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Draken 4.1 beta 2

41_cockpit
The second beta version is now finally available on the Downloads page. :)

This is a preview version of the full version 4.1 which will be released about a month from now. The beta installer includes only one livery and, as in previous betas, an ugly “banner” is floating above the exterior model. Apart from that it is more or less what you will see in the final release.

The changes made between this and the previous beta were numerous and radical, so much that I considered incrementing the version number to 4.2. The FDE (flight model) is completely new, and many of the functions have been rewritten from scratch. But as 4.1 is still unreleased I decided not to “skip a generation” – so 4.1b2 it is.

I will post a full list of changes as soon as possible. The Flight Manual has been updated and covers all the new features and visble changes, so you can always start there. But many of the changes are “under the hood”, so you will only experience them as better performance and functionality.

The beta naturally comes with a few bugs and “cosmetic” issues that I am still working on. If you have any comments, questions or suggestions regarding this release, please use the contact form.

Cheers /Tom

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Options panel

Couldn’t resist another teaser:

Just added a panel to make it easier to enable/disable some resource-heavy features and debugging tools. The options panel will be shown automatically the first time you load the aircraft. After that it can be accessed from the Views menu.

options

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Turbulent days

The new stick and throttle are in place on my desk, and I am finally back on track – although with some turbulence (read on).

warthog

While fine-tuning the FDE this week I experienced a new problem: when flying in altitude or attitude hold mode, the aircraft would suddenly become unstable and then bank hard to either the left or right. To regain control I had to turn off the autopilot. My first thought was that this was related to a conflict between the wing leveler in the FSX autopilot and the custom autopilot functions in Draken, but I soon found out that the phenomenon also appeared in fully manual flight, i.e. with both the FSX autopilot as well as the custom functions completely disabled.

After some digging on the Internet it dawned on me that it was probably a matter of the new FDE in Draken overreacting to the rather rough “turbulence” simulation in FSX. Stock aircraft seem not to be affected, but high-performance addons (such as Draken) can be much more sensitive. The problem is not autopilot-related, but with wing leveler enabled the effect will be more prominent as the plane may be in a hard roll before you have time to react and override the autopilot.

The solution was to simply disable turbulence completely in FSX and use the weather function in FSUIPC instead, which is a lot better. I sincerely recommend this.

Today and tomorrow working on model optimization, trying to reduce polys and texture load as much as I am able. Also adding a new “options” panel for enabling/disabling some visual elements, sounds and fx. Then on to writing documentation for the latest additions and changes, and finally compiling the installer package for 4.1b2.

Stay tuned /Tom

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Stick around

My old Thrustmaster HOTAS Cougar gave up a few weeks ago, which means that I have not been able to finalize the FDE as I could not afford a new controller. The Cougar has seen some repair work and modding over the years and has generally been a good companion, but now it was spitting pieces of aluminum and the pots were all worn out. Today I finally bit the bullet and ordered a Thrustmaster HOTAS Warthog. Not that I can afford it (I can’t), but I’m not going back to cheap plastic sticks.

Maybe as a result of being temporarily stick-less, I decided to add the control stick to the VC. Not the easiest thing to model, but I believe I got pretty close (see screenshots). At the moment the stick contains way too many polys (in the thousands), but I will try to simplify it before release. The trigger cover is animated, the buttons and switches are not. The stick can be hidden if you (like me) think that it is distracting and obscures the instrument panel. But you asked for the stick, and you got it. ;)

stick_work

Once the Warthog is on my desk I will tie things up and release 4.1.

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About the delay

My apologies for not posting for a while but I have had a lot on my plate lately, such as putting my house on the market while looking for a new one. So the Draken project as well as the blog has been on the back burner for a few weeks. I hope you understand.

Actually, the main reason that this project has been moving at a snail’s pace for the last year or two is that I have been restricted for contractual reasons as to how much time and effort I can devote to it. As of this week, I do not have these limitations anymore and can actually work full time on the Draken project for a few months. :) So hopefully there will be some progress and eventually something you can download.

I am very much in love with the latest version of Draken and impatient to share it, but I really need to kill a few remaining bugs first. So please be patient and you will be rewarded…

And while we’re at it, thank you all for your encouraging comments and emails. I am truly humbled by the constant support I recieve in spite of my failure to meet my somewhat overly optimistic deadlines. Thank you for being patient.

/Tom

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New autopilot

The autopilot in the current version (4.0) was originally put together for the FS9 version and then adapted for FSX. It was built on top of the MSFS autopilot, but most of its functions were custom made with local variables. It has been known to be more than a little “quirky”, did not respond to key commands, and I have never been happy with it.

I have spent the last week building a new autopilot from scratch, using as much of the stock FSX autopilot as possible and adding only a minimum of local functions. The new autopilot is still close to the real thing, but it has better performance, is less buggy, and can be controlled completely through FSX key commands.

The aircraft can now be flown comfortably on autopilot up to at least 13000 meters, where it stays at about Mach 0.8 in altitude hold mode. No sudden disconnects, no freezes. I am quite happy. ;)

Getting closer to something I can release as beta 2.

Stay tuned /Tom

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Solved: Variable wet thrust

Finally managed to figure out how to allow manual activation of the afterburner within a certain throttle range, but still prevent it from being automatically activated. :)

The afterburner function in FSX was designed to be activated at a certain throttle setting, which is not how it works in Draken. You should be able to set full throttle without afterburner, then activate it with a key command. To cut off the afterburner you throttle back below ca. 95%. You should be able to regulate wet thrust slightly by moving the throttle within the 95–100 percent range on afterburner.

The afterburner_throttle_threshold value in Aircraft.cfg determines the throttle setting where afterburner is toggled in FSX. If you toggle the afterburner with a key command, the throttle will also be set to this value. Now, setting the threshold value to zero prevents throttle-induced activation, but it also means that the throttle will be cut when afterburner is deactivated. Setting the threshold value to >100% instead will apply full throttle whenever afterburner is toggled. Neither is what we want.

The solution was to set the threshold to zero, then add a gauge function which stores the throttle setting every update cycle, and returns the throttle to that value if the afterburner is toggled. It also adds its own cut-off function so you can regulate wet thrust within a set range. Voila!

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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.

/Tom

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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