Interview: Christian Schmitt

Q: What is your forum/IRC nickname?

Surprise: it’s papillon81. Yes, I’m that guy 🙂

Q: How long have you been involved in FlightGear?

Acording to my mail correspondence it must have been in 2007/2008 when I became an active part. I was unsatisfied with the state of EDDF in the FG scenery (no buildings, lightpoles everywhere), so I teamed up with a guy who had already started some work there. I ended up creating all of the terminal buildings and improving the airport layout. In those days, not many pilots were flying there. This changed in the months afterwards, which was a big boost of motivation, too.

Q: What are your major interests in FlightGear?

My main interest is clearly the scenery and technology connected with it, like GIS. I started to create some custom scenery, like Helgoland, and after I was granted direct access to the mapserver database, I was able to proxy-commit other peoples work, that started to come in. IMHO, the best FDM or aircraft models are useless if you don’t have a nice place to fly, takeoff and land 🙂 So this area is what motivates me the most.

I do also maintain the Gentoo packages (ebuilds) for the GIT versions of FG, SG and TerraGear. All these can be found in the Gentoo Gamerlay repo.

Q: What project are you working on right now?

Some months ago I was fed up of FG being unable to read apt.dat 850 data. So I started digging into the terragear code. Having no experience with C++, it was a steep learning curve, but to my own surprise I was able to convert the original TG parser to read the runway data and other features from the new format files. I started to implement as many features I was able to. Luckily, Pete was already working on the taxiways and surface features. So we teamed up and eventually merged our work together. Since then it has become a really great project to learn and improve FG along the way for me. I hope it will be put into use for the next scenery version. Before that can happen, we need more testers and bug reports (hint! hint! hint!) 🙂

Q: What do you plan on doing in the future?

I will continue to work on Terragear, commit some improvements to the Concorde (my favorite plane in FG) and take care of merge requests. I’d also like to dive more into the FG/SG code and do some adjustments here and there. We’ll see what else the future might bring 🙂

Q: Are you happy with the way the FlightGear project is going?

I’m actually very happy with it. The improvements from 2 years ago up to now are breathtaking. Sometimes it is just amazing what features people start to work on, like Project Rembrandt right now. Also, the work that went into the weather and shader system recently is amazing.

Q: What do you enjoy most about developing for FlightGear?

The fact that we support each other and have a strong community with many very capable people from completely different backgrounds. Knowing that you can build on the work of others and that there is a helping hand in case of problems. Personally I like the FG IRC channel a lot.

Q: What advice can you give to new developers who want to get started on their first aircraft/new feature/Nasal script?

They should first of all have some experience with FG in general, meaning, they should have used the program for some time. We often have people asking questions that they could answer for themselves just by USING FG a bit with different aircraft for a bit longer than just a day or so. If they identify an area where they want to start developing, they should get in contact with the maintainer(s) and seek advice before investing many hours of work.

Advanced Weather v1.4 in Flightgear 2.6+

Part I: Convective clouds

Author: Thorsten Renk

The screenshots shown in the following use shaders, textures and scenery which are for various reasons (incompatible license, too recent development,…) not part of the official Flightgear 2.6 release. However, these are available for download and every feature works with Flightgear 2.6. The following packages need to be installed in addition to get to see the same: lightfield shader package v1.1, Juneau custom scenery, and textures from regional textures v0.1.

An integrated weather system

Without a doubt, clouds, haze and fog are the most easily noticed features of weather in a flight simulation, followed by winds. Advanced Weather v1.4 is however more than a tool to draw clouds and set wind parameters – it is a system with a (limited) understanding what the weather which it currently tries to render is, and it aims to simulate features of atmospheric physics.

This means that different weather phenomena tie together – winds and terrain influence the way cloud formation is taking place, cloud formation and the formation of thermal updrafts is connected, and weather is always understood as part of a large-scale weather pattern involving high and low pressure systems.

At the same time, clouds and atmospheric haze also influence the atmospheric light (and now also the scenery) in an essential way – strong fogging changes the color of sunrises to a blue-grey, wave patterns on the ocean follow the wind strength and direction and rain causes visibly wet runways. Let us have a look at how this works in fair weather.

The formation of convective clouds

Fair weather is typically characterized by convective cloud development: The sun heats the terrain and the air layer just above, thus warm air rises up in ‘bubbles’ and forms thermals, as the air rises, it expands and cools and eventually the moisture condenses into droplets, forming the characteristic, cauliflower-shaped Cumulus clouds. Cumulus clouds are the most common example of clouds formed by pronounced vertical motion of air.

As every glider pilot looking for thermals has to learn quickly, the formation of convective clouds depends on many different factors. The terrain type is crucial – while rock or concrete surfaces heat well in sunshine and may easily lead to well-developed thermals and cloud formation, open water or ice is much less likely to heat up in sunshine and seed Cumulus formation. High points in the terrain mark the spots where the bubbles of warm air are most likely to lift off the ground. Another important factor is the time of the day: The sun needs sufficient time to heat the terrain, therefore Cumulus formation is densest around noon, but the thermal updrafts are strongest in the afternoon, and while pronounced Cumulus clouds are unlikely to form in the morning, the thermal energy accumulated over a day may still give rise to well-developed clouds in the evening.

Let’s follow the development of convective clouds during a day in Juneau (Alaska). At sunrise, only very few clouds form, and they are transient, whispy phenomena (click to enlarge images):

Later in the day, the cloud formation is somewhat stronger. Note how clouds tend to form over mountain peaks, but do not form over open water. Also, no strong cloud development occurs over Taku glacier in the upper left, despite its high altitude, as the ice surface does not heat well in the sun.

At noon, the thermal updrafts become stronger and consequently the clouds become more well-defined. While in the morning the upward motion of air rarely exceeds 0.5 m/s, around noon this becomes rather 1 m/s, to strengthen even more in the afternoon.

Yet a few hours later, the number of clouds decreases again as the thermal irradiation by the sun weakens, but then typically fewer but stronger thermals with larger cap clouds are found.

