Tracking and intercepting NDBs
Why do it if it's not fun?
Joined: Jul 2001
Posts: 4,782
Likes: 12
From: Bournemouth
Get a copy of RANT, and practice, practice, practice!
Another way of looking at it, though: surely your school shouldn't put you forward for any kind of check or test unless they think you're ready? Which leaves one of two options.
Either your school is being less than competent by putting you forward for the check too early, in which case have a chat with your instructor, and if you can't delay the test until you're happy then find another, more understanding, school.
The other option is that your instructors believe that you are at an appropriate standard to be able to do this stage check, and you are setting yourself standards which are too high for your experience.
FFF
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Another way of looking at it, though: surely your school shouldn't put you forward for any kind of check or test unless they think you're ready? Which leaves one of two options.
Either your school is being less than competent by putting you forward for the check too early, in which case have a chat with your instructor, and if you can't delay the test until you're happy then find another, more understanding, school.
The other option is that your instructors believe that you are at an appropriate standard to be able to do this stage check, and you are setting yourself standards which are too high for your experience.
FFF
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Moderator
Joined: Mar 2003
Posts: 2,586
Likes: 0
From: Orlando, Florida
As a slight response to the original question - and possibly something that will only be understood by people who already know how to do NDB tracking - I remember an instructor saying,
"Only look at the top half of the instrument. One end of the needle will be in there - either the pointed (correct) end or the blunt (wrong) end.
Look at the bearing suggested by the needle - is it what you want? If the answer is "No", then turn. Assuming "correct" end of needle turn the correct (same) way (if it's right of what you want, turn right - if it's pointing left of what you want, turn left).
If it's the "wrong" end of the needle turn the "wrong" way. If it points left, turn right."
How much to turn by is another question
"Only look at the top half of the instrument. One end of the needle will be in there - either the pointed (correct) end or the blunt (wrong) end.
Look at the bearing suggested by the needle - is it what you want? If the answer is "No", then turn. Assuming "correct" end of needle turn the correct (same) way (if it's right of what you want, turn right - if it's pointing left of what you want, turn left).
If it's the "wrong" end of the needle turn the "wrong" way. If it points left, turn right."
How much to turn by is another question
Joined: Dec 1998
Posts: 4,282
Likes: 6
From: Escapee from Ultima Thule
The display in the aircraft has an influence on doing things.
An RMI allows you to look at your position using the RMI & needle as a plan view of your position w.r.t. the aid & desired track/bearing. Think of the instrument as an 'astronaut's eye view' of the aircraft, the navaid & 360 deg bearings around the aid.
In this view the following applies:
* The pivot point of the needle represents the NDB (or VOR if you have a VOR/ADF selectable RMI),
* The compass rose represents the earth underneath the aircraft, oriented 'heading up'. Similar to 'track up' on a moving map GPS.
* The aircraft is positioned on the tail of the needle, heading 'up' the instrument panel, and
* Scale is proportional to the most distant item to be visualised. Usually it's the aircraft range but it could be a bearing/distance to be intercepted.
With the above in mind the following information is shown or can be derived:
* Bearing from the navaid (radial if using a VOR data source) by reading the compass rose adjacent to the tail of the needle.
* Bearing to the navaid from the head of the needle
* Relative position & orientation of any desired bearing to or from the navaid.
* With a little bit of practice, the approximate heading needed to intercept another bearing/radial at any distance along the new bearing/radial. This is often referred to as the 'point to point' method. If you plotted this on a CR type flight computer then you can also read the track distance from your current position to the desired intercept point using the CR's underlying graticule.
Unfortunately this is difficult to describe without using diagrams or a model but I'll have a go. Bear in mind pictures.....thousand words...etc etc. so forgive me if prose fails.
Orientation first:
Scenario 1: Imagine flying North on a bearing/radial of 180 deg. That would have the RMI showing a 360 deg Hdg for the a/c, the tail of the needle would show 180 deg (the bearing from the navaid/radial the aircraft is on), the head would show 360 deg (bearing to the station). Try to imagine a miniature a/c mounted on the tail of the needle **always** pointing up the instrument panel & the navaid in the centre. The RMI would also show the 150 bearing from the station to be to your right, crossing at an angle from rear R --> front L & meeting your current track at the navaid. Do the same exercise for other bearings & try to picture where they are in relation to the a/c's position. You could use the wind side of a flight computer to do this exercise.
