Intercept Geometry: Table of Contents
The Intercept Geometry Part IV introduces the Gameplans used to manipulate the Lateral Separation to allow the F-14 to complete the intercept using manoeuvres such as the Horizontal Stern Conversion Turn.
The primary reference is the CNATRA P-825, reviewed in 2017. This is the most recent version available to the public, hence the title.
Horizontal Stern Conversion Turn and the 40k ft of LS goal
After the lengthy discussions about the basic concepts related to the Intercept Geometry, we are finally able to put some of those into practice.
The Horizontal Stern Conversion Turn is the final manoeuvre of a basic form of intercept, and it is used to place the fighter in the rear quarter (RQ) of a non-aware or non-manoeuvring target, In LAR for a Short Range Missile (SRM) employment, whilst also enabling the crew to visually identify (VID) the target during the turn (if weather conditions allow so).
It is also a handy means of rejoining a tanker, and a simple way to practice the intercept.
If Timelines use the range as a means of tracking the progression, the intercept uses “Gates”. Gates are sets of SR and TA (and therefore, LS) that the fighter should ideally fly through in order to ensure the correct positioning during the intercept.
For a Horizontal Stern Conversion Turn the last gate is LS = 40,000ft at SR = 10nm (and therefore, TA = 40). This is, in fact, where we want to be prior to turn into the bandit’s six o’clock (if you visualize it in your mind, it means behind slightly off to the side, ready to perform a sort of “U Turn” behind the target).
Depending on the status of the bandit, the RIO has to come up with a plan (Gameplan) that eventually satisfies the goal mentioned above.
Albeit intuitive and already discussed in the past, for completeness’ sake I set up a quick scenario to determine the difference in terms of VC induced by horizontal offset: two F-14 flying one true head-on, the second parallel head-on towards their relative targets, with 6.5nm (~40,000ft) of Lateral Separation at 20,000ft; every aircraft is flying at 350kts.
- VC = 700kts at any range, until the last mile, due to imprecision in positioning the aircraft in the editor;
- VC = 689kts at 37.5 nm (ATA 10)
- VC = 683kts at 30 nm (ATA 13)
- VC = 662kts at 20 nm (ATA 19)
- VC = 540kts at 10 nm (ATA 41)
- VC = 373kts at 7.5 nm (ATA 62); then the target passed the gimbal limits.
These values should give a good idea of how ATA and VC change depending on the SR.
Target Aspect and Gameplan
The gameplan adopted primarily depends on the Target Aspect:
- Low TA: 0 < TA < 15.
TA < 10 is considered very low and, consequently, the Lateral Separation will be narrow as well. At 30nm and 15° TA, LS is 45,000ft. VC will be close to the sum of the velocities.
- Medium TA: 15 < TA < 35.
At 30nm, the LS in this interval stretches between 45,000ft and 105,000ft, the VC down to 450-500kts. In order to meet the 40k goal, the LS must be reduced before the 10nm Gate.
- High TA: 35 < TA < 45.
LS is around 120,000ft and the amount of LS to be removed to hit the Gate at 10nm is considerable. VC should be around 480kts.
- Very High TA: TA > 45
This case is extreme, the amount of LS is really substantial, the gameplan aimed to reduce it should be implemented as soon as possible if the fighter wants to meet the 10nm Gate.
As mentioned before, the P-825/17 uses 40,000 ft of Lateral Separation as the Gate at which the fighter starts the stern conversion turn towards the RQ of the target.
A LS < 40,000ft will result in the fighter exceeding the conversion, ending up at 5 / 7 o’clock of the target.
A LS greater than 40,000ft may satisfy the positioning aspect only on one axis, ergo lagging behind the bandit, but the fighter may be out of the envelope of its weapons due to the additional time and space required to complete the conversion.
The following is a table useful to visualize the LS computations needed to meet the goal of 40k ft of LS all the way down to the last gate at 10nm:
Following this table, the pairs or SR and TA meeting the LS goal are:
- 15 TA at 30nm;
- 20 TA at 20nm;
- 30 TA at 15nm.
This scenario can be visualized very easily: the fact that TA and SR are inversely proportional means that the fighter is “drifting” to the side as it is getting closer to the bandit, thus creating room for the conversion turn. To simplify, imagine a triangle rectangle built by the BFP and the LS as catheti, where the hypotenuse approximates the FFP until the last Gate.
