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Thread: Rafale news & discussion part XVI

  1. #2761
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    Quote Originally Posted by Ozair View Post
    That is a gross mis-understanding of what is going on in that RAAF Hornet video and also a complete mis-understanding of how high AoA fighters operate. To say that high AoA is not valuable on the Hornet is utter lunacy.
    Only misunderstanding here is coming from you and your wrong interpretation of my post.

    Here is what I have said: "We can notice that most of the time both planes are not going over 30° AoA (that is the limit for Rafale). Even at that AoA the plane has very slow pitch/yaw/roll rate (although probably much better than most other fighters)".

    First, it is the fact that most of the time both planes were not going over 30° AoA. You only have to look at the video. If they find it necessary to constantly go to 40° or 50° AoA to achieve the kill, they would do it.
    I have also claimed (bolded part) that at high AoA there are not many fighter planes (without TVC) that can stay alive against the Hornet in this part of the flight envelope.

    Next thing I said: "Above that, the planes nose pointing rate is dramatically shrinking and drag is rising and that is not the area you can efficiently exploit unless you are flying Su-35S or PAK-FA.
    At such a high AoA those planes have literally few times faster pitch/roll/yaw rates and can point in literally any direction independent of the flight vector/path. F-18 and F-35 simply can't do that. They can fly at 50° AoA, but you can forget about any meaningful/useful maneuverability."

    Just to put that in to a perspective:



    In this video you can observe the roll rate dependence on AoA. Higher the AoA, slower the roll rate.

    Here is the video of Su-35S:



    Look at 7:30.

    Su-35S at about two times higher AoA can finish full 360° roll faster than F-18 doing 180° roll at about two times lower AoA.
    I hope you understand how this translates to nose pointing capability at high AoA. That is the reason I said that the fact that F-18 and F-35 can fly at 50° AoA is not that big of a deal if your oponent can point the nose few times faster than you at that particular part of the flight envelope.


    There is a reason every US fighter jet since the classic Hornet is now capable of 50 AoA or higher. To understand it better I suggest you read the following, https://fightersweep.com/4210/dogfig...-fa-18-hornet/
    I will quote some parts of the text and try to explain them so you can understand it even better.

    But there are many other aspects of aircraft performance besides thrust-to-weight ratio and turn rate. Specifically, turn radius is a very important component to BFM as well. In fact, I would say the Hornet has arguably the best turn radius of any fourth generation fighter.
    This part is a bit misleading. For example, we know that the Rafale is better EM fighter than F-18. It has superior turn rates (sustained and instantantenous), it can pull more Gs, it has superior acceleration and can regain energy much better. Now, if Rafale can pull more Gs at similar speeds compared to F-18, that means it will have higher turn rate, but consequently this also means it will have smaller turn radius.
    So, at the beginning of the fight Rafale will have advantage in both, turn rate and turn radius. True minimum turn radius for any modern fighter plane is usually done at very slow speeds and low Gs and whether F-18 has tighter minimum radius turn than Rafale is open to discussion. But fact remains that until their speed drops to such low level, Rafale with its superior turn rate and turn radius can create opportunity to finish the fight.

    The Hornet flies comfortably at double digit airspeeds and the pilot can literally point the nose anywhere. At the 4:00 minute mark in the video below you can see the aircraft flying comfortably below 120 knots, and the jet isn’t even near the lift limit (i.e not max performing)
    The same thing can be said for Rafale. In the video with F-22 we can see that Rafale is flying comfortably below 100 knots and still remains the excellent ability to point its nose all the way up to 30° AoA.

    Another capability is the ability to execute a rapid energy excursion, and trade energy for nose position. All fighter pilots understand this and use this technique in their own jets, but the Hornet does this exceptionally well. Since the nose position can be pointed well past the jet’s flight path (the definition of high angle of attack), the jet can sell a large amount of energy quickly to point the nose at will. In the vertical, the jet can take advantage of its high AOA abilities with a maneuver called The Pirouette.
    It is known fact that it is very bad to trade most of your energy for nose position at the beginning of the fight. One of the best russian test pilots is claiming this even for the planes equipped with TVC and HMS/D. If you lose much of your energy in the beginning of the fight, the opponent will have enough speed to exit your engagement bubble and if this happens you are dead.
    Again, Rafale with its superior turn rate and turn radius at the bigining of the fight will be the first to create oportunity to shoot. Even if they go low and slow Rafale can hold its own till 30° AoA. It has great handling/nose pointing capability and controllability at that range of AoA and can regain energy much better than F-18. Above that F-18 has advantage, but as we have seen even Hornet pilots dont go above that limit to often.

