Need help understanding The HSI

[jojo]

Great info in this thread :thumbup:

I'll throw my 2 cents :D

 

 

ILS glide slope is fixed and dependent on the runway equipment, so I doubt you can enter it manually. Also not needed to display a runway.

 

You need to enter glide slope in INS to display:

- - shown in Hud to visualize it.

 

So - -O- - is on glide slope, or _ -O- _ you're above GS.

 

GS can change depending on airfields.

[PiedDroit]

You need to enter glide slope in INS to display:

- - shown in Hud to visualize it.

 

So - -O- - is on glide slope, or _ -O- _ you're above GS.

 

GS can change depending on airfields.

Ah ok, it's not the same as the ILS one.

[fjacobsen]

Hi

 

I guess you're puzzled by a translation issue.

 

What we call, here in this topic, "the INS" is in fact the PCN (Poste de Commande Navigation - Nav control panel) / UNI (Unité de Navigation Inertielle / Inertial Navigation Unit).

 

Of course it manages the INS, but not only. If the inertial part of the system fails, the PCN still can be used for other features.

If you set the PCN to CP/PD you may vizualize/enter the "CP" (Cap Piste, Runway Heading) and "PD" (Pente Désirée / Desired Glideslope).

 

If the PCN (UNI) totally fails, you have no more Nav on the IDN (HSI).

 

 

Cm = Cap magnétique / magnetic heading

Cv = Cap vrai / true heading.

 

++

Az'

 

If the PCN both can control the INS and the VOR/LOC/GS stuff (Course, glideslope settings) then I´m Ok with that.

 

INS and DME updates are very common (or was :)).

 

Even INS' with ringlasergyros drift over time.

 

DME updates uses known DME (VOR/DME) to adjust for INS drift.

 

You - or on more complex systems, tune a known DME station.

For the known DME station You know latitude, longitude and altitude of the station. Now knowing Your own altitude (from the altitude encoder) and measuring the DME distance. You do this again for another DME station.

 

Where the two DME distances cross - thats You "exact" location. Doing this will actually give You two positions, but the one closest to You driftet INS position is the one most probable position "exact".

 

This method has been used with INS systems from the very early days and are still done in modern systmes, like FMC's used in airliners.

Isee no reason why this wouldn´t be possible in military jets, especially in fighters where hard maneuvres will add up errors much quicker.

 

I do not expect this function to be featured with the DCS Mirage, but it would be cool if it was.

 

FinnJ

[Azrayen]

I'm not sure the DME update was featured on the UNI-52.

I have in mind the vertical (overfly) and oblique (using radar) updates modes, but not DME.

 

I not, probably it was decided that in wartime relying on DME (over possible hostile terrain) wouldn't be such a good idea?

[fjacobsen]

I'm not sure the DME update was featured on the UNI-52.

I have in mind the vertical (overfly) and oblique (using radar) updates modes, but not DME.

 

I not, probably it was decided that in wartime relying on DME (over possible hostile terrain) wouldn't be such a good idea?

 

Hmm...

 

But relying solely on the INS position for an instrument approach wouldn't be very healthy either when the INS has driftet since last "Overfly" of "Radar" update has been done. Such update types could easily give You an offset of 10-30 meters, not an offset You would like from the runway using the INS for approach.

 

Even the INS units used on airliners from the 1960th had the feature to do DME updates.

 

Remember that DME's often are part of ILS/Localiser and VOR/TACAN systems.

 

And offcourse You would not rely on enemy placed DME's, but I guess You would fly both out and inbound over quite some amount of friendly territory.

 

FinnJ

[jojo]

ILS is THE exception, where of course radio signals takes over other inserted data.

 

But during NAV you update on waypoint.

[simo1000rr]

ILS is THE exception, where of course radio signals takes over other inserted data.

 

But during NAV you update on waypoint.

 

how do you switch between one waypoint to the next waypoint in NAV mode ?

[Azrayen]

But relying solely on the INS position for an instrument approach wouldn't be very healthy either

Agreed, and never told such was the case ;)

[Home Fries]

Such update types could easily give You an offset of 10-30 meters, not an offset You would like from the runway using the INS for approach.

Generally speaking (and published GPS approaches notwithstanding), you care more about absolute position (which is what the INS gives you) when you are enroute, but you care more about relative position (e.g. range/bearing to airfield) the closer you get to your destination (note: this can also apply to a target, but we'll stick with airfields for now).

 

What a VOR/TACAN/ILS gives you is relative positioning indication (as well as glideslope in the ILS). If my INS is 1-2 miles off in the terminal phase of flight, I don't really care because I'm "flying needles" at that point (VOR/TACAN to ILS final). If I'm 8 miles out on approach, my Lat/Long doesn't tell me as much as a TACAN reading of 090/8, which tells me I'm due (magnetic) east of the TACAN (i.e airfield) for 8 miles. If I know my runway heading, I can easily figure out how to get to my Final Approach Fix without the INS.

Edited January 4, 2016 by Home Fries

[IvanK]

So have I got this right ILS Localiser course is always entered via the PCN irrespective of the type of ILS approach being flown INS assisted for the synthetic runway or straight ILS without synthetic runway ?

[CHSubZero]

In the A-10C I use TACAN to find the airport and set the course on the HSI to the runway direction. In the Mirage 2000C I know how to set up and read the TACAN but how can I set up a specific course?

 

Batumi as example:

TACAN = X16

Course = 120°

[jojo]

In the A-10C I use TACAN to find the airport and set the course on the HSI to the runway direction. In the Mirage 2000C I know how to set up and read the TACAN but how can I set up a specific course?

 

Batumi as example:

TACAN = X16

Course = 120°

 

You can't do it like that on TACAN.

Instead you can define an offset point from TACAN in azimuth/ distance.

You can also define a course on INS waypoint with PCN, but it isn't ready yet...