CC BY
16Journal of Siberian Federal University. Engineering & Technologies, 2019, 12(7), 792-801
yflK [629.7.052:621.37]:629.735.45
Compact Radar System Safe Helicopter Landing
Vladimir A. Malyshev and Viktor G. Mashkov*
Military Education and Research Centre of Military-Air Forces «Military-Air Academy Named After Professor N.E. Zhukovsky and Yu.A. Gagarin» 54a Starykh Bol'shevikov Str., Voronezh, 394064, Russia
Received 03.02.2018, received in revised form 20.09.2019, accepted 07.10.2019
Practical realization the radar device is capable safe landing an aircraft of the helicopter type on unprepared sites in any time the day, in VFR and IFR weather conditions, in the presence natural and artificial interference. The calculation range based on measuring the transit time of the signal to the earth's surface and back. The results in each time on the LCD display, applied to it the scale range elevations of objects with a height exceeding the permissible limits, which are in dangerous proximity to the aircraft under.
Keywords: radar system, helicopter landing, unprepared pad, a blind landing.
Citation: Malyshev V.A., Mashkov V.G. Compact radar system safe helicopter landing, J. Sib. Fed. Univ. Eng. technol., 2019, 12(7), 792-801. DOI: 10.17516/1999-494X-0179.
Малогабаритная радиолокационная система безопасной посадки вертолета
В.А. Малышев, В.Г. Машков
Военный учебно-научный центр Военно-воздушных сил
«Военно-воздушная академия имени профессора Н.Е. Жуковского и Ю.А. Гагарина» Россия, 394064, Воронеж, ул. Старых Большевиков, 54а
Рассмотрена практическая реализация устройства радиолокационного типа, способного обеспечить безопасную посадку воздушного судна вертолетного типа на неподготовленные площадки в любое время суток, в простых и сложных метеоусловиях, при наличии естественных и искусственных помех. Вычисление дальности основано на измерении времени прохождения
© Siberian Federal University. All rights reserved
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License (CC BY-NC 4.0). Corresponding author E-mail address: mvgblaze@mail.ru
сигнала к земной поверхности и обратно. Выдача в каждый момент времени на ЖК индикатор, с нанесенной на нем шкалой дальности, отметок от объектов с высотой, превышающей допустимые нормы, которые находятся в опасной близости под воздушным судном.
Ключевые слова: радиолокационная система, посадка вертолета, неподготовленная площадка, слепая посадка.
Landing on an unprepared ground is one of the most difficult aspects piloting of the helicopter, it is associated with an increased risk accidents and casualties. The need for landing on unprepared sites occurs primarily in the military aviation: landing, evacuation, shipping ammunition and supplies in combat - in these tasks it is often necessary to put the helicopter in unprepared or undeveloped area landing (or hover directly above it). Blind landing on unprepared ground becomes the cause a significant percentage of accidents.
One the key problems when landing on unprepared ground are the conditions insufficient visibility (eng. degraded visual environment, CIV). Under CIV means weak or zero optical visibility of the outside environment due to any the following factors or a combination: weak light, adverse weather conditions (fog, snowstorm, etc.), raising the propeller of the helicopter vortex solid particles [1].
When landing on dry or snow-covered soil air jet from the main rotor of the helicopter picks up suspended solids that critically reduces visibility and may lead to an incorrect assessment by the pilot of the helicopter position relative to the earth, moreover, may go undetected obstacles in the landing zone (large stones, static and moving objects). The term «dusty whirlwind» (brownout) describes this phenomenon during landing or takeoff on a dry surface. Similar conditions during landing or takeoff on a snowy surface described by the term «snowdrift» (whiteout). As the entrance of the helicopter in the dusty (snow) cloud visibility intended for planting landmarks worsens, and then eliminated completely [1, 2]. In addition, adverse weather conditions or insufficient light in the landing zone can be shrubs, trees, power lines, masts, buildings, structures, etc.
For a radical solution the question of safety in such situations, it is necessary to develop a special compact radar system intended for installation on aircraft helicopter type and providing a solution to the problem safe landing of the aircraft day and night in all weather conditions.
Code name sample - sensors (PRCTR), comprising a receiving-transmitting unit; a special processor I processing; antenna-feeder device (AFD); AFD PRCTR drive, with a system of stabilization and control; indicator; voltage regulators (if necessary).
