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3 Answers

ADF bearings and the wind

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Instrument Rating

My question is about the good old ADF. Would someone please explain why, when tracking an NDB bearing with wind, the relative bearing is NOT zero? I understand that the wind blows the airplane off course, but doesn't the ADF kind of indicate the angle between the aircraft midline and bearing-to-station? Shouldn't the RB therefore be zero if we're tracking directly inbound, regardless of the wind?

3 Answers



  1. Ron Klutts on Sep 09, 2013

    The ADF doesn’t not anything about the aircraft midline as you call it. It’s sole job is to point at the radio beacon. As the wind blows you off course if you simply turn to put the pointer back on the nose 0° RB then you’ll be flying a circular path around it and no longer going in the direction you want. You may cross the station 90° off of the course you wanted.

    So one must crab into the wind and the pointer will be off the nose by the wind correction angle.

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  2. Wes Beard on Sep 09, 2013

    Some terminology… The relative bearing is the angle the ADF needle makes in reference to top of the ADF. The magnetic heading is read from the heading indicator and indicates the magnetic direction the airplane is pointed at.

    The magnetic bearing is defined as the sim of the relative bearing (RB) plus magnetic heading (MH).

    Now, we are tracking inbound on the 015 bearing to the station. RB is 0 and MH is 015. A left wind drifts us off course. RB is 355 and MB is 015. Always turn in the direction of the head and we turn left to get the head on the opposite side of the gauge. RB is 005 MB is 005. The head always falls. RB reads 010 and MB 005. We are back on course.

    Take out half of the correction angle. RB reads 005 and MB reads 010. To answer your question, the RB will indicate the wind correction when flying a bearing to the station. The needle should not move off of that RB if the wind is constant.

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  3. Aaron on Sep 09, 2013

    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing
    Magnetic Heading + Relative Bearing = Magnetic Bearing

    Learn it, live it, love it. This is the ADF (What I call the Archaic Direction Finder) flying bible. It will tell you anything and everything you need to know. Remember there are two types of ADF: fixed card and moveable card. In a moveable card, ADF flying is easy, because you set your aircraft’s current heading to the top of the dial (when tracking TO the station) and the ADF will point at the magnetic heading needed to track directly to the station. Ron is spot on with his assessment. If you simply try to keep the head of the needle ponted at 360, you’ll end up homing, not tracking to the station. Tracking is the ost direct route, and homing allows the wind to push you into a curved path off course and (possibly) into hazards, or worse, terrain.

    Fixed card is a little trickier, but just remember the “bible” and you’ll be fine. I always liked to think of it like this: the FIXED CARD ADF should indicate your wind correction angle when established on a heading TO the station. Ideally, it should remain constant the whole time tracking to the station. For example, let’s assume you’re tracking a 360 bearing to the station, and you have a wind from 270 at ## knots (in other words, a left crosswind). IN this case, if you simply keep the needle at 360, you’ll end up flying a path arcing to the right of your intended course because the wind will push you to the right. So in order to keep the aircraft on a straight line, as Ron said, you need to angle it into the wind. NOW your ADF will not show 360, but will show some bearing just left of 360 (into the wind), say 330. That means you have a 30 degree correction angle in order to track a straight line to the station. Your exact angle will depend on wind speed and direction, but you get the idea.

    ADF’s are incredibly complicated, and as everything in flying goes, you have to visualize it and conceptualize it and come up with your own ways of figuring it out before it really starts to click. Everyone has their own little ways, but for the FAA, you NEED to know the above formula. Hopefully this helps you understand what’s at play a little better, as it’s a difficult concept to explain over the internet. If you need further clarification, feel free to peruse YouTube. There are some quality simulators on the web too to play around with. My personal favorite is this one:

    http://www.luizmonteiro.com/Learning_ADF_Sim.aspx

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