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Blade Element Theory

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There is a section on the X-Plane site that begins:X-Plane works by reading in the geometric shape of any aircraft and then figuring out how that aircraft will fly. It does this by an engineering process called "blade element theory...."Can anyone provide a link to a more detailed descriprion than the one given there?

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If you want a decent explanation of BET, this site has one, it's for props and not wings (which is what BET was originally for), but the principal is basically the same for wings:http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/propeller/prop1.htmlAl

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Hello !You can read more about this here:http://www.x-plane.com/pg_Inside_X-Plane.htmlHappy flying ! :(

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Chock's link gives an explanation of Blade Element Theory which was developed for propellors. It's in two parts. The first explains how the direction of the airflow can be determined at a particular section. This is also applicable to a wing with a change in notation. The second part uses linear and angular momentum theory based on the airflow through the area of the propellor disk. This isn't applicable to a wing because there is no such area.The description in http://www.x-plane.c...de_X-Plane.html suggests that X-Plane uses Blade Element Theory to determine the direction of the airflow at each sections. Bade Element Theory cannot determine the aerodynamics forces and moments. How exactly then does X-Plane calculate these forces and moments?

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You will notice that the link that was posted is a "students" guide to blade element theory. Blade element theory is what x-plane uses for it's core flight modelling. There are obviously many other factors used in its source code and that will never be shown to the public. If you really want to know about x-planes use of blade element theory, feel free to email Austin. However, I doubt he will share too much info. I CAN tell you that aerodynamic forces and moments can be manually entered by the developer for all areas of the aircraft, but, can also be left to x plane to enter default values. Some different figures off the top of my head that can be entered are:CoG (Aft, center, forward) for the aircraft AND fuel tanksco-efficient of momentCo-efficient of liftco-efficient of drag on the fuselage and engine nacellesRadii of gyrationPhase-out figures for control surfacesThese can all be left at default values as well, but it is almost never accurate if done this way. (This is why so many x plane aircraft do not fly correctly. Insufficient knowledge of what to enter in the various fields by the author).Planemaker is a VERY flexible program and just about anything can be done with it. The foundation of BET still remains and everything is built around that.Airfoil maker is a totally different animal altogether. If you have the sufficient information on ANY airfoil, it can be made to the correct specifications and function as in the real aircraft. These include airfoils for wings AND propellers. Again, it is very hard to get this information and it is why many aircraft for x plane don't fly correctly. Too much guesswork by the author.Don't get me wrong, x-plane is not "perfect". No simulator is. But it can come VERY close. So close that (Shameless plug) the Duchess I made is 98-99% accurate in all areas of the flight envelope. Including the stall characteristics. And I have the charts to prove it.

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You will notice that the link that was posted is a "students" guide to blade element theory. Blade element theory is what x-plane uses for it's core flight modelling. There are obviously many other factors used in its source code and that will never be shown to the public. If you really want to know about x-planes use of blade element theory, feel free to email Austin. However, I doubt he will share too much info. I CAN tell you that aerodynamic forces and moments can be manually entered by the developer for all areas of the aircraft, but, can also be left to x plane to enter default values. Some different figures off the top of my head that can be entered are:CoG (Aft, center, forward) for the aircraft AND fuel tanksco-efficient of momentCo-efficient of liftco-efficient of drag on the fuselage and engine nacellesRadii of gyrationPhase-out figures for control surfacesThese can all be left at default values as well, but it is almost never accurate if done this way. (This is why so many x plane aircraft do not fly correctly. Insufficient knowledge of what to enter in the various fields by the author).Planemaker is a VERY flexible program and just about anything can be done with it. The foundation of BET still remains and everything is built around that.Airfoil maker is a totally different animal altogether. If you have the sufficient information on ANY airfoil, it can be made to the correct specifications and function as in the real aircraft. These include airfoils for wings AND propellers. Again, it is very hard to get this information and it is why many aircraft for x plane don't fly correctly. Too much guesswork by the author.Don't get me wrong, x-plane is not "perfect". No simulator is. But it can come VERY close. So close that (Shameless plug) the Duchess I made is 98-99% accurate in all areas of the flight envelope. Including the stall characteristics. And I have the charts to prove it.
To put it briefly, no one knows. Blade Element Theory only calculates the geometric angles of the airflow , not aerodynamic forces or moments.

