This BET is complicated stuff… I don’t actually know if it connects properly to scientific BET work, but below are the inputs for the current propellor model in MSFS… I did some tweaking with the beta_range variables yesterday, I found beta_range_min and beta_range_max guard the angle of the propellor blades. These were the inputs I tested and what I can say now: they are active, flight changes when you put other values in.
minimum beta_range 11 maximum 43 is default
put the minimum on a negative value, throttle won’t work at all (no forward speed)
put the minimum lower than 8 you won’t be able to take off
put the minimum on 8 or 9 makes the aircraft slower
put the minimum above 20 you loose the drag when taking back throttle
With the minimum set on 11, there some drag while lowering throttle. You’ll notice when you put the min beta range on higher values, you loose that break. Steep descent toward landing will give much more airspeed.
I used in the Modern flight model… i used SDK DA-62
The sim just needs some prop drag modelled, feathering to work, turboprop engine simulation still needs work and helicopter/VTOL (or rotatable thrust vectors) and we’ll be fairly close on the dynamics of this sim. There is still quite a bit of fine tuning to be done, especially on the default aircraft, and moreso on the premium aircraft. Mods have helped this quite a bit though.
Did you just read the post above? Prop drag IS modeled and works. Perhaps not to your satisfaction, but it IS there. @ArcanePython931 just proved it, and the developers have talked about it a couple of times now (that it was always there). Granted, not everything about controlling it was previously exposed to developers, at least not in an understandable way, and they said they are addressing that, and much work was done in that area for SU4 (but not all that is needed).
The developers have said that all that is in the plan over the next three Sim Update releases. So, we’re looking at 4 to 6 months to get a lot of stuff in. But it is there, and they ARE aware of what people are saying and dilligently working to make it all work better, both everything related to beta mode on props and proper turboprop engine modeling (much of which was fixed in SU4, but there is still more to do and planned).
All these people keep coming in here and saying “ahhhh, there’s no prop drag”… based on what? Until @Arcane did the work, I haven’t seen one post proving scientifically that the floaty issue so many complain about is due to a lack of prop drag.
I’m not smart enough to know how to prove it, but, please, if you’re going to state something, prove it.
And, quite frankly, Asobo is going to read these things and say, well, we modeled prop drag, we can prove it’s there, and they’re likely going to ignore the rest of any discussion because there are other things to worry about.
@Flyingscool I only provided proof that the beta_range is active part of the MSFS propellor model. I have not proved yet it can be used for tuning propellor drag (the interesting question in the other topic) or that MSFS complies to BET or correctly implements BET, which dictates a negative beta_minimal would provide reverse thrust. When I put beta_minimal on a negative value, the aircraft would not take off so I think they apply beta_minimal on takeoff (throttle+). But I think MSFS does have a working propellor model !
Haven’t tested the feathering angle. It belongs to the propellor model. The Beta feather parameter in above list is an angle of 80 degrees, which puts the blades in their own wind, stopping rotation more quickly when you take back throttle. Wiki sais it is needed for engine failure situations. It stops the windmill energy loss, the air can flow right through at 80 degrees, so I don’t think it would give extra break. On some aircraft there’s a switch to activate feathered propellors, so it could be used in flight.
There’s a LOT of work. Maybe the propellor model is already there… and it is just a matter of updating parameters to finetune it to each aircraft. DA-62 is no turboprop, but these beta_ parameters certainly have an effect on the simulated propellor… I leave the test to the experts, I’m not used to turboprops.
Helicopters are a different ball game. Hope they’ll keep them separate, don’t mix things up !
I mean the military uses XP to figure out how their models would work in the real world. Shouldn’t that be sufficient and a good clue on how well XP has BET modeled? The military uses the best of the best things for simulations. Yes the technology is old though. I’d love to see a video of XP vs MSFS in real world aerodynamics. I’m trying to learn and not be arrogant here and will switch over to MSFS if there is a valid argument on this point.
The SDK used to have a comparison of a lot of the differences between X-plane and MSFS’s flight model in the flight model discussion. They took it out when they redid the SDK a couple of versions ago.
I’m only responding to the “There’s no propeller drag”. I just want to see proof of the “none”. Mostly, I hate it when people claim things without proof (“See, in the wind tunnel model in the developer mode, when I change the angle of the blade, there’s no effect on the total drag on the airplane” That would be proof, something measurable). Asobo has claimed multiple times there IS drag associated with the propeller. It seems like you’ve proven there is some drag. The claim is “See how the C208 floats down the runway, that’s OBviously because there’s no propeller drag”… Really? Couldn’t it be other factors?
