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New and old developments in aviation technology.
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hornetfinn

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Unread post27 Jan 2022, 08:46

Excellent work there garrya!

Glad that we can help you here Spurts!

I think you should go through this document about jamming LPI radars.
LPI_Jamming_a456960.pdf
(1.88 MiB) Downloaded 81 times


All modern military radars have a lot of LPI features and many can be classified as LPI radars. Those equations in garrya's Excel document are simplified (because they would get very complex quickly) and don't separately take into account things like radar and jammer instantaneous and total bandwidth or number of frequencies used for frequency hopping or modulation or pulse compression. Those things give the radar massive processing gain and that could simply be taken into account by increasing the required J/S in the equations. For example modern LPI radar could have something like additional 20-50 dB gain from those. So insted of requiring 10 dB J/S the required J/S could be 40 dB (or even more). Or if you wish, you could take that into account in the radar antenna gain by increasing it by tht amount. The end result would be the same.

In other words, the radar knows the frequencies it uses and how the radar signals are coded. The jammer does not and has to spread the energy over far wider bandwidth. For example this quote from the document here:

FSK radars are said to have an anti-jam advantage as seen in Figure 62. This advantage is based on the assumption that the jammer knows only the full hopping range and must spread its jamming power over that full frequency range. Assume an FSK radar that has a 2000 frequency hopping sequence which is random or unknown to the ES receiver. The FSK radar can be said to have a jamming advantage of 2000, which converts to 33dB. This means that it takes 33dB more jammer power to achieve a given JSR against this frequency hopper than would be required if it were a fixed-frequency conventional radar.


I think the equations there are exactly what you need to use but you just have to find correct figures to use. I think it's easiest to just assume pretty high required J/S against modern radar.
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sprstdlyscottsmn

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Unread post27 Jan 2022, 13:03

im actually having a problem with the sheet right now is that the only time I get numbers that seem right is when I mistookenly used the wrong values in the equation. I have no formal education in radar so I am trying to learn how to best use these as I go. For example, in your first link on monostatic vs bistatic jamming, the final example I can get to work perfectly, but then I look at this 10MW radar and I think that's completely absurd. Fighters on the high end only have the ballpark of 20kW of power. yet this super mega radar recieves 6.25dB J/S from 17nm from a 1kW jammer with a -5dB gain? Modern jammers have to have Gain greater than zero in order to have directional jamming don't they? How little power is in a jammer?
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Unread post27 Jan 2022, 22:15

Based on stated detection and tracking ranges along with T/R count in the Array, I have the 91N6 Big Bird radar modeled as a 24.3kW (43.9dB) Transmitter/Receiver with a total Gain of 37.2dB one-way, operating at 3GHz (9.5dB)

AESACalcTrial.xls lists tracking my F-15EX with an 18.5m^2 RCS at 577km. Effectively max instrumentation range.

Looking at pictures of the ECM antennas on the F-15 I see they are planar, not linear. EPAWSS claims using 5th gen technology. As such, if I model the ECM antennas as 50W (5 T/R modules, 10W each) I get that they are 1.7" across with a Gain of 11.4dB... at 10GHz... hang on... If I shift the Frequency to 3GHz to jam the 91N6 then the Gain drops to -0.6.

With the 11.4dB gain I was getting a 40dB J/S at 52km and that seemed WAY too close. Correcting the gain to -0.6 gives 208km. Even if only 30dB J/S is required burn through isn't until 66km. So ECM antennas are way smaller/less powerful than I expected and when gain is corrected for lower frequencies.

This same ECM antenna jamming my APG-82 model (20kW, 37.4dB Gain) means the Gj goes back to 11.4dB as I am using 10GHz as the mean frequency. That gives 30dB J/S at 15km and 40dB J/S at 48km. That is quite a bit closer than my previous "yeah, sure, let's go with that" ECM model which gave 113km.

I think I can work with this method.
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hornetfinn

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Unread post28 Jan 2022, 07:09

Here is one very interesting document about jamming modern radars:
https://scholar.afit.edu/cgi/viewcontent.cgi?article=3775&context=etd



Some quick quotes from the document. I try myself to digest the information still...