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If you want to make assumptions, that's your choice. I took the time and explained as much as I could with the time I have. I don't have the time to go into explicit detail. I have made 3 payware add ons for x plane and all fly to within 2% accuracy of all areas of the flight envelope.Like I said, email Austin and ask him about it if you really want to know more about it.

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If you want to make assumptions, that's your choice. I took the time and explained as much as I could with the time I have. I don't have the time to go into explicit detail. I have made 3 payware add ons for x plane and all fly to within 2% accuracy of all areas of the flight envelope.Like I said, email Austin and ask him about it if you really want to know more about it.
I have no doubt that you've built accurate models using X-Plane, and never implied otherwise.Nor did I make assumptions. I eplained the capabilities of Blade Element Theory as set out in the link you endorsed. If there are other links that show how Blade Element Theory can determine aerodynamic forces and moments I'd be most interested to explore them. Can you help?

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It seemed like you were questioning the validity of Blade Element Theories use in a flight simulator. So in one way, you DID imply that it was not possible to build accurate models in x plane using Blade Element Theory.The only person who can give you a clear and concise explanation into how Blade Element Theory works in X Plane is Austin and maybe Ben Supnik.Ben frequents these forums so he will probably see this.

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You mustn't be so defensive or put words into other people's mouths.I simply set out the facts as I understand then and asked for clarification - how exactly then does X-Plane calculate these forces and moments?I haven't yet had a reply.

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I'm not defensive at all. I'm simply replying.Your quote: Blade Element Theory cannot determine the aerodynamics forces and moments. To put it briefly, no one knows. Blade Element Theory only calculates the geometric angles of the airflow , not aerodynamic forces or moments. If I'm reading too much into what you said, I apologize. It's rather obvious, though. The second quote is your own assumption based on your own opinion because as far as you're concerned, your question went unanswered.Anyway, as I said, you probably won't find anyone here who can answer your question to the extent that you want it answered.If you want a definitive answer, ask Austin Meyer.A 747 pilot can fly a 747. Doesn't mean he knows how the FMC is programmed at the Honeywell plant.Developers just work with what they are given. We leave the mathematics and physics part to the simulator.

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Hello ! :( X-Plane is proprietary software and you have to ask the authors from Laminar Research.But you can look how it's done in open-source software like FlightGear's YASim:http://wiki.flightgear.org/Flight_Dynamics_ModelsOf course, YASim is not X-Plane and in YASim you need to know the moment of a propeller when you design the plane.In Wikipedia you'll find a link to QBlade... again, QBlade is not X-Plane, but you can read the source-code:http://en.wikipedia.org/wiki/Blade_element_theoryhttp://fd.tu-berlin.de/en/research/projects/wind-energy/qblade/Happy flying.

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Hello ! :( X-Plane is proprietary software and you have to ask the authors from Laminar Research.But you can look how it's done in open-source software like FlightGear's YASim:http://wiki.flightgear.org/Flight_Dynamics_ModelsOf course, YASim is not X-Plane and in YASim you need to know the moment of a propeller when you design the plane.In Wikipedia you'll find a link to QBlade... again, QBlade is not X-Plane, but you can read the source-code:http://en.wikipedia.org/wiki/Blade_element_theoryhttp://fd.tu-berlin.de/en/research/projects/wind-energy/qblade/Happy flying.
Why should he ask the author from Laminar Research instead of Austin Meyer?Is`nt Austin Meyer founder and CEO of Laminar Research.Leen de Jager

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No need to ask Austin common known facts, as you know yourself.I really prefer get to get serious reactions :( .That interview I cannot play , it does not work.I have heard it before so that is not a problem.He might get better informed visiting the interesting links you gave , thanks.CheersLeen

