tag:blogger.com,1999:blog-5822805028291837738.post6758886360525441272..comments2023-12-09T03:51:33.158-05:00Comments on Various Consequences: Sears--Haack Body for Mini-EstesJoshua Stultshttp://www.blogger.com/profile/03506970399027046387noreply@blogger.comBlogger16125tag:blogger.com,1999:blog-5822805028291837738.post-55439525594729055332014-08-03T22:05:01.341-04:002014-08-03T22:05:01.341-04:00These look fun: disposable rocketsThese look fun: <a href="http://www.thingiverse.com/thing:340086" rel="nofollow">disposable rockets</a>Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-68498229964582822112013-03-27T17:14:19.693-04:002013-03-27T17:14:19.693-04:00Derivative model on thingiverse with improved atta...Derivative model on thingiverse with improved attachment for the fin: <a href="http://www.thingiverse.com/thing:66638" rel="nofollow">Rocket v1</a>Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-86330247486089320862012-07-21T13:54:13.394-04:002012-07-21T13:54:13.394-04:00The folks at RocketCrafters are using FDM to print...The folks at <a href="http://rocketcrafters.com" rel="nofollow">RocketCrafters</a> are <a href="http://www.stratasys.com/Resources/Case-Studies/Aerospace-FDM-Technology-Case-Studies/Rocket-Crafters-Inc.aspx" rel="nofollow">using FDM to print hybrid rocket fuel grains</a>.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-30991819324696290152012-07-17T13:02:46.109-04:002012-07-17T13:02:46.109-04:00The folks at Stanford have a tutorial up demonstra...The folks at Stanford have a tutorial up <a href="http://adl.stanford.edu/docs/display/SUSQUARED/Tutorial+8+-+Optimal+Shape+Design+of+a+Rotating+Airfoil" rel="nofollow">demonstrating shape optimization of a 2D airfoil to achieve minimum drag</a> (<i>wave</i> and <i>pressure</i>, but not <i>skin friction</i> since they are solving the inviscid governing equations).Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-64634798412372216202012-06-17T17:50:15.359-04:002012-06-17T17:50:15.359-04:00Another model rocket part on Thingiverse: fin fixt...Another model rocket part on Thingiverse: <a href="http://www.thingiverse.com/thing:24770" rel="nofollow">fin fixture</a>.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-64358737269668788142012-06-15T17:09:55.077-04:002012-06-15T17:09:55.077-04:00You're right that leading edge separation is a...You're right that leading edge separation is a problem. Nothing in flight maintains a constant angle of attack. I imagine a car would be able to maintain angle of attack at tighter tolerances, but wind blowing in any direction not parallel with the road will cause the same sort of problems in the side-slip plane. One of the other things that might make sharp edges attractive even at Mach<1 is really low Reynolds numbers (much lower than a car at high-way speeds). The answer, like most things, is "it depends".Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-26539093503122288782012-06-15T13:31:30.988-04:002012-06-15T13:31:30.988-04:00> Sharp edges only make sense for Mach>1.
