Using the E6B Flight Computer for Wind Corrections

[blackbird7 3]

Hi all,

I decided to purchase ASA's E6B flight computer to add a little more realism to flight simming when flying GA aircraft, but a couple of questions have come up when attempting to use the E6B for wind corrections:

1. The E6B manual and online articles recommend that I use true course and true wind heading to determine the wind correction angle (WCA) and true heading. They recommend converting from true heading to magnetic heading as the last step. However, the equation on the E6B itself is MC (-L or +R) WCA = MH, suggesting that starting with magnetic course is permissible if you know the magnetic wind heading. Is it uncommon or bad practice to calculate wind corrections using magnetic course (and magnetic wind heading if available) instead of true course and true wind heading? Using MC and MH would seem more practical to me, but I'm unsure since I'm not a real pilot.

2. My second question is, how often do pilots generally calculate the WCAs during a single trip since the wind heading can change over time? Is it instead more common to just let the autopilot deal with the wind corrections?

Thanks,

blackbird

[skelsey 765]

Hello,

1 hour ago, blackbird7 said:

1. The E6B manual and online articles recommend that I use true course and true wind heading to determine the wind correction angle (WCA) and true heading. They recommend converting from true heading to magnetic heading as the last step. However, the equation on the E6B itself is MC (-L or +R) WCA = MH, suggesting that starting with magnetic course is permissible if you know the magnetic wind heading. Is it uncommon or bad practice to calculate wind corrections using magnetic course (and magnetic wind heading if available) instead of true course and true wind heading? Using MC and MH would seem more practical to me, but I'm unsure since I'm not a real pilot.

It doesn't really matter which you use as long as you are consistent. However, it would be much more common to use true because:

- Wind directions in written weather reports/charts are always given in degrees true

- Tracks between waypoints as measured on a chart will always be in degrees true until corrected for variation.

As a result, it's generally easier to work in true. The typical process would be to measure the true track between two waypoints on the chart, note that on the plog, calculate the WCA to give true heading, then apply the magnetic variation to give magnetic heading (and finally, add/subtract the compass deviation to give compass heading -- not really applicable in any FS aircraft I know of).

1 hour ago, blackbird7 said:

2. My second question is, how often do pilots generally calculate the WCAs during a single trip since the wind heading can change over time? Is it instead more common to just let the autopilot deal with the wind corrections?

Well, that rather depends what sort of aeroplane you are flying and what your approach to navigation is :). Most GA types that the average PPL would be flying are not equipped with any sort of autopilot, much less one with GPS coupling/automatic track keeping etc :). However, of course, there are plenty of hand-held GPS/moving-map type devices which are very popular.

That said, what happens if and when you lose the GPS signal and/or the batteries run out?

I would suggest that if you are going on any sort of substantial cross-country flight it would be sensible as part of the planning process to calculate headings and ETAs (remember that with the whizz wheel you will be calculating not only wind correction angle, but also ground speed and therefore ETAs/fuel usage etc) and record these on a paper plog, even if you plan to refer to a moving map type device (and at least in the UK it remains a requirement to have a current paper chart on board) -- otherwise when the batteries run out you are in trouble!

However, all students are expected to learn the basics of visual dead reckoning, which means no GPS and certainly no moving map!

The normal technique is to calculate the appropriate headings/ETAs etc for each leg prior to flight using the appropriate wind forecast data. Once airborne, you then fly the calculated heading. At the halfway point, you would then make an assessment of how many degrees left or right of track you are, and how far ahead or behind of your calculated ETA. You then correct by making a turn of twice the track error (so if you are, say, 5 degrees right of track at the halfway point you would correct by turning 10 degrees to the left) and update your ETA (indeed, on a test you would be expected to tell the examiner "2 minutes late at my halfway point, my new ETA will be...")

The only time one would generally get the whizz wheel out to actually calculate a fresh WCA in flight (and even then somewhat debatable as there are quicker and easier ways to approximate) would be for the purpose of planning an in-flight diversion. However, given that the wind forecast is just that - a forecast, and the actual wind will do what it will in flight -- and there are very many variables, one does have to be careful of measuring with a micrometer and cutting with an axe (how accurately can you hold a heading for instance?). Ultimately for most GA VFR navigation purposes, if you can get within about +/- 10 degrees or so you will arrive close enough to your turning point/destination to identify it!

