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Full text of "Description of the Mortar Range Board, Model of 1914, with Instructions for ..."

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1 

1 

1 

i 

I 


GIFT OF 



'1 




DESCRIPTION 

OPTHB 

MORTAR RANGE BOARD 

MODEL OF 1914 



WITH INSTRUCTIONS FOR CARE 
AND OPERATION 




GOVEHNMENT PRINTING OFFICF 



u 






^0 






• • 



• 1 « 

i 



I A 



War DBPARTMENTy 

Office of the Chief of Ordnance, 

Washington^ March 6, 1914 • 
This Manual is published for the information and government of the Regular Army 
and Organized Militia of the United States. 
By order of the Secretary of War: 

William Orozier, 
Brigadier General^ Chief of Ordnance. 
68030—16 (3) 



303105 



: . '. \. • 






MORTAR RANGE BOARD, MODEL OF 19x4. 



DESCRIPTION. 



The mortar range board is 40 inches long, 12i inches wide, and IJ 
inches deep, and weighs about 32i poimds complete. The franie is 
an almninum alloy casting. It is designed to lay flat on a table. 

The board has three grooves. In the upper 'groove slides two 
zone to zone correction scales. The left zone to zone scale is tis6d 
for determining percentage corrections below normal for the diflPer-* 
ent zones, while the right scale solves the same problem for per- 
centage corrections above normal. Each zone to zone correction 
scale is graduated with the zone numbers, to which is attached a 
sliding pointer to indicate the. working zone. 

The second and third grooves with their slides are designed to 
serve th6 same purpose, but are divided into two parts called upper 
and lower, to keep within the limits of the board. To permit over- 
lapping, graduated ranges 6,450 to 8,100 are repeated on the upper 
and lower range scales; the zone scales are correspondingly repeated. 
In the second and third grooves shde the upper and lower range 
slides. To each sUde is attached by screws an upper and lower 
range scale correction scale. Integral with each upper and lower 
range scale correction scale, and extending downward, is an arm on 
which slides the elevation index slide, carrying with it a transparent 
piece of celluloid marked ^'elevation and time." The index on this 
transparent piece of celluloid is the fiducial Une. Inimediately above 
and adjacent to the upper and lower range shdes are screwed to the 
board the upper and lower range scales, graduated in yards. Shding 
in grooves in the upper and lower range sUdes are the range and 
correction scale indices. On each of these indices is engraved a 
line, one end of which registers with the graduations on the upper 
and lower range scales and the lower end with graduations on the 
upper and lower range scale correction scales. On the lower edge 
of each of the range scale correction. scales is attached a correction 
scale marking strip, made of white celluloid, for convenience in 
tabulating data. Set in the board below the second and third 
grooves are the zone scales. The scales for the eighth and ninth 
zones, using the 700-pound projectile, and the eighth zone, using 
the 824-pound projectile, are detachable from the board. These 

(5) 



* 

* t 



zone'3Caies»hot*ih" iis^ tJJe- assembled to the upper and lower edges 
of the board in slide recesses provided. 

On the frame is an assembling index which must coincide with a 
corresponding index on each of the detachable zone scales. 

All slides are designed to be clamped in any position by means of a 
knurled nut projecting upward from the face of the board. 

OPERATION. 

The range board requires one man to operate. The arm setters set 
their respective arms to the data given by the base end stations and 
the plotter marks the intersection of the arms. Prediction is made in 
the usual manner. The time of flight for the first two predictions is 
obtained by the range correction shde-rule operator setting the slide 
to an approximate range to the set forward point estimated by the 
plotter. After that the slide-rule operator can predict the time of 
flight of the set forward point. The mortar arm is brought up to the 
set forward point and the range of this point is read off by the plotter. 
The sUde is then set and the elevation read off for use in elevating the 
mortars, and also for use of the primary arm setter who sets the drift 
slide pointer to the elevation given and reads off the corrected 
azimuth of the set forward point. The plotter then sets the mortar 
arm to the predicted point and the primary arm setter reads off the 
azimuth of that point. 

Range errors due to velocity errors are compensated for by dis- 
placing the range and correction scale indices a distance correspond- 
ing to the range correction to be made. * All scale graduations being 
logarithmic, the correction appHed operates as a percentage correc- 
tion, and pertains only to a single zone. For obtaining the correction 
factor for a different zone, the zone to zone scale is set so that the zone 
number is opposite the given correction factor on the zone correction 
scale and the new correction factor is read off on the zone correction 
scale opposite the new zone number. The range and correction scale 
index is then set for the new correction factor. 

TEST FOR ACCURACY. 

For testing the accuracy of the board, test-settings are indicated 
by ^'A,'' ^^B,'' ^'C," etc. To test, set the range-correction factor 
'' A'' at the range ^^ A.*' The corresponding calculated elevation and 
time of flight are indicated by the Ughtly engraved reference line 
^'A.'' Proceed in a similar manner for other test-settings. 

The accuracy of the board can also be tested by assuming a zone 
correction factor of 1,000 and setting to any range. The angle of 
elevation and time of flight obtained can then be compared with the 
calculated angle of elevation and time of flight taken from the range 
table. 



' CARE AND PRESERVATION. 

