Operational Performace Comparison: Viper, Beagle, and Stubby

The F-35 compared with other modern jets.
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sprstdlyscottsmn

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Unread post17 Aug 2019, 15:22

Minizap is where I began. Ultimately I became disenfranchised with the fact that it did nothing to simulate missile guidance. Look up how the D has improved range over the C-7. Improved guidance. Minizap is a great starting point but it is not the end all be all
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zero-one

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Unread post17 Aug 2019, 16:58


Pretty informative (for me at least) video on how instability can be both a good and a bad thing for maneuverability.
Admittedly, I was a part of the "more instability is better" crowd.

Though I still thing unstable platforms are generally better for fighters, I now realize that there can be "too much" instability.
Question is, where is the right amount.

I think on the earlier post, the F-16 and F-22 had the highest instability rates on the pitch axis at the weights and speeds where the measurements were taken.

The SHornet was the most neutral crossing between stable and unstable depending on the speed and weight. The F-14 was the most stable, if I'm not mistaken.
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sprstdlyscottsmn

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Unread post17 Aug 2019, 17:37

zero-one wrote:I think on the earlier post, the F-16 and F-22 had the highest instability rates on the pitch axis at the weights and speeds where the measurements were taken.

The SHornet was the most neutral crossing between stable and unstable depending on the speed and weight. The F-14 was the most stable, if I'm not mistaken.

No those are pretty accurate
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garrya

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Unread post17 Aug 2019, 20:10

sprstdlyscottsmn wrote:Minizap is where I began. Ultimately I became disenfranchised with the fact that it did nothing to simulate missile guidance. Look up how the D has improved range over the C-7. Improved guidance. Minizap is a great starting point but it is not the end all be all

Can you please elaborate?
What is the most different in term of guidance simulation between your simulation and missilezip file?
And how does it affect the result?
I don't doubt your accuracy at all, however, I am interested in why does the figure for D is more than 10 times bigger than the B in this case?
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Unread post17 Aug 2019, 23:55

Okay so I am back at my computer now.

Minizap gives the AIM-120B a 1.27nm launch range from 1.4M at 49000ft against a target going 2.5M at 75000ft. At this point it is losing speed.

120b.PNG


Now we will discuss differences between the AIM-120B in minizap and the AIM-120D in my simulation

Fins.
The AIM-120B had the fullsize fins. In the AIM-120C/D the fins are clipped to fit more of them inside the bay of the F-22 (only 4 AIM-120A/B would fit). For the AIM-120A/B the total wingspan is the 21in seen in Minizap and a fin side area of .6966ft^2, all as shown above. The AIM-120C/D has a total wingspan on 17.54 inches and a side fin area of roughly .479ft^2 front and .771ft^2 rear for a .625ft^2 average.

Rocket Motor.
The AIM-120B in Minizap has a 108lb motor with a 230 ISP and a 0.7s boost at a thrust rating 2.6 times the sustain charge and a sustain charge that lasts 10.3s. Doing the math that comes out to a 5329lbt boost and a 2050lbt sustainer. The problem is we know that the AIM-120 does not have a dual pulse motor. We also know the rocket motor was upgraded at the C-5 or C-7, I can't remember which right now. My AIM-120D has a 135lb motor with an ISP of 265 that only burns at one setting for 8 seconds. This gives a thrust rating of 4472lbt.

If I alter the Minizap Calculation with my missile parameters and change nothing else I get a 7.2nm launch range to max pursuit.

120d.PNG


If I step through this in 1 sec increments (like my simulator) I see that it takes 6 seconds for the missile to point to the loft angle and that after 8 s it has only climbed to 53,300ft and 4.96M.

My simulator has the AIM-120D reaching it's climb angle in 3 seconds and after 8 seconds being at 58,900ft and 6.2M.

Over the next several seconds in Minizap the missile is pulling 3-9G while in my simulation the missile is coasting at 0 G, pure ballistic flight profile. The minizap missile climbs to 101,000ft with an apogee speed on 2.5M in 1 second increments, my sim has it coasting to 109,000ft at 4.4M.

I cannot speak to minizap, but I am modeling standard atmosphere from sea level to 130,000ft. I am also using a CFD based wave drag profile for missiles that shows that drag coefficients at and above Mach 3 are the same as the subsonic values.

my current guidance algorithm has the missile coasting until in reaches 75,000ft at M4+ some ways behind the MiG and then leveling off and coasting into the back of it. That is odd. I wonder if the aimpoint was too far out for the glide logic to kick in right.
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Unread post18 Aug 2019, 04:15

Is it really coasting at such short ranges or deceleration is so minor it overcomes it's Mark even if slowly.
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Unread post18 Aug 2019, 04:56

sprstdlyscottsmn wrote:I cannot speak to minizap, but I am modeling standard atmosphere from sea level to 130,000ft.


MiniZap models ISA atmosphere to 98,425 ft, above which there's no atmosphere and no drag so no glide-logic in effect. It's ballistic in a vacuum until the missile drops below 98,425 ft once again, where upon drag is reapplied as per normal to the missile's flight trajectory from there and glide-logic begins to work again.
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Unread post18 Aug 2019, 05:12

madrat wrote:Is it really coasting at such short ranges or deceleration is so minor it overcomes it's Mark even if slowly.


The graphical 'range' displayed is measured relative to the launch aircraft location at end of sim-run, not relative to the missile's actual launch point. So the launch aircraft continues to move in the same direction at M1.4, thus the AIM-120D only moves 7.2 nm downrange with respect to that launch aircraft's location, before the engagement became non-viable for whatever parameter-exceed failure-mode reasoning displayed (in this case insufficient speed remaining to close), and the sim then just gives up and halts the sim-run before the missile completes its flight.

