Sunday, 27 October 2013

A Detailed Examination Of The Range Of Munitions Used In The August 21st Sarin Attack

Thanks to John Minthorne, who has put together this detailed analysis of the range of one munition type used in the August 21st Sarin attack.  John Minthorne is a professional mechanical engineer with around seven years relevant experience.  His relevant experience includes process system design, project management, feasibility and conceptual studies, and computational fluid flow modelling.  The original report and associated files can be found here.

UMLACA Maximum Range Analysis


This report attempts to establish, with a minimal level of rigor, the maximum range that can be assigned to the 330mm-class chemical rocket (the "unidentified munition linked to alleged chemical attacks [UMLACA]) used in the August 21, 2013 attacks on Ghouta, Syria. The report is based on public information including United Nations reports, NGO publications, amateur video & photography of the remains of the weapons, public weather data. In particular, this goal of this report is to determine whether this model of rocket could have been launched from the Syrian Army Republican Guard "base 104", approximately 9.5 km west of the impact sites.


In the early morning of August 21, 2013, the Ghouta residential suburb of Damascus, Syria was struck by a rocket attack that killed hundreds. Representatives of the Syrian Army and rebel forces were quick to blame one another for the attack, and international observer countries including France, the United Kingdom, Russia, and the United States made official but predictable statements  blaming the "opposite side".

In mid-September, Human Rights Watch (HRW) and the United Nations (Sellström) released reports that confirmed the August 21st attack did make use of Sarin. Consistent with the UN Mission's charter, the Sellström report did not assign blame for the attacks. The report did, however, note the azimuth of the ballistic trajectories of two of the munitions used, including a UMLACA that impacted Ein Tarma. The Human Rights Watch, along with several news organizations, noted the the trajectory azimuths intersect deep in Syrian government-held territory, specifically the Republican Guard 104th Brigade military base.

However, this information is only meaningfully damning to the Syrian government if the UMLACA is capable of being fired approximately 9.5 km from the Republican Guard base to the impact site. Much of the flight path less than 8 km from the impact site is identified by Human Rights Watch as "contested" at the time of the launch (Lyons).

Whoghouta.blogspot analysis

One organization to estimate the maximum range of the UMLACA is (sasa wawa). This analysis reported in a maximum plausible range of 3.5 km and concluded that the rockets could not have been launched from the Republican Guard base. This analysis was qualitatively reviewed, and in the opinion of this author the analysis contains a number important flaws. Some of the more significant errors include:
  • Assuming very short burn times (and wrongly stating that such an assumption is conservative). Drag increases as a function of more than the square of the velocity, and as a result the thrust of the rocket motor over time is a crucial consideration.
  • Using hobby rocketry engines as the basis of design. By extension, underestimating the propellant mass and specific impulse.
  • Miscalculating the center of drag, severely underestimating the rocket's stability.
  • Failure to consider wind direction, elevation above sea level, or air temperature.

Summary of available information

Information for this report was gleaned from publicly available information:
  • Published photographs and diagrams based on those photographs, by Human Rights Watch.
  • Field measurements and photographs taken by the United Nations Mission.
  • Secondary sources of ballistic error such as Coriolis forces are ignored.
  • Additional assumptions are listed in the relevant sections of this study.
UMLACA Physical Properties

Propellant Mass

The total impulse of the UMLACA rocket motor is limited by the propellant selected and the volume of propellant used. Since the purpose of this study is to evaluate whether a 9.5 km travel distance can be ruled out, each physical assumption is listed as a range between which the actual values for the UMLACA likely fall.

The total length of the UMLACA is about 2200 mm. Some portion of the nose section is filled with a bursting charge and detonator, so the maximum length of the solid fuel volume is assumed to be 2000 mm. The UN report implies that the motor section may be as short as 1340 mm, so a more pessimistic assumption incorporating a void space inside the weapon's warhead would be a fueled length of 1300 mm.

The external diameter of the UMLACA is 120 mm. Assuming a robust, wall thickness consistent with standard weight pipe, an internal diameter of 110 mm is used. This results in a volume range of between 0.0124 and 0.0190 m3.

The density of high-performance solid propellants varies between 1.6 and 1.86 kg/L (Zandbergen). Applying this value range to the fuel volume range, the rocket's propellant mass is found to be between 19.8 and 35.34 kg.

