I would like to quote more details from that source.
The Phoenix only attains Mach 5 from Mach 2 when launch launched level (no manual loft), at alt of 48,000ft (~14630m).
The source also include a diagram of altitude over time and Mach number over time, this indicate the missile is capable of traveling above Mach 3 for over 60s.
But it doesn’t necessarily meet altitude over time, aka trajectory shaping,.
In the era where Energy–maneuverability theory were accepted into military, at least Aim-54C should have stored its energy as gravitational potential energy by aggressive lofting.
I know this is from Sea Phoenix test, however, I came across this as well:
Tests of the surface-launched Phoenix missile included a firing from what was then known as Naval Weapons Center China Lake, in California, during which a standard version of the missile traveled a distance of 13.5 miles in 90 seconds. This test, however, was less concerned with evaluating end-to-end performance than it was the separation of the missile from its launcher, as well as safety aspects. If they did occur, no other such tests appear to have been documented.
Do we have data on what angle the Sea Phoenix test was launched at? If they were concerned with safety scenario, say Phoenix fell to the ground after lift off, then they won’t launch it to demonstrate performance, instead they probably launch it like, for example, at 70 degrees above horizon and make it fly ballilstic (guidance turned off to avoid autopilot goes HAL).
Then we get the 13.5miles/22km down range not because missile motor’s performs bad at sea level, but simply due to how the launch was setup and it wasn’t intended to fly far.
Also, “travels 22km downrange in 90s” doesn’t mean the missile has landed on the ground, the missile could still be in the air
Inital mass = 463kg
End mass = 293kg
Propellant mass = 463 - 293 = 170kg
Mass flow rate = 170kg / 24s = 7.08kg/s
Isp = F / mass flow rate / g = 17793 / 7.08 / 9.81 = 256s
That’s actually whoppingly good.
This is on par with the HTPB.
We need direct proof that Aim54’s solid fuel has really bad Isp, since the quote “the only definitive data sources we have regarding the AIM-54’s motor performance for any variant” endquote + Math says the Isp is very good.
There are four possibilities I can think of:
The source is wrong
The Math is wrong
The claim that Aim54’s solid fuel has low Isp is wrong.
Or the end mass is wrong.
Even if we use 258kg (from a random reddit post) as end mass, the Isp is still 212s.
Also, surprisingly, dV increases if we have lower specific impulse due to lower end mass.
Isp of 212 + end mass 258kg => dV ~= 1216m/s
Isp of 256 + end mass 293kg => dV ~= 1149m/s
(In game it is 258s + end mass of 293kg, dV ~= 1157m/s. So the Isp in game is mostly fine)
This further proves my point: it doesn’t matter the missile is 60 years old or not, only delta V matters at high alt. If it have same dV when at very high alt where drag doesn’t really matter and flies similar trajectory, it’s gonna has similar range as latest state of the art missile.
Drag matters.
If there is enough air for the missile to create lift to fly, then there is also enough air to slow it down … You can’t have one without the other …
I know that, but the drag is so miniscule and it won’t slow the missile down significantly. For example, when flying at altitude of 30,000m, air denstiy = 0.018.
This means the missile is only experiencing less than 2% of the drag it would have were it to traveling at similar speed at sea level. (0.018 / 1.225 ~= 1.5%)
If we plug in numbers.
Mach 5 at 30,000m + drag coefficient of 0.2 + mass of 293kg
v = 1475
Area = 0.1134m^3
drag = 0.018 * 0.2 * 0.1134 * 1475 * 1475 * 0.5 = 444N
Basically no drag since gravitational force at this point is 2871N.
The missile only needs to glide at around 9 degrees below level to compensate for most of the drag.
Let’s exaggerate this say missile flies for 60s with 2000N of drag force, total impulse from drag is 120,000Ns and translates to a decrease of ~409m/s.
The missile would still fly at over 1000m/s, meanwhile it had covered a ground distance of at least 60km, not including the distance covered during boost; and it only lost about 9400m of altitude in that 9 degree glide. sin(9) * 60,000 = 9386m. It still has 10,000m at disposal before hitting denser atmosphere.