Towards sunset, there is still significant thermal energy left to lead to sizeable cloud development, although the number of clouds as well as the typical strength of thermals is decreasing again. During the night, the development of convective clouds breaks more or less down completely as there is no thermal energy from the sun available.

Interaction of convective clouds, wind and the terrain

Wind meeting a terrain barrier corresponds to an upward-moving airflow, and hence is able to alter the development pattern of convective clouds in an essential way. Consider the following scene above Maui (Hawaii) in the absence of winds. Clouds rim the peak of Haleakala, but do not actually reach all the way up to the mountaintop (note also that due to the different latitude of Hawaii, there is far more thermal energy coming from the sun than in Juneau, leading to a much higher overall density of clouds):

With 20 kt winds coming from the north, the picture changes quite drastically: clouds are now pushed up all the way to the summit of Haleakala by the rising air, whereas the falling air south of the crater creates a lee effect in which convective clouds disappear. The vegetation pattern of Maui reflects these prevaling conditions – while moist air is carried up all the way to the summit of Haleakala, it rains off and irrigates the northern slopes of the mountain, leading to a bright green forest belt. The southern slopes on the other hand see typically falling air and dissolving clouds, and are consequently much drier.

Convective clouds in flight

If the appropriate option is selected, thermals are automatically generated along with Cumulus clouds so that thermal soaring is possible. Combined with the effect of ridge lift, this can make for rather realistic mountain soaring conditions in which a good degree of skill is required to stay in the air.

But the detailed interplay between convection and the terrain leads to interesting scenes also in other planes. Around noon, the peaks of high mountains are often covered in rather dramatic clouds piling up against the slopes.

Further down, the altitude of the cloudbase is no longer determined by the terrain but by the air layers.

And yet, the terrain elevation and the change between land and water imprint a pronounced pattern onto the distribution of density, shape and size of convective clouds.

Convection may also occur due to vertical instabilities in upper air layers, leading to the development of Altocumulus clouds, or at even higher altitudes Cirrocumulus clouds. Here’s an example of the development of Altocumulus fields at 15.000 ft. At such high altitudes, the clouds are no longer influenced by the terrain underneath, but rather by the properties of the air layers between which the Altocumuli form. For instance, Altocumulus development may be caused by the instabilities associated with an approaching cold front, and may thus signal the danger of severe thunderstorms in the near future. The Advanced Weather offline weather generation automatically includes this and other rules of large-scale weather patterns.

Next: Layered clouds, haze, fog and precipitation

FlightGear v2.6.0 Released

Also available in: NederlandsEspañolFrançaisPortuguêsRomână

 

The FlightGear development team is happy to announce the v2.6.0 release of FlightGear, the free, open-source flight simulator. This new version contains many exciting new features, enhancements and bugfixes. Major improvements from v2.4.0 include reduced AI aircraft load times, easier graphics tuning, more sophisticated AI aircraft and improved usability.

Founded in 1997, FlightGear is developed by a worldwide group of volunteers, brought together by a shared ambition to create the most realistic flight simulator possible that is free to use, modify and distribute. FlightGear is used all over the world by desktop flight simulator enthusiasts, for research in Universities and for interactive exhibits in museums.

FlightGear features more than 400 aircraft, a worldwide scenery database, a worldwide multi-player environment, detailed sky modelling, a flexible and open aircraft modelling system, varied networking options, multiple display support, a powerful scripting language and an open architecture. Best of all, being open-source, the simulator is owned by the community and everyone is encouraged to contribute.

Start downloading FlightGear v2.6.0 for free from FlightGear.org

FlightGear – Fly Free!

Some of the major changes include:

Aircraft operations:

  • At selected airports, FlightGear can automatically start at an appropriate parking spot based on the size and type of your aircraft.
  • At airports which support this feature, a visual display of the taxi route on the ground guides you to the active runway, while following the correct taxiways.

AI system

  • To reduce stuttering during model loading and take further advantage of multi-core CPUs, MP and AI aircraft models are now loaded in a background thread.
  • To reduce load times still further, only the parts of the aircraft currently visible are loaded from disk.
  • AI and multiplayer aircraft are no longer silent objects, they can produce sounds just like the main aircraft.

AI Traffic

  • Many new and updated AI aircraft and liveries. Over 80 airlines now populate the virtual skies.
  • The range at which AI aircraft are displayed is now configurable, allowing you to tune FlightGear for best performance.
  • AI controlled pilots have received extensive landing training and now make a more realistic approach and vacate the runway when able.
  • The simulator now assigns an available parking position on startup.

Flight dynamics

  • The JSBSim flight dynamics model received a major overhaul.

Environment

  • The Local Weather package has been further integrated with the FlightGear core, and has been renamed “Advanced Weather”. New rendering techniques allow more detailed clouds with no performance impact. High altitude clouds are rendered more realistically, and clouds move with the wind without impacting performance.

Interface

  • New replay system. Video-player like controls, including slow motion and fast forward. Pilots can now take over the aircraft at any time during a replay. Great for training particular flight phases such as approach over and over again.
  • Aircraft status ratings are displayed in the FlightGear launcher, allowing you to see at a glance the FDM, model, systems and cockpit quality for rated aircraft.
  • Multiplayer settings can be accessed in-sim. You can now choose your callsign, select an MP server and connect within the simulator.
  • Automatic scenery download is now even easier to use. Simply select the scenery directory to download to, and switch it on.
  • Individual graphics effects can now be configured from within the Rendering Settings dialog, allowing you to fine-tune the performance of FlightGear within the sim.
  • The simulation of radio signal propagation has started and will make the reception of ATC messages and navigation aids more realistic in the future.
  • A new set of options makes it easier to create seamless and zoomable multi screen setups.
  • A new performance monitor shows the time spent in each subsystem.

Highlighted new and improved aircraft

Project infrastructure

  • CMake is now the official build system on Linux, Mac and Windows.

Visual effects

  • The sea now looks more realistic. Waves align with the wind, and foam appears at high wind speed.
  • Steep slopes now appear rocky.
  • Runways now appear wet during rain showers.
  • To help aircraft developers, a single shader combining bump-map, specular, reflection and light mapping components is now available.

