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Old 12-30-2016, 11:46 AM   #11
GGTharos
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I'll try to help you out with some details:

In game:

1) You have an effective notch, meaning that against a pulse-doppler radar, your radar return will be rejected if flying below some 100m/s when >10km, and you have to be below 50m/s when <= 10km. This may also depend on PRF setting of the radar. The point is, you need to be slow and you WILL be invisible to the radar unless you are at a higher altitude than the radar emitter.

2) Once you are spotted on radar from afar, even though you might try to evade, you can't really go anywhere very quickly. As a result a fighter can enter the area where you were last seen and search visually or with IRST if so equipped. Finally, AWACS can things unpleasant for you.

3) AI have god-like situational awareness ... once they acquire you, you're in trouble.


In reality:

1) Although your rotor blades generate an overall smaller radar reflection than the fuselage, their return generates a high doppler shift compared to the ground return, and your fuselage - so a doppler radar will process this and show you on the screen regardless of what speed you're travelling at, or what altitude you are at. In a well known incident, a LANDED helicopter was tracked in A2A mode by an f-15E from 50nm away. They fed this to the targeting pod to guide a bomb onto that heli. In other words, if you were facing an F-15 that is realistically modeled, you wouldn't be able to hide, and with modern versions of missiles even counting on ground clutter to increase miss distance might not be useful. Older doppler radars though, like the ones modeled for the flanker and mig (and typically Viggen, F-5, MiG-21) should probably show your rotors as a jamming strobe instead because of the spread of doppler shifts


In conclusion for the game, you need some of the following tools:

1) Situational Awareness, so that you know where the fighters are. Get this info from AWACS, your buddies, your own sensors, whoever and wherever you can get it from.
2) Terrain mask and plan your route if possible in such a way that you will be able to terrain mask. Stick a mountain/hill between yourself and the bandit, preferably before they ever see you.
3) Learn to fly in the notch. Even though you can slow down enough to always be in the notch, learn to fly in it given information from other sources. Put the bandit on your 3/9 and move away from where you were at best speed.
4) Be aware that notching multiple bandits coming from different directions could be difficult or impossible, given that this requires a specific geometry.

You can search the forums for 'notching, doppler notch, radar notch' to read about it and understand how it works.

Quote:
Originally Posted by Neon67 View Post
Hi guys.

I thought DCS implemented restrictions on the radar for chopper flying slower than a certain speed.

However I am still getting locked when I am stationary, hovering at 3 m high, on the ground or on a building.

Is it intended ?

I really struggle to hide myself from Fighters
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Old 12-30-2016, 11:48 AM   #12
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It has nothing to do with classified/unclassified.

It's just old code that hasn't been revised, and you are just being given a break. Helicopters are being given a huge break all in the name of MP

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Originally Posted by Faelwolf View Post
In the Sim, I think it is reduced to unclassified levels, so we get a break compared to R/L. But throw in a spinning rotor disk, and someone could probably rig up a homemade radar with parts from an old microwave and a used satelite TV dish to spot you.
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Old 12-31-2016, 05:07 PM   #13
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thanks for the explaination

Is this implemented for all aircrafts or only russians ?
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Old 09-18-2019, 08:03 PM   #14
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For those interested - This report describes millimeter wave Doppler signature measurements made on a hovering Mi-24 Hind-D helicopter.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a351581.pdf
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Old 09-23-2019, 04:22 PM   #15
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Helicopters DO really struggle to hide from fighters.

If you find yourself in a mission, flying a chopper in a heavy AA environment, your mission has been designed/planned by either an idiot or a psychopath.

Helicopters and fighter jets are like tanks and logistics trucks. They have a TOTALLY different role and ought to NEVER be in direct contact with each other, and if they were, itd mean a huge human failure has taken place somewhere.

If you get shot down by a fast jet in your Ka-50, its because nobody made plan to remove the threat before your mission took place (whether this means a strong CAP presence or neutralising enemy air strategically). No ifs, ands or buts. And DEFINITELY no talk of doppler radar.
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Old 09-23-2019, 04:36 PM   #16
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Quote:
Originally Posted by p1t1o View Post
If you get shot down by a fast jet in your Ka-50, its because nobody
(aka you, the heli pilot)

Quote:
made plan to remove the threat before your mission took place (whether this means a strong CAP presence or neutralising enemy air strategically). No ifs, ands or buts. And DEFINITELY no talk of doppler radar.
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Old 09-24-2019, 07:19 AM   #17
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Quote:
Originally Posted by VampireNZ View Post
For those interested - This report describes millimeter wave Doppler signature measurements made on a hovering Mi-24 Hind-D helicopter.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a351581.pdf
Nice find.
Interesting points in the conclusion:
The returns from the hub fell below the clutter filter @ 200 KHz.
(Only) the front edge of the main rotor was visible with a doppler frequency consistent with its diameter
Both the positive and negative doppler frequencies of the tail rotor were visible only at several aspect angles.

- but also worth noting that the radar used was @ 95GHz (as you said, mm wavelength - guessing ~ 3mm ?), while the AN/APG-65 radar family (F-18 / F-15E) run at 8 - 12 GHz (2.5 cm -3.75 cm ) so the results might not be directly applicable...

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Old 09-24-2019, 01:46 PM   #18
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They are reasonably applicable. As frequency decreases, apparent RCS tends to increase (this is part of the basis of the argument for low frequency radars vs stealth - the other part is structural element sizes wrt wavelength).

There are also radar traces clearly showing helicopter blades vs fuselage for 'good old' surveillance radars - unfortunately those will be a pain to find again.

Long story short, if the rotor's spinning and there's LOS to a reasonably modern radar, you're not hiding.
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Old 09-25-2019, 06:02 AM   #19
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Quote:
Originally Posted by GGTharos View Post
They are reasonably applicable. As frequency decreases, apparent RCS tends to increase (this is part of the basis of the argument for low frequency radars vs stealth - the other part is structural element sizes wrt wavelength).

There are also radar traces clearly showing helicopter blades vs fuselage for 'good old' surveillance radars - unfortunately those will be a pain to find again.

Long story short, if the rotor's spinning and there's LOS to a reasonably modern radar, you're not hiding.
Even a reasonably old radar like an ASR-910 would have no problems detecting a hovering or cruising helo. At least ours had no problem...^^
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Old 09-25-2019, 07:41 PM   #20
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Quote:
Originally Posted by p1t1o View Post
Helicopters DO really struggle to hide from fighters.

"your mission has been designed/planned by either an idiot or a psychopath"

"itd mean a huge human failure has taken place somewhere"
1. Well I fly online mostly, so....
2. Did I mention point 1?

J/K (hope everyone has a sense of humor here)

But I'd say the larger issue is that for most online play are a very real lack of planning utilities. Which largely prevents good coordination on the player side. Then again I've seen it both ways, on blueflag, the helos don't go in until pretty much everything is cleared out (brave KA50's exempted).

Personally, I find most of the helo centric offline content to be pretty reasonable.
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