New Project

The SUL37 project was recently expanded to also include a J35 simulator (SUL35). Though this is an older aircraft which means less systems for me to make programs for, it seems to require the same type of programs. One program for simulating the sight, though not really a HUD I think it was some sort of gyro stabilized reflector sight. One program for the radar and one for some sort of flight computer and simulation of all the systems. I don't really know much about what kind of system the J35 has, but I guess I will find out.

I will not start a new blog for this the SUL35 project, but rather write about it here instead. Now I need to do a lot of research to find out what I need to do. But it will not be necessary to do anything for a while yet. First the mechanical and electrical stuff have to fixed, and that is not my responsibility.

The cockpit is a former Swedish air force J 35J and is fairly complete, except for two gauges and the stick. But this is stuff that will be fixed in one way or another.

My thoughts about radar - part 1

When I got the opportunity to try the AJSH37 simulator at F7 airbase in Såtenäs, I never got to see the radar display in action. The reason for this, they said, was that it was still classified. I thought that was a little strange since this is an obsolete aircraft that was about to be scrapped and there isn't really anything from this system that is used in the new JAS39, except perhaps for shooting boundaries displayed in some weapon modes. When I tried the AJSH37 simulator at SAAB they also thought it was a bit strange but unfortunately their simulator did not have any simulation of the radar image. I got to see the symbology though. And we've been able to get a few glimpses of the radar image through different showcase movies from the air force, and there are a few scenes showing the radar in the film "Älskar älskar inte".

However, at F7 though I never got to see the radar display itself, I got to see the unit that produced the radar image. It was a locker as large as a couple of fridges. The whole simulator was housed in a room as large as tennis court. Inside the locker there were two large vertically placed silver coated glass plates with the topography of Sweden (and some areas around) etched into i. Basically you could say it was a silvery 3D map of the area of operation. The reason there were two plates is that Sweden is a very long country, and it was easier to handle this way. Just above the surface of this 3D map there was a moving unit with a light source, representing the radar of the aircraft, and a camera picking up the light from a "God's perspective". It might sound a bit strange, but it's actually really genius, considering this sim was built in the early 70's. If you think about it, it is almost the way a radar really works.


Take a flashlight and lay it on an uneven surface, like a gravel road, lightening along the surface. Then view the surface from above. You will notice that all bumps will produce small shadows behind them, all in the direction away from the light source. The parts of the surface receiving light are all visible from the the light source, the other parts are dark. So what you see from above is exactly the same as from the flashlight, only from a different perspective. The radar receiver in an airplane is located in the same place as the sender, "light source", not a few miles ahead and above the airplane. However radar also gives you depth information so it's a piece of cake to translate it into a "God's view".

This is a somewhat simplistic view of how a radar works, not considering refraction, jitter effect, polarization etc. But for the purpose of a Viggen simulator it's good enough. After my visit to F7 I started thinking about the possibility to make a similar radar simulation with 3D hardware, using OpenGL. I will discuss this in part 2.

Been busy

I've been very busy at work the last 6 months, so not much have been done on the programs. However I'm now unemployed (have a new work starting in September) which means I have a lot of time to spend on this project. Some progress have been made. It's now possible to give the flight computer data about runway directions on takeoff and landing waypoints and channels for the TILS landing system. For normal waypoints two angles can be defined to mark borders. This is then presented in the radar display (CI).

Further more I have implemented a drift in the navigation, which means that over time the navigation system will be slightly off course. And to counter this you can fix your position by known positions. Since I haven't implemented the radar simulation, radar fixes are not possible. So for the moment you can only fix your position optically.

The whole simulator has now been moved into the bus and has been on tour a few times already. You can find pictures of the move here. This is a part of the project I'm not really involved in since I live several hundred miles from where the simulator is located and can not work with it physically. However in the future I will write some about the hardware since it's imperative to know how that works to understand what I am doing. Now that I've moved the programming diary to this blog, I also hope updates will be more frequent.