Compass Turns - IMC
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Compass Turns - IMC
Hi, can anyone give me some useful tips for doing accurate compass turns on a partial panel. I have just started my IMC so in fact any uselful 'rules of thumb' or tips related to helping me through this rating would be really appreciated. Thanks
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I was told by my instructor not to do compass turns...just do timed ones instead. 3 degrees/second = rate one. They can be done though and this is what I was taught:
If you undershoot when turning onto northerly headings by 30 degrees and overshoot the same for southerly ones then they usually work out OK. Just remember to always give the compass time to settle and also that when you look at a W compass you have to turn away from the digits to get to them.
If you undershoot when turning onto northerly headings by 30 degrees and overshoot the same for southerly ones then they usually work out OK. Just remember to always give the compass time to settle and also that when you look at a W compass you have to turn away from the digits to get to them.
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Agree timed turns, followed by let the compass settle and check, are the way forwards, and I was only taught this method - precisely to avoid the dip problems of compass turns. Though in the event of electrical failure (hence failure of the turn indicator/coordinator) you'd have to know your bank angle for a rate 1 turn (calculated from speed, of course, though I forget the formula because I know what it looks like on the ac I usually fly!)
Tim
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Originally Posted by tmmorris
Though in the event of electrical failure (hence failure of the turn indicator/coordinator) you'd have to know your bank angle for a rate 1 turn (calculated from speed, of course, though I forget the formula because I know what it looks like on the ac I usually fly!)
Tim
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Bit odd for me to say this as I have just done an IMC but why dont you ask the guy sat in the right hand seat ? I assume you trust him and value his input or you wouldnt be paying out a shxt load of money . Thats what he is there for surely
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1. Put your heading on the ADF Card. It helps you to remember what you should see on the compass. It also helps orientate you so that you know if xxx heading is a left or right turn.
2. Using timed turns is easier than reference to the compass but a combinaion of both is best.
3. Look at the ADF. Heading Digits are placed every 30deg.
Rate 1 is 3 deg/ second.
Thus when asked to turn onto xxx heading complete the following;
1. Confirm that the compass heading is still what it should be. If not, reset the ADF card.
2. Count the number of 30deg segments and multiply by 10 seconds.
3. Count the remaining 10 deg segments and multiply by 3 seconds.
Add both together to get timing.
eg heading 290 and asked to turn onto 180
look at card you have 3 30degree segments plus 2 10degree segments. = (3*10) + (2*3) = 33 seconds.
It is a timed turn so Start time then start turn. When time is up, stop turn.
Remember that the turn "co-ordinator" is calibrated for a specific speed and only shows rate 1 if you have 1g, ball in the middle and this speed. However, for the IMC rating simply peg rate 1 and fly in balance.
Having leveled the wings and re-established straight and level flight, check compass. For adjustments of up to 20 degree simply count 1 banana, 2 banana etc For 20 deg plus do another timed turn.
For the compass turn remember to undershoot the nearest pole. Thus in the northern hemisphere undershoot north, overshoot south, no error east or west.
Keep bank angles to 15deg or less to avoid locking the compass card.
The error is about 30degrees at north or south and 0 at East or West. That means if turning onto a heading of north, you stop the turn 30 degrees before you get there. If turning onto south you stop the turn 30 degrees after you pass south.
If turning onto east or west then you stop the turn on the heading.
For points in between simply judge how much to use i.e. a turn onto 045 degrees is under shoot by roughly 15 degrees. i.e. stop tuen 15 degrees before you get there.
As I said previously, the best thing to do is a combination of the two. i.e. Doing a timed turn but if passing through east or west during the turn check that this happens at about the right time.
The most important thing is to be able to fly a constant heading when not turning. It is wandering all over the sky during straight and level that fails most instrument pilots. The turns are expected to firstly be in the correct direction, secondly get you into the ball park heading and thirdly to be finally corrected to the chosen heading which is then maintained.
Hope that helps.
Regards,
DFC
2. Using timed turns is easier than reference to the compass but a combinaion of both is best.
3. Look at the ADF. Heading Digits are placed every 30deg.
Rate 1 is 3 deg/ second.
