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Classification with Peek-a-boo for Indexing Documents on Aerodynamics: An Experiment in Retrieval
R.C.WRIGHT and C.W.J.WILSON
ABSTRACT. A new classification and peek-a-boo cards were used for the analytical indexing of documents on aerodynamics and 100 test questions were put to the system. Degree of success in retrieval is assessed, input and search times are measured, and causes of failure are examined. The combination appears to offer a promising retrieval system for complex but well-defined subjects.
Towards the end of 1956, it was proposed to prepare and (as far as possible within security limits) to distribute to industry a subject index to the reports and technical notes issued by the Aerodynamics Department of the Royal Aircraft Establishment. This index, which might later be extended to include other series of reports on aerodynamic subjects, would be based on a suitable classification system permitting conjunctive specification, and would use a clerical device of the peek-a-boo type (1). The system would employ a minimum of expensive equipment and, if successful, might be applicable to other fields requiring detailed analytical indexing of a comparatively small collection. First, however, it would be necessary to select a suitable classification of aerodynamics, do some trial indexing, and carry out tests on the system. The purpose of this paper is to describe the selected classification, the posting and searching operations, and the tests carried out.
Purpose of the experiment
Main reasons for undertaking the project were:
A reliable analytical index to the 6000 reports in the series was necessary to the Establishment and would no doubt be welcomed by the aircraft industry.
Mr. J.Seymour, a former Librarian of the Aerodynamics Department, had recently developed a classification for aerodynamics which appeared to
R.C.WRIGHT and C.W.J.WILSON Royal Aircraft Establishment, Farnborough, England.
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have many advantages for use in a retrieval system. Experience in its practical application was desired.
Tests had already been carried out with a Uniterm system for cataloguing aircraft structural data (2), and on the N.L.L. card catalogue of aerodynamic measurements (3, 4). Similar evaluation of a peek-a-boo device based on a suitable subject classification was considered desirable.
It was hoped to ascertain whether an analytical indexing and retrieval project in the complex subject of aerodynamics could be designed and operated by professional librarians without specialist subject knowledge, to the satisfaction of the aerodynamicists requiring the information.
PHYSICAL FORM OF THE INDEX
In its final form, the index would be made up of (1) a register, i.e., a list of all documents indexed by the system, in register serial number order; (2) a manual, consisting of (a) an introduction to the system, (b) a list of subject headings in classified order, (c) an alphabetical index to the subject headings; (3) index sheets—one for each subject heading and for each designated aircraft and aerofoil; register serial numbers of documents to be indicated by the positions of punched holes.
For testing purposes, however, it was decided to use only the classification schedule itself and standard 80-column Hollerith cards. Special cards or plates having a higher capacity might later be desirable, but their design, and that of suitable punching and viewing devices, could be left until the retrieval capabilities of the system had been investigated.
Choice of classification
After consideration of the known enumerative classifications of aerodynamics, including U.D.C., N.A.C.A., and the N.L.L. (all of which are used to some extent in the Establishment), it was decided to adopt the classification system devised by Mr. Seymour with this project in mind. After comments had been sought from subject experts, the classification was adopted with slight modifications; it appears as Table 2, together with the number of times each code was used in indexing the first 700 documents. It was expected that further modifications would follow an initial trial period of indexing.
Indexing
THE INDEXERS
The six indexers were professional librarians employed in the Main and Departmental libraries of the Establishment. One of them (A) was librarian
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of the Aerodynamics Department: the remainder (B-F) had experience in aeronautical libraries but no special knowledge of aerodynamics. About half of the indexing and searching was to be done by A, so that the effect of familiarity with the subject and with the schedules might be assessed.
Before starting to index, the indexers met to discuss the schedules and to resolve as far as possible differences of opinion as to the meanings or the use of particular headings. Each person then indexed a number of test pieces, and variations were discussed. It was intended to introduce further test pieces at later stages in order to see whether improved correlation came with experience of the system.
PROCEDURE
For test indexing the selection of documents was not limited to R.A.E. documents, some Institute of Aeronautical Sciences preprints and National Advisory Committee for Aeronautics Research Memoranda being included in order to achieve wider subject coverage, particularly of recent material.
