Missile aerodynamics project
-
I have read many posts here over the years about how the RWR is too accurate and how that missiles cannot be dodged by using a “crossing turn” in front of them. So I guess I might as well throw in my 2 cents…
As to the RWR, I have never operated one in RL nor seen any manuals, as I imagine they are still classified. However just looking at the SPO-15 RWR display from a MIG 29, it seems that it is able to display the direction of a threat to within about 20 degrees of accuracy within the frontal 180 degree sphere of the aircraft (I imagine the number and placement of the RWR antennas plays a large part in accuracy/coverage), as well as whether it is above or below the aircraft. And the signal meter looks like it gives accurate signal strength data.
I have read that the French Rafale can fire missiles based on targets based on RWR data alone.
A valentine One radar detector for your car uses just 2 antennas (front and rear) and can display general direction of threats (front, rear, or sides), as well as accurate data on the signal strength data(visual meter and “beeps”) that you can use with experience to estimate range to threat based on radar type/frequency. It also used digital signal processing logic to help eliminate false alarms based on radar band, directional changes and signal strength. And that is just a $400 consumer device that has been sold for 22 years.
Based on that, it seems believable that the RWR in the F-16 could display some pretty accurate directional and distance data(based on digital processing of signal strength and radar type). My guess is that perhaps RL RWR’s also display numerous false alarms that are not real threats. Unless someone who has actually operated a modern RWR is allowed to speak on the subject though, we can only make educated guesses.
As far as the “crossing turn” method of dodging BVR missiles fired from the front goes, I do not understand why anyone thinks that this could not be effective(if not always wise). Missiles are traveling very fast and have small wings and control surfaces and therefore large turning circles. In Robert Shaw’s “Fighter Combat: Tactics and Manuevering” he describes both a crossing turn across the missile, as well as a high G barrel roll around the missile as effective defensive techniques against threat missiles fired at you from the front quarter, especially against the larger BVR missiles and at higher altitudes(page 61). Now if someone were to fire two missiles at you a few seconds apart, you would probably fly directly into the second one using those methods, or be too slow to reverse the turn(the Russian tactic of firing 2 BVR missiles a few seconds apart may not be just about using a variety of seekers). And although possibly effective, in RL you may not feel as confident turning into a missile unless you have no other option as the “escape button” on a real jet is a bit more unpleasant than on our keyboards!
I’ve got the book to and it doesn’t address fighting an AA-10/11/or 12. At range, after the missile motor has burned out, it would be effective, but neither maneuver sets you up to quickly respond to the shooter closing very quickly with you head on. As just a pure evasion maneuver with good flight support it sounds like good move, but not in a 1v1 scenario WVR. Not knocking the book, the man’s a genius, but I think that tactic is for a specific fight only.
-
As far as shooting at RWR targets, every active radar missile should have that capability based on good datalink and mid-course guidance updates. The problem with such shots is the missile doesn’t fly the best path for energy to the kill but takes a more general route to the area. Then again, as classified as Rafale is, it’s RWR may be sensitive enough to calculate good shots based on the transmission. AIM-54/AWG-9 is still classified and probably for this reason- just the types of viable shots with a good radar, good receiver and RWR, and good data-link mid course guidance updates.
-
Thought I’d post an update on what I’ve learned about the missile behavior so far(after a couple thousand test firings acmi files):
- The atmospheric model(as it pertains to drag on a missile) seems accurate for various alt up to the 40k ft I tested.
- In regard to the thrust entered in the data table, in game the thrust is a few percent low at sea level, 33% too great at 20k ft, and 64% to great at 40k ft. A coded fix would be needed to correct this. The best way to overcome this currently is by using SpbGoro’s approach of using actual thrust in the data tables and then setting a “speed brake” with overly high drag in the the coefficient table at a pre-determined max speed limit. In reality, missile thrust does not increase with altitude, but due to the temp decrease, the burn times would increase similar to those percentages as altitude increased(perhaps that is what Microprose developers were going for?). However, the total thrust impulse would remain about the same as it is at sea level( probably about 3% lower above 35k ft).
