ADF Dip Error
Gizajob
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ADF Dip Error
Hi,
Can anyone point me to a book/ website etc (or else explain here) how adf dip error varies with relative bearing to the beacon? Particularly interested in the example of the turn inbound on a hold. I remember vaguely from IR something about the error being 0 at 60 degrees RB but I might be wrong and I can't remember the rest
can anyone help?
PS - done the search and couldn't find anything.
Can anyone point me to a book/ website etc (or else explain here) how adf dip error varies with relative bearing to the beacon? Particularly interested in the example of the turn inbound on a hold. I remember vaguely from IR something about the error being 0 at 60 degrees RB but I might be wrong and I can't remember the rest
can anyone help?PS - done the search and couldn't find anything.
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http://www.allstar.fiu.edu/aero/adf.htm
There is no quantitative info at this link. They use the term "bank error." Maybe a search using that term may assist.
There is no quantitative info at this link. They use the term "bank error." Maybe a search using that term may assist.
Gizajob
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Thanks for that. Tried 'bank error', which didn't yield anything more...
So I can't find anything on the web, no one here can give a fuller explanation and I haven't seen anything comprehensive in a book (detailing rules of thumb etc etc) either. Must be a blak art or a blakc hole!
So I can't find anything on the web, no one here can give a fuller explanation and I haven't seen anything comprehensive in a book (detailing rules of thumb etc etc) either. Must be a blak art or a blakc hole!
I will try, although it's not easy without visual aids.
The VOR receiver integrates the signal from the beacon with a heading input and deduces which radial it's on. It can work this out regardless of the aircraft attitude. The ADF is a dumb gadget and just points at the beacon. If you're wings level and the beacon is 45 degrees from the nose, it will point 45 degrees off the index. But imagine you are in a 30 degree turn towards the beacon. The relative bearing reduces.
Can't imagine that, well now bank to 90 degrees. The relative bearing of the beacon is now on the nose and you are apparently pointing straight at it.
Still not got it? Well, take your coffee mug off the coaster and place it to the right of the desk. Pick up the coaster and hold it level above your desk. This is your aircraft. Now pick up your biro and place it on the coaster pointing at the coffee mug (the beacon). Now bank the coaster towrds the mug while keeping the biro pointing at the mug. What happens? You should notice the biro turning towards the nose of the aircraft and the relative bearing reducing. Now expalin to your wife how you got the hot drink ring on the desk.
The next question to ask is why we are using stone age navaids in this age of inertial reference systems and GPS.
The VOR receiver integrates the signal from the beacon with a heading input and deduces which radial it's on. It can work this out regardless of the aircraft attitude. The ADF is a dumb gadget and just points at the beacon. If you're wings level and the beacon is 45 degrees from the nose, it will point 45 degrees off the index. But imagine you are in a 30 degree turn towards the beacon. The relative bearing reduces.
Can't imagine that, well now bank to 90 degrees. The relative bearing of the beacon is now on the nose and you are apparently pointing straight at it.
Still not got it? Well, take your coffee mug off the coaster and place it to the right of the desk. Pick up the coaster and hold it level above your desk. This is your aircraft. Now pick up your biro and place it on the coaster pointing at the coffee mug (the beacon). Now bank the coaster towrds the mug while keeping the biro pointing at the mug. What happens? You should notice the biro turning towards the nose of the aircraft and the relative bearing reducing. Now expalin to your wife how you got the hot drink ring on the desk.
The next question to ask is why we are using stone age navaids in this age of inertial reference systems and GPS.
The next question to ask is why we are using stone age navaids in this age of inertial reference systems and GPS.
It's because my employer is far too thrifty to buy and install decent GPS or IRS.
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I thought ADF dip doesn't vary with relative bearing to the beacon. The 'dip' is dictated by the aircraft charateristics and is generally 8-10 degrees when the wings are not level regaredless of RB.
I think what you refer to is that when you are 60 deg to go in the inbound turn you are approx 10 dgrees off the inbound track. Coincidentally this is cancelled out by the dip so it looks like you are showing the QDM to the beacon.
eg. Assume inbound track in 090 on a lh hold, at the gate you will be on the 120 qdm (heading 270) . At 60 degrees to go (heading 150) you have done 2/3 of the turn and have about 10 degreees to go. The qdm will be 100 but dip will be 10 degrees left reading a qdm of 090. If you rolled out at 150 the needle would read 100 (the qdm) .
