Flight Physics

It is all conservation of energy, but the details can be a little tricky:

Thrust, lift, and drag are all forces, and you have to integrate them over distance to find the change in kinetic energy.

Thrust is controlled by the user throttle.

Lift is a fuction of velocity and control surface positions (user inputs).

Drag is a function of velocity (typically to the 4th power) and control surface positions.

You have to keep track of kinectic energy (½mv²) and and gravitational energy (mgh).

Flight control is a typical problem in grad level courses in Multivariable Control Systems.  I will see what I can find on line.

Thanks d-glitch.

I'll have a fiddle.  :-)

Rob.

That link seems to cover just about everything. Excellent. :-)

Cheers!

In a simple model for a single engine plane, you would probably want to include at least five control variables:

Engine thrust which gives you mostly forward motion.  But lift is also a function of air speed.

Left and right wing flaps which affect lift and pitch when they are used together and cause the plane to roll when they are used differentially.

Rudder which is mostly controlls heading.

Tail flaps (that usually work together not differentially) to trim pitch.  They are smaller so they don't do much for lift.

In the Harrier, you have two engines, and I imagine the thrust and angle of the thrust can be set seperately.   That is at least three more control variables.  You might want to limit some of that flexibilty.

You certainly need to keep track of the planes altitude and velocity (x-, y-, and z-components).  These are the state variables related to energy.  

You also need to keep track of the the planes attitude (at least pitch) in order to calculate lift and drag.  Your probably want to ignore yaw and roll.  If you come up with realistic eqations, you will still have to deal with stalls, but you can probably ignore tail spins and flat spins.

You probably want to integrate velocity to find position.

You could call this guy:  http://www.nesta.org.uk/ourawardees/profiles/2920/print.htm

Sounds like he's been there.

And one more link before I go:             http://home.wanadoo.nl/dutchroll/manual.html

Excellent; thank you very much, d-glitch. :)

The harrier has ONE engine and four thrust nozzles.  It's a really hard plane to model, as it's way underpowered-- it can only take off straight up if you take off  considerable ordnance and/or fuel.  With a full load of bombs and gas it needs a considerable runway length to take off.  The usual lift/drag models for airplanes are comllex enough-- with the Harrier you have to add the effects of the steerable exhaust nozzles, and somehow model the backside of the lift/drag curve.     Also when close to the ground the hot exhaust bounces back, with strong temperature effects on the lift and on the engine intake density and thrust.  A real toughie to model and to fly.  And oh yeah, the newer Harriers have a fly-by-wire stability-enhancing computer, which does a lot of the attitude trimming for you, but that's yet another thing you have to model.  Yuck!

Cheers for that grg99  :-)  I love a challenge... ;-)

I hadn't consider some of the points that you'd made above  --  back to the drawing board I guess. :-)

I'm curious to how you're so familiar with the harrier? Do you have experience in aircrafts yourself? Or just a hobby/interest like mine?

Regards;

Oh, by the way; for anyone who may be taking on a similar task (or just interested).. I've come across a very useful resource on the NASA site: http://www.grc.nasa.gov/WWW/K-12/airplane/short.html