Other

  • Additional joysticks and rudder pedals are supported out-of-the-box, including the Logitech WingMan Interceptor, Saitek Pro Combat Rudder Pedals and Thrustmaster HOTAS Warthog.
  • FGPanel, lightweight software to render 2D instrument panels, is now included as part of the release.

Bug fixes

  • See our bugtracker for an extensive list of the bugs fixed in this release.

Windows

  • 64bit version restored and its installation integrated in the main fgsetup installer

Sky Diving Visualization

The Challenge

As a skydiver adds more gear such as front packs and items strapped to legs or arms, the jumper’s basic stability in free-fall is reduced.  It becomes easier to tumble out of control and there is less margin for error.  Similarly, the aerodynamic wake of the jumper may interfere with pilot chute opening (known as “hesitation”). Investigating different gear configurations generally involves vertical wind tunnel testing, or actual tests with jumpers. To avoid some of the cost, and mitigating safety concerns, a tool to computationally analyze these jumpers and their gear is highly desired. Creare, Inc., an R+D research firm in Hanover, NH, under funding from the US Army, developed a Computation Fluid Dynamics toolkit for analyzing jumpers and their equipment, and model the resulting configurations in FlightGear.

Note: a flyable parachutist model is available to download and test at the end of this article.

Fluent (CFD) and Stability Derivatives

CFD = Computational Fluid Dynamics.  ANSYS Fluent is a high end CFD that models flow, turbulence, and heat transfer in 3d.   Imagine being able to take a 3d model of a sky diver (or an aircraft) and place it at different orientations and different poses.  Then for each orientation and pose, run a computer simulation of exactly how the air flows around the sky diver, where pockets of turbulence are generated, and what forces and moments are produced.  Imagine all the combinations of roll and pitch and body poses possible — it leads to a huge number of combinations.  Now imagine repeating that for several different arrangements of front and back packs and other equipment.  You will need a cluster of computers running for days or even weeks to compute all the permutations just for a single pack configuration.  This is essentially a “virtual wind tunnel” running on a super computer cluster of PC’s.

In the case of the parachutist simulation: the amount of computation time required to generate 2 scenarios (with a back pack and without) was approximately 25,000 cpu-hours — or around 2 years of compute time on a single processor PC.  1000 individual simulations were run, each involving approximately 4 million “elements”.

One of the detailed CFD models used by Creare

 

Validation

Real world testing and data collection was performed in a vertical wind tunnel (such as the one linked here.)  This real world data could then be compared to the the Fluent (CFD) results to validate and possibly improve the computer model.

Real Time Simulation

Build-Up of Coefficients:

  • For each component of the model, the local angle of attack and sideslip angle are calculated from the combination of the limb orientation and the overall angle of attack and sideslip of the entire model.
  • For each of the six degrees of freedom, the contribution of the model component to the overall aerodynamic response is calculated from tables of non-dimensional coefficients:
    CFx,y,z = Fx,y,z / ( q * Acomp )
    CMx,y,z = Mx,y,z / ( q * Acomp * Lcomp )
  • The two-dimensional lookup tables are compiled from data extracted from the CFD results in the Solution Database.

Forces and Moments:

  • Aerodynamic forces and moments are transformed from the local frame to the global frame and then summed.
  • Resultant forces and moments then determine accelerations, velocity and turn rates are calculated, and the model iterates.

Creare partnered with Jon Berndt (the founder of JSBSim–one of the core physics engines used by FlightGear) to contribute some clever additions to JSBSim that permit a “blade element” approach to parachutist modeling.  Jon helped tremendously optimizing and integrating the required new code into JSBSim which then ultimately led to its inclusion in FlightGear.  The parachutist physics model is an order of magnitude more complex than a typical aircraft model.

Figure Animation and Posing

The character model is built out of several animated subcomponents: left & right forearms, left & right upper arms, left & right lower legs, left & right upper legs, head, torso, and pelvis.  The model parts are attached in a cascading fashion like a real figure, and each joint can be rotated through all 3 axis (roll, pitch, and yaw.)  In order to avoid unrealistic contortions, sensible joint range of motions are defined.

There are a number of predefined poses where the appropriate joint angles have all been worked out in advance.

  • Box: a neutral pose minimizing rotational or translational motion.
  • Left & Right Translation: mirrored poses that induce a “slide” either to the left or right.
  • Anterior Translation: a pose that induces a forward slide.
  • Posterior Translation: a pose that induces a rearward slide.
  • Left & Right Dorsoventral: mirrored poses that induce a left or right rotation (yaw.)
  • Dorsal: a “spread eagle” pose that maximizes surface area and thus minimizes decent rate.
  • Ventral: a “compressed” pose that minimizes surface area thus maximizes decent rate.
You might notice that these poses map rather neatly into well understood pilot controls similar to flying a helicopter.  For the FlightGear simulation we can mix these poses together in proportion to the corresponding joystick axis deflection and throttle position and fly the sky-diver intuitively.  For those that doubt, this actually works quite well! 🙂

Visualizing CFD Flow-lines

One of the neat things that a CFD analysis can produce are airflow lines that pass around the model.  We can take the 3d flowlines that are produced by the CFD and attach them to the 3d model of the figure.  This allows visualizing the flow lines from any FlightGear perspective.  One interesting technical challenge is that the flow lines need to keep a fixed vertical orientation even though the model may roll or pitch, yet the flowlines must track the heading/yaw of the model.  This can be done by setting up appropriate inverse transformations in the FlightGear model animation configuration file.

Smoke and Trajectory Markers

FlightGear offers additional visualization aids.  The model is set up to support emitting smoke.  FlightGear smoke drifts with the prevaling winds (which can often be substantial at higher altitudes.)  The model is also setup to emit “trajectory markers” at a fixed rate.  The trajectory markers stay fixed in 3d space and represent the actual path the sky diver follows.  In addition they represent the orientation of the sky diver at that point in space.

Where is the Parachute?