The intention was to code all those features of a document which might conceivably be used later as part of an information request. A detailed study of each document was therefore necessary, particular attention being given to the summary, conclusions and illustrations. Postings were made on a 5 by 3-inch card ruled in ten columns as follows:
Thus, to indicate that a document dealt with a fighter aircraft, the code 157 taken from the schedules would be entered as 15 in column 7. All relevant codes were entered, so that the issue date 1953 would be coded as 103, 104, 105, 106, and Mach number 1.3 would be 121, 122, 123, 124. Whenever a sub-heading was used, the main heading above it was also coded. For peek-a-
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boo use, these codes were subsequently transferred to lists in code number order and punched on Hollerith cards.
The only materials and equipment used were common stationery items and a Hollerith hand punch. The processes involved were:
Examination of the document and noting appropriate codes on the 5″×3″ card illustrated above.
Listing the serial numbers appropriate to each code number.
Hand punching the Hollerith cards, which already have typed on them the code numbers, by which they are arranged.
Times taken for these operations are discussed later. The most time consuming, and that needing the highest-paid staff, was (a). Most documents were assigned about 30 codes. At first, indexers were taking as long as 30 minutes for each document: practice, familiarity with the schedules and increasing knowledge of the subject soon reduced this to 15–20 minutes per document. It is doubtful whether an average of about 15 minutes can be much reduced, in view of the careful study of each document which is necessary to any system using highly analytical indexing. The average salary of the indexers employed worked out at 10/– ($1.40) an hour.
Description of tests
The test programme is in two parts:
(a) When about 750 documents have been indexed. To ascertain the effectiveness of the classification, to make any necessary modifications to the schedule, and to remove causes of discrepancy between indexers. Also to assess the cost of indexing and posting and the speed of searching operations.
(b) When about 3000 documents have been indexed. To ascertain the number and relevance of documents retrieved in response to a given question. Also, on the basis of search times, to ascertain the scope and form of the final index (a) for internal use and (b) for possible issue to other aeronautical libraries. Only part (a) of the programme is discussed in this paper.
When 700 reports had been indexed (500 R.A.E. documents and 200 of U.S.A. origin), ten R.A.E. aerodynamicists were asked to collaborate by selecting 10 documents each from the collection and framing one question on each document. The questioners had not seen the classification schedules, and were asked to frame in their own words the sort of question that might occur in their daily work. The questions appear in Table 1. Searching was divided about equally between indexers A and B. Success was defined as the retrieval of the document on which the question had been based. Obviously this had
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to be limited in some way, since a search which retrieved the subject document together with about 50% of the collection could hardly be regarded as an unqualified success. Such a case could be due to faults in retrieval; it could also be due to the question having been so general that it was bound to produce a large number of answers.
After discussion, an arbitrary limit of 5% of the collection (35 documents) was set as the maximum for a search to be regarded as successful. Searches producing more than this number have been classed as “partially successful” provided that the subject document is included.
When a search was unsuccessful, a second search was usually made, either by the same searcher or by the other. Sometimes this consisted simply of widening the original search by discarding one or more of the factors forming the specification. In other cases completely new headings were selected to form a new search plan.
Usually not more than two searches were made, but there were a few cases in which a third search was considered advisable.
Analysis and discussion of results
PERCENTAGE SUCCESS
Of the 100 questions put, 54 were answered at the first search, a further 20 by a second search, and a further 4 by a third. In 7 cases the search was “partly” successful (subject document retrieved, but with more than 5% of the collection), and in 15 cases the search failed completely. An overall success percentage of 78 (plus a further 7% of cases in which the field was appreciably narrowed) is not unsatisfactory having regard to the circumstances in which the test was made. Many of the questions would, in normal information work, have been referred back for amplification.
