Compass Turns - IMC
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I am surprised indeed.
The turn coordinator is only accurate at 1g. The more G the less accurate the indication.
The higher the airspeed, the more bank is required in order to complete a rate 1 turn.
The more bank in a balanced turn the higher the g loading.
In general this is only theoretical since standard turns are at rate 1 or 25 deg angle of bank whichever requires the less bank.
The reason why we use the simple calculation of (airspeed (in knots)/10 ) +7 to obtain an angle of bank for rate 1 rather than simply select rate 1 on the turn coordinator (when using full pannel) is becuase of the inaccuracies of the turn coordinator.
Use the simple equation and the figures measured by contacttower and you will see the errors.
I would laso like to warn anyone about following the advice of "Enter and exit the turn with a rapid roll to/from wings level, to minimise errors. from IO540
Firstly, the turn coordinator shows roll as well as turn and that is why it is used in basic aircraft for a limited panel back-up i.e. you do not have to wait for a rate of turn to develop before discovering that your wings are not level i.e. any roll will cause movement of the indicator. Now please imaging what the turn coordinator does when you apply a large rolling moment.......how easy is it to smoothly find wings level then? Remember also what your instrument instructor taught you when doing unusual attitude recoveries - nose low and banked.
The timed turn will work well enough no matter how slowly you enter the turn provided that you enter and exit the turn at the same rate
Start the watch, start the roll to acheive rate 1. Let's say that you acheive a steady rate 1 at oh 5 seconds. When the time is up you roll out at the same rate and thus you will be back wings level 5 seconds after the required time. The turn lost while making the entry is compensated for by the extra time at the end.
Finally the single speed is the one where you can turn rate 1 in balanced flight with zero roll moment i.e. ailerons perfectly neutral (think about climbing and descending turns here) and only 1g load factor.
Don't think that I have come across that speed often.
Regards,
DFC
The turn coordinator is only accurate at 1g. The more G the less accurate the indication.
The higher the airspeed, the more bank is required in order to complete a rate 1 turn.
The more bank in a balanced turn the higher the g loading.
In general this is only theoretical since standard turns are at rate 1 or 25 deg angle of bank whichever requires the less bank.
The reason why we use the simple calculation of (airspeed (in knots)/10 ) +7 to obtain an angle of bank for rate 1 rather than simply select rate 1 on the turn coordinator (when using full pannel) is becuase of the inaccuracies of the turn coordinator.
Use the simple equation and the figures measured by contacttower and you will see the errors.
I would laso like to warn anyone about following the advice of "Enter and exit the turn with a rapid roll to/from wings level, to minimise errors. from IO540
Firstly, the turn coordinator shows roll as well as turn and that is why it is used in basic aircraft for a limited panel back-up i.e. you do not have to wait for a rate of turn to develop before discovering that your wings are not level i.e. any roll will cause movement of the indicator. Now please imaging what the turn coordinator does when you apply a large rolling moment.......how easy is it to smoothly find wings level then? Remember also what your instrument instructor taught you when doing unusual attitude recoveries - nose low and banked.
The timed turn will work well enough no matter how slowly you enter the turn provided that you enter and exit the turn at the same rate
Start the watch, start the roll to acheive rate 1. Let's say that you acheive a steady rate 1 at oh 5 seconds. When the time is up you roll out at the same rate and thus you will be back wings level 5 seconds after the required time. The turn lost while making the entry is compensated for by the extra time at the end.
Finally the single speed is the one where you can turn rate 1 in balanced flight with zero roll moment i.e. ailerons perfectly neutral (think about climbing and descending turns here) and only 1g load factor.
Don't think that I have come across that speed often.
Regards,
DFC
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The turn coordinator is only accurate at 1g. The more G the less accurate the indication.
).
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But if the AI/AH is working, chances are the DG will be, so the timed turn won't be necessary!
I guess that if you do as your instructor taught you and keep all turns gentle, you won't exceed 1g by enough to make any difference - how accurately can you hold that rate 1 turn on the TC anyway? It's a bit like flying a PAR, when the talkdown controller (bless her cotton socks) says things like 'turn right one degree, heading 003'...
Tim
I guess that if you do as your instructor taught you and keep all turns gentle, you won't exceed 1g by enough to make any difference - how accurately can you hold that rate 1 turn on the TC anyway? It's a bit like flying a PAR, when the talkdown controller (bless her cotton socks) says things like 'turn right one degree, heading 003'...
Tim
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Does that not work whatever speed you're doing?
No. The exact formula for the bank angle required for a rate 1 turn involves a bit of trigonometry, and the (TAS/10)+7 is just an approximation which works for small angles, say below 30 degrees.
The usual place to look for aviation formulae is here.
No. The exact formula for the bank angle required for a rate 1 turn involves a bit of trigonometry, and the (TAS/10)+7 is just an approximation which works for small angles, say below 30 degrees.
The usual place to look for aviation formulae is here.
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The more G the less accurate the indication.
