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Supersonic the hedgehog

Spent the last few weeks tweaking the more esoteric parameters of the airfile, and finally came down with something that I believe I can live with. Still a little bouncy in pitch, but apart from that it flies more or less “on the numbers”. High Mach numbers are now easiest to achieve at around 10 km altitude, and the effective ceiling is somewhere around 15 to 16 km.

Did some aerobatics today at low altitude, staying below 700 kmh all the time on full throttle. Pulling a few G:s will keep alpha up and speed down, as it should. Flies like a dream in my opinion. Roll damping has been adjusted to get a snappier roll, as the real thing could actually do a full roll in 2 seconds. If you liked the somewhat sluggish response of the previous versions you might not feel at home with the new FDE, but this is actually more realistic. I think.

Put the afterburner back in the mix today and started tweaking the afterburner thrust curve and the high Mach drag values. I have been using the NASA EngineSim applet as a starting point, then recalculating those results on the data I have from Rolls-Royce and Volvo for the RM6C engine with the EBK67 afterburner. Feels OK, although I suspect that wet thrust might now be a little too high. Will try to check this with some Draken pilots. Peaks at M 1.75 with bingo fuel at 10 km altitude, this should be more or less accurate according to the real flight manual.

A number of bugs related to the autopilot appeared during this testing round, probably because I have been pushing the limits a bit. Will work on these bugs the rest of the week, then start finishing up for a 4.1b2 release at the end of the month.

Stay tuned /Tom

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Almost there

The new FDE is now “almost finished” – which really means that we are now in the kingdom of Pareto and Murphy. The final stage of any project is inevitably where most of the work is being done, and where everything inevitably goes wrong. That said, I am actually optimistic about releasing 4.1b2 within the next few weeks.

The big difference between the previous (current) version of the Draken FDE and this attempt is that I am now starting with a blank sheet and some good books on aerodynamics, instead of just tweaking a stock FDE until it squeaks. The 4.0 FDE performs OK within, say, 75% of the envelope. The new version will hopefully be able to “touch the edges”.

I started by remodeling the engine, which now produces net dry thrust within 5% of the real thing all the way from the runway to the “coffin corner”. It also has the correct thrust-specific fuel consumption and a more linear throttle response. All based on the sparse documentation from Rolls-Royce, Volvo and Saab that I managed to find.

The next step was to rework the lift and drag parameters to achieve the correct airspeed, angle-of-attack, pitching moment, etc. during climb and cruise. A great help in this was that I finally found some actual airfoil data for Draken. At the moment I am working on stability and control derivatives, which turned out to be the trickiest part. I don’t have the real values, so it is basically a lot of maths, guesswork, and test flights.

Putting the final touches on the derivatives today, then adding the afterburner and starting on the supersonic parts.


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What happened to 4.1?

What ever happened to the release of 4.1 proper? Or the second beta?

The first beta turned out to be riddled with bugs and performance problems – some discovered by me in the weeks following the upload, some duly reported by users. I planned to put out a second beta that took care of most of these bugs, but the issues with flight performance were very troubling and I decided to postpone the second beta while working on the FDE. There is, after all, no point in uploading another version which still does not fly properly.

This is basically the problem: A lot of the engine parameters were totally wrong in 3.x and 4.0 due to my misunderstanding a crucial part of the SDK documentation. To compensate for the erroneous engine params I had been tweaking the aerodynamics to a point where the curves were completely off the chart. I have spent the last month reworking this, starting from scratch and actually following instructions this time. The result is a completely new FDE which gives a more or less correct engine thrust at all altitudes. The next step is to rework the lift/drag parameters to also get the correct airspeed and angle of attack, which is what I am working on right now.

Apart from this I have added a lot more 3D details in the VC and made some changes to the sometimes quirky radios and nav systems. When I eventually upload the next version I will try to include a detailed change list. No promises as to when this will be though, I really want to get the FDE right first.

Stay tuned, /Tom

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New documentation for 4.1 and 4.0

The updated Flight Manual for the FSX version of Draken has now been officially released. A link to the online manual can be found in the top menu, and a printable pdf version (100 pages, 7.5 MB) can be downloaded from the Downloads page.

The new edition covers both versions 4.0 and 4.1 (to be released) and the previous edition can no longer be downloaded.

The online manual has been tested with Firefox (recommended), Chrome and IE9, but as always there may be problems with some browsers. If you have problems accessing the online version, or find any errors in the content, please let me know.

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A change of scenery

Barbro and Anita
The 3d objects in the scenery that is installed with Draken have never been supposed to be authentic, as I never had a clear idea of what these now-defunct navaids really looked like. In version 4.1 they have been replaced with objects that look a little more like the real thing. You can update your existing scenery for 4.0 or 4.1b1 by replacing the “Barbro” scenery folder with the one in this zip file. Remember to make a backup of the old scenery, just in case.

Download Barbro scenery 4.1b2

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Flight Manual 4.1 online

The Flight Manual for version 4.0 has some errors and missing bits and should have been updated long ago. The changes in 4.1b are of course also not covered by the current edition. The problem is that the documentation was created in a proprietary content management system that belonged to a company I no longer work for, and I do not have access to those tools anymore.

So, updating the manual at this point means taking the raw XML files, writing my own XSLT transformations and formatting objects, and parsing the lot through a free formatter like Apache FOP. For those of you who have not yet fallen asleep, this is basically a tedious process including a lot of manual codewriting to get the final result to at least resemble something printable.

Boring as that may sound, I have started doing exactly that. My first step was to write some XSL stylesheets to be able to present the XML content online while updating it.

This documentation is still a work in progress and is updated daily at this point. A printable PDF version will probably follow once the 4.1 version of Draken is released.

Stay tuned /Tom

LINK: Online Flight Manual – Draken 4.1

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Draken 4.1 beta 1 download


The first public beta version of Draken 4.1 can now be downloaded using the link at the bottom of this post. Reading the following information before downloading will probably save both you and me a lot of pain, so please do.

  • Please read the End User License Agreement (EULA) that is included in the installer, and make sure you understand it before completing installation. By installing the software, you are bound by the agreement. The EULA can also be found here.
  • The installer will overwrite any previously installed files relating to Draken in the Effects, Gauges, Sounds and Additional Scenery folders of FSX. If you have made any modifications to these files on your computer, please remember to make backups. To revert to a previous version, just run the installer for that version again.
  • The Flight Manual has not yet been updated to reflect the latest changes. However, it is still compulsory reading before asking me any questions of the “how to start the engine” kind.
  • The navaids in the included scenery (Barbro) are not always at their precise locations, although they are perfectly usable for navigation. They will be corrected in the final release.
  • A brief list of the changes made between 4.0 and 4.1b1 can be found in a previous post. There have been additional changes since then, and I will try to update the change list as soon as possible.
  • Feedback should preferably be sent to me using the contact form but if you already have the address you can also just email me the usual way.

Download link:    [wpdm_file id=2]