Thus when asked to turn onto xxx heading complete the following;
1. Confirm that the compass heading is still what it should be. If not, reset the ADF card.
2. Count the number of 30deg segments and multiply by 10 seconds.
3. Count the remaining 10 deg segments and multiply by 3 seconds.
Add both together to get timing.
eg heading 290 and asked to turn onto 180
look at card you have 3 30degree segments plus 2 10degree segments. = (3*10) + (2*3) = 33 seconds.
It is a timed turn so Start time then start turn. When time is up, stop turn.
Remember that the turn "co-ordinator" is calibrated for a specific speed and only shows rate 1 if you have 1g, ball in the middle and this speed. However, for the IMC rating simply peg rate 1 and fly in balance.
Having leveled the wings and re-established straight and level flight, check compass. For adjustments of up to 20 degree simply count 1 banana, 2 banana etc For 20 deg plus do another timed turn.
For the compass turn remember to undershoot the nearest pole. Thus in the northern hemisphere undershoot north, overshoot south, no error east or west.
Keep bank angles to 15deg or less to avoid locking the compass card.
The error is about 30degrees at north or south and 0 at East or West. That means if turning onto a heading of north, you stop the turn 30 degrees before you get there. If turning onto south you stop the turn 30 degrees after you pass south.
If turning onto east or west then you stop the turn on the heading.
For points in between simply judge how much to use i.e. a turn onto 045 degrees is under shoot by roughly 15 degrees. i.e. stop tuen 15 degrees before you get there.
As I said previously, the best thing to do is a combination of the two. i.e. Doing a timed turn but if passing through east or west during the turn check that this happens at about the right time.
The most important thing is to be able to fly a constant heading when not turning. It is wandering all over the sky during straight and level that fails most instrument pilots. The turns are expected to firstly be in the correct direction, secondly get you into the ball park heading and thirdly to be finally corrected to the chosen heading which is then maintained.
Hope that helps.
Regards,
DFC
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Remember that the turn "co-ordinator" is calibrated for a specific speed and only shows rate 1 if you have 1g, ball in the middle and this speed. However, for the IMC rating simply peg rate 1 and fly in balance.
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DFC is very correct.
If you can find a picture of the internal workings of the Turn Coordinator, all the better. If not imagine a tyre sitting up with the gimbal system attached to the holes in the wheel and springs below this. Crude I know
OK... the gyro spins (say away from you) and an aircraft enters a left turn...the turn is felt as a "push" on the gyro (thinking of the tyre its felt at the 3 o'clock position - now looking at the tyre from the side) through precession (because the gyro is spinning) the system feels the push at the top (12 o'clock). This pushes the gyro (tyre) down and to the right, and through gears the needle goes left.
I hope that made sense.
Now, as the aircraft speed is incresed it takes more initial push for the precession to show the same amount turn on the dial. The only way for you to increase the precession is to increase the angle of bank (which is what you have to do with an increased speed for rate 1).
So it does not sense the speed, but rather the new force and resultant precession as a result of the increase angle of bank for the speed.
If you can find a picture of the internal workings of the Turn Coordinator, all the better. If not imagine a tyre sitting up with the gimbal system attached to the holes in the wheel and springs below this. Crude I know
OK... the gyro spins (say away from you) and an aircraft enters a left turn...the turn is felt as a "push" on the gyro (thinking of the tyre its felt at the 3 o'clock position - now looking at the tyre from the side) through precession (because the gyro is spinning) the system feels the push at the top (12 o'clock). This pushes the gyro (tyre) down and to the right, and through gears the needle goes left.
I hope that made sense.
Now, as the aircraft speed is incresed it takes more initial push for the precession to show the same amount turn on the dial. The only way for you to increase the precession is to increase the angle of bank (which is what you have to do with an increased speed for rate 1).
So it does not sense the speed, but rather the new force and resultant precession as a result of the increase angle of bank for the speed.
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So it does not sense the speed, but rather the new force and resultant precession as a result of the increase angle of bank for the speed.
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I see where youre coming from now...
yes you could make that argument that it does work "through a range of speeds" with the fact that it will show rate of turn at varying speeds - and good enough to use in IMC...but if it showed up as an answer to a question on an exam or during a flight test, Id be weary at picking it without considering all the other options.