- “Weight of missile” in the data table is the burnout weight and “weight of propellant” is just what it says. These 2 added together are the missile launch weight in game. The propellant weight is decreases to 0 in game by motor burn out. I do not know if this is linear over the missile burn time or varies by thrust level over burn time(my guess is linear).
- Although the stock aerodynamic coefficients are in a normal and axial format, the game actually interprets the data as lift and drag. This is plainly seen in tacview as the stock the missiles do not add show any additional drag as angle of attack increases. When the stock normal and axial data is converted to lift and drag format data, the missiles drag obviously increases with angle of attack.
- The AOA max/min and Beta max/min values do not seem to be hard limits to the missiles max angle of attack. In game the missiles can achieve just over 2 times this “limit”.
I get the feeling the Microprose developers were still working on the missiles when they ran out of time perhaps?
For those interested in how I came up with this:
I’ve created a completely new aerodynamic coefficient table(not in the file on the first page, that is stock coefficients in lift and drag format) for the aim-9 based off of some datacom data as well as an actual zero-lift drag table, and using actual sea level thrust table for the aim-9. I have then been running flyout performance tests and comparing them to an actual flyout performance charts for the aim-9l at sea level, 10k and 20k ft. This flyout chart also gives flyout data for an aim-9 “variant” missile modified with aim-120 nose and fins on an aim-9 airframe/motor. I also created an aim-7 based off a tactical missile design document intended for a college course, and compared that to the flyout data it provided at altitudes varying from sea level to 40k ft. I did tests mostly at sea level, 20k and 40k ft, and found that the flyout tests in game produced very accurate results after motor burn out. The problem is that for some reason the code increases the thrust of missiles as the altitude goes up. At sea level the thrust in game appears to be close, if a tiny bit low. At 20k ft, the thrust is 33% too high, and at 40k ft the thrust is 64% too great. I obtained those thrust % results by setting all the drag coefficients(axial as labeled) to 1 on my aim-7, the thrust to a set value (1018 lbs) for over 100 sec burn time and then obtaining the max velocity in game(drag=thrust) at different altitudes. Then I plugged the data into the drag equation (Drag force = 0.5 x P x V^2 x Cd x A) to find actual in game thrust compared to the thrust in the data table. I also found that the using the aim-7 aerodynamic coefficients with a 0.87 modifier(13% reduction) for drag used in an aim-9 missile data file(aim-9 weight, ref area, and thrust) produce flyout results very close to the aim-9 variant(aim-120) flyout tables. -
- The atmospheric model(as it pertains to drag on a missile) seems accurate for various alt up to the 40k ft I tested.
- In regard to the thrust entered in the data table, in game the thrust is a few percent low at sea level, 33% too great at 20k ft, and 64% to great at 40k ft. A coded fix would be needed to correct this. The best way to overcome this currently is by using SpbGoro’s approach of using actual thrust in the data tables and then setting a “speed brake” with overly high drag in the the coefficient table at a pre-determined max speed limit. In reality, missile thrust does not increase with altitude, but due to the temp decrease, the burn times would increase similar to those percentages as altitude increased(perhaps that is what Microprose developers were going for?). However, the total thrust impulse would remain about the same as it is at sea level( probably about 3% lower above 35k ft).
How can you determine the difference between effect? So are you saying because of coded (?) thrust increase become too big the kinematic range in some cases and not because of the atmosphere model? As I know at the level of Falcon the thrust of solid rocket fuel can be treated as static trhust which is independent from altitude.
- “Weight of missile” in the data table is the burnout weight and “weight of propellant” is just what it says. These 2 added together are the missile launch weight in game. The propellant weight is decreases to 0 in game by motor burn out. I do not know if this is linear over the missile burn time or varies by thrust level over burn time(my guess is linear).
I can comfirm this therefore all missile have inaccruate weight data all missiles are heavier than in RL.
- The AOA max/min and Beta max/min values do not seem to be hard limits to the missiles max angle of attack. In game the missiles can achieve just over 2 times this “limit”.
I never tested these but seems to me simply. Just set very, very low values and check the result.
I get the feeling the Microprose developers were still working on the missiles when they ran out of time perhaps?
