FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1962
1962 - 0837.PDF
FLIGHT International, 24 May 1962 835 Flight-test Instrumentation SECOND INTERNATIONAL SYMPOSIUM AT CRANFIELD NEARLY 250 delegates, representing eight countries, attended the second international flight-test instrumentation sym posium sponsored by the Department of Flight of the College of Aeronautics, Cranfield. Of the fourteen papers pre sented, two—given by T. M. Mathison of the Boeing Company and G. R. Mellinger of North American Aviation—created special interest. It is usually well worthwhile listening to someone with tremendous practical exper ience in a particular field; and Mr Mathison could certainly qualify on this count, with twenty years of Boeing flight-test experience. It was refreshing to see an honest approach being taken over the accuracies of instrumentation magnetic- tape recording systems. Some people may have viewed his figures (Table 1) as being pessimistic, in view of current develop ments; but, with many millions of measure ments behind him, the conclusions on accuracies can be taken as statements of fact rather than fiction. His paper may have seemed to some delegates to have missed the applications of wide-band frequency modulation and time-division multiplexing, which are in favour in this country at the present time, hi the author's opinion, had Mr Mathison included this system, alongside pulse- duration modulation, some of the value of his paper would have been lost, for it would no longer have been based on actual oper ating experience. No doubt progress with the Bristol 188 programme, in which a considerable amount of data is time-multiplexed by mechanical switches, on to frequency- modulated subcarriers, will provide oper ational accuracies. L. G. May's paper on the 188 was of topical interest and showed that even on our latest and fastest aero plane we are still using galvanometer recorders, although magnetic-tape and radio telemetry are playing an ever-increasing part in flight research and development. Instrumentation for current and future projects at Boeing is listed in Table 2; but Mellinger's paper showed that North American are gazing into a crystal ball for instrumentation systems to follow those currently projected for the XB-70 or RS-70. This aeroplane, cruising at M3, will pose a number of problems both as regards the number of measurements to be made and the high-temperature environment in which the instrumentation system must work. A digital system is to be used on the B-70, owing to the enormous number of measure ments to be made during flight; Mr Mellinger quoted 1,200 individual para meters (compared with the X-15's 750), and predicted 1,500 channel systems by 1965. Since the structure is a stainless-steel honeycomb, 20 per cent extra leads for the instrumentation are to be built-in, to avoid the extreme difficulty of making modifications during the flight development, if extra channels are ever required. The airborne recorders are allowed to run only intermittently, at the discretion of the pilot, in order to conserve recording time; even so, 70m data points will be recorded on each flight by the digital system alone. In effect, the pilot edits the data in the air, thus decreasing the amount of time spent searching for useful information during the ground replay of the airborne tapes. Mr Mellinger pointed out TABLE I: COMPARISON OF SYSTEM CAPABILITIES (MATHISON) System NBFM Bands 1 to 18 WBFM Standard PDM LLLS PDM PCM bits/sec A: 8.000 B: 65,000 C: 330,000 0:800,000 TDM/FM or PAM/FM rate (frames sec) Continuous Continuous 10 .5 20 30 2.5 10 40 100 200 FO 12.5 Freq range (e/s) 0-6 to 0-1,050 10 to 5,600 0-2 0-3 0-4 0-6 0-0.5 0-2 0-8 0-20 0-40 * COM 0-3 channels (per system) 12 1 90 60 45 30 45 80 160 330 400 PARISON: 24 Speed (in/sec) 7i 60 60 30 3 It 15 60 160 Tape utilization Recording time Channels per 2,400ft tape per (mini lin tape 64 144 S 8 12 16 1,080 720 540 360 128 540 256 80 32 16 8 330 21 40 SBAC RECOMMENDATIONS " * 64 min 560 Error % of full scale System only 3.0 to 5.0 10 t.0 to 2.0 1.0 to 2.0 0.25 to 0.50 ; With 1% trans 3.2 5.1 10 1.4 to 2.2 1.4 to 2.2 1.0 to I.I ? * Assuming 16-track head with two channels reserved for speech and time/reference. TABLE 2: EXAMPLES OF SYSTEM CHOICES (MATHISON) Project A current large missile1 A future commercial transport' A future space-glide re-entry vehicle* A current large helicopter* Type of data Analogue and Digital inputs Vibration Quasi-static variables Flutter and flight load Low-frequency variables Vibration and acoustics Low-frequency dynamic Recording system Main reasons for choice PCM-345,600 bit, Accuracy; large 27 bit/combination word ^Ti^?;.. approximately 400 channels .. man" d'*'"' lnPuts rr ' direct entry to computer Standard FM, 20 channels LLLS PDM 700 channels subcommutated Narrow-band FM, 100 channels PCM—129,600 bit, 9 bit/word subcommutated approximately 900 channels Non-standard FM 29 channels—to 3,000 c/s Frequency-response requirement Proven existing system Requirement for simultaneous recording for cross- correlation Accuracy; large channel capacity Frequency-response requirement Proven existing system Narrow-band FM, especially adapted to 100 channels low-frequency dynamic testing I, probably Minuteman; 2, probably the 727; 3, probably Dyna-Soar; 4, probably the Boeing-Vertol 107.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
