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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to launcher missile systems and, more particularly,
to launcher tubes having means for reducing, or changing, the direction of
the tip-off rates of a launcher missile system.
It is well known that one of the contributing causes of dispersion of a
missile is the deflection imparted to the missile during emergence from
the launcher tube. This deflection is called "tip-off" and has been
considered in the prior art to be primarily a function of the
gravitational forces acting on the missile at a time when the missile
center of gravity has passed the forward end of the launcher tube causing
the missile to nose down and, the magnitude of the tip-off was expressed,
and still is, in degrees per second as the "tip-off rate".
It has now been found that tip-off is more than a function of gravity
acting on a partially emerged missile but is a function of the missile,
the launcher tube, and the launcher tube/missile supporting mechanism
(whether a person or a mechanical device); all acting together as a
system. Tip-off is inherent in the system and it has also been discovered
that tip-off does not always occur in a downward direction but can be any
direction and at different rates depending on the type of system.
With the tip-off thus being in any direction and at different rates, it can
be seen that is is desirable to reduce the tip-off rate in whatever
direction it occurs in the launcher-missile system.
This invention provides a means for reducing the tip-off rate in a
launcher-missile system and this is, therefore, one object to this
invention.
It also might be desirable, in certain instances, to overcompensate tip-off
rate to produce a tip-off rate in the opposite direction, as for example,
if the tip-off rate were downward, to provide a tip-off rate upwardly, and
thus accurately align the missile on its intended course.
This invention also teaches how to not only reduce the tip-off rate of a
launcher missile system but how to provide a tip-off which is opposite to
that occurring in the system, and this, therefore, is still another object
of this invention.
SUMMARY OF THE INVENTION
The invention which attains the foregoing objects comprises a
launcher-missile system in which an open sector is formed in the flared
aft end of the launcher tube so that a portion of the exhaust gases
exiting from the launcher tube does not impinge on the aft end but rather
freely expands into the ambient air through the open sector and thus an
impulse caused by the impinging gases on the remainder of the flared end
reacts in a direction opposite to the open sector, thus reducing the
tip-off rate.
The size and location of the open sector depends upon the desired change in
tip-off rate in both magnitude and direction. The tip-off rate can be
reduced to zero or even given a negative, or oppositely, acting impulse
from the original tip-off direction, if desired, to correctly align the
missile on its selected course.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the shoulder-carrier missile launcher
system incorporating the tip-off rate reducer.
FIG. 2 is an enlarged perspective view of the aft portion of the launcher
tube.
FIG. 3 is a longitudinal sectional view of the launch illustrating a
missile in launch position.
FIG. 4 is a diagramatic end view of the launcher tube illustrating the open
sector.
FIG. 5 is a plot of tip-off rate verses sector angle.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the drawings, there is illustrated a shoulder fired
cylindrical launcher tube 10 illustrated in firing position and being
aimed and fired through the use of suitable sighting means 12 and trigger
means 14. The fired missile will emerge from the forward end 16 while
exhaust gases will flow out the aft end 18.
It is understood, before going further in the description that, while this
invention is shown embodied in a shoulder fired launcher tube, the
invention applies equally well to launcher tubes having mechanical
supporting devices. Too, as shown more clearly in FIGS. 2 and 3, the aft
end has been simplified for the purposes of disclosure by the removal of a
portion of the aft cover assembly normally used in launcher tubes of this
type.
Now continuing on, as shown in FIG. 3, when a missile such as 20, is fired
from the forward end 16 of the launcher tube, as stated before, exhaust
gases will exit out the aft end 18. This is represented by arrows 22. The
aft end is provided with a flare in the form of a conical surface 24 to
reduce the tube recoil by providing a surface against which some of the
exhaust gases expand and impinge directing a forward impulse (pressure
times area times time) I.sub.F which opposes the recoil impulse I.sub.R
imposed on the launcher tube in the aft direction as they react against
the inside wall 26 of the tube.
