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BlackPixxel

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  • Birthday 01/01/1996

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  1. Issue is now resolved, the drag of R-13M got corrected.
  2. In the last update some IR missiles were adjusted, including R-13M1 and Aim-9P-5. When launched under same conditions now, the R-13M1 (here incorrectly labeled as R-3) is reaching a lower top speed (even though impulse/weight according to the config are very close). And then it slows down much quicker than the Aim-9P-5. Being two almost identical looking missiles, that doesn't make much sense to me and indicate that the drag for one of those two missiles must be wrong.
  3. With the 2.9 update there were changes to Aim-9 and R-13 missiles. R-13M1 and Aim-9P-5 are very similar missiles in terms of kinematics. They have a similar shape, and the impulse per weight is also quite close. R-13M1: 66.15 kg*s/kg Aim-9P-5: 69.60 kg*s/kg Yet that Aim-9 reaches significantly more speed, while the R-13 also slows down much quicker. Following graph shows R-13M1 (incorrectly labeled as R-3) and Aim-9P-5 when launched under same conditions: I suspect that something is not right regarding the drag.
  4. But for the determination of the direction of RSN offset, the rate of change in angular rate doesn't matter. The direction of the angular rate itself is what matters. Target line of sight rotates to the right -> RSN is set a bit left of current line of sight line Target line of sight rotates to the left -> RSN is set a bit right of current line of sight line
  5. What exactly do you mean with orbital speed? The angular rate of the line of sight to the target? That is what the Omega in the little formula refers to I think. And in your case, it is negative, as the line of sight from the fighter to the target rotates clockwise. So RSN offset becomes positive, and it causes a flight similar to your last image. But as the formulas show both error components (projection of both position and velocity onto the seeker plane) get divided by values that depend on the remaining time to target. So the commanded overload will be very small in the beginning, which makes the missile turn gently and smoothly after launch, and not instantly try to pull as hard as possible in order to put RSN onto the target. As a result, the RSN offset means the missile will travel less distance and fly a more straight path to the target than if RSN was simply equal to the line of sight direction from the moment of launch.
  6. I have removed my previous post, it had an error. It is propably best to simply post the formulas + descriptions of the modified PN guidance with 2 terms of the R-27 Here is the commanded overload in SARH mode: And here is the flight in inertial navigation: Left side of the formula is in both cases the same: (navigation constant * projection of target velocity onto seeker plane) / remaining time This is essentially the proportional navigation, just that instead of seeker angular rate they take projection of target velocity onto seeker plane and divide it by remaining time of flight. But both are proportional to each other for small angles (small angle approximiation), which is also described in the text. Then there is the second term (which turns it into modified PN), that is depending on the component of angular rate that is created only due to target maneuvering plus some filtering. But, as the text says, it also has its equivalent in the formula for inertial flight, where it is the position of the target projected onto the seeker plane divided by the squared remaining time. According to this, there should not be that much of a difference in trajectory between both types of flight. Although during SARH stage it propably uses angular rate instead of calculating the velocity projection of the target onto the seeker plane first. Your third image is how I would say the missile would fly and how RSN would be pointed. Target is flying to the right, so angular rate of seeker line of sight is rotating to the right. Additional RSN offset according to the formula has inverse sign of angular rate, therefore the offset goes a bit to the left of the pure line of sight. That makes the missile lead a bit more and also creates the most reasonable looking flight path. But to me it seems as if you don't use angular rate, but the derivative of angular rate for RSN offset, which doesn't seem correct. Therefore your sign depends not on the direction of travel of the target, but on its derivative. That creates weird trajectories that don't make sense.
  7. But in this case the negative sign means opposite direction of Omega_0. So the offset angle is towards the opposite direction of angular rate of target line of sight, resulting in less angle for RSN.
  8. The RSN is selected to that at the expected point of seeker activation (and distance to target), the seeker points at the target. But why is your point of seeker activation directly at the same altitude as the launch altitude? It would be somewhere below, as it takes into consideration the extrapolated movement of the target. So the RSN angle would be much less, and the missile would not fly into the opposite direction first, which is a pure waste of energy. After all, there is a negative sign in the angle calculation: So in your scenario, the RSN angle would be less than the line of sight angle, causing the missile to lead more in the beginning towards the direction of the target, and not to fly into the opposite direction. Maneuvering directly after launch will also be very smooth due to the range dependand guidance coefficient, so the missile will not drastically start to lead instantly. Similar to how normal PN with fixed guidance coefficient also becomes more smooth the further the missile is away from the target.
  9. This "fix" for extrapolation mode introduced new issues regarding ECM. If the enemy blinks ECM within 4 seconds after locking the lock instantly breaks. This should not happen when the Su-27 is in an ECCM mode.
  10. @BIGNEWY Could this bug be forwarded again to a dev? It is now very clear what the issue is (see my recent posts). The effective target apect is calculated incorrectly for the seeker lock range estimation.
  11. To further prove my point, here is another test. But at first, take into consideration that in a head on scenario, the ET will get LA at about 7 km on that Su-25. In this new test, the target is off boresight, but its heading is exactly the opposite of mine. So the heading difference is exactly the same 180° as in the case where I fly headon into the SU-25. What is different is only that the target is positioned off boresight, so we fly past each other. It means that I will view the target not from the front, but from a flanking aspect. This should increase my ET seeker range. But it doesn't. I get exactly the same ~7 km LA range. This is because DCS only substracts the directions of me and the target to get the aspect angle, instead of taking the effect of the off-boresight angle into consideration. HEATER_LA_BUG_4.trk
  12. I think I found the issue in the calculation. Here is the same scenario, but I shifted the position of my aircraft in such a way that the heading of me is the same, but that the target is directly in front of me. So the difference in heading angle between target and me is the same as in the previous test. And what do we get? The same launch authorisation range of ~ 9 km. HEATER_LA_offset.trk IR signature is aspect dependant in DCS. So in the Su-27 code it needs to check the aspect angle of the target as one of the factors for a valid seeker lock. But it seems that the DCS code simply calculates the angular difference of Su-27 and target vectors. It does NOT take into consideration, that the off-boresight angle also adds to that angular difference. A pretty bad mistake. This incorrect calculation only happens for the aircraft, once the missile is launched it calculates the true target aspect correctly and as a result is unable to find it. It was launched to early. Would be nice if this could be fixed in one of the next patches.
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