Blade Element Theory

[Leen3131cs 107]

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

[MdMax 233]

Ask Austin Meyer if you want. :( See also this: FSBreak 22

[Leen3131cs 107]

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

[Murmur 3,941]

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

[MdMax 233]

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. :(

[mgh 89]

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 C_L and C_D 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?

[MdMax 233]

So, do they use the "Blade Element Momentum Theory (BEM)" ?

[mgh 89]

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

[GoranM 3,764]

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.

[Guest bukkohc]

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

[GoranM 3,764]

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

Between you and me, I know and agree.But let's give him a chance to contact Austin (IF he does contact Austin).If he keeps asking the same question, then he only reinforces your statement.

[60North 120]

My question remains How exactly then does X-Plane calculate the aerodynamic forces and moments?

XP uses user/designer defined airfoils that contain Cl, Cm and Cd data as a function of AoA for whatever type of airfoils(wings) your aircraft has. Each wing/stabilizer etc can contain dozens of airfoils for both Hi and LOreynolds#, dozens of different incidences, dihedral, sweep etc.These wing properties are then used with blade element theory and forces and moments are calculatedfor each section of the wing.The airfoils can be real data or fictional.Here is an example airfoil, real NACA 2412,The real NACA dataAnd XP's airfoil;

[mgh 89]

Between you and me, I know and agree.But let's give him a chance to contact Austin (IF he does contact Austin).If he keeps asking the same question, then he only reinforces your statement.

I've searched the X-Plane site but can't find an e-mail address for Austin Meyer. The only ones I can find are for support for puchasers and for querying order status. If someone will let me have his address I will e-mail him.I don't know why some of you are so insecure and almost paranoid. It's obvious the X-Plane does generate aerodynamic forces and moments so what's wrong in being interested how it does it?

[GoranM 3,764]

Nothing wrong with wanting to know. But I keep telling you. To get a definitive answer, ask Austin. To be honest, I don't know why you are so eager to know. Have you been this persistent and asked the same questions about FSX's flight model using lookup tables instead of physics?We're not insecure and paranoid. A little annoyed maybe...at your persistence after suggestions were made and explanations given. We replied and you repeated yourself.Email: info@x-plane.comand see how far you get. If Austin hasn't published his email, I'm not sure it's right to share it around.

[Murmur 3,941]

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 C_L and C_D used - they have to be found by some other means. thispoint is evident in all other description of this theory.

See MortenM post.

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.

This is a very clever observation. I think part of the answer is in the description given in the X-Plane website:"3: Coefficient DeterminationThe airfoil data entered in Part-Maker is 2-dimensional, so X-Plane applies finite wing lift-slope reduction, finite-wing CLmax reduction, finite-wing induced drag, and finite-wing moment reduction appropriate to the aspect ratio, taper ratio, and sweep of the wing, horizontal stabilizer, vertical stabilizer, or propeller blade in question."However probably only Austin knows the full details...Marco