The deception jammer is most effective (as compared to the noise jammers) against modern radars which employ coherent integration techniques such as the pulsed Doppler and pulse-compression types. This occurs because radars employing coherent integration techniques have a large processing gain against noise (e.g. on the order of 20 to 60 dB), and hence attenuate the noise jammer signal by that amount, while necessarily accepting any target-like return unattenuated. [3]

In addition, deception jammers are more conservative in terms of power while “noise jammers tend to use a brute-blanket effect” [27] which usually require more power.



The design characteristics incorporated into tracking radars may include Electronic Protection (EP) capabilities. These capabilities may include low antenna sidelobes to reduce noise jamming power and pulse compression techniques to provide the corresponding processing gain to the radar signal while denying the processing gain to any mismatched jamming waveform. Detailed information on the EP capabilities of a typical tracking radar such as fast time constant, sensitivity time control, random PRF, frequency agility, moving target indicator, CFAR receiver, back-bias receiver, dicke-fix
receiver, automatic frequency selection, sidelobe blanking, pulse compression and jammer strobe can be found in [1].



Reducing the ability of the enemy systems to see or hit the aircraft of friendly forces is the basic procedure for reducing susceptibility [24]. Reducing susceptibility can be achieved by passive signature reduction and active countermeasures. While signature reduction delays and degrades the acquisition process of threat system it also enhances
jammer performance by increasing the ratio of jamming to signal (J/S) [25].



That document lead me to this really good (but also really massive with over 600 pages) source for information about EW systems can be downloaded from here:
https://1lib.sk/book/3704769/46f5db

I don't know about copyright stuff, so not sure if I can upload that document here... But that book seems to cover pretty much everything you can ask for about radars and jammers... For example it has very detailed explanation about different radar and jamming equations and ECCM capabilities.
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Unread post01 Feb 2022, 04:39

Here is a flight report of a Rafale B in 1999, it’s a prototype for the F2 standard.

https://www.flightglobal.com/combat-ready/27260.article

Same aircraft in F3 standard ten years later though with less info

https://www.flightglobal.com/flight-tes ... 47.article

I have some patents and papers talking about the PESA RBE2 “RADANT” antenna, about half the French Rafale fleet will continue to use this, in an upgraded form.

https://www.semanticscholar.org/paper/P ... d39e38af2f

https://apps.dtic.mil/sti/pdfs/ADA301940.pdf

https://patents.justia.com/assignee/thomson-csf-radant

https://www.sciencedirect.com/topics/en ... nned-array

https://www.microwavejournal.com/articl ... ys-part-ii

https://citeseerx.ist.psu.edu/viewdoc/d ... 1&type=pdf

Official modes and capabilities

https://omnirole-rafale.com/avionique/rbe2/
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sprstdlyscottsmn

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Unread post01 Feb 2022, 12:14

the flight global articles are behind paywall. I would like to double check my data against the F3 document to make sure I am not using F2 data.
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viperzerof-2

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Unread post01 Feb 2022, 15:42

https://web.archive.org/web/20200310154 ... 47.article Unfortunately the F3 one is less descriptive.

For the F2 one it does tell what the weight is

I took most of the relevant info and posted here

viperzerof-2 wrote:https://www.flightglobal.com/combat-ready/27260.article

Prototype Rafales are limited to a maximum take-off weight of 19,500kg, although, after a modification to the undercarriage, the production aircraft will be cleared to 22,500kg. Eventually, the maximum take-off weight may be further increased to 24,500kg. The empty weight of the aircraft was 10,000kg, with the external stores contributing a further 4,500kg to give a weight without fuel of 14,500kg. The maximum fuel load that could be carried was therefore 5,000kg, of which 800litres, weighing 680kg, was in the centreline fuel tank.

The prototypes have been tested to 22,500kg using air-to-air refuelling (AAR) to top up the external tanks. This is commonplace because it extends the duration and productivity of test sorties and allows several test points to be achieved in one flight at maximum weight. For this flight, the aircraft had a fixed refuelling probe fitted to the right side of the nose ahead of the cockpit. The Rafale FCS has a sub-mode tailored for AAR.


