Understanding gyroscopic systems

I think I have some new insight into but also questions about the MiG-21bis gyroscopic instruments.

Important switches for systems are:

S1. DA-200 COMB. INSTR.; SIG. OF VERT. GYRO OF FDS, AFCS, RDR circuit breaker ДА-200, СИГНАЛ. ГИРОД. КСИ, САУ, РЛС

 

S2. VERT. GYRO OF FDS, AFCS, RDR; GYRO HOR. SIG. ГИРОД. КСИ, САУ, РЛС, СИГНАЛ. АГД

 

S3. GYRO HOR. АГД

 

S4. FDS КСИ

Important lights are:

L1. CAGING OF VERT. GYRO OF FDS, AFCS, RDR АРРЕТИР. ГИРОД. КСИ, САУ, РЛС

L2. red warning light on the gyro horizon indicator АРРЕТИР

• DA-200 combine instrument
  
• Signal of vertical gyro of: FDS, AFCS, RDR
  

In essence it is two systems, the DA-200 instrument (combined vertical speed, turn rate, and inclinometer ball) of which only the turn rate indicator is gyroscopic as the vertical speed indicator is barometric and the inclinometer is an unpowered ball in a liquid-filled glass tube.

The second system is the signalling for the vertical gyro. This isn't the vertical itself, just the warning light (L1) signalling to show when the vertical gyro is not operating at speed and uncaged. When this switch is on and the vertical gyro is off the warning light shines red. When the vertical gyro is powered the light will stop shining when the vertical gyro has come up to speed and uncages which happens in several seconds after vertical gyro power is applied.

Switch S2 is similarly for two systems, the vertical gyro and signalling of the gyro horizon. The vertical gyro provides gyroscopic information for several systems including FDS (KSI), AFCS (SAU), and radar. Signalling for gyro horizon probably applies to the red AGD (KPP) cage button-light showing when the referenced gyroscope is currently caged.

S3 upward, label GYRO HOR. enables the AGD instrument to reference its primary gyroscopic information source. With the switch downward (other systems operating normally) the AGD instrument references a different gyroscopic source. The instrument should function nominally with the switch in either position. Exactly what are the two modes of operation I'm uncertain. The cage signal light seems to be caged when the particular source being currently used is caged.

S4, FDS which I think stands for "flight data system" aka KSI is the system I understand the least. I think it distributes attitude data to the various instruments. The right panel has a placard "Energize FDS only after vert. gyro of FDS, AFCS and RDR is switched on and uncaged" suggesting it depends on vertical gyro functioning properly.

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What is expected behavior from systems in various states? To this we look to manuals which describe checking and emergency procedures.

First, DA-200 is turned on with all other related switches off. The DA-200 includes signalling so vertical gyro warning light comes on. When vertical gyro is unpowered but signalling is on then warning light comes on, check.

But also the AGD warning light comes on too. Interesting. The vertical gyro switch controls AGD signalling and it's still off so we don't expect any AGD signalling. But the AGD light can show if the primary source (gyro horizon) is cage or if the secondary source (vertical gyro?) is caged. It's natural that the AGD is using the secondary source and because the DA-200 switch is on that means signalling for the backup AGD source is working. That's my conclusion. With DA-200 switch on we get secondary AGD signalling while the vertical gyro switch would enable primary AGD signalling. The same red light is connected to both systems.

Next the vertical gyro system is powered. The vertical gyro red lamp should go out within 15 seconds, not instantly. Those RPMs must take a moment to spin up. Presumably if the DA-200 switch had been off we would get no light indications for the vertical gyro (but it would function just the warning lights would stay dark).

What's not mentioned is what the AGD light does during this time. Presumably the light would go out coincident with the vertical gyro caged light but it doesn't say. The indication on the gauge itself (erecting, showing pitch, bank, etc.) who knows.

Next FDS (KSI) is turned on... in "1 to 1.5 minutes" after that the turn indicator (on DA-200) points when the dash panel is forcibly deflected. Now that's interesting that this is done after FDS is on. If the DA-200 would function with DA-200 system switch alone powered then why wait? This might suggest that DA-200 instrument doesn't read without the FDS enabled.

Again "1.5 to 2 minutes" after indicator warning light goes out (AGD) the KPP reads correct. Still sounds like gyroscopic alignment converges over quite some time and FDS may be required for KPP to indicate.

Now gyro horizon (AGD) switch is set up and the instrument has changed over to the "main vertical gyro." Later in section describing failure of FDI (KPP) it is mentioned to "change over to stand-by vertical gyro."

