Su-27, Su-33, MiG-29 HUD and HDD operational modes

Basic HUD symbols

Regardless of the aircraft type, some HUD symbology is unchanged between aircraft.  As an example, we will take a look at the HUD indicators from the MiG-29 МРШ (ROUTE) mode.

2-18: MiG-29 basic symbols

·         In the center of the HUD there is an aircraft datum, indicating aircraft pitch and roll.

·         The current heading is positioned in the upper portion of the HUD. It shows the aircraft’s current heading. (example: 11 corresponds to the value of 110 degrees).

·         Indicated aircraft speed (IAS) is shown to the left of the scale. Above the current IAS, the required airspeed is indicated. It depends on the flight mode, and in the case of route flight mode, it shows the required aircraft speed.

·         Under the numerical speed indicators is a triangular index that shows horizontal acceleration. To the right – acceleration, to the left – deceleration.

·        

To the right of the heading scale, the current altitude is indicated. For altitude less than 1,500 meters above ground level, the radio altitude is indicated to within 1 m. At an altitude over 1,500 meters barometric, the height is shown to within 10 meters. Above the scale the required altitude is shown. This will depend on the flight mode and in the case of route flight mode, it shows the preplanned route altitude.

·         The navigation mark (large ring) shows the flight direction to follow the preplanned route and altitude to the next waypoint. When it is in the center of the datum, you are on-route.

·         The pitch ladder, situated in the right of the HUD, displays current pitch angle.

·         In the lower left corner, the current flight mode is shown.

·         In the lower center part of the HUD, the distance to the selected waypoint is indicated in Km.

When in navigation modes, information on the route (route direction, waypoints, and airfields) is indicated on the HDD.

2-19: HDD types in navigation modes

·         Waypoints are indicated by circular marks.

·         Waypoint number is indicated next to the waypoint.

·         Initial point for glide slope interception is indicated by a diamond.

·         Runways are indicated by a solid rectangle.

·         Current waypoint is framed by a square.

·         All waypoints are connected by a route line.

In navigation mode, navigation information is displayed on the HUD and HDD. There are three navigation sub-modes: МРШ (ROUTE), ВЗВ (RETURN), and ПОС (LANDING). Switching between sub-modes is performed by successive presses of the [1] key.

In ROUTE mode, the route line passes through all planned waypoints.  To switch between waypoints you can use the [~] key. The route line will connect your current position with the selected waypoint.

In RETURN mode, the route line will lead to the glide slope intercept point.

In LANDING mode, the route line will lead to the desired air base. Airfield selection can be chosen by cycling the [~] key.

Navigation mode

·         When in the ROUTE sub-mode, a circular sighting mark is displayed on HUD; this shows the direction to reach the current waypoint point. Above the airspeed and altitude indications are indicators for the preplanned speed and altitude on a given route leg. When the current route point is reached, the sighting mark will automatically switch to the next waypoint. Planned route and waypoints are displayed on HDD. 

·         In the RETURN sub-mode, the sighting mark shows the glide slope intercept point. The shortest line to the glide slope point will be indicated on HDD. Manual switching between airfields is performed by pressing the [~] key. After reaching the glide slope intercept point, the RETURN sub-mode will automatically switch to the LANDING sub-mode and the Tower will provide landing instructions.

2-20: ILS landing

·         In the LANDING sub-mode, the HUD director circle points to the landing airfield.  The direction to the landing airfield is also displayed on the HDD. Different airfields can be cycled with the [~] key. Upon approach, the airport control Tower will provide final directions. A vertical velocity scale appears at the right side of the HUD to indicate the aircraft rate of descent.

There are several beyond visual combat (BVR) combat modes: ОБЗ (SCAN) – scan, СНП (TWS) – track-while-scan, and РНП – АТАКА (STT) – single target track.