It is not unlikey.
I’ve created a completely new aerodynamic coefficient table(not in the file on the first page, that is stock coefficients in lift and drag format) for the aim-9 based off of some datacom data as well as an actual zero-lift drag table, and using actual sea level thrust table for the aim-9. I have then been running flyout performance tests and comparing them to an actual flyout performance charts for the aim-9l at sea level, 10k and 20k ft. This flyout chart also gives flyout data for an aim-9 “variant” missile modified with aim-120 nose and fins on an aim-9 airframe/motor. I also created an aim-7 based off a tactical missile design document intended for a college course, and compared that to the flyout data it provided at altitudes varying from sea level to 40k ft. I did tests mostly at sea level, 20k and 40k ft, and found that the flyout tests in game produced very accurate results after motor burn out. The problem is that for some reason the code increases the thrust of missiles as the altitude goes up. At sea level the thrust in game appears to be close, if a tiny bit low. At 20k ft, the thrust is 33% too high, and at 40k ft the thrust is 64% too great. I obtained those thrust % results by setting all the drag coefficients(axial as labeled) to 1 on my aim-7, the thrust to a set value (1018 lbs) for over 100 sec burn time and then obtaining the max velocity in game(drag=thrust) at different altitudes. Then I plugged the data into the drag equation (Drag force = 0.5 x P x V^2 x Cd x A) to find actual in game thrust compared to the thrust in the data table. I also found that the using the aim-7 aerodynamic coefficients with a 0.87 modifier(13% reduction) for drag used in an aim-9 missile data file(aim-9 weight, ref area, and thrust) produce flyout results very close to the aim-9 variant(aim-120) flyout tables.
When I tweaked te AIM-9M I also discovered even the more or less good performance at SL to 15-20k feet at 30k feet or highet it had ridiculously high burnout speed but I was not able to identifly the exact cause.
-
Im no expert, but I thought that at altitude the thrust DID increase with rocket motors, to the increasing difference between the pressure its ignition creates, and the pressure of the atmosphere around the rocket plume?
I mean, specific impulse of a rocket DOES increase with altitude, and I thought specific impulse was another way of looking at thrust (Im not a rocket scientist, I just play one in a video game).
-
How can you determine the difference between effect? So are you saying because of coded (?) thrust increase become too big the kinematic range in some cases and not because of the atmosphere model? As I know at the level of Falcon the thrust of solid rocket fuel can be treated as static trhust which is independent from altitude.
Yes, I am saying that if you would set a static thrust of 5000 lbs for 5 seconds in the missile data file, the actual thrust in game would be 6650 lbs(50001.33) at 20k ft and increase to 8200 lbs(50001.64) by 40k ft. This results in excessive burnout speeds/range. In fact the only limiting factor on max range in the stock missiles at high altitude is the max time of flight(battery time).
At first I thought that the excessively high burnout speeds as altitude increased was due to the atmospheric model being incorrect. However, I found that that was not the case as the missiles deceleration matched the real life flyout charts at all altitudes for both the aim-9 and aim-7, therefore the air density is correct in game at the altitudes I tested(0, 10k, 20k, 40k ft). I confirmed this using set static thrust and drag in a missile file and with the velocity generated in game plugged back into the drag equation to find the P value(air density) in game. I then set all the drag coeficients to 1 in the data file, and increased the burnout time of the sustainer thrust (1018 lbs) to 115 seconds at burnout. Then I fired the missile at distant same altitude targets at the test altitudes and recorded the velocity when the missile stabalized (thrust = drag). Since I knew that the atmospheric model was correct for density, I used the drag equation (Drag force = 0.5 x P x V^2 x Cd x A) and plugged in the in game air density,missile reference area, 1 for all Cd since I set them all to 1 in the file, and the final stabalized velocity at that altitude. I compared that force result to the actual thrust I used in the data file, which should have been equal if the game was not modifying the thrust. This is how I found the game is increasing the thrust dramatically as altitude rises, to the tune of 33% at 20k ft and 64% at 40k ft. This increase to thrust as altitude increases must be done in code, and it results in very excessive burnout speeds at high altitude. -
Here is an interesting (funny?) story:
The Aim-120 in DCS is very “messed up” currently (can´t even hit a target from 13nm at 25k feet), so one guy (pdf file below) put alot work into it in order to “fix it”.
