The dimensions are incorrect, as is the profile
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ISP has never been accurate to real life in-game, it is also missing some thrust to account for reduction in drag during motor burn time as stated and doesn’t meet certain data points. This is the first iteration of these missiles… I would not be on the side of wagering they are final either… But I wouldn’t say it is due for a nerf either.
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From what I find, the fin dimensions are correct. But I’m applying the shockwave logic just between 2 parallel plates.
Eitherway, the gap-chord ratio is ~1:1.
For drag to be low, there must be no to little interference between the shock waves early on.
Using the ratio I mentioned. The first shockwaves can be deduced. The minimum is when the shockwaves meet at the midpoint of the gap. That is a 45° angle which corresponds to a Mach number of 2.24. The Faster we go, the smaller the angle of the shock wave is. At M4.13 there is a gap at the end which is half of the gap. Here the supersonic air flows without issue and it meets the weaker shockwave of the trailing edge at 2x the chord length. The faster we go, the smaller the angle and less is the effect from other shockwaves. The mass flow rate increases.
Now what happens if we go slower
At M1.4, the angle of the shockwave is 45° and its meets the other shockwave at 1/2 the chord length. The shockwaves meet and there’s interference, Mach number drops and pressure increases. The slower the go, the angle rises, velocity decreases and pressure increases.
Below you can see this part.
When the shockwaves meet the MAch number is slower. This translates to a higher pressure
When velocity decreases even more to the transonic region, the pressure inside the vanes is considerably higher. What happens whe we have a high pressure? We got a a wall. It’s “easier” for the air to go around the fins than through the higher pressure. Remember the higher pressure pushes “out”. You can aswell put an airbrake…
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cont…
Also, as you saw above, the pressure behind the fins is high. That’s ALLLLL the parasitic drag. It decreases considerably at high (>M5) mach numbers as the supersonic flow just passes through.
Look at the shockwave, created. The MAch number of it. The pressure is high, all that makes the air to just spill around it as there’s less resistances. Same way if there’s an airbrake, there’s less resistance to move around it.
That was on 2d.
Go 3d and the case at Mach 4.13 and Mach 2.24.
This is the area which the air will flow by the trailing edge of the chord. At Mach 2.24 that is zero and meets it just at the end. At M4.13, the area where the air will cross will be 25% of the total area.
You also got the strong interference at the diagonal lines. Increasing pressure and all that even at high Mach numbers.
The calculations I did were at thin plates where the thickness is négligeable. Once you actually add a thickness to them, the imaginary tip of the shockwave will be ahead of the tip of the object and the shockwaves will meet earlier.
You can see below. The shockwave intersection is closer to the thin plate. If both were thicker, the intersection would ahead than that of a reallly really thin plate. AS shockwaves meet earlier, drag is higher.
The point being, that whole above Mach 1.3 grid fins superior less drag and everything is not true at all. That would be around Mach 5, which the missile doesn’t go.
Just imagine trying to push your plane around from Mach 0.8 to M1.4 with 32 airbrakes…
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No
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I advise you to study the original source on lattice handlebars
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We stated it benefits greatly from launches above 1.3 mach and has superior energy retention at high supersonic regions. This is still absolutely true, to pretend the grid fin (which needs far less deflection for sharp maneuver) will not benefit more so than a planar fin in these regions is interesting. You’ve gone and made a lot of good points but it seems you are being intentionally misleading.
Especially with the comment I quoted, there aren’t 32 ‘airbrakes’. There are 4 maneuvering surfaces. Are the JAS-39s canards airbrakes?
In any case, the missile is only ever briefly at this region of speed and we have already discussed and covered the fact that it has relatively low impact on the performance of the missile overall. Planar fins have advantages, but the grid fins are more useful for the design goals of the R-77. You won’t see a missile like the Phoenix or AMRAAM above 25° AoA irl, the instability is too high. The grid fins are clearly superior for accuracy, control, and strike a fantastic balance for their use as a medium range missile.
The deltaV of the R-77 is already higher than the AMRAAM, and as I’ve discussed… They hadn’t given it the missing ~15% thrust to account for reduction in drag during motor burn time and the drag must be reduced when loft is removed so that it still meets the performance criteria.
Your discussion of grid fins is entertaining, but unless you have performance charts for the missile I’m not sure you’ll be able to change the in-game model based solely on hand drawn models of supersonic grid fin wave drag.
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Also as we can see, the shapes are not the same at all.
From what I measure, proportions match up. Chord-gaps is roughly 1:1
do you mind sharing the prf?
Changes in the angle of attack over time.Conventional steering(а) wheel and grille (б)
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Seems like it would make for a poor tradeoff for a missile intended for use on stealth airframe, as frictional heating increases significantly once you move into the supersonic regime.
Which if sustained would light the aircraft up like a Christmas tree for any IRST/ IIRSTS / EOTS system worth its salt, making you much more detectable and thus defeating the point since it would telegraph the intent to launch a missile, tens of seconds in advance of it actually occurring.
It would make sense change to a more conventional control surface arrangement to arm something like the Su-57 that may heavily rely on minimizing its signature to function.
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That’s exactly right, and the sole reason to move towards planar fins for the R-77M is to aid the stealth features of the Su-57.
It may very well minimize IR and RCS.
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grid fins significantly reduced drag at high supersonic, equal in subsonic and only briefly does it have significantly higher drag in transonic region. They offer significantly improved stability and AoA over traditional fins but also a much larger radar cross section.
To be honest, that sound hard to believe. If grid fin are that good then they should be more popular with SAM. From USA SAM such as SM-2, SM-6, ESSM to the Russian SAM such as 9N96, 48N6, 40N6, to the China SAM such as HQ-9 , HQ-12 all use conventional planar fin instead of grid fin.
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We already know grid fins to be superior for high supersonic drag. A more powerful missile would benefit more from grid fins than from conventional, this is a step back in performance for the R-77M to enhance its niche use in the Su-57.The R-77M using a lower RCS fin design is a by-product of Russia’s shift towards stealth fighters. Nothing more.
If that was the case, how come R-33 and R-37 on Mig-31 still use planar fin instead of grid fin?. These missiles surely spend much longer time in supersonic regime and Mig-31 is not designed for stealth by any mean
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The problem is in the starting area. Where the grid shows itself worse. And SAM needs speed.
Well, the swing of the handlebars is also important here.
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And you don’t want to calculate the size of the grid for such a huge rocket
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