NWS and WOW sensor

[CapExcellent]

Hello,

I'm doing some research regarding how the WOW (weight-on-wheel(s)) sensor actually works, it's conncetion/correlation with the NWS (nose-wheel-steering) system.

1. WOW: Does it close the sensing loop by a "simple" contact, proximity sensor or
something more sophisticated (light-sensitive measurement like the one
used in CNC technology)?
2. NWS: Nothing is impossible in aviation, therefore: If the WOW sensor on the
nosewheel would be malfunction, would that mean that the crew has no
means of directional control at slower airspeeds (lets assume below
50knots, rudder inputs become less responsive) except for differential power?

And taking everything into consideration, would a worn out drag/shock strut affect the WOW sensing IN THE SAME MANNER as a bouncing airplane where the WOW system initally delays (sec./fraction of a second) an output signal to assure that the airplane is actually on the ground? Basically, once the plane decelerates and load is reduced on the nosewheel the WOW system would open the loop again rendering the NWS inop! What if the pilot has applied full rudder, with a "closed" WOW signal leading to max NWS rudder "mode" deflection and suddenly the WOW loop opens and the airplane goes left/right? :} Could this happen?

Hope it all makes sense and I would really appreciate any constructive input!:ok:

Cheers,

CE

PS: If it is of any help, I am referring more onto turboprop airplanes such as Atr, Dash, Embraer, Dornier etc.

[leewan]

1. WOW sensors are usually of the simple contact proximity sensor.
2. There are at least 2 WOW sensors in each aircraft. If all fail at the same time(very rare), most a/c's NWS steering would be inop. In such cases, the pilot simply stops the a/c on the runway and requests for towing assistance. The A380s quite often had this problem with a faulty BSCU.

Most a/cs WOW sensor is placed on the NLG. Some on the MLG. The a/c estabilishes it is in ground mode once the oleo/shock strut starts to get compressed. So, for a worn out shock strut or a decelerating plane on the runway, the a/cs shock strut would still be compressed letting the a/c know it's in ground mode.
You can see when a 747s go into ground mode simply by looking at the nose wheel light. It only lights up when the a/c is in ground mode.

[Clandestino]

If NWS fail for whatever reason, the aeroplane can always be steered during landing roll or rejected take-off by differential braking. So no combination of exotic WOW failures will make it uncontrollable at low speeds.