How to make an IT guy feel stupid...

[digital.poet]

Give him something with 'computer' in the title, that doesn't make any sense to him! :)

Bought a mechanical flight computer from my flight school a couple of days ago. All those lines sure are pretty! So I am going through the little booklet with the instructions and have started to get my head around using it for simple multiplication and division and unit conversion calculations. Now I have moved on to wind drift calculations and I am totally confused again.... "set the what arc to what now?" ;)

For the record, I prefer the types of computers that have buttons and work in 0's and 1's.

The thing that has me tickled about all of this is that, while I was pretty good at maths at school, I remember once (during a short rebelious phase) being 'removed' from my mathematics class for loudly protesting during my geometry class. I think the phrase I used at the time was something like, "I am *never* gonna use this crap for anything!". Now I am reading my nav book, starting at this mysterious 'slidey' device and analysing triangular vectors.

I am sorry Mr Smith.... truely I am!

[digital.poet]

Actually folks, rather than me just posting generic diatribes, perhaps I should ask a question with it.

There is something I am not really 'getting' here. I have worked my way through basic muliplication, division, distance, time and speed calculation and I am now onto conversions. All was going well through straight distance, volume and weight conversions, but I am confused when it comes to, "How much will 182 imperial gallons weigh in pounds?". Confused because the questions keep references a 'specific gravity' figure. Could anybody tell me what this represents? I would assume that gravity is pretty constant (at least at this scale) until much higher than I tend to go in my C-172!!

Where does this 'specific gravity' value come from?

Thanks :)

[Crosshair]

Specific gravity, also known as relative density, is basically the "heaviness" of something relative to water.

It's a dimensionless value, but you can say that the specific gravity of something is the mass of a liter of it in kilograms.

The specific gravity of water is 1; the specific gravity of 100LL fuel is 0.72.

[digital.poet]

Ahhh make sense. Thank you.

[J.A.F.O.]

For the record, I prefer the types of computers that have buttons and work in 0's and 1's.

It's a well known fact that 100 out of every 5 people don't understand binary.

[rans6andrew]

100 out of every 5 eh.

Is that the same as "There are 10 kinds of people, those that understand binary and those that don't"? :)

Also, is it still necessary to use a whizz wheel to get through the Nav ground school? I thought that I was given the choice of whizz wheel or electronic when I was going through it. I still chose the whizz wheel as I was a bit nostalgic for my old slide rule, electronic calculators were just being accepted when I did A level physics and no one could afford them when I did my O levels.

G-MYMH.

[digital.poet]

Is that the same as "There are 10 kinds of people, those that understand binary and those that don't"?

Yes, I think so. Also similar to how only DEAD people understand hexadecimal and how programmers always confuse christmas and halloween because 31 oct = 25 dec ;)

I love geek jokes!

G-EMMA,

Excuse me for relishing in your agony, but I am glad I am not the only one. I have spent a few more hours with the whizz wheel tonight and we are starting to get on a little better. I am absolutely certain that it is one of those things that is going to seem really easy once I piece it all together.

Apparently, according to my FI, I am supposed to be using the 'wind down' method. I feel like (geek joke alert!) lonestar in the movie 'spaceballs'..... "It will be revealed to you at the proper time!" :)

I like the spreadsheet idea though. I might have to try that myself.

[Saab Dastard]

I resurrected this post of mine from 2001 that may be of use:

There are 3 vectors in the wind calculation:

Wind speed and direction
Heading & IAS (or more accurately TAS)
Track and ground speed If you know 2 of these you can calculate the third, but remember that a vector has both magnitude and direction.

In the usual flight planning problem, the wind velocity vector is known (from forecast), but the other two are actually unknown, insofar as you will know your desired track but not the ground speed and you know your IAS but not your heading.

This is why the problem requires an iterative 2-step (or more) approach to solution - the "jiggle".

