F-35 Analysis Performance

Discuss the F-35 Lightning II
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spazsinbad

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Unread post01 Aug 2018, 03:38

I got tired of my attempts to make the page (from previous page this thread) more readable so youse are left with this....
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RAN FAA A4G Skyhawk 1970s: https://www.faaaa.asn.au/spazsinbad-a4g/ AND https://www.youtube.com/channel/UCwqC_s6gcCVvG7NOge3qfAQ/
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viper12

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Unread post01 Aug 2018, 14:17

CAS and TAS aren't exactly interchangeable...

It's also why temperature and altitude play such a big role in the initial speed, acceleration and end of turn time values I've given. Unless my math is wrong, there's a very specific reason why I gave 48.72 seconds for the turn, with 4 digits.
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aengineer

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Unread post01 Aug 2018, 14:47

Shoot, :doh: that's why the temp change is so large, that will make a big difference. I'm at work now, I'll have to fix it tonight.
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viper12

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Unread post01 Aug 2018, 16:30

To be fair, I've just noticed an assumption I've made when computing to get the 48.72 seconds, which would probably change the result by a few to several percents compared to real results.
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aengineer

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Unread post02 Aug 2018, 05:19

Yeah to properly integrate and get the TAS for the total time gets into some nasty transformations. I'd probably need to write a code to do it properly and calculate TAS continuously and not make any other assumptions since the change in mach number isn't insignificant. Now using a rough estimate that I found online I get around 195.8° but I don't know how trustworthy that guesstimate is. But it seems the initial Mach number is ~1.

Guesstimate Equation: https://www.flightsim.com/vbfs/showthre ... sion-Table
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viper12

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Unread post02 Aug 2018, 14:29

No no, the angle is much bigger. A rough approximation is done using a = omega*v, a the centripetal acceleration here and omega the turn rate, so you can guess the range of psi with the initial and final speed values.
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viper12

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Unread post03 Aug 2018, 23:55

Ah, I see a mistake in the paper ; you somehow wrote 9*sqrt(80) instead of g*sqrt(80), leading to some big error.
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aengineer

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Unread post04 Aug 2018, 03:06

Hey, if I correct that I get 945°. BUT, I wrote a short script with a root solver to solve for CAS at each time step and then I get 800°.
I must have missed a simplification in the CAS to TAS equations in Raymer because it doesn't look like a linear transformation to me, but the graphs seem to show that, all speeds are in m/s and Phi is in degrees. This doesn't seem right either, these numbers are pretty big, but I'm gonna check my code again to see if there are any typos.

TAS&CAS.JPG


Phi.JPG
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