CAUSES OF FAILURE
(a) Causes of complete failure
Question numbers
1
7
12
32
34
36
39
40
51
53
57
66
81
88
93
Misleading question
X
X
Question misinterpreted
X
X
Indexing omission
X
X
X
X
X
X
X
X
X
X
X
X
Schedule inadequacy
X
X
X
(b) Causes of partial success
Question numbers
17
23
24
26
28
61
70
Question insufficiently specific
X
X
Indexing omission
X
X
X
X
X
Schedule inadequacy
X
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(c) Causes of earlier failure when third search successful
Question numbers
37
41
48
67
Question misinterpreted
X
Indexing omission
X
X
X
(d) Causes of earlier failure when second search successful
Question numbers
4
5
11
22
25
31
33
35
49
55
Misleading question
X
Indexing omission
X
X
X
X
X
X
Faulty search
X
X
Search too specific
X
X
Schedule inadequacy
X
X
Question numbers
56
60
65
72
76
84
86
87
96
97
Indexing omission
X
X
X
X
X
X
X
X
Search too specific
X
X
Clerical error in posting
X
(e) Summary. A total of all the above single or contributory causes of complete or partial failure may be helpful in pinpointing the chief weaknesses of the system.
Semantics
Misleading question
3
Question insufficiently specific
2
Question misinterpreted
3
8
Input stage
Indexing omission
34
Schedule inadequacy
6
Clerical error
1
41
Output stage
Faulty search
2
Search too specific
4
6
Total
55
It will be noted that the largest single factor was indexing omission, and this in turn is believed to be attributable mainly to lack of subject knowledge. Next largest is the “semantics” group, failure in communication between the questioner and the searcher.
The six cases of schedule inadequacy, together with other omissions noted in indexing the first 700 documents, will lead to minor revision of the classification. At this time, reconsideration will be given to the necessity for retaining some headings which have hardly been used at all, and others which have
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been used so often as to render them almost useless for retrieval purposes.
The six cases of failure at the output stage are not considered significant: none persisted beyond a first search, and with peek-a-boo it is possible to make several searches in a few minutes.
NUMBER OF CODES USED IN INDEXING
Average number of codes used in indexing 700 documents
28.96
Average number of codes used in indexing the 54 documents successfully retrieved at the first search
30.59
Average number of codes used in indexing the 15 documents which could not be retrieved
30.07
Indexer A used an average of 30.50 codes for each report.
Indexer B used an average of 32.94 codes for each report.
Indexers C−F used an average of 29.12 codes for each report.
All these averages, except the first figure of 28.96, are based only on the 100 documents on which questions were asked.
ANALYSIS BY INDEXER
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All indexers used about the same average number of codes per document, but the success achieved varied with the indexer’s subject knowledge. Indexer A was in charge of a specialised library for aerodynamicists; B, in charge of a more general aeronautical library, had considerable experience in aviation and in library services; C to F had served in aeronautical libraries for periods varying from 5 years to only a few months.
RELEVANCE OF DOCUMENTS RETRIEVED
In the N.L.L. tests (3, 4) searchers were able to make a rough assessment of the relevance of each document retrieved by an examination of the detailed information printed on the N.L.L. punched cards. In the present case it would have been necessary to refer each document, or an abstract of it, to the questioner. This being a time-consuming operation, it was decided to do so only on a sample of 20 successfully answered questions. These were further restricted to cases in which 3 to 12 documents had been thrown up in the retrieval process. In 20 cases, therefore, questioners were presented with abstract cards or documents and they decided whether the documents retrieved, in addition to the ones on which their questions were based, were truly relevant in terms of their questions as set.
Total documents retrieved for the 20 questions came to 146 (the number of aspect cards correlated varied from 1 to 5, but was usually between 2 and 4). It was found that 70 documents were relevant, 18 were of marginal relevance, and 58 were irrelevant. This makes a broad ratio of 3.5:1:3, which appears to be satisfactory, although it is clearly desirable to reduce the marginally relevant figure. This can probably be achieved by improved indexing.
Time studies
INPUT
Accurate time studies were made of three main aspects of the input stage of this project. These were: times taken to index each document, times taken to post code numbers to a ledger, and times taken to transfer this information to punched Hollerith cards.
Time to index documents. Indexer A, who was responsible for half of all indexing, timed himself on 17 occasions. This was done only after considerable experience of indexing difficulties and detailed knowledge of the schedules had been gained. 153 documents were indexed in 31 hours 5 minutes, which gives 13.5 minutes per document.
Time to post index numbers. All papers indexed had their codes recorded on the card described in “Procedure” under “Indexing.” These codes were
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then transferred to a plain ledger to facilitate eventual punching. In 18 operations, codes for 474 documents were posted by 2 persons in 19 hours 16 minutes, which gives 2.4 minutes per document.