This for example is the “defintion” for the 120C (kinda DCS mis.dat thingy)
Name = AIM_120C, – AIM-120C
Escort = 0,
Head_Type = 2,
sigma = {5, 5, 5},
M = 161.5,
H_max = 26000.0,
H_min = 1.0,
Diam = 160.0,
Cx_pil = 2.5,
D_max = 21000.0,
D_min = 700.0,
Head_Form = 1,
Life_Time = 90.0,
Nr_max = 40,
v_min = 140.0,
v_mid = 540.0,
Mach_max = 4.0,
t_b = 0.0,
t_acc = 3.0,
t_marsh = 6.0,
Range_max = 61000.0,
H_min_t = 1.0,
Fi_start = 0.5,
Fi_rak = 3.14152,
Fi_excort = 1.05,
Fi_search = 1.05,
OmViz_max = 0.52,
warhead = warheads[“AIM_120C”],
exhaust = {0.8, 0.8, 0.8, 0.2 };
X_back = -1.61,
Y_back = -0.089,
Z_back = 0.0,
Reflection = 0.0329,
KillDistance = 15.0,ModelData = { 58 , – model params count
0.4 , – characteristic square (õàðàêòåðèñòè÷åñêàÿ ïëîùàäü)– ïàðàìåòðû çàâèñèìîñòè Ñx
0.045 , – Cx_k0 ïëàíêà Ñx0 íà äîçâóêå ( M << 1)
0.09 , – Cx_k1 âûñîòà ïèêà âîëíîâîãî êðèçèñà
0.02 , – Cx_k2 êðóòèçíà ôðîíòà íà ïîäõîäå ê âîëíîâîìó êðèçèñó
0.016, – Cx_k3 ïëàíêà Cx0 íà ñâåðõçâóêå ( M >> 1)
1.2 , – Cx_k4 êðóòèçíà ñïàäà çà âîëíîâûì êðèçèñîì
1.5 , – êîýôôèöèåíò îòâàëà ïîëÿðû (ïðîïîðöèîíàëüíî sqrt (M^2-1))– ïàðàìåòðû çàâèñèìîñòè Cy
0.7 , – Cy_k0 ïëàíêà Ñy0 íà äîçâóêå ( M << 1)
0.8 , – Cy_k1 ïëàíêà Cy0 íà ñâåðõçâóêå ( M >> 1)
1.2 , – Cy_k2 êðóòèçíà ñïàäà(ôðîíòà) çà âîëíîâûì êðèçèñîì0.29 , – 7 Alfa_max ìàêñèìàëüíûé áàëàíñèðîâà÷íûé óãîë, ðàäèàíû
0.0, --óãëîâàÿ ñêîðîñòü ñîçäàâàéìàÿ ìîìåíòîì ãàçîâûõ ðóëåé– Engine data. Time, fuel flow, thrust.