Requirements PRCTR to ensure work assignment under the following conditions of flight carrier:
- flight altitude 50...10 m;
- minimum allowed pitch and roll;
- providing a sensing of the earth's surface in the regime of incoherent pulse radar with the following parameters:
a) millimeter wavelength range X = 8 mm (f = 37,5 GHz);
b) a linear resolution 1 m in range and azimuth;
c) the removal the zone survey is not dependent on the altitude of the aircraft is 15 m;
d) the range detection ground (sea) objects must be 100 m;
- indicating object level indicator on the LCD with an interval 0,5 s.
Analysis of radar PRCTR
Structurally PRCTR performed by the functional block method in the form of separate units and devices. Digital indicator hazardous area is installed in the helicopter cockpit on the instrument panel. Two transmit-receive module mounted under the fuselage.
PRCTR is a dual-channel non-coherent pulse radar station (radar), which is characterized by the following:
- every time the ground surface is irradiated by a nanosecond-duration radio pulses, and the radiation of the probing signal occurs through two narrow spaced antenna. One the antennas rigidly mounted, the antenna pattern (AP) is directed downwards under the aircraft. The second antenna is rotating in the horizontal plane the platform and includes a tilt mechanism of the antenna in elevation. AP this antenna sequentially scans the region of the earth's surface under the aircraft at some distance from the vertical, describing a circle in the horizontal plane. Depending on the current height of the aircraft changes the angle the antenna in order for the scanned region did not change;
- processing the received signals incoherent, dual channel, comes down to measuring the time signal the earth's surface and back through two channels. The time interval between the emitted and the reflected pulse - current distance to the object. The difference in delay signals the first and the second channel at each moment time, taking into account the correction factor for the slant range the second channel indicates the relative elevation the place landing of the aircraft.
The main objective PRCTR the results in each moment time (period of repetition T = 0,5 s) on the LCD indicator printed on it a scale distances the markers from objects with a height exceeding the permissible limits, which are in dangerous proximity under the aircraft. The calculation range PRCTR is based on measuring the transit time the signal to the earth's surface and back. The time interval between the emitted and the reflected pulse is measured by counting the number measurement pulses generated by a highly stable oscillator.
Method pulse distance measurement, which is the basis algorithm of functioning PRCTR is as follows.
The launch the device measuring the current distance is performed at the time the radiated pulses from the synchronizer of the radar (Fig. 1). As a result, the generator the counting pulses (GCP) begins to form a sequence pulses with repetition period Tc„, and TCH<<Tu, where the repetition Tu period of the probing pulses. At the same time begins to form the gate pulse in the shaper pulse selector (SPS). At the time formation the leading edge of the pulse selector feature selector impulses (SI). As a result, the digital pulse counter (DPC) start to do the counting pulses (CP) and DPC counts the number of pulses received at its input.
from GCP SI
synchronizer t SPS
from outDut receiver
Fig. 1. Principle of operation radar PRCTR
Counting the counting pulses continues until, until the locking mechanism SI. Locking of SI occurs at the iime fonmation thetratlingedge the selectorputse,which occurs upon entrance of SPS the signal reflected from the target from the output of the receiver radar. Thus, the output the DPC resuiting digital code ccoreshnnding to tiie deloyiimon,) Che signalreliectadSrom the target. Therefore t = ^jC„,tclii^re thef, -nomCer of dopgputecsreceieednnehempur of UUrDPC td. Hence the distance D ten iti€r iasgut
(D
2 2
Due to the foci thai ilic measured volue range in eaca ctannd ahange only when the number Nd ahanaes pe r nnio, tgeneis a diiureCoreUerenco t, acd oencc tlet range to fanget discrete and equal AD = 0,5cT„.
Clear countdown the distance to the target is possible when td < Tu. Therefore, choosing the is tte arobingpueseinc aaredeterntine i maximemtauge Ztmn« should be found from
the condition
2 m
P > t m =-— . (2)
u l anKi
i
Givan tiia foci ^Ht^c D^ u 50 ne, and yenee /¿^ ii he3 ^ end rej)etition eeriod is taken with ecme mcrgin oquas to At gn 1 |t.c
Besed ef the lect ihat the error in determining the relative elevation the place of landing aircraft shall not exceed 1 m, the error in determining the distance to the obje ct ic chosen equal to AD = 0,5 m and Tc„ must not exceed3ns.
n<rr a given meximnm range tlie sodat iC^onil she deeded erroi defimiiun AD you can define the maximumnumberbitsofthebinarycounter is needed to implement DPC,fromthe condition
sn o CcaKC / — s7
s o Znc— s .
