APG-81 power output wattage

Cockpit, radar, helmet-mounted display, and other avionics
  • Author
  • Message
Offline
User avatar

ricnunes

Elite 1K

Elite 1K

  • Posts: 1918
  • Joined: 02 Mar 2017, 14:29

Unread post07 Mar 2019, 14:26

popcorn wrote:Didn't Viktor Belenko claim that MiG-25 pilots were instructed to switch off their radar while on the ground. It was apparently powerful.enough to.kill.a.rabbit at extended distances.


Yes, I also read/heard about that too.
I never actually got to know if this is some sort of "urban myth" or if that story actually has something real about it?


hornetfinn wrote:That makes some sense as directing powerful beam towards a radar can do some damage if the beam and radar operate in the same frequency band. This is because radar is designed to collect very low powered signals when it is receiving and putting a lot of RF power in the same frequency band is very likely going to damage the receiver or associated circuitry (mostly Low Noise Amplifier, LNA). All radar receivers are well protected when the radar is transmitting, but there is less protection when receiving (to keep the system as sensitive as possible). It depends on radar design how well protected the LNA and receiver are, but those can be protected pretty well with good design.

I think most likely effect would be blinding the radar temporarily when talking about modern military radars. Basically that would make the targeted radar receiver protection systems to kick in and make it unable to receive anything. Still the range would likely be relatively short, although it might be usabel even in real life.


Thanks for the great insight about the subject hornetfinn :thumb:

So correct me if I'm wrong but an "electronically attacked" radar would be far more vulnerable when scanning on passive mode compared to active? (and I gather that radars also scan in passive modes, no?)

But this also may mean that a direct consequence of a radar being better shielded against such "electronic attacks" (even when scanning in active mode) is that the radar's detection (and tracking) range would be reduced even further in order to take into account the receiver's shielding, is a correct interpretation on my part?

If the above is correct then I would conclude that the advantage of the F-35 against other (4/4.5th or bigger RCS aircraft) could be even bigger than what we imagine since in real life the enemy aircraft's radar will have an ever shorter detection range (against a F-35 for example) due to the need of a better shielding or else suffer the consequences (of an actual "electronic attack"). Am I thinking correctly here?
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
Offline

hornetfinn

Elite 2K

Elite 2K

  • Posts: 2726
  • Joined: 13 Mar 2013, 08:31
  • Location: Finland

Unread post08 Mar 2019, 13:24

ricnunes wrote:Thanks for the great insight about the subject hornetfinn :thumb:

So correct me if I'm wrong but an "electronically attacked" radar would be far more vulnerable when scanning on passive mode compared to active? (and I gather that radars also scan in passive modes, no?)

But this also may mean that a direct consequence of a radar being better shielded against such "electronic attacks" (even when scanning in active mode) is that the radar's detection (and tracking) range would be reduced even further in order to take into account the receiver's shielding, is a correct interpretation on my part?

If the above is correct then I would conclude that the advantage of the F-35 against other (4/4.5th or bigger RCS aircraft) could be even bigger than what we imagine since in real life the enemy aircraft's radar will have an ever shorter detection range (against a F-35 for example) due to the need of a better shielding or else suffer the consequences (of an actual "electronic attack"). Am I thinking correctly here?


I'm glad I can help ricnunes! :)

Well, all pulse radars operate in switching between active and passive modes. Basically when transmitting, the system basically switches the transmitter path on and receiver path off. Otherwise the receiver electronics components would fry from the transmitted power. Then the receiver path is switched on and transmitter path is switched off. Then receiver path listens to very weak echos coming from radar waves reflected from anything they make contact with (targets, bird, ground etc).

There is also possibility of using the radar totally passively. Then it acts like a very big ESM antenna. It would then listen to any RF energy received within the frequency range of the system. In that mode the frequency range can be quite a bit wider than when used as radar. But it would likely still be relatively narrowband (but very sensitive) ESM system. Modern AESA systems can also interleave these modes extremely fast, so the system can be radar antenna, EW antenna ESM antenna and communications antenna basically at the same time. Especially when the whole system is designed for such flexibility (like in F-35).

