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.

Interview: Stuart Buchanan

Q: How long have you been involved in FlightGear?

I’ve been contributing for the last 5 or so years, and was using it before that.

Q: What are your major interests in FlightGear?

I dip in and out of lots of things. I’ve spent a lot of time in the last couple of years working on the 3D clouds, and before that random vegetation. I’ve created a couple of aircraft (vulcanb2,flash2apittss1c), and maintain a couple more (c172pa4fCub). I also help maintain The Manual. I’m one of the moderators on the forums, and I sometimes remember to write something for the Newsletter.

Like many contributors I spend way more time messing around with things rather than actually doing flights! I enjoy warbirds (the p51d is a big challenge for me), and the c172p or Cub for some easier flying.

Q: What project are you working on right now?

Trying to get more performance out of the 3D clouds! I’m also looking at improving the HTML output of The Manual, so it’s easier to use online.

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

Less fiddling, more flying! I have a 14 month old daughter so my FG time has been constrained, and will become more so in the future.

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

Absolutely. FG has never been healthier. With all the hard work people like James Turner and others have put into our Jenkins build server we’re now able to produce releases every 6 months. That’s a massive step forward from even two years ago. The range and quality of aircraft in the hangar continues to increase, and Martin’s continual work on improving our scenery infrastructure will pay huge dividends in the future.

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

Getting the chance to work with a great group of people, even if I never get the chance to meet them in real life. Coming across a really nicely modelled aircraft or some new feature I never knew existed.

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

Well given the number of people that fail to RTFM, my work on The Manual 🙂

I also think people get used to new features very quickly, so they effectively disappear. When I created the first proper forests (with a lot of help from Tim Moore), it was pretty exciting as we’d never been able to have that density of foliage before. Nowadays we all take it for granted.

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

Start small. Modify an existing aircraft rather than create a new one from scratch. It’s tempting to start something new, but the amount of time and effort required to actually create a worthwhile aircraft with any realism is huge. We stand on the shoulders of giants in FG, so you might as well take advantage as much as possible!

Q: What do you do outside of FG?

I have a wife and 16 month old daughter and live in Edinburgh, Scotland. I work as a manager in a software development company (Metaswitch Networks). I’m also a keen climber and telemark ski tourer.

Q: Any real life flying experience?

I own and fly a flexwing microlight (aka trike) from East Fortune airfield just outside of Edinburgh (EG32 in FlightGear).  I’ve got about 200 hours so far and did a 7 day flying trip to the Isle of Wight in the south of England in 2010.

 

Preparing for a new Release

The FlightGear release team is just warming up to prepare the next release. This will be version 2.6.0 to be made available on February, 17th 2012 and our second release following our release plan. Users can expect a dramatic improvement in the visual system, improved AI traffic at assorted airports, a new video-recorder-style replay system and many, many more great new features.

Follow the progress of release team at the forum.

Soaring with the ASK-13

Soaring in Innsbruck

Author: Thorsten Renk

Innsbruck, 6 am on a warm summer morning just after sunrise. The first members of the aeroclub vacationing with their gliders get out of the tents and observe the weather. There is thin Cirrus coverage overhead, and the first weak Cumulus clouds are forming already. Winds are a steady 10 degrees from East – it looks like a promising day for soaring. I get the ASK-13 out and ready.

(In reality, we would not have the plane out like this in the morning – it’s dangerous to let light planes with excessively long wings lie around in 10 kt winds – either it would have a hangar space, or it would be disassembled in a trailer – but there are some things even Flightgear doesn’t simulate.)

The Local Weather subsystem of Flightgear has a fair amount of knowledge of convection and thermals. For instance, it includes the time into the decision what thermals are formed, and the strength of early morning thermal activity is thus a good guide for the strength later in the day.

Around noon, the thermal activity has significantly increased and thick Cumulus development is seen over the mountain ridges. I’m getting ready for a winch launch in the ASK-13. The ASK-13 is a rather old glider with a glide ratio of 28 optimum (i.e. it covers 28 m distance while sinking 1 m), thus it is not suitable for covering large distances, but it has very good slow-flying properties, and thus it can circle in very narrow thermals.

There’s no need to make a flightplan – soaring can’t be planned. I’ll simply get up there, have a look around and see what possibilities there are, and if I don’t catch a thermal quickly, I’ll land back on the field and do a second winch launch. Soaring in most locations is about finding the thermal updrafts beneath Cumulus clouds and circling them to get altitude. In the mountains, there is additionally the upward deflection of wind by mountain ridges, called ridge lift, which also leads to vicious sink in the lee of the mountains. Flying a glider in the mountains is difficult – often you may have to circle in a confined valley, you may unexpectedly get into a lee and lose a lot of altitude, or you may be forced to land in an unsuitable location.