This exercise is setup as a free-fall simulation, not a parachute simulation so there is no chute modeled.  Instead the simulation is mercifully paused when the altitude reaches 100′ above the surface.

Download and Fly

Follow these instructions to download, install, and fly the Creare Parachutist model:

  • Note: the parachutist model is not compatible with FlightGear v2.4, you must fly this model with one of the v2.6 release candidates, or the official v2.6 release scheduled for February 17.
  • Download the Creare_Parachutist-v1.0.zip file.
  • Unzip it into your FlightGear “Aircraft” folder.
  • Start FlightGear and select either –aircraft=Parachutist-Scenario1 or –aircraft=Parachutist-Scenario2
  • Make sure you specify  an initial altitude (such as –altitude=10000), otherwise you will just be sitting at the end of the runway working on your tan.
  • Press F1 and F2 to toggle the two available dialog boxes on/off.
  • You can manipulate the joint poses individually or select from a set of pre-defined poses, or select “Joystick” control and fly with a joystick (or keyboard or mouse) similar to flying a helicopter or airplane.

Credits

  • Dietz, A. J., Kaszeta, R. W., Cameron, B., Micka, D. J., Deserranno, D. and Craley, J.”A CFD Toolkit for Modeling Parachutists in Freefall”, presented at the 21st AIAA Decelerators Conference in Dublin, Ireland, 23-26 May 2011. Paper AIAA 2011-2589.
  • The Creare Freefalling Parachutist model was developed by Anthony Dietz (Principal Investigator), Richard Kaszeta , Benjamin Cameron, Daniel Micka, and Dimitri Deserranno of Creare, Inc., as part of an SBIR Phase II project sponsored by the U.S. Army RDECOM Acquisition Center under Contract No. W91CRB-08-C-0135. Additional contributions we made by Curt Olson and Jon S. Berndt as consultants. The resulting parachutist model is unvalidated and therefore, should not be used other than for demonstration purposes. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the US Army RDECOM Acquisition Center.  Due to the significant contributions made to the project by several open source developers,  Creare has released a version of the resulting parachutist model to the open source community for continued development and use.  The FFTK itself continues development as a proprietary Creare project. For information on the FFTK itself, please contact Richard Kaszeta at rwk@creare.com, or 603-643-3800.
  • Flightgear modeling, animation, and scripting – Curtis L. Olson

Interview: Durk Talsma

Q: What is your forum nickname?

Hehe, guess once. 🙂

Q: How long have you been involved in FlightGear?

Almost since the beginning, actually. I first heard about the project in 1997, when I got an email from Curt Olson, in response to a posting on the usenet newsgroup rec.aviation.simulators.

Q: What are your major interests in FlightGear?

I like the open nature of the project and the possibility to contribute at various levels.

Q: What projects are you working on right now?

I am actually doing several different things for FlightGear. My main project is developing a fully integrated AI air traffic system that contains autonomous vehicles, an ATC system that interacts with both AI controlled aircraft and with the user controlled aircraft. In addition to that, I am one of the editors of the main website, editor of the FlightGear facebook page, involved in the release process, code committer, and organizer of the annual FlightGear booth at FSWeekend in Lelystad (EHLE). In addition, I have recently taken over the administrator role for taxidraw.

Q: What do you plan on doing in the future?

I don’t expect the AI system ever to be finished, so I’m fully concentrating my coding efforts on this project.

Q: Why is it that you are interested in flight simulation or aviation in general?

As a kid I was fascinated by space travel, the Apollo missions to the moon, etc, watching every program on TV, and reading every book I could lay my hands on. As a six-year old, I visited Schiphol (EHAM) airport for the first time, and that sparked my fascination for the big jet airliners. Kind of like every kid at one stage, I wanted to become a pilot. My real interest in aviation didn’t start until I was nearly 20 though, after visiting an airshow at Leeuwarden airforce base (EHLE). This was around the same time as when I got my first PC, a second hand 286DX, which I bought from a relative living in Germany, with a 40 Mb hard disk and 1 Mb of ram. It had a German version of Microsoft Flight Simulator 4.0 preinstalled. So, in addition to learning to “fly” I learned the German word for “crash” as well.

Q: Are you happy with the way the FlightGear project is going?

Yes absolutely. We are currently in the process of further improving our infrastructure, by setting up things like the release plan, formalizing the rules for commit access, aircraft maintenance, and we’re brainstorming about feature requirements for the long term. Firm ideas are present for modularization of the FlightGear code, and some ideas for an integrated launcher GUI have recently been coined in a very informal setting. It will certainly take quite some time before these plans are all realized, but I think that the project is more vital and alive as ever. I’m also just amazed at some of the recent developments, such as Frederic Bouvier’s project Rembrandt, Thorsten Renk’s, local weather system, or Martin Spott’s ongoing efforts to build a unified infrastructure for scenery generation.

Q: What do you enjoy most about contributing to FlightGear?

I think there are a number of aspects that I really enjoy. One of them is the collaboration with other people. Being part of the development team, we’re all pretty much equals, and regardless of one’s age, background, occupation, political or religious conviction, we all share something we like and like to collaborate on. That is really enjoyable. It may also happen that somebody just jumps in and finds a solution in no time for a problem that has been cracking my brain for ages. For example, Adrian Musceac, recent work on generating AI traffic patterns was really something amazing. Likewise, I enjoy the interaction with many other talented people, such as Brett Harrison, who’s just so amazing at making convincing liveries. Obviously there are many other talented people around whom I really enjoy working with and it’s a shame I can’t name them all. Secondly, I also really enjoy having the privilege of being the first to experience a new feature for the first time. I was the first person ever to see the sun and moon appear in a desktop Flight Simulator, and that is a little bit special.

Q: Are there any “hidden features” you have worked on in FlightGear that new users may miss?