FDS which I think stands for "flight data system" aka KSI is the system I understand the least

KSI literally means "Course Indication System" and is responsible for creating and distribution of vertical situation and magnetic course signals. Whole KSI consist over 15 elements, here is the schematics:

Exactly what are the two modes of operation I'm uncertain

MiG-21 have two gyro units: main and auxiliary, pilot just switching between them in case of failure of main unit, no difference in KSI work. Those 1,5-2 minutes is needed for achieving appropriate gyro units speeds and synchronization with magnetic sensor and additional correctors. 2 minutes is in standart conditions ( what means in Soviet terminology: sea level and +15 deg temperature ), in cold conditions can be few minutes longer.

Excellent. I rely on you for such details.

I am curious when vertical gyros are functioning but KSI is off and AGD switch is downward (or upward) what is the KPP indication? I do not know which systems are functioning partially or totally without KSI.

At the beginning I have to explain some important issues, without which many things can be hard to understand. Soviets had different rules of device descriptions in they's cockpits, Western aircrafts had all described straight on panels, type of device, work mode etc, Soviets mixed everything, some descriptions were straight, some were devoted groups of devices, some were using code names like “product 02”. Additionaly some stuff had doubled names. So, most important thing:

1. KSI does not exist as a device, it's only a collective name for a set of devices used for navigation. Description of the "KSI" switch is misleading, it supplies voltage to several separate devices at the same time, the "AGD" switch only changes between the main and spare gyroscope and is not use for gyro power up. Typical KSI set contains: GA-2 main gyro, sychronization mechanism MS-1, magnetic sensor ID-2M, correction mechanism KM-3, control panel PU-3, course indicator IKL-2 ( type 75B have NPP indicator ), amplifiers U-12, U-18 ( two units ), forwarding unit BR-4, synchronization button 5K, diode unit BD-1, gyro “type 458”, voltage converters, etc. We have 3 KSI variants: “KSI” for early MiG-21, “KSI-2” for late variants ( including our from DCS ) and “KSI-3” for two-seaters, but in most documents all them are called shortly “KSI”, what can be misleading.

2. The aircraft that we have in the game (type 75B) .... don't have AGD-1 on board, which was replaced by KPP-MK, just from the previous variants part of cockpit descriptions remained. Generally KPP-MK ( and AGD-1 in previous variants ) is not part of KSI.

Aircraft have 3 gyro devices: two gyros “type 458” and one GA-2M. First “458” feeds only KPP-MK ( AGD-1 ), second “458” is a part of KSI and is used as vertical gyro unit for feeding SAU, RP-22, RSBN, APP-155 ( and as a emergency source of signal for KPP-MK ( AGD-1 )), GA-2M is used as horizontal gyro ( direction signal source ) for DA-200, SAU, RP-22, APP-155 etc.

GA-2M gyro unit.

"Type 458" gyro device.

So, switch “GIROD KSI, SAU, RLS, SIGNAL AGD” powers up two gyros in the same time - “458” for KPP-MK ( AGD-1 ) and “458” for KSI, switch “DA-200, SIGNAL. GIROD KSI, SAU, RLS” powers on GA-2M, switch “KSI” turns on all others devices but generally pilot turns on correction devices ( ID-2M and KM-3 ) by this switch .

I am curious when vertical gyros are functioning but KSI is off and AGD switch is downward (or upward) what is the KPP indication?

Actual vertical situation, both “458” works the same way, so no difference in indications.

I do not know which systems are functioning partially or totally without KSI.

Totally without “KSI” switch on is able work KPP-MK, partially DA-200 ( air pressure channel only, theoretically device should work normally but without correction turn value reading will be incorrect ).

This is roughly my thinking about KSI, a network for data.

KSI set:

GA-2 main gyro

MS-1 synchronization mechanism

ID-2M magnetic sensor

KM-3 correction mechanism

PU-3 control panel

course indicator IKL-2 ( type 75B have NPP indicator )

amplifiers U-12, U-18 ( two units ),

forwarding unit BR-4,

5K synchronization button

diode unit BD-1,

gyro “type 458”

voltage converters, etc.

DA-200 switch: Enable GA-2 gyro spin power

Vert Gyro switch: Enable Type 458 (KSI systems) and Type 458 (KPP) gyro spin power

AGD switch: Choose KPP data source between Type 458 (KPP) dedicated or Type 458 (KSI systems)

KSI switch: Correction mechanisms, magneto flux compass, mag sync, support equipment

I don't understand "signal" related to switch DA-200/Signal gyro vertical gyro (KSI) and switch Vertical gyro/Signal AGD. Is "signal" for red warning lights on dash and KPP cage button or is it "signal" for attitude values?

It sounds like Type 458 are pitch-bank gyro and GA-2 is yaw gyro (NPP/DA-200).

Without KSI compensation KPP/AGD would drift over time and need to be recaged?

