Viggen HOJD CISI switch issue

[stickz]

Question for those experts with the viggen.

 

Been plagued for ages wondering why the HUD altitude selector switch HOJD CISI seemed to occasionally physically lock in the LD (barometric) position. Tonight I finally found out when it occurs.

When in NAV master mode and RHM (radar height) selected, when my altitude hits 2.5km (climbing) the switch physically switches to the LD position. Any attempt to switch back does not work (switching noise occurs but switch locks back to LD). I know the radar height only works to 600m but it seems strange that the switch mechanically moves (although not impossible). Even stranger that it occurs at that height. It also seems illogical that flying over high terrain it does not then indicate ground rising to within 600m below you. When I drop back below 2.5km it is again switchable.

Also in LANDING/NAV mode it also locks into LD @500m.

Is this normal occurence?

 

Can find no mention in bugs, anyone else seen this - or is it some fault on my installation (or my searching ability)?

[tykbry]

Have noticed the same problem in LANDING/NAV

[RagnarDa]

Yes there is a little electro magnet that puts the switch in LD position when above a certain altitude and when at final. Don't think you could override it.

[stickz]

thanks for answer Ragna. Been driving me nuts trying to discover when it occurs.

I take it then that if above the trip height (2.4km it seems) and the ground rises above you, the viggen jockey is totally dependent on either terrain avoidance mode of the radar, VFR or pre flight planning for a warning.

Did they hire a dutch computer programmer to be involved in writing the mission computer code?

[renhanxue]

thanks for answer Ragna. Been driving me nuts trying to discover when it occurs.

I take it then that if above the trip height (2.4km it seems) and the ground rises above you, the viggen jockey is totally dependent on either terrain avoidance mode of the radar, VFR or pre flight planning for a warning.

Did they hire a dutch computer programmer to be involved in writing the mission computer code?

Nah, the design is completely bulletproof, since the highest mountain in Sweden (Kebnekaise) tops out at just under 2100 meters. Saab left plenty of margin of error, don't worry. :V

 

Seriously though, the reality is that the Viggen was very tightly coupled to its intended operational niche and area. This was most definitely not an expeditionary aircraft. In reality, you would not be able to use the navigational computer at all in most of the areas on the maps currently available or announced for DCS (the exceptions being the western half of Caucasus and the small part of Normandy that lies east of Greenwich). The reason for this is that on the real nav computer, you can enter the longitude and latitude in any order, and it'll autodetect which is which. It can do this because it comes programmed with the restriction that longitude must be greater than 0° but smaller than 40°, while latitude must be greater than 40° but smaller than 90°. If you're east of Sochi-Adler, west of Greenwhich or south of Madrid, you better have brought a paper map and your dead reckoning A-game, because the computer is completely useless to you.

 

Not that you would have been entering latitude/longitude manually all that often in reality though, the computer came preprogrammed with plenty of common Swedish landmarks and airfields accessed via the REF codes. They're input via the same entry mode on the data panel as the lat/lon coordinates (REF/LOLA, remember?) so that's why the seemingly pointless latitude restriction of 90° is there - the computer knows you're inputting a REF code rather than a coordinate if the first digit is a 9. On the JA 37 I think they reduced the max latitude to 85° to make room for more preprogrammed points, though.

Edited October 25, 2018 by renhanxue

[stickz]

Thanks for the extra insight renhanxue. I knew the limitations imposed for the locations and that in reality nevada and persian gulf would be out of zone. Just not aware that it included the vertical also. Unlike the lat/long, it just seems somewhat of an unecessary limit. Needing a special switch for this purpose plus code. And I cannot really think of any logical reason for it, even if you are not reasonably expecting to see higher terrain (its still 800m higher than uk has).

 

Nice to know its not bug, and that I have found out why and when.

Its lovely to fly and fight in (apart from those blooming mavs).

 

Its image caught my imagination way back in the early 70s (those then novel canards) even when working on lightnings blasting your senses daily (just to show my age).

Only a tornado could shift it from number 1.