Yes, my original contribution to FlightGear was some code to calculate the position of the Sun, Moon, and even the planets. Both the sun and moon are pretty much taken for granted now, but back then (in 1997) FlightGear was the first PC based simulator that actually had a physical rendering of the sun and moon! Nobody will probably even see the planets, but I got the code almost for free, once I figured out how to calculate the solar and lunar positions, so their a little bit of an Easter egg. After finishing the celestial code, and before starting the AI traffic system, I initiated many projects that I subsequently handed over to others. As such, I have extended the time calculation code to deal with local time, and to allow the user control over the time of day, and implemented the original graphical user interface (GUI) system, and the original 2D cloud layers.

Q: What advice can you give to new contributors who want to get started on their first aircraft/new feature/Nasal script?

Be optimistic, be naïve, be realistic, and start modestly. Set yourself an attainable goal! I should probably explain what I mean by this. When we started out, back in 1996-1997, we were what I would now describe as incredibly optimistic in the sense that we believed that we could pull this off, but we were also somewhat naïve in the sense that we really didn’t have any firm idea about the challenges that lay ahead. But, we were able to pull it off, so this shows that we were right after all. But, if you want to contribute don’t start with your magnum opus. Before starting out, take some time to familiarize yourself with the project, get to know the code base, data structure or workflow. In addition, making a good first impression helps. Over the years we’ve seen a tremendous amount of grand ideas and not many of them have materialized, so we’re naturally a little apprehensive you may not find an immediate warm welcome, but if you do come up with a well thought-out idea, you may convince the development team, especially if you can substantiate your ideas with some working code to back it up.

Q: Have you previously used other flight simulators or simulation software in general?

Well, as mentioned before, I started out with FS4, and have pretty much had every version since then, until FS2004. The latter version got me interested in the AI system. When I started playing with the FS2004 equivalent of the ATC system I and began to notice its programming flaws. Determined that I could do this better, I started drawing out my own plans, and since than, I haven’t really touched any other simulator.

Q: How does FlightGear compare in your opinion?

I like FlightGear better because it’s a platform that is constantly moving. I almost exclusively run the cutting edge development version, so occasionally you’re in for a little surprise. Be it positive or negative. But that keeps things a little exciting to me.

Q: Do you remember what first got you interested in FlightGear? How did you learn about FlightGear? In other words, why did you actually download and try FG?

Yeah, that’s a long story. I was reading the usenet rec.aviation.simulators quite frequently at the time, had been exploring Linux for a few years, and finished my C++ programming course at university. This was around 1997, so the Linux distros weren’t as advanced as they are these days, and you still had to do quite a lot yourselves. One particular afternoon, I came across a usenet posting, which read “OPEN LETTER TO ALL FLIGHTSIMULATOR DEVELOPERS”. This was around the time that Microsoft FS97 was the latest version, and many users were dissatisfied. The original poster wanted to write a letter, on behalf of every dissatisfied user, to ask for a better version, asking the big game companies to incorporate their wish list. I responded to the thread, stating that if we really wanted a sim of our own, we should probably do it ourselves. I remember being a little anxious, because I wasn’t sure whether I would actually be able to substantiate that claim, if we were to follow it up. So, a few days later, I was actually a little apprehensive when I opened up my mailbox and found an email from a guy named Curt Olson, inviting me to have a look at, what would eventually become the flightgear.org website. Well, the rest is history I guess…

Q: What was your first impression about FlightGear?

That’s a really interesting question, because there was no FlightGear so to speak of. When I joined, Curt had hacked together a few proof-of-principle demos; the one I downloaded was called linux-demo-0.0.7.tar.gz, if I recall correctly, and it consisted of a small sample of elevation data from a chuck of terrain near Arizona, source code of a primitve (by today’s standards) OpenGL based viewer, a copy of Bruce Jackson’s larcsim FDM, and a simple keyboard interface. But it was exciting to get it to compile, and run!

Q: Compared to other flight simulation software, what are FlightGear’s major benefits in your opinion?

It’s scalability, open architecture, and the fact that it can be a great test bed for ideas, as well as the fact that there is no need for third party add-ons. By bringing every suitable user contribution into a single repository, we essentially create our own add-ons, and in the long run that should remove the burden from the end user to search for extensions.

Q: Do you think it is necessary to know how to program in order to contribute to FlightGear?

No way. In fact it never really has been a requirement, even in the old days when there was a lot more emphasis on C++ development, we already had a need for non-coding developers. Think about documentation writers, etc. These days, the balance is actually really shifting away from programming to artwork. The FlightGear world is essentially still largely an empty place, so we really have a need for high-quality buildings. Many of the exciting developments going on right now are in the development of new scenery textures, 3D modeling, and livery painting. These are actually skills that I essentially lack, so I have a lot of respect for the people working in these areas.

Q: Have you ever used FlightGear professionally or for educational purposes?

I once tried in my previous job, but the computer we bought for the project had serious overheating issues, so the project never really came off the ground. In the mean time, I found a different job, so the project was shelved.

Q: What about FlightGear as a “game”, do you think it can be used as such?

Probably, I like to use FlightGear purely for fun, so usually I just make up my own challenges, such as performing a bad weather landing, taking off and landing on an aircraft carrier, or playing with my latest AI/ATC code. Once finished, the ATC code will add a little bit of a game element, because it will expect you to fly specific routes, arrive at specific locations at a specific time, so as not to clash with other traffic etc etc. The system isn’t finished yet, but with some hacking I did quite recently manage to complete a traffic circuit under guidance of the ATC system, and it’s quite tricky to do right. So, there are some “gamey” aspects of FlightGear that are quite realistic and hopefully challenging. Having said that, I see absolutely no need for any formal gaming rules, or game like features such as setting off explosives and the like. Like many of the other developers, I like to keep FlightGear civil(ized). I don’t object to simulating military aviation though, as long as it doesn’t serve the purpose of glorifying death and destruction.

Q: On average, how much time do you spend working with/contributing to FlightGear?

Hard to say, it varies quite a bit with my day job requirements, but I think on average maybe one or two hours a day.

Q: Which of the more recent FlightGear developments do you consider most interesting/appealing?

