If I lower the drag now, the effects of the thrust increase will likely make it overperform (maybe). I can play around with it a bit more and see to what single % increase (or decrease for drag) I can settle for both thrust and drag and see if it’s suspicioulsy convenient. I doubt it though, but I also like to know where the current rocket engine numbers even come from.
Also is the current weight of the SLM correct? It seems it has about 60kg of fuel right now. Idk if it’s realistic to get 200+ kN s of impulse out of that.
I don’t know where but I could have sworn to read >250 kN for the SLMs missile motor somewhere.
As I stated somwhere above, the normal rules for the rocket motor don’t seem to apply here as they don’t use a standard aluminium propellant but something that contains lithium to a certain degree (deep red flame instead of orange/yellowish).
I am not necessarily doubting the amount of impulse, but more with the current fuel mass it’s an outlier if given that 250 kN s. Right now the engine thrust seems to be tuned to be in line with most other engine performances, which is likely not correct either.
AIM-9L has 57240 N s of impulse with 27 kg of fuel, which is 2120 N s/kg
IRIS-T has 67690 N s of impulse with 38.8 kg of fuel, which gives a fairly low 1744 N s/kg
Most engines from quickly checking fall between this 1500-2500 N s/kg range
Current in-game SLM has 148050 N s of impulse with 63 kg of fuel, which gives 2350 N s/kg, which seems in line with other engines. If it was 250 kN s with 63 kg of fuel, you’d get 3968 N s/kg. Is pretty high, but honestly I am not well versed enough in rocket propellant to know if this is normal or even a valid way to compare rocket engines, by say their fuel efficiency.
*I know this measure is pretty closely related to Isp, but I think that one takes into account the entire engine
That seems awfully low? The SLM is more than 60 kg heavier than the standard IRIS-T (155 kg vs 88 kg) so it having only 25 kg more fuel is kinda… strange? Especially as the rocket motor is the only thing that is bigger (longer, larger diameter) for the SLM while everything else (guidance, warhead) has the same size as the standard IRIS-T.
Strange. Guessing from the size (two third with much larger diameter and therefore volume and half a meter more length) it should weight much more than only 22 kg more than the standard IRIS-T. Even if the propellant would be exceptionally light with 2-3 g/cm³.
Actually, now that I look at it, I think it’s just Isp what I am noting down. Just without dividing by the gravitational acceleration (say roughly 10), not completely sure if I can just take just the fuel and not the total engine weight though.
I know at least that an Isp of 150-250 is fairly realistic, 400 would be really high on the other hand, if it does use solid fuel.
The best source we have for weight does state weight between 140-150kg, and that source is a polish defense book that featured some production details, the first SLM missiles were only 152mm so those might have weighed 110kg but the ones currently in production and we have in WT are 180mm so heavier as well.
Jecka is currently ordering that book, i hope gaijin will consider it even if it’s a polish source.
And it has Mach 3 speed as well, but again we’ll have to see if it’s a good enough source for gaijin.
Edit: the website where he found it and the books mentioned in the sources
Could be because of the different burn profiles. Different mixtures of propellant in each stage (four for the standard IRIS-T, two for the SLM), different grain geometry and so on.
Not really as the IRIS-Ts four stage burn profile is fairly complex with a focus on maneuverability (especially at the moment of launch) to hit targets maneuvering targets in a 360° sphere nearby while the SLM seems to be optimized for extremly strong boost from the start and high speed sustain to hit targets way further out and only in a 180° half-sphere, so only 90° course corrections in a fairly big radius are needed. One being air- and the other ground-launched is also a factor.
Many such cases of Gaijin moving the line for Russian vehicles and armaments while saying ‘We believe this is wrong’ or ‘We believe this is a clear marketing lie’
Ukrainian press releases have made some public statements about the IRIS-T SLM speeds, and those were rejected for not being reliable, yes, the country that’s operating IRIS-T right now is not a reliable source lmao.
It’s not some occult knowledge that it can achieve Mach 3, it’s probably going to be shut down under the same pretext or that “it does not come from the country of origin” which was the last excuse they used when we tried foreign sources (an excuse the devs have never used before).
It seems that devs are under some strict rules for rejecting any source that isn’t from Diehl themselves, so that buffs cannot be applied, I’m not very hopeful, but we have yet to see.
This is actually a REALLY interesting theory, cuz it would actually explain quite a bit.
According to this paper from 2018, composite rocket fuel with an AL-Li additive exhibit increased performance and, interestingly, significantly reduced HCl production:
The increased performance of the motor is also supported by this study from 2023, along with it stating that Al-Li additives also reduce the size of the condensed combustion product(the metal particles in the exhaust)(CCP), which may also effect how visible the smoke trail is:
Spoiler
Which takes us to this ol’ piece of info regarding missile smoke trails:
Spoiler
Propellants with an Al-Li additive would be characterized as “metal fuel”, which would suggest it to still have a smoke trail due to the metal particles in the exhaust gases, this is why smokeless propellants eliminated the metal portion of the propellant despite the reduction in thrust, but in the case of an Al-Li propellant, it seems they chose to reduce both the HCl portion along with the CCP size of the contrail, which would explain why the IRIS-T seems to have more smoke than something like the AIM-9X, which appears to have gone all in on the “no smoke” idea, but less smoke than something like a Pantsir missile:
Picked these pics cuz they were all (except 1 of the 9X ones) in similar environments (deserts), which is important to match since temperature and humidity play a role in formation of smoke/contrail:
So an AL-Li composite propellant might actually explain 3 things; the high range, the reduced smoke, and the flames colour.
All that being said though, Id have to see proof that the rocket motor is in fact using a propellant with lithium inside. They definitely do exist commercially, such as ALITEC produced by the US company “Anduril”, claiming a 40% improvement in range:
But afaik, NAMMO Raufoss doesn’t openly state they have any lithium propellants, so at the end of the day, we’re speculating.
Lithium is also very light, 0.534g/cm^2, which could explain the marginal increase in weight despite the substantial increase in size over the baseline IRIS-T.
Fun little bit of coincidence; if you multiply the 148050Ns of impulse by the 40% improved range claimed by Anduril for ALITEC, you end up with 207270Ns of impulse and 3290N*s/kg, which clears the “200kN+” statement, granted I know range isnt 1:1 proportional to thrust though. I just think its an interesting coincidence👀
Of note, the Ukrainians are not only “a country” operating the IRIS-T SLM, they are by far the country operating the most IRIS-T SLM’s, along with being the country with the most combat experience with the IRIS-T SLM…
They rejected sources from Diehl themselves as well, so I wouldnt put any faith in them accepting any source that would buff the missile in any way.
They’re clearly on strict rules to refuse any and all possible buffs to the IRIS-T missile family in general…😐