Specific and Total Impulse

The specific impulse of a rocket motor will have a profound effect on its performance. As a motor becomes more efficient, it can increase the final velocity of a rocket exponentially higher. This effect is more muted in a subsonic or transonic rocket than in an orbital or sounding launch vehicle, however. Military propellants have specific impulses in the range of 210 to 260 s (2060 – 2550 N*s/kg) (Zandbergen). Multiplying this range by the propellant mass gives us a total impulse for the UMLACA of 40800 to 90100 N*s.

Maximum Thrust

Gases escape a rocket nozzle in a predicable fashion. The fluid flow velocity through the nozzle throat is Mach 1, such that the total thrust generated by a rocket motor varies roughly proportionally to both the chamber pressure and throat area (Platzek). Unfortunately, no information appears to be publicly available documenting the precise the throat area of the rocket motor. The Human Rights Watch report contains one photograph of the rear of the motor and a tape measure, allowing estimation of the nozzle throat to be very roughly 50 mm. Assuming a chamber pressure of 7 MPa, this would equate with a maximum thrust of around 22 kN. Given the very large amount of uncertainty on this number, no conclusions can be drawn from this. It is simply noted that the estimated maximum possible thrust is within an order of magnitude of the thrust a designer would desire for this weapon.

Thrust Characteristics

A solid-fuel rocket has a practical maximum burn time – the regression rate of propellant is lowest in a solid grain geometry, but is still non-zero. Regression rates for typical high-performance propellants vary from 5 to 25 mm/s (Zandbergen), corresponding to a theoretical maximum burn time of 80 s to 400 s for a 2 meter, solid grain rocket motor. The longest total burn time considered in this study was 45 s, well within the realm of feasible achievability.

The amount of thrust a solid-fuel rocket provides over the course of its burn broadly customizable by changing the chemistry and structure of the rocket grain. For a rocket with no lift and poor drag characteristics such as the UMLACA, maximum range will be achieved with a short, high thrust initial impulse followed by a long, low thrust burn to sustain velocity at low transonic speed (~0.7M or 240 m/s). A thrust/time profile of this shape is both achievable and commonly found in military rockets (Platzek).
Environmental Considerations


A rocket spends a significant amount of time in flight. In evaluating the maximum distance a rocket may travel, the velocity of the wind encountered must be considered. At 2:00 AM on the morning of the attack, the wind at Damascus International Airport was blowing from the WSW (about 248°) at a sustained speed of 6.9 miles per hour (3.1 m/s) and increasing (Weather Underground). Wind speed is typically higher a significant distance above the ground; for the purposes of this analysis the wind velocity is assumed to be an average of 4 m/s from 248° (37° from a pure tailwind from the rocket trajectory of 285°. Correspondingly, a rocket azimuth of 143° relative to a 4 m/s wind was used in the OpenRocket software trajectory models. For ~60 s long flights, this adds a few hundred meters to the range. If meteorological information shows that higher-altitude tailwinds were present, this could increase the maximum range by a high single-digit percentage.

Atmospheric density

Aerodynamic drag is proportional to the density of the fluid through which the projectile travels. The temperature in Damascus at 2:00 AM on the morning of the attack was about 73°F (22.7°C) – if a standard atmospheric temperature of 15° is assumed, drag will be overstated by about 2.8%. The elevation of the targeted area in Ghouta is about 760 meters above sea level – if sea level elevation is assumed, drag will be overstated by about 9.5%. Since the temperature profile of the atmosphere above Damascus is not known, trajectory models assumed a standard atmospheric temperature and a launch elevation of 760 m above sea level.

Relative elevations

A projectile on a nominally parabolic trajectory will travel a greater distance if its impact location is of lower elevation than if it flies over a flat plain. The topography of northern Damascus is dominated by Mount Qasioun, a 1151 meter high peak. The areas of Ghouta targeted are lower, around 760 meters above sea level. Since the rocket attack was obviously not launched from the peak of Qasioun, the actual difference in elevation was less than 400 meters. This difference in elevation is not considered in these range calculations, since the actual launch elevation is not precisely alleged. This means that the maximum ranges shown are conservative by a small degree (probably 0.1-0.2 km) due to the relative elevations of the launch and impact sites.

Maximum Range Calculation

Physical Rocket Model

A model of the UMLACA and derivative UMLACA with a more aerodynamic nose cone were created in the Open Rocket program. Both models were modified from a model downloaded from the whoghouta.blogspot web site. The models are described in the two tables below; dimensions are in mm, roughnesses are in um, and masses are in kg (unless noted otherwise).