Time to punch Hollerith cards. Codes for 500 documents were transferred from the ledger and punched on Hollerith cards in 19 hours 30 minutes. This was done in 12 operations by 2 persons, at an average of 2.34 minutes per document.
Total times for each document subject-indexed by the system described therefore consist of 13.5 minutes for indexing, 2.4×2 minutes for posting, and 2.34×2 minutes for punching, or 22.98 minutes. These are the three time-expensive parts of the programme, but, if an allowance of 5 minutes for extracting or filing papers or associated clerical processes is made, it is reasonable to assess inclusive time for subject indexing and all allied clerical effort as an average of 28 minutes per document. Half of this is relatively expensive indexing. No great reduction in any of these times can be expected.
OUTPUT
The output stage of this system consists firstly in relating a question to the classification schedules, in carefully assessing the best aspect cards to be used,1 in correlating these cards and reading the holes punched all through. With practice, these were found to be rapid processes which, depending on the complexity of the question, could be performed within 2–10 minutes. The second phase consists of removing the relevant serially numbered abstract cards from the file, and offering them to the questioner, who may then wish to see some of the actual documents represented by the cards. The total output stage should not normally exceed 15–20 minutes.
Conclusions
The combination of subject classification and peek-a-boo appears to have many advantages as a means for the analytical indexing of documents in a well-defined subject such as aerodynamics. There would appear to be a market for the commercial development of “miniaturised” cards or plates having a capacity of 20,000 or more positions and of appropriate punching and viewing equipment.
1
Bernier (5) has found, theoretically, that “discovery of unexpected documents by use of a manipulative, correlative index is usually highly improbable if the number of terms taken at a time in searching is four or more….” It was found, as described in the paragraph on relevance of documents retrieved, that the number of peek-a-boo cards correlated usually fell within the range 2–5.
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Best results have been obtained by indexers with subject knowledge, and “production” indexing should be undertaken only by such indexers.
The classification used was basically sound, but requires expansion in some areas and contraction in rather more, so as to achieve less variation in the number of times code-numbers are used. In many cases scope notes are required.
A survey (6) of the report literature actually in use by a typical group of aerodynamicists shows that 98% of the reports were less than 10 years old and 83% less than 5 years old. This finding is likely to influence schedule revision and may necessitate re-appraisal of the scope of the present project. It also tends to minimise one criticism of peek-a-boo, i.e., that it is necessary at intervals, depending on card capacity and accession rate, to start a completely new index.
REFERENCES
1. WILDHACK, W.A., STERN, J., SMITH, J., Documentation in instrumentation. American Documentation 5, 223–237 (1954).
2. CLEVERDON, C.W., THORNE, R.G., A brief experiment with the Uniterm system of co-ordinate indexing for the cataloguing of structural data (unpublished).
3. VESSEY, H.F., Test of N.L.L. card catalogue of aerodynamic measurements (unpublished).
4. VESSEY, H.F., SEYMOUR, J.R., Test of N.L.L. card catalogue of aerodynamic measurements. II (unpublished).
5. BERNIER, C.L., Correlative indexes and the blank sort. American Documentation 9, 32–41 (1958).
6. WILSON, C.W.J., Report literature used by aerodynamicists (unpublished).
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TABLE 1 The 100 questions and the searches based on them
Question No.
Question
Search plan
Documents retrieved
Indexer
Codes used
Searcher
Success or failure
Remarks
1
Effect of incidence on pressures recorded on a Hunter aircraft.
(a) 365
362
(Hunter)
(a) 14
B
21
B
F
Peek-a-boo cards for aircraft names are not yet available, but would normally be used. In this case neither “Hunter” nor “365-Incidence” was indexed.
(b) 365
417
362
(b) 1
A
F
Searcher B misunderstood the question as relating to aerodynamic pressures: document related to pitot-static tube pressures. “Pitot static tubes” had been noted by indexer as a desirable new heading.
2
Aerodynamics of struts
349
264
10
C
36
A
S
3
Spinning tunnel instrumentation
397
417
1
B
22
A
S
4
Early methods of measuring rates of climb (relative merits of barograph and cinematograph)
(a) 417
369 378
(a) 0
A
26
B
F
“417-Instruments” not indexed.