Power ratio
In accordance wtih the range equatio n of the radar
2 PQuGSaVyAdr
D4 = N .-, (3)
( 4n)0 N 0 R0an
regardkss tlws CypeproWngs^nal receiving resolution lm in ecnge andazimuth impulse requires a transmitter power 1 mW at specific eifeetivo refleciion sarfece underlying surface ayd = - 14 dB, the desiredslgnalfbackground oreng/intemalnosse R0 = 20 dBn tOe lc^s^r eiof thepre cessing an = 20 dB, the powerspectral densityrnnse c0 = 4 x (0~21 W/Hz, dutycycle
Q = T = 170
for the duration the probe pulse x„ = 6 ns, G = 200, the antenna gain and effective area of antenna Sa = 0/152 m2.
To provide predetermined energy capacity either antenna of large area and low average power of the transmitter, either a small antenna, but at a higher transmitter power.
PRCTR shkuneincalvvs the use nanose concl pvtees (6 ns) to seduce the «dead zone» (lack impulse raalar) up tolO iv anv ehe tslculaeiov evroreted^tance to objece-0en this case, the antenna cwiieh htGh spend, letaaV ^livc^^^^dv^si^at^tse^^ir^eoai^GVS^rSe^a^. Must alrtpvavide isolation between the receiving and transmitting channels for the attenuation the penetrating signal transfer channel in recedver.
As the probing signal, without overloading the system PRCTR additional processing, it is better to use a simple and widespread sequence unmodulated rectangular pulses duration with x„ carrier frequency ofZ = 37,5 GHz.
To obtain resolution in the range of 1 m requires pulse durations
2Sr „ tu =-e 6ac.
c
When Tu = 1^s,duty cycle Q =170 that can beimplemented intheexisting components.
Depending on the tactical tasks solved PRCTR to reduce the weight and size dimensions the antenna system PRCTR selected millimeter wavelength range X = 8 mm. In the range wavelengths X = 3 mm difficult to realize in practice the individual elements the block diagram PRCTR, for example, reference oscillator, antenna switch, etc.
Block diagram
The main elements PRCTR include a transmitter that generates radio-frequency pulses; antenna-feeder device that emits radio pulses and receiving them after reflection; a receiver for amplifying and converting the reflected pulses; a display; a synchronizer for coordinating operation the transmitter, receiver and indicator. The possible auxiliary devices can include radar system adjustment the carrier frequency for suppression of active noise.
Transmitter
The synchronizer trigger pulses the reference oscillator the transmitter that generates the radio millimeter wavelength range X = 8 mm with a duration 6 ns rectangular shape. As a reference generator small capacity it is possible to use vacuum small generators on the basis lamp backward wave or Gunn diodes and avalanche transit-time diodes.
Antenna-feeder device
This device includes two antennas, antenna switch and control system diagram for the mobile antenna.
One the antennas rigidly fixed, AP directed vertically down under the aircraft. The second antenna is rotating in the horizontal plane the platform and includes a tilt mechanism of the antenna in elevation. Control system depending on the current height the aircraft governs AP this antenna. It includes a mechanism rotation and tilt the antenna, the angle sensor antenna and the control unit.
Based on the system requirements PRCTR to determine the working area in the implementation the planting should come from the following positions (Fig. 2):
- thewidththezonearound the helicopte r 1 m;
- removal zone R = 15 m (determined based on the size the helicopter with working propellers, for example, thesize the MI-8 is 26 m);
- working Mghe PRCTR ttroue ee mt(j 10 m.
Bceeh on teleia eequiremenOi (resolution and aitituderange),the aegle inclination the movable antennashouldbechanoed énaanouda nce with the law of
RSr/ 2
a = arctg—-, (4)
тек
where dr the resolution in range, Нтек the current altitude of the aircraft. Which corresponds to the angle 17.2° andamaximumheight 50 mand57,2°at aminimum height 10 m.
The variation the angle the antenna in time need to implement discretely, depending on the elevation changes the aircraft. If the step is equal dr, the error determining the removal work zone PRCTR defined as AR = tga, will be changed from 30 cm to 1,55 m, which will have a significant impact on the accuracy of the system PRCTR in General. Therefore, it is additionally necessary to carry out the aggregation omanagement system the omobile antenna with onboard inertial systems, measurement error changes the height which does not exceed a few centimeters.