Flightgear simulates both thermal and ridge lift and (in a very experimental way) in principle also wave lift. Ridge lift is dependent on the wind, terrain roughtness and the local terrain slope, whereas thermal lift is dependent on factors like terrain type and terrain elevation – just as in real life, strong lift does not form over open water but rather over surfaces which heat up in the sun. So, looking for rock surfaces or elevated terrain where a thermal is more likely to form are meaningful in Flightgear as in real life.

A winch launch gets us up into the air quickly – with a good climber like the ASK-13, 500 m altitude are possible (European gliders measure the altitude in meters, not in feet). Winch launch takes a bit getting used to, as it leads to quite rough acceleration and climb more resembling the performance of a rocket than of a plane, but is fun after a while.

The altitude gained in Flightgear winch launches is a bit generous when compared with reality. What launches are supported depends on the plane – several gliders allow aerotow in addition to winch launch. Aerotow allows to get to significantly higher altitude and basically any position, but is in reality much more expensive than winch launch.

Just after disconnecting from the winch, all of Innsbruck lies before us. I’m now turning south, as there are some promising clouds on the slopes there. I have to find a thermal quickly – there are none on the valley floor, so the actual altitude reserve I have are not 300 m above valley floor with 200 m for a safe landing, but far less since I have to look above elevated terrain.

And we enter the first thermal! It’s even a fairly decent one, with a net lift of more than 1.5 m/s. While strong thermals can give lift of 3-4 m/s, starting out low I have to use what I can get – this is not the time to be picky. Properly centering a thermal when entering from below requires some skill – there is no visual reference provided by the cap cloud, so this has to be flown by instruments.

A thermal in Flightgear is not just a uniform area of lift – it has a fairly complicated structure. There is a rim of turbulent air, and an outer layer of sink, the lift is strongest in the center of thermal, the whole column of rising air is slanted and a bit wasp-waisted, so the radius entering a thermal low is smaller than right beneath the cap cloud. Optionally, thermals also have a time evolution, i.e. they form and die off after a while.

After a good ten minutes work, we reach the cloudbase with a good 1500 m more on the altimeter. Now it’s time to go fly some mountains!

The ASK-13 is a twin-seater – a view from the back seat position (taken either by a passenger or an instructor) as we head south into Stubaital – Widdersberg just ahead slightly yo the right.

The ASK-13 can actually take a passenger (sitting on a different computer) via dual control in the backseat position.

Some gorgeous views of the Alps!

Here, I’m using the Innsbruck Custom Scenery, which received a lot of attention also by model developers in recent years, and is hence rather spectacular (see http://www.flightgear.org/forums/viewtopic.php?f=5&t=5350 in the Forum).

Since I’m now hugging a western slope, there is some amount of ridge lift available. The wind is not strong enough for me to really gain altitude, but by going close to the slope I can almost compensate my sink and hence make distance without losing altitude. The downside is that the wind is definitely strong enough to create substantial sink on leeward slopes, so I have to be very careful where I fly.

Heading into a small valley. Soaring is all about realizing possibilities – here the cloud looks very promising, and if I get a good strong thermal, I might even be able to cross the slopes to the right into the next valley. But it will not be easy – the terrain will restrict my circles, so I may not be able to center a thermal properly. I decide to give it a try.

This isn’t going well at all… First, there is some leeward sink coming in, reducing my altitude. Then, the thermal is there, but it is too weak and too small to really lift me up. In the center, I get half a meter of lift, but I can’t keep the plane stationary there, and circling the thermal my net lift is down to almost nothing. Moreover, I am running out of time – the cloud drifts towards the western slope, and I can’t follow it with the altitude I have left – I decide to abandon before conditions become unsafe.

As in real life, a promising cloud doesn’t guarantee a strong thermal. There is some randomness in the correlation between cap cloud size and thermal lift, and even a strong thermal may be in practice not flyable because its radius is too small. The thermal system is not designed to make soaring easy, but to make it a realistic experience, and disappointments are part of the experience. Soaring is not just heading to the next cloud to catch the next lift – one also has to be prepared for the case that no lift can be had there.

Turning around, the situation isn’y actually dangerous yet (in the event, I just need a 50 m strip of relatively level grass to land, which is easy to be had), but it’s not good either. I don’t really want to land in the countryside, because my team might otherwise face a long drive with the trailer to get the plane back. First, I have to head back into Stubaital.

