7/27/2019 Reflector Gun Sights 2 (Nov 25th 1943)

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\OVEMBER 25TII,1943 LI H T 9-:.IQof theappropr ia te radiusas.ormal practice for r ing and. isights.\ disability of the reflectorsightis the lack of cont ras tbe-tween the lumino us graticuleand very bright backg round s. Insuch circumstances, therefore, itis necessary to enhancethe con-trast by interposing a d immingscreen betweenthes ightand thetarget. The dim ming screendotsnot, as m igh t be t hough t ,dim thegraticule image, as theimageis in fact a vir tual imageformed by light ray s reflecteddirect from the optical unit tothe obs erver s eye. The inter-positionof the dimm ing screen,therefore, dims only the targetand background, the graticuleimage appearing bright by contrast.

To operatethes ight, thelam])is switchedon and itsbr ightnessiSbtrolled by a dimmer switch.Itisthen used in j u s t the samewayas theo lder Ring-and- BeadSight, with thegrea t advan tagethat , provided that the s ight iscorrectly focused, small varia-tionsof the eyeposit io n relativeto the s ight do not affect itsaccuracy.Improving upon the above principles, the P i lot sRe-flectorGunSight Mk. II hasbeen developed. This sight,whichisi l lustrated oppo site , isusedforfixed guninstalla-tions and is, therefore, r igidly attached to the aircraft,usually behind thewindscreen and in the line,of sightofthe pilot. Thema jor differences from the Mk.I l l A* freegun sight described above is t h a t a range estimator isincorporated and thehood is dispensed w ith.The optical system iscontained within a cast light alloybody,at theuppe r end of which is mounted the reflectorand dimming screen, and at thelower end the detachablelamp holder. As before, the central portion of the bodyis externally m achin ed spherical in order to provide anadjustable mounting.

Pilot s MarkIIreflectorgunsight.

The graticule differs int h a t itis etched on to the flator lowersurface of an opaque concaveplane lens and consists of ntranslucent r ing and bead andtwo cross-wires. The cross-wires are interrupted centrally,the vert ical wire stopping shorta t the r ing and the horizontalone extending nearly to thecentre, its inner e nds bein^masked to a varying degreebythe base /rang e mech anism.Thediameter of the r ing whenpro-jected on to the target planesubtends a constant angleandi ts radius represents the correctdeflection for a target crossingspeed of ioo m . p . h .Immediately below the grati -culeis abase / ran ge m ask whichis rotatable by the range andbase heads situated just belowthe spherical mou nting. Rota-tion of the heads causes themasktoincreaseordecreasethegap between the twohorizontalwires. Theset t ingof the maskis differentially controlledby thetwo heads, increments of rangeprogressively reducing the gapand increments of base, i.e..apparent spanoftarg et, increas-ing it. The purpose of therange /bas e m echanismispr imarilytoobvia te thetendencyto open fire while still out of effective range; it is notintendedtofunction as arange-finder in theaccepted sense .To operate the sight, thegraduation mark on the basehead is set to an est imate of the targe t span based onrecognition of the t a rge t type and paying due regard toany obliquity of aspectof thet a rge t . Therange head isse t to therangeat whichit is desired toengage the t a rge tand the l amp is then switched on, its br ightness beingcontrolled by the dimmer switch. Fire is then withheldwhiletherange closes un til the target fillsthe gapbetweenthe horizontal cross-wires.W e areindebtedto theMinistry OfAircraf t Prod uctionfor theabove notesandi l lustrations.

RUSSI N DIVE BOMBER

A PE 2taxyingto thetake-off pointofVoroshilovgrad airfield. ThePE 2 sonamed after itsdesigner Petlyakov)is a high-speedlight bomber whichcan beusedforeither precisionordive bombing.