To determine the type and size the antennas, first the required AP we use the Fig. 2. Since the fixed AP with a decrease in height VS the resolution of the radar is improved, then AP at the maximum operating altitude PRCTR should be 20<,,5 = 1,05°. At a minimum height PRCTR in such AP the resolution will be about 0,6 m.
As an antenna with such a narrow AP and small size size is advisable to use mirrored parabolic antenna (MPA), which consists the irradiator and the mirror (Fig. 3, where: h - depth of the mirror; f - is the focal length; 2ф0 - angle of aperture; L3 - maximum linear opening). The mirror converts the curvilinear wave front of the radiator to a flat front, wherein the aperture is provided MPA synphasicity field.
From the theory antennas according to the amplitude-phase distribution, the width of the AP can be estimated using the ratio:
20,5 =5 89"-^
(5)
Solving the inverse froMern, L3 = eZTS,, = 45 cm. The sidelob e level get is qual minus 17 dB, and the directiv ity factor
To convert spherical front MPA in the flat front, you ne ed to use; a mirror with a parabolic profile. For caiuulueioo ot rti^^ctr^r anfennes ery ueoC on ihuratio:
How 2^ = 120°geta f = 19,5 cmand h = 6,5 cm.
The bandwidth operating frequencies is? determined MPA acceptable reduction of the gain and the allowable change width AP MPA deCcmuned l the polaridilion Che radiator.
As irradcataee use a weakle dicectroneC antenwa tiere are po^cit; fefleeaers and linear. Point reflectors form a spherical wave front and these include open end the waveguide, helical antenna and hornantenna.
The main requirements for irradiators, are: the formation the desired wave front; AP feed needs to provide a certain «interception» energy mirror; minimum shading the aperture the mirror. Most often usnd as rpflaaCacg MgA tlea oj>in end tge wavtggkte. Rir tlie aieadaed waveguide width the AP in Che Eedane in, anO in iCe emplane. To increase rhe BOTTOM intlie H-ilane 120° it is possible to cee tde laradiator (,]F>ih- 4, rp = ha°i, wit= a = mnr and =3 = 3sh mm, are calrulaCe d from the formulas
2ldh = 66— and 2605 =5\— respectively. ii ' no
To ensure circular scan mobile antenna region around the aircraft and display object level indicator on the LCD with an interval 0,5 s, it is necessary that the angular velocity rotation the platform (disk's) was 120 rpm (2 revolutions/s). To reduce the requirements on the frequency rotation is possible due to the increase in the period of review space, the dependence is directly proportional.
The tilt mechanism the antenna in elevation should work to change the altitude of the aircraft in increments 0,1 m, then the error capture in the study area will not exceed 15%.
D0 = — <=40 013.
(6)
¿2=1612 andL =4/ • tg ) .
(7)
h
f
Fig. 3. Mirror parabolic antenna
Fig. 4. Opening feed
Fig. 5. Horn antenna
Width AP fixed antenna should not exce e d 30° in E and H-planes. In this case, in order to reduce the final cost the system PRCTR advisable to uao a horn antenna (Fig. 5) . Horn ante nnas are a simple and bro aObang aetennas.
To calculate the optimal H-plane secto rial horn are used in thefollowing ratio:
(HI, =7= boa 20=5=80A; (8)
3a ap
to calcalate the; E-plaves ectorial horn
RL = ^aod205 = 56 A. (9)
Therefore,withX=8 mm, a = 21 cm, b =1,5cm and Ronm = 2 cm.
Receiver
The receiver should bs performed in the homodyne scheme with a low noise radio frequency amplifier (LNA) to as little as possible to li mit idn rec eptio n weak signal s . The I) andw iclth there ceiver should be consistent with the spectrum width the received signals.
Considertbe principle hppration PRCTR simplified bionk eiagram etig. 6). High-stability reference oscillator high-frequency vibrations by using frequency modulator generates a predetermined form the probe pulse signal at the carrier frequency, which is triggered by the signals the synchronizer is to ensure consistency the entire transceiver system. In the power amplifier at the output the transmission path is not necessary, since a power 1 mW obtained directly from the reference oscillator.