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how exactly then does X-Plane calculate these forces and moments?
Hi,Blade Element Theory (BET) actually allows calculation of both airflow angle and aerodynamic forces and moments (see the first link given in this thread, at the paragraph "5. Propeller Thrust and Torque Coefficients"). In the case of X-Plane, the BET is evidently tailored to work with wings (but AFAIK X-Plane uses BET also to model propellers), hence "propeller thrust and torque" in this case become "wing lift and moment".Among the advantages, BET allows a sufficiently accurate modeling of wing forces and moments in various flight regimes, simply taking into account wing geometry and airfoils characteristics.Among the limitations, the current implementation of BET on X-Plane, AFAIK, does not model spanwise flow. For this reason, it's not capable of modeling the drag reduction effect of winglets.BET has various other advantages and disadvantages. A more complex method is the Vortex Lattice Method ( http://en.wikipedia.org/wiki/Vortex_lattice_method ). It allows a more accurate calculation of forces and moments on wings, fuselage, and also models spanwise flow. It's computational very intensive so it cannot be done in real time in a PC flight simulator. But maybe we'll see it implemented in X-Plane someday! :)Marco

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BET has various other advantages and disadvantages. A more complex method is the Vortex Lattice Method ( http://en.wikipedia.org/wiki/Vortex_lattice_method ). It allows a more accurate calculation of forces and moments on wings, fuselage, and also models spanwise flow. It's computational very intensive so it cannot be done in real time in a PC flight simulator. But maybe we'll see it implemented in X-Plane someday! :)
I think that's something for the K Computer version of X-Plane. :( The K Computer is capable of performing more than 8 quadrillion calculations per second (petaflop/s).Let's wait until 2040 to get this kind of performance on our smartphones. :(

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Blade Element Theory only calculates the geometric angles of the airflow , not aerodynamic forces or moments is a statement of fact, not an assumption. Look at this link http://www-mdp.eng.c...ller/prop1.html which has been put forward and endorsed as an explanation of Blade Element Theory. In particular consider:Blade Element Theory does not calculate the values of CL and CD used - they have to be found by some other means. thispoint is evident in all other description of this theory.Also the forces calculated are simply section forces tcalculated on the assumption that there are no aerodynamic interactions between different blade elements. The equations show that. In reality there are aerodynamic interactions which, in the case of a wing, affect the spanwise distribution of lift. Without these interaction the spanwise lift force distribution would be constant on an plain untapered, unswept, untwisted wing with constant cross-section. In fact, it isn't an approximates to an ellipse with zero lift at the tip.My question remains How exactly then does X-Plane calculate the aerodynamic forces and moments?

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Blade Element Monmentum Theory is only applicable to a propeller, not a wing. Look at the diagram in 3. Axial and Angular Flow Conservation of Momentum.There is a blue annulus of radius r, width dr swept out by the propellor blade. Its area is 2πr.dr For a wing, which is not rotating, r =so that the subsequent equations for tthe forces and moments ( ΔT & ΔQ) also become infinite because they include r

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Blade Element Theory only calculates the geometric angles of the airflow , not aerodynamic forces or moments is a statement of fact, not an assumption.
I'm not disagreeing with you. Your assumption is not based in that. I'm telling you that BET is at the core of x-plane and there are many other factors that can be included to make x-plane simulate flight USING blade element theory as a core feature with other code written in to compliment it. I have always said that. I'm not sure why you continue to disregard it.
Also the forces calculated are simply section forces tcalculated on the assumption that there are no aerodynamic interactions between different blade elements. The equations show that. In reality there are aerodynamic interactions which, in the case of a wing, affect the spanwise distribution of lift. Without these interaction the spanwise lift force distribution would be constant on an plain untapered, unswept, untwisted wing with constant cross-section. In fact, it isn't an approximates to an ellipse with zero lift at the tip.
Again, there is more to x-plane than JUST BET.
My question remains How exactly then does X-Plane calculate the aerodynamic forces and moments?
My answer remains. You won't find an average user or developer to give you the answer you are looking for. I have suggested to you, at least twice, to ask Austin Meyer...X-Planes developer and owner.I don't really understand why you are so intent on knowing how x-plane works beyond what has already been explained to you and why you have so far refused to send Austin Meyer an email.

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My answer remains. You won't find an average user or developer to give you the answer you are looking for. I have suggested to you, at least twice, to ask Austin Meyer...X-Planes developer and owner.I don't really understand why you are so intent on knowing how x-plane works beyond what has already been explained to you and why you have so far refused to send Austin Meyer an email.
I think we all know why he is "so intent"........The MSFS camp has a really hard time. for some reason, coming to grips with the fact that X-Plane is making some serious in-roads into the flight simulator arena while their beloved program is on the ropes.... retooling itself. They don't like it.....Craig

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