Drag Modifications

Any designer tasked with extending the range of the UMLACA would immediately consider improvements to the rocket's drag. With a Cd of about 1.0, the rocket's drag is several times the value to which it could be reduced with relatively superficial modifications. The nearly blunt front of the rocket generates about 80% of the subsonic total drag.

The UN and HRW reports both sketch the UMLACA with a completely blunt end, but the least is known about the front portion of the rocket because it is damaged upon use by the bursting charge and subsequent impact with the ground. The front plate includes six threaded holes which could be used to attach a light-weight aerodynamic nose cone. As such, the possibility that rockets fitted with nose cones were used on August 21 cannot be ruled out. Since addition of an aerodynamic nose dramatically changes the maximum range of the UMLACA, maximum ranges were established both with and without the aerodynamic nose cone.

Rocket Motor Design

Six hypothetical rocket motors were evaluated, three per drag condition of the UMLACA. All utilized an initial boost phase to accelerate the rocket to about 0.7M (240 m/s), followed by a lower sustainer thrust to maintain flight speed. Two used total impulses of 40800 N*s, the lower end of the estimated motor impulse. The remaining motors used the higher end of the estimated impulse, about 90100 N*s. The full .eng data for each motor can be found here.

Software Limitations

For convenience, this study matched the "whoghouta" blog's selection of Open Rocket as the software to simulate the UMLACA trajectory. The UMLACA is several times larger than a typical large single-stage hobby rocket, and its characteristic geometry likely challenges the software in ways that were not the focus of its development.

Simplification of Fin Layout

The Open Rocket software does not support modelling of a circumferential band around the perimeter of the tail fins. This band is parallel to the air stream, generating significant drag as well as contributing to the stability of the rocket. To model the ring's contribution to drag and efficiency, the fin height was increased from the actual dimension of 95 mm to 135.6 mm, replicating the total fin material area of 0.179 m2.
In addition, the enclosed nature of the air stream through the fin assembly may create directional flow effects more pronounced than a more simple fin arrangement. Study of the airflow through this fin assembly is an excellent candidate for further study of the UMLACA's aerodynamics.

Transonic and Supersonic Drag Performance

The UMLACA is likely but not certainly an exclusively subsonic weapon. The coefficient of drag of an object in a fluid flow stream is not constant; it changes with velocity. At about M0.8 the Cd beins to increase, peaking locally at M1.0 and dropping to an intermediate value for low supersonic values (Heinrich). The Open Rocket software attempts to model these changes in Cd, but for a rocket with such an unusual shape as the UMLACA it is likely that the modelled transonic behaviour is not fully accurate.


For the UMLACA without drag-reducing features, the maximum distance travelled was about 6.5 km, for the UMLACA4 motor curve at a launch angle of 43° from vertical. Maximum distance travelled using a 41 kN*s motor was about 3.3 km.

If the UMLACA weapons used in the August 21st attacked had aerodynamic nose cones, their maximum range could be in excess of 15 km. With a range of 15 km, the UMLACA5 motor curve did not produce the greatest travel distance but its lower average thrust kept the more streamlined rocket at transonic speed (increasing confidence that the simulation is accurate).

  • The rocket with a blunt nose has mediocre drag characteristics. A designer seeking to maximize the weapon's range could add a nose cone to the weapon, which would greatly reduce the drag coefficient and increase the range. The presence of threaded holes on the front plate of the rocket could be an indication that this was, in fact, done.
  • The rocket is aerodynamically stable and unlikely to tumble or excessively oscillate in flight.
  • The publicly available information on the UMLACA (particularly the chemical variant) leaves a large margin of doubt as to the rocket's range and flight characteristics.
  • On the basis of the publicly available information referenced in this report, an attack from the Republican Guard 104th Brigade base cannot be ruled out as implausible.
  • The maximum range of the UMLACA is probably between 3.3 km and 6.5 km, increasing to 15 km if a nose cone were installed.


  1. Thank you for the analysis!

    You may find my response here (scroll down to the last section):

    The bottom line: The analysis overestimates the engine's total impulse by a factor of 2, and the drag coefficient by a factor of around 4. Once corrected, range estimates should be similar to all other analyses (i.e around 2.5 km).

    Would love to work together to reach a consensus estimate.

  2. This analysis is riddled with errors. Most significant is the naive assumption of a solid rocket charge, whereas most military rockets have a grain comprised of multiple tubular sticks of propellant clamped together to form a stack similar to drinking straws in a container. The result of this is a much lighter propellant load and a much faster burn time - typically 1-3 seconds.

