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F-16CJ HUD types

Canvas is FlightGear's new fully scriptable 2D drawing system that will allow you to easily create new instruments, HUDs and even GUI dialogs and custom GUI widgets, without having to write C++ code and without having to rebuild FlightGear.

Re: F-16CJ HUD types

Postby HelldiverSquadron » Mon Apr 28, 2014 6:43 pm

OK. I know some about Nasal now, as I have been learning it from scratch, but this is quite daunting. I'm surprised FG hasn't gone further in making decent realistic HUDs. The current ones are great, yes, but for fighters and strike aircraft that worm and lead are essential.
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Re: F-16CJ HUD types

Postby hvengel » Mon Apr 28, 2014 9:41 pm

The lead computer code has only been available since shortly before the FG3.0 release so it is very new and is currently only used by one aircraft. There is a lot going on in it's algorithm as it is solving a constantly changing complex physics problem in real time. So until this code or something like it became available there was no way to do a computing gun sight in FG without implementing something similar which is non-trivial. Since it has only been available for a few months people are only just beginning to give its use in additional gun sights serious consideration. There a dozens of post WWII fighter aircraft in FG that should have lead computing gun sights but do not and I expect that we will see the lead computer used more widely in the future particularly if radar range finding is available.
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Re: F-16CJ HUD types

Postby HelldiverSquadron » Mon Apr 28, 2014 9:43 pm

OK, cool. The only one is the K14 in the P-51D by you, right?
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Re: F-16CJ HUD types

Postby hvengel » Mon Apr 28, 2014 9:56 pm

K-14A yes. The K14 is a different less capable computing gun sight that is really a USN MK-21 with USAAF markings.
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Re: F-16CJ HUD types

Postby HelldiverSquadron » Mon Apr 28, 2014 10:13 pm

Hilarious. I searched Google for the "USN MK-21" and it came up with a rifle. Haha OK thanks! I can't wait until it's really developed.
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Re: F-16CJ HUD types

Postby Johan G » Tue Apr 29, 2014 9:35 am

Unfortunately the mark numbers are used on many things. There is of course the sight and the rifle, but there are also binoculars, torpedoes etc.

My way around it is to do an image search, and perhaps refine the search or use another search string. Too bad sometimes already knowing what search string to use is half the answer. :roll: I guess persistence is key. ;)
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Re: F-16CJ HUD types

Postby Hooray » Tue Apr 29, 2014 1:50 pm

hvengel wrote in Mon Apr 28, 2014 9:41 pm:The lead computer code has only been available since shortly before the FG3.0 release so it is very new and is currently only used by one aircraft.


Sorry if this has already been answered (only skimming ATM), but maybe we should work out a way to come up with a simple tutorial/integration guide, given that you mentioned that it's been designed such that it should support being interfaced for different purposes ?
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Re: F-16CJ HUD types

Postby hvengel » Tue Apr 29, 2014 4:10 pm

Good point. There is already some documentation and at this point it is somewhat K-14A specific although it does cover the settings needed for the lead computer. I intended this to help others use the lead computer and the K-14A but I think it probably should be more extensive than it currently is and it needs to be divided into two documents - one that covers the lead computer only and one that adds information for the K-14A. Also something that is typical for developers is that we end up being so familiar with things that stuff we think is obvious is really not obvious to others so our documentation tends to have gaps that can be confusing.

One of the reasons that I offered to work with someone on integrating this into a new aircraft was that this would give me an opportunity to have someone new to the code work through the process so that I could see where the documentation (and perhaps functionality) gaps are (IE. where did they stumble) and fix those. Since it has been a few months it is probably a good idea to review the existing docs and fix any apparent issues before someone else tries to use it.

One other consideration is that this has only been used with a gun sight that has manual ranging so integrating it into something like an F-16 we will need to setup a radar ranging system. The lead computer or the radar system will need to be extended to interface the range info from the radar system to the lead computer. Probably not very difficult (likely less than a dozen lines of Nasal since all that is needed is to have the radar system push the range, in feet, to the designated target to the /controls/armament/gunsight/range property) but once this is in place other aircraft with radar ranging gun sights will be very simple to integrate although the reticle animation will still be a significant issue for some aircraft.

