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Stealth: A retro-style F117A simulator


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Hi there!

I've started work on a little side project and figured I'd share some progress updates here. It's a simulator for the F117A in the style of the old Microprose DOS game:



I always had a soft spot for those graphics as well as the stealth gameplay in that title. The different radar types and associated tactics required weren't particularly realistic, but they were fun and engaging. With that in mind I started mapping out my goals: A large procedural terrain, flat vector graphics, low poly models, not too much emphasis on accurate realism BUT no simplistic arcade game either. I have to remain realistic as to how much time I can put into this and how difficult some of the tasks will be.

I started with the terrain engine, worked on the scale of things as well as the overall visuals:



I posted this on simhq and got some nice positive feedback, so I started work on this in earnest. Here's some shots of sea vessels with mesh-based lights:




Here's a video of takeoff and flight along with the first version of the SAM radar simulation, RWR sound system, and guided missiles:


And here's the latest video showing a ground based SAM vehicle with turret rotation:



I'm going to go for a very approachable flight sim here: HOTAS works fine, but keyboard+mouse input is also very much usable. Heck you can even fly JUST with the keyboard. Avoinics won't be 100% accurate, I am going to take a lot of liberties in the interest of gameplay. I do like the idea of having an optional realism setting that forces realistic loadouts and other restrictions, but the default mode will include a (very limited) AA loadout. 

I have experience with implementing VR support so that is not out of the question, but I'm not adding that until lateron. I also would love to have some cooperative (or even versus) multiplayer support down the road. Again I have experience with that (I implemented my own lobby system and all that) but I'm not going to focus on that for now. I know what to look for to avoid making multiplayer impossible to add though.

I've got one chap who offered to make a cockpit model for me, but I'm very much looking for more help. So if anyone's interested, please shoot me a message!

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A little update: 

I've been testing out doing FLIR in the MFD. Works fine, though I haven't been able to do a working thermal highlight shader yet. But what I do have is proper FOV zooming on locked targets, could make that controllable of course for a more realistic avionics suite.



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20 minutes ago, mikew said:

Looking good! You've captured the F117A atmosphere nicely.
If that's a 'little side project'. I assume you're a professional Unity developer.

Thanks! No, I write software for air traffic control and air traffic management. And no, it's a lot less exciting than you might think ;)


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Finally got the FLIR to render vehicles properly! That was a lot less straightforward than anticipated and sadly there's a lot of bad advice on stackoverflow and the official forums. Stuff like: "Just duplicate the meshes and hide one of them for one camera each". 

Next up: Manual slewing, zoom control, and working on MFD symbology



Started work on the MFD UI as well:



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Yeah and it turns out the first one is getting aliased to death in the cockpit. So the second one it is! 

I do have a problem now however: The gameplay side of things asks for an emissions meter and I don't have a good spot in the "real" F117A cockpit to put it. In the old game it looked like this:


Left are bars that depict the incoming radar energy. On the right, the red bar signifies the threshold of detection. Rolling the aircraft, opening the bay doors etc. makes that bar grow. If the incoming radar bars overlap with the right bar, the radar can detect you.

I was thinking about integrating this with the MFD, but the more I look at how much this would destroy the authentic look of this iconic UI, the less I want to do that. And integrating it into the RWR is also difficult. But perhaps a little bargraph thingy below the RWR?

EDIT: Here's the current MFD in action:


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Since today the F117A can shoot back! I'm going for a similar method as in the Microprose game: In realism mode you are restricted to two hardpoints and a selection of GBUs, unguided munitions, and even the nuclear payload that was available. In casual mode you also get access to Hellfires and a LOAL variant of the AGM-65E, as well as two extra AIM-9 hardpoints. Right now only the laser guided missiles are supported, though GBUs are next on the agenda. It'll be quite some time later when I start to think about unguided payloads, since the UI calculations for those is going to be a major effort.

Speaking of UI calculations, I've added an attitude indicator. Well the first version thereof, rather. Turns out it's suprisingly difficult to implement that in Unity, both due to the way the rotations are handled, and because the way the UI renders things. I've got things reasonably well working but it's still technically wrong, so certain orientations don't display correctly. I need to figure this out before I can think about working on the HUD. 

No damage calculations on targets yet.