(b) 369
378
(b) 14
B
S
5
Applications of the Ludwig-Tillman skin friction formula
(a) 128,137
136,154
349,352
(a) 4
A
28
A
F
Indexers had noted skin friction as a necessary new indexing term.
(b) 113,128
137,352
(b) 12
A
S
6
Effect of rate of approach to a stall on the stall CL
365
350
26
B
47
B
S
378, if used, would reduce the number of documents to 3.
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Question No.
Question
Search plan
Documents retrieved
Indexer
Codes used
Searcher
Success or failure
Remarks
70
The ram efficiency of air intakes let into the sides of a wing or body.
(a) 281
282, 285
13
B
42
A
F
“282-Located on aerofoils” not indexed.
(b) 281, 285
40
A
P
71
Is the temperature recovery factor of a laminar boundary layer altered by separation of the boundary layer?
137
139
142
10
A
27
A
S
72
Data required from tests employing the NACA Technique for obtaining free-flight stability data from models fitted with an all-moving tailplane which moves automatically between stops under the influence of the aerodynamic forces on it.
(a) 112, 115
117, 338
406
0
A
46
A
F
(b) 115, 117
406
8
A
S
73
For assisted take-off, what are the advantages of a liquid fuel rocket over a solid fuel rocket?
171
271
377
3
B
32
B
S
74
What are the handling qualities of the Javelin aircraft at high lift coefficients?
350
378
17
B
38
B
S
The 17 documents will be reduced substantially when the name Javelin (used in indexing) has been represented by a peek-a-boo card.
75
What reports from the Royal Aircraft Factory appeared during the 1914–18 war on aircraft stability theory.
100, 113
114, 117
349, 355
1
A
15
A
S
76
To what extent may disturbances present in a wind tunnel invali
(a) 125, 137
141, 195
12
B
30
A
F
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date tests made in the tunnel to locate the position of boundary layer transition on a wing at subsonic speeds?
(b) 112, 137
141, 195
392
11
A
S
Indexer omitted to index Mach numbers.
77
What changes in piloting technique are necessary for the safe landing of an aircraft without an undercarriage on an aircraft carrier adapted to receive it?
331
367
4
F
21
A
S
78
Can Falkner’s 9-point method (for calculating the aerodynamic loading on a wing) be simplified for application to a swept wing of low aspect ratio?
113
368
195
206
212
5
E
33
B
S
79
A method is required for calculating the spanwise distribution of lift on a wing of low aspect ratio at high subsonic speeds, including allowance for the non-linear variation of lift with incidence.
350
362
212
125
123
113
2
A
35
B
S
80
Wanted: a good theoretical treatment of the downwash field behind a low aspect ratio wing including the behaviour of the tip vortices at supersonic speeds.
113
144
122
143
6
A
24
B
S
81
Information is required on numerical methods employed in the theoretical determination of the drag of a slender body of arbitrary cross-section.
113
240
352
14
A
16
A
F
“240-body” not indexed.
Paper was on area rule, which was indexed.
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Question No.
Question
Search plan
Documents retrieved
Indexer
Codes used
Searcher
Success or failure
Remarks
82
What methods have been tried in flight to improve the damping of lateral oscillation of high-speed aircraft?
112, 193
339, 355
357, 373
405
2
A
33
A
S
83
Have we any experimental measurements of the influence of aero-elastic distortion on the effectiveness of trailing edge flaps on rectangular wings?
112
374
315
308
3
A
38
B
S
84
What reports give design charts for the determination of the downwash angle at the tailplane for tapered wing planforms with plain flaps at low speeds.
(a) 144, 126
315, 202
2
A
50
B
F
“202-tapered” not indexed
(b) 144, 126
315
11
B
S
85
Approximate methods to suggest the requirements of an auto-control system for the control of the “long period” or “phugoid” motion of an aircraft.
278
373
9
A
16
A
S
86
Experimental measurements at supersonic speeds of the flow field in the vicinity of a body of revolution at high angle of incidence.
(a) 112, 122
253, 365
0
A
39
B
F
“365-high incidence” not indexed.
(b) 112, 122
253, 128
34
B
S
87
Calculations to indicate the effect of introducing inertia
(a) 109, 302
356, 358
4
C
25
A
F
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weights and springs into a power-operated control system for the longitudinal control of an aircraft.
