RSBN-6C: KPP/FDI needles

[Redglyph]

DCS 2.5.3.23954

 

I'm comparing the behaviour of the KPP horizontal and vertical needles to the user manual (Mig 21Bis Pilot's Flight Operating Instructions, available on Avialogs among others). The test was made on Nevada terrain near NTTR.

 

The needles I'm reporting are (4) and (8) on the KPP/FDI diagram (also called ADI in the DCS manual).

 

There are 3 modes:

• - navigation "NAVIG" (RSBN channel)
  
• - landing "LDG" (PRMG channel)
  
• - "LETDOWN" or most probably, "descent" (RSBN), this is called "PROCEED" in the DCS English cockpit and manual, which I find strange, perhaps a translation issue? (Пробив, is that from Пробивание? I don't speak Russian so I'm at a loss)
  

 

From the original manual, see FDI explanations in attachment:

• (b) means that in NAVIG (RSBN channel), needle 8 = track position relative to aircraft position
  
• © means that in LETDOWN (RSBN ch) or LDG (PRMG ch), needles 4 and 8 = flight path relative to aircraft position
  

 

What I see in DCS:

• NAVIG: 8 = aircraft position relative to track (if aircraft right of track, needle is right, opposite of what is expected), 4 = ? seems to be stuck high instead of neutral
  
• LDG: 8 = localizer position relative to aircraft (OK), 4 = localizer glide path relative to aircraft, except when the aircraft is too high but there is no pitch channel failure flag (I think it's the left 'T' flag in DCS, though the figure pg 54 has no legend for those flags), (so, mostly OK when channel received). It also seems like the glide path needle 4 is too high, especially when approaching the runway.
  
• LETDOWN (or "proceed" in DCS): 8 = aircraft relative to track, 4 = ? (not clear)
  

 

So it seems that in DCS:

• "proceed" should be renamed to something more clear
  
• LETDOWN mode should work differently, for now it's the same as NAVIG for 8 and unknown for 4, it should be the flight path relative to the aircraft for 8 and probably neutral for 4
  
• NAVIG mode should have track relative to aircraft on 8 (and not the opposite), unless it's badly expressed in the original manual (or unless I misinterpreted it)
  
• LDG mode, 4 should be checked, is it too high?
  
• shouldn't the pitch flag be set when the aircraft is too high in LDG mode and the 4 needle is stuck at the high position (and should the needle be stuck there?)
  
• shouldn't the 4 needle in neutral when not used (NAVIG mode)?
  

 

I tried to compare to the L-39C, but couldn't find any documentation on how to select the PRMG or RSBN channels on the Nevada map, I assume they haven't been implemented at all from the posts I've seen, and that navigation is not available on that map.

 

I didn't test the NPP (or CCI), it looks like the needles 5 are behaving like 4 and 8 of the KPP, which is not what is described in the Pilot's Flight Operating Instructions manual.

[Frederf]

NAVIG: 8 = aircraft position relative to track (if aircraft right of track, needle is right, opposite of what is expected), 4 = ? seems to be stuck high instead of neutral

Indicator "8" in NAVIG is related to orientation of course and bearing needle. There are essentially four cases by combination of flying away or toward station, course-bearing parallel or antiparallel. As of current version the "8" indicator is showing relative direction of track correctly in three of four cases. When heading away from station and the selected course is either parallel or antiparallel with bearing the indicator shows which direction track is relative to your current view.

 

When approaching station and course and bearing needle are (near) parallel then it will also read normally. However in the case of approaching station and needles are approximately anti-parallel then indication is reversed. I believe correct behavior is to show relative direction to track or anti-track direction (whichever is closest in angle) either closing or growing range. Until this is changed you will have to ensure parallel needle alignment (bubble matching short hollow arrow end) for normal "8" steering directions.

 

LDG: 8 = localizer position relative to aircraft (OK), 4 = localizer glide path relative to aircraft,

Indicator "4" is driven to limit of range in NAVIG because there is no height guidance in this mode. You would think it would be driven off the scale so as to be hidden but I am told that it remains slightly in view.

 

except when the aircraft is too high but there is no pitch channel failure flag (I think it's the left 'T' flag in DCS, though the figure pg 54 has no legend for those flags), (so, mostly OK when channel received).

T & K flags should only hide on valid pitch (T) and bank (K) steering coming from automatic or command guidance mode enabled (green buttons lower left area of cockpit). The flags will display in landing mode if the command or automatic steering is not used (showing that the pitch and bank steering is not to be used). T and K are Russian labels translated to English as P and R.

 

It also seems like the glide path needle 4 is too high, especially when approaching the runway.

PRMG glide slope signal should be 2°40' for normal operations but in reality this can be set for each installation at an airbase. In DCS it is in excess of 5° (actually it is almost exactly double 2°40').

 

LETDOWN (or "proceed" in DCS): 8 = aircraft relative to track, 4 = ? (not clear)

Letdown "4" will show vertical guidance. It is about 10km height at ~120km away and 600m within ~22km and a slope between them. It works well enough. It should work like NAVIG but with vertical guidance.

shouldn't the 4 needle in neutral when not used (NAVIG mode)?

There is a severe danger to tell pilot "altitude is fine" when it is off. So "4" should either be hidden or pegged to command a climb when data is not valid.

 

I didn't test the NPP (or CCI), it looks like the needles 5 are behaving

"5" on CCI should show PRMG position on PRMG signals only, the warning flags the same.

 

Also FDI "9" and "12" are only moved when using command or automatic landing program. Otherwise they are de-energized to form a cross in the center of the instrument.