Justin S. McFarland wrote: ><Anyone know why the main tank has a rounded bottom .vs. cone? My ><guess was the added mass and difficulty flowing the H2 into the ><shuttle overwhelmed the potential lower drag. > > >The aerodynamics for this object declare that a rounded bottom will not >propagate large shock waves as is the case for any sharp turn and >subsonically cause 'nasty' vortices. Granted I did not do CFD on it, but >that seems to be the general rule. > >For a cone to really 'work' the object should have a rocket beneath it. >This is because the exhaust plume actually "cleans-up" the aerodynamics. > >Sutton makes mention of this in that particular chapter. > Hey, good call; I hadn't thought of looking in Sutton for aero stuff.
I also notice table 4-3 that gives a Cd factor for a 0 degree AOA to be about 0.15 for the V2, varying with mach number (check it out if you've got Sutton, there's an awkward peak at mach 1.2 with Cd upto 0.4 that's mostly gone by mach 3). Wonder how this scales with size of rocket though- possibly small rockets have to worry about higher relative viscosity? OTOH I found a water rocket web page that implies that the Cd for a nose cone varies between 0.6 and 0.8 or so; and Randall was using 0.7 for his simulations (as was I). I'm wondering if this figure only works at low mach, and as mach goes up the Cd goes down, or whether there's a scaling law; but that's a bit speculative at this point. Anyway, if the Cd could be as low as 0.15 then my simulations should do much better on their race for orbit, I'll plug it in and try. I'm still wondering what Cd the Mockingbird would have faced at their smaller size. I also found a good link to some information on aerodynamics of hypersonic shapes: http://www.aerospaceweb.org/design/waverider/waverider.shtml There's an equation for a flat plate that gives Cd of about 0.15 or so for a 1 in 4 angle to the flow- I think a cone should be the same Cd. And of course the Roton used the cone shape. Conclusions? Nope. I must admit I'm a bit confused right now. I haven't managed to explain why some sources give a Cd of 0.7 and the V2 manages 0.15 according to Sutton, but atleast the hypersonic theory lines up with the V2. Anyone? ;-) >J. S. McFarland, Kittyhawk Technologies > >_______________________________________________ >ERPS-list mailing list >[EMAIL PROTECTED] >http://lists.erps.org/mailman/listinfo/erps-list > _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
