FLYING ON INSTRUMENTS

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Peter Armstrong
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Oct 12, 2018 4:36 am

Orientation using the RBI
The aeroplane can be orientated with respect to the NDB if you know:
The magnetic heading (MH) of the aeroplane (from the compass or direction indicator); plus
The relative bearing (RB) of the NDB from the aeroplane.
In practice, magnetic heading is flown using the direction indicator, which should be realigned with the magnetic compass in steady flight every 10 minutes or so.

The Rotatable-Card ADF
The rotatable-card ADF is an advance on the fixed-card ADF, because it allows you to rotate the card so that the ADF needle indicates, not relative bearing, but magnetic bearing to the NDB. Do this by aligning the ADF card with the DI compass card each time the aeroplane’s magnetic heading is changed.
To align a rotatable-card ADF:
• Note magnetic heading on the direction indicator; then
• Rotate the ADF card, setting magnetic heading under the index
When the ADF card is aligned with the DI, the ADF needle will indicate the magnetic bearing to the NDB. This eliminates any need for mental arithmetic. Note also that the tail of the needle, 180 degs removed from its head, indicates the magnetic bearing of the aeroplane from the NDB.
Any time the aircraft changes magnetic heading, you must manually align the ADF card with the DI (ensuring of course, that the DI is correctly aligned with the magnetic compass.
If desired, the rotatable card can still be used as a fixed card simply by aligning 000 with the nose of the aeroplane and not changing it. The next step up from a rotatable card is one that remains aligned automatically, a radio magnetic indicator (RMI)
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Peter Armstrong
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Sat Oct 13, 2018 1:29 am

The Radio Magnetic Indicator (RMI)
The RMI display has the ADF needle superimposed on a card that is continuously and automatically aligned with magnetic north. It is, if you like, an automatic version of the rotatable-card ADF – an automatic combination of the direction indicator and RBI.
The RMI is the best ADF presentation, and the easiest to use, but unfortunately the most expensive and usually only encountered in more sophisticated aircraft.
The RMI needle will always indicate the magnetic bearing to the NDB. The tail of the RMI needle will indicate the magnetic bearing from the NDB.
As an aeroplane turns and its magnetic heading alters, the RMI card (which automatically remains aligned with magnetic north) will appear to turn together with the ADF needle. In reality, of course, it is the compass card and the RMI needle that remain stationary, while the aeroplane turns about them. Before, during and after the turn, the RMI’s needle will constantly indicate the current magnetic bearing to the NDB.
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Peter Armstrong
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Oct 26, 2018 12:28 am

Dual Pointer ADF

Some aeroplanes are fitted with two ADF receivers, and have two needles superimposed on the one dial. Sometimes the indicator has a function switch that causes a needle to point, not at an NDB, but at a VOR ground station. This gives the pilot more flexibility in using radio navigation aids.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Fri Oct 26, 2018 12:42 am

THE RELATIVE BEARING INDICATOR (RBI)

Operational Use of the RBI – Orientation, using the RBI to Obtain a Position Line
A position line is a line along which the aeroplane is known to be at a particular moment. A position line (PL) is also referred to as a line of position (LoP). A position line may be obtained by a pilot either visually, or by radio means.

Two position lines that cut at a reasonable angle are needed for a fix. For the aeroplane to be on both position lines simultaneously, it must be at a point of intersection. It is possible to fix position using a combination of radio aids including ADF/NDB, VOR and DME.
A position line can be considered from two perspectives:
From the aeroplane, i.e., the position line from the aeroplane to the NDB that a pilot would see, as either a relative bearing (RB) or a magnetic bearing to the station (known in the UK as a (QDM); or
From the NDB ground station (which is necessary if the aeroplane’s position is to be plotted on a chart) as either a magnetic bearing from the station (known in UK as a (QDR) or a true bearing from the station (known in the Q-code as QTE).
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Tue Dec 11, 2018 4:39 am

Sorry for not being around for a while. I misplaced some of my notes when moving and, some of my scribbles I could not understand (as bad as my typing LOL). Anyway, I am back and hope to continue my thoughts on radio navigation and instrument flying. I am not a journalist so bear with me when I transcribe my notes into readable text. And, also, I may sometimes slip into my British mode when trying to describe some elements of my techniques and charts.

True Bearings from an NDB
Normally when instrument flying, you would not bother to plot positions on a chart. However, if like me, you decide to do so, then the easiest method on a visual chart is to use true bearings from a ground station, i.e., bearings from a ground station related to true north (as indicated on the chart by the meridians of longitude)
Intercepting a track
Having orientated yourself with respect to an NDB, you know the answer to the question “Where am I?” Now ask “Where do I want to go”? and “How do I get there?”
STEP1 - Is always to orientate the aeroplane relative to the NDB, and to the desired track.
STEP2 – involves a turn to take up a suitable intercept heading, considering where it is that you want to join the track.
STEP3 – involves maintaining the intercept heading and waiting:
• For the head of the needle to fall if inbound;
• For the tail of the needle to rise if outbound:
• To + or – 030 for a 30 deg intercept;
• To + or – 045 for a 45 deg intercept
• To + or – 060 for a 60 deg intercept
• To + or – 090 for a 90 deg intercept
STEP4 – involves a turn onto the desired track and allowing for a suitable wind correction angle to maintain it.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Tue Dec 25, 2018 2:57 am

Visualising where you are, and where you want to go
The direction indicator (DI) can assist greatly in visualising the situation. All you need to do is visualise the desired track on the DI. With a model aeroplane on the tail of the needle tracking as desired, it becomes quite clear what turns are necessary to intercept a desired track.

If you become disorientated, a simple procedure is to take up the heading of the desired track. Even though not on track, the aeroplane will at least be parallel to it, and the ADF needle will indicate which way to turn to intercept it.

TRACKING
Tracking inbound to an NDB
The ADF/NDB combination is often used to provide guidance for an aeroplane from a distant position to a position overhead the NDB ground position. This is known as tracking. Just how you achieve this depends to a certain extent on the wind direction and speed, since an aeroplane initially pointing directly at the NDB will be blown off course by a crosswind.
Tracking towards an NDB, with no crosswind effect
With no crosswind, a direct track inbound can be achieved with a heading that maintains the ADF needle on the nose of the aeroplane.
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Re: FLYING ON INSTRUMENTS

Post by Peter Armstrong » Mon Jan 07, 2019 4:49 am

The Radio Magnetic Indicator (RMI)
The RMI combines the relative bearing indicator and direction indicator into one instrument, where the ADF card is aligned automatically with magnetic north. This considerably reduces pilot workload by reducing the amount of visualisation and mental arithmetic required. Even the rotatable card (which allows you to align the ADF card manually with magnetic north) lightens the workload, since it also reduces the amount of visualisation and mental arithmetic required.
The discussion that follows applies to both the RMI and the rotatable-card ADF, except whereas;
The RMI is continuously and automatically aligned with magnetic north;
The rotatable card must be re-aligned with the DI by hand following every heading change (and of course the DI must be re-aligned with the magnetic compass by hand every 10 minutes or so).
Orientation
An RMI gives a graphic picture of where the aeroplane is:
• The head of the RMI needle displays QDM (magnetic track to the NDB): and
• The tail of the RMI needle displays QDR (magnetic track from the NDB
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