(b) 278, 302
355, 358
7
A
S
88
Experimental data on the effects of slipstream on tailplane effectiveness at high subsonic
(a) 112, 144
236, 358
125, 123
5
A
43
B
F
The abstract card, issued with one of the 5 documents, refers to the subject document. Mach numbers.
(b) 112, 123
144, 236
10
A
F
“144-slipstreams” and “236-tail-plane” not indexed.
89
Experimental determination of the relationships between turbulent boundary layers on flat plates and cones at zero heat transfer.
112
140
137
333
11
A
35
B
S
90
Experimental measurements at high subsonic speeds of the pressure distribution over the leading edge of a two-dimensional flat plate with a rounded leading edge.
112
125
333
362
4
A
31
A
S
91
Wind tunnel tests at supersonic speeds on a canard configuration with ramjets.
112, 122
172, 192
392
1
A
54
A
S
92
Manometers for automatic measurement of pressures in supersonic wind tunnels.
122, 362
391, 392
417
4
B
23
A
S
93
The effect of small asymmetries at the nose of a cylindrical body at supersonic speeds.
(a) 240, 249.
122, 255
3
C
37
B
F
“249-straight parallel sides,” and “255-interest at nose” not indexed.
(b) 240
249, 122
43
B
F
(c) 122
240, 255
10
A
F
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Question No.
Question
Search plan
Documents retrieved
Indexer
Codes used
Searcher
Success or failure
Remarks
94
Theoretical methods for determining the performance of wing-tip controls.
113, 302
307, 322
3
B
35
A
S
95
Any information on moving-wing guided missiles.
164, 322
195
5
A
49
B
S
96
Wind tunnel tests at supersonic speeds on two-dimensional aerofoils.
(a) 112
122, 195
338, 392
7
B
34
A
F
“392-wind tunnels” was indexed but not punched.
(b) 112, 122
195, 338
10
A
S
97
Rapid recording methods for measuring signals from strain gauge wind tunnel balances.
(a) 417, 413
391, 416
0
A
18
B
F
“413-balances” not indexed.
(b) 391
416, 417
2
B
S
98
Design of a six-component strain gauge balance for use in supersonic wind tunnels.
392, 391
413, 122
5
A
23
B
S
99
Flow at supersonic speeds over bodies of non-circular cross-section.
240, 254
122, 128
11
A
27
B
S
100
Experimental information about the lift on wings at hypersonic speeds.
112, 120
195, 350
10
A
40
A
S
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TABLE 2 Classification schedules
Code No.
Timesa used
Bibliographic characteristics
Pre 1935
100
77
“ 1945
101
149
“ 1950
102
194
“ 1955
103
500
Post 1934
104
633
“ 1944
105
555
“ 1949
106
505
“ 1954
107
192
Data/Tables/Methods; for Calculation/Reference
109
58
Bibliography/Survey
110
18
Dictionary/Directory/ Nomenclature
111
0
“Experiment”/Reports observation
112
524
“Theory”/Other
113
230
G.B.
114
493
U.S.A.
115
203
Other foreign/ International
116
3
RAE/NACA/AGARD
117
621
Firms
118
3
Other
119
77
Mach number/velocity
≥2.0
120
107
≥1.2
121
176
≥0.9
122
253
≥0.6
123
280
<2.0
124
393
<1.0
125
324
<0.6
126
236
Stationary
127
12
Flow/Fluids studied
128
359
Ideal fluid
129
20
Gas
130
328
Liquid
131
18
Real fluids other than Air/Water (including Rare air/Slip flow, etc.)