    A simple example of this is Typhoon which has an AoA limit similar to the Rafale yet they have created the AMK modification with one of the key purposes being to increase AoA to improve WVR combat against high AoA fighters. If the French were building the Rafale from fresh today, there is no way it would be limited to 30 AoA...
    No one is arguing that it is better to have higher limits and better controllability for your plane, it is just you who didn't understand what I was talking about. And Rafale and EF2000 dont have similar limits and handling properties at high AoA. Rafale is superior in this regard.

  2. #2762
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    Quote Originally Posted by TomcatViP View Post
    No


    The resorption of this problem was a two pronged approach: immediate (somewhat what you describe) and long term.


    Like the SH. I beg to differ, that makes a (significant) difference.
    Again (AoA scale):
    M2K < F16 <= Rafale < F15 < F14 < SH <= F35 > SU35 > Mig29


    The roll limitation and yaw authority is a decreasing function of the AoA. Yes. The function however are much different from one plane to the other. This depends on the aero geometry of the airframe. The F35 has "full" authority at max AoA. Canards also have a negative impact, especially when they are straight (planar) and close coupled (the asymmetry will diverge increasingly with the affected airflow). The J20 for example counter this effect with a significative diedral angle. On the video where both J20 are displayed at an airshow, you can see this.
    Sorry I won't be replying, it would be only waste of my time and I don't have much time for writing.

  3. #2763
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    Quote Originally Posted by Peregrinefalcon View Post
    Only misunderstanding here is coming from you and your wrong interpretation of my post.

    Here is what I have said: "We can notice that most of the time both planes are not going over 30° AoA (that is the limit for Rafale). Even at that AoA the plane has very slow pitch/yaw/roll rate (although probably much better than most other fighters)".

    First, it is the fact that most of the time both planes were not going over 30° AoA. You only have to look at the video. If they find it necessary to constantly go to 40° or 50° AoA to achieve the kill, they would do it.
    I have also claimed (bolded part) that at high AoA there are not many fighter planes (without TVC) that can stay alive against the Hornet in this part of the flight envelope.
    The problem is your whole argument is based on a video taken of two Hornets flying one set... You have viewed them flying at 30 or less AoA and argue that state is a near constant, claiming that they could have gone higher they would have but didn't. You do not know the constraints they were operating under, the type of threat they may have been simulating, the respective fuel states, any payloads they were carrying. The same applies for the SU-35 demo.

    Attempting to extrapolate what you have from those videos without knowing the above is in error. You do not have enough information to make the claims you are making.

  4. #2764
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    Quote Originally Posted by Ozair View Post
    That is a gross mis-understanding of what is going on in that RAAF Hornet video and also a complete mis-understanding of how high AoA fighters operate. To say that high AoA is not valuable on the Hornet is utter lunacy. There is a reason every US fighter jet since the classic Hornet is now capable of 50 AoA or higher. To understand it better I suggest you read the following, https://fightersweep.com/4210/dogfig...-fa-18-hornet/

    A simple example of this is Typhoon which has an AoA limit similar to the Rafale yet they have created the AMK modification with one of the key purposes being to increase AoA to improve WVR combat against high AoA fighters. If the French were building the Rafale from fresh today, there is no way it would be limited to 30 AoA...
    I am definitely not an expert -- however please allow me to quote a person who is an expert:


    It all comes down to maintaining energy. We had the highest sustained turn rate for a 360 of anything in the air in 1979.

    Sure, we could have pulled 9 gees at 20 deg AoA and a bit slower, same for 25 deg. Meanwhile we are losing 20 knots per second and having our brains splattered all over the HUD as the gomer strafes us. So the ramp from 15 deg to 25 deg was there to prevent that. We lost some nose pointing ability that the "normal" jets had, but we generally didn't have to sweat it.

    We could also move the stick anyplace we wanted and not depart. We could roll really nice at 25 deg AoA and not have to sweat keeping the stick from moving a mm left or right and then using rudder to roll (ask Double Ugly folks about this).

    One thing to look at is acceleration toward the center of the turn compared to speed. THAT is what determines your turn radius. And we could pull 9 friggin' gees at about 350 knots and hold it forever when below about 10K. NOBODY could touch that in those days and for some years afterwards.

    I initially whined about the FLCS limits until I flew the thing. Made me a believer in a few seconds.

    That's my story, and I'm stickin' to it,
    http://www.f-16.net/forum/viewtopic.php?t=10416

    (boldface added by me)

  5. #2765
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    Quote Originally Posted by Loke View Post
    I am definitely not an expert -- however please allow me to quote a person who is an expert:




    http://www.f-16.net/forum/viewtopic.php?t=10416

    (boldface added by me)
    Have you spoken with GUMS before? He acknowledges that HOBS missiles and HMS change the way WVR combat is now conducted.