The engines took 5s to achieve full thrust, at which point the aircraft was accelerating briskly at 0.56g (longitudinal). The stick back speed was 150kt (277km/h) and the aircraft lifted off at about 165kt after 15s, including the time taken for the engines to accelerate. It was easy to keep straight in the 7kt crosswind component from the right using nosewheel steering up to 60kt, at which point it automatically disengaged.

Rotation to a suitable take-off attitude was easy, although I initially underestimated the pitch responsiveness and corrected forward rather more aggressively than I would have liked to maintain the initial climb flightpath angle (FPA). The undercarriage retracted in 5s, with no trim change. The FCS laws change from angle-of-attack (alpha) to g demand with the undercarriage retracted.

The initial climb to 10,000ft away from the Istres circuit area and westwards across the serene Carmargue countryside was made at full dry thrust at 340kt (a nominal rather than ideal speed) at an FPA of 15º.


The Rafale FCS automatically trims the aircraft in all three axes. In pitch, it trims for 1g flight, so speed changes are made without the pilot needing to retrim manually. The only time that conventional static stability is introduced is above 16º alpha, the normal approach incidence, with the undercarriage down. Throughout this flight, the autotrim system worked well and unobtrusively. I was briefed, but could not check, that the system copes with asymmetric loads, such as a hung-up bomb.

Once level at FL100, at 300kt and 85% engine core speed (NH),I made a few turns before manoeuvring the aircraft more aggressively. Immediately I was reminded how useful a well-sorted HUD is for accurate flying. Level turns at 45º (90% NH) and 60º (93% NH) angle of bank merely required keeping the aircraft symbol on the horizon line and adjusting engine thrust to keep the energy markers at neutral. This was an easy, straightforward and intuitive process that gave level turns accurate enough for any instrument-rating examiner.


Four full-stick rapid rolls through 360º were made at 1g and 2g at 300kt. The roll acceleration was good and, in each case, the roll was completed in 3.5-4s. The peak roll rate was about 150º/s. Without the heavy external stores, the FCS would have allowed a higher roll rate of 250-270º/s. The aircraft was inverted briefly in level flight - something only a test pilot would attempt with two large cruise missiles and three external tanks on board - and remained easy to fly accurately. The FCS limits negative g as well as positive g, although I did not bring in the g limiter during this test point.

Finally, before climbing to high level, a hard turn was made, starting at 330kt using full reheat, principally to test the behaviour of the FCS. This was the first moment in the flight for controlled aggression. I simply rolled the Rafale into a nose-down steep turn and, as the reheat became effective (about 2s), moved the stick quickly to the aft stop. The aircraft responded by rapidly achieving 5g at 17-18º alpha, turning smoothly and without buffet with the stick held on the aft stop.

Heading north towards the mountains, we climbed to 25,000ft. I wanted to explore the Rafale's handling at high level at the Mach limit in the current configuration - 0.9 indicated Mach number - and in a typical long-range cruise condition. The climb also gave me an opportunity to look more closely at the autopilot.


At a typical cruise speed of M0.82/347kt, the aircraft could sustain a 60º banked turn at maximum dry power. Slamming the throttle to maximum reheat and rolling quickly into a full stick-back hard turn to simulate a break away from a threat gave a rapid response, automatically limited initially to 18.8º alpha and 4g. As the turn progressed, the FCS allowed the incidence to increase to 19.2¼ alpha as the airspeed decayed. Again, I was impressed with how easy it was to extract the maximum performance from this heavily loaded aircraft.

Rolling back to wings-level flight, I re-engaged reheat for a level acceleration from M0.6 to M0.9 in 35s. As the aircraft approached the Mach limit (M0.9) for this configuration, there was a slight airframe or aerodynamic rumble from the external stores. At M0.9, I quickly retarded the throttle to idle, without any noticeable trim change, and selected the airbrakes out to decelerate the aircraft rapidly back to M0.6 in 37s. There was no trim change with engine thrust variations at this or any other time during the flight.



