[Info-vax] OT: Aircraft pitot tubes and clustering.

[John Santos]

In article <wsadna1iV5njXLbWnZ2dnUVZ_u2dnZ2d at giganews.com>, rgilbert88
@comcast.net says...> 
> David Mathog wrote:
> > JF Mezei wrote:
> > 
> >> BUT, they found cases where 2 probes failed at the same time and by the
> >> same magnitude. This caused the remaining one to be kicked out despite
> >> being correct, and the 2 errorneous ones to be used because the
> >> differences between them are within bounds. As a result, the aircraft
> >> used very wrong values for the air sensors.
> > 
> > This could happen if the most common tube failure mode was to take the 
> > output voltage to ground or supply voltage.  Then if two failed in the 
> > way they are most likely to they will read exactly the same thing.
> > Presumably the software should reject readings in these failure mode 
> > voltage ranges out of hand, but it might not.
> > 
> > Regards,
> > 
> > David Mathog
> > 
> 
> No voltage necessary in the case at hand.  At least in light aircraft 
> the pitot (impact) pressure is used, in conjunction with the static 
> pressure, to determine the airspeed.  It can be done with nothing but 
> plumbing and a pressure gage.  AFAIK this approach is used in most aircraft.
> 
> The pitot tube and the static pressure port are both things the the wise 
> pilot checks as part of his preflight inspection.

Sure, for a human looking at the gauge, if it's pinned, he'll ignore it.

But JF was talking about an automated flight control system, which means
the purely mechanical instrument needs to be digitized, which means 
electronics...

-- 
John Santos
Evans Griffiths & Hart, Inc.