Standard question and a very common real world question for heavier aircraft.

(a) figure out the fuel burn from your position (B) back to A and deduct that (plus contingency) from the total usable fuel at B.

(b) use the resulting fuel to figure out your PNR from B towards C and back to B.   You have addressed the B to A bit at (a), above.

do you remember any of the answers that were available? was it multiple choice or type in?

Hi there, can anyone please guide me? I'm preparing for for CPL performance exam and just have questions just to make sure I'm on the right track 

1. What is the exact drift angle that has to be in order for us to find ETAS, 5 degrees or 10 degrees?

2) I am using the E6B (ASA) model. How can I use it to find the ETAS? Because I hear some people here saying that in this type of computer, the ETAS has already been accounted for; if so, does that mean I just put in my wind and velocity and turn the wheel to my heading and then slide it up or down to my given TAS and under the center of the graticule I find my GS and don't need to go through all the processes of finding the crosswind and all calculations or something else? Please, I need your guidance; I'm a bit confused 

Also, if I have to find it through calculation, can I use the wind component grid that is printed on it?

Ali,

Afraid that you have been led up the garden path during your training. Happens to lots of people because a LOT of the training people really don't know what they don't know and, so, errors and lack of knowledge beget more folks with lack of knowledge and so it keeps going on.

What is the exact drift angle that has to be in order for us to find ETAS, 5 degrees or 10 degrees?

First point - finding ETAS has absolutely nothing to do with the drift angle's having some particular value or not, as the case may be.   

Background - There are two main types of pilot navigation computer:  The first is

(a) the Dalton (mostly now clones), often called the E6B, which term dates back to the USAAC/USAAF stores designation for the device developed by Philip Dalton back in pre-WWII days.   The Dalton is the device with the sliding bit displaying drift splays.  From your post, it is pretty evident that you are using a Dalton clone.  The other common device is

(b) the CR (now mostly clones - which doesn't have any sliding bit) which dates back to a device developed by Ray Lahr (a United Airlines pilot) for UA in the early 50's which, subsequently, was purchased by Elrey Jeppesen (also, at the time, a UA employee).   The story has become a bit clouded with mix-and-match terminology being introduced in more recent years.   You will see CRs styled along the lines of "E6B Circular".   These are plain old CR clones and have absolutely nothing to do with the E6B, which is a plain old Dalton.  My guess is that the term was introduced for some misguided perceived marketing advantage to pick up a few more sales.   

Although it is difficult to find a definitive story, my take is that Jeppesen, with his sideline embryonic aviation company, wanted a device which was "different" to Dalton's, for marketing differentiation.   Lahr, being an ex-USN pilot, would have known of the WWII German DR2 device developed by Knemeyer before WWII and used that as the starting point for the CR design.  Lahr didn't coin the ETAS term - that was introduced by Jeppesen (or his team) after he purchased the rights to Lahr's device in the mid-50s.

Now, these two devices each will solve the wind triangle, which is the aim when you need to figure out things like what heading you need to fly from A to B and what groundspeed you might end up achieving.   However, while using the same basic navigation triangle, each does the solving deed in a quite different way.   

The Dalton draws the navigation triangle and solves it geometrically by measuring lengths and angles.   Dead simple and works really well.

The CR does the trick trigonometrically which is a mathematical technique but ends up with the same answer.

It follows that there is no necessary link between the two, ie, if you are using a Dalton, you dance the Dalton two-step while, if you are using the CR, you do the CR jive.   There is no mix and match.   You use the appropriate solution protocol for whichever gadget you might choose to use.  Please, forget all about trying to incorporate a Dalton bit into the CR or vice versa.  A bit like driving a Mercedes or a BMW.  Both are nice, both do much the same thing (get you from A to B) but there is a bit of a difference driving one or the other. 

IMPORTANT BIT TO KNOW - the Dalton approach DOES NOT USE, HAS NO USE FOR, AND HAS ABSOLUTELY NO INTEREST IN, ETAS while the CR MUST ALWAYS FIGURE OUT ETAS to calculate an accurate geometric length needed to figure out groundspeed.   The CR ALWAYS USES ETAS WHILE THE DALTON NEVER USES ETAS.   

So, where does the 10° and 5° nonsense come from ?   Dead easy to answer.