Simulating the end of the cruise portion of a high-low attack profile, we descended at idle thrust into the low-level part of the flight over the picturesque ridges and gorges of southern France. On the way down, I reselected the autopilot and the flightplan route and engaged the terrain following (TF)system at a set clearance height of 500ft above ground level (AGL). The aircraft descended at 14º FPA and began to level off automatically as it passed 1,500ft AGL. I engaged the autothrottle at 400kt and sat back with my hands off, but close to, the controls as the aircraft followed the scheduled route across rugged terrain.

Despite many years' experience of flying TF systems, I still found it impressive to allow an aircraft to fly hands-off close to the ground through mountain passes and across ridges. The autopilot used from 3g to 0.2g and accurately crossed ridgelines at 500ft AGL. It is anticipated that the TF system fitted to the Rafale BO1 will eventually be cleared to 100ft AGL over land and 50ft over water.

The Rafale TF system uses a radar altimeter as the primary sensor and a digital data map of the earth, rather than a radar system. This has two advantages. Firstly, it eliminates the radar emissions that can be detected and jammed by an enemy. Secondly, the TF system has information about the terrain profile all around and can manoeuvre the aircraft to the maximum allowed either via the autopilot or manually by the pilot. During this flight, the aircraft, under autopilot control, crossed a ridgeline in an 85º banked turn at 3g - a manoeuvre that would surely get a pilot's attention at night or in cloud.




Much as I was enjoying flying at low level, I wanted to finish my investigation of the aircraft's handling before recovering back to Istres, so, with maximum dry power applied, a climb at 16º FPA was begun, initially to 5,000ft. This brief check in the climb profile allowed time for a dry power level acceleration from 309kt to 460kt in 35s.

When cleared by air traffic control, the Rafale was further climbed into the height block between 5,000ft and 10,000ft. Once level, it was accelerated to M0.88 for a hard turn using full reheat to the FCS g limit. Although I entered the turn quickly, the voice warning (female) informed me that I had slightly exceeded the configuration limit of M0.9 (it was M0.91). The FCS limited the aircraft to 5.2g.

Once in the turn, I adjusted the roll and pitch attitude so that the aircraft decelerated, still turning with full back stick, so that, at 330kt, the FCS transitioned from the g to the alpha limit of 20.8º, an incidence that was maintained until I rolled out at 200kt. Finally, to give the FCS a further hard test, I made full-stick rapid rolls with the stick held fully back. At the incidence limit, the aircraft took 6s for a 360º roll and 5.5s at the g limit of 5.4g. The rolls were smooth and the roll rates even. Given the configuration, this is an excellent performance.



On the way back to Istres, the Rafale was slowed down with the undercarriage lowered (taking 5s) to full back stick. With 1,410kg of fuel remaining (aircraft weight 15,900kg), the minimum speed was 120kt at 18º alpha. As noted before, the ideal approach incidence is 16º alpha and, above this incidence, the control column must be deflected aft of neutral. At 18º, the voice warning reminds the pilot to reduce incidence.

The final manoeuvre before entering the circuit was to loop the aircraft from 3,200ft. As with inverted flight, I suspect only test pilots would expect an aircraft to loop while fitted with two cruise missiles and three fuel tanks. The minimum entry speed was 360kt, but I elected to use 390kt to give myself a slightly wider margin in view of the aircraft's heavy configuration. Using 4.5g at the entry to the loop and full reheat until pointing vertically down, the manoeuvre was easy to fly and totally undramatic. Without trying to minimise the size of the loop, the maximum altitude was 9,500ft and the aircraft was back in level flight, having gained 1,000ft on the entry height.

Compared with simple general aviation aircraft, modern automated fighter systems are easy to manage in the circuit. Two right-hand circuits were flown to Runway 15 with a wind of 190º/16 kt, gusting to 20kt. At Kerherve's suggestion, during the first circuit I used the autothrottle to maintain 16º alpha from midway along the downwind leg all the way to touchdown - this constant incidence technique is favoured by naval pilots.