Oh and the plane will get RWR. We can talk about an option to disable this for realism nuts, but it's my game and I want this in for gameplay reasons :)


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Today I made targets actually destructible, added proximity fuzes to missiles, and compiled most of the literature I was able to get into a set of MFD pages:


Group 1 (top menu)

ATT: Attitude indicator, general flight information (speed, altiude, autopilot status, etc)
STAT: Status display, stealth and damage status overlaid on airframe outline
SMS: Stores Management System, fuselage outline with payload/pylon status and weapon selection
TEST: Test display

Group 2: (bottom menu)

HSD: Horizontal Situation Display with tactical map
MMD: Moving Map Display
FPL: Flight Plan / Waypoint List
TGT: Target information / reference image, to help the pilot to pick the right target to attack
WPN: Weapon camera view


I've begun work on the STAT page but it's really just a static page right now. I've also reworked the FLIR cursor because as it turns out some of the commercial F117 flight sim addons out there use incorrect symbology.

The TGT page will be inspired by the experimental IRRCA avionics upgrade which added the capability for the pilot to receive updated threat information as well as revised mission plans and entire new target information including reference images. Which works well for a game because I really don't want to simulate you flipping through a booklet of deadtree-based imagery to find your target ;)


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Looks like a lot of work.  I'm not a jet sim fan, but I hope it works out for you and those who are.

Back in a former life I was an air traffic controller.  Went from flat radar displays, pushing plastic target markers (shrimp boats) to upright digital displays (which could be dropped horizontal when the computer failed, which happened often in the early days.  That career came to an end in the now long-forgotten PATCO strike.  I went on to other things, including a long stint at writing fictional tales on Combatsim.

Good luck.

Old Guy

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I vaguely remember Reagan firing the ATCs, although at the time we had a similar purge of any union controlled industry or organization as part of the 'Chicago School' monetarist policies that were in vogue at the time. Must have sucked to be personally affected. :(

I'm looking forward this F117 project being finished. I'm assuming it will fit on the 3 floppy disks of the original? :)

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I did a compile recently and it came out to 50 megabytes. I think we can get that down a bit once I get the low poly models and can get rid of some of the rather high res placeholder stuff.

Oh and I've developed one of the first real operational electronic flight strip system (went from resistive panels to WACOM Cintiq even) so... I might have a slightly different perspective on air traffic controller strikes. On the first deployed system the controllers actually sabotaged the EFS so they could keep working with their paper strips. Then again that was on a site where the tower controllers and the approach guys were locked in an actual court battle against each other. Any new ATM-related system being designed is scrutinized for whether or not it endangers controller jobs. And I guess that's the opposite extreme.

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Today I started work on the RCS/RWR system (yes I know, the original plane didn't have that, but it's needed for gameplay reasons and I can always disable things for added realism)

It works similar to the old DOS game: You have bars on the left that show the incoming radar energy, and a bar on the right (not implemented yet) shows your radar signature. If the two bars overlap, your return energy is strong enough to be detected by the enemy radar. As for rules, I've already implemented some basic functions like your signal is lowered by flying below 1000 feet, attenuates slightly with altitude, and your distance also plays a role in the equation. What's coming next is the airplane attitude and dependence on radar type, so you have to play the radar type / flight path game to be able to evade detection.



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29 minutes ago, Toumal said:

Today I started work on the RCS/RWR system (yes I know, the original plane didn't have that

I didn't believe that, but after 5 seconds of searching, it seems you're right. :)
Some interesting comments here:
....ok, it's off the internet, but some of it could be true. :)

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Yeah it seems like this aircraft was really limited in its avionics and sensors.

Fun fact: I found out that my "automatic targeting" was actually very close to how things worked back then: The system would require you to lase a landmark on your way to the target, take that as a reference, and then the FLIR crosshairs would be dropped automatically on the planned target. Manual adjustments were possible, sure, but in principle the idea was that the system would find the approximate position of the target for you, and let you do the fine adjustments.

I have not implemented any kind of mission planning or mission targets yet so I will have to figure out how to best represent this in a way that's workable in a game.

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At least it gave the pilot something to do in a mission otherwise pre-planned in minute detail...
...and that's a hard thing to handle in game design. I doubt any part of a real F117 mission was boring when flying the real aircraft, but it's not quite the same when sitting at a PC at home.

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Well unlike in the real aircraft, in this game you know when a radar illuminates you. So there's plenty more to do in the game than in a real F117 en-route.

There was an experimental upgrade that allowed the aircraft to receive updated threat information and the computer would display an alternate route that fit the parameters, and the pilot was then to either accept or disregard that revised plan. That system was never used in combat but it goes to show that it's not completely outlandishly unrealistic for an F117 game to have a tactical map with up to date SAM positions, or a RWR for that matter.

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