There are quite a few. Of the individual projects, I really think that project Rembrandt (Frederic Bouvier’s shadow rendering code) is really exciting. But so is the new effort to unify all the shaders, the atmospheric haze and scattering, and Thorsten Renk’s local weather. I’m also quite happy with the progress we made with the AI traffic/ATC system, even though it’s not finished yet. But, what I think is perhaps even more exciting are some of the long-term infrastructural changes we have recently discussed. I can’t say too much about that yet, because many of the ideas haven’t been formalized yet, but making FlightGear more modularized by making use of HLA technology, and perhaps a more integrated GUI and launcher program are some of the exciting developments that I can see happening in a few years from now.

Q: Is there some feature that you’d truly like to see in FlightGear one day?

Yeah, there are some. Obviously, I’d like to see my own project come to it’s full potential, but in addition to that, I would like to see full scenery development of the polar regions of our planet. One year ago I visited Antarctica in real life, and this is just a very exciting area for flying. I’d also like to see the possibility of lower earth orbital space flight, more seamless terrain textures.

Q: What do you think could be done to attract even more new users and contributors to FlightGear?

Establish a good balance between developing new stuff and doing some public relations work. For the project the key question for survival is not to attract many users, but to attract potential contributors. Obviously, the way to do this is to attract many users, and to hope that there will be a few potential contributors among them.

Q: What about interacting with the FlightGear community? Any tips/experiences you’d like to share?

Nothing really special; just use your everyday courtesy, and keep realizing that we’re all volunteers. I’m usually not that active on the forum or mailing list, but I can tell from 15 years of experience that an intelligent and reasonable response is far more likely to create some momentum than a hurried response that is written in a spur of emotion. Also, I have observed that there is hardly any relation between action and words on either the mailing list or the forum. So when your new to the community, just hang around, get to know the characters and try to establish whom you can trust to be a knowledgeable source of information and who just raises a lot of dust.

Q: Have you ever recommended FlightGear to other users, friends/family?

Not really, my friends and family aren’t really into flight simulation.

Q: Is there anything else you’d like to share with us?

Yeah, have a lot of fun, and if you can try to contribute something to the project.

 

FlightGear v2.6 Release Candidates

This is the place to find the v2.6.0 release candidates as they become available.  We would really love for everyone to download these “test” releases and give them a try.  The target date for the official FlightGear v2.6.0 release is February 17.

Download FlightGear v2.6 Release Candidates:

What’s New?

I think I found a bug …

  • Please review the following FlightGear forum topic.  Here you can get some ideas on what to look for and what to test.  And if you do find something wrong, where to post bug reports so they can get properly addressed.

What would it be like to fly a rocket into space?

Do you want to earn your astronaut’s wings?

Author: Thorsten Renk

Real spaceships aren’t actually piloted into orbit. The risk that a human being, strapped to his acceleration seat and under a crushing acceleration of 4 g for a prolonged period of time is unable to fly with the precision required to reach orbit is far too great, and real spacecraft reach orbit on autopilot.

But what would it be like? Welcome to a scenario in which a Russian Vostok spacecraft has been acquired by the USA and fitted for a manually flown mission.

This is the launch vehicle assembled at Edwards Airforce Base. The actual capsule is hidden under an aerodynamically formed protective cover. Below it is the third stage of the rocket, with its exhaust nozzle visible. All this is mounted on top of the huge first and second stage. Unlike many US rockets, which use sequentially burning stages, the first stage of the Vostok launch vehicle consists of four boosters which burn along with the long, cylindrical second stage.

The inside of the spacecraft is a very small place. There are no big windows (and currently the protective cover blocks the view outside in any case), so there is not so much to see except the instruments. In front of me is the main instrument panel, and to the right is the stage control panel, left of it the control handle.

Here’s a closeup onto the main instrument panel. Since I won’t be able to see anything of the outside during much of the ascent and the descent, this is what I will have to navigate with. The most important instruments are in the lower half of the panel – altimeter, inertial speed indicator, vertical speed indicator, dynamical pressure, orientation and acceleration. This isn’t enough to fly with any precision, say to rendezvous with ISS – but that’s not what the Vostok is for, it’s made to carry a human into orbit and back, and this is what I will do.

One of my most important aids however is a handwritten cue sheet which tells me roughly at what altitude, velocity and orientation the rocket should be at a given time. Without such reference, it is very hard to gauge whether the rocket is on a good ascent path or not.

Unfortunately, the ‘not being able to see too much’ is also a technical limitation. The Flightgear rendering engine is not designed to handle views from low Earth orbit, and even with the cutting edge development high altitude and extreme visibility rendering I’m using in the following, the view doesn’t really measure up to real views of Earth from orbit.

After igniting the engine, the thrust takes a few seconds to ramp up, but the Vostok rocket delivers a solid 2 g initial thrust with first and second stage burning, so I lift off quickly. After the first few seconds, I rotate the rocket around its main axis such that I am facing my launch heading. To make use of Earth’s rotation, launches are done eastward. As soon as I reach the desired heading, I push the ascent path out of the vertical along my launch vector to about 60 degrees with the horizon. During ascent, I will thus be more and more hanging face-down in the capsule, facing Earth at all times. Which is very reasonable, because in case of any instrument malfunction, this gives me at least a rough visual reference. Of course, the actual forces in the capsule are nothing like hanging face-down, the acceleration always pushes me back into the seat.

After passing about 20.000 ft, the dynamical pressure starts growing large, and I have to throttle back to avoid damage to the rocket. After all, a rocket is little more than a thin shell around fuel tanks: For instance, the second stage weighs roughly 100 tons at liftoff, but its empty weight is a bit over 7 tons. The air thins rapidly, however, and thus the dynamical pressure decreases quickly and I go to full thrust again. Once above the pressure peak, I push the nose of the rocket further down to 30 degrees with the horizon and start building up forward velocity while Edwards AFB vanishes below.

The full power of the JSBSim flight dynamics and atmosphere model affects this part of the ascent, and so the interaction between rocket and atmosphere is as realistic as the available data on the Vostok can make it.

