# Pendulum effect / dynamics

Hi, im trying to impliment better / more realistic pendulum effect into my paragliding simulator.

When a paraglider turns hard it results into a dive, but as the center of mass is near the pilot and higher lift/drag on the wing, it soons swings / pendulums back into level flight.

Im trying to impliment this but im not sure how, currently i have it just return to level flight which is incorrect. It would pendulum a few times before it settles.

Im not amazing with physics and maths so you will have to bare with me.

Hope you can help.
Andy

sophiecentaur
Gold Member
2020 Award
Hi
The formula for the period of a simple pendulum is
t = 2π√(l/g) and the motion is sinusoidal (google pendulum and you'll we what I mean
where l is the length of the pendulum and g is g.
Your value for l would be roughly the distance form where your 'middle' is to the centre of effort (dunno if that's the right term but it is the term used for boat sails)
This pendulum would be pretty damped by the floppy wings so you could probably assume 'critical damping'.
It would be easy to write a formula giving the angle as a function of time, using the above ideas. I am assuming that you just want it to 'look right' and to avoid too much theory.
http://webphysics.davidson.edu/applets/animator4/demo_damped_sho.html" [Broken]
for an animaton and
http://en.wikipedia.org/wiki/Harmonic_oscillator" [Broken]
for some graphs and the full works.

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Andy, I'm not sure why you need to explicitly implement the "pendulum effect". I mean, if you have all the aerodynamic forces, cg calculations etc working, won't they take care of the swinging and dampening?

BTW, this is what I call a http://www.youtube.com/watch?v=K6wImByVPgM", lol. Took me a while to understand how they can do that. :)

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sophiecentaur
Gold Member
2020 Award
Andy, I'm not sure why you need to explicitly implement the "pendulum effect". I mean, if you have all the aerodynamic forces, cg calculations etc working, won't they take care of the swinging and dampening?

BTW, this is what I call a http://www.youtube.com/watch?v=K6wImByVPgM", lol. Took me a while to understand how they can do that. :)

That stuff has to be risky. If you're not rotating fast enough, you could end up falling down into the canopy and you'd die. But when you're in your early twenties, that consideration doesn't come into it!

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Yeah exactly. Those extremists wear reserve chutes (sometimes 2) but I couldn't imagine being able to deploy it when you're tangled in the main canopy hurtling toward the ground.

Edit: Actually, I just found a video where this sort of happens. Watch from about 1:10 onwards. Very lucky guy.

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Andy, I'm not sure why you need to explicitly implement the "pendulum effect". I mean, if you have all the aerodynamic forces, cg calculations etc working, won't they take care of the swinging and dampening?

BTW, this is what I call a http://www.youtube.com/watch?v=K6wImByVPgM", lol. Took me a while to understand how they can do that. :)

Hi Janger, i agree but i seem to run into alot of problems with it and at first i thought it was simply my programming and me not quite understanding it and doing it incorrectly, as i have now tried and tried and tested and more testing im startin to belive there might be a bug in the implimentation of newton game dynamics physics library in the engine im using.

Ill do some more spcific testing to try and nail this.

Them guys are crazy in the vid, how ever much i think it is crazy cool I wouldnt ever like to try it. :)

Thanks
Andy

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Bugs, lol.

I replied to your PM the other day then forgot to send it. I had put my aerodynamic simulations on hold due to other projects getting in the way but your progress has got me back in to it. And like you have been fighting niggly bugs. I discovered my plane was exploding into pieces due to the wings being too light compared to the fuselage. Also C4D's fixed connectors aren't really fixed - they vibrate a little bit which upsets all the forces. Workarounds, workarounds. Damn annoying.

Anyway, I started doing a simple parachute simulation to show you how the 'pendulum' movements are very damped as sophiecentaur said. Then realized the dynamics aren't as simple as it seems.

How are you modelling the dynamics of the paraglider? Are you assuming the canopy to be a rigid body? If so then that could be a problem for the realism aspect, and how it behaves when not in horizontal, stable flight. If you could explain what forces you're calculating and how they are being applied, I may be able to help. But I don't think you can simply treat a paraglider as a fixed-wing craft and have it look 'real'.

BTW, you can get email notification of PM's. The setting is in the 'Edit Options' part of your control panel.

Dave.