Scenario 2: Flying N. but positioned on the 270 deg bearing from the navaid. The RMI would still show 360 for the Hdg but the tail of the needle will be on 270 (ie bearing from the navaid) & the head on 090 (the bearing to the station). Still try to imagine the miniature a/c mounted on the tail of the needle. That would show the a/c on the 270 bearing and a right turn of 90 deg is needed to track 090 to the station. The 300 bearing crosses from front L --> rear R, the 240 bearing behind from rear L to abeam at the station.
Similarly to Scenario 1, picture other bearings on the RMI.
Interception:
Once you can picture the a/c position on the RMI and where a desired bearing is then it's also possible to see how much to turn to have a track that will cross the desired bearing at some point before or after the navaid.
A development of this is to use the circumference of the RMI to represent the largest distance in the intercept problem eg if you're at 20 nm & want to intercept a bearing at 10 nm then the circumference equates to 20 nm and the point to intercept would be midway between the circumference & the centre along the desired bearing. Using this then a straight line between the two points is also the track to get there. To find the required heading, match a parallel line that starts from the centre of the RMI & goes to the circumference - I use my pen or pencil. Whatever compass direction is under your pen is the heading needed to get to the intercept point**.
This sort of technique - particularly the orientation part - can be used on a standard fixed card ADF in combination with the the a/c's Direction Gyro. You'll need to use your pen (or count convenient divisions from the head/tail/left or right abeam to the head/tail of the ADF needle. Transpose the pen's orientation (or the same number of divisions in the same rotational direction as on the ADF) onto the DG. This is a pseudo-RMI since those same divisions you count mark where the ADF needle would be *if* the DI was also an RMI.
You could also rotate the ADF card if it's a rotating card type. I generally don't because I can't be bothered having to do it for every single heading change. I'd rather count the convenient divisions on the ADF & then count the same amount on the DI to find where the ADF needle would be
Once on a heading to intercept it's important to confirm that the heading is appropriate to achieve what you intend. On an outbound intercept the TAIL of the needle must be in a position to RISE towards the desired bearing (on an RMI) or rise towards the same number of divisions on a fixed card as there are between your HDG & the bearing on the DG. For an inbound intercept the HEAD of the needle must be on the opposite side of the nose as the heading is from the desired bearing ie HDG to the left of the desired bearing then head of needle to the right of the nose) AND in a position to fall to the bearing.
**In nil wind. Any wind will put an error in this no different to flight planning on the ground using track as heading techniques. Bear in mind it's all based on an NDB so utmost precision is hardly to be expected.
An RMI allows you to look at your position using the RMI & needle as a plan view of your position w.r.t. the aid & desired track/bearing. Think of the instrument as an 'astronaut's eye view' of the aircraft, the navaid & 360 deg bearings around the aid.
In this view the following applies:
* The pivot point of the needle represents the NDB (or VOR if you have a VOR/ADF selectable RMI),
* The compass rose represents the earth underneath the aircraft, oriented 'heading up'. Similar to 'track up' on a moving map GPS.
* The aircraft is positioned on the tail of the needle, heading 'up' the instrument panel, and
* Scale is proportional to the most distant item to be visualised. Usually it's the aircraft range but it could be a bearing/distance to be intercepted.
With the above in mind the following information is shown or can be derived:
* Bearing from the navaid (radial if using a VOR data source) by reading the compass rose adjacent to the tail of the needle.
* Bearing to the navaid from the head of the needle
* Relative position & orientation of any desired bearing to or from the navaid.
* With a little bit of practice, the approximate heading needed to intercept another bearing/radial at any distance along the new bearing/radial. This is often referred to as the 'point to point' method. If you plotted this on a CR type flight computer then you can also read the track distance from your current position to the desired intercept point using the CR's underlying graticule.
Unfortunately this is difficult to describe without using diagrams or a model but I'll have a go. Bear in mind pictures.....thousand words...etc etc. so forgive me if prose fails.
Orientation first:
Scenario 1: Imagine flying North on a bearing/radial of 180 deg. That would have the RMI showing a 360 deg Hdg for the a/c, the tail of the needle would show 180 deg (the bearing from the navaid/radial the aircraft is on), the head would show 360 deg (bearing to the station). Try to imagine a miniature a/c mounted on the tail of the needle **always** pointing up the instrument panel & the navaid in the centre. The RMI would also show the 150 bearing from the station to be to your right, crossing at an angle from rear R --> front L & meeting your current track at the navaid. Do the same exercise for other bearings & try to picture where they are in relation to the a/c's position. You could use the wind side of a flight computer to do this exercise.