DA-200 switch: Enable GA-2 gyro spin power

Vert Gyro switch: Enable Type 458 (KSI systems) and Type 458 (KPP) gyro spin power

AGD switch: Choose KPP data source between Type 458 (KPP) dedicated or Type 458 (KSI systems)

KSI switch: Correction mechanisms, magneto flux compass, mag sync, support equipment

Yep you right, except magneto flux compass, if you mean KI-13 this instrument is fully mechanical, if you mean course scale on NPP ( or IKL ) she is powered by GA-2.

I don't understand "signal" related to switch DA-200/Signal gyro vertical gyro (KSI) and switch Vertical gyro/Signal AGD. Is "signal" for red warning lights on dash and KPP cage button or is it "signal" for attitude values?

If I understand correctly documents "signal" is devoted "not ready" state, on KPP this means visible flags "K" and "T", for NPP there is red lamp on right from the radar's scope ( lower lamp, upper is for engine oil signalization ). No blinking SORC lamp in this case.

It sounds like Type 458 are pitch-bank gyro and GA-2 is yaw gyro (NPP/DA-200).

Yep.

Without KSI compensation KPP/AGD would drift over time and need to be recaged?

NPP/UKL for sure will drift , not sure for KPP, need check this ( because according my present knowledge KPP/AGD is a independent device from KSI ).

Sure, I just mean "source of magnetic compass info" whatever the exact device.

I thought K and T flaps are for pitch and bank needle (yellow) validity only for autopilot approach guidance. Is "AGD signal" including the red cage pushlight? But you answered the question, signal means error warning system.

KPP drift would depend I guess if 458 gyro(s) has correction mechanism included or relies on KSI system.

I thought K and T flaps are for pitch and bank needle (yellow) validity only for autopilot approach guidance. Is "AGD signal" including the red cage pushlight? But you answered the question, signal means error warning system.

Both instruments "KPP" and "NPP" have "K" and "T" blinkers/flags but for different purposes. NPP's "K&T" shows lack of external radio signals from PRMG, or RSBN's landing channels malfunction, KPP's "K&T" shows 458 gyro malfunction or signal lack when gyro not ready.

KPP drift would depend I guess if 458 gyro(s) has correction mechanism included or relies on KSI system.

Yep, you right KPP will drift. I've checked MiG-21UM avionics description, and KPP gyro needs correction from WK-53 mechanismus which is part of KSI. So without turned on KSI switch KPP although is able work separatelly will drift over time.

The reason I ask is PRMG uses the KPP flags relating to the landing guidance needles.

Runway Approach in Command Control Mode

80. When the CCI localizer channel failure warning flag closes its window, the tail of the relative bearing pointer coinciding with the final turn commencement index (the relative bearing pointer deflecting from the set course pointer by 10 to 12°), depress the CMD CTL button light, check for disappearance of the R(K) roll channel failure warning flag on the FDI and bring the aircraft in line with the runway, making the final turn at a bank of 30°.

...

Notes:

1. Should the glide path channel failure warning flag disappear from its window, the P(T) pitch channel failure warning flag appearing in view on the FDI), the horizontally-disposed command control pointer of the FDI will be commanding the pilot to maintain the altitude he had by the time of the malfunction. Then do not follow the directions of the horizontally-disposed command control pointer, but rather follow the recommended distance and altitude values of Table11 for checking the descent regime.

...

Runway Approach in Automatic Control Mode

82. ...before intercepting the runway approach course, depress the COMD CTL button light and check for disappearance of the R(K) roll channel failure warning flag on the FDI. Set the command control pointers within the limits of the simulated aircraft position (central) circle, then depress the AUTO CTL button light.

...Before intercepting the glide path transmitter beam (at a distance of 14 and 15 km to the runway threshold), make sure that the P(T) pitch channel failure warning flag has disappeared from view on the FDI.

...

The FDI can indicate the following (Fig. 18):

(d) command control signal in the roll and pitch channel (when the RSBN equipment is functioniong in the LANDING mode, the FDI pitch (P) and roll ® channel failure warning flags disappear from view);

(e) engagement and serviceability of the command control and automatic control modes during landing approach, as monitored by the pitch (P) and roll ® channel failure warning flags disappearing from view.

Maybe T/K flags show other warnings in other modes but for PRMG approach they are showing when command pointers go invalid. I don't know if they are shown or hidden normally in NAVIG or LETDOWN modes.

You right, I've made mistake, I was writing KPP/AGD all the time and finally I mixed they functionality. Lately I'm flying a lot Mi-8 and there AGD have flag :music_whistling:, KPP have of course gyro malfunction lamp ( inside cage button ) and those flags are for RSBN.