    Fast burn time is very important as it negates much of the gravity effect.

    The remaining errors are far to numerous to list here. A proper debunk to supplement sasa wava's will be provided on the whogouta website.

    While I am preparing a suitable response, other items to consider that are plain wrong are the external dimensions of the missiles, the structural weight of components, the air temperature, wind speed, and direction, and the mass of the payload. e.g. the missiles have a payload dimension of 360mm not 330mm.

    The sasa wava figures are reasonably derived but in my view optimistic - the actual range is probably closer to 2000m under optimum conditions.

  3. hey nice post meh, You are one of the best writers I've seen of recent. I love your style of blogging here. this post reminds me of an equally interesting post that I read some time ago on Daniel Uyi's blog: How To Take Actions Everyday .
    keep up the good work friend. I will be back to read more of your posts.


  4. E-heh-heh. This is a clumsy attempt to pulling the owl on globe.
    Burning time - 2 seconds - everybody knows it.

    فلاش داريا هااام تصوير مسار أحد صواريخ أرض أرض

    What will happen to UMLACA and the old Soviet engine "Grad" - see "". Only 2.5 kilometers from the real engine, not fantasy.

    Dear Moses von Brown, do not believe - John deceive you.

    1. How come this one burns for clearly more than 2 seconds then?

    2. Sometimes its best to keep things simple. This video is just the type of signature I would expect when you bolt the equivalent of a small/medium sized (filled) trashcan to the front of a 122mm or equivalent rocket motor. The reduced range should be no surprise either.

    3. BM - your example has a maximum 4 second burn based on audio - and even that is suspect as the missile is at least trans-sonic if not supersonic at the very end part of the burn

    4. "How come this one burns for clearly more than 2 seconds then? "

      Good question.
      In my opinion, it was two different missiles, judging engine exhaust (see And in fact, there was a rocket bigger than UMLACA.

    5. The video shows a burn time of 3 seconds (or more), which is the same burn time seen in the Liwa Al Islam videos.
      In any case, burn time is not that important for range. long burn times mean less drag but more gravity impact and vice versa. These two effects mostly cancel each other.

    6. "a burn time of 3 seconds (or more), which is the same burn time seen in the Liwa Al Islam videos."
      There was also 2 seconds - just seen "tracer" at night. If we assume that sound should be taken into account - the rocket has flown several hundred meters.

  5. Enough of your fraudulent 'revelations' Brown Moses. It is anti-Assad forces that are stopping inspectors visiting the last two chemical weapons sites in Syria. If these 'innocent rebels' really were the victims of a chemical attack it would be in their interests to be rid of them. All your feeble analysis' and YouTube phoney videos cannot change the reality on the ground in Syria.

    1. Perhaps we should do a bit of linguistic analysis of rebuttals published under anglo-saxon names, to see if the author is a native English speaker.

  6. "It should, however, be pointed out that most rocket artillery motors have a quite short burn time – usually less than 3 seconds. This is contrary to the impression one might get when observing rocket artillery. After this short time, the rocket may still burn and eject smoke, but just slivers of propellant are burning and the acceleration is very weak or completely absent." The Rocket Artillery Handbook, Ove Dullum.
    Norwegian Defence Research Establishment 2010.

  7. Hello, I found UMLACA launch video posted by Asad's NDF:


    1. Nice find!!!
      This one also shows a 3 second burn time.
      It's hard to estimate size here, but it looks like this is the giant UMLACA version seen in the "red berets" version. It also seems to have the small nose cone of the giant UMLACA.

    2. Fantastic find, I love it when they do that, shame they don't show the launch platform.

    3. I'd agree with your assessment, Sasa wawa, it does seem to be the larger type, the proportions seem a bit different from other versions, and it has that rounded nose cone.

  8. Here's the reply of the author of the report:

    Thanks to Sasa Wawa for his feedback! A point of clarification – the purpose of this study was to identify what flight distances can be ruled out at implausible. Travel distances are intentionally aggressive. I stand by my finding that ranges in excess of 15 km can be ruled out as implausible, but that a launch from 9.6 km is indeed possible.

    Here are some replies. Italics are quotes from myself and from Bold are my responses.