  6. #2766
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    i nodded the direct following reply:
    Generally getting slow in a 1v1 fight is okay if and only if there is just one other jet out there to fight against. The F-16 excels at 1v1's and will do just fine slow. But if there is more than one bad guy... don't get slow. The F-16 with the FLCS does a great job not getting slow.

  7. #2767
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    Quote Originally Posted by Ozair View Post
    Have you spoken with GUMS before? He acknowledges that HOBS missiles and HMS change the way WVR combat is now conducted.
    I thought we were discussing dogfights?

    With HOBS missiles I thought the nose pointing was less important, and more important was SA?

  8. #2768
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    Quote Originally Posted by Ozair View Post
    Have you spoken with GUMS before? He acknowledges that HOBS missiles and HMS change the way WVR combat is now conducted.
    yes, in so way that maintaining speed increases in importance over nose pointing

  9. #2769
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    Quote Originally Posted by Loke View Post
    I thought we were discussing dogfights?

    With HOBS missiles I thought the nose pointing was less important, and more important was SA?
    HOBS stands for high off boresight. So an ability for the missile to see a target, and subsequently be launched against such target, from the launch aircraft. If you have two aircraft with reasonably similar turn rates but one has the ability to pull higher AoA then that aircraft's ability to put their missile seeker onto the target first means they are more likely to have the first shot.

    Obviously there are a number of factors that influence the above but WVR has moved from what Gums spoke about with high sustained turn rates to high instantaneous turn rates and high AoA to get that first shot opportunity (in the highly unlikely event that the fight ever gets that close).

  10. #2770
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    Quote Originally Posted by Loke View Post
    I am definitely not an expert -- however please allow me to quote a person who is an expert:




    http://www.f-16.net/forum/viewtopic.php?t=10416

    (boldface added by me)
    Yes, and as he says right in the text you quoted... he is talking about 1979 back when the F-16 was brand new and doing what it did best.

    Now fast forward 35 or so years to some of the accounts provided by F-16 pilots who have transitioned to the F-35....

    The F-35 provides me as a pilot greater authority to point the nose of the airplane where I desire. (The F-35 is capable of significantly higher Angle of Attack (AOA) than the F-16. Angle of Attack describes the angle between the longitudinal axis of the plane – where nose is pointing – and where the aircraft is actually heading – the vector). This improved ability to point at my opponent enables me to deliver weapons earlier than I am used to with the F-16, it forces my opponent to react even more defensively, and it gives me the ability to reduce the airspeed quicker than in the F-16.

    Update: Since I first wrote this post, I have flown additional sorties where I tried an even more aggressive approach to the control position – more aggressive than I thought possible. It worked just fine. The F-35 sticks on like glue, and it is very difficult for the defender to escape.

    It may be difficult to understand why a fighter should be able to «brake» quickly. In the offensive role, this becomes important whenever I point my nose at an opponent who turns towards me. This results in a rapidly decreasing distance between our two airplanes. Being able to slow down quicker provides me the opportunity to maintain my nose pointed towards my opponent longer, thus allowing more opportunities to employ weapons, before the distance decreases so much that a role reversal takes place.

    To sum it up, my experience so far is that the F-35 makes it easier for me to maintain the offensive role, and it provides me more opportunities to effectively employ weapons at my opponent.

    In the defensive role the same characteristics are valuable. I can «whip» the airplane around in a reactive maneuver while slowing down. The F-35 can actually slow down quicker than you´d be able to emergency brake your car. This is important because my opponent has to react to me «stopping, or risk ending up in a role-reversal where he flies past me. (Same principle as many would have seen in Top Gun; «hit the brakes, and he’ll fly right by.» But me quoting Top Gun does not make the movie a documentary).

    Defensive situations often result in high AOA and low airspeeds. At high AOA the F-16 reacts slowly when I move the stick sideways to roll the airplane. The best comparison I can think of is being at the helm of ship (without me really knowing what I am talking about – I’m not a sailor). Yet another quality of the F-35 becomes evident in this flight regime; using the rudder pedals I can command the nose of the airplane from side to side. The F-35 reacts quicker to my pedal inputs than the F-16 would at its maximum AOA (the F-16 would actually be out of control at this AOA). This gives me an alternate way of pointing the airplane where I need it to, in order to threaten an opponent. This «pedal turn» yields an impressive turn rate, even at low airspeeds. In a defensive situation, the «pedal turn» provides me the ability to rapidly neutralize a situation, or perhaps even reverse the roles entirely.
    https://theaviationist.com/2016/03/0...-hand-account/

  11. #2771
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    Quote Originally Posted by obligatory View Post
    yes, in so way that maintaining speed increases in importance over nose pointing
    No, the lesson is to avoid a turning fight if possible. Even when sustained turn rates mattered in a WVR scenario, the aircraft would bleed speed and altitude as the fight progressed. The fight does not happen in a two dimensional plane and pilots will trade energy for turn rate (especially when defensive). Today, the conventional thought is: kill the enemy as quickly as possible to avoid becoming vulnerable (loss of SA "tunnel vision, low energy state for a prolonged period) . That is why instantaneous rate of turn, pitch and yaw rates, combined with good subsonic acceleration matter.
    Last edited by FBW; 18th March 2017 at 21:51.