ОБЗ (SCAN) MODE

ОБЗ (SCAN) mode is first activated by pressing the [2] key.  This is the primary BVR search mode.  Up to 24 targets can be detected.  It’s also necessary to turn on one of the fire control sensors (radar or IRST) before targets can be detected and engaged.  In BVR mode, the fighter’s radar is normally used.  The radar enables target detection at longer ranges, and also the use of semi-active radar homing (SARH) missiles.  Information necessary for target search and lock on is displayed on HUD.  The range scale can be controlled with the [+] and [-] keys.  The scan pattern can be slewed discretely through three azimuth positions, center – right – left.  The scan pattern can be slewed in elevation using one of two methods - smoothly by direct elevation slewing, or discretely by the range-angle method.  To use the range-angle method, first you should set the expected range to target in kilometers using the [Ctrl-+] and [Ctrl--] keys, then set the expected target elevation difference with respect to your aircraft  using the [Shift-;] and [Shift-.] jeys, also in kilometers.  The expected range you set is indicated under the azimuth coverage mark at the bottom of the HUD, and the expected elevation difference is indicated to the right of the elevation coverage mark on the right side of the HUD. 

When the fire control sensor detects a target, it is represented by a small, horizontal row of dots on the HUD.  “Friendly” targets responding to the radar’s identification system (IFF) are represented by a double row.

2-21: SCAN mode - BVR

·         Range scale is changed by the [+] and [-] keys.

·         The expected target aspect hemisphere is controlled with the [Win-I] key.  АВТ (ILV) mode can be used if the target aspect is unknown.  The expected target aspect determines the pulse repetition frequency (PRF) to be used by the fighter radar in search mode.  High PRF (HPRF), which provides the longest detection range against approaching forward-hemisphere targets, is indicated by ППС (HI), whereas medium PRF (MPRF) for receding rear-hemisphere targets is indicated by ЗПС (MED).  In АВТ (ILV) mode, high and medium PRFs are interleaved on alternate bars of the radar scan pattern.  This provides all-aspect target detection at the expense of a 25% reduction in maximum range.

·         An air target is indicated on the HUD as a horizontal row of dots.  The number of dots corresponds to the approximate size of the target as measured by its radar cross-section (RCS).  One dot indicates a target RCS of 2 sq. m or less, two dots – from 2 up to 30 sq. m, 3 dots – from 30 up to 60 sq. m, and four dots - 60 sq. m or more.  Tactical fighters typically have RCS values between 3 and 30 sq. m, dependent upon the type, external payload, and aspect angle.  Most fighters are thus usually displayed on the HUD as a row of 2 dots.  Friendly aircraft have an identification marking in the form of a second row of dots positioned above the main one. 

·         The «И» symbol on the left side of the HUD indicates that the radar is turned on and actively transmitting. 

·         The radar cursor for target designation is moved by using the [;], [,], [.], and [/] keys.

·         The expected range to target (often derived from AWACS and GCI data), as set by [Ctrl-+] and [Ctrl--] keys and is indicated at the bottom of the HUD under the azimuth coverage bar.  The elevation coverage of the radar scan pattern is calculated from this parameter. 

·         The expected relative altitude of the target with respect to your aircraft, as set by the [Shift-;] and [Shift-.] keys is indicated on the right side of the HUD, next the elevation coverage bar.  This parameter is also used to calculate the scan pattern elevation coverage.

·         The elevation angle scale is also at the right side of the HUD.  The scale limits are ±60 degrees, indicated by inwards facing tick marks at the top and bottom of the scale.  A third inward tick mark represents the horizon.  Outward facing tick marks represent the viewing angle of the HUD.  Next to the fixed elevation scale is a moving elevation coverage bar, which indicates the limits of the scan pattern in elevation.  It cues the pilot to look in the same direction as the radar scan pattern, using the HUD as a reference.  If the elevation coverage bar is between the HUD tick marks on the elevation scale, then the radar is searching for targets in the elevation zone visible through the HUD.

·         The azimuth coverage bar is displayed at the bottom of the HUD. It has three fixed positions corresponding to the selected scan pattern azimuth: left – center – right.