– t_statr t_b t_accel t_march t_inertial t_break t_end – Stage
-1.0, -1.0, 8.0, 0.0, 0.0, 0.0, 1.0e9, – time of stage, sec
0.0, 0.0, 6.41, 0.0, 0.0, 0.0, 0.0, – fuel flow rate in second, kg/sec(ñåêóíäíûé ðàñõîä ìàññû òîïëèâà êã/ñåê)
0.0, 0.0, 16325.0, 0.0, 0.0, 0.0, 0.0, – thrust, newtons1.0e9, – òàéìåð ñàìîëèêâèäàöèè, ñåê
80.0, – âðåìÿ ðàáîòû ýíåðãîñèñòåìû, ñåê
0, – àáñîëþòíàÿ âûñîòà ñàìîëèêâèäàöèè, ì
1.0, – âðåìÿ çàäåðæêè âêëþ÷åíèÿ óïðàâëåíèÿ (ìàíåâð îòëåòà, áåçîïàñíîñòè), ñåê
40000, – äàëüíîñòü äî öåëè â ìîìåíò ïóñêà, ïðè ïðåâûøåíèè êîòîðîé ðàêåòà âûïîëíÿåòñÿ ìàíåâð “ãîðêà”, ì
40000, – äàëüíîñòü äî öåëè, ïðè êîòîðîé ìàíåâð “ãîðêà” çàâåðøàåòñÿ è ðàêåòà ïåðåõîäèò íà ÷èñòóþ ïðîïîðöèîíàëüíóþ íàâèãàöèþ (äîëæåí áûòü áîëüøå èëè ðàâåí ïðåäûäóùåìó ïàðàìåòðó), ì
0.17, – ñèíóñ óãëà âîçâûøåíèÿ òðàåêòîðèè íàáîðà ãîðêè
50.0, – ïðîäîëüíîå óñêîðåíèÿ âçâåäåíèÿ âçðûâàòåëÿ
0.0, – ìîäóëü ñêîðîñòè ñîîáùàéìûé êàòàïóëüòíûì óñòðîéñòâîì, âûøèáíûì çàðÿäîì è òä
1.19, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, êîýô ôèëüòðà âòîðîãî ïîðÿäêà K0
1.0, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, êîýô ôèëüòðà âòîðîãî ïîðÿäêà K1
2.0, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, ïîëîñà ïðîïóñêàíèÿ êîíòóðà óïðàâëåíèÿ
25200.0, – äàëüíîñòü ïîëåòà â ãîðèçîíò ñ ðàñïîëàãàåìîé ïåðåãðóçêîé Navail >= 1.0 íà âûñîòå H=2000
3.92, – êðóòèçíà çàâèñèìîñòè äàëüíîñòü ïîëåòà â ãîðèçîíò ñ ðàñïîëàãàåìîé ïåðåãðóçêîé Navail >= 1.0 îò âûñîòû H
3.2,
0.75, – áåçðàçìåðíûé êîýô. ýôôåêòèâíîñòè ÑÀÓ ðàêåòû
70.0, – ðàñ÷åò âðåìåíè ïîëåòà
– DLZ. Äàííûå äëÿ ðàññ÷åòà äàëüíîñòåé ïóñêà (èíäèêàöèÿ íà ïðèöåëå)
63000.0, – äàëüíîñòü ðàêóðñ 180(íàâñòðå÷ó) ãðàä, Í=10000ì, V=900êì/÷, ì
25000.0, – äàëüíîñòü ðàêóðñ 0(â äîãîí) ãðàä, Í=10000ì, V=900êì/÷
22000.0, – äàëüíîñòü ðàêóðñ 180(íàâñòðå÷ó) ãðàä, Í=1000ì, V=900êì/÷
0.2,
0.6,
1.4,
-3.0,
0.5,
},After THIS much dedication and analysis >>>> : https://dl.dropboxusercontent.com/u/600721/AIM120C5%20Performance%20Assessment%20rev2.pdf
all what was changed was a single value.