In any case, all radars or other similar receivers are somewhat vulnerable to very powerful RF signals when they are receiving. But the range where real damage can occur is relatively short no matter what system is used and what the target system is. With fighter radar sized and powered systems we are talking about some kilometers at most against almost any radar. I could see it used against enemy missile seekers as countermeasure for example. HOJ will not work if the seeker is totally blinded and unable to receive anything.
Offline
User avatar

ricnunes

Elite 1K

Elite 1K

  • Posts: 1918
  • Joined: 02 Mar 2017, 14:29

Unread post08 Mar 2019, 17:37

Thanks for the great reply there, hornetfinn :D

I just have one more question:
Does the story mentioned by popcorn (Mig-25 radar "frying" rabbits alongside the runway when taking off with the radar on) has any credibility or possibility of being true or is it a sort of an "urban myth"?
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
Offline
User avatar

sferrin

Elite 3K

Elite 3K

  • Posts: 5195
  • Joined: 22 Jul 2005, 03:23

Unread post08 Mar 2019, 17:44

ricnunes wrote:Thanks for the great reply there, hornetfinn :D

I just have one more question:
Does the story mentioned by popcorn (Mig-25 radar "frying" rabbits alongside the runway when taking off with the radar on) has any credibility or possibility of being true or is it a sort of an "urban myth"?


It was in the book, "MiG Pilot" and was quoting Victor Belenko, MiG-25 pilot.
"There I was. . ."
Offline

swiss

Senior member

Senior member

  • Posts: 362
  • Joined: 10 Jan 2017, 14:43

Unread post08 Mar 2019, 20:22

hornetfinn wrote:Getting any kind of real world damage from RF power alone is very unlikely except in very short ranges. This is because the radiation quickly gets spread out over very large area.

Even if AN/APG-81 had 100 kW of output power (not possible with current tech really) and very narrow beam of say 2.5 degrees (extremely high efficiency from the antenna), the power would be very small even at 1 km away. That 2.5 degrees beam would cover an area of approximately 2 000 square meters (or over 21 000 square feet). That would mean only 50 Watts of radiated power for each square meter. In real life it would be smaller due to energy absorption and dissipation in the atmosphere. That kind of radiation would not affect anything, especially not radiation hardened or shielded military electronics. Even human beings would need at least 20 times higher radiated power to have real health problems (1000 W/square meter is usually used here). And that would need to be average power, not peak power. Beyond couple of hundred meters/yards, you need very big radars (like ground radars or AWACS) to have any kind of radiation effects on anything. Even those huge radars would only be really dangerous to couple of kilometers at most.

AN/APG-81 probably has many ways of attacking electronics systems, but raw radiated power is not going to be one of them.


Interesting to know. I always wondered, if this claims are true about the APG-81 and other advanced AESA Radars.
Offline
User avatar

ricnunes

Elite 1K

Elite 1K

  • Posts: 1918
  • Joined: 02 Mar 2017, 14:29

Unread post08 Mar 2019, 21:17

sferrin wrote:
ricnunes wrote:Thanks for the great reply there, hornetfinn :D

I just have one more question:
Does the story mentioned by popcorn (Mig-25 radar "frying" rabbits alongside the runway when taking off with the radar on) has any credibility or possibility of being true or is it a sort of an "urban myth"?


It was in the book, "MiG Pilot" and was quoting Victor Belenko, MiG-25 pilot.


Thanks for the pointing out the (original) source, which I didn't know.

However was this actually a real thing or was it basically an "exaggeration" meant to prove/point out how powerful the Mig-25 radar was at the time?
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
Offline

wrightwing

Elite 3K

Elite 3K

  • Posts: 3119
  • Joined: 23 Oct 2008, 15:22

Unread post08 Mar 2019, 21:24

ricnunes wrote:
sferrin wrote:
ricnunes wrote:Thanks for the great reply there, hornetfinn :D

I just have one more question:
Does the story mentioned by popcorn (Mig-25 radar "frying" rabbits alongside the runway when taking off with the radar on) has any credibility or possibility of being true or is it a sort of an "urban myth"?


