What exactly is the "viewable" section of radar on a military plane?
Posted by Thunderoad2015@reddit | aviation | View on Reddit | 24 comments
Hey all. I know nothing about aviation so sorry if this is a stupid question. I was watching top gun and there's a training scene in which they say "nothing on radar he must be behind us". Is that true? Does radar only point one direction? And if so. What if they were flying at 2k feet and the other plane was in front of them at 20k feet? Would the vertical difference matter? And if in that scenario what if the higher plane was horizontally 2f in front of the radar plane vs 1 mile. Would that matter? What exactly is the "viewable" section of radar?
BrianWantsTruth@reddit
In simple terms you can treat radar like a flashlight beam. If the flashlight is mounted to the nose of the jet, and can sweep side-to-side, it gets a wider view. When you see a classic “radar screen” with the line sweeping around in a circle, it’s like a lighthouse withe the beam sweeping around. When you see the large military planes with a big disk mounted on top, the disk is housing a radar that spins in a complete circle like a lighthouse.
This is also why radars can compromise stealth: if two people are in a pitch black gymnasium, trying to find each other, when one person turns on their flashlight it makes them visible to the other person.
This is a very simplified summary but it can help you understand the basics.
Broad-Part9448@reddit
So how does an F35 do beyond visual range combat? It gets it's radar data from an AWACS or something and launches it's missiles based on that info?
St-JohnMosesBrowning@reddit
No, its own radar can see farther than the human eye can see so that’s inherently BVR.
Broad-Part9448@reddit
My point was that if an F35 is in stealth mode then it wouldn't have its radar on otherwise it would get detected
Any_Confection_3064@reddit
thats not how radar works their radar has to detect you it cant detect radar just objects on the radar
ElMagnifico22@reddit
That’s not true. APG81 and other comparable radars are designed so as not to be detected. I can assure you that F35 pilots don’t get detected by turning their radar on.
St-JohnMosesBrowning@reddit
Ah okay that’s a fair question. The answers are complicated and mostly classified.
Tailhook91@reddit
It has lots of sensors and tricks that allow it to still get high quality tracks at beyond visual range. How they work is extremely classified.
blindfoldedbadgers@reddit
There’s a system called Link-16 which enables NATO platforms to share data with each other, whether it’s a ship, plane, or ground unit. F-35s use a stealthy version of this called MADL to get track data from AWACS, ground radars, etc which they can then throw a missile at. Once the missile is close enough it uses its own sensors (radar or heat) to lock on to the target.
There’s also Low Probability of Intercept radar that uses various techniques to make it harder for the enemy to see the “flashlight” as it were, and makes it harder for them to tell where its being shone from if they do see it. I don’t fully understand how this works though so I’ll let someone else explain.
martinmrocks@reddit
Phenomenal explanation.
LUBE__UP@reddit
Radar works by bouncing radio waves off objects (doesn't even have to be solid, even clouds can reflect it, which is how weather radars work). The radars used in fighters are large, so they can't really be mounted all around the plane. Instead they're usually carried in the nose, which means it can't look directly backwards because whole rest of the plane the radar is mounted on is blocking its field of view.
If you don't care about keeping things in a small & agile package, you can mount your radar nice and high to allow for a 360 degree FOV (at least on the horizontal plane)
How far left / right / up / down it can see depends on the radar.
SwoopnBuffalo@reddit
Sorry to be 'that guy', but radar bounces back against the suspended water droplets in clouds, not the water vapor of clouds themselves. You can have a cloudy day and a clear radar screen because there's no precipitation inside the clouds.
Festivefire@reddit
the radar is essentially a dish on a swivel inside the nose cone, it can sweep side to side and up and down, the traverse limits in each direction vary from radar to radar, but many modern fighter radars have quite a lot of vertical sweep range so they can detect targets that are high above them and low below them. Think of it as a squared cone. It is true that the radar basically always points forwards, except for on AWACS aircraft which usually have a big dish on top which contains a rotating radar array that shoots out the side of the dish, not the top or bottom. Generally speaking, the way it is displayed to the pilot is on a plot showing azimuth and distance, and usually somewhere on the side of this display will be an indicator as to the vertical scan position of the radar which will tell you how high above or below you, they are. With trigonometry you (or the fire control computer getting data from the radar) can determine the altitude of the other aircraft based of the altitude of your own aircraft, the vertical angle of the radar, and the range to the target aircraft.
_Abe_Froman_SKOC@reddit
For a full and complete answer you'll have to go to college, study engineering, get hired by the government, get a security clearance, then a need to know.
Conversely, you could just enjoy the movie. :)
Shadowrend01@reddit
The radar is mounted in the nose. It has a fairly wide arc and elevation (the exact coverage area is not something that can be openly discussed), but something behind you/outside of this arc won’t be visible.
haji1096@reddit
Depending on the beam width and range of the radar, aircraft can fire radar guided missiles while the aircraft is not pointed directly at the target.
haji1096@reddit
Different type’s of radar antenna move at different rates and radiate different patterns.