Back in the day, when Jeppesen was first playing with his newly purchased device, he noted that, as the drift angle varied, so did the difference between TAS and ETAS.   As the drift angle got smaller, the difference got smaller.   Further, he noted that, for practical use in the aircraft, once the drift angle got down to less than, say, 10° or thereabouts, it didn't really matter whether the pilot did the correct calculation or roughed it out by assuming that ETAS was around about the same value as TAS.   So, the Jeppesen and, subsequently, clone user manuals, all suggested that the pilot ignore the correct solution and just use TAS in lieu of ETAS if the drift angle were less than about 10°.

However, if you do this when you want an accurate answer, like in the exam, you will come unstuck.  More importantly, using this approximation is pretty stupid, as it takes you all of about 1-2 seconds longer to figure out ETAS and get the CORRECT answer.    CASA, realising that this was the case, suggested in its advice to ATPL candidates, that they should NOT use the Jeppesen approximation.   However, to keep the peace with everyone who believed the approximation nonsense, CASA suggested that, if you really wanted to use it, then only use it with drift angles less than 5°.   For these very small drift angles, the difference between ETAS and TAS is very close to zero so it doesn't matter for the exams.   However, it is still stupid because it is super easy and quick to use the standard solution with ETAS.   From a functional point of view, you will round ETAS off to TAS at these small drift angles because that makes practical sense.    So that's where the 10° and 5° came from.

How can I use it to find the ETAS ?

Dead easy, although it is easier on older styles of the Dalton as they had a squared grid on the slide.   All you have to do is draw from the end of the TAS vector a right-angled intercept to the ground speed vector and the length of the intercept on the groundspeed vector is ETAS.  No more, no less.   However, while you can do that, it is of absolutely no value to you other than if you are looking at a question relating to the CR where ETAS is important and, for whatever strange reason, you want to work out the ETAS value.

I hear some people here saying that in this type of computer, the ETAS has already been accounted for

All that says is that the folks saying such stuff don't understand how the two devices work - ie, they are by rote users - step 1, step 2, step 3 ....   The Dalton has absolutely NO interest in, or use for, ETAS and, most certainly, doesn't calculate it anywhere in the Dalton solution to the wind triangle.   ETAS is ONLY of relevance to the CR's trigonometric solution.   Period !

While you can figure out ETAS (for whatever strange reason) it is of NO practical value for you to do so, IF you are using a Dalton device.

if I have to find it through calculation, can I use the wind component grid that is printed on it?

First, you don't need to find ETAS for a Dalton solution.  If you were using the CR, the CR's solution presents the trigonometric stuff right there for you to read off the value of ETAS just to the left of the TAS index mark.

Second, if you really want to calculate separately to the CR's solution protocol, just use the CR as it is - the multiplication is right there on the outside scale for you to read off.   The equation is ETAS = TAS x cosine (drift angle).  You have set the TAS index on the inner scale (which is just the 10 scale mark on the log scale) against the TAS value on the outer scale.   Then, when you move left to the drift angle on the inner scale to read the ETAS value on the outer scale, all you are doing is running that equation I gave above.

Third, the squared wind component grid (on the CR) is there to provide some information relating to the wind velocity part of the wind triangle - nothing to do with ETAS.   I am not sure what grid you are talking about on the Dalton, as most Daltons, these days, don't have the square grid which, originally, was on the sliding scale.   That won't be of any use to you in calculating ETAS as you would need to have the grid able to be positioned over the triangle to do the right-angled intercept as described above.   Perhaps you can explain just which grid you are referring to and we can offer further comment ?

@john-heddles Thanks, John, for your detailed reply. I'm using the E6B ASA model, the aluminium one with the slide (I believe that's Dalton); however, I also have the circular blue disc one (I guess you call it 'CR'). I know how to get the ETAS with the circular one. My apologies in advance for my stupid questions, but for questions related to PNR and ETP in the CASA exam, if the drift is greater than 10 degrees, is TAS accurate to get the GS from, or i have to calculate ETAS because it's not a direct headwind? The thing I'm confused about, for the E6B Dalton aluminium is, do I still need to calculate the ETAS or the computer desinged to bypass it and it will give me the accurte GS just by  puting my  wind direction and wind velocity, rotate it to my track, and slide it UP/DOWN for my TAS, then get my GS?

the aluminium one with the slide 

That's the Dalton (or E6B).

circular blue disc one (I guess you call it 'CR').

That's the CR.   If it is labelled "E6B Circular", or something similar, that's marketing hype with a hope to flog a few more by confusing the issue.   Nothing to do with the E6B, it is a CR.

