## Rocket Terms

### Rocket Terms

Quote:

>I think I know these, but would prefer a reality check.
>I'm running a Mac program that calculates center of pressure.
>It asked me for the following
>Semispan
>Mid chord
>Root chord
>Tip chord
>Sweep back distance
>Anybody like to define these for me before I assume the wrong thing!

|             | _  _  _  _  _  _  _  _  _  _
|             |\                         |         |
|             |  \                       |         |
|             |    \                     |         |
|             |      \                   |         |
|      .      |        \                 |         |
|      |      |          \               |         |
|      .      |            \             |         |
|      |      | _   _  _ \  _  _  |_       |
.      |\               \ _  _ \_  _  |_  _
|         \              |     |     \       \  Sweep
\            |     |       \  Root Chord
\          |     |
\        |     |
\      |     |
\    |     |
\  |     |_ _ Tip chord
\|  _|_ _ _
|<--------->|  Exposed Semi-Span
|<-------------->|  Semi-Span

The Root Chord is the length of the fin where it attaches to the body.

The "Semi-Span" used in the Barrowman equations is actually the
"Exposed Semi-Span", which is the distance perpendicular to the
body, from the body surface to the Tip Chord.

The true Semi-Span (which is NOT used in the Barrowman equations), is
the distance from the body centerline to the fin tip.  The full span
would be the distance from tip to tip.

The Tip Chord is the length of the fin tip.  Note that this length is
also parallel to the body. and the Root Chord. The straight Barrowman
equations on which the program is based only address strictly
trapezoidal fins with the tip parallel to the root.  For fins where
this is not the case, use an estimated Tip Chord (and possibly Span),
such that the trapezoid is approximately the same area as the real
fin.  Also try to keep the fore-aft area distribution of the estimate
about the same as the actual fin.

The Sweep is the longitudinal distance from the leading edge of the
Root Chord, to the leading edge of the Tip Chord.

The "Mid Chord" demonstrates an unfortunate limitation of the program
you're using..  Barrowman developed these equations in the slide-rule
days, and was striving to minimize the necessary calculations -
thereby taking the relatively easier route of measuring the mid-chord
span.  However this distance can be easily calculated from the other
dimensions, and many current Barrowman programs do that and do not
require this measurement or entry.  The Mid-Chord Span is the distance
from the center of the Root Chord to the center of the Tip Chord.

GC