Radome /radar effectivness.
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Radome /radar effectivness.
we recieved a 744 radome in the shop the other day that was so full of moisture you could almost swim in it.
I was wondering if Small amouts of moisture showed up onthe radar screen? or does it need a fair bit of water in it to effect the radar reception?
I was wondering if Small amouts of moisture showed up onthe radar screen? or does it need a fair bit of water in it to effect the radar reception?
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When the radome becomes saturated with water the range of the radar decreases rapidly, to useless.
I once had a radome that had been damaged and filled with Bondo. It took a long time to get around the ominous cloud that appeared just off to the right of the nose!!
I once had a radome that had been damaged and filled with Bondo. It took a long time to get around the ominous cloud that appeared just off to the right of the nose!!
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A water logged radome is bad news. The water will freeze at high altitudes and you will be lucky to pick up a Cb at 20 miles. That is because a thin coating of ice absorbs the radar beam and very little energy goes beyond the radome. We had this trouble on a B737-200 during operations over the Central Pacific region. For example, we could normally pick up a large island like Guam (60 miles long)on the 180 mile range - but it would only show up at 80 miles. Big Cb would not show until you were on top of them. No fault found by the techs. The ice had melted by then.
I took photos of the radar screen and of Cb and sent them to Bendix. Bendix said check the radome for moisture. The techs then found pin hole damage in the radome. They baked the radome in a special oven - which dries out water - and repaired the holes. No further problems.
I took photos of the radar screen and of Cb and sent them to Bendix. Bendix said check the radome for moisture. The techs then found pin hole damage in the radome. They baked the radome in a special oven - which dries out water - and repaired the holes. No further problems.
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Radomes are generally of honeycomb construction and erosion or pin holes in the outer skin can allow water to accumulate within the radome structure. Without regular inspection, including moisture testing and prompt repairs, moisture ingress into radome structure is inevitable. Such moisture attenuates the energy emitted by the radar and, since the transmission power through the radome is reduced, the returns are also weak. The effect is the same as having dirty glass on your car headlights; the lights are dim and you don't see so well. Being so close to the dish, any energy reflected directly back from the radome doesn't actually affect the display because the receiver circuits are disabled for a suitable time interval after each pulse is transmitted to prevent such effects.
At first, radar returns grow weaker and there is a loss of range; you don't see weather at the longer ranges and where the strength of weather returns gradually increase as they get nearer, this may be mistaken for a loss of STC in the receiver. As the water inside the radome structure builds up and output signal attenuation increases, the returns grow weaker and weaker until finally the radar becomes useless. Often, the radome delaminates and splits due to the water within the material freezing and forcing the outer layers apart but more usually the only symptom is loss of radar sensitivity.
Meters are available to measure the moisture content on radomes and should be used by your maintenance staff whenever pilots report weak returns. Unfortunately the current trend to combine the avionic trades has reduced overall skill levels, particularly in the Radio & Radar specialisation, and competence levels have declined noticably in recent years. From what I have seen and heard of recent radio examination questions, practical aspects have suffered at the expense of esoteric theory. Too often the response to a radar defect in the Tech Log is simply to "change the box" without bothering with the basics.
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At first, radar returns grow weaker and there is a loss of range; you don't see weather at the longer ranges and where the strength of weather returns gradually increase as they get nearer, this may be mistaken for a loss of STC in the receiver. As the water inside the radome structure builds up and output signal attenuation increases, the returns grow weaker and weaker until finally the radar becomes useless. Often, the radome delaminates and splits due to the water within the material freezing and forcing the outer layers apart but more usually the only symptom is loss of radar sensitivity.
Meters are available to measure the moisture content on radomes and should be used by your maintenance staff whenever pilots report weak returns. Unfortunately the current trend to combine the avionic trades has reduced overall skill levels, particularly in the Radio & Radar specialisation, and competence levels have declined noticably in recent years. From what I have seen and heard of recent radio examination questions, practical aspects have suffered at the expense of esoteric theory. Too often the response to a radar defect in the Tech Log is simply to "change the box" without bothering with the basics.
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Through difficulties to the cinema
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Blacksheep,
could you direct me to a good website with airborne weather radar theory ? i'm particularly interested in it's operating frequencies and what happen when different ranges are selected.
HS
[This message has been edited by HighSpeed (edited 15 February 2001).]
could you direct me to a good website with airborne weather radar theory ? i'm particularly interested in it's operating frequencies and what happen when different ranges are selected.
HS
[This message has been edited by HighSpeed (edited 15 February 2001).]
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It is true that a large percentage of radar problems are actually problems in the radome. Whoever posted that note that "only moving water" paints is wrong.
Best source is Capt Dave Gwinn. Knows radar better than anybody from an operator standpoint, teaches seminars, etc. Don't waste your time with Archie Trammel unless you're only interested in applying the ideas to light airplanes.
Go to the Honeywell web site and do a search for Gwinn and you'll find him. I'm sure you can get information through them.
Best source is Capt Dave Gwinn. Knows radar better than anybody from an operator standpoint, teaches seminars, etc. Don't waste your time with Archie Trammel unless you're only interested in applying the ideas to light airplanes.
Go to the Honeywell web site and do a search for Gwinn and you'll find him. I'm sure you can get information through them.
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Shore Guy, If you leave it until the "moisture" can be detected by weight you're too bl**dy late! 
That's why they invented radome moisture detection meters. (For any "heavies" that are reading this, these meters can also be useful for finding moisture in regular structural honeycomb sections - before they delaminate.) As with all things, prevention is better than cure so it is really important to check radomes for pin prick holes at every maintenance visit. It only takes a couple of minutes to look and its much easier to fix pin holes than to strip the inner skin, dry with infra red heaters and reskin the radome. And you still have to fix the pin holes afterwards anyway!
HighSpeed, Prof2MDA is right on. Honeywell, (now combined with the former AlliedSignal and then collectively combined into General Electric) are a good source of information. Check out the website at www.cas.honeywell and use the contact information to politely scrounge for info. They are usually quite generous to genuine inquirers. E-mail me if you have any trouble and I'll see if I can help.
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That's why they invented radome moisture detection meters. (For any "heavies" that are reading this, these meters can also be useful for finding moisture in regular structural honeycomb sections - before they delaminate.) As with all things, prevention is better than cure so it is really important to check radomes for pin prick holes at every maintenance visit. It only takes a couple of minutes to look and its much easier to fix pin holes than to strip the inner skin, dry with infra red heaters and reskin the radome. And you still have to fix the pin holes afterwards anyway!HighSpeed, Prof2MDA is right on. Honeywell, (now combined with the former AlliedSignal and then collectively combined into General Electric) are a good source of information. Check out the website at www.cas.honeywell and use the contact information to politely scrounge for info. They are usually quite generous to genuine inquirers. E-mail me if you have any trouble and I'll see if I can help.
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Through difficulties to the cinema
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Blacksheep,
Thanks for the info. My experience is that moisture in the radome presents more of a operational challenge to flight crews because of the greatly reduced power (supposedly compensated for my computer/software enhancement) of newer radars. My opintion is that the newer lower power radars have a much greater attenuation problem and are more susceptable to degradation due to radome moisture problems than the earlier highter powered x and c band radars (does anyone make c band radars anymore?).
Thanks for the info. My experience is that moisture in the radome presents more of a operational challenge to flight crews because of the greatly reduced power (supposedly compensated for my computer/software enhancement) of newer radars. My opintion is that the newer lower power radars have a much greater attenuation problem and are more susceptable to degradation due to radome moisture problems than the earlier highter powered x and c band radars (does anyone make c band radars anymore?).
