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jcomm

11.30 will be Even Better !

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I also agree with many points.

But I don't think LR ever hid or said that simply because XP uses BET, then its flight model is flawless.

It's true that in several instances, Austin took too long to acknowledge some significant issues of XP flight model, like the torque bug or the crosswind behaviour, and that is not a good thing.

Regarding sideslip (and crosswind) behaviour, I would never use a virtual fuselage in Plane-Maker, since it gives very little control over its aerodynamic forces, but rather use an airfoil where the degree of control over aerodynamic coefficients is much more fine grained. But I don't know if there's any aircraft designer that does that.

 

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Posted (edited)
On 5/11/2018 at 8:33 PM, Minos said:

No one could ever improve BEMT because this is already pure perfection, so why should Austin devote time to that?

BET is only perfect if the aircraft model it uses is also perfect (not just close) down to things like surface textures, rivets and so on. It's also incredibly difficult to troubleshoot problems with models based on blade element theory - if you think you've got the model correct and the aircraft doesn't fly as expected, what do you do? There's a reason why full sized commercial flight sims usually use table-based flight models as they're much easier to tweak to make them more accurately match the real aircraft.

Edited by vortex681

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53 minutes ago, vortex681 said:

BET is only perfect if the aircraft model it uses is also perfect (not just close) down to things like surface textures, rivets and so on.

This is a common misconception with regard to how BET is conceived to be used. BET, as used by current flight sims, is not (of course) a fully fledged, real time CFD solver, able to predict the aerodynamic forces of rivets, vortex generators, etc. The main difference compared to a conventional table-based FM is that, instead of having a single aerodynamic object with a single set of aero coefficients, you have multiple objects with multiple sets of aero coefficients, and they interact with each other. 

So, modeling the effect of vortex generators and the likes, is correctly done simply by considering their effect in the global aero coefficients of the surfaces where they are (wings, stabilizers, etc.).

53 minutes ago, vortex681 said:

It's also incredibly difficult to troubleshoot problems with models based on blade element theory - if you think you've got the model correct and the aircraft doesn't fly as expected, what do you do?

This may be partly true, but also depends on several other factors. For example, knowing the details of how BET is implemented in a given flight sim. Or, having extensive output of the actual forces calculated by the flight model when flight testing. Fortunately, the latter is present in XP, with the numeric and visual data output and the cycle dump of the flight model.

But yes, generally speaking, troubleshooting a BET flight model requires more steps, it's just a thing that comes with it.

53 minutes ago, vortex681 said:

There's a reason why full sized commercial flight sims usually use table-based flight models as they're much easier to tweak to make them more accurately match the real aircraft.

Also true. But each type of flight model can be more or less suitable for any given application. The fact that table based flight models are used for full sized sims, doesn't mean that they're the best choice for a military, soaring, aerobatic, etc. PC flight sim.

 

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