D-Scythe Posted January 16, 2005 Posted January 16, 2005 ...with motor burn approaching 30 seconds seems to give very slow acceleration compared to some of the others Motor burn for the AIM-54C is 37 seconds, boost-sustain, according to Julian, or Jewels, on the Ubi forums.
D-Scythe Posted January 16, 2005 Posted January 16, 2005 Watched the Combat Archer video, Recorded several AAM shots. 1:11 AIM-7 2:55 AIM-7 3:52 AIM-7 3:55 AIM-120 4:00 AIM-7 4:10 AIM-9 4:20 AIM-9 or AIM-120 The AIM-120 shot at 3:55, SK, DID loft. Watch that sequence again, and follow the just barely visible smoke trail (from a supposedly smokeless rocket motor). Note that the 4:20 missile shot may also have been an AIM-120, since the motor seemed to be fairly smokeless and the bandit did not dump bucket loads of flares like it did for the previous AIM-9 missile footage. Debatable though.
SwingKid Posted January 16, 2005 Posted January 16, 2005 Motor burn for the AIM-54C is 37 seconds, boost-sustain, according to Julian, or Jewels, on the Ubi forums. Link? According to the official-looking "Naval Air Training Command Strike Fighter Intercept Procedures Textbook" P-825.pdf of May 2002 that I downloaded somewhere long ago, the motor burn time is 27 seconds. But I don't fully trust this source. Not that this makes much difference to miniZAP though. As far as I can tell, making the motor burn longer has little effect on maximum range. What seems to matter much more is total impulse and propellant-to-weight ratio. The AIM-120 shot at 3:55, SK, DID loft. Watch that sequence again, and follow the just barely visible smoke trail (from a supposedly smokeless rocket motor). Hmm, good catch, I didn't notice that the first time. Are you by any chance sure that is loft, and not just firing at a look-up target? (Not trying to be argumentative, just checking) Even if the missile steers into a loft climb, it is still launched horizontally. The F-16 can pitch up to 45 degrees at the moment of launch to fire the AIM-120 directly into the loft trajectory, significantly more efficient I think. For this reason I have separated these in miniZAP as two parameters - "Preprogrammed Loft Angle" (self-steering) and "Launch Loft Angle" (F-16-style), which may be combined as desired for experimentation. -SK
Kula66 Posted January 16, 2005 Posted January 16, 2005 Its an F-18, but this vid CLEARLY shows shows the a/c performing a pre-launch climb .... http://www.dreamstriker.com/videos.htm Shame about the start of the vid ... it gets better! Not so sure about the loftsot at 3:55 ... James
GGTharos Posted January 16, 2005 Posted January 16, 2005 Keep in mind that the 54C pops up to 160k feet ... drag? What drag? [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
SwingKid Posted January 16, 2005 Posted January 16, 2005 Its an F-18, but this vid CLEARLY shows shows the a/c performing a pre-launch climb .... http://www.dreamstriker.com/videos.htm Wow, terrific find! HUD video and everything! Now that's definitely lofted. Can anyone explain why the HUD seems to have three aspect indicators around the ASE circle, apparently showing mostly pursuit targets, yet he has a Vc of 1000 kts while flying only 330 kts, apparently showing a 670 kt approaching target? and what is the little "18" hovering around on a dotted line? Checking my JF/A18 manual.. -SK
SwingKid Posted January 16, 2005 Posted January 16, 2005 But that has more to do with cross-sectional area drag, rather than weight given the velocities attained, no? Cross-sectional ("form") drag is IMHO over-rated for missiles. After speaking to some aerodynamicists, I think that skin ("friction") drag usually dominates these objects. For a missile of constant internal volume, making it longer and thinner decreases form drag but increases the total surface area and thus the friction drag. Vice versa for fat missiles. The optimum to minimize total drag is apparently a length:diameter ratio of about 11:1, closer to the "long-range" AIM-54 and AA-9 than to the long slender AIM-7, -9 and -120. EDIT: Just had a look at your MiniZAP program, thanks for making that available, and I see you have modelled those effects (and the long and thin R-27ER did beat the short fat AIM-54 for total range ... :) ) My pleasure. With which settings did you get this result? With default launch altitude and speed I have the AIM-54 with much longer Rmax than R-27ER.. -SK