Name = AIM_120C, – AIM-120C
Escort = 0,
Head_Type = 2,
sigma = {5, 5, 5},
M = 161.5,
H_max = 26000.0,
H_min = 1.0,
Diam = 160.0,
Cx_pil = 2.5,
D_max = 21000.0,
D_min = 700.0,
Head_Form = 1,
Life_Time = 90.0,
Nr_max = 40,
v_min = 140.0,
v_mid = 540.0,
Mach_max = 4.0,
t_b = 0.0,
t_acc = 3.0,
t_marsh = 6.0,
Range_max = 61000.0,
H_min_t = 1.0,
Fi_start = 0.5,
Fi_rak = 3.14152,
Fi_excort = 1.05,
Fi_search = 1.05,
OmViz_max = 0.52,
warhead = warheads[“AIM_120C”],
exhaust = {0.8, 0.8, 0.8, 0.2 };
X_back = -1.61,
Y_back = -0.089,
Z_back = 0.0,
Reflection = 0.0329,
KillDistance = 15.0,ModelData = { 58 , – model params count
0.4 , – characteristic square (õàðàêòåðèñòè÷åñêàÿ ïëîùàäü)– ïàðàìåòðû çàâèñèìîñòè Ñx
0.045 , – Cx_k0 ïëàíêà Ñx0 íà äîçâóêå ( M << 1)
0.09 , – Cx_k1 âûñîòà ïèêà âîëíîâîãî êðèçèñà
0.02 , – Cx_k2 êðóòèçíà ôðîíòà íà ïîäõîäå ê âîëíîâîìó êðèçèñó
0.016, – Cx_k3 ïëàíêà Cx0 íà ñâåðõçâóêå ( M >> 1)
1.2 , – Cx_k4 êðóòèçíà ñïàäà çà âîëíîâûì êðèçèñîì
1.5 , – êîýôôèöèåíò îòâàëà ïîëÿðû (ïðîïîðöèîíàëüíî sqrt (M^2-1))– ïàðàìåòðû çàâèñèìîñòè Cy
0.7 , – Cy_k0 ïëàíêà Ñy0 íà äîçâóêå ( M << 1)
0.8 , – Cy_k1 ïëàíêà Cy0 íà ñâåðõçâóêå ( M >> 1)
1.2 , – Cy_k2 êðóòèçíà ñïàäà(ôðîíòà) çà âîëíîâûì êðèçèñîì0.29 , – 7 Alfa_max ìàêñèìàëüíûé áàëàíñèðîâà÷íûé óãîë, ðàäèàíû
0.0, --óãëîâàÿ ñêîðîñòü ñîçäàâàéìàÿ ìîìåíòîì ãàçîâûõ ðóëåé– Engine data. Time, fuel flow, thrust.
– t_statr t_b t_accel t_march t_inertial t_break t_end – Stage
-1.0, -1.0, 8.0, 0.0, 0.0, 0.0, 1.0e9, – time of stage, sec
0.0, 0.0, 6.41, 0.0, 0.0, 0.0, 0.0, – fuel flow rate in second, kg/sec(ñåêóíäíûé ðàñõîä ìàññû òîïëèâà êã/ñåê)
0.0, 0.0, 16325.0, 0.0, 0.0, 0.0, 0.0, – thrust, newtons1.0e9, – òàéìåð ñàìîëèêâèäàöèè, ñåê
80.0, – âðåìÿ ðàáîòû ýíåðãîñèñòåìû, ñåê
0, – àáñîëþòíàÿ âûñîòà ñàìîëèêâèäàöèè, ì
1.0, – âðåìÿ çàäåðæêè âêëþ÷åíèÿ óïðàâëåíèÿ (ìàíåâð îòëåòà, áåçîïàñíîñòè), ñåê
40000, – äàëüíîñòü äî öåëè â ìîìåíò ïóñêà, ïðè ïðåâûøåíèè êîòîðîé ðàêåòà âûïîëíÿåòñÿ ìàíåâð “ãîðêà”, ì
40000, – äàëüíîñòü äî öåëè, ïðè êîòîðîé ìàíåâð “ãîðêà” çàâåðøàåòñÿ è ðàêåòà ïåðåõîäèò íà ÷èñòóþ ïðîïîðöèîíàëüíóþ íàâèãàöèþ (äîëæåí áûòü áîëüøå èëè ðàâåí ïðåäûäóùåìó ïàðàìåòðó), ì
0.17, – ñèíóñ óãëà âîçâûøåíèÿ òðàåêòîðèè íàáîðà ãîðêè
50.0, – ïðîäîëüíîå óñêîðåíèÿ âçâåäåíèÿ âçðûâàòåëÿ
0.0, – ìîäóëü ñêîðîñòè ñîîáùàéìûé êàòàïóëüòíûì óñòðîéñòâîì, âûøèáíûì çàðÿäîì è òä
1.19, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, êîýô ôèëüòðà âòîðîãî ïîðÿäêà K0
1.0, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, êîýô ôèëüòðà âòîðîãî ïîðÿäêà K1
2.0, – õàðàêòðèñòèêà ñèñòåìû ÑÀÓ-ÐÀÊÅÒÀ, ïîëîñà ïðîïóñêàíèÿ êîíòóðà óïðàâëåíèÿ
25200.0, – äàëüíîñòü ïîëåòà â ãîðèçîíò ñ ðàñïîëàãàåìîé ïåðåãðóçêîé Navail >= 1.0 íà âûñîòå H=2000
3.92, – êðóòèçíà çàâèñèìîñòè äàëüíîñòü ïîëåòà â ãîðèçîíò ñ ðàñïîëàãàåìîé ïåðåãðóçêîé Navail >= 1.0 îò âûñîòû H
3.2,
0.75, – áåçðàçìåðíûé êîýô. ýôôåêòèâíîñòè ÑÀÓ ðàêåòû
70.0, – ðàñ÷åò âðåìåíè ïîëåòà
– DLZ. Äàííûå äëÿ ðàññ÷åòà äàëüíîñòåé ïóñêà (èíäèêàöèÿ íà ïðèöåëå)
63000.0, – äàëüíîñòü ðàêóðñ 180(íàâñòðå÷ó) ãðàä, Í=10000ì, V=900êì/÷, ì
25000.0, – äàëüíîñòü ðàêóðñ 0(â äîãîí) ãðàä, Í=10000ì, V=900êì/÷
22000.0, – äàëüíîñòü ðàêóðñ 180(íàâñòðå÷ó) ãðàä, Í=1000ì, V=900êì/÷
0.2,
0.6,
1.4,
-3.0,
0.5,
},… one wonders …
-
Thought I’d post an update on what I’ve learned about the missile behavior so far(after a couple thousand test firings acmi files):
- The atmospheric model(as it pertains to drag on a missile) seems accurate for various alt up to the 40k ft I tested.
