First take a look at this (anyway theres 3 drag areas top, front and side areas of a jet)
but lets talk about only two top view area and frontal area.
how should i calculate drag force since: drag = sin(angleofattack)*drag_force_of_firstarea + cos(angleofattack)*drag_force_of_secondarea doesn't seem to work as it should.
What angle are you using for "angleofattack?"
How are you calculating "drag_force_offirstarea?"
This is a fairly crude approach to drag force. A simpler, but equally crude, approach would be to use the area of the aircraft projected onto a plane perpendicular to the direction of motion.
How are you expecting drag to work?
I would be inclined to treat the wing and tail as two lifting surfaces and then apply some NACA Lift & Drag curves.
You could do a similar thing for the fusalage (treat it as a long-chord wing section).
I calculate drag by: drag_coefficient* ( (denisty * vecolity squared) / 2.0f) * drag_area
angleof attack is angle between model pitch and moving direction
brucedjones
Posted Yesterday, 02:51 PM
This is a fairly crude approach to drag force. A simpler, but equally crude, approach would be to use the area of the aircraft projected onto a plane perpendicular to the direction of motion.
How are you expecting drag to work?
wtf?
CombatWombat ill take a look at it.
doesn't seem to work as it should.
As a simple approach to drag, your equations appear adequate. If that doesn't "seem to work," what are you expecting (as asked above) that you're not getting?
whenever i raise my nose (even to 0.5 degree) i get massive drag that prevents me from reaching 302 knots
float AngleOfAttack = AngleBetweenVectors(vel,ThrustForce_vec);
float tmpangle = RadToDeg(AngleOfAttack);
LiftCoeff = sin(AngleOfAttack) / 2.0f;//+0.050;
DragForce_vec = reverse_point(vel); DragForce_vec = Normalize( DragForce_vec ); i_drag_force = DragForce_vec;
DragForce_vec = vector_multiple(DragForce_vec,0.080f * ((dens * squareSpeed)/2.0f) * cos(tmpangle*imopi)*3.6f); //the thrust drag force
i_drag_force = vector_multiple(i_drag_force,1.280f*((dens * squareSpeed)/2.0f)* sin(tmpangle*imopi)*38.0f);
DragForce_vec = DragForce_vec + i_drag_force;
float LiftForce = 0.50f * LiftCoeff * dens * squareSpeed * 38.0f;// <--- LIFT AREA
LiftForce_vec.x = YPRangle.AIR_MATRIX[4]; /up
LiftForce_vec.y = YPRangle.AIR_MATRIX[5];
LiftForce_vec.z = YPRangle.AIR_MATRIX[6];
LiftForce_vec = vector_multiple(LiftForce_vec, LiftForce);
result_force = GForce_vec + ThrustForce_vec + DragForce_vec + LiftForce_vec;
Assuming that you've stepped through your code, checking values at each line: in which line do you get unexpected values?
((dens * squareSpeed)/2.0f) * cos(tmpangle*imopi)*3.6f)I'm not sure what all you're variables and factors represent. However, a simple drag force would be proportional to 1/2*density*v2*area. If I understand your diagram and angles correctly, the area should be proportional to the sin(angle), not cos.
not exactly cos of 0 is 1 and second area produces then drag with full force, anyway we can close this topic for now
