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AF447 Thread No. 3

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AF447 Thread No. 3

Old 15th Jun 2011, 14:56
  #2061 (permalink)  
 
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RR_NDB

Digital signals had no problems with wire wrap connections in the 60s and 70s. That was one of the ways Burroughs built some of their mainframes in that era. I bet the RF was basically contained on one card and brought down to a rather low frequency or to sampled data before it was shoved out onto the wire wraps. OR the cards were connected via SMA for the RF connections.

I saw a lot of that in the bad old days. (And if wrapped just a tad tight vibration was unkind to the wire wraps because of the inherent nicks in the wires on the square edges of the posts.)
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Old 15th Jun 2011, 15:00
  #2062 (permalink)  
 
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HazelNuts39, is the pitch angle trace in figure 3 from the FDR released info (so far)? How confident are you of pitch angle to timeline synchronization for your graph?
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Old 15th Jun 2011, 15:05
  #2063 (permalink)  
 
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Good old days

JD,

I saw a lot of that in the bad old days


In the good old days the wire wrap indeed was a very good approach.

About wiring issues, are you familiar with Kapton issue?

This is IMO the real monstrosity.
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Old 15th Jun 2011, 15:06
  #2064 (permalink)  
 
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Bear, the A in OODA is Act, not Agility.

For those unfamiliar, OODA is Observe, Orient, Decide, Act

You then go back to Observe, hence the loop. Your loop is a continuous process until the point where what you observe makes you decide to stop acting. At that point, in theory, you are at equilibrium, or have achieved the desired state of whatever it is you are doing, or trying to do.
Are you sure aircrews should study OODA? With patience and calm being part of the Air Bus check list, how will you fold AGILITY into the Loop?
bear, FFS, OODA describes what pilots DO when they fly.

Your instrument scan and your control inputs on a hand flown ILS or VOR in crap weather is a perfect application of OODA in flying. You have desirerd performance parameters (airspeed, altitude, position, course, heading, track, descent rate, glide slope, etc) and you make constant small corrections until you have iced the heding, power, nose attitude, trim, etc, to achieve the desired glide slope on course, on speed, needles centered, until MDA or DH and you Observe the runway, decide to land, or To Go Around. (Or you decide to cheat down a few feet to take a peak below mins and maybe it all ends in tears ... )

OODA came from a pilot, Boyd. No surprise, since it is what pilots do. He gave it a name. He applied it to dogfights, a similar process to the above: run through the OODA loop faster than your opponent (get inside his decision cycle) until you get into that sweet spot for Fox 2, and shoot.
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Old 15th Jun 2011, 15:29
  #2065 (permalink)  
 
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JD,

icehart says, "(hope that does not apply to Airbus)". Sadly, it does.
Where? Cabling? System Interconnections? Are you concerned with a/c aging?

Did you see how they soldered WWII internal radio wiring gear, against a/c vibration? For example, the soldering of BC348s, ART13, etc. Practically zero chances to fail. (Despite nearby dynamotors, etc,)
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Old 15th Jun 2011, 15:35
  #2066 (permalink)  
 
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What with private conversations on wiring it's becoming harder to remember just what this thread is really about.
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Old 15th Jun 2011, 16:15
  #2067 (permalink)  
 
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@HazelNuts39 re http://www.pprune.org/tech-log/45283...ml#post6515113

Is it possible to deduce from your great graphs at what point the zoom climb becomes 'ballistic'? Strikes me that a some point before the apogee airspeed and pitch wouldn't be be able to generate enough lift for level flight - and the only way out would have been a carefully managed pitch down and controlled descent past the apogee. Was FL375 @ M0.68 sustainable? Guess need to make assumptions about engine thrust and response time if not already full.. At what point on your graphs was/should the stall warning be triggered?

