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Thread: USB stick data recording, blackbox-like housing?

  1. #41

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    Good starting list

    Frank: Good list to start with. I would add anything that's already on a bus as those are normally cheap and easy parameters. Angles of pitch and roll are always helpful, too.

    Now that you've opened the can of worms, engineers and accident investigators never have enough data, but designers never have enough memory ... and nobody has enough money or can afford the added weight and complexity. This is sooooooo way cool.

    Bottom line:
    You are so on track with this one. Fantastic idea. I look forward to learning more in the new thread.

  2. #42
    bwilson4web's Avatar
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    When my 30 minutes, new-thread posting was lost when my internet connection went out, I decided to
    reply with shorter notes:
    Quote Originally Posted by Frank Giger View Post
    I've been turning this over in my head as a broader project - data recording.

    Thinking that the product would be aimed at GA/homebuilding, it doesn't need to have the conprehensive data points as in commercial aviation. With that in mind, what should it record?

    First blush:

    Engine RPM
    Oil temp
    Oil pressure
    Stick and rudder positions*
    Mixture control position
    Carb temp
    Throttle position
    Airspeeds - IAS and ground (the latter handled by GPS)
    The flight profile could be handled by GPS, I reckon.

    I don't know if voice recording is really required; maybe that's because I think it would be very boring to hear me chuckling on beautiful days and growling at a less than perfect touch and go.

    Another question is data polling frequency. Maybe every second to save memory space?

    * This could be done pretty cheaply and with little weight. It's a three Hall Sensors, and the polling and recording software is used in every decent gaming HOTAS and rudder pedal set.
    These are important and offer significant information:
    • Engine RPM - yes
    • Oil temp - for climb testing, yes
    • Exhaust temperature - yes
    • GPS - absolutely, first derivative is velocity, second is acceleration
    • airspeed - complements GPS to factor out winds aloft
    I'm not so sure about these:
    • Oil pressure - cabin report is required but this really is the pressure relief valve
    • Mixture control position - calibration is a problem but EGT does a better job
    • Carb temp - cabin report for ice detection, yes, recording not so much
    • Throttle position - not so sure, fuel flow is better if available
    • Stick and rudder positions - not so sure, adds weight
    As for sample rates, generally faster is better but run-length encoding solves the volume problem. Run-length means recording a data value and a counter about how long it remains within a narrow band of values. A simple compression technique, it saves a lot of space without spending a lot of CPU cycles.

    I've found sub-second in the 0.1-0.2 range is about as fast as one wants to record. This is in the same time-scale as human response time so what one feels or does can be correlated to recorded events. Below 0.1 seconds is the range of vibration or engine tuning, not really flight recording. Above one second gets to be so coarse as to be difficult to find useful performance correlations.

    Bob Wilson

  3. #43
    bwilson4web's Avatar
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    Quote Originally Posted by steveinindy View Post
    Can I request that a few accelerometers be tossed into the mix for the sake of crash survival research? Ideally, :-At The center of mass of the aircraft-In the back rest of each of the seats (ideally would be hip height, shoulder height and one in the head rest).Measuring longitudinal, vertical and lateral accelerations.
    Many personal devices like iPhone and iPad have three axis accelerometers and there are apps to record them. However, I've found they have a lot of 'noise' and 'drift.' They are OK for short events but not really useful for vehicle studies. A better approach is to use a Gulf Coast Data Concepts, USB Accelerometer.

    I have two and used them in a Prius brake pause study. I also used one to confirm the physics of a Wichitech, tap-hammer. When I start engine and flight testing, I will use them to measure vibration of the engine vs engine mount and engine mount vs firewall anchors to look for resonances. In flight testing, I'll affix them to the elevator and aileron bell-cranks to look for the early indications of flutter and resonance. But for ordinary flying, I would use GPS recorded data.

    Now if your interest is in accident G loads, mythbusters often uses shipping "G" force, one-time use gauges. These are small, light weight units that break or indicate the maximum"G" force experienced. I just Googled "shock timer" and "shock sensor" and got several hits.

    Bob Wilson

  4. #44
    steveinindy's Avatar
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    Now if your interest is in accident G loads, mythbusters often uses shipping "G" force, one-time use gauges. These are small, light weight units that break or indicate the maximum"G" force experienced.
    Yeah, that's not accurate enough to tell anything useful in terms of actual science. It will give you some vague ideas but we already have those.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  5. #45
    Matt Gonitzke's Avatar
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    Quote Originally Posted by bwilson4web View Post

    I've found sub-second in the 0.1-0.2 range is about as fast as one wants to record. This is in the same time-scale as human response time so what one feels or does can be correlated to recorded events. Below 0.1 seconds is the range of vibration or engine tuning, not really flight recording. Above one second gets to be so coarse as to be difficult to find useful performance correlations.

    Bob Wilson
    I'll have to check my notes from my flight dynamics class in college, but I think flight test data is typically recorded at 30Hz, which is a lot more frequently than every 0.1 second. Unwanted background noise can be filtered from the data without too much trouble.

  6. #46

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    I stuck carb temp in there because icing is almost impossible to ascertain after an engine-out landing (surviveable or not); the pilot that is aware of icing and can report it almost always also deals with it before he's engine out! The probes are readily available and not horribly expensive.

    Stick and rudder position can be done at about an ounce or two, including wires - potentiometers are really light weight and small! You're right in that it's low on the totem pole - spins are a function of cross control and could be moot; I stuck it in as something I thought was pretty cool.

    I'll also admit that I put oil pressure in there because it's a gauge on the panel as much as anything else.

    I also agree that throttle position might be a less than optimal thing to measure; I put in mixture control position with the assumption that there isn't an EGT.

    Dunno about accelerometers on seats - it might become a cost and installation nightmare.

    I wonder if the computers they put in cars might be a good starting point, as they monitor a host of things and record it for download by mechanics (or at least errors - capturing the data stream itself shouldn't be that much a strain).
    The opinions and statements of this poster are largely based on facts and portray a possible version of the actual events.

  7. #47
    steveinindy's Avatar
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    Dunno about accelerometers on seats - it might become a cost and installation nightmare.
    It wouldn't be that hard and since it's not an "avionics" component, one would not have to use the more expensive TSO'd stuff.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  8. #48

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    Data at 10 times/sec (0.1 sec) would be great. The original "in-the-background" monitors recorded at 1 sample/sec, and they where useful. Looking at today's flight test data won't help much as with sub and super-comming, the rates are typically customized between 1 and 10,000 samples per second depending on the parameter. On a funny note, when I started in Flight Test, we had to change tape reals every 20 minutes or so. Today we can fly for days (literally) and record 6,000+ parameters at a main frame rate of 250 samples/sec. ... and pull off a little solid state drive when we're done.

    I vote for control positions and aircraft attitude. I still like your original list.

    On a related but somewhat different topic, I think it would be great to go after the 3 big fatal accident causes: controlled flight into terrain (CFIT), VFR into IFR, and stall. With GPS we have the ability to eliminate CFIT, aural attitude reminders could catch most of the VFR into IFR scenarios (think Kennedy), and stall is a very simple, aural AOA indicator. What this thread is doing is fantastic; it's always great to know what happened. But it would be better if we could intervene before we loose another friend.

    Bottom line: This thread topic is awesome, and YOU are how things get done. Thanks!

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