The ability to glide at over Mach 3 for over a minute is the secret sauce (in addition to being ARH) that makes Aim-54 having superior range and extremely deadly in the 70s.
The battery is Phoenix’s limitation, not the kinematics. This is similar to the limitation of Aim-120, except the later variant (like 120D) where Raytheon constantly advertised it magically gained 50-100km range without any change in specific impulse or aerodynamics, while in fact they just swapped in a better battery that holds more charge and allow missile glide further at subsonic speed.
The diagram of the launcher shoes a 30 degree vertical angle, which is what I launched it at. They also said it was a 100% untouched, unmodified Phoenix in any way. It was an off-the-shelf example slotted and launched.
That is true, but the in-game model travels further in the same amount of time which suggests motor or drag overperformance (or both), which agrees with my assessment earlier about how it was modeled.
17,000 newtons isn’t for 24+ seconds. 17,000 newtons is generally given the Mk60 motor alternative not seen in-game, and for around ~20s. Flexadyne is closer to 230-240s at sea level for the RDS-5XX series propellants, which are also utilized by the AIM-9C/D and other motors.
In-game we have 14,350 for 30s, and that is in-line with the sources used. Though I will say DSplayer has not updated the sources list for QUITE some time. It must be realized that this performance is already for high altitude, where ISP would have increased due to increase in exhaust velocity from the reduction in ambient pressure.
Math showing 257-266s impulse is correct for the in-game thrust and burn times;
Spoiler
AIM-54A (correct weight)
Initial Mass = 443.613
End Mass = 273.063
Propellant mass in-game = 170.55kg (376 pounds)
Real propellant mass fraction = 364 pounds (11 pounds of ablatives are accounted for in WT)
Mass flow rate of correct weight AIM-54;
170.55 / 30 = 5.685kg/s
Mass flow rate not including excess ablatives in formula;
165 / 30 = 5.5
AIM-54A (correct weight)
Isp = F / mass flow rate / g = 14350 / 5.685 / 9.81 = 257
Isp = F / mass flow rate / g = 14350 / 5.5 / 9.81 = 266
I don’t really care to do the math and figure out what the thrust and burn time should be at sea level, but if it maintains the higher altitude efficiency at 266s down to sea level, you can see why it is “overperforming” in that regard.
The source used for that explanation was wrong, therefore the math is wrong, the claim that is has low ISP is correct because it is early 60’s CTPB utilized in a number of other projects, the end-mass of the AIM-54C is incorrect but it is correct for the AIM-54A. The fuel fraction is correct. McGregor tells us (as well as the yellow book for hazardous explosives) that the fuel mass is 364 pounds for the AIM-54A’s mk47 motor or ~165kg.
Without delving into this conversation too much, the switch to a new motor on the AIM-54C was only known because they switched to reduced smoke. They continued making newer propellants for the Mk36 and the AIM-120 long after the last public acknowledgement of a motor change.
They can get away with these kinds of improvements because like with the Mk36, it was improved over time from AIM-9D to AIM-9L and then was only really discussed that it was being changed as they swapped to reduced smoke there as well.
Even the reduced smoke motor for the AIM-54C was poorly documented and not well known except for some budgetary discussions.
Anyhow, the AIM-120 being flown in a more ballistic manner would not be able to effectively utilize the extra range. It was claimed that it could technically be fired straight up and then dive on a incoming head-on target and effectively “intercept” it when launched at 250km range but this really isn’t impressive since the horizontal distance covered by the AIM-120 isn’t as much as a more optimal path that reduces time to target at closer launch ranges.
I only cautiously agree with this part, only if we can confirm that the 22km ground launch test was indeed conducted by firing at 30 degrees.
The issue is I’m struggling to find the angle they launched during the Sea Phoenix test; instead I found secondary source claiming the launch has safety consideration and wasn’t meant to demonstrate the performance.
