Mental Dead Reckoning For Navigation

[tobyethan]

I did my CPL training at a RAAF Flying club whwre the military QFI's encouraged us to use mental dead reckoning using some simple maths and formulas (ie time, groundpseed, drift correction). Took me awhile to get used to it, but boy I loved not having to pull out that whizz wheel to do nav calculations.

My questions:
1. Is it worth it to teach the average GA stud this kind of stuff?
2. What are the some mental dead reckoning "rules" That I can start my studs on?

I would welcome any input from any ex-RAAF/RAN/RN/RAF/USN/USAF/GA QFIs out here?

[GT]

Plastic Flyer,

In answer to your first question, I believe (for what that's worth) that it is vital that all pilots are taught mental DR. Surely this is navigation in its purest and simplest form, and should be amongst a pilot's skills for use when required (airborne diversion planning being just one example).

As for your second question, I'm sorry but I dont't really have the time to go into that here, however, estimating track and max. drift are always a good place to start. I'm sure, though, that the others on (in?) this forum will oblige.

Regards, GT.

[Lima Xray]

Plastic Flyer

Would you be so kind to elaborate on your RAAF mental dead reckoning methods for ‘us’ GA FI’s to appreciate.

Thanks
L X-

[juswonnafly]

P F,

Like GT I don't have too much time right now but I have a question for you. Do you mean use the mental stuff when airborne or when pre flight planning? For what it's worth I teach all my students to plan and fly without using a whizzwheel, then when they are spatially aware I show them the whizzwheel method.

Personally I think the whizzwheel leads to all sorts of confusion and takes about 4 times longer to plan a flight. Also students all too often correct for drift on the 'wrong side'

I'll elaborate later when I have more time, gotta go flying now

cheers

JWF

[bluskis]

By coincidence I have just posted the following on the Wannabees section.
In the early days I was often confused as to which way to turn the computer to compensate for drift, and as a final check for error, mentally checked that my calculated heading meant I would be leaning (heading) into wind relative to the intended track.
The computer is a remarkable piece of design, but certainly not instinctive, even to those who are practiced at vector diagrams.

[BEagle]

First work out your 'max drift'. This is simply the wind speed divided by your TAS (in nautical miles per minute) and the answer is in degrees - don't worry about why, it's all to do with 1 in 60 style approximation. So if the wind is 30 kts and your TAS is 90 Kts, max drift is 30 divided by 3/2, i.e. 20 degrees.

Then examine the angle between your track and the wind - and remember how an analogue watch face looks! Obviously if the wind was 90 deg off track, you'd apply all of max drift. If it was 60 off, you'd use 86.6%, 45 off 70.7%, 30 off 50%, etc, etc. But that's too hard, so if you assume that 60 or more degrees off is 1x max drift, 45 off is 3/4, 30 off is 1/2, 20 off is 1/3, 15 off is 1/4 (the same fractions as minutes of an hour) then it becomes close enough for approximate use and is easy. Thus if you're doing a TAS of 90 kts on a track of 050 and the W/V is 100/30, to maintain track you need to turn right by about 3/4 of the max drift of 20 deg, i.e. to a heading of 065 deg.

Similarly, consider the groundspeed. If the wind is 90 deg off, it should have no effect on GS, if it's on the nose it'll have 100% effect. So again you can use the 'clock code' - if the wind is 60 deg off use (90-60) as the clock fraction to use, i.e. 30 or 1/2 the wind strength. In the case above the wind was 50 off the nose, so you'd use 90-50=40, i.e. 2/3 of the windspeed (2/3 of 30 being 20) to apply to your TAS to obtain groundspeed - in this case it would become 70 kts. So what would have taken 7 minutes in still air will now take 9......

If you work out max drift before flight and draw the W/V on your map, you can fairly quickly come up with heading and GS without needing a whizz wheel! It's called 'Mental Dead Reckoning' or 'MDR', by the way. But don't forget to NB whether it's a head or tailwind that you're dealing with!!

[ 12 January 2002: Message edited by: BEagle ]</p>

[juswonnafly]

Nice one BEagle!

That's at least 2 of us who advocate the max drift method.

To take it a stage further.....when diverting a stude on a nav ex, I get them to turn onto their intended hdg, note time, look at DI, calculate drift from the 'picture', then alter hdg. THEN look at DI again and check wind angle for g/s.....this of course emulates the 'refining process' that takes place on the whizz wheel.

For what it's worth I truly believe that the whizz wheel over complicates the pre flight planning and should only be taught after the stude can navigate without one.

Cheers

JWF

[Noggin]

The Prayer Wheel is for Nav Exams, the rest should be done mentally every time!

[fireflybob]

Beagle - music to my ears!

Only had a student last week at the local club who had applied the drift the wrong way on every single leg of a triangular having used the computer (remember when it was called a "Dalton" computer - they were the days!!).

Seems like we need to return to a more common sense approach and basic airmanship.

[eyeinthesky]

For some more methods of not getting lost, look in the Private Flying forum under 'Help needed, can't navigate" or something like that.

[foxmoth]

For time markers en route remember that 10% of G/S is 6 mins - usually about 9-10 miles for most light aircraft. Another thing I was taught is that most peoples thumbs ( the last part of it) are about 10 miles on a 1/2 mil map, measure yours before you use it though to double check,so you can say a thumb (plus or minus a fraction as appropriate) is 6 mins, a pre marked pencil works even better for this, cut 5 mile then 1 mile marks along the pencil.

[tobyethan]

To all of you who have replied to my original question: thanks very much. I am getting some great info.

I was reading some stuff from a RAAF training manual on medium level nav and would like to share a bit of mental DR for establishing position. The rule was developed I think, for ab-initio students flying the CT-4 Airtrainer (ie "Parrot"). Here goes:-

(Time of most current positive fix - Time of last positive fix) X 2 = Your current position in Nautical Miles from the last fix. The RAAF rule of thumb is that the "parrot" at that 130 KIAS (?) speed range with say +/- 25 KTS for headwin/tailwind: means that there is some leeway in multiplying by "2" (i.e. 2 NM/minute). This worked for me, when the instructor used to ask the dreaded question: "so, where are we?" Of course, there is the little caveat in the text that says that this will only work if you fly accurately.

Plastic Flyer After taking a 9000 hour 737 pilot flying in a Jabiru: "So what does it feel like to fly in an aeroplane that ways less that a 737's APU?

[fireflybob]

Just recalled that I was first taught the "Mental Dead Reckoning" System whilst training at Hamble in 1969!!

What goes around comes around?

[tobyethan]

FireflyB,

Re: Mental DR, Hamble '69.

How / what did the instructors teach. I guess from your experience, I'm trying to build a lesson plan of what to teach my own studs, without overloading them with too much info.

Thanks.

[Guy Pearson]

The best thing about Mental DR is that the batteries do not go flat!

[Checkboard]

They can get overloaded though! <img src="wink.gif" border="0">