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  1. #21
    Captain Bill Scott's Avatar
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    Speaking as an old fart but somewhat younger in flying hours, I agree wholeheartedly with Phil. Flying up above broken clouds, dartimg between them and so forth is all very well, but I've no interest in embarking on IFR flight through a solid layer of cloud. To do so is dangerous, full stop.
    However, there is a chap on this forum who has tested a pair of 'foggles' as a flying aid for more testing conditions


  2. #22
    Captain Phil Perry's Avatar
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    Thanks Bill,

    And I didn't know that the Iphone FOUR had a genuine GYRO built in...... but nonetheless, I have read in this forum that some of you STILL believe that it is perfectly possible to fly in cloud without a properly fitted and calibrated gyro horizon. . . . .

    It Isn't, and it never was. Physiomedical dynamics do not permit it.. . . .and never will.

    The above advice from another poster with regard to Instrument Appreciation flight in a properly equipped aircraft along with an instructor, is probably the best advice I've seen today.
    Last edited by Phil Perry; 28-12-10 at 19:13 PM.
    Skype : PilotPhil312 E: cosigngraphic@yahoo.co.uk Ham Radio Station - G4 OHK 10 Mtres FM, 2 metres fm, 70 centimetres fm, and lurking about on15, 20 and 40 metres ssb as well. . . . .


  3. #23
    Co-Pilot ANDY1973's Avatar
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    The Problem with GPS based Attitude Reference



    This video gives a great demonstration of why using GPS as an attitude reference is fraught with danger.

    The Problem

    Play the video from the start. At about 10 secs, the aircraft rolls to the right; pause the video when the wings are level (it's at about 15 sec). Try and stop it with the horizon perfectly level. Now compare the horizon with the attitude reference on the Garmin. It shows about 35 degrees left wing low with the horizon level!

    Why Does This Happen

    The problems all stem from the inherent delays in a GPS system.

    GPS systems give a very accurate position. But they do this by averaging out lots and lots of position readings and using some very clever maths to come up with an average. This averaging out all takes a bit of time to carry out, which is the source of the problem.

    GPS systems also give us a track. They do this by looking at where they are right now, and comparing that with where they were a moment ago. As they are comparing the present with the past, there is a bit of a delay in showing a change of track. To understand this, imagine that you are heading North, and then were able to turn instantly onto East. The GPS is showing your track based on where you are now with where you were, say, 1 second ago. As you start heading East, the GPS would still show you heading North. Half a second later it would show heading North-East, and only 1 second after you made the turn would it actually show you on the correct track. That's a bit of a wordy explanation, but I hope you can see that deriving track from GPS positions is always going to have a bit of lag in it.

    To give the display of bank angle, the GPS looks at rate of change of track. It then makes a couple of assumptions to derive bank angle. It assumes that the change of track has all come about by a level & balanced turn being made (try turning with rudder in a 3-axis and the GPS will show an angle of bank instead; I suspect that for a flex it would just mean that the bank angle is inaccurate as the aircraft is unlikely to be in balance in a turn). If you roll the wings to a given bank angle, it takes a little bit of time for the turn to get going (adverse yaw, inertia etc) so we have yet another source of lag in the system.

    Also, there in the same way that it takes a moment or two for the GPS to work out your track from two positions, it also takes a little while for the GPS to work out your rate of change of track!

    So, we have lag in deriving a GPS position, we have lag in calculating an aircraft track from those positions, and we have lag in calculating the rate of change of track. That is why in the video above it takes maybe 3 or 4 secs before the GPS actually shows the attitude of the aircraft.

    Is this a big problem?

    Damn straight it is! But I'm going to put the kettle on before I try and convince you!

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  5. #24
    Co-Pilot ANDY1973's Avatar
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    Why Lag is a Really, Really Bad Thing in a Control System

    I hope you agree from the video that there is a lag in the attitude display from the GPS system (and that's a purpose built Garmin 496 there!), and hope that the explanation why was reasonable convincing. The big question that follows is "So what!?!"

    It all comes down to a bit of control theory. One way to analyse aircraft flight is to think of the aeroplane, instruments and pilot as one system. We make a control input with the stick, bar, throttle, pedals or whatever. The aircraft responds. We look to see if the response is what we wanted, then make a correcting input on the controls. In essence, we are the "feedback" in the system that keeps everything under control.

    Control theory can get very mathematical and complicated very quickly, and there are very few hard or fast rules; except one, big one. Any delay or lag in the feedback loop is a very bad thing. And to illustrate why, I'd like to introduce a simple demonstration.

    The Hotel Shower - No lag

    Let's imagine you're in a nice 5* hotel. You step under the shower; the water's just a little bit too cold. You turn the clearly labelled temperature controller clockwise just a smidge and the water instantly responds by warming up to the perfect temperature. Sounds good, eh!

