PPRuNe Forums IFR- working out the drift in flight, how?

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 30th May 2001, 03:10 #1 (permalink) AV8 consultants Guest   Posts: n/a IFR- working out the drift in flight, how? Ok, I have been told to halve the wind speed to get max drift then work out where the wind is coming from and apply the factor to give actual drift i.e 30 degs =0.5 Is there an easier way that does not involve number crunching? my brain is overloaded enough with flying the twin and making radio calls and intercepting tracks etc. I think I need and additional 6 meg computer chip to be installed to handle this all at once, especially on short trips. Any tips for doing the above and getting the grey matter to absorb all the inputs from external sources? I have the typical "brain goes to mush mode" when too much info is trying to be processed at the same time. Any comments or easy tricks regarding I/R would be sooooo appreciated.
 30th May 2001, 03:30 #2 (permalink) IFollowRoads Guest   Posts: n/a Rule of thumb I was given for the IMC was that somewhat awkward WV/TAS * 60 Having a similar sort of problem as it sounds like you are in the IR, my instructor offered 'work out the max drift on the ground, and then use either the sixths rule or clock rule in the air' Worked for me
 30th May 2001, 12:15 #3 (permalink) chicken6 Guest   Posts: n/a I concur. I'm getting my IR current again after a four-year VFR instructing stint and my advice to you is do it on the ground. Every time. If however you are just going out for a beacon-bashing exercise, you can cope with a VOR fairly easily. Steer the track (so HDG=TK) and see which way the needle goes, then reintercept and set 5deg drift the appropriate way. If 5 doesn't work, reintercept and try 10deg etc. etc. As for ADF tracking, well if I figure it out I'll let you know. I do know that steering the track tells you which way you need to go to intercept, and watching the movement tells you how much drift to offset. As for the rest, it's all jiggery-pokery and black magic (the technical term is 'judgement', but good judegement comes from making mistakes so we're all pretty stuffed really). If you find a good ADF tracking method (for inflight use) can you please let me know?
 30th May 2001, 12:36 #4 (permalink) Gerund Guest   Posts: n/a Chicken6 - I find the method you suggest for tracking to, from, a VOR works just fine for NDBs as well.
 31st May 2001, 07:31 #6 (permalink) Join Date: Aug 1998 Location: Ex-pat Aussie in the UK Posts: 2,704 Drift when flying IFR? Dial up the VOR radial, stay centred on it. The difference between your heading and track is your drift! Not really trying to be smart here, just that I never bothered with the drift flying IFR, just staying on track is enough.
 1st Jun 2001, 00:02 #7 (permalink) Ivan Ivanovich Guest   Posts: n/a Yeah, never used to calculate drift in the air or on the ground during IR. Just follow the needles and experiment with 5deg drift at a time. All you have to do is know which way the wind is blowing from. It works on the ILS, too. You can even get away without calculating drift in the Hold. Again you just need some idea of where the wind is coming from. In the hold, just fly a heading into wind, then aim to be on the gate at 2.8d from the beacon and you can't go wrong. It's exactly the position to be in regardless of wind. Worked everytime for me. If you want to work out drift then this is what to do. At 150K (Seneca cruise) max drift is 4deg for every 10 knots of wind ie 15kts = 6deg. etc. Then use clock code to work out fraction of drift applicable. ie when wind is: 60 deg off heading = all the drift applies 45 = 3/4 of the drift 40 = 2/3 30 = 1/2 etc eg: HDG = 340deg wv = 320/25 max drift = 2.5 x 4 = 10 deg clock code = 20deg therefore use 1/3 of 10deg ans: drift = 3deg In the hold at 120Kts use 5 deg per 10kts At 90 kts (warrior, or ILS) use 6deg per 10Kts. Hope this helps. Just practise doing the numbers over and over whilst driving or doing some other task. becomes easy after a while - you can even do it on the approach. Good Luck
 1st Jun 2001, 14:45 #8 (permalink) chicken6 Guest   Posts: n/a Gerund I did another flight today and I think you're right (now), it's just that as of two days ago I couldn't intuitively tell (on an ADF dial) which side of me the track was on, but after another few hours I think I've got it now. I've also developed another VOR tracking method (and of course I'm almost certainly not the first to figure this one out) - get on track, figure out which side of you the wind is coming from (from ATIS or forecast), steer that way and if the needle moves, steer towards it (ie left of centre or right of centre) until it goes back to the centre. Then halve the difference between original and new headings and hold that. Checkboard, I have been getting strong hints from my instructors that if I can do everything on the ground first the flight will go better and they seem to be telling the truth! And I couldn't read an ADF with that confident "I'm definitely here and my track is definitely over there" feeling, that's why I'm on this thread...can now though. And I haven't been doing much cross-country work so the aids are always pretty close (~5 nm) therefore quite sensitive. ------------------ Confident, cocky, lazy, dead.