  12. #2772
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    Quote Originally Posted by Peregrinefalcon View Post
    Sorry I won't be replying, it would be only waste of my time and I don't have much time for writing.
    I am on it 100%. Glad we finally reach a gentle agreement.

  13. #2773
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    Quote Originally Posted by obligatory View Post
    afaik, gripen aoa limit is set to 26 degree, while having been tested up to 115 and can be parked indefinitely at 60-70
    Yes, and just like the last time you brought this up... what you are describing is an aircraft "parked" at an extremely high AoA while essentially falling out of the sky. Not an aircraft that is truly capable of maneuvering at those AoA while remaining in control.

  14. #2774
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    Quote Originally Posted by hopsalot View Post
    Yes, and just like the last time you brought this up... what you are describing is an aircraft "parked" at an extremely high AoA while essentially falling out of the sky. Not an aircraft that is truly capable of maneuvering at those AoA while remaining in control.
    Apparently there are a considerable amount of posters on here that think twin tails are for looks.

    Yup, and even if the Grip and Raf could "park" at those AoA in testing, there is a h•ll of a good reason the FCS prevents them from those AoA operationally. Love to hear one of these posters explain how either aircraft could deal with an asymmetric load inducing a yaw with no control surface available to counteract it.

  15. #2775
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    Quote Originally Posted by halloweene View Post

    as usual sexy words meaningless. Canards have a "full active airflow control"...
    Thank you for the sexy. If that have raised somewhat the debate on an aviation forum, that would be an achievement by itself. But I don't see what you mean by "have". Surely you wanted to write "are", which they are somewhat, if take the term as its root understanding that active is the opposite of passive.
    However, this passionate discussions started when I raised the point of the introduction of Active flows ctrl meanings in modern airframe and made the difference with a surface exposed in the airstream or a flap, distinguishing this way the 80'ish design from the more modern beast like the 35. In that sense, Canards are just flaps, just like an aileron etc... I do understand that you want to point the work done by Dassault (and all other) on the coupled canards benefits. It is simply that this (and I wrote this already) is an illusion* and a technological dead-end. From the Tsagi to the NASA, through the RAE or the RLM, all have discarded this solution for good reasons, especially when it comes with a delta wing. At Dassault, they went straight to the wall despite all the indicative signs. I used to talk long ago about a Canards theology.

    Well l'erreur est humaine my friend. And bladibladabla


    *One hint (or another set of sexy words as you say), the average time of the airstream to develop along the chord (and hence build its sets of Cp, Cm, Beta divergence) is the ratio b/w c, the chord and Va the speed of the airflow. The canard when set as the surface that actively control the flow over the wing by the FCS (as it was first on the Rafale until this was somewhat inhibited) has to react at the end of this time lag. The longer, the lager, the more acute would be the necessary correction in term of amplitude and frequency of action. Dynamic lift being frequency driven (imagine a high bypass filter) -> you are more exposed to it with a longer chord.

    On the X29, the chord is small (swept wing) and that plane reached tremendous alpha (and negative pitch) despite being closed coupled as well.
    This solution was also adopted for the Su30 (again, swept wing and minimal canards that makes it more a mustache than a Canard attribute).

    Plenty other things could be said but that's no more the point now.



    Last edited by TomcatViP; 18th March 2017 at 22:20.

