over centering cams - how do they work?

[sugar99]

I work for a top aircraft manufacturer customer support division. A question i was asked about one of our business jet aircraft is "does the passenger door utilize over centering cams." I have never heard this term before.
Does anyone know what this is and could you describe how it works....examples???

thanks

Mark

 

[Sparweb]

Look at your own knee. If you keep it back, you can stand with your leg rigid. Move the knee a bit forward, until it is "centered", then you are standing with the joint balanced and the muscles in your leg are providing the restraint to keep the parts in place. Move the knee forward, and everything collapses.
Your knee isn't a "cam", so the analogy only works so far as the effect goes. A cam is cylindrical, but isn't perfectly round. The cam has one (or many) knobs that, when it rotates, can push on another object.


STF

 

[jbknudsen]

I would imagine that the assembly is an over centering cam design. If you send my your e-mail, I have an avi file that might help you visualize the process.

Jay
jayk@dicarinc.net

 

[markll1]

Many aircraft use over-center locking in their landing gear drag braces, side braces, and jury struts. Most of these utilize a hydraulic actuator to unlock or move the over-center lock out of its locked position.

 

[metman]

Look up toggle in a dictionary and hopefully there will be a picture.

The beauty of a toggle joint or over center device is that the transverse force applied to the elements to be held in place is dramatically multiplied by the locking/unlocking force. Once locked, the unlocking motion must go back thru the centerline and the unlocking force albiet a small fraction of transverse then must ramp-up to a maximum value as it passes thru center making it very unlikely to unlock accidently even from vibration if designed correctly.

Jesus is THE life,
Leonard