NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

0201-20-2300 May, 1955 I4.087

Evaluation Test

of a

Modification Kit

for the

AN/AT/Q-2A Aircraft Searchlight

by

J.A. LeReche

and

J.W. Lane, Sr.

NBS Test No. 21N-52/5U

Naval Aircraft Lighting Group

Photometry & Colorimetry Section

NBS

Washington, D. C.

Sponsored by

Bureau of Aeronautics, EL 5211

Department of the Navy

Was hington, D . C

.

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re Approved for public release by the

unless permission is director of the National Institute of

25 ,d.c. Suchper Standards and Technology (NIST)

tally prepared if tl on October 9, 2015

n part, is prohibited

indards, Washington

jort has been specifiport for its own use,
.

. 'I l l

r
Evaluation Test

of a

Modification Kit

for the

AN/AVQ-2A Aircraft Searchlight

I. Introduction

In the course of operational experience with the AN/AVQ-2A aircraft

searchlight it was found that malfunction of the thermo-optical focus

control system was a relatively frequent cause of failure of the searchlight. Accordingly, the National Bureau of Standards, at the request of

BuAer, undertook to develop an improved focus control method. Several

kits, consisting basically of an n obturator -probe" device, but including

as well several other improved components, were furnished to the fleet

for evaluation along with NBS Report 135U "Instruction Book for the

Modification of the AVQ-2A Aircraft Searchlight". The fleet evaluation

tests were generally successful. The results of the fleet evaluation

as well as additional data obtained at NBS were examined carefully and

final designs for a modification kit were issued in NBS Report 3156,

"Construction Details for NBS Modification of AN/AVQ-2A Aircraft

Searchlight"

.

This report gives the results of evaluation tests of a pre -production

modification kit, based on the one designed at NBS, and manufactured by

the Strong Electric Corporation.

II. Material Tested

One pre-production modification kit furnished by the Strong Electric

Corporation under Contract No. NOas 5U-887-f was received for test in

September, 195k*

III. Test Procedure

The modification kit was installed on a new AVQ-2A searchlight, and

checked for conformity with the design details given in NBS Report 3156.

The modification kit was installed according to the instructions

given in NBS Report No. 135U* Each part was carefully checked for ease

of mounting on the searchlight unit. The modified searchlight was

operated for a life test of 100 hours, consisting of a duty cycle of

one minute on and four minutes off. The operation of the arc was constantly checked and data of its performance obtained t hroughout the 100-

hour life test.

IV. Test Results

The parts of the modification kit were packaged aid labeled in

individual packages. They were free of tool marks and their appearance
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was good.

The AVQ-2A searchlight, modified with the kit provided, operated

satisfactorily. The following discrepancies in the cons traction of

parts of the kit were noted: (Part designations are those given in

NBS Report No. 3156).

1) The filister screws (part No. 18) provided to fasten the

douser to the douser slider arm had heads which were too long and had

to be replaced with screws with shorter heads in order that they would

not strike the negative head support rod clamp. The three screws

furnished were all of the same length, 7/l6“, instead of two 3/8“ long

and one 5/8“ long screws as were furnished in the original kit. This

feature reduces the number of different spare parts required for maintenance of the kit. The negative head support rod clamp that is located

near the douser had been filed on one side so as to permit clearance for

the douser mounting screws. However in order to facilitate assembly and

allow for interchangeability of parts, the use of the proper size filister head screws and interchangeable support rod clamps is advisable.

2) Both lava and “Mycalex” insulating washers were provided

and tried on the equipment* the “Mycalex” washers proved to be less

fragile and more suitable for this application.

3) The slot in the contact brush (part No. 28) designed to

fit over the positive drive shaft did not fit exactly on the shaft. This

did not, however, interfere with the normal functioning of the searchlight.

U) For fastening to the douser slider arm, the douser has an

integrally cast slotted bracket which saddles and clamps the douser

slider arm. In the original NBS douser design, the mounting screw holes

drilled thromgh the part of the bracket which fits on the outside of the

douser arm were not tapped, so that as the mounting screws were tightened

the saddle of the bracket would clamp the douser arm. In the douser

manufactured by the Strong Electric Corporation, the holes in the outside

of the bracket were tapped, preventing the proper clamping action of the

douser bracket to the douser arm. (For this test the holes in the bracket

were drilled out and installed on the douser arm in accordance with the

original design.

)

5) The spring provided to return the douser after the arc has

been struck (part No. 56) was not strong enough and the douser remained

retracted occasionally. The spring was replaced with a stiffer one such

as was used in the original NBS modification kit. Occasional malfunction

of the douser mechanism was averted by proper lubrication of sliding

parts with a special arc mechanism lubricant supplied by the Strong

ELectric Corporation. If a lubricant is used, the mechanism should be

cleaned and relubricated each time the searchlight is serviced.
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V* Discussion

The AVQ-2A searchlight equipped with the modification kit manufactured by the Strong Electric Corporation operated satisfactorily

for the duration of the 100-hour life test after it was corrected as outlined in ’’Test Results".

During periods of poor arc operation such as when the current

is abnormally high, black deposits may form on the controlling edge

of the obturator, directly above the positive carbon. These should

be removed after each flight as they may reduce the accuracy of focal

control of the arc. In extreme cases, if the deposits are not cleaned

off for some time they may build up sufficiently to cause serious malfunction of the arc. To minimize the formation of deposits on the

controlling edge of the obturator-probe, the cause for any arc misbehavior should be determined and corrected if possible.

During normal arc operation, the upper half of the obturatorprobe facing the arc may become coated with an ash or powder deposit

and the entire obturator-probe will be oxidized; this does not interfere with the normal operation of the arc.
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