So you are using the specific impulse of the ER? 281 s? When the calculations on the r77 give 236s( for both 4.5s-30.4kN and 6s-22.8kN), only way its higher is with the 6s-30.4kN giving 315s or lower with 4.5s-22.8kN for 177s
Different rocket. 77 is 200mm in diameter while 27series is 230mm. Its also 2x lighter than the ER and 70% of the 27Rs weight. Its 22% shorter than ER and 8% shorter than R.
All this give a much lower ballistic coefficient at end of burn. To get the same Bcoef would be for drag on the ER to be 1.83x higher than that of the R77. Or 1.22x higher on the R.
Looks like you did a VERY optimist calculation imo.
I used a standard of around 250s impulse for the R-77, which is nominal for a 1990’s missile from the East. The AIM-7F by comparison is ~262s. The achievement of 280s was possible only for the West at this time, I am not certain where you got that figure for the R-27R/ER.
Of course all of the available information for the missiles is different. I am solely using the specific impulse. Weight of the R-77 and burn time along with all other measures are entirely different. The R-27R and R-77 are only likely similar in propellant type and efficiency.
I don’t know how you sit here and constantly talk about other people in such a negative manner while adding precisely nothing to the conversation. Please contribute or don’t say anything at all.
@MaMoran20 the following site is used for determining specific impulse of R-77… the data can be considered a primary source but unfortunately the source itself is not usable for the forum. If you want more data on it - you can join the site and contact the people who posted the information.
It is stated the following information:
175 kg launch weight
118 kg burn-out weight
Burn time of 4.5-6s
So we can do some simple math;
Burn time (4.5s) * force exerted (assuming ~22854.96 - 30473.28 (Newtons), for this we will use same as R-27R at (25,125 N) and divide by 9.81*(launch weight - empty weight which would equate to 57kg).
The result is ~269s for the 4.5s burn time. For the 6s burn time the math comes out around 202s. The intermediate result is 235s which means thrust is either a bit higher, or burn time is a bit lower than 5.25s. If the 235s impulse is correct, we are close to the expected performance of the motor.
If anything, the results show a 235s impulse and this is a bit on the low end. I’ve gone with this 5.25s burn time and 235s impulse for my in-game model. Do you think this is fair or should I change it up?
These are the 7 average mass flow rates for the 2 different burns.
And these are the 4 specific impulse(s) iterations. You see on 2 cases it falls on 236s. Total impulse of 137,126 Ns. Then you have 1 optimist case and pessimist case. The low end really is 178s for specific impulse, not 236s.
Why don’t you just try both iterations? 6s for 22,854N and 4.5s for 30473N. Can’t say much for drag really but test with a chart for rear aspect at 1100kph and 900kph TAS.
I don’t have rear aspect data for comparison to the AMRAAM
I’ve tried both of the other burn times and adjusted drag a bunch but ultimately I think that increasing specific impulse above 260 isn’t correct, nor is reducing it to 200. As you said, 235s or so seems about right.
I actually think the drag is currently WAYYYYY too high, but it still has the energy to reach the target at 80km provided battery life limit is extended beyond 80s. I realize I forgot to change the drag coefficient back down to a more reasonable 2.6-2.8 in that screenshot. Tests were with too high of a drag coefficient.
@MaMoran20 What do you estimate for the performance of the AIM-120A’s specific impulse and deltaV? I seem to be getting 10-20% higher deltaV for the R-77 with the impulse numbers we went over.
I put them together. 80km at 10km alt at Mach 1 (R27 charts are given with 1100kph TAS and 900 kph)its a bit excessive don’t you think. When in both cases its half that range.
Dunno, on the old forum I saw from 240s to 260s. Not sure really but thrust values are given
26,689N (6000lbf) for 1.5sec
And 13,344N (3000 lbf) for 5.5 sec
One of those charts we discovered is fabricated from a Russian magazine allegedly and the other is fabricated based on outdated information from the Indian defense forum. Neither are good data for R-77 / AIM-120.
R-27ER is battery limited, probably worse than the R-77 in that regard as well.
Those burn time and thrusts equate to ~240-250s impulse for the AIM-120 and I think that is pretty accurate. They had a focus towards shelf life and reduced smoke rather than purely focusing on performance.
I have a propellant mass of ~17kg for booster (starting weight of 155.13kg and empty of 138.1374kg).
After the booster we have a empty weight of 107.8kg for a total booster + sustainer weight of ~48.13kg.