  16. #2776
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    Quote Originally Posted by hopsalot View Post
    Yes, and just like the last time you brought this up... what you are describing is an aircraft "parked" at an extremely high AoA while essentially falling out of the sky. Not an aircraft that is truly capable of maneuvering at those AoA while remaining in control.
    spinning around your own axis isnt maneuvering, and at least some fighters point too slow for it to be of any use
    Pitch Rate
    Insufficient pitch rate exacerbated the lack of EM. Energy deficit to the bandit would increase over time. Therefore, there were multiple occasions where it would have been tactically sound to accept excessive energy loss in order to achieve a fleeting WEZ. The CLAW prevented such shot opportunities (and hindered defeating shots). This included high energy conditions such as immediately off the perch. The average Nz achieved during the breaks or turn circle entries were typically "'6.5 or less despite a rapid full aft stick pull and then decreased as energy depleted and the aircraft slowed on the limiter. Insufficient pitch rate also occurred at slower speeds such as during gun attempts. Instead of catching the bandit off-guard by rapidly pull aft to achieve lead, the nose rate was slow, allowing him to easily time his jink prior to a gun solution. From a guns defensive perspective, the lack of nose rate (or alpha rate) also prevented creating closure because the bandit could react to the gradual onset even when near the front of the control zone.
    High Angle of Attack
    Due to the energy and pitch rate limitations described above, there were not compelling reasons to fight in this region. Some cues that the aircraft was entering high AOA included a bleed through buffet back to a smooth jet, diminished wind rush over the canopy, and full aft stick with no pitch rate. The leading edge flaps were noticed as an additional visual cue when looking across the circle or aft of 3/9. They don't seem to be as pronounced in the f-16 but due to a much larger size in the F-1SA, they were easily perceived while fighting the bandit.

  17. #2777
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    Quote Originally Posted by obligatory View Post
    spinning around your own axis isnt maneuvering, and at least some fighters point too slow for it to be of any use
    You found that old report where a test pilot critiques flight control laws... congrats I guess?

    Meanwhile dozens of operational pilots flying aircraft with presumably updated software have formed a completely different impression...

    A Direct Comparison. Thirty-one experienced pilots currently flying the F-35A were asked to rate the energy and maneuvering characteristics of their previous fourth-generation fighters in a combat configuration throughout the dogfighting maneuver envelope in a combat configuration[23] after jettisoning their external stores. They were then asked to rate the performance of the F-35A using the same scale, with fuel and internal munition loads associated with a combat loadout[24] under their current G and CLAW restrictions.[25] The F-35A compared well to the four other fighters (F-15C, F-15E, F-16C, and A-10) in most every regime. (For the total results and responses from the pilots of each respective fighter, see Chart 1.)

    Each pilot was then asked to select which fighter he would rather fly in combat if he were to face a clone flying the other jet in six different air-to-air situations. (See Chart 2.) If the pilot selected an F-15C in a short-range setup, for example, he felt he could outperform a pilot of equal abilities in the F-35A. Pilots selected the F-35A 100 percent of the time in beyond-visual-range situations and over 80 percent of dogfighting situations where energy and maneuverability are critical to success.





    The F-35A was not designed to be an air superiority fighter, but the pilots interviewed conveyed the picture of a jet that will more than hold its own in that environment—even with its current G and maneuver restrictions. In the words of an F-16C Weapons School Graduate and instructor pilot now flying the F-35A, “Even pre-IOC,[26] this jet has exceeded pilot expectations for dissimilar combat. (It is) G-limited now, but even with that, the pedal turns[27] are incredible and deliver a constant 28 degrees/second. When they open up the CLAW, and remove the (7) G-restrictions, this jet will be eye watering.”[28]
    http://www.heritage.org/defense/repo...and-concurrent


    Thanks for playing.
    Last edited by hopsalot; 18th March 2017 at 22:33.

  18. #2778
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    maybe rafale & gripen came to the same conclusion as F-35, that there were no compelling reasons to fight over angles over 30 degree ?
    in addition to the drag it incur, there's also a direct loss of thrust in the relevant direction the more AoA you pull,
    so you're going full deceleration and become a relatively stationary target

  19. #2779
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    Quote Originally Posted by obligatory View Post
    maybe rafale & gripen came to the same conclusion as F-35, that there were no compelling reasons to fight over angles over 30 degree ?
    in addition to the drag it incur, there's also a direct loss of thrust in the relevant direction the more AoA you pull,
    so you're going full deceleration and become a relatively stationary target
    Or -maybe- they did what every other fighter design team does and set the limiter at more or less the aircraft's aerodynamic limits.

  20. #2780
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    no, no fighter does that, heres a couple of responses as to why f-16 for example doesnt:

    ----------

    It all comes down to maintaining energy. We had the highest sustained turn rate for a 360 of anything in the air in 1979.

    Sure, we could have pulled 9 gees at 20 deg AoA and a bit slower, same for 25 deg. Meanwhile we are losing 20 knots per second and having our brains splattered all over the HUD as the gomer strafes us. So the ramp from 15 deg to 25 deg was there to prevent that. We lost some nose pointing ability that the "normal" jets had, but we generally didn't have to sweat it.

    We could also move the stick anyplace we wanted and not depart. We could roll really nice at 25 deg AoA and not have to sweat keeping the stick from moving a mm left or right and then using rudder to roll (ask Double Ugly folks about this).