Although you could invent more checks, the only really important actions are to put the undercarriage down and check the fuel. The aircraft remained easy and straightforward to fly, the HUD helping considerably with the approach. The aircraft symbol was displayed on the HUD velocity vector and there were 3º descent markers. The optimum approach incidence was shown by two bracket symbols, which were either side of the aircraft symbol at the correct incidence. All the pilot has to do is adjust the flightpath so that the 3º markers are beside the touchdown point, put the velocity vector on the threshold and control the speed to achieve the approach incidence. Perhaps that sounds difficult, but in practice it is straightforward in the Rafale or any other aircraft.

Shortly before touchdown, the velocity vector was raised from the touchdown point to about halfway down the runway to give an easy flare into a perfect touchdown at 132kt. Applying full throttle to execute a touch and go tripped out the autothrottle.

The final circuit to land was flown using manual throttle control, which I found no more difficult than with autothrottle and allowed me to fly the final turn at a slightly higher speed and lower incidence. After landing, the gusty crosswind held the right wing up until I positively de-rotated the aircraft on to the runway.

The total flight time was 1h and the landing was made with 690 kg of fuel remaining. As I taxied back, a Mirage 2000 was beginning another rehearsal for the Paris air show.
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Unread post01 Feb 2022, 18:09

So I believe that the figure of the Rafale accelerating from 250 knots to 600 in 20 or under 20 seconds is known. However not much about the aircraft’s conditions at the time of measurement. This article mentions the pilot doing just that and has pictures of the aircraft. Rafale B, two Mica IR on the wing tips, one centerline tank, fuel state unknown.

https://www.google.com/amp/s/www.ndtv.c ... 5271/amp/1

https://www.ndtv.com/photos/news/thunde ... hter-13535
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Unread post02 Feb 2022, 12:10

sprstdlyscottsmn wrote:Based on stated detection and tracking ranges along with T/R count in the Array, I have the 91N6 Big Bird radar modeled as a 24.3kW (43.9dB) Transmitter/Receiver with a total Gain of 37.2dB one-way, operating at 3GHz (9.5dB)

AESACalcTrial.xls lists tracking my F-15EX with an 18.5m^2 RCS at 577km. Effectively max instrumentation range.

Looking at pictures of the ECM antennas on the F-15 I see they are planar, not linear. EPAWSS claims using 5th gen technology. As such, if I model the ECM antennas as 50W (5 T/R modules, 10W each) I get that they are 1.7" across with a Gain of 11.4dB... at 10GHz... hang on... If I shift the Frequency to 3GHz to jam the 91N6 then the Gain drops to -0.6.

With the 11.4dB gain I was getting a 40dB J/S at 52km and that seemed WAY too close. Correcting the gain to -0.6 gives 208km. Even if only 30dB J/S is required burn through isn't until 66km. So ECM antennas are way smaller/less powerful than I expected and when gain is corrected for lower frequencies.

This same ECM antenna jamming my APG-82 model (20kW, 37.4dB Gain) means the Gj goes back to 11.4dB as I am using 10GHz as the mean frequency. That gives 30dB J/S at 15km and 40dB J/S at 48km. That is quite a bit closer than my previous "yeah, sure, let's go with that" ECM model which gave 113km.

I think I can work with this method.


https://www.atlantis-press.com/article/6396.pdf
Spread_spectrum_6396.pdf
(758.34 KiB) Downloaded 73 times


Spread spectrum [1] is more precise: an RF communications system in which the baseband signal bandwidth is
intentionally spread over a larger bandwidth by injecting a higher frequency signal. As a direct consequence, energy used in transmitting the signal is spread over a wider bandwidth, and appears as noise. The ratio (in dB) between the spread baseband and the original signal is called processing gain [2]. Typical spread-spectrum processing gains run from 10dB to 60dB.


So processing gain can be very high for the radar which would make it rather difficult to jam for an aircraft with large RCS. While that document is about RF communications, the same principles about spread spectrum signals work with radars also.