(Having said that having just fiddled with RANT dip appears to be +-10 degrees heading to or from the beacon decreasing to nil abeam the beacon - never knew that)
I think what you refer to is that when you are 60 deg to go in the inbound turn you are approx 10 dgrees off the inbound track. Coincidentally this is cancelled out by the dip so it looks like you are showing the QDM to the beacon.
eg. Assume inbound track in 090 on a lh hold, at the gate you will be on the 120 qdm (heading 270) . At 60 degrees to go (heading 150) you have done 2/3 of the turn and have about 10 degreees to go. The qdm will be 100 but dip will be 10 degrees left reading a qdm of 090. If you rolled out at 150 the needle would read 100 (the qdm) .
(Having said that having just fiddled with RANT dip appears to be +-10 degrees heading to or from the beacon decreasing to nil abeam the beacon - never knew that)
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Just to simplify it the ADF works on a directional reciecver, loop and sence aerials, all be it they are digital these days. Not as good as the the old manual analogue ones, picked up the radio stations better. If you bank the acft you bank the aerial therefore create the error.
Dan Winterlands analogy, despite upsetting the wife explains it great.
In practise in cloud in turbulence, icing at night, who cares, even with a bit of map shift the FMS is just s good.
Dan Winterlands analogy, despite upsetting the wife explains it great.
In practise in cloud in turbulence, icing at night, who cares, even with a bit of map shift the FMS is just s good.
Gizajob
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Dan, that's a fab explanation of dip - thanks a lot. Luckily I'm not married so the only people I had to explain my odd behaviour to were the folks in the office...18g - that's what I was after as well cheers. It makes sense to me that the error disappears abeam the beacon (try it with the coaster/ pen model).
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Over 40 years, or so, I must have heard thousands of wierd explanations as to why certain 'aviation things' do what they do. Dan Winterland! No one will ever beat that one. Superb
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Dan, Doesn't the needle point away from the beacon, rather than towards it in a bank.
Isn't the wobble caused by the electricity being bent around the airframe as the wing dips into the path of the signal rather than the angle of the receiver? Anyone know the real reason.
Isn't the wobble caused by the electricity being bent around the airframe as the wing dips into the path of the signal rather than the angle of the receiver? Anyone know the real reason.
Are we talking about quadrantal error, or something else? If QE, then it is not quite as Dan's eloquent explanation would suggest. Quadrantal error is caused by the presence of the aircraft in the electromagnetic field of the NDB transmission and is specific to individual aircraft. If you want to be really precise you can even draw up a QE correction chart.
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Dan Winterland: Cool never thought of it like that
ADF/NDB's at night can be a killer though, I'm alway learning new perspectives from here --- It's like 10^7 million flight hours wrapped up and packkaged on one website, althogh I love Airliners.net too, but since B 747-Skipper left along with Jetguy... it's a lot less fun PPrune is the greatest
rhovsquared
ADF/NDB's at night can be a killer though, I'm alway learning new perspectives from here --- It's like 10^7 million flight hours wrapped up and packkaged on one website, althogh I love Airliners.net too, but since B 747-Skipper left along with Jetguy... it's a lot less fun PPrune is the greatest
rhovsquared
The needle will always point at the beacon. It's the direction loop on the aerial which apparently rotates in relation to the beacon - but as far as the pilot is concerned it's the compass card on the RBI/RMI. Whatever way you are pointing, it will always swing towards the nose of the aircraft in a turn.
This is the 'dip error'. It's significant if you are turning onto a final track. If you're in a turn and roll out exactly on your inbound track, you will find out you're a couple of degres out when wings level. A bit of a b%gger if you're outside the 5 degrees and you can't descend on the procedure and you're close to your descent point. I used to teach students on light aircraft to use 10 degrees of bank to turn on final track on an NBD procedure. But the aviation authority where I work for a living still insists we fly NDB approaches usung an RMI in 747s turning onto the final track at 25 degrees AoB. In this case you have to delay the roll out by a couple of degrees.
Quadrantal errors are influenced by the structure of the aircraft. Add this to night error, coastline error and the thing's habit of pointing at thunderstorms and you can see what a poor navaid it is.
This is the 'dip error'. It's significant if you are turning onto a final track. If you're in a turn and roll out exactly on your inbound track, you will find out you're a couple of degres out when wings level. A bit of a b%gger if you're outside the 5 degrees and you can't descend on the procedure and you're close to your descent point. I used to teach students on light aircraft to use 10 degrees of bank to turn on final track on an NBD procedure. But the aviation authority where I work for a living still insists we fly NDB approaches usung an RMI in 747s turning onto the final track at 25 degrees AoB. In this case you have to delay the roll out by a couple of degrees.
Quadrantal errors are influenced by the structure of the aircraft. Add this to night error, coastline error and the thing's habit of pointing at thunderstorms and you can see what a poor navaid it is.