After about 90 seconds, the fuel of the first stage boosters is almost spent, and the reduced mass of the launch vehicle ramps up the acceleration to 4 g and beyond. Once again, I throttle back to stay below 4 g to avoid damage to the rocket. At about 120 seconds, the first stage is out of fuel, and I separate the boosters. I am now high enough that air friction is negligible, and so I also blast the protective cover off the capsule and can take the first look outside (nothing much to see though). The second stage is still heavy at this point, and so the thrust goes back to about 2 g as we climb the 100 km altitude limit into space.

The whole flight dynamics changes quite drastically during a mission from the initial launch vehicle to the re-entry of the capsule. Also the weight of spent fuel is a significant factor. All these effects are quite distinctly felt during ascent to orbit.

At this stage, I have to start watching my ascent casefully. The second stage separation should bring me roughly to my orbital altitude with about zero vertical speed so that the third stage burn just keeps me at this altitude while accelerating me to orbital velocity of a bit more than 28.000 km/h. However, the second stage reaches more than 4 g thrust towards the end of its burn, while the third stage starts with barely 0.5 g thust, so any mistake I make at this stage will at best take very long to correct with the 3rd stage burn, at worst be unrecoverable. Thus, I control the pitch angle very carefully and monitor altitude and vertical speed.

About 5 minutes after launch, the second stage burns out and I separate it as well and ignite the third stage. Flying a rocket is very different from flying an airplane – while an airplane reacts to its immediate surroundings and doesn’t remember much of what was five minutes ago, the rocket’s current state is pretty much determined by what happened the last five minutes. If the ascent to this stage was bad, there’s nothing much I can do to correct it now. But my altitude and speed after 2nd stafe separation are within reasonable parameters, and so I continue build up speed while keeping my altitude with the half g thrust the third stage provides.

Another five minutes later, close to reaching orbital velocity, I have to throttle down. The speed must be reached quite accurately, otherwise I might go into an elliptical orbit rather than an almost circular orbit. And this is problematic, because the TDU has even less thrust than the 3rd stage, so if the 3rd stage brings me too high, I might not be able to de-orbit at all.

There are also technical reasons – Flightgear currently isn’t designed to handle an altitude above 150 km, so I have to reach an orbit below 150 km and above 100 km where the atmosphere is thin enough.

I watch the perigee indicator carefully, and as it starts rapidly climbing, I separate the 3rd stage – I am in orbit! Apogee and perigee indicators read 128 km and 140 km, so while not completely circular, this is reasonably good.

Flying to this stage isn’t easy – only three Flightgear pilots have to my knowledge reached a stable orbit with the Vostok spacecraft. You have to work for your astronaut’s wings!

From this point, I only have the minimal thrust of the TDU available to turn the spacecraft and decelerate. Rather than aerodynamical controls, I now have to fire thrusters to change my attitude, so the spacecraft handles once again completely different.

JSBSim handles the attitude control thrusters just as well as the aerodynamical controls, and the spacecraft handles again very plausibly at this stage of the mission.

There’s not much to do while drifting along in the orbit. Look out and watching the sunrise is nice though.

The cutting-edge development experimental lightfield shader brings out the Earth shadow moving across the terrain, the stark shadows in low light and the differential light dependent on altitude very nicely.

To de-orbit, I turn the spacecraft around and fire the TDU main engine to use up the remaining fuel. This lower my perigee such that it intersects with the atmosphere – the friction will have to take care of the rest. Then I separate the TDU as well. At first, the first gentle touches of the atmosphere lead to a tumbling motion of the capsule, this then stabilizes as the drag increases, and I start falling faster and faster.

If you though the 4 g during ascent where tough, then you haven’t experienced re-entry yet. As the capsule finally reaches the lower atmosphere, a deceleration force of 8 g and more brutally brings me from orbital speed to a few hundred km/h. I simply black out during this stage.

Flightgear optionally simulates blackout and redout due to extreme acceleration at set limits.

By the time I get conscious again, I have an altitude of about 10 km and most of the speed is gone. Time to get the brake parachute out and kill the rest of the forward motion. After the braking parachute has done its job, I get the main parachute out, and once my vertical motion has slowed down, the final task is to activate the soft landing sensor.

Close to the US west coast, I gently splash into the ocean. Nothing to do now except to sit tight and wait for the recovery crew to pick me up…

Interview: Olivier Jacq

Q: How long have you been involved in FlightGear?

I’ve been following FG closely since FlightGear 0.9.8. So, checking on the Wiki, this already dates back to… 2005!

Q: What are your major interests in FlightGear?

At first, I was using FG as a “casual” user, mainly contributing positions in my local area (Brittany) and especially the Brest area (cause I’m not that good at 3D modelling!). So I would say my major interest is in definitely in the scenery side of FG – and HHS choppers!

Q: What project are you working on right now?

This is HIGHLY confidential! But because Christmas is coming soon, I’ll give you a small written preview on this early present! Still under development, I’m working on automated scripts to add/delete/update shared or static scenery objects/positions within FG, in order to ease the actual submission process, both for the user and the scenery maintainers. The tool to add unitary positions is now in production (see below)!

Q: What do you plan on doing in the future?

I have at least a few months before all scripts are finished and under production, so I think when they’re all done, I’ll take some time to use them and add more objects positions into FG myself!

Q: Are you happy with the way the FlightGear project is going?

I am especially happy to see the latest developments in FG, as the release plan and the many works going to make the scenery better: shaders, weather, and especially scenery which needs to be regenerated and enhance (have a look at the apt.dat 8.50 work in the forums, it’s awesome!). FG is really becoming better and very much comparable to other sims.

Q: What do you enjoy most about developing for FlightGear?

FG is relying on so many exciting parts: GIS, 3D modelling, database, web, network… and there are so many advanced technologies to implement (eg radio propagation early support)… it’s amazing and there is no other software where all this is needed but flight sims. A real concentrate of technology!

Q: Are there any “hidden features” you have worked on in FlightGear that new users may miss?

I was at the origin of the photorealistic scenery for Brest. To be precise, I had the idea and asked for the permission to use the data (as it is CC-BY-SA). Then Nels and others have been working on the patch for SG, etc.

