nighthawk2174

Do you have the original documents these fin diagrams come from?

That'd be good enough considering the limited nature of information.

Concerning the motor shape is there a diagram that exists your work is matched too? Do we know the propellant type as well?

A few questions regarding the R77 - What are the dimentions of the lattice fins and chord profile? -How much is known about the motor? -How much is known about the radar seeker?

I don't think there is a simple method by wich you could calculate it except at very low machs. Shock interactions basically make it so that you need CFD or wind tunnels to do this. You could probably estimate with a drag build up method but it'd have large error margins on it.

L/D of ~2.4 which is reasonable and the shock angles are reasonable close for M2.5 at 5deg. The original paper I posted was at ~2.15 L/D and Russian document was ~2.2. Also are these body axis force coefficients or wind referenced?

https://ntrs.nasa.gov/api/citations/20040110952/downloads/20040110952.pdf A NASA paper I remembered seeing a few years back may be worth a look.

The plot has mach number listed with associated plot colors. M2.0 would be a light green to green'ish teal color. While upstream appears to be a light-medium blue instead. If upstream is M2.0 based on the expansion fans angular width i'd expect a much higher post fan mach. M2.5 - M 2.8 depending on how you measure out the fan angular width. But it itself appears to also be awfully close to M2?

Is this plot for those condtions you listed?

Probably being lost in translation what i'm saying is that the chart you posted lines up with what i'd expect to be the points where you get direct interaction, shock reflections directly off the opposite fin. However this does not preclude the main shocks hitting and reflection off each other (which will still chock flow) while still within a chord length of the tip of the lattice. Shocks off the lattice will nearly follow the oblique shock tables for thin plates. The angle at which the shocks will only interact with each other (as in shock off shock reflection) more then a chord length from the lattice tip can be calculated. This is why flow is still chocked even up to M2.5 not as bad as with all the shock reflections at a lower mach such as M1.5 but it is why the L/D still remains poor except at very high machs 4.0+. Ok

Yes I do the tradeoffs are that by increasing tbar you decrease drag but also decrease lift and dynamic stability. Essentially larger boxes makes it have lower L/D with worse stability, but the sooner you stop getting shock reflections interfering with each other. The chart you posted will be the point where the shock angle is such that you stop getting shock reflections for various tbar's and aoas. The shocks will still interact inside the lattice at least until a much higher mach usally M4+. The pressure coeficent drawings fin outline is making it difficult to tell but the shocks in that example are not interacting with the other plate of the lattice just with the other sock/expansion fan which is to be expected for that mach and angle. null Also from your images tbar appears to be closer to 1.4, scaled such that chord = 1". Doc I linked with the pressure coeficent iso's is ~1.48 inner to inner surface.

I haven’t made anything up; it is up to you to disprove what I’ve presented. You’ve provided no definitive proof to back the numeric results you listed. Said results don’t align with a substantial amount of wind tunnel and CFD data from NATO, US Army, and academic sources, including your own Russian sources that you posted earlier. I’ve studied lattices at a high level in university and have conducted my own CFD research on them. The numeric results you presented earlier simply don’t align with well-known data points from multiple reputable sources. The static pressure profile you posted matches nearly the pressure profile from the below report which is at M2.5 and 20deg of aoa. The expansion fan on the leward side of the lattice and the shock on the windward side match the above. Indicating to me the CFD results you posted are almost ceratinly from a higher angle of attack then claimed. CFD_analysis_of_grid_fins_for_maneuverin.pdf

This data your presenting is not lining up, not even with data you posted earlier. Do you have a screenshot of the numerical readouts or is this just what was told to you? You said that this data was for M2.5 5deg aoa I can't imagine that the fins halfway deflection point is only 5deg. Looking at the shocks if this is at M2.5 the angle the shocks are at would indicate a deflection of closer to 20deg not 5deg. null We also have the CD and CY values you posted earlier for the M2.5 case: null L/D at 5deg is 2.2 and at 20deg is 2. From the original study I posted at 5deg its Cy=0.25 and Cx=0.12 for a L/D of ~2.1. I don't have ref area used in the numbers you posted but assuming that the 2Kn of lift is right - sea level + STP - then drag using the coeficents provided would be 906N of drag not 420|430N.

Gotcha did you run the CFD you posted, if so you have the numeric results? Also tbh i'm suspicous of those numbers as that is rather quite high and doesn't line up with the graphs you posted or the wind tunnel results I posted.

2D only flow?