ADF needle "dip"

[Sim Dude]

this occurs when tracking an ADF Needle which Dips toward the side of turn, ie bank right and the needle will "lead" into the turn which if not anticpated will cause an overshoot which now requires a correction the other way. Lots of guys know it happens and call it "Dip" or "Quadrantal error" or "turning error" and anticipate by rolling out early

anyone have a technical explantion of why this occurs ?

no publication i have been through (AP 3456 and various commercial items) says anything about it at all.

its certainly woke up our instructer Cadre here but no one knows WHY

to sort out terminolgy its not quadrantal error (signal bending caused by airframe) or dip as in near a pole or beacon.

it seems to be independant of range but dependant on relative bearing ie most anticpation required if ADF is on the nose or tail and least if its off the beam.

any help of interest

Sim Dude

[Alex Whittingham]

I too would like to know. I have two theories, one is that reflected signals from the wing in the turn contribute to a sort of quadrantal error that is not present in straight flight, the second is that the top of the loop aerial acquires a signal in the turn which it otherwise would not, a sort of night effect. Neither theory really attaracts me and I've never found anyone who could explain it without blathering. Luckily the ATPL syllabus steers quietly away from the subject!

[Stan Evil]

Quadrantal error and dip are two separate errors.

Quadrantal error features in many text books and is caused by the cruciform shape of the aircraft. It occurs whether the wings are level or banked and is worst on signals from stations bearing 45°, 135°, 225° and 315° from the aircraft. Fortunately, most ADF tasks involve tracking directly towards or away from a beacon so quadrantal error is not a factor. However, when using the ADF for pure fixing stations on or near the quadrants should be avoided.

Dip is something different and does not affect all aircraft; it depends on the antenna, with small, combined antennae being particularly susceptable. It is caused (according to a man at Bendix/King) by shielding of the directional antennae by the sense antenna in a turn. It is worst when the station is directly ahead or behind you and is minimal for stations on the beam. The thing to remember is that the top of the needle (head or tail) always dips towards the low wing when you bank. The amount it dips is typically a maximum of 10°.

[redsnail]

I reckon it dips because it is a crap instrument! :mad:

(Been wrestling with one all bloody day)

G'day Alex.

[big pistons forever]

Here here Redsnail ! The day they decomission the last NDB will be the day of a party to end all parties :D Thank god for GPS assisted NDB approaches ;) , it sure reduces the scare factor. I really don't miss the NDB only approaches , sliding below aerodrome 25 nm safe altitude with the peaks on all quadrants still in the clag and trusting your life to that wobbly needle. I remember one comitted athiest got religion on the NDB into Terrace BC one ugly winter day :eek: Heres to better living through high technology:)

[BEagle]

......as will the day the Canadians consign the last Loc BC approach to history - and relocate the navaids at Gander to somewhere more useful on the aerodrome! But there again, Gander is probably best avoided altogether...

[Alex Whittingham]

I like the Bendix King explanation, it explains why some systems suffer from dip & others don't. How about quadrantal error then? some books say it is caused by reflections from the airframe, some say by the magnetic fields in the aircraft.

G'day Reddo, how's Junior?

[redsnail]

G'day Alex,
Just got a call today that Junior has landed safely in Scotland. Pity I am near Luton! :( He'll be on the road real soon. :D Might take him to the Gatbash. :D
Cheers


The Elite computer training synthetic trainer actually simulates dip! I couldn't believe the mongrel thing! :eek:

[Code Blue]

BEagle wrote:
Canadians consign the last Loc BC approach to .....Gander is probably best avoided altogether...

I'm cut to the quick sir.

The fact the navaids are scattered around is to help develop your sense of adventure.

I find hand flying the backcourse to be an excellent recurrency exercise. But there again I'm probably biased.

If you're ever at a lose end here give me a shout.

Rgds
CB