ADF Dip - how to make a correction for it?

[JulieFlyGal]

I've read about ADF dip and what causes it, but I'd like to know how one can make a correction for it. I'm flying a PA44 for the instrument rating ... an NDB approach using an RMI requires an outbound leg of 239 degrees, and then a right turn to 071 inbound to the aid. In the turn I monitor the RMI needle and all looks good for a perfect intercept, but then after rolling out to wings level, the blasted needle moves!! Grrrrr!! :ugh:

So my question is, is there a formula, rule of thumb, old wives tales etc, that one can use to estimate when to rollout so I minimize the ADF dip error? My instructor doesn't seem to think so, and suggested I rollout to wings level at 90 degrees in to the turn to reasses my bearing to the station and then again at 45 degrees and so on. But I'd rather do a smooth turn on to the inbound track just like how the big boys/girls do it in the airlines. Any tips?

[thetimesreader84]

Can't remember exactly, but I think i used to allow 5 degrees for Dip when I did my IR on the PA44.

[Capot]

There was a thread in May 2002 on this, but I don't know how to link it...........

and January 2002, and July 2006, according to Google.....

[forget]

https://www.pprune.org/archive/index.php/t-13757.html

Capot, Just copy the url and paste it.

[Centaurus]

but I think i used to allow 5 degrees for Dip when I did my IR on the PA44.

Are you sure you are not getting confused with compass needle dip near the north and south poles. If you are in those far latitudes you are probably temporarily uncertain of your position?

Lag in ADF readings in a turn may be a quadrantal error problem. Write it up in the maintenance release.

[JulieFlyGal]

Forget, thanks for the link ..so it's suggested that;

To counter it, anticipate by lagging your roll out a bit . I'm sure someone more clever than I could work out how much lag would be necessary depending on the cosine of the angle of bank, but I was taught to use th TLAR method. (That Looks About Right). It is a function of the angle of bank, regardless of aircraft type.

so, by "lagging your roll out a bit" as suggested above, mean delaying my rollout past 071 (from my example above), or does it mean rolling out before the RMI needle reaches 071?

[pushapproved]

It's been a while since I've had to think about dip, it's usually automatically resolved in the bigger machines I fly these days!

As far as your bank angle goes for your PA44 you would, in theory, always be doing a rate one turn, (10% of TAS +7: ie. if you were flying at 130kts = 13+7= 20degress bank angle). Dip is usually around 10-15 degrees towards the lower wing so you would normally allow the needle to go past the required track by approx 10 degress, then roll wings level and wait to see where its settles, I don't think there is any need to roll out at 90 & 45 degrees to go, that just delays the turn and could make more work for you when you have to roll the other way to get back on track! Hope that makes sense?!

[JulieFlyGal]

so you would normally allow the needle to go past the required track by approx 10 degress, then roll wings level and wait to see where its settles,

pushapproved, thanks for that. I'll try that next time I fly and see how it goes.
cheers!