Look at the "Flight Range" figure on the right-hand side "Trajectory Calculation" column and it shows 34.156 nm (63 km) of total flight distance for the missile from launch point, while the Rmax remains only 7.1534 nm (~20% of actual range).

The altitude reached was only 94,365 ft so the missile was indeed still coasting in a standard atmosphere and washed-off about M2.5 from its peak speed, while coasting post burn for about 59 seconds.
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Unread post18 Aug 2019, 05:30

madrat wrote:Is it really coasting at such short ranges or deceleration is so minor it overcomes it's Mark even if slowly.

coasting in the sense that it is unpowered and maintaining altitude as it slows down from M4 to M2.8 at impact.
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Unread post21 Aug 2019, 11:39

sprstdlyscottsmn wrote:If I step through this in 1 sec increments (like my simulator) I see that it takes 6 seconds for the missile to point to the loft angle and that after 8 s it has only climbed to 53,300ft and 4.96M.

My simulator has the AIM-120D reaching it's climb angle in 3 seconds and after 8 seconds being at 58,900ft and 6.2M.

Over the next several seconds in Minizap the missile is pulling 3-9G while in my simulation the missile is coasting at 0 G, pure ballistic flight profile. The minizap missile climbs to 101,000ft with an apogee speed on 2.5M in 1 second increments, my sim has it coasting to 109,000ft at 4.4M.

I cannot speak to minizap, but I am modeling standard atmosphere from sea level to 130,000ft. I am also using a CFD based wave drag profile for missiles that shows that drag coefficients at and above Mach 3 are the same as the subsonic values.

my current guidance algorithm has the missile coasting until in reaches 75,000ft at M4+ some ways behind the MiG and then leveling off and coasting into the back of it. That is odd. I wonder if the aimpoint was too far out for the glide logic to kick in right.

So, if I understand this correctly the differences in range came from the fact that you and whoever made missile zap use different missile CFD model (missile's drag coefficient) right?
btw shouldn't Cd change with speed due to Reynold coefficient?
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Unread post21 Aug 2019, 15:21

My Cd changes with Mach based on the results of a Computational Fluid Dynamics (CFD) study. This results in my simulator imposing less drag at high speeds which greatly improves range. The study I reference was performed AFTER minizap was created. Minizap is an amazing tool and I model a lot of what I output with my missile simulator based on what I liked from Minizap and what I wish it could do (namely tracking a maneuvering target or engage a target from a given range)
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Unread post29 Aug 2019, 15:46

Just putting this out before I forget (which I will by the next time I post an update) my missile numbers are going to change as the rating was done with 1 second intervals before and is now going to be done with .1 second intervals for better accuracy. An example is the above discussed tail chase range of an AMRAAM D fired against a high fast tail chase target. With a 1s interval a 48nm launch range resulted in a max alt of 108,870 ft, total distance flown of 120nm in 180sec. With a 0.1s interval the max launch range drops to 35nm, Max alt of 100,354ft, 103.6nm flown in 171.2 sec.

I also just found a hole in my loft logic for tail chase shots. Closing that up now.

EDIT** Fixing the loft problem gain 2nm back for a 37nm launch, Max Alt of 100,076ft, 109nm flow in 179.8sec.
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Unread post30 Aug 2019, 04:45

sprstdlyscottsmn wrote: ... my missile numbers are going to change as the rating was done with 1 second intervals before and is now going to be done with .1 second intervals for better accuracy. An example is the above discussed tail chase range of an AMRAAM D fired against a high fast tail chase target. With a 1s interval a 48nm launch range resulted in a max alt of 108,870 ft, total distance flown of 120nm in 180sec. With a 0.1s interval the max launch range drops to 35nm ...


Why is it varying so much with time-slice increment step? Is this interpolation?

And why not just default the sim to 0.01 sec steps, and then output the results in the increment time-step size that you want it to display them?
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Unread post30 Aug 2019, 07:23

SU-35 finally get R-37/RVV-BD
31A08A18-CCF0-42E8-97BA-61571C6F3FD1.jpeg

84DD1834-3598-496F-B19C-7CD1FC8B2706.jpeg
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Unread post30 Aug 2019, 15:09

element1loop wrote:Why is it varying so much with time-slice increment step? Is this interpolation?

And why not just default the sim to 0.01 sec steps, and then output the results in the increment time-step size that you want it to display them?

If I was running a program then maybe I could do that. I don't program. I'm just an Aerospace Engineer. My missile simulator is an excel spreadsheet 119 columns (parameters used) wide by 3,001 rows (total instances calculated) deep. This allows me to run a 5 minute missile TOF at 10Hz. The big advantage of my current setup is that if I want the target to perform an evasive maneuver I can link it in from my performance spreadsheet. Older versions of my analysis had a missile joust complete with evasive maneuvers and that became difficult to manage. It took hours to run a BVR engagement while my current "no maneuver, probability only" scenario takes about 30 minutes. I am concerned however that it won't tell the whole story.

sigh, maybe I need to go back to the long form with evasive maneuvers.

garrya wrote:SU-35 finally get R-37/RVV-BD

Really now? Well I would be remiss if I didn't add this. Adds a new element to the analysis too, asset protection. Hmm, maybe I need to change my mission set a tad. Glad I only did the Eagle. It always sucked when I would get so far (like when I "finished" air to air once with all aircraft) only to have to go back and fundamentally change everything.

**EDIT** Okay I speced the R-37 to have a 150nm flight range when fired by a Foxhound (2.5M @75,000ft). As this missile was a Foxhound exclusive I consider it prudent to consider all range claims to be made from this type of profile. Launches against incoming aircraft can occur at the 400km range mentioned while this gives a ~300km range against an orbiting target (e.g. AWACS, Tanker) Range will be significantly less from an Su-35S but will handedly out stick the R-77.
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