- In regard to the thrust entered in the data table, in game the thrust is a few percent low at sea level, 33% too great at 20k ft, and 64% to great at 40k ft. A coded fix would be needed to correct this. The best way to overcome this currently is by using SpbGoro’s approach of using actual thrust in the data tables and then setting a “speed brake” with overly high drag in the the coefficient table at a pre-determined max speed limit. In reality, missile thrust does not increase with altitude, but due to the temp decrease, the burn times would increase similar to those percentages as altitude increased(perhaps that is what Microprose developers were going for?). However, the total thrust impulse would remain about the same as it is at sea level( probably about 3% lower above 35k ft).
- “Weight of missile” in the data table is the burnout weight and “weight of propellant” is just what it says. These 2 added together are the missile launch weight in game. The propellant weight is decreases to 0 in game by motor burn out. I do not know if this is linear over the missile burn time or varies by thrust level over burn time(my guess is linear).
- Although the stock aerodynamic coefficients are in a normal and axial format, the game actually interprets the data as lift and drag. This is plainly seen in tacview as the stock the missiles do not add show any additional drag as angle of attack increases. When the stock normal and axial data is converted to lift and drag format data, the missiles drag obviously increases with angle of attack.
- The AOA max/min and Beta max/min values do not seem to be hard limits to the missiles max angle of attack. In game the missiles can achieve just over 2 times this “limit”.
I get the feeling the Microprose developers were still working on the missiles when they ran out of time perhaps?
For those interested in how I came up with this:
I’ve created a completely new aerodynamic coefficient table(not in the file on the first page, that is stock coefficients in lift and drag format) for the aim-9 based off of some datacom data as well as an actual zero-lift drag table, and using actual sea level thrust table for the aim-9. I have then been running flyout performance tests and comparing them to an actual flyout performance charts for the aim-9l at sea level, 10k and 20k ft. This flyout chart also gives flyout data for an aim-9 “variant” missile modified with aim-120 nose and fins on an aim-9 airframe/motor. I also created an aim-7 based off a tactical missile design document intended for a college course, and compared that to the flyout data it provided at altitudes varying from sea level to 40k ft. I did tests mostly at sea level, 20k and 40k ft, and found that the flyout tests in game produced very accurate results after motor burn out. The problem is that for some reason the code increases the thrust of missiles as the altitude goes up. At sea level the thrust in game appears to be close, if a tiny bit low. At 20k ft, the thrust is 33% too high, and at 40k ft the thrust is 64% too great. I obtained those thrust % results by setting all the drag coefficients(axial as labeled) to 1 on my aim-7, the thrust to a set value (1018 lbs) for over 100 sec burn time and then obtaining the max velocity in game(drag=thrust) at different altitudes. Then I plugged the data into the drag equation (Drag force = 0.5 x P x V^2 x Cd x A) to find actual in game thrust compared to the thrust in the data table. I also found that the using the aim-7 aerodynamic coefficients with a 0.87 modifier(13% reduction) for drag used in an aim-9 missile data file(aim-9 weight, ref area, and thrust) produce flyout results very close to the aim-9 variant(aim-120) flyout tables.You are wrong about #4 the code reads and interprets axial coefficients not lift and drag.
