Blade Element Theory

[mgh 89]

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?

[Chock 17,769]

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

[Superpilotv2 2]

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.c...ller/prop1.htmlAl

Looks like lots of math.

[MdMax 233]

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

[mgh 89]

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

That's the section if referred to in my original post, which leaves questions unanswered.

[GoranM 3,762]

See "Chock's" post. Reply number 2.http://www-mdp.eng.c...ller/prop1.htmlYou'll still find some people say that lookup tables can do the same thing..I say, after reading the above article, feel free to make up your own mind.

[mgh 89]

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?

[GoranM 3,762]

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.

[mgh 89]

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.

[GoranM 3,762]

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.

[mgh 89]

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?

[GoranM 3,762]

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.

[mgh 89]

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.

[GoranM 3,762]

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.

[MdMax 233]

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.