posted 01-23- 05:18 AM               

1) How are forces applied at Airpts? Are the forces calculated as moments of inertia, i.e. as a force applied at a distance from the model origin? or the parts origin?

or, put another way.....

If I moved the Airpt of a polygon further out, does the force change, or just the place where the force acts.

2) Is the amount of lift generated by a wing proportional the the air area?

or

Do two wings with half the air area, with airpts in exactly the same place give the same effect as one wing with all the air area?

3) How does the sim model a control surface's effectiveness? If you have an aileron on a wing, you don't define any properties other than in the wing. You tell the sim the wing has an aileron, but you don't define any aileron properties other than the dof. Does the sim make an assumption based on the parent wings data?

Been doing some testing on the above, but I don't seem to be able to get that answer the questions. I need to know more about why thingsare happening in order to make them controllable!

posted 01-23- 07:51 AM               

(1) The airpoints are the location where the forces are applied. i.e. the sim takes the input for angle of attack, altitude, velocity...references the airfoil and wing properties and calculates the force. The calculated lift and drag force is then applied at the airpoint. When all the forces....lift drag at airpoints, (thrust and engine torque are also lift and drag) and gravity force, inertia properties and location of center of gravity (based on the inertia boxes).... the game can use physics 101 to calculate the next location and orientation of the plane.

Moving the airpoints forward or backward will affect the pitching characteristics of the plane, moving the airpoints side to side will affect the roll characteristics. Keep in mind that the airfoil data is calculated for 1/4 the chord of the wing so to be accurate you will want to try to place your airpoints at 1/4 chord... also the side to side location of the airpoints depends on the shape of the wing and the lift distribution along the wing.

Short version: by moving the airpoints you just move the place where the force acts.

(2) If you look at the airfoils (ie using SVs airfoil editor), you will see values for lift, drag and moment given in terms of CL, CD and CM at different angles of attack... (you will also see CL', CD' and CM' which are related to turbulence). These values are coefficients which can be used to calculate the actual forces. The formula for Lift force looks something like this:

Lift = CL*(p*U^2*A)/2

p is the density of the air (changing with altitude) U is the forward velocity of the aircraft and A is the area (of the section related to that particular air point). The drag force and pitching moment are calculated the same way... (induced drag, based on airK and airAR is also calculated and thrown into the mix)

Short Answer: Yes, the amount of force generated at an airpoint is proportional to the area. If you have two airpts with identical wing properties, you should get twice the lift force. (but I might have forgotten something )

(3) The control surface properties are in the airfoil.ppf file. The foilup and foildn sections give the properties of the airfoil with the airfoil up and airfoil down (I think at 60 degrees each way). The sim checks the deflection of the control surface and references the airfoil.ppf file depending on the deflection and airmax. ie. with an airmax of 0.5 a full control deflection will give you about 1/2 the effect of what's given in foilup or foildn.

Short answer: Sv's airfoil editor lets you look at the effect of foilup and foildn. Combine that with airmax and you can get a good idea of aileron and flap effectiveness for each airfoil.

...feel free to correct me... I don't exactly consider myself an expert at this stuff...

posted 01-23- 09:07 AM               

Flaps forces are calculated in some hard coded flap equation, we have no control over this. Also I hear there might be moment problems with flaps.

Also it is key with OpenPlane to have multiple airPts per wing, usualy one for th root and one for the tip, but more are possible. The allows the outer part of the wing to have its own angle of attack, and also lets you simulate wash-in. This way you can get tip stalls, snap rolls, and more realistic spins.

You can add more than one airPt to a single object, but OPS does not support showing where multiple airPts (the blue line) are on one single object. Most WW2 planes have one airPt per wing object anyway.. but the WWI planes almost all have (coming in the pack) multiple points per wing object.

The key thing that is hard for me to remember, and I am not 100% sure I am correct, but pretty darn sure:

Drag is aplied at the airPt opposite the direction of travel of the wing (this is also oposite the direction of the airflow).

Lift force is applied upwards perpindicular to the airflow!!! (now perpinduclar to the wing!)