132
8
Homogeneous fluid/Total immersion
133
8
Other/Free surface/ Mixed flow
134
38
In own right
135
26
In relation to solids
136
279
Boundary Layer
137
94
Flow/Fluids studied
Other
138
27
Laminar/Streamline flow
139
51
Turbulent flow
140
59
Transition
141
42
Separation
142
36
Vortices
143
45
Slipstreams/Wakes/ Downwash
144
89
Jets
145
27
Blowing
146
16
Suction
147
28
Shock waves/Mach lines/ Compressibility
148
76
Circulation
149
4
Condensation/Evaporation
150
4
Convection
151
5
Dissociation
152
1
Gusts
153
16
Heating
154
41
Cooling
155
28
Acoustics/Noise/Sonic bangs
156
6
Aircraft/Aircraft components Aircraft “Type”
Fighter
157
117
Bomber
158
38
Transport
159
22
Personal
160
8
Other
390
38
Shell
161
1
Bomb
162
12
Target
163
3
“Missile”
164
47
“Single” engined
167
90
Multiple engined
168
67
Jet propelled
169
146
Turbojet
170
90
Rocket
171
33
Other/Ram, pulse
172
18
Propeller driven
173
85
Turbo prop
174
21
Other
175
24
Rotary wing aircraft
176
23
Towed
177
7
Sailplane
178
7
Lighter than air
179
3
Kite
180
3
a Times used in the indexing of 700 documents.
OCR for page 798
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Code No.
Timesa used
Aircraft/Aircraft components
Aircraft “type”
Parachute
181
6
Other method of propulsion
182
0
Seaplane
183
16
Amphibian
184
1
V.T.O. Type/Flying platform, etc. (not helicopters)
185
4
Composite aircraft
186
0
No wing
187
14
No body
188
5
No tailplane/No foreplane
189
50
No fin
108
20
With multiple fuselage
190
8
With fins other than single tail fin
191
15
With foreplane/Canard
192
6
Components present and/or studied
Complete aircraft
193
286
Other
194
324
Wing
195
361
Monoplane
196
229
Biplane
197
16
Cruciform, Y, etc.
198
26
Other
199
1
Untapered
201
57
Tapered excluding delta, arrow
202
67
Triangular/Delta/Arrow
203
104
Other (circular, “W,” etc.)
204
6
Unswept (inc. 10° sweepback)
205
102
Swept
206
177
Forward
207
2
<40°
208
45
≥40°
209
108
<50°
210
87
≥50°
211
43
Aspect ratio <4
212
89
Aspect ratio ≥3.5
213
67
Aspect ratio ≥6
214
18
Leading edge sharp
215
15
Wing
Leading edge ducted
216
5
Leading edge drooped
217
3
Cambered
218
25
Uncambered
219
11
≥8% thick
220
56
<8% thick
221
42
Interest in/at/near—wings
Planform
222
89
Aspect ratio
223
28
Sweep
224
37
Taper
225
19
Other/span
226
25
Section
227
63
Camber
228
25
Thickness
229
34
Other/profile
230
35
Twist
231
22
Dihedral/anhedral
232
4
Leading edge
233
42
Trailing edge
234
61
Tip
235
42
Tailplane/Foreplane
236
79
Fin
237
35
Propeller
238
32
Rotor
239
22
Body
240
139
Pointed nose
241
74
Other nose
243
24
Pointed tail
244
18
Other tail
246
54
Fineness Ratio ≥6
247
43
Fineness Ratio <6
248
15
Straight parallel sides
249
58
Other
250
42
Rotationally symmetric/ Body of revolution
253
80
Other
254
23
Interest in/at/near—Bodies
Nose
255
17
Tail
256
29
Section
257
10
Sides
258
18
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OCR for page 799
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Code No.