The capability of a platform’s radar is classified. But generally the radar is positioned in the nose. Under the nose is a radar antenna that moves (slews).
If you go to a civilian airport you can see ASR9 and ASR11 radar. The antenna’s move in a circle. This causes a time differences between the measured position of a target.
Usually estimation and filtering is used to propagate the track between radar updates.
Now this is the perspective of just one radar system.
Now imagine an AWACs system combining its look down radar, with the sensors from friendly airplanes / other sources. A system like that will generate more accurate tracks for targets
herpafilter@reddit
There are a lot of caveats and things specific to specific aircraft here, so this is super generalized.
The radar antenna transmits and receives in a roughly conical beam extending from the nose of the aircraft. The exact angle of the beam is variable depending on a bunch of things, but its narrower then you might expect. Just like your eyeballs, in order to search more of the sky the antenna is mechanically panned up and down, left and right within the nose cone. The limits of the search area in front of the aircraft depends on a lot of things, but you can ballpark it as 90 degrees left and right, and perhaps 60 degrees up and down. There are aircraft with separate rear or side facing radar but it's rare in fighters.
The mechanical motion of the antenna takes time so the more of the sky you search the longer it takes to fully cycle through that pattern. During that time you may not see an aircraft in a patch of sky the radar isn't looking at, and even if you do the rate at which you'll get updates is slower. So it's typical for fighter aircraft to limit their scan to specific areas to increase the update rate.
digger250@reddit
A mechanically pointed antenna is becoming more rare in fighter jets. AESA has replaced this in all of the most advanced militaries.
herpafilter@reddit
Yeah. The Super hornets in the movie could have either a -65 or -79 radar, the 79 being AESA. I'm not sure what percentage of the E/F fleet still has -65s, if any. In any case, even AESA radars have field of view limitations, and are actually more narrow overall then gimbled antennas.
Zealousideal-Wash367@reddit
Generally about 60 degrees off the nose for most fighters is a pretty good rule of thumb. Vertical is a little different. Pilots tell the radar what angle to look up/down so they may or may not see something 18000 feet above them (also depends on distance because it’s a cone). Generally a formation will coordinate so that an aircraft is looking high and the other would look low. Obviously that’s all highly situation dependent based on mission, threat, and a dozen other factors.
Usernamenotta@reddit
Basically, it depends on the airplane and radar set itself. Some common things. Radars do not have 360 view. It is more like a cone growing out of the nose. The reason is simple. If you had a 360 view, 40% of the information would be just your own aircraft. This being said, you can get close to 360 view by installing multiple radar receivers on your aircraft. However this is quite a new technology and requires some computing power. (well, 'new', I think 20 years now at least). What I mean is that it s possible that a Hornet would not have this capability. As for height difference, as I have mentioned. You have a cone in front of your aircraft. It s very close to a hemisphere, but there are still blind spots. The closer you are and the higher the elevation difference, the more more chances there are you are in a blind spot. As for distance, signal dissipates over distance and interference. However, that takes some distance. I think a fighter mounted radar has a range of around 80-150 km
Western_Airport269@reddit
RADAR is an acronym for RAdio Detection And Ranging, which is important to know because now you know RADAR uses radio waves and an antennae with transmitters and receivers connected to a processor to then give you the readout. For MOST planes, minus the AWACS and other electronic type birds, the radar is confined to the nosecone, which means it, at most, has a slightly greater than 180 degree field of view, as it can't transmit backwards through the body of the plane, and putting a transmitter/receiver at the back end of the plane adds weight and complexity, among other things. SO, in most scenarios, if a plane is within the \~180 degree field of view in front of the plane, and not blending into the ground clutter or rain or anything else that affects RADAR propagation, you should be able to see it.
This is why modern Air Forces are so focused on the AWACS/AEW element, as they give 360 degree coverage, the radar can cover a larger radius, due to being able to be more powerful, you have radar operators in the back of the plane who's main duty is monitoring tracks and vectoring friendly aircraft onto whatever tracks are deemed necessary of warranting extra attention, and also can increase the chances of fighters surprising other planes.
RADAR is similar to a flashlight at night-you can often see the flashlight, and thus be aware of the person holding the flashlight, long before the flashlight holder sees and becomes aware of you. So having AWACS up and then using a datalink to send the radar feed to fighters instead of the fighters radiating is a good tactic. This is talked about in countless books, it's in no way classified.
TLDR-RADAR has a field of view limited by the size, shape, placement, and power of it's antenna. So TopGun wasn't wrong.
KCPilot17@reddit
Specific degrees vary by the specific radar, but most are not 360. Elevation degrees also vary.
BL is it depends.