Quote:
Originally Posted by Tesla
I understand what you are saying with the commercial restrictions, but even within that is the fact that all the work that has gone into that area indicates that a flat plate angle of 12-15° is around the optimum in that application, there would be no difference in cost or inconvenience to set flat plate boat tails to 5° if that was found to be the optimum angle in that application.
There is no argument that an extended boat tail along the lines of the template would be a far superior option, but where there is a length restriction there seems to be more effective outcomes by using a more aggressive angle, how much of this is due to the boattail effect, base cavity wake seperation or other effect I don't know, but all the evidence points to a superior outcome when such restrictions are in place.
Admittedly the best results achieved are usually only in the 5-10% range for FE, so there is obviously a lot more scope for improvementsand this may well follow the lines of the dryden van where progressive curvature was used rather than straight panel, but it still appears that if you can't go beyond the 20% mark in length then a more aggressive approach may yield the best improvement in FE.
I still haven't been able to locate any reasonable info on the GM "Optimum" tail you have mentioned a number of times, but still looking around every now and then.
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*The GM 'OPTIMUM' tail is very much like the last boat tail shown in the 15th graphic of #248(permalink),page 25,of the 'boat-tail-trailer' thread.
*This configuration yielded Cd 0.214 for the basic trailer van body sans wheels in ground proximity.
*With wheels,you might expect the drag to rise to Cd o.264 with wheels on the ground.
*Which would leave an additional streamlining potential of 54% on the table.
*Baron von Koenig-Fachsenfeld measured Cd 0.159 for a 1936 Omnibus,intercity passenger bus model with a near-'Template',extensible boat tail.
*The 1987 Renault V.I.R.A.G.E. measured Cd 0.29 with the 'longest' boat tail they tested.
*Walter Korff suggested Cd 0.20 for his more organic design of the early 60s.
*If you'd like to see GM's actual work,I'd contact the university and find out how they got it.Or perhaps the public information office at GM's headquarters.