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84

In many cases, yes you can fly under the radar because typical civilian radar is line of sight, meaning that it has to have a straight unobstructed path to an object in order to "see" it. This is because it works by sending a radar signal out and waiting for it to reflect off of something. If it reflects off of another object, like the ground, a mountain, ...


67

It is certainly possible to fly "under the radar." Military pilots practice a type of flying called nap-of-the-earth for exactly this purpose. This tactic is primarily used by smaller fighters and attack aircraft, but larger planes like the B-1 are also capable of this. Here is why this tactic may be useful: In civil aviation, mountains or other terrain can ...


62

Basically everything that consumes power on an aircraft can potentially cause interference, short-circuits, or otherwise jeopardize the safety of flight and therefore must be switchable. Sometimes the switch is in the form a button, otherwise by a fuse. There are several particular reasons that the transponder can be turned off. If the transponder ...


44

To add some data to Matthew's answer: Anti aircraft missiles come in basically 4 types (some others have been tried but aren't in common use). Active radar homing Passive radar homing Infrared homing Laser guided Active radar homing has a radar in the missile sending out signals. Those signals can be detected and classified by the target aircraft. Passive ...


43

Would a homemade lawn chair balloon be visible on ATC and collision avoidance radar? It might be visible to ATC, but, at best, only as one of several inconspicuous unidentified red dots. It wouldn't appear on aircraft collision avoidance displays (TCAS) and would not trigger any TCAS alerts. Radar cross section Balloons, and clusters of balloons are ...


38

They looked out the window! If you are talking about a developing thunderstorm, especially during the day, they can be quite easy to see in front of you provided decent visibility. Here is some good footage of what it looks like to fly around a towering cell, you will note its fairly easy to see. At night, lightning, even in the clouds tends to be a ...


35

Only in military applications nowadays, primarily helicopters as the system doesn't require the alignment process of the INS system, is not subject to GPS jamming, is very accurate when flying low (as opposed to high and fast over oceans), and most helicopters don't do the occasional barrel roll (the system is belly mounted to track the ground below). (Calm ...


33

Radar resolution is defined in terms of degrees of arc (or alternatively in steradians/solid angles) and as such, the further away from the radar, the larger volume is being sampled. At altitude and some distance from the radar you should have a bit of leeway on how loose of a formation you can fly and show up as one contact on the radar display. I'm not ...


33

Note that for advanced radar systems, moving helicopters might always be distinguishable from cars and other objects, due to the fact that helicopters have moving rotors. While I have no information on military systems, I know the systems by robinradar can separate drones from birds by using doppler shift techniques. Doing this on an actual, full-size ...


29

It is a wind tee; it serves the same function as a wind sock. It is designed to resemble an airplane from the air so that pilots overflying the field can more easily determine in which direction they should land. The top of the "T" is the front of the airplane and represents the direction in which an airplane should land. When the wind hits the vertical ...


26

Secondary Surveillance Radars work on 1030 MHz and 1090 MHz. Most primary radars work at higher frequencies. Signals at these frequencies do not follow the curvature of the earth very well. They work best in line of sight. Aircraft far away from the radar must be at high altitude to be above the horizon, otherwise they are "under the radar" In flat terrain ...


26

The Secondary Surveillance Radar system provides range in a method similar to primary radar: by measuring the time between the transmission of the interrogation signal and reception of the reply. The range is proportional to the time difference, minus a constant that allows for the aircraft transponder to perform processing. This would not work if ...


25

The answer is yes (in most cases) but it has little to do with the helicopter itself. 5 meters (~16.5 feet) AGL is quite low to the ground. Chances are you are simply below the radar horizon for whatever the local radar facility is. At that height you are even below trees, buildings and the like. This of course is affected by the distance to the radar unit ...


24

A general search radar, because it has to search a much larger portion of the area around the plane, can only scan so many times a second. When that radar finds a target, and the pilot commands the system to lock onto the target, it enables a different radar system, that searches a much smaller portion of the area around the plane where the target is known ...


24

Primary radars are sensitive enough to pick up even large birds. A lawnchair ballon would certainly register if the settings allow. To suppress the signals from birds and other non-aircraft objects, a minimum speed is required for primary radars to show a blip to the controller. Since the lawnchair is moving with the wind, it will be filtered out, unless the ...