    One thing to look at is acceleration toward the center of the turn compared to speed. THAT is what determines your turn radius. And we could pull 9 friggin' gees at about 350 knots and hold it forever when below about 10K. NOBODY could touch that in those days and for some years afterwards.

    I initially whined about the FLCS limits until I flew the thing. Made me a believer in a few seconds.

    That's my story, and I'm stickin' to it,

    -------------------

    Generally getting slow in a 1v1 fight is okay if and only if there is just one other jet out there to fight against. The F-16 excels at 1v1's and will do just fine slow. But if there is more than one bad guy... don't get slow. The F-16 with the FLCS does a great job not getting slow.

  21. #2781
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    Quote Originally Posted by hopsalot View Post
    Yes, and as he says right in the text you quoted... he is talking about 1979 back when the F-16 was brand new and doing what it did best.

    Now fast forward 35 or so years to some of the accounts provided by F-16 pilots who have transitioned to the F-35....



    https://theaviationist.com/2016/03/0...-hand-account/
    Thanks -- I now better appreciate that high AOA limit does offer an advantage.

    I tried to find the AOA limit for various a/c -- for Gripen some sources reported 50 degrees whereas other mentioned 26. Is the 50 degree number wrong, or is it a "war setting"?

  22. #2782
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    Quote Originally Posted by hopsalot View Post
    You found that old report where a test pilot critiques flight control laws... congrats I guess?

    Meanwhile dozens of operational pilots flying aircraft with presumably updated software have formed a completely different impression...



    http://www.heritage.org/defense/repo...and-concurrent


    Thanks for playing.
    I thought this was Rafale thread?

    Thanks for playing

  23. #2783
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    Quote Originally Posted by TomcatViP View Post
    Thank you for the sexy. If that have raised somewhat the debate on an aviation forum, that would be an achievement by itself. But I don't see what you mean by "have". Surely you wanted to write "are", which they are somewhat, if take the term as its root understanding that active is the opposite of passive.
    However, this passionate discussions started when I raised the point of the introduction of Active flows ctrl meanings in modern airframe and made the difference with a surface exposed in the airstream or a flap, distinguishing this way the 80'ish design from the more modern beast like the 35. In that sense, Canards are just flaps, just like an aileron etc... I do understand that you want to point the work done by Dassault (and all other) on the coupled canards benefits. It is simply that this (and I wrote this already) is an illusion* and a technological dead-end. From the Tsagi to the NASA, through the RAE or the RLM, all have discarded this solution for good reasons, especially when it comes with a delta wing. At Dassault, they went straight to the wall despite all the indicative signs. I used to talk long ago about a Canards theology.

    Well l'erreur est humaine my friend. And bladibladabla


    *One hint (or another set of sexy words as you say), the average time of the airstream to develop along the chord (and hence build its sets of Cp, Cm, Beta divergence) is the ratio b/w c, the chord and Va the speed of the airflow. The canard when set as the surface that actively control the flow over the wing by the FCS (as it was first on the Rafale until this was somewhat inhibited) has to react at the end of this time lag. The longer, the lager, the more acute would be the necessary correction in term of amplitude and frequency of action. Dynamic lift being frequency driven (imagine a high bypass filter) -> you are more exposed to it with a longer chord.

    On the X29, the chord is small (swept wing) and that plane reached tremendous alpha (and negative pitch) despite being closed coupled as well.
    This solution was also adopted for the Su30 (again, swept wing and minimal canards that makes it more a mustache than a Canard attribute).

    Plenty other things could be said but that's no more the point now.



    Waoh! time = length/speed Woot! thanks for info. TREst is hot air as usual. (i) inhibition of canard : pure invention. (ii) time lag omgz! i guess DA engineers (not reputable at all when speaking about aerodynamics...) didn't take that into account. (iii) Ok an illusion... Ridiculous.

  24. #2784
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    Quote Originally Posted by Loke View Post
    Thanks -- I now better appreciate that high AOA limit does offer an advantage.

    I tried to find the AOA limit for various a/c -- for Gripen some sources reported 50 degrees whereas other mentioned 26. Is the 50 degree number wrong, or is it a "war setting"?
    Gripen is ~26. Where did you see 50?

    As we have discussed for the Rafale, Gripen, and other aircraft in flight test they will put aircraft in all kinds of weird conditions in flight test. (which is where you will get the accounts you see so often on messageboards) Operational Gripen's will be limited to something in the mid-20s.

  25. #2785
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    Quote Originally Posted by obligatory View Post
    no, no fighter does that, heres a couple of responses as to why f-16 for example doesnt:

    ----------

    It all comes down to maintaining energy. We had the highest sustained turn rate for a 360 of anything in the air in 1979.

