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Calculating forces, speed,acceleration of a plane

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3 replies to this topic

#1WiredCat  Members

Posted 21 February 2012 - 05:51 PM

I am trying to make the plane fly by calculating forces of thrust gravity drag and lift (but now i am only using now two forces: gravity and thrust)

nvm because i dont have a lift force because of Cl = 2 * pi * attack angle = 0.0ff

the stupidiest thing now i see that: my plane always goes down towards gravity vector even when thrust force is 2 times greater than gravity force and acts in the opposite direction

second issue is that: i cant calculate proper normalized vector (normalized gravity force vector)
in example: i have plane pos: x=50 000 m y = 100 m z = 30 000 m and the normalized vector is something like this: x = 0.7; y = 1.5, z= 0.4; and i donkt know why the y is fck-ing 1.5 here

i always get this effect (lol clouds are 320 km away form the surface - and we are in south america )

i use these equations:
F=m*a
s=v*t
s= v0*t+a*t*t*0.5

i start the simulation with this:

MODEL->t = GetTickCount();
MODEL->pos = position;
MODEL->old = position;

	void __fastcall TVehicle::ProcessFrame()
{
int p = GetTickCount();
float x =  abs(float(p-t))/1000.0f;
if (x <=0 ) return;
t3dpoint kk;
kk = YPRangle.rf; //thrust force orientation

float Front_force = Throttle_to_force( Throttle );   //thrust force val
float Q = eGForce * mass;	// gravity force val

t3dpoint  TForce_vec;
t3dpoint  GForce_vec;

TForce_vec  = YPRangle.rf;				 //thrust force direction (movement)

t3dpoint c; c = vectorAB(pos, zero);//center of earth
GForce_vec  = Normalize( c ); //g force direction

//density
float drag_force = 0.350*pressure*(V*V/2.0f);

GForce_vec = vector_multiple(GForce_vec, Q);
TForce_vec = vector_multiple(TForce_vec, Front_force);

//Cl = 2 * pi * pitch angle (in radians)
//L = .5 * Cl * air_density * V^2 * A
t3dpoint VA;  //acceleration vector

VA = ALL_FORCES / mass;	  // a = F / m

float dk = ( x*x ) / 2.0f;

VA = VA * dk;  //(a * t^2 )/ 2

float h = V*x;
VA = VA + h;				  //V0*t +	(a * t^2 )/ 2

//s = V0*t + (a * t^2 )/ 2

t = GetTickCount();
V = n3ddistance(pos,old) / x;  // s = V / t	so calculate velocity
old = pos;
}


what am i doing wrong ?

now wypadkowa is ALL_FORCES :] no its not irricht its mine engine

#2Tom KQT  Members

Posted 22 February 2012 - 05:41 AM

I would certainly start with getting rid of GetTickCount() in this kind of use. Resolution of this function is somewhere between 10 and 20 ms, which absolutely isn't enough even for applications running at mere 60 FPS. Try QueryPerformanceCounter() instead.

I didn't have much time to dive into your code, I just noticed that it's quite chaotic and confusing. You should give better names to your variables. For example your "x" is usually called "dt", or "delta_time".
X should be strictly reserved for coordinates.

And short names like VA, h, V, dk tell nothing about their meaning, especially when for example "h" doesn't mean "height".

#3WiredCat  Members

Posted 22 February 2012 - 05:51 PM

never mind i was adding translation vector to float ( but i should add vector to vector )

and the GetTickCount() has resolution such as 1 ms not 10 ms

#4Tom KQT  Members

Posted 23 February 2012 - 01:18 AM

and the GetTickCount() has resolution such as 1 ms not 10 ms

Nope, it doesn't.
It seems to have a 1 ms resolution, because it returns a DWORD value in miliseconds. But if you test it better, you'll notice that when for example you are calling the function repeatedly, it may return something like
5411
5411
5411
5411
5411
5425
5425
5425
etc.

In fact, you won't get two succeeding values with difference of 1 ms, it will be returning the same value and after some time the value will suddenly increase in a step.

This limited resolution is mentioned also in the official documentation
http://msdn.microsof...v=vs.85%29.aspx

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