    The Hotel Shower - With Lag

    This is probably a more realistic scenario for most of us. Let's now imagine that we're in a hotel where the shower takes ages to respond to any movements of the controller. Perhaps it takes 10 secs for the boiler to respond to any command from the shower.

    So get under the slightly cold water, and turn the controller clockwise to try and warm it up. Nothing happens, so we turn it a bit more, and a bit more, and a bit more. Finally it starts to warm up and it gets to a temperature we like. However, this is actually the setting we had 10 seconds ago. So although we now leave the controller alone, the water continues to get hotter and hotter. We turn the temperature controller down, but the water is still getting hotter. You can't help yourself now, as the water is burning, so you turn the controller all the way down. It starts to get cooler, then gets nice, then starts to freeze. You then turn the controller up, and the cycle starts again.....

    What has this got to do with aircraft?

    The delay in the attitude reference with a GPS, works just like the delay in the shower control system. When we stopped the video at 15s, the aircraft was wings level, just where we wanted it. But in cloud, with the attitude reference showing 35 degrees angle of bank we would have been putting in the control input to get the aircraft to roll. By the time the attitude reference showed wings level, we might have been at 35 degrees angle of bank in the opposite direction. This is, most definitely, a bad thing and is the start of what is known as Pilot Induced Oscillation (or aircraft-pilot coupling if you don't like the implicit blame in "pilot induced")

    There's more to it than just the delay in deciding whether or not the system would have a divergent tendency to PIO. But a large delay is very, very likely to make the aircraft uncontrollable. And there is one more factor which makes PIO more likely.

    In the shower example, it would be a lot easier to get out of the cycle of turning the water up then down if we weren't standing under alternately freezing then scalding water. But if the skin is blistering on your back, you won't be able to turn the tap down slowly, waiting 10 seconds between each movement. Likewise, if you are in cloud and afraid that you are imminently going to die in a ball of flame and twisted metal, you will not be able to make small control inputs then wait a few seconds between each one to see if it has had an effect.

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  7. #25
    Co-Pilot ANDY1973's Avatar
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    Conclusion

    A GPS based attitude reference is not really an attitude reference. Rather it uses a "wings" indicator to show which way you were turning a few secs ago.

    It does not provide any information that the aircraft compass does not give you more accurately.

    Because of the inherent delay with the instrument it is highly likely that it would be difficult for an experienced instrument rated pilot to maintain control of the aircraft in IMC, and highly unlikely that a successful recovery from an unusual attitude could be made.

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  9. #26
    Captain Sean McDonald's Avatar
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    Thanks Andy - I've just done 10 hours initial training and obviously have a lot to learn (as opposed to being thick). I found the shower analogy very useful and I'm sure others will too.


  10. #27
    Roger Mole
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    This old chestnut seems to keep coming up and invariably it starts in the same sort of way - someone has got into cloud either by accident or design and how, although they found it scary, say that they now reckon they'd be able to get themselves out of trouble if/when a similar thing happened to them in the future. Unfortunately though you never hear from the ones who did something similar and didn't get away with it - mainly because they're not around now to tell the story. When you read Dave's account of what he was doing it's easy to get very blase, say 'I told you so', and poo poo all the 'old farts' who then jump up and tell you not to do it. But the difference is that the ones who tell you not to do it always include people who have had some kind of IMC training whereas the ones who tell you to go ahead almost certainly do not.

    I don't know if it's because when you start IMC training you need to be shocked, but in the very early stages you have an exercise when your instructor tells you to shut your eyes and tell him what the aircraft is doing while he has control. Then he asks you to open your eyes and without exception every new instrument trainee is amazed when they open their eyes and see how mistaken they are, not just once but several times to drum the lesson in. What's the lesson - you can't rely on your senses, no matter how clever or experienced you might think you are. You have to rely on your instruments.

    So for starters, where does that leave us with microlights? Well, you can't just buy any old Chinese made cheap bit of kit and expect to rely on it to save your life. So that excludes a lot of the stuff that we fit into our kites. Also, for even the best quality, calibrated instruments to be fit for IMC purpose, they have to be installed in a stable instrument platform, and I'm sorry chaps but that excludes just about all microlights in my book. Flying for a long period in IMC in a light group A single is exhausting enough - and that's in something which has considerably more inertia and is much more trimmable in level flight than any microlight that I know of.

    'Phooey', you say, stick in an electric AH and you're good to go. Well maybe you'll get away with it if you're lucky with no proper IMC training in a fixed wing - but in a flex? Forget it. It's been shown time and again and there has been an ongoing debate going on for months if not years as far as I'm aware, regarding the fact that an AH just doesn't work properly in a flex (what do you attach it to - the pod or the wing because neither gives the right results). I've watched and read it with interest and as the main proponents looking for effective solutions are big flex enthusiasts, I have to conclude that at present at least, it has to be fact. And as I also recall from the work that I've read about that was done a year or two ago by University researchers (was it under Guy Grattan?) it was demonstrated that in zero vis cloud even an experienced flex pilot lost control and was well on the way to a tuck on average within I think it was 19 seconds.