It was never clear to me exactly how the A340 airprox zoom climb was successfully recovered - pilot or AoA protection avoiding the stall warning using full thrust and pitch down?
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Old 15th Jun 2011, 16:37
  #2068 (permalink)  
 
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Did you see how they soldered WWII internal radio wiring gear, against
a/c vibration? For example, the soldering of BC348s, ART13, etc.
Practically zero chances to fail. (Despite nearby dynamotors, etc,)
More radio . I too had a mispent youth, starting around age 11 building s/w
valve radios and well remember command sets, hro, R1155 etc. The soldering
procedure was different than that for bucket style connectors though. Wires
and parts were first fed through a hole in the tag or valveholder, before
being wrapped round the tag at least once to make a good mechanical joint before
soldering. Such soldered joints are very reliable, especially when done by a
dedicated (as they were then) and skilled workforce who took pride in doing
the job right. The inspectors even dabbed paint spot on every joint in those
days in some cases, unheard of now. The wire was often cotton covered,
cable harnessed and tied down, all of which absorb vibration quite well.
Larger components, such as caps, chokes and power resistors etc, were nearly
always screwed down to the chassis before wiring. The command sets in particular,
were beautifully lightweight engineered, with mica sealed components and
invar plates used in the tuning capacitor for stability.

In the states in 1977, flew in a DC3 between cities at one point and could
not believe it when I went up front and saw a rack full of command receivers
and associated transmitters etc, in an alcove just behind the crew. All the
black crackle paint and smell of hot valves and motors took me back several
decades ...
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Old 15th Jun 2011, 16:41
  #2069 (permalink)  
 
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RetiredF4,
Thanks for your interesting post, and for drawing my attention to the recent contributions of mm43, A337ab, and PJ2. Must admit that, since reading completely the deluge of about 50 pages of posts in the first four days much of it rubbish I've only been reading bits here and there until I happened to spot a significant typo in Smilin_Ed's pertinent post yesterday. (My own response to the BEA Update on May27/2011z had provoked no PPRuNe feedback.)

You make a strong case for the possibility that the deep stall from about FL350 in the descent (AoA +40) might have been sans-issue (even disregarding the height required for any recovery). gums and others have talked about the pitching-moment problem on the previous thread, and I guess that's the essence of your proposal. Like a THS movement in the nose-down sense, down elevator would itself increase the already positive AoA of the THS, whose aerofoil was producing lift in the opposite direction to that for which it was designed. Can we assume that an increase in its AoA from +40 would decrease the vertical component of its lift? Probably.

On the other hand, at the FL380 apogee (pitch and wing-AoA +16), the THS AoA would have been "only" +3 (already producing lift in the wrong direction). At that stage, therefore, there was still a possibility of pitching the nose down with forward stick. My expectation that, with full forward stick, "the AoA would have started to reduce immediately" seems to be justified up to that point and perhaps a few seconds longer.
An irony of the BEA Update is the way they are confident enough to state AoA data for moments in time when the FBW system had probably ruled the data invalid on the basis of (false) low-airspeed indications.

One possible explanation for the PF's apparent reluctance to try and pitch down before the deep stall is, as I suggested on May27, that his (unrecorded) ASI might have been over-reading. Later, about 20 seconds after passing the cruise altitude (FL350) in the descent, he said "I don't have any more indications."

At that stage in the descent, with wing AoA not quoted, but probably over +40, the BEA reports that "the PF made pitch-down inputs. In the following moments, the AoA decreased..." Was that merely coincidence?
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Old 15th Jun 2011, 16:43
  #2070 (permalink)  
 
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Originally Posted by JD-EE View Post
RR_NDB....I bet the RF was basically contained on one card
I remember nifty bits of thin coax that could be wire-wrapped, and that kept the "RF" (bus and clock frequencies) more or less where they belonged.
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Old 15th Jun 2011, 16:56
  #2071 (permalink)  
 
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Quote:
Originally Posted by JD-EE
RR_NDB....I bet the RF was basically contained on one card
I remember nifty bits of thin coax that could be wire-wrapped, and that kept the "RF" (bus and clock frequencies) more or less where they belonged.
Also common for higher frequency/critical nets was the use of twisted pair with one side wrapped to nearby ground pin. This worked fairly well up to 30Mhz or so.
I did manage to get a 66Mhz clock line to behave by slipping a tiny ferrite core over the driver pin before connecting the wire but that was definatly at the limits.

Another reason wire wrap worked fairly well was that the boards had solid ground and power planes that provided good decoupling and return paths. A common "newby" mistake was to carefully lay all the wires in neat XY rows, this resulted in really bad crosstalk, the best bet was to use direct routing and avoid parrallel runs.

As I recall the original Cray super computers used WW twisted pairs for a lot of interconnect, all of carefully specified lengths so signals would line up as desired.


Thread No 4 continues Here.
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