Timesa used
External store
259
38
Engine nacelle
260
32
Other
261
7
Wing mounted
262
26
Other
263
7
Strut mounted
264
11
Other
265
6
Canopy/Radome/Turret/ “Blister”
266
8
Bomb bay/Release gear
267
6
Guns/Armament
268
19
Escape device
269
2
Aerial/Antennas
270
2
Assisted take-off device
271
7
De-icing gear/Icing
272
4
Fuel/Fuel system
273
3
Fuel tank
274
12
Crew accommodation
275
2
Load/Passenger accommodation
276
3
Dirt excluders/Ventilation
277
5
Automatic control/ Servomechanisms/ Stabilization
278
31
Float/Planing surface
279
12
Undercarriage—Land
280
9
Internal flow
281
96
Located on aerofoils
282
26
Located on bodies, nacelles
283
34
Other/pipes
284
30
Intakes (divide as exits)
285
51
Exits
286
20
Nose/Tail
287
23
Side
288
11
With centre-body
291
21
No centre-body
292
9
Ducts
293
47
Straight sections
294
3
Bends
295
2
Contractions/ Expansions
296
20
Nozzles
297
21
Diffusers
298
18
Other
299
1
Convergence/ Divergences
300
4
Total enclosures
301
9
“Control” device
302
179
Attitude
303
71
“Control” device
Drag increase
304
34
Other purpose
305
42
Boundary layer control
306
17
Wing-located
307
104
T.E. region
308
76
L.E. region
309
21
Other
310
11
Fin located
311
26
Foreplane/Tailplane located
312
34
Body located
313
13
Other location
314
5
Flap type
315
93
Plain
316
23
Split
317
18
Other
318
16
Spoilers/Vortex generators
319
15
Fences/End plates/Flow guides
320
17
Auxiliary aerofoils/Slats
321
12
All moving component/ Tip
322
16
Tabs/Balancing devices
323
20
Parachute
324
10
Thrust reversal/Jet deflection
325
10
Other objects
Engine
326
74
Compressors/Turbines/ Windmills/Fans/Pumps
327
42
Cascades/Stators
328
5
Ground/Runways/Ground Facilities
329
11
Catapults/Launching devices
330
11
Ships/Watercraft
331
6
Man/Medicine
332
6
Flat Plate
333
28
Cylinder—perpendicular to flow
334
3
Particles/Droplets
335
5
Other solid
336
6
Geometry
3-Dimensional
337
274
Other
338
73
Full scale
339
173
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Code No.
Timesa used
Other
340
261
Rough surface/(Surface condition)
341
17
Steps
342
11
Projections
343
21
Fairings/Junctions
344
16
Distortions/Bumps/ Indentations
345
13
Recesses/Gaps
346
9
Perforated/Porous/ Slotted surface
347
35
Variable shape
348
12
Aerodynamic interest
349
569
Lift
350
193
Drag
352
232
Thrust
353
43
Moments/Stability/Control Moments
354
184
Stability
355
176
Control
356
102
Lateral
357
108
Longitudinal
358
209
Directional
359
88
Hinge
360
30
Damping
361
44
Pressure/Velocity distribution
362
192
Loads/Loading
363
83
Interference/Relative position
364
89
Stalling/High incidence
365
53
Sideforce/Sideslipping
366
34
Spinning
251
27
Landing/Take-off
367
56
Level flight
407
28
Diving/Descent/Gliding
368
34
Climbing
369
24
Turning
370
21
Hovering/Flapping
242
14
Separating/Jettisoning
371
13
Buffeting
372
15
Flutter/Oscillation
373
48
Aeroelasticity
374
23
Magnus effect
375
0
“Area rule”
376
10
Operation/Design
377
92
Load/Capacity/Performance/Range/Speed
378
79
Operation/Design
Economics
381
16
Reliability/Maintenance/ Safety/Accidents
382
25
Civil operation
383
17
Military operation/ Strategy/Tactics
384
45
Ballistics interest
385
20
Structures/Materials interest
386
47
Mechanical interest
387
35
Electronics/Radar/Radio
388
24
Mathematics
389
51
Principal test equipment/ Technique
Described
391
133
Wind tunnel
392
261
Continuous/Fan drive
393
45
Intermittent
394
8
Shock tube
395
4
Special purpose tunnel/Test rigs
396
23
Spinning tunnel
397
10
Water tunnel
398
4
Ballistic range
399
4
Analogy/Simulator
400
4
Ditching tank
401
2
Towing tank/Moving channel
402
12
Models mounted on air-craft
403
1
Tracks/Sleds
404
1
Free flight—Piloted aircraft
405
92
Free flight—Models/unpiloted
406
41
Components
408
24
Power/Flow production
409
15
Other
410
13
Auxiliary Apparatus/Technique
411
58
Model Design/Construction
412
49
Balances
413
18
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Code No.
Timesa used
Principal test Equipment/ Technique
Scale Effect/
414
31
Corrections/ Calibration Telemetry
415
8
Data Handling/ Methods/Computers
416
10
Flow visualization
252
51
Instruments
417
59
Combustion
418
17
Meteorology
419
8
Optics
290
4
Photography
165
11
Total postings in indexing 700 documents
20,270
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Representative terms from entire chapter:
supersonic speeds