[Chock 17,769]

Depends on the application, level of precision required and whether it's an exam or a check, but in short, no, it's not that uncommon for day to day stuff to use magnetic, as much as anything for expediency. Ded reckoning and flying deliberate offsets to landmarks is usually the way for most GA pilots, so unless you were flying hundreds of miles, close enough is generally going to be good enough with E6B stuff although for exam, they'd expect you to do it all properly.

With regard to the second question: As with everything these days, and in particular with more sophisticated avionics and autopilots which can adjust for drift offsets etc, coupled with the wealth of useful data presented to you on PFDs etc, it's becoming less of an actual necessity to make manual calculations for navigation in practical day to day terms, as noted, more a case of for exams to ensure proficiency for emergencies should equipment not be functioning properly.

Pilots do need to be able to operate the aeroplane when things go awry and in recent years we've seen quite a few accidents occur when those skills have slipped and pilots have been too reliant on equipment. The inability of pilots to be able to do basic 'stick n rudder' stuff and work things out the traditional way etc, was one of the issues highlighted by Air France Flight AF447, which was the Airbus A330 that stalled and crashed into the South Atlantic after the Pitot Tubes froze up and one of the pilots didn't use some basic piloting skills to fly them out of trouble because he was too reliant on the autopilot and the avionics. Thus the emphasis for professional pilots as a result of incidents such as these (as it should be for all pilots really unless they are looking for trouble), is to not have them neglect the basics, and that includes being able to use an E6B and being able to do some calculations without one too. So...

Raw data calculations as they are called (i.e. being able perform hand flown course corrections and steering inputs from calculations made from basic information) is still a big part of pilot examinations and proficiency check rides. But some of those checks are to ensure you know how to do this kind of thing quickly...

Let's say I am making an approach onto a runway with a magnetic heading of 270 degrees, and I have a 12 knot crosswind coming from 300 degrees and my approach speed will be 120 knots. I can easily calculate how much I need to offset the nose to one side to take me right onto the piano keys: I multiply the crosswind component of 30 degrees (300-270=30) with the speed of that crosswind (30x12=360). I'm coming in at 120 knots, so I divide 360 by that approach speed and that'll give me a value of 3 (360/120=3). That's how many degrees I'll need to offset into the wind from the runway's heading of 270. There's no need to use an E6B for that sort of stuff, it's one of a few quick calculations professional pilots are expected to be able to do.

Strictly speaking, a professional pilot, (in that example), should then set the heading bug to 273 degrees and fly that heading precisely if they are doing an approach manually, and one would hope a pro pilot does indeed do that sort of thing. If I was doing an exam, I'd do that too, but for flight sims, I go a bit more 'seat of the pants and rules of thumb' on such matters, for example; each diamond of the localiser deviation markers on a PFD represents an offset of 4 degrees, so since I'd need an offset of 3 degrees, I'd steer a bit to the left of the first deviation marker to the right of the magenta diamond. That'd be close enouh to 3 degrees for me and would do the job well enough when combined with the view out of the window when coming over the fence lol. After all, we are supposed to be flying the things.

 

Edited August 24, 2018 by Chock

[skelsey 765]

10 minutes ago, Chock said:

each diamond of the localiser deviation markers on a PFD represents an offset of 4 degrees

Off-topic, but are you sure?

Full-scale deflection of the CDI when a localiser is tuned is equivalent to an angular deviation of 2.5 degrees, so one dot is 0.5 degrees.

Typical PFD localiser displays are expanded, so each 'dot' on such a display may actually be quite a bit less than 0.5 degrees...

[Chock 17,769]

Yes you're right, it's 0.8 degrees, not 4 degrees, was chatting to someone whilst typing that lol previous stuff. Just goes to show what distractions do lol. So I should have said about three of them for the offset for a bit of seat of the pants correcting.

Edited August 24, 2018 by Chock

[blackbird7 3]

Thanks gents for the great insights and responses. 🙂 This is really helpful, and it will add a new dimension to flight simming for me.