During firing of the missile 20 from the launcher tube 10, the missile can
be deflected from its intended course. This deflection is called "tip-off"
and is a function of the design of the missile, the launcher tube, its or
their respective centers of gravity, and the launcher tube supporting
mechanism, whether the latter is a person or a mechanical device. These
factors all act together as a system and, it has been found that tip-off
does not always occur in any one direction but can be in any direction and
in different amounts depending on the type of system. The amount of such
deflection per unit time is called tip-off rate and is measured in degrees
per second.
This invention provides a means for reducing the tip-off rate in
launcher-missile systems and, in the embodiment shown, to accomplish this
results, the conical surface 24 of the aft end 18 of the launcher tube 10
is provided with a space, or open sector, 30 formed by removing material
from the full 360.degree. conical surface. With this open sector 30, or
discontinuity, embodied in the conical surface 24, some of the exhaust
gases, which are normally impinging on the full 360.degree. surface to
produce the aforesaid recoil reduction, are now vented to ambient air,
that is, simply allowed to expand upwardly as illustrated by arrows 32.
Such vented gases do not induce a forward component of force on that
sector with the result that there is an imbalance which forces the aft end
in the direction opposite from the open sector, which for the purposes of
this disclosure, is represented by a downwardly directed impulse I. Of
course, as mentioned before, the impulse I need not be directed down since
its direction is a function of the location of the open sector in the
360.degree. conical surface.
Turning now to FIG. 5, which is a graph wherein tip-off rate (X direction)
is plotted against sector angle (Y direction), it will be clear that the
downward pulse I is a function of the angular amount of open sector that
is removed from the 360.degree. conical surface. This graph of FIG. 5
illustrates an actual original design launcher tube having a downwardly
directed tip-off rate of 24 degrees per second and is identified by the
wording "original design". This rate is considered excessive in any
launcher-missile system, particularly a shoulder fired system, since there
is a possibility of not only the inaccuracy in the launch of the missile,
but harm to the user. Thus, accepting the concept of an open sector 30 in
the conical surface, and taking into consideration many factors including
the center of gravities involved in the system, calculations were made
which indicated that the tip-off rate in the original design launcher tube
could be reduced to zero with a 70.degree. open sector. This is
represented by .theta. in FIG. 4. The calculated reduced tip-off rate is
represented by the cross over of the curve identified as "calculated" at
the zero Y line on the graph of FIG. 5 and shown to be at a sector angle
of 70.degree.. This graph also shows that according to the "calculated"
curve, the tip-off can be given an oppositely directed rate or an up
tip-off rate, in the case of a downwardly directly tip-off rate, as
represented by the continuing of the cross over of the curve above the
zero tip-off rate point, up to and limited to 180.degree. sector angle
removed from aft cone.
In actual practice, however, it was determined that the inventive concept
did indeed work but more sector angle would be required to be removed than
calculated to reduce the tip-off rate to zero. This is represented by the
curve identified as "actual" and was plotted from the results of a series
of firings utilizing the same launcher tube and missile design. Thus,
under actual testing less than a zero tip-off rate was reached with the
removal of a portion of material to a sector angle of about 70.degree..
Extrapolation of firing data also showed that in this particular system, a
removal of about 140.degree. would give a zero tip-off rate and that an up
tip-off rate, again in the case of a down tip-off rate, could be also
accomplished by removing even a greater amount of material but less than
180.degree. to form a greater sector angle.
While the foregoing refers to the removal of a sector from the cone section
already manufactured as part of the aft portions of the launcher tube,
obviously, the open sector can be formed during the initial manufacture of
the conical surface once having understood the teachings of this invention
and having arrived at the desired tip-off rate reduction and direction
thereof.
From the above description it can be seen that there is provided a means
for reducing or changing the tip-off rate, both in magnitude and
direction, and while the invention has been illustrated and described by
means of a single embodiment it is to be understood that changes and
modifications may be made therein without departing from the spirit and
scope of the invention which is defined by the appended claims. For
example, the 140.degree. point in FIG. 5 is for a specific system, any
other system would have a different design more similar to, but different
from, FIG. 5.
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