{"id":3508,"date":"2017-08-19T16:10:53","date_gmt":"2017-08-19T14:10:53","guid":{"rendered":"http:\/\/www.verticallimits.nl\/?p=3508"},"modified":"2017-08-19T16:14:45","modified_gmt":"2017-08-19T14:14:45","slug":"giga-86mm-kilo-12g-cato-final-thoughts","status":"publish","type":"post","link":"https:\/\/www.verticallimits.nl\/?p=3508","title":{"rendered":"GIGA 86mm &#8211; KILO 12G CATO Final thoughts"},"content":{"rendered":"<p>Final thoughts on the CATO \/ overpressurization&nbsp;of the KILO 12G&nbsp;KNSB&nbsp;motor at the LRE 2017 launch:<\/p>\n<ul>\n<li>The motor had&nbsp;a very conservative port-to-throat area ratio&nbsp;of 1.5 to prevent velocity based erosive burning. This resulted in a higher than necessary,&nbsp;&nbsp;Kn<sub>average<\/sub>&nbsp;of 700 and thus higher Maximum Expected Operating Pressure (MEOP).<\/li>\n<li>Mass flux based erosive burning. Little has been described&nbsp;about this phenomenon and KNSB&nbsp;or &#8220;candy&#8221; propellants&nbsp;although it&#8217;s widely known among the APCP&nbsp;community. There is an informative article about both velocity and mass flux based erosive burning called: &#8220;Erosive burning design criteria &#8211;&nbsp;Charles Rogers&#8221;. By modifying the SRM&nbsp;2014 excel file I was able to calculate the mass flux for the&nbsp;KILO 12G&nbsp;KNSB motor at:\n<ul>\n<li>KNSB&nbsp;coarse: 5,15gr\/s-mm<sup>2<\/sup><\/li>\n<li>KNSB&nbsp;fine: 6,87gr\/s-mm<sup>2<\/sup><\/li>\n<li>As an&nbsp;example, maximum mass flux for APCP&nbsp;at 55-96bar is approximately 1,41-2,11 gr\/s-mm<sup>2<\/sup><br \/>\n&nbsp;Although my gut feeling says that KNSB&nbsp;and candy propellants in general are not very susceptible&nbsp;to mass flux based erosive burning, the above mentioned figures might be&nbsp;a bit on the aggressive&nbsp;side.<\/li>\n<\/ul>\n<\/li>\n<li>It appears&nbsp;the &#8220;KNSB&nbsp;coarse&#8221; propellant burn rate&nbsp;in SRM&nbsp;2014 software isn&#8217;t as well documented as the &#8220;KNSB&nbsp;fine&#8221; propellant. Although it provided&nbsp;accurate&nbsp;simulations on the KILO 6G&nbsp;motor,&nbsp;I suspect it isn&#8217;t properly&nbsp;characterized at a Kn of 700 \/ chamber pressure of 100bar. Keeping the same motor configuration but only changing the KNSB&nbsp;propellant from coarse to fine resulted in an increase of the MEOP&nbsp;from 98 to 130bar. Since the casing (theoretically) starts to yield at 110bar&nbsp;and bursts at 160bar. I suspect a higher than 110bar&nbsp;chamber pressure, shortly after ignition, caused the motor&nbsp;to overpressurize.<\/li>\n<li>Collapse of the bottom grain \/ casting tube&nbsp;due to the high G-forces&nbsp;causing nozzle blockage&nbsp;thereby overpressurizing the motor.<\/li>\n<li>(micro) Fractures in the propellant due to the &lt;0\u00b0C temperatures at night thereby increasing the burning area.<\/li>\n<li>In any of the above mentioned cases, the safety margin on the design pressure and the yield pressure of the casing, without static testing, proved to be too small.<\/li>\n<li>As a note: the grains were some of the nicest grains I cast with a very high density (average density ratio&nbsp;of 0,983) due to the spring-loaded&nbsp;mold design.&nbsp;Motor assemble went without a hick-up, nothing was forced and the liner fitted perfectly with no buckling. With confidence I can say the failure is not related to any of these items. Furthermore the casing ruptured in a typical hoop failure manner. Initiation appeared to be about 2 grains from the forward closure side of the motor. Since the casing failed it is expected that there was a chamber pressure exceeding 150-160bar. The forward closure remained in place with no blow-by validating both&nbsp;the forward bulkhead retention, as well as the o-ring&nbsp;design.<\/li>\n<\/ul>\n<p>I will machine another nearly identical&nbsp;motor,&nbsp;make some minor alterations and static test this motor in September 2017.<\/p>\nngg_shortcode_0_placeholder\n","protected":false},"excerpt":{"rendered":"<p>Final thoughts on the CATO \/ overpressurization&nbsp;of the KILO 12G&nbsp;KNSB&nbsp;motor at the LRE 2017 launch: The motor had&nbsp;a very conservative port-to-throat area ratio&nbsp;of 1.5 to prevent velocity based erosive burning. This resulted in a higher than necessary,&nbsp;&nbsp;Knaverage&nbsp;of 700 and thus higher Maximum Expected Operating Pressure (MEOP). Mass flux based erosive burning. Little has been described&nbsp;about<\/p>\n<p><a href=\"https:\/\/www.verticallimits.nl\/?p=3508\" class=\"more-link themebutton\">Read More<\/a><\/p>\n","protected":false},"author":5,"featured_media":3519,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"footnotes":""},"categories":[7],"tags":[38,37],"_links":{"self":[{"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/posts\/3508"}],"collection":[{"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3508"}],"version-history":[{"count":18,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/posts\/3508\/revisions"}],"predecessor-version":[{"id":3536,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/posts\/3508\/revisions\/3536"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=\/wp\/v2\/media\/3519"}],"wp:attachment":[{"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3508"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3508"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.verticallimits.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3508"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}