23

It works the same way any radar works. An antenna broadcasts a pulse of energy and listens for its reflection and interprets the power of the reflection to calculate the reflectivity factor Z, expressed in decibels dBZ (helpful because return power varies across many orders of magnitude). Weather radar can see water, hail, bugs, birds, bats and bigger ...


23

It's a lighted 'wind tee'. this website shows various wind direction indicators


23

You are seriously over estimating the technical capabilities of the time. The gun-sight is not much more than an intricate slide-rule. You had to feed it information about the target size/aircraft type and it used the gyro information from your own aircrafts turn rates to project a reticule circle on the glass. The position of the projection is offset ...


22

The device you are talking about is called a transponder. This is a device that listens for a signal (an interrogation) and responds with information about the airplane including an ATC assigned code, altitude information and additional aircraft info for certain equipment. There are 2 ways ATC watches airplanes: Primary Radar Secondary Surveillance Radar ...


21

The things you mention would matter, if you wanted to know the distance to 6 or more significant digits. But ATC does not need that precision. They need to be able to tell whether it's 4 nmi (too close), 5 nmi (still sufficient, but getting in trouble) or 10 nmi (no worry, but should not be heading directly towards each other). That is one significant digit. ...


20

Everything including the flight recorder has a power switch or circuit breaker. Electrical devices occasionally malfunction, and you don't want a sparky transponder setting the plane on fire when you can just turn it off and use the other one.


20

The class of ATC radars that you are talking about is secondary radar. Secondary radar works by transmitting an interrogation signal on 1030 MHz to which the transponder replies on 1090MHz. There are several modes of interrogation. For civil ATC, modes A,C and S are important. The uplink signal (interrogation) is a simple pulse encoding (Mode A/C) or a ...


20

Your question: What is the logic behind the delay of the signal and how is the echo signal later bound with the signal sent? Short answer A PESA is an array of individual antennas. Each antenna radiates the same signal, except the phase. The phase adjustment for each antenna allows for the non-moving array to behave like if it could be rotated, i.e. the ...


20

The JSTARS (Joint Surveillance Target Attack Radar System) military radar developed and used from 1991 was particularly good at identifying helicopters. JSTARS was designed to identify moving objects on the ground, such as tank columns and supply convoys used by the Iraqi forces during Operation Desert Storm. It used a doppler radar suspended below a large ...


19

IFF systems use a transponder/interrogator combination to allow aircraft to issue challenges, receive responses, and do the friend or foe test. BAE Systems has a transponder product page with a little info, and Wikipedia (yeah yeah) has a reasonably thorough description and history of IFF. According to NATO STANAG 4579 (abstract): This NATO BRID is a ...


19

It certainly seems so. Stealth aircraft are not invisible to radar, only less visible. Under certain conditions the adversary will be able to get a radar lock: At close distance With very high (focused) radar energy At certain angles of incidence Given these risks and the low weight of chaff, it wouldn't be be wise to not carry it. One source that ...


19

There are a few different ATC Systems and Radar Screens being used throughout the world, so there will be no set standard which applies globally, as vendors and setup differ. The ATC screen can be adjusted to show what information the controller needs, and some items are universal to all positions being served (Callsign, Speed, Altitude, Assigned Altitude), ...


18

With the proper knowledge of the aircraft systems almost anything can be turned off. That's what we do at the end of almost every flight day. Most of the communications systems can actually be turned off fairly easily, but the average person would not know how to do it. In airplanes like the 777, there are multiple ways that they communicate but all of ...


18

SSR can work independently and this is quite common as well. Primary radars cost a lot to maintain, and as more and more planes are equipped with transponders, primary radars are being shut down. Many areas now have secondary radar coverage but no primary radar coverage. SSR only relies on replies sent as a response to its own interrogations. This works ...


18

I´ll second John K´s recommendation of Fate is the Hunter for a first hand account of flying in the 30s and 40s. The style can be a bit too laden in floritures, trying to lend a certain mystique to flying that still existed when it was published, but the content is sound and if you want a glimpse into the aviation world of that era, it is a great read. To ...


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