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Weather Radar
Hi everyone,
I understand there are many different weather radar systems on many different aircraft, however would like to know what the average beam width is across the different systems in particular the Collins radar beam width. Assuming a 3 degree beam width and a tilt of - 2 degrees (or 2 degrees down) would this mean that the beam width is covering an area of .5 down to 3.5 degrees down (ie. 1.5 up and 1.5 down from the central position of -2 degrees). Have researched the Collins radar system and instructional guide however nowhere does it discuss the radars beam width. Would appreciate it if anyone could tell me whether I'm on the right track. |
Airborne wx radar beam width varies according to antenna size. Generally, the larger the antenna, the less the angular beam width. Smaller antenna, less tilt down is required in order to receive ground returns at a specific distance and height above the surface. Brand does not matter in this respect. There are charts and diagrams to illustrate the concept all over the web. Enjoy!
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As Westhawk pointed out, the radar antenna's beam width is not linked to brand but antenna size.
A 30" diameter flat-plate antenna will produce about 3 degrees of beam width. a smaller diameter would give a wider beam. Now that is for flat-plate. For other shapes, results may differ, but in commercial aircraft I believe this to be almost exclusively flat-plate antennas. Although I don't know the whole product range of Collins, I suspect they offer radar equipment to fit in various aircraft size, and give options for different flat-plate diameters. A reference section regarding angle, distance and beam width of radar equipment can be found in the book "M3: Mental Math for Aviators". Of course other sources can be found online too. newifr, which aircraft is your Collins equipment mounted on? Do you know the antenna diameter? |
Best information can be found in the maintenance manuals (AMM) found in your airline in the hands of its engineers.
These manuals should specify not just what weather radar is fitted to the aircraft, but include more detail with dimensions and detailed description of usage. The chapter on weather radar in the AMM on B737 includes so many more pages then I've ever seen in any FCOM, including the beam width of 5.4 on the airframe it referred to, its hinging, dish dimensions etc etc |
"Hingeing" on a planar array aerial, e g 737NG?
Maybe not...........................?:confused: |
Barkingmad, please explain.
Are you saying that the 737ng antenna does not actually move? I'm currently studying B1 Module 11 and I haven't come across that concept in my notes or text books so far. |
Flat Plate Antenna The flat plate antenna transmits and receives RF pulses. The flat plate antenna is an array of radiation slots. The RF pulses radiate from each of the slots. The antenna makes a beam 5.4 degrees high and 5.4 degrees wide. The antenna weighs 6 lb (2.7 kg). It is 23 inches wide. Antenna Pedestal The antenna pedestal contains these items: * Scan motors * Antenna position monitors * Elevation and scan disable switches. There is a horizontal scan motor to move the antenna +/- 90 degrees from the airplane centerline. There is also an elevation scan motor to move the antenna +/- 40 degrees up or down. This value includes manual tilt selection from the WXR control panel. There is a zero position monitor and an incremental monitor for each motor. These monitors send antenna horizontal scan and elevation scan position data to the WXR R/T. There are elevation and azimuth scales that permit a visual measurement of the tilt and scan angles. "Hingeing" on a planar array aerial, e g 737NG? |
In which case I stand corrected re moving parts.
I was under the (mistaken) impression the NGs radar had a hi-tech flat aerial which scanned electronically with the plate facing forwards, mounted solidly on the bulkhead and no movement, hence the lack of clunking as the old fashioned mechanical dish hit the stops and reversed its travel as in older "classics". Back to the books again for me, no more darkened room for a while...............:confused: |
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Underfire, re your photograph, I notice it is of the installation on a "Classic" -500 series, without winglets.
Any chance of one of the 'NG' installation please, just to put this one to bed? Sorry about late response, but I'm just back in from the cold....................... :) |
Barking...
Grab a grog and enjoy a video just for you! Look underneath the nose radome of a 737-800 - Sjap's 737 maintenance experience exchangeSjap's 737 maintenance experience exchange |
Thanks again Uf, but though a close-up of NG innards, I didn't see any hinges or other obvious wobbly bits.
I'm now left wondering where the original rumour of a Fixed Planar Array came from? Over to you guys/gals with access to the MMs.......? :) |
Barking mad, the wobbly bits you are looking for are at 47 to 49 seconds and about 1 minute 17 secs.They are not that obvious or heavy duty as the plate is quite light.
I've worked on dozens of 737 NGs . None had a fixed plate.All physically scan. Not saying the ones you talk about don't exist somewhere but not in my experience. |
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Again, many thanks underfire, that puts that one to bed.
The rigidly mounted planar array must have referred to some other aircraft, it will keep what's left of my brain busy trying to recall where I came across it! :) |
A complete non expert here - interesting topic but something surprised me It looks like the RF duct goes throught the pressure bulkhead - what is done to keep the pressure integrity - the duct doesnt look as if its built of anything more than normal for RF so where is the air seal done?
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The waveguide seal is normally in the bulkhead fitting.
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Assuming a 3 degree beam width and a tilt of - 2 degrees (or 2 degrees down) would this mean that the beam width is covering an area of .5 down to 3.5 degrees down (ie. 1.5 up and 1.5 down from the central position of -2 degrees).
From the first post that opened this thread: And the answer is ..? |
Beam
Yes, 1.5 up and 1.5 down from the central position of -2 degrees.
Tilt control is the most important factor for proper manual operationof the radar. When outsideair temperature falls below -40 °C, thunderstorm tops are formed entirely of ice crystalsand reflect very little radar energy. Significant down tiltis required to ensure that the radar beam is picking up the more reflective part of the storm that is at lower altitudes. Over land ground clutter can be used to determine proper tilt within 160NM of the aircraft. Within 160 NM, tilting the radar so that some groundclutter appears in the outer most range scale keeps the antenna pointedtowards the reflective portion of the thunderstorms. A 28-inch flat-plate antenna produces a 3.5°-wide beam. At ranges less than 80 NM, this produces a fairly narrow and well-focused beam. Beyond 80 NM, the beam diameter increases until at 300 NM it is equal to 105,000 feet. To put this into perspective, at this distance, it would take a storm cell over 22 NM tall and wide to fill the beam. Because the beam remains fairly focused within 80 NM of the aircraft, it is recommended that weather evaluation be done only when the weather is within 80 NM of the aircraft. Beyond 80 NM, the radar should be used primarily for strategic planning and weather avoidance. The following formula can be used to calculate the approximate beam width at any range: Beam width (in feet) = (Distance in NM x 3.5)+ 00 20NM: 7,000 40NM:14,000 80NM: 28,000 100NM: 35,000 160NM: 56,000 |
Overwater tilt setings
Recommended Over Water Tilt Settings
Altitude (feet) 40 NM 80 NM 160 NM 40,000 -7° -3° -2° 35.000 -6° -2° -1° 30,000 -4° -1° 0° 25,000 -3° -1° 0° 20,000 -2° 0° +1° |
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