Kula66 Posted January 16, 2005 Posted January 16, 2005 Plus drag from fins etc ... some missiles (Python, Magic, Archer) seem to have loads of wings/fins etc ... Are the Adders fins supposed to be draggier than expected? James
SwingKid Posted January 16, 2005 Posted January 16, 2005 Can anyone explain why the HUD seems to have three aspect indicators around the ASE circle, apparently showing mostly pursuit targets, yet he has a Vc of 1000 kts while flying only 330 kts, apparently showing a 670 kt approaching target? D'oh! Those aren't aspect indicators, that's the range circle! Plus drag from fins etc ... some missiles (Python, Magic, Archer) seem to have loads of wings/fins etc ... Are the Adders fins supposed to be draggier than expected? I found fins very tricky to model. It's not just their size, but also their shape and location on the missile that contributes to drag. The air immediately behind a control fin is more turbulent, and if this turbulent air contacts the missile body, then the drag coming from the missile body can be increased as a result. This is apparently a significant contributor to the short range of Sidewinder and other missiles with control surfaces near the nose, and the long range of AIM-120 with control fins in the tail. Whatever the purported drag effects of the R-77's special control fins may be, the fact that they are mounted in the tail, where they can make no turbulent contribution to overall friction drag, gives me serious pause buying into their "draggier" reputation when modelling them. How much draggier? By far the biggest drag from fins though is the induced drag caused when they are steered. Although some attempt is made to model fin drag, the ideal max-range trajectories in miniZAP generally involve a minimal amount of steering, partially to try and avoid this particular question. Thanks for interest, -SK
olaleier Posted January 16, 2005 Posted January 16, 2005 Can anyone explain why the HUD seems to have three aspect indicators around the ASE circle, apparently showing mostly pursuit targets, yet he has a Vc of 1000 kts while flying only 330 kts, apparently showing a 670 kt approaching target? and what is the little "18" hovering around on a dotted line? Checking my JF/A18 manual.. -SK Just guessing, but perhaps those are range indicators? Rmax, Rmin and such...there's a little indicator inside the ASE circle as well, while the aspect indicator is on the outside. Not sure what the dotted line is. edit: woops, you already got it :wink:
Kula66 Posted January 16, 2005 Posted January 16, 2005 I like the way the steering dot (can't remember its proper name) is at the top of the HUD as he starts the loft ... and centers are the 'optimum' point ... The comment about the R-77 fins being draggy is pure WEB rumor ... no factual basis AFAIK ... I guess the drag induced on the body by forward fins is why ASRAAM has little tail mounted fins ... I guess the tradoff is in the moment they produce ... big front mounted fins give you a big turning moment, and over short range, drag is the acceptable price! Hence the Germans dropped ASRAAM for IRIS-T ... ASRAAM was not manauverable enough for them! James
GGTharos Posted January 16, 2005 Posted January 16, 2005 I have a research paper on simulating such fins. My guess insofar as the drag goes here is the creation of a large turbulent area (much more so than a conventional fin) right behind the missile which may then interact with the lattice itself or possbily create a more significant low-pressure area behind the missile itself ... However my aerodynamics knowledge is zero so ... pure guess on my part. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
GGTharos Posted January 16, 2005 Posted January 16, 2005 Nice vid ... they blacked out the launch range but it does give you an idea of the proportions of the AMRAAMs Raero, Rmax1 and Rmax2 ... Not sure what the 18 that was sticking out there way - may have been angle-off. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
olaleier Posted January 16, 2005 Posted January 16, 2005 Nice vid ... they blacked out the launch range but it does give you an idea of the proportions of the AMRAAMs Raero, Rmax1 and Rmax2 ... Not sure what the 18 that was sticking out there way - may have been angle-off. Just thinking in type here...I think it's related to the missile and not a target cue, because it disappears as soon as the missile is launched. It might be related to loft angle. The steering dot is at 20-something degrees, the line might indicate minimum loft needed for current range.