The reason why we use the simple calculation of (airspeed (in knots)/10 ) +7 to obtain an angle of bank for rate 1 rather than simply select rate 1 on the turn coordinator (when using full pannel) is becuase of the inaccuracies of the turn coordinator.
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FWIW, this is what is said about turn indicator (not coordinator) errors in my (CAA-flavour) CPL course notes, as produced by the sadly now defunct Professional Pilot Study Centre:
"The rate of turn indicated will only be correct when the aircraft is flying at the true airspeed for which the instrument has been calibrated. Providing that the actual TAS is within 100kts of the calibrated TAS the error in indicated rate of turn should not exceed plus or minus 5% of the actual rate of turn. The instrument over-reads if TAS is higher than the calibrated airspeed."
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But if the AI/AH is working, chances are the DG will be, so the timed turn won't be necessary!
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Pprune is well up to strength on this! Irrelevences galore.
The original question is in partial panel IMC flying. You have no attitude or DI info, they are covered up. No information is available on angle of bank (or pitch). This is to simulate loss of the suction pump, which in the standard old style systems causes loss of both AI and DI.
As IO540 says, just put the TC onto rate 1 marker for the number of seconds for the required turn, at 3 deg/sec. I've always found it easy. I've never heard of a 'g' correction, but at rate 1 in a light aircraft it is negligible anyway.
The original question is in partial panel IMC flying. You have no attitude or DI info, they are covered up. No information is available on angle of bank (or pitch). This is to simulate loss of the suction pump, which in the standard old style systems causes loss of both AI and DI.
As IO540 says, just put the TC onto rate 1 marker for the number of seconds for the required turn, at 3 deg/sec. I've always found it easy. I've never heard of a 'g' correction, but at rate 1 in a light aircraft it is negligible anyway.
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Personally I prefer the UNOS (undershoot/overshoot) method i.e. non-timed. Seems to be more accurate and require less fine-tuning after roll-out. The timed method relies on your standard rate turn being spot on during the whole turn whereas monitoring the compass throughout the turn (as in the UNOS method, described above) gives you an instantaneous cue to roll out.
I often combine the two - I use the UNOS method and roll-out. If the heading is slightly off I'll correct with a short timed turn one way or the other.
Each to their own!
I often combine the two - I use the UNOS method and roll-out. If the heading is slightly off I'll correct with a short timed turn one way or the other.
Each to their own!
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The reality of timed turns is that they are suprisingly accurate.
One isn't going to be doing a 360, normally. Typical turns will be on ATC direction, say 20 left or right etc. That is about 7 seconds. You don't need a stopwatch for that - just count to 7 at about the right speed, and you will roll out on the '20' as accurately as anybody could have flown the desired heading anyway.
I never did timed turns before the IR, and every one I did was spot on, and most of the time (for the slight turns) I wasn't even using a stopwatch to time them.
Try it one day. It really works.
One isn't going to be doing a 360, normally. Typical turns will be on ATC direction, say 20 left or right etc. That is about 7 seconds. You don't need a stopwatch for that - just count to 7 at about the right speed, and you will roll out on the '20' as accurately as anybody could have flown the desired heading anyway.
I never did timed turns before the IR, and every one I did was spot on, and most of the time (for the slight turns) I wasn't even using a stopwatch to time them.
Try it one day. It really works.
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Pprune is well up to strength on this! Irrelevences galore.
MikeJ, that raises an interesting issue. However, please don’t take my comments here as a personal attack as I can assure you they’re not intended as such.
Frequently when a thread here broadens from the original post, there’s a queue of people ready to step in to criticise. But why, and for what purpose? Generally speaking, the broadening of a topic allows it to be more thoroughly explored and that, quite often, can be truly educational. Surely that’s a plus? In any event, doesn’t the ‘expanding discussion’ process merely follow normal real-life human intercourse … or are these forums (which in their entirety could be described as ‘irrelevances’ with about as much justification) supposed to create a virtual interplay that’s quite different from established social norms?
Closely related to this is the desire of posters here to close down threads that, presumably, espouse views that differ either from their own or from the accepted norm. A classic example in the last couple of days has been the ‘RT at the hold’ debate. Yes it got heated, and yes maybe one or more of the protagonists portrayed themselves as a cross between a playground bully and a foul-mouthed lout. But, close the thread down because some posters were questioning whether an ATCO’s views and CAP413 had considered all the possibilities? Why? Some of those doing the questioning combine powerful intellect with considerable flying experience. What is it that compels people to step in and attempt to ‘control’ those contributions? Indeed, in the case of the RT thread, what is it that motivated those people actually to PM BRL urging him to cull the thread?
Not normally one for psychology, yet on PPrune I’m increasingly finding these questions interesting!
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I agree Islander2, I don't see why people have a problem with thread drifts (as long as the original question has been answered, which in this case I think it has). With reference to the RT thread I was slightly disappointed that it was closed down...if people don't like a thread they can just ignore it...I don't see why they feel the need to PM the mods.