It goes without saying that this is not the scenario we want if the goal is employing an AIM-7 or an AIM-54, as their performance peak vs targets with low TA and high VC. Both conditions are met as the FFP gets closer and closer to the BR and the TA is low (this scenario will be discussed more in-depth later).
- Creating and maintaining a good level of SA is more important than knowing the exact value of LS at any given moment;
- Task fixation is very dangerous and can easily become saturation. Avoid it!
Practising how to manipulate the TA to increase, decrease or maintain the LS is important and very helpful, especially if you are new to this.
Details of the Modern Gameplans
The following is a quick look at the Gameplans suggested by the P-825/17 to ensure that the gate 40k at 10nm is met. Note that in all these examples the bandit is not aware or “cooperating”: it is not jinking, countering the manoeuvres of the fighter or denying LS.
Sketches: Modus Operandi
The sketches of the Tactical Information Display in Aircraft Stabilized mode and the Detail Data Display both for Pulse and Pulse Doppler modes are not meant to be extremely precise or to scale.
In particular, I did not calculate VC as a function of the ATA for the DDD in PD mode: I placed the target image depending on the VC at that moment, compared to the others rather than its value.
The images depicting the TID AS have a set of dashed lines every 15°, whereas the others represents the settings of the AWG-9 (±10°, ±20°, ±40°, ±65°).
I plan to put together a video about the gameplans here discussed and other concepts later on.
The first turn
When the BVR Timeline was discussed, I stripped it of as many aspects related to the Geometry as possible. Now it is time to put such parts back, a piece at the time.
Post commit, the fighter turns towards the target (Point and Assess). Point and Assess involves placing the target in the F-14’s radar scan zone (on the nose) and determining the Target Aspect, calculating the Lateral Separation and evaluate how to satisfy the goal of 40k ft of LS.
Depending on the TA, the fighter can now turn to generate LS, turn to zero cut to preserve LS or turn to collision to remove undesired LS.
After the first turn and assessing the TA, the RIO decides the next step. There are a number of techniques used to manipulate the LS, the following are described in the P-825/17.
Low TA / no LS Gameplan
The fighter wants to manoeuvre and build LS to meet the usual LS goal of 40k ft at 10nm. Intuitively and thanks to the precedent discussions, we know that turning away from the bandit has the effect of increasing the Target Aspect, and subsequently the Lateral Separation, on top of decreasing the VC (remember the previous part of the series, the “Cut-away“).
This plan, named “Kick and Build” takes advantage of these considerations to satisfy the goal.
- The RIO places the contact at 50ATA cold, this builds separation;
- When the goal is met, the fighter turns to the Bandit Reciprocal. This stabilizes and maintains the LS;
- At 10nm, TA is increased to 40.
In other words, the goal is transforming a True Head-On situation into a Parallel Head-On situation.
The F-14 can place the target to the gimbal limits if necessary, increasing the 50ATA angle suggested by the P-825/17.
Remembering what was discussed in Part III, the first turn is a Cut Away in order to increase LS up to the desired 40,000ft, a further turn to TA to FH = BR to maintain such separation and lastly a turn to Cut < CB (Pure pursuit) to converge at the target’s 6 o’clock.
- Phase I: Detect and Correlate. The contact appears on the radar, and it is correlated with the controller;
- Phase II: Point and assess. The fighter places the target on the nose, the amount of LS is determined;
- Phase III: Turn to place the target at 50 ATA cold, by turning away from the target, LS is generated. The RIO should monitor the drift as the contact may drift out of the radar scan volume;
- Phase IV: Turn to BR. When the LS goal is met, the RIO commands the pilot to turn to the Bandit Reciprocal. As discussed in the previous parts, this manoeuvre captures the LS.
(Note: following gameplans will combine Phase I and Phase II into a single step.)
P-825, 7-18, shows four images of the radar attack display, manoeuvre after manoeuvre. What I don’t get is why VC never moves from 585 kts. Umh…
Medium TA (15 < TA < 35)
- Rather than aim for the 40k ft of LS goal, the fighter should turn to BR and let TA reach 40;
- When TA = 40, then the fighter should place the bandit on collision until 10nm.
If the scenario is co-speed, the turn to place the contact on collision is quite simple: since the bandit will be drifting during the turn, the rule of thump is that the bandit drifts 1° every 20° of FH change. The turn to capture 40 TA should be of about 80°, and it should be started when the contact is 36TA, usually corresponding to 36ATA.