 2nd Jun 2001, 11:28 #9 (permalink) Gerund Guest   Posts: n/a chicken6 - Glad to hear that everything is coming together on the NDB/ADF. Everyone struggles with this one and then it suddenely clicks. I also agree with Checkboard about the drift! What is all this working out the drift stuff? I was never taught it, and have never used it. I remember Sherlock Holmes telling Watson, (who was astounded that he didn't know the earth went round the sun), that he was going to forget it as soon as possible. He had enough to remember already! Any calculation, either in the air, or on the ground is bound to be wrong. Is this a JAR thing? Required by the learning objectives, but never used in real life? Can anyone enlighten me? [This message has been edited by Gerund (edited 02 June 2001).]
 3rd Jun 2001, 14:59 #10 (permalink) chicken6 Guest   Posts: n/a Not a JAR thing, I'm on the wrong side of the world for that! Just that all the other methods require you to get off track to be able to stay on track, which doesn't sound that smart or efficient to me. And we don't have radar control in this part of NZ either, so ETAs and therefore proper nav logs are still a necessity. If you're going to get the groundspeed you might as well read off the drift while you're on the flight computer...(One day I'll be able to look back and say "when NDBs were still around" ...) Anyway, doing it all on the ground beforehand was good enough to get the renewal signed off today. And with 20 knots on the ground and I don't know how much at 3000' I think it was well worth it. Woohoo! ------------------ Confident, cocky, lazy, dead.
 3rd Jun 2001, 17:05 #11 (permalink) Gerund Guest   Posts: n/a chicken6 - Sorry about putting you in the wrong country! Careless of me! NZ is a great place - spent three months there a few years ago; just wonderful! Many congratulations!!
 5th Jun 2001, 12:54 #12 (permalink) chicken6 Guest   Posts: n/a Cheers And based on the rule that says "of all the people interested in something, only 10% will actually do something about it", here is the address of the simulator I mentioned somewhere http://www.visi.com/~mim/nav I emailed the author thanking him and he said there is a new version in the works with some more features like zoom in/out, more instruments etc. Just make sure you practice with wind occasionally! No wind looks great, but is NOT good training value rah rah rah. ------------------ Confident, cocky, lazy, dead.
 5th Jun 2001, 17:12 #13 (permalink) hugh flung_dung Guest   Posts: n/a Why use watches or calculations to work out the drift when the DI/HSI can do it for you? As others have said, you can work out max drift (drift angle at 90 degrees to wind) from MD=(windspeed x 60)/TAS. In flight you can use the DI/HSI to visually gauge the drift..... - Turn so hdg=trk, the MD vector is now at right angles to your trk. - see where the wind direction is on the rose and drop a line (parallel to your hdg) from this point onto the MD vector. - the drift is the fraction of the MD vector between the centre and where the dropped line touches it. This all sounds complicated in words but it's very simple to use and takes less than 2 minutes to teach with a picture.
 5th Jun 2001, 21:07 #14 (permalink) Tinstaafl Guest   Posts: n/a ...especially if you confine the guestimate of the fraction of MD to 1/2, 1/3, 1/4. As for working out actual drift I set track as heading & wait to see which way I start to drift. after a couple of deg. drift I re-intercept track & then use about 5 deg or 10 deg as a starting figure. Wait & watch then readjust - bracketing any previously tried wind correction angles. If you already suspect that there will be drift then don't use the initial TR=HDG: Make an educated guess & use 5 or 10 deg as the starting point. With practice you soon become able to `guess' a suitable drift allowance based on rate of drift.
 5th Jun 2001, 21:31 #15 (permalink) Gerund Guest   Posts: n/a Tinny - I agree with you and Checkboard. In flight, you suck it and see! Then nail it down. As long as you are maintaining track, using either ADF or VOR, then drift is the difference between heading and track. What I can't understand is why anyone would would want to do arithmetic on the ground, or worse still in the air, to calculate a figure that is bound to be wrong, and is likely to change significantly througout a flight and approach. Of course, I would agree it's helpful to know where the wind is coming from, but you find that out pretty damn quick in any event!!! So many people have given methods of calculation, using watches, DIs, etc that there must be some sort of rationale. I am concerned I might be missing out! Someone, please enlighten me on why they want to do this by calculation rather than by finding out by flying the needles, and put me out of my misery!
 5th Jun 2001, 22:07 #16 (permalink) juswonnafly Guest   Posts: n/a Gerund, Stay cool, don't worry you are not missing anything. All of the above mentioned methods work very well, just use the one you prefer. As a matter of interest my method is better suited to VFR nav without radio aids (ideal for ppl/cpl skill test though). Enjoy JWF

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