Spiraling Under Control

One of the staples of fixed wing autopilots is the circle hold.  A circle hold is the closest thing you can get to a pause button with a vehicle that must be in constant forward motion to stay aloft.  There are a few hidden challenges in the task, including wind compensation and some unexpected coupling that can lead to weird looking oscillations if not handled well.  People have been doing circle holds with UAV’s for a long long time, so I don’t bring anything new to the table, but it is always fun to play, err I mean experiment.

Circles


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Visualizing Circle Holds

(If it was me, I’d click on the “watch on youtube” icon in the lower right corner and select 480p and go full screen — but that’s just me.)

Flying a continuous tight circle pattern around a fixed ground reference point is about the closest thing we can get to parking an airplane in flight. It isn’t too hard to do a lazy orbit around the point, but we want to keep the radius fixed, even if there is a wind. This means that as we fly around the perimeter of the circle we have to continually vary our bank …
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Better FlightGear Smoke

Overview

A popular way to create smoke effects in visual simulation is through particle systems.  Briefly, a particle system emits particles.  Each particle can have a texture as well as a variety of physical characteristics.  Particles can be shot or just placed in the world.  If you shoot your particles you can control a randomize range of angles and speeds.  You can give your particles a life span in seconds and have them grow or shrink over their life.  Particles can have mass and surface area which affects their motion.  They can move relative to the world or relative to …
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