The scales and slides and the recesses for them should be kept free 
from sand or dirt. 

The scales and other movable parts should be cleaned and oiled 
occasionally with sperm oil. 

When not in use the instrument should be covered. 

Spare parts should be ordered from the nomenclature given below : 



niustra- 

tion 
nnmber. 


Piece 
mark. 

• 


1 


5K 


2 


5K 


3 


6G 


'4 


6G 


5 


5C 


6 


5G 


7 


5E 


8 


5E 


9 


6D 


10 


6D 


11 


6L 


12 


6L 


13 


2B 


14 


5P 


15 


5P 


16 


5A 


17 


5A 


18 


5A 


19 


5U 


20 


5U 


21 


1SD- 


22 


5D 


23 


5U 


24 


5U 


25 


5N 


26 


5N 


27 


4E 


28 


5B 


29 


6J 


30 


5M 


31 


6H 


32 


3A 


33 


3G 


34 


3B 


35 


3D 


36 


6H 


37 


5H 


38 


5H 


39 


6A 


40 


6A 


41 


2A 


42 


2A 


43 


5V 


44 


5V 


45 


5W 


46 


5W 


47 


5X 


48 


5X 


49 


5X 


50 


5X 



Name of part. 



.- V 



Correction scale marking strip (upper). 

Correction scale marking strip (lower). 

Correction scale marking strip upper screws. 

Correction scale marking strip lower screws. 

Elevation index (upper). 

Elevation index (lower). 

Elevation index slide f upper). 

Elevation index slide (lower). 

Elevation index screws (upper). 

Elevation index screws (lower). 

Elevation index slide stop screws (upper). 

Elevation index slide stop screws (lower). 

Frame. 

Index clamp screw (upper). 

Index clamp screw (lower). 

Knob lower zone scale (8-700 lb.). 

Knob lower zone scale (8-824 lb.). 

Knob lower zone scale (9-700 lb.). 

Knob zone to zone correction scale (right). 

Knob zone to zone correction scale (left). 

Knob elevation index slide (upper). 

Knob elevation index slide (lower). 

Knob for range slide ^upper). 

Knob for range slide (lower). 

Knob for index clamp screw (upper). 

Knob for index clamp screw (lower). 

Lower range scale. 

Lower range scale correction scale. 

Lower range scale correction scale screws. 

Lower range slide. 

Lower range scale screws. 

Lower zone scale. 

Lower zone scale (8-700 \h.). 

Lower zone scale ^8-824 lb.). 

Lower zone scale (9-700 lb.). 

Lower zone scale screws. 

Pin for elevation index slide (upper). 

Pin for elevation index slide (lower). 

Pin for zone to zone correction scale (right). 

Pin for zone to zone correction scale (left). 

Pin stop for zone to zone correction scale (right). 

Pin stop for zone to zone correction scale (left). 

Pin for index clamp-screw knob (upper). 

Pin for index clamp-screw knob (lower). 

Pin stop for range and correction scide index (upper). 

Pin stop for range and correction scale index (lower). 

Pin for zone to zone correction-scale clamp screw (nght). 

Pin for zone to zone correction-scale clamp screw (left). 

Pin for upper range slide clamp screw. 

Pin for lower range slide clamp screw. 



8 



niustra- 

tian 
nmnber. 


' Piece 
mark. 


51 


5Q 


52 


5Q 


53 


5G 


54 


5G 


55 


6K 


56 


6K 


57 


6£ 


58 


6E 


59 


5S 


60 


5T 


.61 


. 5J 


62 


5J 


63 


6M 


64 


6M 


65 


6F 


66 


6F 


67 


5F 


68 


4D 


69 


6A 


70 


6H 


71 


6J 


72 


5L 


73 


40 


74 


60 


75 


6B 


76 


4B 


77 


6H 


78 


5R 


79 


5R 


80 


4A 


81 


6H 



Name of part. 



Range slide upper clamp screw. 

Range slide lower damp screw. 

Range and correction scale index (upper). 

Range and correction scale index (lower). 

Range and correction scale index upper stop screw. 

Range and correction scale index lower stop screw. 

Scale-index bar right stop screw. 

Scale-index bar left stop screw. 

Scale index (right). 

Scale index (left). 

Spring for elevation index slide (upper). 

Spring for elevation index slide (lower). 

Scale-index bar (right). 

Scale-index bar (left). ' 

Scale-index bar right screw. 

Scale-index bar left screw. 

Upper range-scale correction scale. 

Upper zone scale. 

Upper zone-scale screws. 

Upper range-scale screws. 

Upper range-scale correction-scale screwB. 

Upper range slide. 

Upper range scale. 

Zone to zone correction scale fright). 

Zone to zone correction scale (left). 

Zone to zone correction-scale guide. 

Zone to zone correction-scale guide screws. 

Zone to zone correction-scale right clamp screw. 

Zone to zone correction-scale left clamp screw. 

Zone correction scale. 

Zone correction-scale screws. 



War Dbpartubnt, 

Office of the Ohief of Ordnance, 

Washington, March 5, 1914* 

Torm No. 1676. 

S2g8Q/499. 

Ed.Noy.2-ie-a00. 



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