It was in the book, "MiG Pilot" and was quoting Victor Belenko, MiG-25 pilot.


Thanks for the pointing out the (original) source, which I didn't know.

However was this actually a real thing or was it basically an "exaggeration" meant to prove/point out how powerful the Mig-25 radar was at the time?


It was said that they couldn't fire up the radar, while on the ground, as it was dangerous within ~1000 yards.
Offline
User avatar

geforcerfx

Forum Veteran

Forum Veteran

  • Posts: 836
  • Joined: 10 Feb 2014, 02:46

Unread post09 Mar 2019, 03:03

That could also be a cooling limitation, like the F-35. Needs the cold bleed air at high altitude to do max performance of the radar.
Offline

optimist

Forum Veteran

Forum Veteran

  • Posts: 898
  • Joined: 20 Nov 2014, 03:34
  • Location: australia

Unread post09 Mar 2019, 04:25

I read, they got the idea of a microwave because the chocolate in the pocket was melting, while in front of or working around the radar.
Aussie fanboy
Offline

SpudmanWP

Elite 3K

Elite 3K

  • Posts: 8210
  • Joined: 12 Oct 2006, 19:18
  • Location: California

Unread post09 Mar 2019, 04:48

Well, one of the first microwave ovens to this day is still called the "radar range" for a reason.

"The early bird gets the worm but the second mouse gets the cheese."
Offline

stealthflanker

Enthusiast

Enthusiast

  • Posts: 21
  • Joined: 03 Sep 2017, 12:41

Unread post19 Apr 2019, 09:18

Rather crude estimate could be made.

Based on approach here :
viewtopic.php?f=38&t=53650

Unfortunately there are no information released on cooling type or cooling capacity of the F-35, the one that can be spared for radar. One assumption that could be made is to use fuel as the heatsink. Thus roughly more fuel means more cooling capacity.
As posted in the thread that one example is AN/APG-79 which requires about 15 KW of cooling. Another one i tried to estimate is the improved MiG-35 which have about half (7.9 KW) of cooling capacity. Putting them on linear with their respective fuel capacity allows regression equation to be developed. The equation is kinda crude Y=0.003X-6.7112 Where X is the amount of fuel and Y is the cooling capacity. Only based on 2 data unfortunately. At the moment i'm still searching for more possible data or maybe a method for better accuracy.

The aircraft chosen would be F-35B as it appears to carry the least amount of fuel (5996 Kg) compared to other F-35 variants (about 8000 Kg). Thus the cooling requirement for the APG-81 would likely be based on it. Plugging the variable in one may got around 11.3 KW of cooling capacity.

Then one could attempt to estimate the limit of average power output of the radar. We may assume similar parameters in the thread that i posted. Except that the number of modules is 1676 for APG-81 and cooling capacity is 11.3 KW.

The calculation yield the limit of average power output of 4416 Watt. If we assume, 25% duty cycle of pulse doppler operation. The peak power of the radar is about 17.6 KW.
Offline

SpudmanWP

Elite 3K

Elite 3K

  • Posts: 8210
  • Joined: 12 Oct 2006, 19:18
  • Location: California

Unread post19 Apr 2019, 22:05

One thing you are missing is the Heat-Exchanger capacity for fuel-based coolers, yet another unknown component in the equation.

Two planes could have equal amounts of fuel but if one has double the heat-exchanger capacity then that throws any calculations out the window.

The F-35 has a ring of heat exchangers in the fan duct

Image

The heat exchangers are located midway on the F135 engine.

