tag:blogger.com,1999:blog-2675974463524895416.post7820812510866663302..comments2024-03-28T10:26:00.255-05:00Comments on An Ex Rocket Man's Take On It: Preliminary Acceleration Margins for Baseline PodGary Johnsonhttp://www.blogger.com/profile/06723964751681093047noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-2675974463524895416.post-19270287473238589942010-09-16T11:47:18.591-05:002010-09-16T11:47:18.591-05:00For Fatjohn 9-13 and 9-14: Sorry, I forgot how t...For Fatjohn 9-13 and 9-14: Sorry, I forgot how to tell you how to get fuel flow numbers. In the data I posted for any particular Mach-altitude point, there are both thrust (lb on a 1 sq.ft area engine, or really lb/sq.ft frontal thrust density for any size engine) and Isp (sec, which is really lb-sec/lbm) data. Divide thrust by Isp to get fuel flow rate in lbm/sec for the 1 sq.ft engine, or really lbm/sec-sq.ft for any size engine. The reference area is the outside of the biggest cross section, at the combustor.Gary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.comtag:blogger.com,1999:blog-2675974463524895416.post-80723431469759666102010-09-14T21:11:34.000-05:002010-09-14T21:11:34.000-05:00This one is for FatJohn 9-13 and 9-14: I'm no...This one is for FatJohn 9-13 and 9-14: I'm not so sure about going much lower in takeover Mach with the supersonic-designed ramjet inlet I used in my study. For one thing, the external shock detaches from the spike below Mach 4, drastically reducing air capture. <br /><br />As for rocket accelerations, we used 10 to 20 gees quite routinely in solid propellant missile work. <br /><br />GWJGary Johnsonhttps://www.blogger.com/profile/06723964751681093047noreply@blogger.comtag:blogger.com,1999:blog-2675974463524895416.post-57593936165084643772010-09-14T02:52:41.760-05:002010-09-14T02:52:41.760-05:00Edit: Based on more precise data: would it still b...Edit: Based on more precise data: would it still be a viable concept if ramjet takeover occurs at 27000 feet and burnout happens at 90000 feet at mach 5? Could one perhaps design the ramjet for takeover to occur at for example Mach 1.2 at 21000 feet? I do not see the advantage of having the ramjets attached after the self acceleration potential goes under 1, thus it would be essential to at least attain a self acceleration potential in excess of 1 during the entire burn. In fact using the ramjets as boosters, the self acceleration potential should be greater then the acceleration of the launcher which could be assumed to be about 4. Based on your graphs, this would only be the case for maybe a 15 second window, probably rendering my low acceleration concept inefficient.fatjohnhttps://www.blogger.com/profile/02659582537948618479noreply@blogger.comtag:blogger.com,1999:blog-2675974463524895416.post-15973697126948056352010-09-13T15:11:06.665-05:002010-09-13T15:11:06.665-05:00Hello, Mr Johnson, I have been working on analysin...Hello, Mr Johnson, I have been working on analysing rocket trajectories concerning gravity losses. As you may know gravity losses can be reduced by increasing the thrust/weight. <br /><br />Now unfortunately it seems that one just cannot have a rocket with an intitial thrust over weight of around 5 what you are proposing. This due to the economics of high thrust engines, the requirement to perform a fast pitch over to initiate a gravity turn under high stresses and low in the atmosphere, a much higher maximum dynamic pressure, increasing acceleration when using liquid rocket stages (satellites cannot bear the vibrations encountered at say 10 g's) and maybe others. <br /><br />Also, the idea of waiting until 80,000 feet and mach 6 to start your gravity turn does not make sense since you want to build up your circular velocity as soon as possible. But where I might find an application is to use ramjet engines at boosters to increase the acceleration from say 2.5 to 4g's after the maximum dynamic pressure is reached. However this peak is usually reached at 30,000 feet and at Mach 1, mach 1.5 is probably reached at 35-40000 feet. This indicates around a 30-40 seconds burn left untill the ramjets ceiling is reached. <br /><br />So, with this in mind, I have a few questions. Can other ramjet designs be made with a higher ceiling or starting at lower speeds? How much thrust can a ramjet deliver? To avoid clustering of jets, can a ramjet get near the 0.5-1 MN of thrust without getting too big (meaning +2 meters diameter and + 10 tonnes in mass?) How much fuel does a ramjet use per Newtonsecond or poundhour or whatever you use? And finally, what is your take on it? It would be nice to hear another view on my assumptions why high acceleration can't be done but please even if you disagree, also approach the question as if I'm right. Thank you very much.fatjohnhttps://www.blogger.com/profile/02659582537948618479noreply@blogger.com