Missile deceleration
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Very valuable info, duly noted, for the propulsion.
For the deceleration, the aero coefficients are off for a lot of missiles. Phoenix included. BUT :
You said you fired it “dumb”. That is not what they did. The flight profile in the article was tailored to their measurements, while in your case, it will be purely ballistic. The missile will obviously gain more speed as it falls down. You should fire at a target at the same alt, far away, and check what is the speed of the missile after 55-57s.
Anyway, you need to do a lot of tests to achieve something satisfactory.
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link edited, my bad!
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No it was figured with a dumb firing. Pg 9 says that the calculations were done with a no guidance fixed fin configuration. At least to me this denotes a ballistic firing calculation.
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The missile also didn’t have a warhead correct? Did it have a dummy load with the same weight as the warhead? The falcon BMS AIM-54 decelerates quickly during maneuver and very quickly due to drag at angles 10 and below. I wouldn’t try to match the NASA test vehicle specifically unless the AIM-54 turns out to have too much energy during the end game.
The test vehicle has the nosecone separate once test objectives are met for speed- therefore it should decelerate much faster than a “wartime” AIM-54, which keeps a clean sleek airframe until the kill. The NASA test is great for initial acceleration, climb and speed over range and maximum range. -
Excellent point indeed. Its then really easy to fix : the axial coefficients (or Cx) are too low, at least at AOA 0, and probably for other AOAs too. The normal coefs dont play for a 0 lift, 0 AOA flight.
The radome removal thing is just a concept for application. The charts are done with simulations, based on public data.
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Ok after playing with the Cx I’ve matched the charts for the 0 and 30 degree launches. Speed at burn out for the 0 degree was mach 3.31, and for the 30 degree launch was mach 3.77. Both shots fell back below mach 1 with in 1 second of the chart time. The 45 degree launch actually sent the missile into space, or more accurately so high that the world turned completely black, and the physics seemed to stop working. I stopped following it after it passed 280,000 feet. I don’t think that shot is possible in falcon.
The Cx was a good tip thanks crusader.I will test this versus some targets later to make sure I didn’t Bork the maneuvering
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Very interesting thread,especially Cola’s thread
I want to ask something specific.
Is there a parameter in the Aim120 file that corresponds to how much lead the missile will put after the pickle?? -
Ok after playing with the Cx I’ve matched the charts for the 0 and 30 degree launches.
If you want to share the info, you can PM me so these modifications are included in the stock install
Is there a parameter in the Aim120 file that corresponds to how much lead the missile will put after the pickle??
Yes :
2 # boost guide lead 1 # sustain guide lead 1 # terminal guide lead 1 # Boost Guide nav 2.2 # sustain guide G Nav 2.6 # terminal guide G Nav ```They interact on a complex fashion, best is still to play with them and see.
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generally we have noticed that although the AMRAAM envelope is quite realistic, there is a problem on the amount of lead pursuit it takes thus affecting its bleed rate. From pickle to pitbull the amount of lead is almost 0 while from pitbull to timeout the lead is more generous and perhaps more realistic.
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But does it need to lead pursuit so much at longer distances?
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But does it need to lead pursuit so much at longer distances?
Yep, its among the most efficient guidance algorithms. Idea is : if target manoeuvers too much, the energy wasted by the missile to keep up with it is not much compared to the energy wasted by the target itself.
Better guidance algorithms implement correction for delays between target updates, lag of command inputs and actuators. An excellent summary here . Dont look to much for the formulas, its not that useful for the common man :mrgreen:
In BMS and F4 in general, proportional navigation (not exactly lead pursuit) is the one implemented. There is no lag of commands, but the interval between updates is not taken into account. BTW, its also why you can avoid an AIM-120 at Mach 1, head on, especially in Multiplayer where the network adds a lot more lag to position updates.
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Ok after playing with the Cx I’ve matched the charts for the 0 and 30 degree launches. Speed at burn out for the 0 degree was mach 3.31, and for the 30 degree launch was mach 3.77. Both shots fell back below mach 1 with in 1 second of the chart time. The 45 degree launch actually sent the missile into space, or more accurately so high that the world turned completely black, and the physics seemed to stop working. I stopped following it after it passed 280,000 feet. I don’t think that shot is possible in falcon.
The Cx was a good tip thanks crusader.I will test this versus some targets later to make sure I didn’t Bork the maneuvering
to be honnest, modding Missiles without a proper tool based on Actual Code is impossible….i mean you cna not really test IN GAME your changes and process would be much too long.
Proper dev tool is needed for this liaise with l3crusader in PM if you are interested.
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I found this Nasa paper on the phoenix
https://archive.org/details/nasa_techdoc_20060004771
I was trying to match the chart (blue line first)on pg 10, but no matter what I do the missile has about 9 secs too much flight time. The motor should burn for 27 total secs. the first 3 seconds of burn should be small as the missile falls from the plane and the rest a continuous boost. With the values set at 0(0 sec), 100(1 Sec), 2400(4 Sec), 2400 (27 Sec), and 0 (28 Sec) I can match the first 27 seconds of the chart perfectly, but the missile just doesn’t want to slow down. It usually hits the ground at 64 secs going 1100knts. It should drop under mach 1 between 55-57 secs. What can be done to make the missile decelerate faster.
I matched launch conditions Mach 1.2 at 45000ft missile fired dumb off the rail.
Check the missile dat files of Korea '80s MOD, it has much more accurate thrust, spec. imp. and weight data as original model.Years ago sources were posted about AIM-54 by ODS or SpbGoro in suggestion thread. I also modeld the drop effefct.