СНП (TWS) MODE

Another BVR combat mode is СНП (Track-While-Scan or TWS).  It is activated from the ОБЗ (SCAN) mode by pressing [Alt-I].  The radar can correlate tracks for up to 10 targets simultaneously in СНП (TWS).  The main distinction from SCAN mode is that the radar retains target parameters, like elevation and velocity vector, while continuing to search for additional targets.  The HDD provides a top-down view of the tactical situation including all tracked targets, together with their direction of travel and position.

TWS mode provides automatic target lock on (transition to STT).  This is enabled by moving the radar cursor over a target.  The cursor will “snap” to the target and follow it thereafter.  Auto

matic lock on occurs at a range equal to 85% of the calculated maximum weapon launch range.  The pilot can force an earlier lock on by pressing the [Tab] key.

2-22: СНП (TWS) MODE

The HUD symbology in СНП (TWS) mode is similar to that of ОБЗ (SCAN) mode.

·         СНП - ДВБ (TWS – BVR) in the lower left corner of the HUD indicates the current mode.

·         Weapon stations carrying the chosen weapon are indicated along the bottom of the HUD.

·         The chosen weapon is indicated in the lower right corner of the HUD, beneath the elevation angle scale.  The 27ЭР above indicates R-27ER missiles.

·         The range scale at the left side of the HUD features three thick inwards facing tick marks.  Going from the top downwards, these are: Rmax - maximum permitted launch range vs. non-maneuvering target, Rtr - maximum permitted launch range vs. maneuvering target (“no-escape zone”), and Rmin - minimum permitted launch range.  

СНП (TWS) mode is only available together with ППС or ЗПС selected.  The interleaved-PRF ABT mode is not compatible.  This mode therefore requires head-on or pursuit target aspect to be known in advance.

The following information is displayed on the HDD in СНП (TWS) mode:

 

Aircraft Cockpit Instruments For ussia

2-23: HDD for СНП – ДВБ (TWS - BVR)

·         Scanned azimuth is shown in dark green.

·         Selected elevation angle of the scan pattern is displayed on the left.

·         Selected azimuth position of the scan pattern is displayed at the top.

·         Triangles denote hostile targets.  A short line indicates the direction of motion.

·         Circles denote friendly aircraft.  A short line indicates the direction of motion.

·         The own fighter symbol is fixed near the bottom of the HDD.

·         Display scale is indicated in the lower right corner.

Атака – РНП (ATTACK – STT) MODE

After locking up the target in either mode, SCAN or TWS, the radar automatically switches to Single Target Track (STT) mode.  It stops tracking all other targets and additional information is indicated at the HUD in the following form: 

2-24: АТК – ДВБ (ATTACK – BVR) MODE

·         Rmax – maximum permitted launch range vs. non-maneuvering target.

·         Rtr - maximum permitted launch range vs. maneuvering target.

·         Rmin – minimum permitted launch range.

·         The attack symbol indicates an active radar lock.  After missile launch, the attack symbol flashes at a frequency of 2 Hz.

·         Aspect angle shows target velocity vector in the plane turned in the HUD vertical plane.

·         АТК – ДВБ mode is displayed in the HUD left lower corner.

·         The arrow indicating current range to target moves along the range scale. 

·         A round dot indicates the radar antenna position relative to the fighter heading.

·         The director circle is superposed over the target in the HUD.

·         The ПР (LA) Launch Authorized symbol appears when the target enters the permitted range limits and any other launch conditions are satisfied.

In STT mode, all radar energy is concentrated on the target to provide greater accuracy and reduce the probability of tracking failure, which may be caused by target countermeasures.

Note that this radiation-intensive mode is interpreted by enemy RWR as a “lock” and preparation for missile launch.  As a result, using it may prompt the target to take evasive action or to start a counterattack.

2-25: HDD АТАКА – РНП (ATTACK – STT)

·         In the STT mode, the scanned zone becomes a narrow direction-indicating radar beam.

During missile launch the radar changes to continuous wave illumination.  This is unambiguously interpreted by the enemy warning system as a missile launch and usually prompts some form of defensive measures.

