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 post10 Jan 2019, 16:52

So, I just re-did the CAP mission using the updated radar information using the AESACalc. I am thinking about reducing the text in the "blow by blow" section. Maybe get rid of speeds and altitude, just shots and range, and pK?
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marsavian

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Unread post10 Jan 2019, 18:09

Speed/altitude provides context, it's all good.
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shania

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Unread post10 Jan 2019, 18:20

Keep as much info as possible:) Graph with alt and time/or distance of planes and missiles will be also nice to have.
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garrya

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Unread post11 Jan 2019, 06:41

sprstdlyscottsmn wrote:So, I just re-did the CAP mission using the updated radar information using the AESACalc. I am thinking about reducing the text in the "blow by blow" section. Maybe get rid of speeds and altitude, just shots and range, and pK?

IMHO you should keep as much info as possible :D , though when possible it is better to use graphic illustration than to use text.
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marsavian

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Unread post11 Jan 2019, 11:40

I noticed the turn chart for the air to air mode for the F-15SA has a quite sharp drop after corner velocity compared to clean. Is that due to the weight of the CFT and extra fuel or its drag and how was it computed ? With the computed thrust/weight ratios at 36kft are these with afterburner i.e. is the thrust of the -229 at that altitude only around 10 klbf with afterburner, just over a third of sea level rating ?
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sprstdlyscottsmn

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Unread post11 Jan 2019, 16:04

marsavian wrote:I noticed the turn chart for the air to air mode for the F-15SA has a quite sharp drop after corner velocity compared to clean. Is that due to the weight of the CFT and extra fuel or its drag and how was it computed ?

I'm looking at the turn chart now.
Capture.PNG

The "Air" configuration does not show a sharp drop after corner velocity (0.9M in this figure) in the ITS or STR curves. After corner velocity ITR for Air is the same as Clean. After corner velocity STR for air is gradually decreasing. There IS a marked reduction in ITR before corner velocity for Air when compared to Clean due to the drastic increase in weight. Please clarify what you are asking about so I can help.

marsavian wrote:With the computed thrust/weight ratios at 36kft are these with afterburner i.e. is the thrust of the -229 at that altitude only around 10 klbf with afterburner, just over a third of sea level rating ?

Yes they are in afterburner. If you re-read section 1.3.2 on Thrust to Weight I explain all the factors that go to reduce engine thrust below rated levels.

In this case, at 36,000ft the air density is 29.8% that of sea level. There is also a gearbox loss that is fixed at 15% of rated military thrust, or 2,670 per engine. I also assume an airflow loss at lea level of 1,869lb for friction on the inlet. I double the airflow loss for afterburner due to the increased speed. The airflow loss does get reduced proportionally to air density.

So if we take the rated engine thrust of 29,500lb and move it to 36,000ft at zero airspeed we apply the air density factor.
Now we are at 8,791lb. Take out the gearbox loss next, as the systems being powered by the engine don't care about what altitude the plane is at, they need power. Now we are down to 6,121lb. Afterburner airflow losses is nominally 3,738 but is reduced to 1,114lb due to reduced air density. Now we are down to 5,007lb of installed static afterburning thrust.

But thrust goes up with speed, especially at altitude. My model has a 70% increase in engine thrust for this speed and altitude. That gets applied to the air density corrected rated thrust after airflow reduction (7,677lb) to raise it to 13,051lb. The gearbox, like the taxman, always gets its due, lowering the thrust to 10,381lb.
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marsavian

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Unread post11 Jan 2019, 16:16

Thanks you answered all my queries, I was looking at the chart in a descending fashion as a pilot would bleeding energy, I should have said before corner velocity and you explained it was the extra weight. Thanks again for some nice quality work, I also wonder if an air to air mode without CFT scenario could be explored too just to get a more cleaner comparison with Su-35 ? What also was interesting was the clean ITR peaked before corner velocity, at what G was that ?
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sprstdlyscottsmn

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Unread post11 Jan 2019, 16:29

marsavian wrote:Thanks you answered all my queries, I was looking at the chart in a descending fashion as a pilot would bleeding energy, I should have said before corner velocity and you explained it was the extra weight. Thanks again for some nice quality work, I also wonder if an air to air mode without CFT scenario could be explored too just to get a more cleaner comparison with Su-35 ? What also was interesting was the clean ITR peaked before corner velocity, at what G was that ?

Don't confuse the terms. Corner velocity is defined as the speed where ITR peaks. It is very weight and altitude dependent.

I have the ability to look at an F-15SA with no CFTs, and even the curiosity, but in the end this is supposed to be an Operational Performance Comparison, and operationally CFT equipped aircraft use them 100% of the time. I specifically checked historical loadouts for F-15Es doing Air Sovereignty missions. CFTs, Wing Tanks, and Targeting pods to go with the Sparrows, Sidewinders, and AMRAAMs.
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Unread post12 Jan 2019, 07:15

Realizing there is a problem in my probability calculations. How can there have been a 0.7% chance of both aircraft surviving in the score area when I calculated a one-in-a-million chance that they both survive the dogfight? 17 discrete events that can be at odds with each other as far as which event negates what and how that impacts the odds. I know this much, the odds that the F-15SA survives and the Su-35S dies cannot be below 60%, as it gets two "free" shots that, if they succeed, the Su never gets to fire.
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