The point is that those coefficient are complete BS in database therefore results are not correct at all
-
The Aim-120 in DCS is very “messed up” currently (can´t even hit a target from 13nm at 25k feet), so one guy (pdf file below) put alot work into it in order to “fix it”.
If the target turns and descent to SL very quickly this is real especially in case during the moment of launch the aspect was good for this turn. The NEZ is no so big of AIM-120 as many people wish to believe.
-
If the target turns and descent to SL very quickly this is real especially in case during the moment of launch the aspect was good for this turn. The NEZ is no so big of AIM-120 as many people wish to believe.
You are describing a specific scenario, but that is not the case.
Molni, it is soo bad in DCS atm, that people wait to 10nm over 20-25kfeet to actually “reach” the target with the Aim-120. That´s RUBBISH!
The missiles maneuver “from the rails” bleeding off all energy early on, but that is not what missiles of that classification do.
Instead they intercept a “probable meeting point” with as less as possible Gs spent in early stage in order to be able to spent all the “turn-ability” on terminal stage (like in BMS).
Look up “proportional navigation guidance” and you know what i mean and compare that with DCS Aim-120 acmis.PS: Afaik, they are very aware of the problem (or bug) and hope to get it fixed.
-
Yes, I am saying that if you would set a static thrust of 5000 lbs for 5 seconds in the missile data file, the actual thrust in game would be 6650 lbs(50001.33) at 20k ft and increase to 8200 lbs(50001.64) by 40k ft. This results in excessive burnout speeds/range. In fact the only limiting factor on max range in the stock missiles at high altitude is the max time of flight(battery time).
At first I thought that the excessively high burnout speeds as altitude increased was due to the atmospheric model being incorrect. However, I found that that was not the case as the missiles deceleration matched the real life flyout charts at all altitudes for both the aim-9 and aim-7, therefore the air density is correct in game at the altitudes I tested(0, 10k, 20k, 40k ft). I confirmed this using set static thrust and drag in a missile file and with the velocity generated in game plugged back into the drag equation to find the P value(air density) in game. I then set all the drag coeficients to 1 in the data file, and increased the burnout time of the sustainer thrust (1018 lbs) to 115 seconds at burnout. Then I fired the missile at distant same altitude targets at the test altitudes and recorded the velocity when the missile stabalized (thrust = drag). Since I knew that the atmospheric model was correct for density, I used the drag equation (Drag force = 0.5 x P x V^2 x Cd x A) and plugged in the in game air density,missile reference area, 1 for all Cd since I set them all to 1 in the file, and the final stabalized velocity at that altitude. I compared that force result to the actual thrust I used in the data file, which should have been equal if the game was not modifying the thrust. This is how I found the game is increasing the thrust dramatically as altitude rises, to the tune of 33% at 20k ft and 64% at 40k ft. This increase to thrust as altitude increases must be done in code, and it results in very excessive burnout speeds at high altitude.Well, the alternative of specifying specific impulse against air density is probably more computationally intense. That thrust increase does seem more extensive than you would think, though.
So, has the stock had changes in this area in 4.33?
-
The “thrust bug” was corrected with the 4.33 release, it now produces realistic results. The stock BMS aerodynamic missile data was also updated to be much better (although I still think the drag on the aim-120 is too low). I did some work on my own missile data file after 4.33 was released based on public data, but haven’t worked on it I over a year.