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Originally Posted by Islander2
FWIW, this is what is said about turn indicator (not coordinator) errors in my (CAA-flavour) CPL course notes, as produced by the sadly now defunct Professional Pilot Study Centre:
I'm wondering if the issue could be that the steeper the bank, the more the turn rate is produced by pitching, rather than yawing? For instance, a 90 degree banked turn would mathematically be entirely pitch, rather than yaw, and might possibly indicate no turn rate in the turn coordinator.
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Hi everyone - I had my lesson on compass turns on Friday afternoon following a classroom session with my instructor . We went over both methods ie UNOS and the timed turn. He said he didn't mind which one I used and suggested I try both before making a decision. I was rubbish at both, but was surprised to find slightly more accurate using UNOS. I thought I would find the timed method by far the easier of the two! Not entirely sure how much time is allocated to this in the air but boy will I need some practice. Now as I said in my original question has anyone got any other hot tips for the IMC! Thanks all.
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Poppy,
Just a further thought on limited panal turns. I thought about the alternative of timed v using the mag compass whilst flying yesterday.
As you know, IO540 and myself came out strongly for the timed method.
You have no direct information on angle of bank (or pitch). To fly reasonably accurately requires constant attention to the remaining primary instruments. The standard layout puts the TC at the lower left, and the ASI above it, with the Alt to the right of the blanked off AI.
The mag compass is to your right, above all other instruments, and often, as in my aircraft, roof mounted. It is outside the field of view when flying on the primary instruments. In short, you cannot see the TC and the mag compass at the same time. The more you turn your head to follow the mag compass, with all its wobbles in turbulence, as well as the previous mentioned errors, the less accurately you will be flying the aircraft in maintaining rate of turn and altitude. The timed method obviously only works if you retain the rate one turn accurately, but this I have always found easy if the mag compass is totally ignored until it will have settled 10 secs after levelling out.
In my aircraft, and I think most, the clock is within the field of view of the primaries, and I don't bother with the stopwatch. My examiners, in all the multitude of renewal tests I have taken, have normally asked for 60deg or 90 deg turns, ie 20 or 30 secs, not 20 deg which as IO says can be done simply by counting to youself. I wouldn't trust myself to count to these longer times. But given the instruction on the heading to finish on, you can always take a few seconds to know the time required, decide clock positions of the second hand for start and finish times, and start and finish the turn accordingly. As IO says, it really does work, provided you attend to keeping the TC on the rate one mark, and don't take sneaking glances at the mag compass.
It means being well practiced in simply maintaining the rate one turn, before expecting accuracy in turns to a new compass heading. Certainly for me it means that I can maintain much better altitude accuracy than if ones eyes are moving to the mag compass during the turn.
Whilst the test gives wider tolerances on accuracy when on limited panel, I have always set myself the achievement of the same tolerances of full panel flying, and really do not think I could do this if I attended to the mag compas during the turn. (And whilst I'm IMC rated, I also set myself the IR tolerances.)
Just a thought.
Just a further thought on limited panal turns. I thought about the alternative of timed v using the mag compass whilst flying yesterday.
As you know, IO540 and myself came out strongly for the timed method.
You have no direct information on angle of bank (or pitch). To fly reasonably accurately requires constant attention to the remaining primary instruments. The standard layout puts the TC at the lower left, and the ASI above it, with the Alt to the right of the blanked off AI.
The mag compass is to your right, above all other instruments, and often, as in my aircraft, roof mounted. It is outside the field of view when flying on the primary instruments. In short, you cannot see the TC and the mag compass at the same time. The more you turn your head to follow the mag compass, with all its wobbles in turbulence, as well as the previous mentioned errors, the less accurately you will be flying the aircraft in maintaining rate of turn and altitude. The timed method obviously only works if you retain the rate one turn accurately, but this I have always found easy if the mag compass is totally ignored until it will have settled 10 secs after levelling out.
In my aircraft, and I think most, the clock is within the field of view of the primaries, and I don't bother with the stopwatch. My examiners, in all the multitude of renewal tests I have taken, have normally asked for 60deg or 90 deg turns, ie 20 or 30 secs, not 20 deg which as IO says can be done simply by counting to youself. I wouldn't trust myself to count to these longer times. But given the instruction on the heading to finish on, you can always take a few seconds to know the time required, decide clock positions of the second hand for start and finish times, and start and finish the turn accordingly. As IO says, it really does work, provided you attend to keeping the TC on the rate one mark, and don't take sneaking glances at the mag compass.
It means being well practiced in simply maintaining the rate one turn, before expecting accuracy in turns to a new compass heading. Certainly for me it means that I can maintain much better altitude accuracy than if ones eyes are moving to the mag compass during the turn.
Whilst the test gives wider tolerances on accuracy when on limited panel, I have always set myself the achievement of the same tolerances of full panel flying, and really do not think I could do this if I attended to the mag compas during the turn. (And whilst I'm IMC rated, I also set myself the IR tolerances.)
Just a thought.