And here we are – plenty of fields to use as landing sites just in case. And a very long way to go back to Innsbruck – all the way to the end of the valley. It looks impossible, but… there is still the ridge lift. Unfortunately, no thermals to help us out of this – the only visible clouds are on leeward slopes, and that’s a very bad idea to try. So I decide to fly very close to the slope to catch most of the ridge lift and try to get back to Innsbruck.

And… it works just fine – with just 50 m altitude loss I make it back – since the valley floor now drops, I have plenty of altitude to spare for my approach to Innsbruck.

Safely back at Innsbruck, and time for the next person to get into the plane and enjoy flying the Alps. I had hoped to fly a longer trip (I did manage to climb above the Habicht once with spectacular views into Italy), but then, soaring can’t be planned, and especially in the mountains, the conditions are often difficult.

A trip to Tenzing-Hillary Airport

A trip to Tenzing-Hillary Airport

Author: Thorsten Renk

One of the most dangerous airports in the world, Tenzing-Hilary Airport, also known as Lukla airport, hugs a small plateau in the Himalayan foothills. It is the gateway for trekkers into the Sagarmatha national park and climbers trying to reach the summit of Mt. Everest. The runway has a length of 460 m and a 12 degree slope – it needs aircraft with STOL (short takeoff and landing) capacities to operate from it. Usually DHC-6 Twin Otter or Dornier Do 228 aircraft, weather permitting, connect Kathmandu and Lukla. Today we will make the trip with the Beechcraft 1900D, a more modern commercial twin-engine turboprop which is also up to the task ahead.

Preflight preparations begin at Kathmandu airport. We will take off before dawn and experience the sunrise in-flight over the mountains. The route is about 70 miles due east from Kathmandu, just along the main mountain range. In good weather, several major summits are visible. Lukla itself is not equipped for instrument approaches, so we have to approach in VFR flight.

Many airports in Flightgear have a set of night textures, making the models visually appealing not only during day but also when it’s dark. Similarly, for many airplanes the cockpit lighting is modelled in some detail. Here, I have switched on the main panel light to illuminate my cockpit during flight preparations. The aircraft models also usually have strobe, nav, taxi or landing lights simulated.

Today, we have broken cloud cover over Kathmandu. As we climb, dawn approaches and the sky brightens, outlining the towering mountain ranges. Kathmandu has an elevation of 4300 ft, Lukla of about 9300 ft, but even this altitude is not even halfway up to Mount Everest with a bit above 29.000 ft. In fact, since the B-1900D is only certified up to 25.000 ft, we wouldn’t even reach the summit at top altitude.

At sunrise and sunset, Flightgear models the different level of light available on the ground and in the air. While it may still be dark on the ground, more light reaches the plane at higher altitude.

A few minutes later, the sun comes above the horizon and sky and cloud lights up while the terrain is still in deep shadow.

For this flight, I am using a development version of Flightgear which experiments with an improved modelling of atmospheric haze layers and shading of the terrain during sunrise and sunset. The result are quite impressive views of the sky. Presumably, this feature will become available with the regular release of Flightgear 2.6.

As we reach Lukla valley, the sun is up and some morning fog hangs in the lower foothills of the mountain ranges.

Now we turn into the approach, and Lukla valley is right before us. There is some fog in the upper valley, but the airstrip itself is clear (it can barely be seen just below the left windshield wiper).

We fly close to the left valley edge to have more space for the final approach. This means crossing some ridges at low altitude and sets off terrain warnings.

Many planes in the Flightgear world have instrumentation which warns about insufficient terrain clearance or potential collisions with incoming traffic.

Now it’s time to turn right into the 060 final approach. The wind is bad – it comes almost right from the rear, but as you’ll see shortly, the approach to runway 30 isn’t exactly available.

Here we are, lined up with the runway. Time to get the gear out and to decelerate a bit.

Some wind drift as we come in – last minute corrections. Lukla is not an airport for missed approaches or second chances – there is a solid rock wall right behind the runway and no chance to pull up. We have to hit the runway now, no matter what happens.

This fairly detailed model of Lukla is an addon to the official Flightgear scenery.

And… here we are, braking real hard.

Welcome to Tenzing-Hillary airport. We hope you enjoyed the flight with us!

In case you find the idea that Air New Zealand would operate in the Himalaya a bit odd, Flightgear offers The Livery Database where many more liveries from all over the world can be found for popular aircraft.