After antenna switch, a periodic sequence of pulses is radiated by each antenna (movable and stationary) within its specified radiation pattern. The polarization the radiated and received waves is determined by the design the antennas (polarizers). At full polarization sensing and reception, each
- 799 -
Fig. 6. Asimplified block diagram PRCTR
antenna generates four independentchannelsfor thereception thewaveswith polarization GG, VV, GV and VG. Ft^eAat,]^itetie siruii^u^el^lKGTIil^^c^on^sti^^ire^d o nalhenhannels.
TSt syetem gr^bi^i^zeliGT anl noetrol mo^nGS APtha mnliSt nntenna in nccrrdence with the require. l^^^elt^^i^ensSG't surfate. Whep<ilelese oping» the reniew anlennaprovides nontinuous illumination aelven atsa (rinpt tie enrth's snrfeteny tracOlng them when yon clteant the relght and trajectesyofalrcraft.Thls it mhnltfredbn tlct rtgnals ansm inertinl snsicmt and sensors of angular positions
Automatictwitchinfthc transmirtenhceailnet ^t tht reccrnifn mlenm is intheswiach.TGe choice switch ts primarily for insertttn sos^t;, ttalatson getwcen ciannelt nndrwltchsime. Modern twitches have the capobiHty implementing a complete transition from reception mode to transmission in units nanoseconds, whlto sspnoficantty rcnuceslhedead t^t^r^e hissbllity mitlimntes radar.
Thn amentia swltuG can t> e mahel nShenoпh offunetianaltyfimsShn mlceowave module on GIS technology using open-frame switching p-i-n diodes or using MEMS technology.
Electromagnetic waves reflected from objects in the viewing area receives both fixed and movable antennas to form two signals corresponding to the channel height measurement (fixed antenna) and the channel range (movable antenna). After amplification in low noise amplifier radio frequency electromagnetic pulses high frequency oscillations received on the second input the mixer. Next is the quadrature processing and detection.
From the output the amplitude detector signals are fed to the threshold device, where the detection threshold is set in accordance with the criteria detection, and the measured variance the noise Dm.
For the case using packs of radio pulses Nn = 5 (x„ = 6 hc, Q = 2) is videointerior, where noncoherent accumulation signal, allowing to increase the ratio signal/noise at the input the threshold circuit. However, the use packs nanosecond pulses with a low duty cycle, requires further study the feasibility this on the existing components.
In the structural diagram depicts a two-channel signal processing unit, which performs counting the counting pulses prior to the receipt signals from the threshold circuits and generates a digital code corresponding to the delay time the signal in the channel range and digital code corresponding to the delay time the signal in channel height. The code values the height and angle the movable antenna unit angular position sensors is calculated, the estimated range the study area («ring» overview of the mobile antenna). This value is compared with the measured range and if the difference exceeds the threshold level, the results level the indicator the dangerous object in the area landing the aircraft. The threshold level should change depending on the current height the aircraft, which should be considered in the processing unit. To determine the angular position the threat object relative to the aircraft in a processing unit receives data from inertial sensors and angular position sensors.
The functioning the system processing is provided by a set algorithms for solving problems (algorithmic, software) and hardware (analog and digital processors, and computers).
When implementing the proposed scheme should be paid special attention when selecting the reference oscillator of highly stable millimeter band ultrashort pulses, high-speed antenna switch for transmitting and receiving channel and rotating the gyro-stabilized platform.
Conclusion
Thus, the implementation industry-developed sensors for the safe landing an aircraft the helicopter type in the conditions insufficient visibility on an unprepared ground will reduce the risk accidents and casualties.
References
[1] Сажаем вертолет вслепую: обзор технологий синтетического зрения [Электронный ресурс] - Режим доступа: http://www.geektimes.ru/post/280278/ - Заглавие с экрана. [Plant the helicopter in the blind: technology overview synthetic vision [Electronic resourse] - Access: http:// www.geektimes.ru/post/280278/ (in Russian)]
[2] Особенности взлетов и посадок на пыльных, песчаных или заснеженных площадках [Электронный ресурс] - Режим доступа: http://www.svvaul.ru/component/k2/600-osobennosti-vzletov-i-osadok-na-pylnykh-peschanykh-ili-zasnezhennykh-ploshchadkakh/ - Заглавие с экрана. [Features takeoffs and landings in dusty, sandy or snow-covered sites [Electronic resourse] - Access: http://www.svvaul.ru/component/k2/600-osobennosti-vzletov-i-osadok-na-pylnykh-peschanykh-ili-zasnezhennykh-ploshchadkakh/ (in Russian)]
