I thrashed on that problem off and on for more than a decade, and never
could replicate the method from the published literature. I use ONC from
Sierra Engineering, and I can guarantee you the shapes it generates are
not parabolas in any way, shape or form.
http://www.sierraengineering.com/ONC/onc.html
Doug Jones, Chief Test Engineer
XCOR Aerospace
1325 Sabovich
Mojave CA 93501
(661) 824-4714 x117
cell 661 313-0584
On 12/1/2016 4:00 PM, Graham Sortino (Redacted sender gnsortino for
DMARC) wrote:
I was wondering if anyone could point me towards an example of how to fit a function to G.V.R. Rao’s parabolic approximation of a bell nozzle given the initial angle θn and corresponding start point as well as final angle θe and point?
I’ve been following through the example on page 83 of Huzel and Huang https://books.google.com/books?id=TKdIbLX51NQC&lpg=PA76&ots=slcXbGfst7&dq=modern%20design%20initial%20parabolic-contour%20wall%20angles&pg=PA83#v=onepage&q=modern%20design%20initial%20parabolic-contour%20wall%20angles&f=false
... which uses θn=27.4 (x,y) = 21.9,12.99 and θe=9.8 (x,y)= 102.4,46.7 but it leaves out an example of how this is actually solved. Presumably because it is so trivial but I’m getting a bit stuck on it. I believe an example of this can be found in the Rao paper "Approximation of Optimum Thrust Nozzle Contour", however, I cannot seem to find a copy online so I was attempting to work this out on my own.
I understand a parabola can be calculated via several methods including via 3 points, which I could have if I use the top and bottom portions of the curve or if I assume the vertex to be the middle of the throat. However, I’m thinking that what is intended is that I’m supposed to use only the two points and angles (eg. slopes) to calculate and it wasn’t clear to me how this should be done.
Kind Regards,
Graham