    1. "Assuming very short burn times (and wrongly stating that such an assumption is conservative). Drag increases as a function of more than the square of the velocity, and as a result the thrust of the rocket motor over time is a crucial consideration." Response: Not sure to which analysis this relates, but the most recent analysis (method 5 above) uses a burn time of 3 seconds, which is what is seen in the Liwa Al-Islam videos. Claiming that the UMLACA has an optimal thrust curve is highly doubtful when the rocket is obviously not optimized for range (e.g. high diameter, thick steel body, discontinuity in shape, non-aerodynamic fins). However, for calculating an upper theoretical limit, I don't mind assuming this is the case. So far a few experiments I did with thrust curves hardly affected range, and in the OpenRocket models provided by John, the effect seems to be about 5%. This is probably since longer burn times also mean longer flight times, which result in more gravity impact.
    A - Gravity drag is less significant for a blunt-nosed rocket with a Cd of around 1. Any thrust that would accelerate a more streamlined body to above ~M0.8 is wasted on the extremely high drag forces. For lower Cd's, the length of the thrust curve does indeed become a less significant of factor. The fins did not seem that bad to me.

    2. "Using hobby rocketry engines as the basis of design. By extension, underestimating the propellant mass and specific impulse." Response: This was shown to be incorrect. In the discussion below with Scarlet Pimpernell three Grad rockets were shown to have a specific impulse that is similar or lower than the OpenRocket engines.
    A - The source for specific impulse was provided in the study; 260 s is a high but plausible specific impulse for a solid rocket. Using literature to identify performance criteria is a more robust means of analysis than comparing with a single model of rocket or comparing with specific impulses of a few hobby rockets.

    3. "Miscalculating the center of drag, severely underestimating the rocket's stability." Response: I assume this relates to Method 1 above. I haven't checked yet but agree that this could be the case. However, Method 5 assumes an optimal trajectory with no loss to instabilities and reaches a similar range.
    A - Unfortunately Sasa Wawa's spreadsheet treats Cd as a constant, which is not valid for speeds above M0.7. This is not problematic at subsonic velocities, but is a problem when comparing results with a supersonic projectile such as the Grad.
    We appear to agree that the rocket is effectively stable.

    4. "Failure to consider wind direction, elevation above sea level, or air temperature." Response: Wind and temperature were indeed ignored since they have negligible effect. Elevation was incorrectly ignored in Method 1, but this was corrected in Method 5.
    As noted elsewhere, the spreadsheet has its own problems. For ~60 second flight times, ignoring wind will generate over 5% error (comparable to the volume fraction issue you pointed out).

    1. Responses part 2:

      1. Propellant Mass - Here I believe I found a major oversight. John assumes that all of the engine's volume is filled with fuel. This is never the case. A large part of the volume is composed of voids designed to control the thrust curve (see examples here and on page 35 here). By comparing the propellant mass of the largest engines in OpenRocket to their volume, I found the average portion of volume used is 0.62 (assuming 2.5 mm casing and after filtering engines with special thrust curves that can be below 0.5), with the highest being 0.69. I assumed 0.65 in Method 5, but will gladly update it based on reliable evidence. Just to prove the UMLACA is not filled to capacity: Typical burn speeds of propellants ("regression rates") are below 10 mm/sec. This would mean that if the UMLACA was filled to capacity, its engine would take over 3 minutes to burn (and would probably never take off). Another small correction: The UN report gives a rocket length of 2.04 m (1.34 + 0.7), from which the booster charge and nozzle should be deducted. I estimated 1.8m for the engine length, and 1.9m in the optimistic scenario.
      A - Technically, purely end-burning rockets do exist though I agree that the UMLACA is not an example. I did consider the volume ratio and ignored it as insignificant, but I should have noted and justified this assumption. Please note that hobby rockets have much lower volume fractions than heavier rockets; Zandbergen suggests a Kv of 0.8-0.95. More specifically, a dual-thrust configuration such as I proposed can have excellent volume fractions; see Himanshu Shekhar's Burn-back Equations for High Volumetric Loading Single-grain Dual-thrust Rocket Propellant Configuration for a more involved analysis. For the curves I proposed (roughly 5:1 boost:sustain thrust ratio), a Kv of 0.95 is appropriate. While 10mm/s is a quite typical regression rate, as I alluded in my report the rate can be varied by around an order or magnitude. It is indeed quite plausible to design a rocket of the dimensions described, with a volume fraction near unity and a burn time on the order of 30 seconds.

      Another contributor suggested that all military rockets have multiple, tubular grains; this is demonstrably false.

      2. Specific Impulse - 2550 Ns/kg is an extreme example. The analysis of the three Grad rockets mentioned above shows a range of 1937-2272, and the largest engines in OpenRocket and ThrustCurve are 1966-2272.