Q: What advice can you give to new developers who want to get started on their first aircraft/new feature/Nasal script?

Well, they have to check that noone is already working on it, or to get in contact with him. Most of all, I would advise them to start on small projects first. For instance, a LOT of cockpits need enhancement. So try to make existing aircrafts better, rather than try to build yet another one from scratch. Keep this for later and focus on what needs to be enhanced now. FG will then look so much better to our fellow downloaders.

Q: Have you previously used other flight simulators or simulation software in general?

I remember having a flight simulator called “ILS” on my TRS-80… and next I moved, as a lot of people, on Microsoft Simulator when I was 7 or 8 on 10 Mb hard drives 😉

Q: Do you remember what first got you interested in FlightGear? How did you learn about FlightGear? In other words, why did you actually download and try FG?

FG was the only free and open source advanced flight simulator I found under GNU/Linux, so when I decided to moved my computer fully to GNU/Linux, the choice was quite easy. Its success and improved quality over the years confirmed this choice was good!

Q: Compared to other flight simulation software, what are FlightGear’s major benefits in your opinion?

Apart from the fact that it is free and opensource, I would say that its central scenery database and mapserver is one of its major features, compared to other flight sims where you have to download here, download there, add patches, etc… what a mess it becomes on your hard drive after a few years of addons!

Q: Do you think it is necessary to know how to program in order to contribute to FlightGear?

Not at all, contributing to scenery object positions is for instance very easy (it’ll be even easier after my script goes in production ;-). So everyone should be able to contribute to FG (in a proper manner), that’s the way to success!

Q: Have you ever used FlightGear professionally or for educational purposes?

I’ve been talking about it in my job, so show its quality, even sometimes compared to professional ones I have seen there. I would definitely recommand a stronger relationship between FG and professional/educational worlds.

Q: On average, how much time do you spend working with/contributing to FlightGear?

For a few weeks, I’ve been working for around 3 to 4 hours per week developing scripts. It’s been a while since I haven’t been having a flight in FG!

Q: Which of the more recent FlightGear developments do you consider most interesting/appealing?

I would definitely vote for the work on fgfs-contruct and 8.50 data format support. The anaglyph support is amazing too.

Q: Is there some feature that you’d truly like to see in FlightGear one day?

I hope sometimes we’ll be able to add GPL-photorealistic pictures on top of actual layers. Looking forward to OSM-based roads scenery release too and multi-core support.

Q: What do you think could be done to attract even more new users and contributors to FlightGear?

The fact that FG software is not localized into other languages can be a real drawback for some users and is often shown as such when magazines or forums talk about FG. If this support is added back, I will definitely work on the French translation!!

Q: What about interacting with the FlightGear community? Any tips/experiences you’d like to share?

As many others, I regret the way some people ask for features like: “do this aircraft, I NEED it”, or don’t even have a look at the Wiki or forums archives to get an answer to their questions. Ask politely, try to understand the way FG community is organised, search for archives, don’t pollute threads and everything will be better!

Q: Is there anything else you’d like to share with us?

The future of FG belongs to you: each of you can make it better, whatever your skills or interests are. So don’t say: this is missing, try to add it or ask the community what you can do for help!

Interview: Gijs de Rooy

Q: How long have you been involved in FlightGear? What was it that made you join?

According to the forum software I joined all the way back in July 2007. One year earlier I was one of the first users of Google SketchUp, free 3D modelling software. After modelling several buildings in my home town, Amsterdam (and placing them in Google Earth) I started working on Amsterdam Airport Schiphol. By then, Google Earth had a (simple) built-in flight simulator. Amsterdam would be the first airport to be modelled especially for that, that was my plan at least…

While modelling Schiphol, I stumbled across this free flight sim, called FlightGear, that wasn’t a game, unlike Google’s. In one of my first posts on the FlightGear forum I asked for someone to place my models into FlightGear’s scenery. Georg (Heliflyer) placed my first buildings. I took some effort, but I finally managed to place buildings myself. Sadly the guy that introduced me to FlightGear and gave me a hobby that would last up till today, passed away in 2009.

Q: Do you have real world connections with aviation or IT?

Since two months I’m studying Aerospace Engineering at the University of Delft. So far I really like this mix of hobby and study. Before starting this study my only connection with aviation (other than traveling) was a one hour flyinglesson in a twinprop, I got for my birthday. If you have a chance to do such a flight, I’d defenitely encourage you to do so. It’s an amazing experience.

Q: What are your major interests in FlightGear?

One of the things I like about FlightGear is the wide range of things one can get involved with: modelling, texturing, writing manuals, collecting data etc. and of course flying itself. Therefore I have a very long list of interests. However, there are three key parts that I particularly enjoy; being the development of scenery and aircraft and helping others by writing wiki articles and replying to questions at the forum.

Q: What project(s) are you working on right now?

My main development projects right now are the Boeing 747-400 and Dutch scenery. Both can be considered as never finished; there are always things to add/improve.

Q: On average, how much time do you spend working with/contributing to FlightGear?

Until this year I spent roughly 4 to 5 hours a day on FlightGear related things. Now that I’m studying I have less free time, but still several hours a day on average. Most of that time is taken up by non-development stuff, like the forum, wiki and livery database. Over the years I’ve been spending way too litle time on the actual flying.

Q: What do you plan on doing in the future?

I would really like to bring the 744 to a state where a real pilot cannot spot a thing that is missing in the simulation.

Q: What advice can you give to new developers who want to get started on their first aircraft/new feature/Nasal script?

Starting something new is easy, completing it is much harder. I could have never guessed I would still be working on the 744, three years after I started!

I’ve always been telling newcomers to start improving existing features. It’s a great way to familiarize yourself with the project. By looking into existing aircraft’s files for example, you will quickly find out how those files are linked together and what their purpose is.

And above all: enjoy the process! Things will go slow, will require lots of dedication and you will do a lot of work that ends up being useless; but once you’ve got to a certain level you’ll know it was worth it.