“Pickle!” yelled Rivers into the intercom to key my attention to our altitude. I depressed the pickle button on the control stick and felt the hesitating lopsidedness as the single 500-pound rockeye was released. I yanked back on the stick, broke our rate of descent 800 feet above the water, and snapped the Intruder into a left 6½-G turn while pumping out three sets of flares, two at a time. I unloaded the G and dumped the nose to keep our airspeed up, accelerating away from the Polnokny but turning our hot engine burner canisters straight at any heat-seeking SAMs that might be trying to target us. I pumped out another set of flares and made a 4-G jink to the right. Back into the right-hand turn, Rivers and I both craned our necks to look for missiles and mark our hit. It seemed to take forever for the canister to open and dispense its hundreds of tiny bomblets, but finally we saw the pattern of the small explosions—the majority had gone long, harmlessly into the water, with perhaps a dozen of the tank-busting bomblets impacting the deck amidships.
The Mk20 Rockeye is a conventional free-fall cluster bomb carrying 247 Mk 118 Mod 1 bomblets. It is a very effective weapon versus armoured targets, personnel and even ships. Each bomblet weights 600 grams, and has a 180 grams high explosives shaped-charged warhead, capable of penetrating about 190 mm or 7.5” of amour.
Rockeyes & DCS
There are two versions of the Mk-20 in DCS, but their function is identical (source: near_blind). Although it is capable of dealing with armoured targets, the HP-like system currently used by ground vehicles means that the Mk-20 loses part of its performance, as it can’t score mobility kills or disable vital parts of the vehicle.
Since the bomblets scatter on the targeted area, they can be rippled using a low interval to cover a greater distance, a-la carpet bombing. However, by doing so, they may not destroy an armoured target entirely. In these cases, releasing Mk-20s in pairs can somewhat offset the problem.
In DCS, only 21 Mk 118 bomblets are spawned as the canister opens. This can be a means of reducing the resources needed to calculate the trajectory of each of them (dropping a CBU in a crowded server in 2012 used to crash the server…).
This brief study assumes that there is a correlation between the visual representation and the effects on the ground. Following a few dozen tests, there seems to be. Thus, the objective is understanding if and how the trajectory of the bomblets can be understood and manipulated, if necessary, to obtain the desired effect on the target.
In particular, it seems that the bomblets’ trajectory follows the “mother’s” for the most part, as shown in the picture above.
Effects Of Release Altitude and Attack Parameters
The altitude, dive angle and speed of the attacking aircraft affect the trajectory of the bomb and how the bomblets scatter once they are released.
The following are a few examples of releases, to give you an idea.
- ΔT1 is the time difference between the release of the bombs and the time at which the canister opens;
- ΔT2 is the time difference between the opening of the canisters and the impact of the bomblets;
- Values are collected from TacView and slightly approximated;
- Altitudes are AGL. Test #8 and #12 are level toss and dive toss deliveries (elevation ~100ft). In the other cases, the elevation of the targeted area is ~1100ft.
Unfortunately, it is very hard to measure the area covered by the bomblets. However, it seems that higher altitude and steeper dive angles tend to “splash” the bomblets over a wider area, probably due to the greater horizontal component of the bomb’s velocity vector.
Take this aspect into consideration when planning the attack.
This also means that the attacking aircraft can “force” the trajectory of the Rockeye (or any bomb, really) by, for example, performing a high-speed, almost levelled, low-altitude pass and thus providing a considerable amount of forward momentum to the bomb.
The figure below shows one example; only one Mk-20 was employed. However, the high-speed pass barely scratched the paint of the three BMPs placed as targets (one of the BMPs lost a few decimetres of HP…).
I then performed a CPTR TGT drop, aiming slightly beyond the targets (Figure below), starting from 10,000ft and releasing at ~7500ft AGL. It ended up too long, but it is actually useful in this case, as it makes comparing the two results much simpler.
The next figure is a collage of the two previous images. The difference it terms of area covered by the bomblets is remarkable.
This result opens a series of interesting planning considerations: for example, if employed against armoured targets, concentrated bomblets may be preferable. If the goal is hitting a small moving ship or unarmoured vehicles or infantry, then a wider effect is preferable. On the other hand, to improve the effect over a greater area, more Mk-20 can be released at the same time, or with a pre-defined ripple interval.
The only way to have a more meaningful answer (hopefully), is working the maths.
I noticed that there seems to be a linear trend between the angle at which the Mk-20 is flying when it opens to release the bomblets, and the altitude at which this happens. This relation is, however, affected by the release speed.
Plotting the collected values into a chart gives the result shown in the next image. The value located above each data point is the Release speed.
If this observation is correct, then the crew can have a general idea of what the result of the bombing will bring, given defined pre-planned parameters.
Another way to look at the results is from the point of view of the delivery parameters, rather than the bomb itself. The chart in below tries to help in this regard (click on the chart to enlarge it).
The release speed seems to influence the bomb pitch angle more at lower altitudes, then its important diminishes at higher altitude.
Data points #6 and #7 are of particular interest. The release parameters are very similar, but the speed is drastically different, and the impact on the angle is noticeable.
The impression is that, assuming constant release speed, the top-left part of the distribution is where the pitch angle is less steep. Moving towards higher altitude and steeper dive angles increase the Mk-20’s pitch, but for different reasons:
- high altitude allows the bomb to disperse its forward momentum, thus falling like a brick thrown horizontally from the window;
- high steep angle transmit a noticeable downwards momentum to the bomb, thus reducing the horizontal momentum. Imagine the same brick thrown from the window, but this time downwards.
What the release speed seem to be doing, is shifting the chart left and right: releasing faster increase the area where the pitch is less steep; vice versa, flying slower decreases it.
The figure below is an intuitive representation of the concept, not based on actual data, as many more datapoints would be required.
I tested the Electrical fuze options available in DCS, using the same delivery parameters each time, and monitoring for any difference in terms of pitch, opening altitude, or timings.
There is no blatant difference between the different electric fuze settings in DCS at the time of writing.
The mechanical fuze should be set to “N” (Nose) to correctly operate the bomb (source: F-14 DCS Manual). However, setting “N/T” (Nose – Tail) seem to be work under most conditions.
Using the same data collection scheme used for the electric fuze, I tested three deliveries using the N/T mechanical fuze:
Again, there is no immediately apparent difference between the “Nose” and “Nose/Tail” settings of the mechanical fuze.
The biggest take-away of this brief overlook of the Mk-20 Rockeye cluster bomb is the understanding of how the delivery parameters can affect how the bomblets spread. In fact, condensing the bomblets into a smaller area can improve the odds of hitting the same target multiple times, thus increasing the probability of killing a tough target. If the desired effect is the destruction of soft-skinned targets over a wider area, the delivery should be planned to maximise this aspect, favouring less steep pitch angles.