      A - 2550 N*s/kg (260 s) is a high-performance but plausible specific impulse, broadly supported by literature. The intent of this report was to make aggressive assumptions to establish the maximum plausible range.

      Together with the overestimation of the propellant's mass above, this results in a Total Impulse value of 90000 Ns, which is twice my most optimistic estimate of 46000.

      A - In my opinion, 46 kN*s is not the highest plausible impulse for a rocket with these external dimensions. Time permitting, I can update the rocket curves to account for the volume fraction I ignored, bringing the impulse down to ~85 kN*s. An important correction, but not enough to substantially change the conclusions.

    2. Responses part 3

      3. Environmental Considerations - Generally agree. Small correction: Elevation in Zamalka is 700m, not 760.
      4. OpenRocket model - A few minor corrections: (a) According to the UN, warhead diameter is 360mm and not 350mm. (b) Body tube length is 1.34m and not 1.55m. (c) Sarin weight is 60kg and not 50kg (56 liters). (d) The warhead's inner tube is missing. (e) The two thick steel plates on both sides of the warhead are missing (around 10mm?). (f) The thick steel blast plate is missing (over 70mm). Images here.

      A - The dimensions were based largely on the HRW report. The UN report goes out of its way to point out the dimensions are approximate. The 56 L volume was +/- 6 L, less the container wall thickness and any "unknown components." The two larger plates are included as the transition pieces, which I made 8 mm thick.

      My impression is that none of these mass or dimensional adjustments (save external diameter, which appears to be within the margin for measurement error) have a significant impact on ballistics. Would you agree?

      5. Fin Layout - I like the idea of adding the ring to the fins' area.
      6. Drag - This is the most important part of the calculation. First, as shown above there are good reasons to assume no nose cone is used: (a) There doesn't seem to be one in the videos we have, (b) no remains were found in any impact site, despite minor damage to all other parts, and (c) other features of the UMLACA were not optimized for range (high diameter, thick steel body, discontinuity in shape, non-aerodynamic fins) so there is no reason to assume this was done for the nose cone.

      A - Yes, the only physical indication that there might be the means to control drag is the ring of threaded holes around the front plate. Videos of a related weapon flying short distances would not be expected to have drag modifications if they do exist, and since the purpose of the study is to determine what ranges can be ruled out as implausible. The front portion of the UMLACA is heavily damaged upon use, so again it is plausible that a light weight nose cone would separate from the warhead on detonation or be damaged beyond recognition upon being driven into the ground by the body of the munition. Difficult to prove the negative in this case, unfortunately.

      Even if we do assume a nose cone, OpenRocket's drag coefficient estimate of 0.21 is wrong. As mentioned above, model rockets are 0.75, and a bullet is 0.3.

      A - A handgun bullet such as a 9mm parabellum would be around 0.3 subsonic Cd. A more streamlined bullet such as match-grade rifle bullet would be about 0.3 at supersonic speeds, and around 0.13 at subsonic velocity.

    3. Responses part 4
      A coefficient of 0.21 would be a very aerodynamic rocket, which is definitely not the case here. When looking at the drag calculation by component (in Analyze/Component Analysis), the inaccuracy becomes obvious: it gives the half-spherical nose cone a drag coefficient of 0.01 (!), while here a half sphere is estimated at 0.42.

      A - Your summary here is egregiously incorrect. A Cd of 0.42 for a half sphere is for just that – a half sphere flying through the air. Most of the drag the Reynolds numbers encountered during subsonic flight would be from air being whipped past the sharp edge and forming a turbulent, low pressure region behind the projectile. The UMLACA is not a flying half sphere. At subsonic speeds, the pressure drag on a spherical nose cone is indeed negligible.

      The shape of the UMLACA with a nose cone at subsonic velocity appears to actually be surprisingly aerodynamic. It is effectively an ogive cylinder (extended ogive nose cones are not better than hemispherical at subsonic speeds) with an extended 120mm rocket portion that I think may result in less drag than a blunt full-bore tail. Just a plain ogive cylinder with no extended tail has a subsonic Cd of around 0.15 (Heinrich 18).

      So, based on my experience the subsonic Cd of a UMLACA passes a "sniff test", but there is some complex physics going on here and drag is frequently counter-intuitive. There are three ways to verify the drag coefficient – computer modelling, wind tunnel testing, or test firing. Unfortunately I do not currently have access to the appropriate software to do an off-the-clock test like this (and without knowledge of the geometry of the actual weapons used, any study would still be conjecture). If someone, perhaps affiliated with a school program, has access to an appropriate product it could add a very interesting data point with respect both to the Cd and the air flow around the fins.