Image
"The early bird gets the worm but the second mouse gets the cheese."
Offline

f119doctor

Newbie

Newbie

  • Posts: 12
  • Joined: 13 Mar 2019, 00:07

Unread post19 Apr 2019, 23:13

The F135 fan duct heat exchangers (HEX) can be a mixed bag. With the engine at low power, the airflow through the duct may only be 50F higher than ambient, which is cool enough to be an effective heat sink. However, at high power, the fan duct airflow can be 400F or higher which makes it very difficult or impossible to dump heat from the avionics into the bypass stream under these conditions. The system has multiple valves to bypass the duct HEX when they are heating more than cooling. I don't know the full interaction between the IPP, ECS,and engine duct HEX, but it is complicated. The good news is that at high power, you have lots of fuel flow available to cool the various aircraft systems and dump this heated fuel into the engine burn stream.

The fan discharge air is always cooler than the 9th stage HPC bleed air, which can be 1000F+ at high power, so you can use one of the duct heat HEX to pre-cool the high pressure bleed air before it gets to the ECS / IPP system.
P&W FSR (retired) - TF30 / F100 /F119 /F135
Offline

eloise

Elite 1K

Elite 1K

  • Posts: 1631
  • Joined: 27 Mar 2015, 16:05

Unread post20 Apr 2019, 03:15

stealthflanker wrote:Rather crude estimate could be made.

Based on approach here :
viewtopic.php?f=38&t=53650

Unfortunately there are no information released on cooling type or cooling capacity of the F-35, the one that can be spared for radar.

There are some ambient air used as heat sink
F-35integratedSubSystems2.gif

Image

stealthflanker wrote: One assumption that could be made is to use fuel as the heatsink. Thus roughly more fuel means more cooling capacity.
As posted in the thread that one example is AN/APG-79 which requires about 15 KW of cooling. Another one i tried to estimate is the improved MiG-35 which have about half (7.9 KW) of cooling capacity. Putting them on linear with their respective fuel capacity allows regression equation to be developed. The equation is kinda crude Y=0.003X-6.7112 Where X is the amount of fuel and Y is the cooling capacity. Only based on 2 data unfortunately. At the moment i'm still searching for more possible data or maybe a method for better accuracy.

The aircraft chosen would be F-35B as it appears to carry the least amount of fuel (5996 Kg) compared to other F-35 variants (about 8000 Kg). Thus the cooling requirement for the APG-81 would likely be based on it. Plugging the variable in one may got around 11.3 KW of cooling capacity.

Then one could attempt to estimate the limit of average power output of the radar. We may assume similar parameters in the thread that i posted. Except that the number of modules is 1676 for APG-81 and cooling capacity is 11.3 KW.

The calculation yield the limit of average power output of 4416 Watt. If we assume, 25% duty cycle of pulse doppler operation. The peak power of the radar is about 17.6 KW.

Cooling of Mig-35 is only 1/2 of F-18E? :shock:
Offline
User avatar

spazsinbad

Elite 3K

Elite 3K

  • Posts: 22690
  • Joined: 05 May 2009, 21:31
  • Location: ɐıןɐɹʇsn∀¯\_(ツ)_/¯
  • Warnings: -2

Unread post20 Apr 2019, 03:53

Graphic above is from this PDF no longer available at URL so attached below:
The Evolution of Electric Military Aircraft 29 July 2011 Dr. Mark T. Maybury Chief Scientist United States Air Force

http://www.avweb.com/pdf/electric-aircr ... rcraft.pdf

HA! PDF found here: https://web.archive.org/web/20121020152 ... rcraft.pdf (5.5Mb)

Forum links to earlier citations of this PDF: viewtopic.php?f=22&t=15917&p=201494&hilit=symposium+electric#p201494 & viewtopic.php?f=60&t=19215&p=224458&hilit=symposium+electric#p224458 FUEL/range: viewtopic.php?f=22&t=15917&p=282804&hilit=symposium+electric#p282804
Attachments
electric-aircraft-symposium-2011-07-29_evolution-of-military-aircraft.pdf
(5.24 MiB) Downloaded 45 times
RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
PreviousNext

Return to F-35 Avionics

Who is online

Users browsing this forum: No registered users and 3 guests