GGTharos Posted January 16, 2005 Posted January 16, 2005 Not that line, look to the right - dashed line with an '18' sticking out of it. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
olaleier Posted January 16, 2005 Posted January 16, 2005 Not that line, look to the right - dashed line with an '18' sticking out of it. That's the line I'm talking about! :) The angle-off is in the ASE circle on top of the arrow that points to the designator box. The dashed line disappears a few seconds after the shot, suggesting to me it is a missile cue, not a target cue.
Kula66 Posted January 16, 2005 Posted January 16, 2005 Except that the steering dot seems to indicate a steeper angle ... 22/23degs whereas the line says <20 ... Loads of info in the HUD :) .... dots, arrows, pointers ... James
olaleier Posted January 16, 2005 Posted January 16, 2005 Except that the steering dot seems to indicate a steeper angle ... 22/23degs whereas the line says <20 ... Yes, that's why I thought the steering dot would indicate best loft angle, while the line indicates minimum loft angle for the current range.
Kula66 Posted January 16, 2005 Posted January 16, 2005 Also, the line moves from 5o'clock to about 3 ... hmmm James
SwingKid Posted January 16, 2005 Posted January 16, 2005 Yes, that's why I thought the steering dot would indicate best loft angle, while the line indicates minimum loft angle for the current range. The minimum loft is probably indicated when the steering dot enters the ASE circle. This seems to occur at around 14 degrees pitch. I also can't tell what the dotted line is "attached" to. It's not really at 4 or 5 o'clock since it doesn't rotate around the center of the ASE circle but rather around the bottom, where numerous symbols appear clustered together. -SK
Kula66 Posted January 16, 2005 Posted January 16, 2005 Looks like its attached to the bottom of the circle ... possibly to the pointer pointing to the target box .... it disappears just after missile launch, so I guess it is to do with that ... Edit: I happen to have a copy of JF-18 to hand and it doesn't show the line... The arrow just past 12:00 is the min range queue, the next arrow is the No Escape zone (say 15miles) ... so any guess on the launch range? Its at Max aerodynamic ... 35? James
olaleier Posted January 16, 2005 Posted January 16, 2005 The minimum loft is probably indicated when the steering dot enters the ASE circle. This seems to occur at around 14 degrees pitch. Yeah, that makes more sense I guess. I also can't tell what the dotted line is "attached" to. It's not really at 4 or 5 o'clock since it doesn't rotate around the center of the ASE circle but rather around the bottom, where numerous symbols appear clustered together. -SK Since it remains at a constant angle to the horizon (rotates on the HUD as the plane rolls), there has to be some relation to attitude. It seems to be flashing between 16 and 18 in the later moments. Also, the number on the lower right (0.2 -> 0.6) seems like a nav distance figure. Is it?
GGTharos Posted January 17, 2005 Posted January 17, 2005 I heard that proper shaping of the front end of the missile can significantly change the shape (and thus effect) of the supersonic cone. other possibilities may include 'air friction grease' or perhaps a nose cone so designed that only some of it creates the majority of the cone, thus actually 'altering' the radius of the missile for the purposes of drag modelling in this case. Now keep in mind that I don't know that this is what'sbeing done, but I've seen similar tricks done elsewhere (and in different context) sometimes, so maybe this is possible here as well. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
GGTharos Posted January 17, 2005 Posted January 17, 2005 Okay, I'm missing something here ... long and thin is pretty much used against fighters for the most part ... Short and Fat typically has large unameuverable targets and typically requires long range. Or rather, range is desireable. Now, I'm not debating that you must evacuate the gas - merely that there might be tricks you can do to actually not have to do with an increase in rag proportional to a square but perhaps close to linear or at least logarithmic in some way. [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
GGTharos Posted January 17, 2005 Posted January 17, 2005 Okay, well ... what about trying this from another angle ... drag certainly does not equal efficiency, but certainly you could call an airliner 'short and fat' and quite blunt ... hm, but it's subsonic, so never mind ... [sIGPIC][/sIGPIC] Reminder: SAM = Speed Bump :D I used to play flight sims like you, but then I took a slammer to the knee - Yoda
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