Making claims without proof is useless.
There are definitely issues with the propeller model, and with using Beta range. But Asobo has discussed this, and they’ve charted out when they’ll be fixing it. How well they fix it is anybody’s guess. But I trust they will make an effort, and will eventually get to something useful.
Yes, they do. You’re right. I work in the industry as a modeler. I’ve seen researchers use X-Plane for a variety of topics, including flight test verification. This strip theory model holds up just fine. No one is arguing that it isn’t. For posterity, here are a few articles which show X-Plane’s application for such a thing:
But to say that jamming their model into MSFS would be a be-all, end-all fix to the flight model issues MSFS is having is not really a good or necessary solution in my opinion. I say so because we’re really just talking about the choice of method for calculating the baseline aerodynamic force and moment calculation here. Both methods do the same thing - they chunk up a sub-model of the flight vehicle and come up with forces on the elements based on the current environment. My argument is just that MSFS starts this process with a much finer discretization of the flight vehicle than X-Plane, which probably buys us a lot of fidelity in certain situations. It means that MSFS is doing a better job at capturing the local variations in aerodynamic force over the flight vehicle surface, which can make a difference in terms of fine grained perturbations in the air mass model. I am hoping MSFS will improve their SDK to help us gain a better understanding of what exactly they’re doing under the hood, but the framework seems very sound from what they have shown us so far.
All in all, the issues we’ve all been complaining about as a community really have less to do with the baseline aerodynamic force calculation, and more with the corrections needed to make the flight dynamics model feel more realistic. These corrections are not BET. They’re just such things that the baseline aerodynamic calculation doesn’t do a great job with, like supersonic drag corrections and all those additional handwavey kludges Austin put in their sim in version 11.40. Laminar Research has had to go through these over the years, and so will Asobo.
Have you ever been in the military??? After 22 years of service I find the comment that the military uses the best of the best to be hilarious … sorry, but that isn’t a point I would use to support any argument.
I’ve seldom seen such a ridiculous claim on a flight sim forum. The military (or at least, the military of any nation capable of building a modern combat aircraft) has access to professional computational fluid dynamics software, and the hardware to run it on, and doesn’t need to resort to consumer-grade entertainment simulators to figure anything out. At least, not once they have got past the drawing-sketches-on-the-back-of-an-envelope stage.
I’ve seldom seen such a ridiculous claim on a flight sim forum. The military (or at least, the military of any nation capable of building a modern combat aircraft) has access to professional computational fluid dynamics software, and the hardware to run it on, and doesn’t need to resort to consumer-grade entertainment simulators to figure anything out.
Except, they often still do. It’s good practice to make use of any reasonable analysis tools to get the answer you’re looking for. Doesn’t matter if they also have CFD. You can’t efficiently run a CFD model and a 6-DoF state model, but we obviously have an abundance of evidence that you can run a lower-order aerodynamics model in place of that CFD and get a real-time answer. If you’ve got multiple tools at your disposal, use them all and compare them against one another.
That’s the back-of-the-envelope stage. You don’t use that to “figure out how their models would work in the real world”. You use it as a sanity check before you build a detailed model.
The bottom line is LR is an aeronautical engineer, he works from that perspective only, nothing wrong with that.
I don’t think ASOBO are bothered to the extent LR are, also X-plane is used commercially and is used in flight training, so the flight model will always come before eye candy… Rightly as its main job is to simulate flight.
Arguably it does not have great weather, however contrary to popular belief it models all the things msfs weather does, but visually it’s not as nice however plugins + $$ solves that.
Put a plane on the runway in X-plane and then create a 20kt headwind blowing on to the plane and you will see the flight surfaces wobbling and moving as the wind blows across them or adjust the wind but you will see the surfaces reacting to the wind. This does not happen in msfs or not the last time checked… Not saying this makes X-plane better, just saying msfs and X-plane come from two different ideas and approaches.
Msfs is now moving in the right direction, will it be as good as or better who know (please take visuals out of the equation no one can compete with msfs on that) time will tell.
At the moment I love both, there are times I’d be happy to go msfs exclusive, but then a flight in Xplane even with the awful scenery at times, it’s not always bad just reminds me how high fedilty it is, and also reminds me that it’s still IMHO miles ahead in some aspects especially airliners etc.
I don’t get this. First of all the term “beta” is wrong if it does anything in flight, the fact that the DA62 has these parameters while not having a beta mode of operation already proves that those are flight mode (alpha) parameters.