I know how to get the ETAS with the circular one.

.. and dead easy that is.   Set the TAS index (really that is the slide rule's CD scale's "10" index) which sets you up for the multiplication.   Eyes around to the left drift angle mark and you are running the equation

ETAS = TAS x cos(drift angle)

No more, no less.

My apologies in advance for my stupid questions

There are NO stupid questions !!   However, folks who don't ask their questions are being a tad silly by that omission.   The aim is to sort out the question and the confusion.   Then the problem goes away.

for questions related to PNR and ETP in the CASA exam, if the drift is greater than 10 degrees, is TAS accurate to get the GS from, or i have to calculate ETAS because it's not a direct headwind?

Unfortunately, you have been brainwashed by those who don't quite know what they are talking about.   So let's unbrainwash you, shall we ?   

For the Dalton (E6B) forget ALL about ETAS.   ETAS has NOTHING to do with the Dalton's solution.   

For the CR, ALWAYS calculate ETAS as that is the CORRECT MATHEMATICAL process for the CR's trigonometric solution.   

Jeppesen didn't help anyone by the suggestion that it was a good idea to use TAS instead of ETAS for small drift angles.   However, once you get down to a few degrees drift, ETAS and TAS get closer together and, for nil drift, they are exactly the same. In the aircraft, for small drift angles, it doesn't matter although the approximation is pretty stupid as the ETAS value is sitting there, right in front of you, on the device.   For the exams, ALWAYS do it the correct way and include ETAS (not TAS) in the GS calculation, noting that, for nil drift, ETAS = TAS.

... and to be very specific ...

 in the CASA exam, if the drift is greater than 10 degrees, is TAS accurate to get the GS from

Absolutely the wrong way to go.   As drift increases, the correct ETAS value gets further and further away from (less than) TAS.  You MUST NOT USE TAS for other than very small drift angles.

.. for the E6B Dalton aluminium is, do I still need to calculate the ETAS

Absolutely NOT !    ETAS has NOTHING to do with the Dalton solution.   The Dalton solution is pure geometric graphics, the same as doing the triangle solution on a blank sheet of paper using pens, protractors and rules.   If you are using a Dalton, rub ETAS right out of your thinking processes.

.. or the computer designed to bypass it

The Dalton "bypasses" ETAS calculations as the graphical solution doesn't need ETAS and has absolutely NO interest in ETAS.   ETAS is only of relevance to the CR's trigonometric approach to the solution where the sum are figured along the TR/GS vector.

.. will give me the accurate GS just by puting my wind direction and wind velocity, rotate it to my track, and slide it UP/DOWN for my TAS, then get my GS?

That's it. 

Just as an aside, the geometrically correct sequence is to run the W/V vector DOWN (not up) with the HDG vector direction set.   While the other camp sees some strange value in running the vector UP from the grommet and still gets a satisfactory answer, the correct geometry is to run the vector DOWN from the grommet.   I have no idea where the alternative idea arose but I might speculate that it was to have some similarity to the CR solution ?   Certainly, Dalton, in his patent paperwork, uses the correct geometry.

@john-heddles, thank you  John. God bless you. Definitely learnt something new

Patrik, several observations, if I may.

(a)  Please don't use so many decimals.   It confuses us old blokes and is a tad silly.  83.46 minutes.  Really ?   That gives you an answer precision of less than one second.    Maybe better to round off your answers to no more precision than, say, the conservative minute.   Fine for you to run your internal calculations to calculator architecture precision, but please round off the answer to something a bit more useful and reasonable.

(b) Google ?    Instantly one has to be wary.   Google can be very useful, sometimes, and, at others, totally a time waster.   One needs to be very discriminating as to which links Google suggests.   The reader needs to assess site validity and competence.

(c) the answer ?    I will prefer to jump over the complexity of your numbers.    However, were you going to consider reserves at all ?   It gets a tad sweaty when your last few miles back to homeplate is on tank fumes only.

Perhaps you might have another go at the solution ?

@john-heddles Yea sorry no one has said the formula for that question. So, I tried googling to see what they said. That may be confusing for people I will remove it 🙂

Patrik,

All OK. good sir.     The message going forward is to be careful with Google's suggested links.   Somehow (and that is not always easy to do) the user has to assess the integrity and competence of any given link.   

Generally, for fuel planning, try not to fuss about equations.   It is easier and more intuitive to run the sums in the conventional tabular manner.   Also, that approach makes for an easier time detecting errors.