------------------
-Sv =FC=

WWI in SDOE!

posted 01-23- 09:41 AM               

What I have been doing is attempting to model changes to flight characteristics through damage.

What I have done is:

Added 4 extra 'wings' by copying and pasting the B17 wingtip. Each is a child of the original wingtip. Surplus properties are retained, but all the airfoil properties are kept. This includes the ailerons. Air area has been divided equally between the 5 'wings'

As damage occurs, wing layers are detached, thus reducing the total air-area, and therefore, I thought, the lift. These 'wings' don't seem to bother the AI any. I got some effective loss of lift, but wondered about the ailerons.....they operated without change. If I reduced their effectiveness by the same factor, they should contribute the same total effect...or do they?

I tried making tiny 'wing' boxes and spreading them over the wing surface, but this caused the amount of lift to go haywire. Even when I moved the air-pts to sit over the original, the lift was less than the original wing. This was what set me wonderign about the air-pts and how they worked. In theory, from what Bishop has said, that idea SHOULD work. If the forces are defined and the air area etc. calculated, then move the air point to wherever, it should be the same as far as the sim engine is concerned.

posted 01-23- 11:48 AM               

1) Create a "secondary wingtip" in the same position as the primary wingtip (a simple copy of the original will do). Delete the "airControl" and "airObject--aileron" properties from the obAirfoil of the original wingtip, but LEAVE them on the secondary wingtip. The secondary wingtip, when detached by damage, will take the aileron PROPERTIES with it, and your aileron will stop functioning (but the one on the other wing will still work). Now, reduce the airArea of the secondary wingtip to about the area of an aileron. It may take some trial and error to get the areas of the primary and secondary wingtips to "feel" right, because, as you probably suspected, two wings half the size of the original don't act EXACTLY like the one wing did before. It's important to keep the secondary wingtip area small, because you don't want the AI pilot to bail out when he gets an aileron shot off. If he loses BOTH ailerons, he WILL bail, no way around that, other than to take control of that plane yourself. The Aussie Spits I did use this feature, but it's not completely refined.

2) As before, attach a secondary wingtip, with all the aileron properties intact. But this time, on the primary wingtip, delete ALL wing properties, except "airWing." Then, create an obFunc for the primary wing that CREATES all the wing properties, EXCEPT for the airControl and airObject--aileron properties. In this case, you keep the airArea of the primary (in the obFunc only) and secondary wingtip the same, because when the secondary wintip (with aileron) gets shot off, you're going to call the function that CREATES the primary wing properties (without aileron). In other words, you replace your "aileron-ed" wing with an "un-aileron-ed" wing using an obFunc. See Raider's newest Mustang Beta for an example of just how to do it. Less trial and error here, because you're not fiddling with the areas.

You can do the same thing with the wing sections containing flaps, to get a situation where ONE flap works and the other doesn't, which will roll the airplane, which is kinda cool and pretty realistic. However, the AI doesn't like that one very much

In either case, don't forget to add the new wing parts to the master list of wing objects in the main fuselage object, or you won't be able to use the aileron trim on the new wing sections.

As for having pieces of wing blown off in sequence, you're going to have to keep the initial parts fairly small, or the AI is going to think its wing is gone and bail out, or the enemy will break off their attack, thinking the plane is dead. Not sure what the "threshold" is for when the AI gives up the ship. I've had the AI actually do a TAKEOFF in a plane where I had the flap wing section shot off, but then I've also seen the AI not be able to fly with just a missing aileron, which is "easy" for the human pilot to handle. As far as losing aileron control goes, I think you'll like the effect better if you just lose the aileron all at once, rather than losing 2 or 3 little aileron pieces one-at-a-time. For that, just leave the aileron properties on one wingtip part, and when that one goes, you'll have half of the aileron authority you had before. BUT, if you used Raider's obFunc wings as above, you COULD make a SERIES of wings, each activated by obFunc, and give each subsequent aileron a LOWER airMax value than the previous one. This will decrease the effectiveness of that aileron in steps, by limiting its travel. You can even leave the aileron properties attached to all the wing parts, and just make the last one have airMax=0 to "freeze" its aileron. (At least I think that'll work)