do so much work - when you make it spend a part of that to run packs or anti-ice it will have to deliver less power for forward thrust. That´s why you need to reduce RPM to keep the total power of the engine constant.

In other words - you need to burn so much fuel to make the engine spin at a certain speed (N1). If you extract compressed air, the engine would turn a little slower even while adding the same fuel per minute. Imagine a car that is limited to 100 horsepower. You run at that horsepower and the speed is 150mph. Now you turn on the headlights, radio, window heat and a bunch of other things that use electricity and put a drain on your generator. The car will slow down....

Did I make sense?

Hi Meshboy - we will keep your offer in mind and understand your desire. I have been running through two of several tutorial flights we are planning for the documentation (KSAN - KLAX, KTUS KTUS - KLAS). It´s a lot of fun to think of how to show people all the features, take pictures, write the text... and it is amazing to think that the plane is far enough to really fly it to do the tutorials already and not miss any features!


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Makes sense. The point is that N1 isn't identical with the engines "workload" (measured by fuel flow) what makes N1 the wrong figure to estimate the real stress on the engine IF packs and anti-ice are engaged.

Reduction of pressure (by bleed air) means more fuel-flow to maintain the same N1 and thus no reduction of stress but more stress. So N1 has to be reduced to stay within limits...yep.



Edited by FloB
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