It will only show the proper rate at one airspeed though, as DFC stated. However, for say a C152 or PA28 the speeds they go are slow enough to ignore the error - with the error also depending on mechanical errors like friction, wear and tear, et al.
Remember too that (and I assume this is the same with the JAR's - correct me if Im wrong) when IFR your turns should always be at rate 1 or 30* of bank, which ever is the least, so above 230 knots you will always be 30* and below it will be rate 1.
But if you can get to 230 in 152 without becoming an unintentional parachutist...youre a better pilot than I.
yes you could make that argument that it does work "through a range of speeds" with the fact that it will show rate of turn at varying speeds - and good enough to use in IMC...but if it showed up as an answer to a question on an exam or during a flight test, Id be weary at picking it without considering all the other options.
It will only show the proper rate at one airspeed though, as DFC stated. However, for say a C152 or PA28 the speeds they go are slow enough to ignore the error - with the error also depending on mechanical errors like friction, wear and tear, et al.
Remember too that (and I assume this is the same with the JAR's - correct me if Im wrong) when IFR your turns should always be at rate 1 or 30* of bank, which ever is the least, so above 230 knots you will always be 30* and below it will be rate 1.
But if you can get to 230 in 152 without becoming an unintentional parachutist...youre a better pilot than I.
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" It will only show the proper rate at one airspeed though, as DFC stated."
This is really not correct. A properly operating turn coordinator directly measures *rate of turn* through gyroscopic techniques. It is independent of airspeed. If you have the aircraft stationary on the ground, put it on a turntable and turn it at standard rate, 3 deg/sec, the turn coordinator (or turn and slip) will show a Rate 1 turn.
This is really not correct. A properly operating turn coordinator directly measures *rate of turn* through gyroscopic techniques. It is independent of airspeed. If you have the aircraft stationary on the ground, put it on a turntable and turn it at standard rate, 3 deg/sec, the turn coordinator (or turn and slip) will show a Rate 1 turn.
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Forget the compass during the turn - it reads rubbish.
Only a fresh graduate of the CAA/JAA "must sort the men from the sheep" exam system will remember which way the compass errors go, and few people will be able to remember this nonsense under any sort of workload in a real partial panel situation.
Times turns are the only way - 3 degrees per second. Enter and exit the turn with a rapid roll to/from wings level, to minimise errors.
The turn coordinator reads Rate 1 irrespective of airspeed !!
Only a fresh graduate of the CAA/JAA "must sort the men from the sheep" exam system will remember which way the compass errors go, and few people will be able to remember this nonsense under any sort of workload in a real partial panel situation.
Times turns are the only way - 3 degrees per second. Enter and exit the turn with a rapid roll to/from wings level, to minimise errors.
The turn coordinator reads Rate 1 irrespective of airspeed !!
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My method (avoids hard caculations).... set the ADF card as you've described. Pretend it's the face of a clock (analogue !) . When you have a second hand on a clock it sweeps past each 'major' division every 5 seconds. So, read round ADF card to from 'north' to your required heading and count seconds for each major division, 5 seconds, ten seconds, 15 seconds, etc. [Easier done than described]. Then double it. That's the time required to turn at rate1.
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My method (avoids hard caculations).... set the ADF card as you've described. Pretend it's the face of a clock (analogue !) . When you have a second hand on a clock it sweeps past each 'major' division every 5 seconds. So, read round ADF card to from 'north' to your required heading and count seconds for each major division, 5 seconds, ten seconds, 15 seconds, etc. [Easier done than described]. Then double it. That's the time required to turn at rate1.
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Originally Posted by DFC
Remember that the turn "co-ordinator" is calibrated for a specific speed and only shows rate 1 if you have 1g, ball in the middle and this speed. However, for the IMC rating simply peg rate 1 and fly in balance.
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Not speed dependant at all. A rate one turn will produce 3 degrees a second turn. In a minute, you will have turned 180 degrees. The faster you go, the larger the radius of turn, but you would have still only turned 180 degrees. One of the reasons published holds have a max speed rating to keep you in the protected area.