We know the diagram exists and also know the program didn’t get to the mock up and prototype stage, all of the tests were function validation.
e.g. Launch Phoenix from stationary, install AWG-9 on ship and see if it works.
But that means they were quick dirty tests and, although we may find secondary source, accuracy and usefulness in determining performance is questionable without more details on the actual setup.
Given the unlikely hood of finding information on exact Sea Phoenix test setup, I propose we do a simple test.
I did the Math for thrust at sea level (but I don’t know how to use CDK).
Assuming Isp was reduced to 230s at sea level (dV becomes 1031m/s with ingame initial/end mass).
We know Isp = thrust / mass flow rate / g
Thus sea level (Isp=230s) thrust = 230 * 5.67 * 9.81 ~= 12785N
If you have time, you can repeat that 30deg launch test while reducing Aim54’s thrust to 12785N.
If actual test were condcuted with launch at 30deg, then missile in game should have traveled around 25km in replay at T+90s.
displacement = ground distance covered / cos(launch angle) = 22 / cos(30deg) ~= 25.4km
The loft profile of the missile will self-correct it to a lower 17 degree angle, we do not know the real world missile loft parameters but it would also self-correct itself.
Given that the real world loft parameters are unknown I suggest we test with a 30 degree launch and no loft profile as well as a 30 degree loft with the in-game AIM-120 loft profile.
ISP is going to be above 230 in my opinion, but what we don’t know is how much the burn rate changes based on altitude. This is dirty math that may have a negative effect on the test. There are just so many variables that we aren’t able to account for.
Yes I’m assuming Aim-54C since that one has improved avionics and autopilots.
If we go with 3315N of drag, assuming missile never goes ballistic and total speed loss will be 678m/s.
There are still 768m/s of speed remaining after 1 minute since burnout.
If missile went ballistic with 0 AoA in a portion of its flight (say follow the velocity vector and nose down slowly), then it would have lost even less speed.
None the less, even if we assume it didn’t do anything to minimize drag loss, assuming a constant deceleration for simplicity.
The average speed is still over 1000m/a, the missile would have flown 60km in 1 minute, with speed over Mach 2 and 20000m altitude to spare, which it can use another 10,000m of altitude to glide or dive and maintain Mach 2+ all the way down to at least 10,000m
I agree. Sadly I only took physics as hobby in University =(
If I use this source, take the lowest Isp=245s at sea level, plus the fuel mass you mentioned, so we can ignore the incorrect end mass of Aim-54C ingame.
Then the dirty Math becomes:
Mass flow rate = 165 / 30 = 5.5s
Isp = thrust / mass flow rate / g
Sea level (Isp=245s) thrust = 245 * 5.5 * 9.81 ~= 13219N
The propellant as tested in a lab does not correlate with the impulse of the in-service ordnance it is used on. Likely because laboratory testing still shows a delivered ISP while maintaining near perfect chamber pressure conditions and without mass production changes to the motor designs.
Seeing as it entered production / service around the same time as the Phoenix went to full scale engineering development we can assume small improvements and potentially slightly higher impulse from the Phoenix, as well as better build quality due to size. Hence why I stated 230-240s and why 250+ is unlikely.
@sudo_su1@SE_8749236
Something to consider is that the nozzle will be overexpanded or underexpanded at sea level depending on which altitude the nozzle was optimized for. (to benefit more from a loft and for the purpose it was built). It is possible the ISP would suffer from a more vacuum oriented nozzle once it reaches lower altitudes.
Seeing as it lofts naturally, to give it the benefit of the doubt a more aggressive profile should be given imo.
The thrust and burn time would likely change, more so just the burn time. I suspect peak and minimum thrust will be similar but the most varied change is in burn time. Either way, I could test this. I’ve been lazy as of late though after grinding out the J-11A, Su-27SM, and J-10A
So per the latest BR changes the non Fakour armed F-14s are going up and are receiving no buffs at all.
might as well just folder the tech tree F-14A because there is even less reason to use it now given the AIM-54 is now going to be forced to fight against superior AAMs even more.
