Doug,
Thank you. Your note made me feel so much better because I felt a bit foolish I
could not figure this out :)
Also, thanks for the reference. I believe RPA published this as well and allows
the export of the curve but I hadn't found a way (yet) to see the actual
function. I had wanted the function so that I could add features like coolant
and outer wall dimensions.
Best,Graham
On Thu, Dec 1, 2016 at 7:58 PM, Doug Jones<djones@xxxxxxxx> wrote:
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