Second thing is, why does changing the minimum blade angle influence operation at high power setting? It shouldn’t matter were you put the minimum blade angle, unless you are operating at idle it shouldn’t affect operation. If you put the minimum too high it might prevent the engine to accelerate to take-off RPM but otherwise it shouldn’t affect performance.
A value lower than 8 should not affect take-off performance, unless set to an insane angle. Around -3 degrees should be ground idle where there is no thrust (nor reverse thrust) generated on ground at zero speed, this means there is less drag on the engine, the engine should therefore be able to spool up quicker to take-off RPM. Maybe you found a significant flaw there .
Maybe the DA62 is not the best aircraft to test those kind of things since it is FADEC controlled and uses a single lever concept (no idea how this is simulated in FS2020). Maybe changing the min blade angle seriously screws something up there.
I have no idea how the SDK or developer mode works but just a simple test below. I found that the Cessna 172 and Beech G36 are fairly accurate. The problem is with turboprops, the TBM and Kingair seem to have no prop drag at all:
Test of glide ratio on the TBM 930:
Maximum weight, 120 kts glide speed, flown with FLC on autopilot, prop feathered and windmilling. I cut the engine (by closing fuel selector) overhead an airport at 3000 ft, ISA, no wind, glided down to 0 feet, paused the sim, took the drone camera to check my location, looked it up on Bing maps and measured the distance.
Prop. Feathered:
Propeller speed = 260 RPM
Glide range: 17.5 km = 57400 ft
Glide ratio = 57400 / 3000 = 1:19,13
Prop. windmilling:
Propeller speed = 960 RPM
Glide range: 17.1 km = 56088 ft
Glide ratio = 56088 / 3000 = 1:18,70
My methods are a little bit mickey mouse and the autopilot leveled off slightly when doing the glide ratio test with feathered propeller because I put 0 ft in the altitude preselect so thats were the extra 400 m likely comes from. It is safe to assume that there is absolutely no drag modeled on the TBM at least…
Next test, FLC at 120kt in descend, measuring vertical speed:
80 degrees is too low it should be around 87 degrees blade angle. At 80 degrees the prop will remain windmilling, it would be at a low RPM and therefore create low drag, but it won’t fully feather and stop the prop from rotating.
The blades will never be in “their own wind” btw, the prop stops spinning because there is no lift created. Essentially a propeller blade acts like a asymmetrical aircraft wing, when put at a 87 degree blade angle (-3 degree angle of attack) forces will be zero and the prop spools down and eventually stops spinning due to drag from the engine.
When you take back the throttle the propeller should go to its fine pitch stop (flight fine), not feather. The feathering angle should only affect engine operation when feathering the prop, in no other situation is this angle relevant.
When feathered the prop won’t produce any windmilling drag indeed, just a little bit of form drag like any other object moving through the air. All aircraft with the ability to feather (mostly multi-engine and turboprop aircraft) have either a switch, an auto-feathering system, or most commonly a detent when you pull the prop lever all the way back to feather the prop. Feathering only has use in flight, I can’t think of any use on ground.
Unless talking about a free turbine turboprop, you don’t actually want the propeller to feather on ground as you won’t be able to start the engine with a feathered prop due to higher load on the starter. That is why most aircraft have start-locks which engage on ground to keep the propeller in fine pitch when shutting down.
Asobo has aeronautical engineers on staff, too. It’s not like they pulled this flight model stuff out of a hat.
For those who need it, here’s What Asobo developed as their new flight modeling basis with FS2020. Per contract with Microsoft, it had to devolve to the FSX flight model, but, it’s really light years ahead, of both FSX and X-plane. The description used to have a comparison with X-plane at the end of the discussion, but, last time I checked, that text had been stripped out.
I take that back, they just took them out by name, but they still refer to X-plane. Scroll all the way to the end of the first link and then scroll up a few sections. Most of the document just covers the aerodynamic equations and how to convert from one reference frame to another with them.
Granted, they don’t discuss the propeller here other than the vortex forces, but, to that point, having been reading it for a while, I think this document was written a long time ago, and was used to sell their concepts to Microsoft to get the contract for the simulator.
The problem is, like with the turboprop ITT, the basics are way off.
You can fake correct prop drag in a certain range by altering the prop curves.
Playing with the blade angle in the cfg file is the wrong end, that’s basically just for fine tuning the basic prop curves.
But that was already possible in FSX.
The problem is that, as @anon50268670 explained over and over again that the essential aerodynamic part of the prop drag calculation is missing.
Since the blade angle varies along the span, you can watch the feathered prop slowly starting to rotate again if you increase the speed on a free turbine turboprop.
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