Know How...

Jun 25th 2015

Know How... 149

Vortex Ring State, Zymbit, and KH250 Build

Why Helicopters crash, Zymbit, and build the KH250.
Although the show is no longer in production, you can enjoy episodes from the TWiT Archives.
Category: Help & How To

We talk about a phenomenon that can happen with rotary-wing craft called "A Vortex Ring State", a fast way to integrate your Arduino, Raspberry Pi and Atmel designs, third party DNS, best HD for your old computer, Ruckus ZoneFlex R500, and the KH250 reveled.

Helicopter pilots have known about VRS for decades:
* While you're flying a rotary wing, there is "upflow" -- As the wing passes through the air, it pushes air down (creating upwards thrust) while also pulling air UP near the mast and blade grip because those surfaces are not an airfoil.
* In directional flight, this isn't a problem because you're moving away from the upflow.
* However, in hover or decent, the upflow can increase from the mast and blade grip
* If the upflow fully engulfs the rotary wing's lifting surfaces then you lose lift RAPIDLY.
** Essentially, the helicopter decends into it's own downwash, losing lift

This VRS has been responsible for many accidents with rotary wing craft
* The V-22 pilot training has been modified specifically to account for VRS
* The Blackhawk that crashed in the Osama Bin Laden raid was lost because of VRS
* It's something that EVERY roatary-wing pilot needs to consider.

Getting out of VRS is easy, but also tricky
* The problem with VRS is that as a craft loses lift, the natural tendency is to increase throttle to regain lift.
* But increasing throttle just WORSENS VRS - You just create more turbulent updraft which will increase your rate of decent
** This is something that we see with quadcopters all the time.

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