When semiactive radar homing (SARH) missiles are used, it’s necessary to illuminate the target until the missile hits.  When active radar homing (ARH) missiles are used, it’s necessary to illuminate the target until the missile seeker switches to active homing, beginning from a distance of 15 km from the target.

SCAN – IRST MODE

Use of the Infra-Red Search and Track (IRST) system as the chosen sensor changes the HUD symbology accordingly.

When searching with IRST, target information is displayed in the HUD azimuth-elevation coordinates (as opposed to the azimuth-range coordinates when searching with radar).  Azimuth is along horizontal, elevation angle along the vertical axes respectively.

After the locking the target with the help of the IRST cursor, the display switches to the ATTACK mode described earlier.

 

Aircraft Cockpit Instruments For Russian Aircrafts

2-26: ОБЗ – ДВБ (SCAN – BVR) Mode with IRST as chosen sensor

·         The “T” symbol at the left side of the HUD indicates IRST operation.

·         The name of the chosen mode is displayed in the left lower corner.

·         Target mark is displayed in the azimuth-elevation angle format.

·         The pitch elevation of the scan pattern is displayed at the HUD center-right.

Since the target’s RWR cannot detect the laser rangefinder employed by the IRST, this sensor makes it possible to conduct a “stealth” attack.  For this type of attack, only “heat-seeking” missiles with seekers that employ infra-red homing (IRH) can be used.

Digital Datalink

The Su-27 and Su-33 carry the necessary radio equipment to receive digital target information directly from off-board sensors (A-50 AWACS aircraft and ground-based EW radars) without using voice communications.  The command post transmits the air combat tactical situation to the fighter, and this data is then displayed in a top-down view on the HDD to improve the pilot’s situational awareness.  This tactical display shows the positions of all aircraft detected by off-board sensors, using the fighter’s own position as a reference.  The digital datalink is automatically active when the fighter radar is first turned on ([I] key), so long as a friendly AWACS aircraft or early warning (EW) ground radar station is available in the mission.  The datalink will remain active, and targets will continue to be displayed on the HDD, even if the radar is thereafter switched off.

2-27: HDD with active AWACS datalink

It should be noted that some AWACS-detected targets appearing in the dark green triangular zone may not be visible to the fighter’s own radar, if they are outside the radar elevation scan limits in altitude.  The fighter’s own radar should be controlled with the help of the HUD display.

Work in Complicated Countermeasures Conditions

In complicated countermeasures conditions, when the enemy uses passive and/or active radar jamming, the TWS mode cannot be used.  SCAN mode should be used instead.  In the conditions of strong radio-electronic countermeasures the radar cannot determine the range to the target – instead, a vertical jamming strobe of randomly flashing target marks appears in the HUD along the jammer’s bearing.  Detection of ECM in the radar scan pattern also causes the “АП” (active noise) symbol to appear at the right side of the HUD.  Nevertheless, it is possible to obtain a bearing-only “angle-of-jam” (AOJ) lock on the countermeasures strobe and to launch semi-active radar homing (SARH) missiles, which in this case will guide in the passive “home-on-jam” (HOJ) mode.

The AOJ lock is effected by using the [;], [,], [.], and [/] keys to move the radar cursor over the countermeasures strobe, and pressing the lock-on [Tab] key.  The fighter radar will then point its antenna in the direction of the noise source and track it.  The target range displayed in the HUD with an active AOJ lock is not measured by the radar but rather provided by the fighter pilot (e.g. according to instructions received by radio), with the default value 10 km.  If the entered target range is longer than the range of the chosen missiles for this altitude, then missile launch requires either that the entered range is manually reduced with [Ctrl--] until the “ПР” symbol appears, or that launch authorization override is enabled with [Alt-W].

It should be noted that when using missiles against a jamming target, the lack of range information can make it difficult to gauge when to shoot - the target may be outside the permitted launch zone.  In addition, missiles flying in the passive mode have a lower probability to hit the target.