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Performance course quiz issue

  • Caseycouche
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Caseycouche created the topic: Performance course quiz issue

Hi, just wondering how close you actually have to be with the marker when selecting speeds on the ias? I was marked incorrect on 3 of them by seemingly ridiculous margins. Please see attached
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  • John.Heddles
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John.Heddles replied the topic: Performance course quiz issue

It would appear that you have a reasonable concern.

The current FAR 23 requirement is at www.ecfr.gov/cgi-bin/text-idx?SID=1117f1....1.23_11545&rgn=div8

Suggest you follow up with the examiners and query why you have been penalised ... certainly, I, and I imagine Bob and his cohort, would be interested in the answers.

Engineering specialist in aircraft performance and weight control.
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  • Caseycouche
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Caseycouche replied the topic: Performance course quiz issue

Here's a few more I got slapped with an incorrect for...
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  • John.Heddles
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John.Heddles replied the topic: Performance course quiz issue

It might assist if you were to post the questions as you saw them rather than the screenshots in your post ? It might be that we don't have all the relevant matters which needed to be taken into consideration ..

Also, the screenshots are a tad difficult for old eyes to read .... a bit bigger might assist.

Engineering specialist in aircraft performance and weight control.
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  • justus101@gmail.com

justus101@gmail.com replied the topic: Performance course quiz issue

Hi All,

Finding thew same problem with these questions.

Have attached a copy of one of the questions. The answer given is the correct one, however the system isn't picking it up right.
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bobtait replied the topic: Performance course quiz issue

These exercises are based on drill using the formula with a calculator.

Flight fuel = Total distance x fuel flow ÷ Ground speed.
Flight fuel = 180 x 6.9 ÷ 132 = 9.4

If you used a slide computer, you would not be able to get that degree of accuracy. The CASA exam will have margins applied to accommodate students who use the slide computer,
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  • John.Heddles
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John.Heddles replied the topic: Performance course quiz issue

Following on a bit from Bob's comments in the last post ...

The following may be of interest and use to those who prefer whizz wheels over gadgets which can end up with a flat battery .. I presume some folks still do use slide rule nav kits (E6B, Dalton, CRs, etc.) rather than, or in addition to, the plethora of electronic calculators in the market these days ? Certainly, old folks, like I am, do ... but that might just be out of force of habit, I guess.

The nav computer (multiplication and division) scales are just plain old garden variety scientific slide rule C and D scales and use logarithmic principles to run the sums. You don't need to know anything about logs to use them but, if you are interested in how they work, there are many URLs on the net which go into inordinate detail for you to peruse ..

The main considerations are precision (how many significant digits can be read or estimated) and accuracy (how close is the instrument read result to the "real" answer).

Assuming accurate construction, the main factor is length of the scales. The circular slide rule (such as the nav computers) has a small advantage here over the typical straight slide rules which, in the past, were used more generally by techo folks such as engineers and scientists.

For the normally marked instrument, precision will vary along the scale from around 4 digits towards the "1" end to 3 digits towards the "9" end. In each case, the final digit is estimated by eye when using the instrument (ie it is interpolated).

Accuracy should be OK for nav computers to around 0.1% or a bit better. So, if you need an answer to ten decimal places (and that probably indicates that you are running the sums inappropriately), use an electronic calculator with sufficient precision .. not a slide rule. For practical calculations in the aircraft, the slide rule is fine provided you use it with a bit of care and attention .. you really don't need to know the distance to run precise to a micron when the accuracy is nothing like that. Similarly, one of my pet things is the often seen weight and balance figures where CGs are presented to a precision of a tenth or a hundredth of a millimetre when the accuracy is probably somewhere around 5 - 10 mm, at best, for a light aircraft

An important consideration in slide rule use is to minimise the number of operations. So, for the previous calculation, one would run that on a slide rule as 180/132 x 6.9 which is one setting of the instrument, rather than as it was written, 180 x 6.9 / 132 which is two settings. As for any calculation with underlying or inherent errors, each additional integral calculation involved in getting to the answer increases the overall final error.

Engineering specialist in aircraft performance and weight control.
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