kel

I am interested in writing a helicopter simulation, the problem I am having is coming up with a model to describe it.
I know that I have one variable time, and 3 dependent variables, rudder, rotor angle, and rotor speed, but I don't know how to put that together to form an equation I can compute.

I know it will end up looking like:
Xs(t)=
Ys(t)=
Zs(t)=
Xv(t)=
Yv(t)=
Zv(t)=
all depending on the results of the dependent variables. I would also need a method for including other effects in these equations (wind, ground buffer, auto-rotation, the vortex effect stuff when you descend really fast) I think I can do that by multiplying all the constants in each equation when any of those cases happen, but if anyone has a better way.

Thanks in advance

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Peetster

You are asking for the equivalent of a Masters Degree in Aeronautics. I don't think we could ever cover it all in a thread. Start here:

http://www.copters.com/helo_aero.html

kel

Those are just a list of individual effects, I need the actual mathematical model behind it. It's not really a masters level task, it's a complex bit of engineering/ multi variable calculus.

I already know or can develop a model for all those forces which are mostly common sense. They don't provide equations for those forces anyway. What I need the 3 dimensional model to describe the problem as a whole. 3 vectors of velocity, and 3 coordinates of position. denoted by
Xs(t)
Zs(t)
etc

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icy_ca

Helocopter physics is actually very easy. "They're so ugly the earth naturally repels them." - my dad circa 1961

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gar1976

Whirly things whirl at a veolocity of X, and the magic power inside lifts the thing!

wlcm

the equations are probably pretty difficult since you'll need a whole bunch of intial conditions to solve anything. there are probably more variables in there too, like the tail rotor and its properties, air density at particular elevations.

If you could actually make a good helicopter simulation, you'd probably want to go get lockheed or whatever helicopter company to hire you.

if you want things basic, you could just say that the rotors create a force F and totally work with that. then you can model it with simple trig.

If you want to take into account all those other secondary effects, then you'd probably need at least a course in fluids and probably a few courses in differential equations and vector calculus. Just using constants probably won't cut it.

cheerios

ya know, honestly, as someone who made it nearly halfway to a mechanical engineering degree, I can't solve this. wlcm's got it about right. simplify the problem, and it'll become simpler. er... EASIER, I meant easier, I swear!

kel

Would take a completely different approach, it would simulate the displacement and flow of currents of air over each individual surface. You can treat air as a vector and sorta ray trace it, or you can create a partical system with actual air particles with mass and velocity and implement a concept of high and low pressure. Equations of orientation and position don't even enter into the picture because the particle system "knows" by it's very nature how to translate the helicopter. The lockheed approach requires a supercomputer :-P. I just want to create a believable simulation, I don't care about the simulation being accurate, just believable. My question was how to phrase the problem as a simple mathematical system. It's very doable with the right background. And it's mindless to implement in code once someonce formalizes it into a set of functions.



At every point in time t I need to calculate the position and orientation of the helicopter based on a few dependent variables, namely, rotor speed, rudder speed (the rudder is actually a second rotor, the rudder pedals slow down and speed it it up), and rotor angle. Those are the only dependent variables I want to start out with. This is mostly some complex linear algebra which I am studying right now for this purpose, and some multi-variable calculus. Undergrad level ;-)

The equations that calculate the position and orientation at time t are constant for every set of dependent variables. So everytime the pilot modifies rudder, rotor, or collective the constants in the equations are recalculated. I just want the equations and the method to calculate the constants. Simulating various effects and nuances of h/c is pretty easy by simply tweaking various cases once you have a system like this.

The problem is that all the existing engineering texts just tell the engineer how to predict performance based on certain phsyical features and not how to actually flat out calculate the whole shebang. That's left to the programmer with the supercomputer :-P

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