    Anyway, there you go for what it's worth. As far as I can see we who fly microlights are disadvantaged in all of the three essentials for safe IMC flight - instruments, instrument platform and training, but you need to make your own mind up. But please bear in mind what I said above before you stick your neck out and go cloud flying - I don't know of anyone who has had IMC training saying 'Yeah, go on, have fun, just do it'. It's only the ones who haven't who do. That's in my experience anyway.

    One last thing - during IMC training you start by learning how to fly in IMC with a full panel and as you progress and become more experienced, your instructor begins to knock instruments out. And when he does, it's amazing how quickly you revert to making the kind of errors that could easily be fatal - so flying with a partial panel takes quite a bit of skill and practise. So how can you expect to fly successfully in IMC in a microlight which has a much reduced partial panel, and without proper training? You might be lucky, on the other hand......
    Last edited by Roger Mole; 30-12-10 at 20:57 PM.

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  12. #28
    P Kelsey
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    Short & sweet answer is : Don't even think about getting into IMC in any Microlight ( Yes a 3 axis microlight with a Gyro Artificial Horizon or Electric Artificial Horizon will probably give the pilot a chance of survival, but still not advised ) but getting into IMC in a flexwing is almost certain to end badly.

    Sadly Martin Bromage's accident is a terrible reminder of this and he was classed as a very experienced microlight pilot.
    Last edited by VinceG; 31-12-10 at 20:20 PM.


  13. #29
    Captain Phil Perry's Avatar
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    Hi Guys,

    Andy's brilliant ( in my view ) post on this subject highlights two important points. If an aircraft is to be flown in zero visibility, the attitude feedback information MUST come from the aircraft system itself, and NOT from a remote source, whether this is a bunch of satellites or whatever, otherwise there will always be time lag which is unacceptable.

    Secondly, TRAINING.

    Roger has hit this on the nail precisely, so there is no need to add to it.

    There will always be those who will want to push outside the standard envelope, whether this be through boredom with "Normal" safe flight after a while..., or a genuine desire to KNOW for personal achievement. We are all aware that the pioneers achieved the level of technology we now enjoy by doing just that; but along with the advancements comes an extension of the KNOWLEDGE BASE, with it's attendant risks.

    I don't have any idea if flexwing development will, one day permit safe flight in solid IMC; perhaps it will, perhaps the very physics of the machine will finally preclude this, but one thing IS certain in my opinion,.. this subject WILL continue tho pop up with new people entering the pastime.

    The difference between IMC in a three axis platform has been mentioned above, in the sense that it may be safer to attempt such flight if "Wearing" a stick and rudder; in my experience as a flying instructor on light aircraft many years since this was most certainly NOT the case, unless all of the students I had were equally lacking in hand / eye coordination, and this I strongly doubt.

    In all first time cases where a student was exposed to actual IMC with a FULL panel, ( Not just a Chinese AI or a GPS ! ) the student almost invariably began to get into some kind of difficulty with spatial disorientation effects beng evident in sometimes less than forty seconds. This is why it takes many hours of rigorous training before a pilot can demonstrate safe control in these conditions, AND THEN IT HAS TO BE PRACTICED on a reasonably regular basis.

    The UK IMC rating is a very good start, I sincerely hope that the Europeans don't wreck this rating, but even this is only about a quarter of the training required for a full instrument rating. The fact that there are very few private pilots in this country who posess such a rating should tell you something.

    The arguments will go on, and the old farts will continue our attempts to advise!!

    HAPPY NEW YEAR EVERYONE.
    Skype : PilotPhil312 E: cosigngraphic@yahoo.co.uk Ham Radio Station - G4 OHK 10 Mtres FM, 2 metres fm, 70 centimetres fm, and lurking about on15, 20 and 40 metres ssb as well. . . . .

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  15. #30
    Roger Mole
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    Thank you Phil, from someone who had such a rating in another life

    I know from the snippets I've garnered about your past life and experiences that you and Andy, of course, have gone much, much further than I though, and I have the greatest respect for your knowledge and experience. Having seen how discussions on this subject, elsewhere mainly, have ended up going I would never dream of trying to lecture anyone about it. I would just end by saying one thing, though. Please don't treat cloud and poor vis lightly, because in flying, it's when you least expect it that you get your bum bitten. As Phil mentioned earlier, with cloud can come icing and heaven forbid that just when you're having loadsa fun demonstrating your mastery of the white stuff that at that precise moment your donkey decides to stop. In my case, because I have a high mounted engine, when I reduce torque, I have to shove the nose down. What do you need to do? Do you think you can cope with all the workload that you'll have at that moment and be able to concentrate on your instruments to retain some kind of control in zero vis? Do you want to try?


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