      Since there seems to be a bug in the drag calculation module, I suggest we use the spreadsheet in Method 5 above from now on, instead of OpenRocket. It also allows more visibility into the calculations.

      A - For reasons listed above, the spreadsheet is not accurate for velocities above Mach 0.7.

      Update: Amund Hesbol has communicated with OpenRocket's developer, who confirmed that the drag calculations for such a non-standard design are unreliable.

      A - Obviously if the designer of the software has reservations it should give us pause (I did note in my study that the drag modelling may not be fully accurate). Nevertheless, as summarized above I think a subsonic Cd of less than 0.25 is plausible for the munition with nose cone.

    4. Responses part 5
      Additionally, the analysis has the following shortcomings:
      1. No sanity checks are given for the assumptions made in the simulation. For the results to be trusted, they should be applied to known artillery rockets (e.g. as I did for Falaq-2) and show that they give the true results. John - would be great if you can prepare a few.

      A - As discussed above, the UMLACA rocket is an unusual shape. The fact that some artillery rockets have shorter ranges is not evidence that another rocket may have longer range. Similarly, it probably is possible to select a thrust curve that propels the Falaq-2 more than 10.8 km. The designers probably did not do this for other reasons, such as time-on-target and accuracy. This does not mean that it is implausible that a modified Falaq-2 could hit a target 15 km away.

      2. It ignores the two videos we have, in which the UMLACA flies less than 2.5 km, despite its trajectory not being exceptionally shallow or high (as evident by the rocket's apparent velocity and sound level).

      A - These videos are not of the actual weapons used in the attack, so there is no reason to think that they would be identical to the August 21 weapons. In particular, it would be more important to target high explosive weapons accurately. In any case, an example of the rocket flying a shorter distance does not make a longer flight implausible.

      3. It fails to explain how a rocket with a significantly smaller engine and worse aerodynamics than the Falaq-2 manages to travel a longer distance (15 km compared to 10.8).

      A - The Falaq-2 is a different rocket. It travels at supersonic speed and has a heavier payload. There is no reason to think that two very different vehicles must have ranges proportional to any superficial characteristic such as launch mass. As discussed above, the UMLACA with a nose cone may have subsonic drag performance comparable to a rocket with more "streamlined" appearance.

      Summary: John Minthorne's analysis overestimates the engine's total impulse by a factor of 2, and the drag coefficient by a factor of around 4. Once corrected, range estimates should be similar to all other analyses.

      Once again, I'm excited that this discussion is happening. John has improved on my analysis in sev

    5. Oops, cut the last bit off, it's "Once again, I'm excited that this discussion is happening. John has improved on my analysis in several points, and I hope that he too will incorporate the feedback I provided, leading to an overall better and more reliable result.

      A - While I do not share your feelings about my analysis, I do also enjoy the discussion."

    6. What a cornucopia of dissimulation and ass-covering to support a fantasy theory that at its heart is politically driven to implicate if at all possible the SAA in the Ghouta gas incident.

      The ground-truth is that NO examples of this type of missile have ever been observed to fire more than 3km, and all known examples have burn times in the range 1-4 seconds, predominately 3 seconds and less.

      The author would have us believe that on the night of August 20/21 the SAA suddenly unleashed an entirely new type of missile with a completely different type of warhead and payload, and that, despite very strong similarities and dimensions to known instances, managed to fly 9.5 up to 15 km on its first flight! That is at least three and up to 5 times further than ever recorded!

      yeah - right!

    7. Charles, unless you can act in a civil manner I'm just going to delete all your posts. Try to follow sasa wawa's example.

    8. As politely as possible, can simply explain how a missile type of known range and capacities can suddenly, and crucially, develop three to five times the range and then land with extraordinary range precision - a most a few hundred metres variance - a tiny percentage of the range and not ever seen before in unguided missiles.

      Can you explain how that is a better answer than a missile type fired at typical short ranges achieving typical variance in range?

    9. As neither a rocket scientist or engineer I'm not qualified to do so, but John Minthorne is more qualified to do so, and he's give his answers in great detail. Based on his answers it seems the presence of a nose cone seems to make a significant difference in the range, and we've seen videos where a nose cone is both absent and present.

    10. So you are saying the SAA added a secret nose-cone - none of which have been found in Ghouta - that miraculously tripled or pentupled the range?

