Will the FBW with C* law be implemented ? - Page 5 - ED Forums
 


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Old 08-24-2019, 05:45 AM   #41
sk000tch
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Originally Posted by bbrz View Post
2. You have a link or example when flutter occurs on the F/A-18 during normal ops 'at the edge of the envelope'?
I don’t see anything specific to C variant... what’s next specific lot? A to C didn’t involve aerodynamic changes; radar, avionics, and armament don’t change oscillations (unless you’re adding heavy armament to wingtips or something). The LEX fences on every Hornet variant are a fix for the stabilizer flutter caused by the LEX vortices. Despite the fences at high AOA and low speed can still be dangerous: https://youtu.be/_ak2N0idC44

MCAS is a questionable example btw, pretty unique scenario. Regardless, all sims break down at edges of envelop. I fly competitive acro and I’ve never flown a sim that even comes close to accurately modeling any maneuvers involving complex or asymmetric stall like basic inside snap roll, and forget any gyroscopic stuff like lomcevaks or any tumbling.
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Old 08-24-2019, 06:03 AM   #42
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Guys, I got a question. To clarify, I'm not contesting anyone post: bbrz and sk000tch; You guys are having your own conversation and I not arguing any of your points. I am simply curious about something.

Does anyone think the NASA paper 1538, written in 1979 has any relevance to the DCS F-16? Specially considering the aircraft has change drastically since then and the study did not used real aircraft, only simulated aircraft.

I am just curious, Not looking for anything else. I don't have a secret agenda. Just curious if anyone thinks that paper has any relevance.
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Old 08-24-2019, 07:04 AM   #43
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No kidding on the off topic....

To answer your question though that paper came out right after f-16 came into service, and is frequently cited by every academic paper that follows. It’s old, but while avionics have changed significantly, aerodynamics are the same now as they were then (our understanding of control laws have improved, largely due to this type of work, but the physics are the same). The paper is hundreds of pages of analysis and data re of FLCS. Between that and subsequent papers, detailed equations and matrices that govern the multi-input -> multi-output FBW details (down to specific control surface angle as a function of stick pressure and AOA), where coupling and limiters are activated, are all publicly available. Later articles get into detail about thrust, which is often difficult to model as the thrust generated at various throttle positions/fuel flow/inlet temps and different altitudes is hard to come by. Drag is the same way, you can find tables of ram drag values for the turbine... that kind of info isn’t available for other planes (even the a-10).

Again I don’t k ow if it’s because of the novelty of a low longitudinal stability FBW design (in 1976 at least), the widespread adoption/number produced or just its age, but the result is a ton of very detailed information in the public domain. That takes a lot of the guess work out of the modeling process for ED, ensures we should get a high fidelity simulation, and avoids the problem of utilizing documents that are available online but really shouldn’t be when creating the module.
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Old 08-24-2019, 07:29 AM   #44
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So even tho the paper did not used real aircraft, and the aircraft they use to simulate had different horizontal stabilizers. Even tho the aircraft simulated had a different Flight control computer with different logic and different limiter. Considering the flight control computer and many components that send information to the computer and how the computer use that information has change. Even tho the aircraft have different weight and balance, different engines, the angle of the flight control can travel is different, the paper is still relevant to you.


Ok thanks.
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Old 08-24-2019, 07:55 AM   #45
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I’m just a pilot/engineer, not a dev, so I probably have no idea what I am talking about. I did come across this while looking for some info to answer your question:

In a paper/post discussing the flight model of a popular f-16 simulator, the dev stated “I will try to explain you as simply as possible what were the challenges of the F-16 development, and the way the real engineers (and consequently BMS) have developed and improved the FLCS ... Please note that this is mostly based on the NASA Technical Paper 1538 (TP 153 Simulator Study of Stall / Post Stall Characteristics of a Fighter Airplane with Relaxed Longitudinal Static Stability”
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Old 10-08-2019, 10:48 AM   #46
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Originally Posted by sk000tch View Post
My point is that the atmosphere is alive, its why every pilot is nearly a meteorologist... yet when was the last time you studied a METAR and made a go/no-go decision in DCS?

nearly a meteorologist?
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Old 10-09-2019, 05:44 PM   #47
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Hi guys,

i was wondering if the F16 will have FBW and more specifically the C* law.

I think the F16 was the first aircraft to have the FBW C* law than would be used and modified by Airbus for their A320 and above and later on byt BOEING but with the C*U law.


From what i understand, is that the C* law is base on pitch rate demand at low speed ang G demand on high speed. Besides it is fligh path stable, so for instance, if you fly at 200 kt IAS level and accelerate to 500 kt IAS, you should remain level, maintain path in turns..., in a conventional aircraft ( Direct law) you would pitch up or down if you decelerate.

http://www.icas.org/ICAS_ARCHIVE/ICA...PAPERS/605.PDF
No because the F-16 has its own FBW code and what you describe would hinder its performance.
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