tag:blogger.com,1999:blog-4871088750473093560.post3752601173463941906..comments2024-02-19T11:10:16.893-08:00Comments on Brown Moses Blog: A Detailed Examination Of The Range Of Munitions Used In The August 21st Sarin AttackBrown Moseshttp://www.blogger.com/profile/17562126209980810351noreply@blogger.comBlogger38125tag:blogger.com,1999:blog-4871088750473093560.post-85992941230168774182013-11-14T11:52:42.737-08:002013-11-14T11:52:42.737-08:00now your search for online money ends here, you to...now your search for online money ends here, you too can start earning cool commissions today. click on the link below for more info. <br />http://www.50dollarJob.com/index.php?refer=21697Anonymoushttps://www.blogger.com/profile/03093122277902667252noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-60986031234392461922013-11-08T02:25:50.489-08:002013-11-08T02:25:50.489-08:00Hi
Nice one! I like the outfit of the characters. ...Hi<br />Nice one! I like the outfit of the characters. Wish i could do the same thing too but im not that techie.i like the outfit of “from farmer to warden”.. really interesting <a href=" http://dandjstudio.com/”>wedding photography Seattle</a>Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-43735520179919620942013-11-01T07:59:23.226-07:002013-11-01T07:59:23.226-07:00— So some unlikely assumptions are being made.
On...<i>— So some unlikely assumptions are being made.</i><br /><br />Only the green humanoid from a parallel universe can make such assumptions. We use the facts on our Earth. <br />Can I see fragments of <b>the nose fairing</b>, found in Zamalra? - No - There is no need to invent new entities.Lucumhttps://www.blogger.com/profile/07601047267335818966noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-84021540229140367562013-11-01T05:57:27.974-07:002013-11-01T05:57:27.974-07:00I agree, but at this point we're discussing wh...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.Anonymoushttps://www.blogger.com/profile/16560859391032391947noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-55204900953656553682013-11-01T03:34:50.610-07:002013-11-01T03:34:50.610-07:00sasa,
Nose cones do help but the ground-truth is ...sasa,<br /><br />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.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-13478018096197517292013-10-31T18:56:15.854-07:002013-10-31T18:56:15.854-07:00Update: Just got an expert opinion. Nose cone coul...Update: Just got an expert opinion. Nose cone could get drag to 0.6-0.7, and range to 3.9 km. More here: http://whoghouta.blogspot.com/2013/09/umlaca-simulation.htmlAnonymoushttps://www.blogger.com/profile/16560859391032391947noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-25608303062024924862013-10-31T15:00:42.517-07:002013-10-31T15:00:42.517-07:00"Rocket Science? Aerodynamics? Aircraft Engin...<i>"Rocket Science? Aerodynamics? Aircraft Engineering?"</i><br />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?!Lucumhttps://www.blogger.com/profile/07601047267335818966noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-41127297996192352912013-10-31T05:52:43.166-07:002013-10-31T05:52:43.166-07:00The mutli-tubular propellant profiles presume a pr...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.<br /><br />There can be huge differences in power due to chemistry changes:<br />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. <br /><br />The first video of an UMLACA that was posted here, a while back, certainly appeared to show a very energetic exhaust.<br /><br />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.<br /><br />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. <br /><br />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. <br /><br />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.)<br /><br />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. <br /><br />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. <br /> Medawarhttps://www.blogger.com/profile/05119173935699236303noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-40901405828510983632013-10-31T05:31:57.150-07:002013-10-31T05:31:57.150-07:00Perhaps we should do a bit of linguistic analysis ...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.Medawarhttps://www.blogger.com/profile/05119173935699236303noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-12812072063055472112013-10-31T03:22:03.802-07:002013-10-31T03:22:03.802-07:00John Minthorne
Engineering Intern at Corbin Consu...John Minthorne<br /><br />Engineering Intern at Corbin Consulting Engineers <br /><br />Pursuing PE qualification and continuing a career in mechanical engineering.<br />Specialties<br /><br />Semiconductor tool installations<br />Basebuild feasibility studies and design<br />Data center heat modeling and cooling design<br />Process system flow modelling<br /><br />http://www.linkedin.com/pub/john-minthorne/12/548/870<br /><br />Rocket Science? Aerodynamics? Aircraft Engineering? Zip.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-33449518619890256972013-10-29T23:38:41.629-07:002013-10-29T23:38:41.629-07:00"a burn time of 3 seconds (or more), which is...<i>"a burn time of 3 seconds (or more), which is the same burn time seen in the Liwa Al Islam videos."</i><br />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.Lucumhttps://www.blogger.com/profile/07601047267335818966noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-29607892834007785052013-10-29T21:51:53.220-07:002013-10-29T21:51:53.220-07:00Thanks again. My response:
http://whoghouta.blogsp...Thanks again. My response:<br />http://whoghouta.blogspot.com/2013/09/umlaca-simulation.htmlAnonymoushttps://www.blogger.com/profile/16560859391032391947noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-69930349930381103032013-10-29T04:45:18.832-07:002013-10-29T04:45:18.832-07:00So you are saying the SAA added a secret nose-cone...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?<br /><br />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)<br /><br />You now say that the 2500m range can suddenly extend to 9500 - 15,000 metres by adding a different nose-cone? Really!<br /><br />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?<br /><br />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.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-49859147964140575202013-10-29T04:18:52.050-07:002013-10-29T04:18:52.050-07:00As neither a rocket scientist or engineer I'm ...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.Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-41149814655034196302013-10-29T03:54:59.706-07:002013-10-29T03:54:59.706-07:00As politely as possible, can simply explain how a ...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.<br /><br />Can you explain how that is a better answer than a missile type fired at typical short ranges achieving typical variance in range?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-43545388155373866972013-10-29T03:43:44.778-07:002013-10-29T03:43:44.778-07:00Charles, unless you can act in a civil manner I...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.Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-69610157609163878982013-10-29T03:24:32.933-07:002013-10-29T03:24:32.933-07:00What a cornucopia of dissimulation and ass-coverin...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.<br /><br />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.<br /><br />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!<br /><br />yeah - right!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-72638861146629948912013-10-29T01:32:06.440-07:002013-10-29T01:32:06.440-07:00Oops, cut the last bit off, it's "Once ag...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.<br /><br />A - While I do not share your feelings about my analysis, I do also enjoy the discussion."Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-25619741860895776562013-10-29T01:31:19.470-07:002013-10-29T01:31:19.470-07:00Responses part 5
Additionally, the analysis has th...Responses part 5<br />Additionally, the analysis has the following shortcomings:<br />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.<br /><br />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.<br /><br />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).<br /><br />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.<br /><br />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).<br /><br />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.<br /><br />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.<br /><br />Once again, I'm excited that this discussion is happening. John has improved on my analysis in sevBrown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-81259522756492199472013-10-29T01:31:01.346-07:002013-10-29T01:31:01.346-07:00Responses part 4
A coefficient of 0.21 would be a ...Responses part 4<br />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.<br /><br />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.<br /><br />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).<br /><br />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.<br /><br />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.<br /><br />A - For reasons listed above, the spreadsheet is not accurate for velocities above Mach 0.7. <br /><br />Update: Amund Hesbol has communicated with OpenRocket's developer, who confirmed that the drag calculations for such a non-standard design are unreliable.<br /><br />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.<br />Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-19478682393807056192013-10-29T01:30:39.672-07:002013-10-29T01:30:39.672-07:00Responses part 3
3. Environmental Considerations ...Responses part 3<br /><br />3. Environmental Considerations - Generally agree. Small correction: Elevation in Zamalka is 700m, not 760.<br />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.<br /><br />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.<br /><br />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?<br /><br />5. Fin Layout - I like the idea of adding the ring to the fins' area.<br />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.<br /><br />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.<br /><br />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. <br /><br />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.<br /><br />Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-48126513809596545492013-10-29T01:30:10.305-07:002013-10-29T01:30:10.305-07:00Responses part 2:
1. Propellant Mass - Here I bel...Responses part 2:<br /><br />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.<br />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.<br /><br />Another contributor suggested that all military rockets have multiple, tubular grains; this is demonstrably false.<br /><br />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.<br /><br />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.<br /><br />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.<br /><br />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.<br />Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-66008413366479961512013-10-29T01:28:12.964-07:002013-10-29T01:28:12.964-07:00Here's the reply of the author of the report:
...Here's the reply of the author of the report:<br /><br />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.<br /><br />Here are some replies. Italics are quotes from myself and from http://whoghouta.blogspot.com/2013/09/umlaca-simulation.html. Bold are my responses.<br /><br />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.<br />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.<br /><br />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.<br />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.<br /><br />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.<br />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.<br />We appear to agree that the rocket is effectively stable.<br /><br />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.<br />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).<br />Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-21964332557369942672013-10-29T01:11:50.327-07:002013-10-29T01:11:50.327-07:00I'd agree with your assessment, Sasa wawa, it ...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. Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.comtag:blogger.com,1999:blog-4871088750473093560.post-58313549576194863052013-10-29T00:41:30.802-07:002013-10-29T00:41:30.802-07:00Fantastic find, I love it when they do that, shame...Fantastic find, I love it when they do that, shame they don't show the launch platform.Brown Moseshttps://www.blogger.com/profile/17562126209980810351noreply@blogger.com