    Sure, we could have pulled 9 gees at 20 deg AoA and a bit slower, same for 25 deg. Meanwhile we are losing 20 knots per second and having our brains splattered all over the HUD as the gomer strafes us. So the ramp from 15 deg to 25 deg was there to prevent that. We lost some nose pointing ability that the "normal" jets had, but we generally didn't have to sweat it.

    We could also move the stick anyplace we wanted and not depart. We could roll really nice at 25 deg AoA and not have to sweat keeping the stick from moving a mm left or right and then using rudder to roll (ask Double Ugly folks about this).

    One thing to look at is acceleration toward the center of the turn compared to speed. THAT is what determines your turn radius. And we could pull 9 friggin' gees at about 350 knots and hold it forever when below about 10K. NOBODY could touch that in those days and for some years afterwards.

    I initially whined about the FLCS limits until I flew the thing. Made me a believer in a few seconds.

    That's my story, and I'm stickin' to it,

    -------------------

    Generally getting slow in a 1v1 fight is okay if and only if there is just one other jet out there to fight against. The F-16 excels at 1v1's and will do just fine slow. But if there is more than one bad guy... don't get slow. The F-16 with the FLCS does a great job not getting slow.

    No, any WVR fight is to be avoided, and that is where the major emphasis of the F-35's design is.

    If for some reason the F-35 finds itself in a WVR engagement it clearly has some pretty formidable capabilities. (and it is hardly the first aircraft to be designed with very high AoA performance, which can only be used at low speeds... the F-18, Super Hornet, Su-30MKI, F-22, Su-35, etc, all have similar or better ability to perform such maneuvers)

  26. #2786
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    Quote Originally Posted by halloweene View Post
    I thought this was Rafale thread?
    I will keep that in mind next time you start posting about the Rafale anywhere but here....
    Last edited by hopsalot; 19th March 2017 at 11:52.

  27. #2787
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    Quote Originally Posted by hopsalot View Post
    No, any WVR fight is to be avoided, and that is where the major emphasis of the F-35's design is.

    If for some reason the F-35 finds itself in a WVR engagement it clearly has some pretty formidable capabilities. (and it is hardly the first aircraft to be designed with very high AoA performance, which can only be used at low speeds... the F-18, Super Hornet, Su-30MKI, F-22, Su-35, etc, all have similar or better ability to perform such maneuvers)
    i think you didnt read the comments, or didnt understand them:
    f-16 was software limited for the better good, as was gripen and everyone else with more control-ability than thrust
    can make use of.
    bottom line: dont get slow if there is any way around it.
    i believe gripen had a aoa limiter of 50 degree for about the first half of its career, but was later on changed to 26,
    note sure on this one tho, i didnt follow the gripen until the E variant was proposed.
    if i were to guess i would guess they changed aoa limit the moment they got iris-t missile
    Last edited by obligatory; 19th March 2017 at 12:00.

  28. #2788
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    Quote Originally Posted by obligatory View Post
    i think you didnt read the comments, or didnt understand them:
    f-16 was software limited for the better good, as was gripen and everyone else with more control-ability than thrust
    can make use of.
    No, the F-16 is software limited because it will go out of control. Spare us your ignorant rambling and spend some quality time with google.

  29. #2789
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    Quote Originally Posted by hopsalot View Post
    No, the F-16 is software limited because it will go out of control. Spare us your ignorant rambling and spend some quality time with google.
    Agree with hopsalot.
    F-16 was/is prone to depart from controlled flight under certain kinetic situation. Further more it has sever difficulty in restore controled flight once it depart. Imo you would need ample altitude for that. The FBW in F-16 goes a long way in making the jet carefree handeling for the pilot.
    But as it is with aerodynamics, there are compromises.
    The F-16 is ustabile in Subsonic, it succeeded in its designed goal, of ITR/STR.
    But even with its FBW, its still prone to depart from flight. Which is now in 2017, a by-product of F-16 design being long in the tooth.

    Short and simple; Its aerodynamic has limitations.
    No FBW software algorytmics will change this.
    You would need to redesigned the jet or put on integrated TVC with its FBW to counter this.

    Anyway I,m sure Gripen also have aerodynamic limitations. Although I don't know exactly where/how.
    IT probably is a more forgiven design if it should depart from controlled flight.
    Last edited by haavarla; 19th March 2017 at 13:26.
    Thanks

  30. #2790
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    Quote Originally Posted by haavarla View Post

    Anyway I,m sure Gripen also have aerodynamic limitations. Although I don't know exactly where/how.
    IT probably is a more forgiven design if it should depart from controlled flight.
    Of course it does... here is a snippet of an article on those limitations:

    The topic of air combat at high angles of attack has gained much interest since the seventies, when it made reappearance, perhaps helped by the not-so-reliable air-to-air missiles of that era. Air combat seemed to end up like a classic dog-fight, with decreasing speed and subsequent high AOA. Many early supersonic fighters had a tendency to stall out of the sky when entering this region of the flight envelope, to the dismay of its pilots, as recovery was often difficult, if not impossible.