      The simulations show nose-cones add to a range that is abysmal without them - maybe 1500 metres (similar to the SLUFAE). With a nose-cone the range can sometimes get up to 2500 metres (I know, I've run many dozens of models over a wide spectrum of weight, thrust curves, physical dimensions, and fin arrangement)

      You now say that the 2500m range can suddenly extend to 9500 - 15,000 metres by adding a different nose-cone? Really!

      The harsh reality is that the dimensions of the rocket tube dictate the total impulse. That can be frigged with a bit to balance thrust vs time, but not much. You throw a missile in the air at - according to your correspondent - subsonic speeds and expect it to fly huge distances after its motor burns out at 3, max 4 seconds?

      Your correspondent also is obviously unfamiliar with conventional rocket artillery. They all use grains with a cavity to get high impulse. They also manipulate the oxidiser grain size profile to get specific burn profiles - as a balance between burn pressure and container strength (weight). The only military rockets I can think of that don't use grain cavities (or at least very sparingly) are the RPG-7 and various long range anti-tank missiles where the rockets are used as a velocity sustainer in essentially a flat ballistic trajectory.

    11. Thanks again. My response:

    12. Update: Just got an expert opinion. Nose cone could get drag to 0.6-0.7, and range to 3.9 km. More here:

    13. sasa,

      Nose cones do help but the ground-truth is there are no nose-cones, specifically in the ghouta Eskimos. They are irrelevant to any statement about range of the Ghouta missiles.

    14. I agree, but at this point we're discussing whether it's even possible that the rockets came from a Syrian base. So some unlikely assumptions are being made.

    15. — So some unlikely assumptions are being made.

      Only the green humanoid from a parallel universe can make such assumptions. We use the facts on our Earth.
      Can I see fragments of the nose fairing, found in Zamalra? - No - There is no need to invent new entities.

  9. John Minthorne

    Engineering Intern at Corbin Consulting Engineers

    Pursuing PE qualification and continuing a career in mechanical engineering.

    Semiconductor tool installations
    Basebuild feasibility studies and design
    Data center heat modeling and cooling design
    Process system flow modelling

    Rocket Science? Aerodynamics? Aircraft Engineering? Zip.

    1. "Rocket Science? Aerodynamics? Aircraft Engineering?"
      Please do not waste Your time on him - You can see right away - a rogue. Lazy rogue - he had not read anything on the topic. How he can take the "Eskimo" from Zamalka burning time 29 seconds, if the flight just 20 seconds?!

  10. The mutli-tubular propellant profiles presume a profile actually designed for an artillery rocket, when the propellant might have been manufactured for something else, like an air-air missile. In which case it might well be pre-cast cylinders with a single star-shaped hole down the middle.

    There can be huge differences in power due to chemistry changes:
    the CVR7 rocket is the same size as the older 68mm air to ground rockets it replaced, but produces double the energy. The motor in the Shorts/MBDA Starstreak missile is clearly very energetic indeed for its size, too.

    The first video of an UMLACA that was posted here, a while back, certainly appeared to show a very energetic exhaust.

    Commentators do need to remember that the article does indeed only attempt to determine what sort of range can absolutely be RULED OUT, rather than precisely what the range was. 2km does seem a bit short, but 15km does seem a reasonable figure, not for a practical maximum range, but for an absolute maximum range, above which any claim could be safely discounted.

    In terms of practical chemical warfare, it was done in WW1 using Stokes mortars with ranges in the hundreds of yards rather than miles, and the short range was actually desirable as they were trying to flood nearby trenches with gas prior to an assault.

    Ranges in the hundreds of miles, as with Scuds and the discontinued Argentinian Condor missile, tend to go hand in had with a very high speed of arrival which might destroy sarin, but possibly not more stable agents like VX.

    There's also the issue of knowing what you are aiming at and what you are hitting, and where the gas cloud is going after that. All of which tend to concentrate our attention on the sort of distance when an observer could see the effects from a hill or tall building within field telephone or walkie talkie distance of the launcher. (Field telephone would be wiser from the intelligence point of view.)

    No-one is accusing the UMLACA of any great accuracy, and even with an area warhead like sarin, I think the accuracy would be an issue over about 9km even if it could travel 15km.

    So if one approached things from the other end: what sort of range would the designer actually try to achieve? I'd suggest 5km to 8km for nay practical military effect, much further would make it a random terror weapon like a Scud or a V2.

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