If not co-speed, the RIO should assess and command the turn depending on ΔV. Whatever the case, the TID in AS helps to set up the collision quite quickly.
- Phase I: Point and Assess, TA and LS is determined (30 nm);
- Phase II: since the TA is close to the goal yet not enough, the RIO can command the pilot to turn to BR and let the TA increase;
- Phase III: when the TA reaches 40°, the RIO commands the pilot to put the bandit on collision until 10nm.
Notes: the gameplan for medium TA is simpler than the previous. Since the TA is close to 40, the simplest solution is flying Zero Cut until the drift causes the Target Aspect to increase and meet the desired amount (40 TA). Then the goal is to maintain 40 TA until 10nm (equal to 40k ft of LS) by using the Collision Course. This last part of the manoeuvre is represented in the box in Image 4.
From the point of view of the TID AS (Image 6), the bandit will be drifting away from CB, until the TA goal is met. Then, when collision is established, the drift stops.
The manoeuvre to place the contact on collision covers about 80°: 40° to turn into the target, 40° to place the target on the opposite ATA.
In order to make the image simpler to understand, I tried to add some “dynamism” to it (Image 7).
High TA (35 < TA < 45)
This scenario is by far the simplest. The TA is already close to the target, and it just has to be corrected and captured by means of Collision (Image 8).
The TID in Aircraft Stabilized mode displays a target on collision with its vector pointing towards the F-14 (Image 9).
The DDD in Pulse mode (Image 10) is another simple means to determine the successful Collision by monitoring the drift (Image 10).
Very High TA (TA > 45)
- Turn to place the banding 50-60 ATA hot with 0.1IMN speed advantage;
- When 40 TA is reached, turn to collision and match speed (leading to a stable TA, until 10nm).
If the fighter cannot meet the goal of 40k ft of LS at 10nm, there is an alternative manoeuvre available. It is covered in the next paragraph.
- Phase I: Point and Assess, the RIO determines the geometry;
- Phase II: the RIO commands a hard turn to place the bandit at 50 ATA (Hot) plus 0.1 IMN speed increase. The goal is removing LS by primarily reducing the TA;
- Phase III: when the TA reaches 40°, the excess speed is removed and the bandit is placed on Collision to capture the TA until 10nm.
This scenario is potentially simpler in DCS but can easily become more complex to handle: outside the training environment focus of the P-825/17, the RIO can command Gate to the pilot, or even place the target at 60 ATA Hot, very close to the gimbal limits. These manoeuvres have a number of potential unwanted side effects. For example the bandit can become aware of the fighter, turn away and leave the volume scanned by the AWG-9. The fighter can also reach the goal of 40TA too fast and not react quick enough, having then to increase LS again. Moreover, the speed excess may not be removed, making the next phase of the intercept more complex than necessary.
(This table is the same available in the P-825/17, 7-23.)
|TA Assessment at 30nm||Initial LS||First Turn||Second Turn||Third Turn|
|0 – 10||0 – 30k||50 ATA Cold||Bandit Recip||Collision at 40 ATA Hot|
|20||60k||Bandit Recip||Collision at 40 ATA Hot||Nose-on at 10nm|
|30||90k||Bandit Recip||Collision at 40 ATA Hot||Nose-on at 10nm|
|40||120k||Collision at 40 ATA Hot||Nose-on at 10nm|
|>= 45||135k+||50-60 ATA Hot with 0.1IMN speed advantage||Collision at 40 ATA Hot and remove speed advantage||Nose-on at 10nm|
I noticed three recurring manoeuvres or steps used by the gameplans here discussed. Highlighting them that can help to understand the procedures:
- “Point and Assess” is the first step. By placing the bandit on the nose, ATA = 0, so TA is simply BR → FH, as discussed in the previous parts of this series, so the gameplan can be determined in a matter of a couple of seconds;
- Zero Cut or parallel head-on. When FH = BR, the Lateral Separation does not change;
- Collision Course. When on collision, the Target Aspect does not change.
Point #2 and #3 mean that when one of the two goals is achieved, then the fighter can capture that value and aim to meet the other. Therefore the game becomes trying to match one of the two parameters (LS or TA), then letting the second evolve until it satisfy the Gate goal.
What if the goal of generating 40k ft of Lateral Separation is not met before the limit of 10nm? The contingency manoeuvre is called Displacement Turn and will be discussed in the next part, along the final manoeuvre, the Counterturn, that concludes the horizontal stern conversion turn.