    The Viggen aircraft had gone through a program of spin testing in the late seventies, that verified the rather benign high AOA characteristics of the canard layout, a fact contrary to what was known on some contemporary aft-tailed foreign fighters. So this was also an argument favouring the Gripen canard layout. Early investigations in vertical spin tunnels and tests in different rotary rigs and subsequent simulations, also pointed to acceptable spin behaviour.
    Note, they are talking about recovery from a spin... not controlled flight.

    A very substantial flight test program that recently was concluded for both the single as well as the two seat Gripen versions has also fully verified the excellent recovery capability, both in manual test mode and in the normal automatic mode. There exists a requirement in the Gripen project specification for a spin recovery capability, and if this can not be shown, a spin prevention system must not allow a departure to happen. Flight testing has also verified that the EFCS matches this additional demand. Double insurance might be said to exist.

    As remarked previously, the only externally visible “fix” to the airframe are a pair of small strakes behind the canard surfaces. This type of “flow augmentation system”, often serving the purpose of directional and lateral stability enhancement at high AOA, is not uncommon on fighters; suffice to mention the Eurofighter and the Mirage 2000.

    A spectacular Gripen aircraft departure and ensuing crash at a public air display in 1993, was the cause of modifications and revisions to the EFCS control laws in order to cure certain ailments there, one example being pilot induced oscillations (PIO). Among the changes was one pertaining to canard deflection angles at high AOA in combat mode, to increase margins for the trailing edges surfaces to run into a geometrical limitation, and thus possible longitudinal stability loss and eventual departure.

    Yaw and roll stability at high AOA is strongly dependent on canard incidence, and slightly above the MLL boundary, stability drops off rapidly, becoming unstable earlier for canard deflections in the region of minus 10 to minus 25 degrees. Obviously, this incidence range was avoided. Instead small positive values of canard deflection were used in the control law’s schedules. This was beneficial, as it meant that the trailing edge surfaces were positive, that is rear end down, thus giving more positive lift. But now it was realized that in some conditions, a physical, geometrical limitation to the elevons might be encountered, which momentarily caused loss of stability.

    A low speed wind tunnel program had immediately been instigated, and for the first time the large low speed wind tunnel model’s electrical engines, that normally were used only to provide discrete incidence changes to facilitate operations, where now deflected continually during a run.

    A bunch of “fixing devices” was tried, and success was instant with several of these. The earlier rapid drop of stability was now completely over-bridged, and the plots showed good, continuous behaviour, indicating at dramatic improvement of the flow characteristics in that a delay of separation occurred to slightly higher alphas. A new canard trim schedule could now be introduced that eliminated the risk of the control surfaces being limited in its travel.

    The flow phenomenon, commonly called “dynamic lift”, perhaps more aptly called aerodynamic hysteresis, has been the object of intense interest in some countries for decades, not the least has this been the case in Russia. Its best public known, practical application may well be the awesome aerobatic display performed by test pilot V.G. Pugachev and his “cobra” turn in a Sukhoi Su-27.

    When these hysteresis effects manifested themselves during high AOA/spin tests in the specially modified second Gripen prototype, they came as no surprise. Years prior, low speed wind tunnel tests with pitching motion of the model had already demonstrated the presence of marked unsteady flow effects, hysteresis, in the post stall alpha regime. Normal force hysteresis was most evident, but all the other components, except side force, had their share.

    In the high AOA and spin tests that has taken place since 1996 and recently concluded successfully, the normal tactic was to initiate the tests with a near vertical climb with speed dropping off to near zero and a rapid increase of AOA up to extreme angles, and the aircraft could then be “parked” at 70 to 80 degrees of alpha. When giving adverse aileron input there, a flat spin with up to a maximum of 90 degrees per second of yaw rotation started and could then be stopped by pro aileron input. Recovery followed, whenever commanded.
    http://raf-fly.blogspot.com/p/aerody...of-fourth.html

    Note, these are exactly the sorts of test that fanboys misunderstand.

    Flying a Gripen straight up and throttling down until it is essentially falling out of the sky with its nose pointed up don't represent controlled flight or any sort of general capability to operate at those extremely high AoAs.

    What the article is talking about is the Gripen's ability to recover from such a scenario should a pilot be foolish enough to put the jet there. What they are not saying is "the Gripen can be flown at 70-80 degrees AoA," only that if a pilot defeats the AoA limiter in the described manner that the jet can probably recover if enough altitude is available.

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