An approximation is made, based on the assumption that heading and track are initially the same. It is then necessary to enter the revised heading to refine / confirm the calculation. In strong winds or large angles between track and wind direction it may be necessary to do this more than once.

In effect you are solving the problem: given wind velocity, heading and IAS, what is your track and ground speed? You are assuming a value for heading, and then checking that the assumption is correct by solving the problem and ensuring that the answer is your desired track, and iterating as required until it does.

Also remember that you are always blown from heading to track, so if you are ever unsure about whether to add or subtract the drift, just look at the direction of the wind on the map and then see how it relates to your track line - which way will it blow your aeroplane, and will you need to increase or decrease your heading to compensate?!

Stick with it, it gets easier!


SD

[draccent]

My e6b thing leaves me scratching my head. :uhoh:

[K1200Sagian]

Me too, doing the nav exam. What fun that is.

Slide rules were last used by me in 1971.......

This is a belter for your opinion.

The pics in the Nav Manual (Godwin) shows the Pooleys CRP Computer, which is not set up the same as my Transair TSP...........

Example 1.

I set the cursur 10 m,, the the inner to 9.1 as in page 25 of the manual, and the box underneath says altitude not air speed.

Is it me??

[Whirlygig]

I am sure that when I sat my PPL Nav exam, I used an electronic calculator (non-programmable) and I do all conversions and calculations that way - I'm nerdy enough to remember conversion factors to four decimal places.

However, electronic flight computers were not allowed.

Cheers

Whirls

[PompeyPaul]

...I think there's 2 things you won't learn without an instructor.

One is RT
The other is the whizz wheel

It's possible to crank through the Nav book and pick it all up but I think it would take for ever.

Now I've got the PPL I do most of my calcs on a calculator. I stil maintain that the whizz wheel doesn't really have the precision you need to get the accuracy that the exams require.

Get ready for a LOT of long division & long multiplication!

[Major Major]

Having waded through the Nav book cover to cover my instructor explained it better in an hour's ground school and, crucially, explained what I needed.

Still think it's pretty amazing that you can put a cross on, jiggle a bit, read off some values and it turns out to be spot on.

So I have no trouble with the wind drift side, or with converting GS to leg time, but can I remember how to multiply two values for to get moments? Can I hell.

Who wouldn't use a calculator for 232lbs at 87.5in? You just would.

BTW, same with Radio Nav; an hour with the instructor more or less nailed the theory.

[rsuggitt]

You know those triangles you can draw of track, heading, and wind ?

Well, when you use a whizz wheel, that's what you're constructing. That same triangle.

[davidatter708]

Think a crp1 is confusing you should try my watch it has the same thing but on the bezel cept its minute but good fun in ur skills test to do eta on ur watch saved me some mental brain power. useless post i know but there is always one its about my turn
dave

[PompeyPaul]

but what about the exam? Do the questions give very similar answers or will it be obvious?
This is what makes Navigation the hardest exam, imho. It's NOT a maths test, if you put the numbers they give you into a calculator the precise answer is not there. You have to select the answer that is nearest to what you have. This can be very close.

I.e you decide that it will take 35 mins, you may well get something like

a) 10
b) 25
c) 47
d) 60

You plumb for B because it's marginally closer than the other.

Some of the other questions will require insane amounts of precision. The one that I really struggled with was a bearing question, I got something like 38 degrees, the choices I had were

A) 20
B) 36
C) 40
D) 50

On the whizz wheel, especially with slightly thick navigation pens that 4 degrees of accuracy can be pretty tough to get.

Others may disagree and think that all questions are mathematically perfect, but I got the distinct impression the right answer wasn't there, and you had to pick the "most right one".

[Dark Star]

MM

232x87.5

87.5 is 7/8ths of 100

1/8 of 200 is 25
1/8 of 32 is 4
so 1/8 of 232 is 29

232-29=203

203x100=20300

much quicker than a calculator and no finger trouble !