I...> Sharp edges only make sense for Mach>1.<br /><br />I disagree. I've been frustrated by how much solid info I've been able to find, but I suspect a Sears Haack body is ideal at all speeds. It's just not as important at much lower speeds. I know the rounded front is popular for well below mach one, and I suspect it's probably good enough for most things, but I feel like that largely comes from people assuming wing shape is optimized for minimal drag, when the rounded leading edge of wings actually has more to do with avoiding sudden stalling as the angle of attack increases. <br /><br />Best point I can give you is how sharp the leading edges of solar race cars have gotten. And one of the problems with that is the sharper it gets, the more careful you need to be with exactly how high that edge is relative to the widest cross section. <br /><br />Most of my interest in aerodynamics is related to trying to design a ridiculous car: http://www.eternalmachinery.com/ecar/Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-13177058193093128792012-06-07T19:54:36.023-04:002012-06-07T19:54:36.023-04:00darxus, thanks for your comment. You're right...darxus, thanks for your comment. You're right; minimizing the wetted area is a good rule of thumb for streamlined bodies.<br /><br />I think there are lots of ways you could optimize the shape; the best way depends on what performance parameter you care about most.<br /><br />It's a little silly to begin with to use this shape for a mini-estes rocket. The shape is based on an area distribution for minimum <i>wave</i> drag. This is really not a factor for anything powered by a 1/2A Estes blackpowder motor. If you really want to optimize for this low Mach regime you'd likely have nice, big round leading edges (think of a teardrop). Sharp edges only make sense for Mach>1.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-75713763769850004232012-06-07T14:58:16.582-04:002012-06-07T14:58:16.582-04:00I don't know much about aerodynamics, but I...I don't know much about aerodynamics, but I've been very curious about these things.<br /><br />Wouldn't it be better to optimize for minimal surface area than volume (skin friction drag)? Maybe that comes out the same?<br /><br />And wouldn't it be better to wrap the engine in a cylinder of minimum width, then just cut off the front of a sears-haack body and stick that on the front of the cylinder? Minimize maximum cross section? If you need to wrap an aerodynamic shape around a cylinder, is there any reason not to have the center... cylindrical?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-81827835987240424632012-05-28T09:17:07.196-04:002012-05-28T09:17:07.196-04:00I found another mini-motor part on thingiverse: Pi...I found another mini-motor part on thingiverse: <a href="http://www.thingiverse.com/thing:15287" rel="nofollow">PicoRocket</a>.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-5171723780437139912012-05-27T20:19:01.711-04:002012-05-27T20:19:01.711-04:00Updated post to include Mk2 geometry, and more det...Updated post to include Mk2 geometry, and more details about Blender/Meshlab/Shapeways work-flow.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-35783106231499182282012-05-25T13:39:08.708-04:002012-05-25T13:39:08.708-04:00Updated post to include pictures of damage caused ...Updated post to include pictures of damage caused by static fire test.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-22696808053714627352012-05-24T20:22:01.007-04:002012-05-24T20:22:01.007-04:00Updated to include picture of Shapeways print in t...Updated to include picture of Shapeways print in their "Transparent--Detail" material.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-69629235199305412692012-05-23T18:34:15.723-04:002012-05-23T18:34:15.723-04:00Updated post to include motor fit check on ABS pri...Updated post to include motor fit check on ABS printed part: not quite ready for prime time.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-82944123613309742902012-05-19T12:06:44.191-04:002012-05-19T12:06:44.191-04:00Well, that original part had 0.35mm thick walls, a...Well, that original part had 0.35mm thick walls, and the minimum wall thickness Shapeways recommends for the white nylon material is 1mm. Here's <a href="http://www.shapeways.com/model/576519/mini_estes_sears_haack_ringfin_bin.html%22" rel="nofollow">an updated part</a> with thicker walls (and a ring fin!). I haven't even done a back of the envelope on the static stability, and it looks a little iffy, but I think I'm just going to print it and fly it.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.comtag:blogger.com,1999:blog-5822805028291837738.post-59798178894590003112012-05-13T16:09:20.515-04:002012-05-13T16:09:20.515-04:00The shapeways tutorials recommend leaving a hole s...The <a href="http://www.shapeways.com/tutorials/" rel="nofollow">shapeways tutorials</a> recommend leaving a hole so that the powder can be removed from interior cavities. So <a href="http://www.shapeways.com/model/569719/sears_haack_solid_scaled.html" rel="nofollow">this part</a> should work pretty well with the <a href="http://www.eos.info/en/products/materials/materials-for-plastic-systems/pa-22002201.html" rel="nofollow">selective laser sintering</a> process that they use. I ordered a couple out of their white nylon material, and their transparent material.Joshua Stultshttps://www.blogger.com/profile/03506970399027046387noreply@blogger.com