There are currently a total of 12 properties that are used to configure and interface to the lead computer. 8 of these are configuration properties that give the lead computer aircraft and gun sight specific info (gun offset - vertical and horizontal relative to the sight line in feet, elevation angle relative to 0 alpha in degrees, muzzle velocity - feet per second, ballistic coefficient, harmonization range - in feet, maximum azimuth and elevation of the gun sight in mils). 2 are run time input parameters - power on/off and range to target - in feet, 2 are output - elevation and azimuth in mils relative to the sight line. These last two drive the sight animation. I need to expose the time step and the damping factor configuration parameters to have this be fully generalized.

A mil is a 1 foot deflection at 1000 feet. The lead computer is capable of giving steady state (IE. constant G maneuvers) solutions that are accurate to less than 1.1 mils at a 2000 foot range (IE. with in 2.2 feet).
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Re: F-16CJ HUD types

Postby HelldiverSquadron » Tue Apr 29, 2014 4:32 pm

Thanks, Hooray. That's a point most certainly worth consideration. I know FG isn't geared towards combat, but even X-plane and some FSX fighters have HUDs that compute algorithms based on data gathered from the terrain and other aircraft/vehicles. Documentation would be nice. Is there a link to some for at least the ol' K14?
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Re: F-16CJ HUD types

Postby hvengel » Tue Apr 29, 2014 8:13 pm

If you have FG3.0 you have some docs for the K-14A and the lead computer in Aircraft/lead-computing-gunsights. Look in the README file and also at the Nasal and XML code in that directory and it's sub-directories. The animation code or the K-14A sight reticle is complex because of the manual ranging system the sight uses and is over 500 lines of code in total (Nasal and XML). With radar ranging the reticle will be simpler and much easier to animate.
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Re: F-16CJ HUD types

Postby HelldiverSquadron » Tue Apr 29, 2014 11:48 pm

Aye, that it will...
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Re: F-16CJ HUD types

Postby hvengel » Wed Apr 30, 2014 3:28 am

I just spent 2.5 hours updating the gun sight computer documentation. This has been pushed to git. I divided the documentation into a lead computer document and a K-14 document. These are README files in the root of the lead-computering-gunsights directory.
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Re: F-16CJ HUD types

Postby HelldiverSquadron » Wed Apr 30, 2014 12:43 pm

Hey, thanks. Where on GIT?
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Re: F-16CJ HUD types

Postby Johan G » Wed Apr 30, 2014 2:22 pm

You can find it in fgdata/Aircraft/Instruments-3d/computing-gun-sights. Hvengels last changes are in commit #f5cfc3a


Side note: One of my favourite aircraft, the Dassault Mirage F1, had in the early versions a HUD with a mirrored in compass scale, a horizon line and what I think would be an altimeter scale and what would seem like a more or less mechanical gun sight with a 6-diamond aiming reticle probably fed by some kind of ranging mode of the aircraft radar (the South African Mirage F1 HUD looked like this, Greek like this). Interestingly, there seemed to be no flight path marker and in the very earliest versions the aiming reticle was fixed when used air-to-ground.
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Re: F-16CJ HUD types

Postby hvengel » Wed Apr 30, 2014 3:15 pm

Interesting - these reticles look EXACTLY like the K-14A reticle. Could these sights still be using manual ranging in the early 1980's? On the K-14A/GGS-III class sights the six diamonds are controlled by the throttle handle and the pilots twists the throttle handle to change the size of the circle inclosed in the diamonds to tell the gun sight the range to the target (there is a second control to set the target wing span and the pilot matches the diamond circle to the wing span).

If these sights are using radar ranging then why do they have the manual ranging diamonds? Are these just a left over appendage from an earlier era? Or are these GGS-III/K-14A derivatives that have been retro fitted with radar ranging. If that is the case then the gun sights would have been mechanical (IE. driven by a gyroscope) and other than the ranging system would have been very much like a K-14A/.GGS-III with similar lag and damping issues.

I know that early in the transition from the manual ranging sights to full radar ranging that the earliest US radar ranging model was the K-18 which were basically K-14A derivative with a ranging input that was basically a servo that was driven by the radar system. But that was supplanted by more advance radar ranging systems very quickly. The K-18 was only used for a few years and mostly in older aircraft that were still in service (the P-82 for example) during the Koren war. By 1953 F-80s and F-86s had much more advance gun sights (the A1-C) and by the late 1960s accelerometers and inertial navigation systems along with digital computers had replaced gyroscopes in these systems.

Standard procedure for the GGS-III/K-14A class gun sights was to use the fixed reticle and the (also fixed) rocket ladder for ground attack depending on which weapon system was being used. So I am not surprised that these Mirage aircraft at one point had a fixed ground attack reticle.
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