How many extension models/augmentations to the crude BET model is running under the hood?

BET alone is not able to solve the complexity of wings and rotors moving through a live medium (air particles in this case), basically whenever the aerodynamic forces are assymetric, such as full rudder side slips, BET needs "bandaid".

It's been years and years since I studied aerodynamic engineering at the university, but I do recall during our labs, we had to apply at least three correctional equations on top of the crude BET.  And this was for single engine propeller planes with docile performance.

Out of curiosity, what type of augmentations to the BET has Austin applied? There has to be quite a few in order to simulate flight that accurately.

I think no one here can answer that. Have you thought about asking Austin?

3 hours ago, SAS443 said:

How many extension models/augmentations to the crude BET model is running under the hood?

Yeah like Franz says, you're gonna have to ask Austin. That's hardly a problem though. A well done BET is hardly crude. A good BET model is way better than bad CFD. Remember the point cloud count I referred to earlier? If you drop below a million, you're pushing into 'bad' territory. That's exactly why FSX sits at the core of 2024's CFD. FSX IS the correction "extension" for 2024's CFD, because by itself, that CFD is terrible..

Yeah, the wonders of autocorrect…

Which is still worlds better than the monkey.

14 hours ago, blingthinger said:

What I'm getting at is time-to-convergence. It will converge. You'll get an answer. And it will arrive in ~1/30 of a second.

Make that 2 days instead of 2 weeks, but the results being junk either way because some input variable just does not behave in a logical fashion or is simply buggy.

 

 

6 minutes ago, Bjoern said:

Make that 2 days instead of 2 weeks, but the results being junk either way because some input variable just does not behave in a logical fashion or is simply buggy.

🙂  🙂 Let them have some hope!

5 hours ago, blingthinger said:

. A well done BET is hardly crude

If it's well done it means it has departed from the isolated BET model and is supplemented with one or more corrective models on top. Which is the root of my original question.

So do you want to take a guess what Austin has done, based from your wide array of experience in both flight modelling and real life experience as a pilot?

1 hour ago, blingthinger said:

🙂  🙂 Let them have some hope!

I think we are past that if even XP diehards finds 2024 a great simulator. 

https://forums.x-plane.org/index.php?/forums/topic/289879-msfs-2024/&do=findComment&comment=2812371

"The flight. Removing all the aids the flight model amazes me, and being used to the quality of XP for years I was ready to find defects. For now, in flight, I have not found them, on the contrary I find that the controls and inputs respond (for the type of planes I know best) realistically, or at least they are quite similar to the best XP flight model. The maneuvers on the ground need improvement."

You need to learn to adore garbage, blingthinger.

25 minutes ago, SAS443 said:

isolated BET

Please do dredge up and dust off what you remember from uni: what constitutes an 'isolated BET'? And what correction factors did you apply then that make it so disgusting to you now?

50 minutes ago, blingthinger said:

so disgusting to you now?

Never said that. Focus on the discussion.

50 minutes ago, blingthinger said:

what constitutes an 'isolated BET'

I paraphrase one of our textbooks

" Principles of Helicopter Aerodynamics" (Leishman, 2006):

"The isolated application of Blade Element Theory assumes a blade element experiences aerodynamic forces solely due to the local flow conditions around it. While this method provides a first-order approximation of rotor performance, its accuracy is limited to idealized scenarios where interactions between the blade and the wake, or time-dependent aerodynamic phenomena, are negligible. Such an approach is most effective for conceptual analysis or for validating more comprehensive models"

And that's where we started off, then adding dynamic correction models on top and something called "Prandtl’s tip-loss factor" if I read my notes correctly.

I have since long forgotten about this, I am not an engineer, I got approved for the classes due to my pilot background. I'm not snart like Engineers 🙂

But I digress... apologies.

Austin is by no means running plain BET in XP12. There are loads of correction factors on top. But few around here seems to have any idea what it can be. Which I find little odd since XP12 FM has staunch support in these forum (naturally and understandably) but no one seems to be able to dissect it. 

I have no problems with XP12 FM, It is terrific as we all know. But there is a layer of Austins magic sparkling dust (since nobody can elaborate further on it), and that is what actually makes it so great.

Yes XP12 FM is great. But can anyone explain why?

Edited December 1, 20241 yr by SAS443

2 hours ago, SAS443 said:

But can anyone explain why

Well we all know what Austin will do to test a theory, Driving car with fuselage on pole out the window etc etc

3 hours ago, SAS443 said:

 

Yes XP12 FM is great. But can anyone explain why?

30 years of industrial scale research and the subsequently accumulated trade secrets.

Edited December 1, 20241 yr by mSparks

3 hours ago, SAS443 said:

The isolated application of Blade Element Theory

OK! I think you're clear now. I'm detecting some possible English-2nd-language artifacts, so do focus here. First, 'crude' does have negative connotations. Sometimes applied in conjunction with 'counterfeit' or 'fake'. In this context, that's more....asoboCFD territory (not FSX, mind you)

Second, there is no such thing as 'isolated BET' in and of itself. The above text must be where you're accidentally confused. The theory itself isn't "isolated" unless the user forces it to be isolated in the algorithm.  The theory itself simply states that one can slice up a wing surface into discrete elements and calculate forces on each element based on force coefficients, local gas state and geometry parameters. Agreed? Now, that author does point out that it is unable to predict the following:

3 hours ago, SAS443 said:

scenarios where interactions between the blade and the wake, or time-dependent aerodynamic phenomena

which is somewhat dubious given that the theory itself doesn't prescribe how the force coefficients may be acquired. Which means that for the main wings at least, it is perfectly adequate and for the empennage it's adequate most of the time (think wing wakes, yes?).

So what you're really bothered about here is the fact that Austin/LR touts it as BET, when in reality it's BET & Friends (e.g. Prandtl at the least, certainly others) applied to both rotating and stationary wings and they should adjust their marketing accordingly, not to mention that current branding leaves the poor lonely fuselage out to dry, sticking out the side of his Tesla ride (or was it top, mjrhealth??)? What you're also getting at is that brinx should modify the title of this forum post and that going forward, all of XP's adoring fanbase should refer to it as BET^* instead of merely BET?

Edited December 1, 20241 yr by blingthinger

1 hour ago, blingthinger said:

Sometimes applied in conjunction with 'counterfeit' or 'fake'.

That"s your free interpretation. 

In a Thesaurus you would find it described as basic, rudimentary or rough. 

Which takes me back to the initial point. BET alone, without anything extra, is just that, crude. You need every "friend" you can get for ground effect, tip/root loss corrections, dynamic stall models, momentum theory and all those gentlemen with weird names and their equations.

1 hour ago, blingthinger said:

which is somewhat dubious given that the theory itself doesn't prescribe how the force coefficients may be acquired

This section should be called "X-plane enthusiast argues that a distinguished professor in Aerospace engineering is not truthful, credible nor reliable in his litterature " (referencing work that is probably used at all universities worldwide)

Because that is what dubious means, regardless of my - what was it now - English 2nd language imperfections.

So, if you don't mind, I have more faith in an accomplished author and professor than in a random forum poster. I think most reasonable individuals would say the same.

Edited December 1, 20241 yr by SAS443