Scenario 2: Flying N. but positioned on the 270 deg bearing from the navaid. The RMI would still show 360 for the Hdg but the tail of the needle will be on 270 (ie bearing from the navaid) & the head on 090 (the bearing to the station). Still try to imagine the miniature a/c mounted on the tail of the needle. That would show the a/c on the 270 bearing and a right turn of 90 deg is needed to track 090 to the station. The 300 bearing crosses from front L --> rear R, the 240 bearing behind from rear L to abeam at the station.
Similarly to Scenario 1, picture other bearings on the RMI.
Interception:
Once you can picture the a/c position on the RMI and where a desired bearing is then it's also possible to see how much to turn to have a track that will cross the desired bearing at some point before or after the navaid.
A development of this is to use the circumference of the RMI to represent the largest distance in the intercept problem eg if you're at 20 nm & want to intercept a bearing at 10 nm then the circumference equates to 20 nm and the point to intercept would be midway between the circumference & the centre along the desired bearing. Using this then a straight line between the two points is also the track to get there. To find the required heading, match a parallel line that starts from the centre of the RMI & goes to the circumference - I use my pen or pencil. Whatever compass direction is under your pen is the heading needed to get to the intercept point**.
This sort of technique - particularly the orientation part - can be used on a standard fixed card ADF in combination with the the a/c's Direction Gyro. You'll need to use your pen (or count convenient divisions from the head/tail/left or right abeam to the head/tail of the ADF needle. Transpose the pen's orientation (or the same number of divisions in the same rotational direction as on the ADF) onto the DG. This is a pseudo-RMI since those same divisions you count mark where the ADF needle would be *if* the DI was also an RMI.
You could also rotate the ADF card if it's a rotating card type. I generally don't because I can't be bothered having to do it for every single heading change. I'd rather count the convenient divisions on the ADF & then count the same amount on the DI to find where the ADF needle would be
Once on a heading to intercept it's important to confirm that the heading is appropriate to achieve what you intend. On an outbound intercept the TAIL of the needle must be in a position to RISE towards the desired bearing (on an RMI) or rise towards the same number of divisions on a fixed card as there are between your HDG & the bearing on the DG. For an inbound intercept the HEAD of the needle must be on the opposite side of the nose as the heading is from the desired bearing ie HDG to the left of the desired bearing then head of needle to the right of the nose) AND in a position to fall to the bearing.
**In nil wind. Any wind will put an error in this no different to flight planning on the ground using track as heading techniques. Bear in mind it's all based on an NDB so utmost precision is hardly to be expected.
Jet Blast Rat
Joined: Jan 2001
Posts: 2,081
Likes: 0
From: Sarfend-on-Sea
A rule I use that may clarify and simplify some of what has been said, for use in the air, is:
Pull the tail
Push the head.
i.e. if you wish to return to the correct track inbound (i.e. with the arrow head up) then set the heading the opposite side of the arrow head, to "push" it towards the desired track. Outbound (with the arrow's tail up) then set the heading the same side as the required track, but further off, to "pull" the tail onto the desired track.
Pull the tail
Push the head.
i.e. if you wish to return to the correct track inbound (i.e. with the arrow head up) then set the heading the opposite side of the arrow head, to "push" it towards the desired track. Outbound (with the arrow's tail up) then set the heading the same side as the required track, but further off, to "pull" the tail onto the desired track.
TightYorksherMan
Joined: May 2002
Posts: 1,573
Likes: 1
From: Peak District
Forget all this push and pull business confused the heck out of me!!!
If your tracking to a beacon (i.e following the head) =
if the needle is right of your intended track - turn right.
If the needle is left of the intended track - turn left
If your tracking away from a beacon (with the tail at the top) =
if the tail is right of your intended track - turn left
if the tail is left of your intended track - turn right
any probs pm me!
<<edit: That's what I said, isn't it?>>
If your tracking to a beacon (i.e following the head) =
if the needle is right of your intended track - turn right.
If the needle is left of the intended track - turn left
If your tracking away from a beacon (with the tail at the top) =
if the tail is right of your intended track - turn left
if the tail is left of your intended track - turn right
any probs pm me!
<<edit: That's what I said, isn't it?>>
Last edited by Keygrip; 6th April 2005 at 04:33.
Joined: Aug 2001
Posts: 1,178
Likes: 0
From: BFS
Push the head pull the tail.
Don't try to visualise anything. you want the head to be somewhere push it. You want the tail somewhere pull it. End of story. Job done!! IMHO that is!!!!
PS get rant!! Costs less than 15 mins in aircraft - ie a couple of messed up holds!!
Don't try to visualise anything. you want the head to be somewhere push it. You want the tail somewhere pull it. End of story. Job done!! IMHO that is!!!!
PS get rant!! Costs less than 15 mins in aircraft - ie a couple of messed up holds!!