There is also the thing that jammer would likely need to work against multiple radars at the same time and over wide bandwidth. Modern AESA antennas would help as they'd be more flexible than traditional antennas with fixed and mostly non-directional beams. So they can probably focus their beams when needed and unfocus when wide coverage is preferable. Very wideband transmitters (all types) tend to have very low output levels compared to narrowband transmitters. That might explain why EW transmitters have low output power levels.
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Unread post02 Feb 2022, 18:47

Thanks a bunch. I will be re-working all this soon.
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Unread post04 Feb 2022, 13:10

Just found another very interesting document about jamming vs. radars. It's very old but goes through things in understandable way and has some interesting test results about radar vs jammer.

Found it here: https://nrc-publications.canada.ca/eng/view/object/?id=b9fcc735-c3e6-4221-97d5-a5a62268b787

FM_barrage_jamming_of_radar_21274065.pdf
(7.22 MiB) Downloaded 56 times


Mc/s is MHz and comes from Mega-cycles per second. Dicke Fix receiver is an older electronic protection measure used in radar to counter the effects of jamming. Modern days the radars use much more complex EP measures which make it difficult to understand how everything works in real life. Not sure if those results could be helpful for your work Spurts, but maybe there are some interesting info anyway.
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Unread post06 Feb 2022, 01:19

Supercruise (supersonic speed without afterburner): Make 1.2 to 10,973 m (36,000 ft)
max. Mach speed in horizontal flight: 2+ from 8,537m (28,000ft) to 16,768m (55,000ft)
max. Speed near the ground: Make 1.15 (1,390km/h)
Service summit height: 55,000ft to 65.000ft
Acceleration from standstill to takeoff: less than 8 seconds
Initial climb capacity: 17,567m/min
Ascent to 9,146 m from a standstill: 86 seconds (official factory specification)
Ascent to 13,000 m from standstill: 70 seconds (fruit. Katz, JG73 in abendblatt.de)
Ascent to 10,670 m and acceleration onMake 1.5 out of standstill: under 2.5 minutes
Acceleration of 200 knots (~370 km/h) onMake 1 (~1,240 km/h) at sea level: 30 sec.
Acceleration from Mach 0.9 (~951 km/h) to Mach 1.2 (~1.267 km/h) in tropopause: 40 sec.
Acceleration from Mach 0.9 (~951 km/h) to Mach 1.4 (~1,479 km/h) during tropopause: 62 sec.
Fuel consumption at 1,500m altitude at Mach 0.9 (~1,050 km/h) : 85 kg/min
Required runway length (sea level, 15°C): below 700 m
Launch route with hunter armament: ~300 m
Landing distance with hunting armament: ~600 m
max. Load multiples: +9 g / -3 g
max. Load capacity: 470 kg/m2
max. Thrust/weight ratio: 130 kg/kN

http://eurofighter.airpower.at/technik-daten.htm

This is from an unofficial Austrian Air Force website. I can’t confirm much but it seemed interesting. The Austrian’s used the most basic barebone Tranche 1.
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Unread post23 Apr 2022, 05:05

Okay, so I had to re-do a bit of my F-35A/B/C model to account for reports of the F-35C "often" reaching 1.6M even with external AIM-9s, the F-35A being faster from 250 knots (assumed CAS, comes out to ~0.75M) to Mach 1 than both a Viper and a Raptor (assumed 36,000ft since the same statement said the Viper was faster to Mach 2 which starts about 36,000ft). All that without changing the time from 0.6M-0.95M at 15,000ft and 0.8M-1.2M at 30,000ft. I got it all to work. The more data points I can match the more accurate my model becomes.
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Unread post23 Apr 2022, 12:00

sprstdlyscottsmn wrote:Okay, so I had to re-do a bit of my F-35A/B/C model to account for reports of the F-35C "often" reaching 1.6M even with external AIM-9s, the F-35A being faster from 250 knots (assumed CAS, comes out to ~0.75M) to Mach 1 than both a Viper and a Raptor (assumed 36,000ft since the same statement said the Viper was faster to Mach 2 which starts about 36,000ft). All that without changing the time from 0.6M-0.95M at 15,000ft and 0.8M-1.2M at 30,000ft. I got it all to work. The more data points I can match the more accurate my model becomes.

:mrgreen: I'm currently hiring someone to do simulation of fighters and weapon RCS using blender and HFSS, when the result are available, I will send you (total free). You can add these diagram/map into your file
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