Cockpit mental arithmetic

[Captain_djaffar]

Such a nice thread

one really instructive thread indeed it is.thanks to you all.

[Henry Hallam]

Could this thread be made "sticky"? It's a lot of useful information in one place.

[Robbo0885]

This one might sound simple to everyone, but I am the worlds worst at mental math.

What was killing me was diversions, where my instructor would ask how long it will take. Speed for the leg, 87kts distance 18nm. I would tie my head in knots trying to figure it. Somebody told me a much easier way to think of it.

Divide the speed by 10, so this gives the distance covered every 6 mins, i.e. 8.7 nm. I find this way I can then put this into distance, i.e. approx 12mins.

I'm sure many of you are looking at this and going "yeah, thats obvious!" but I found working out the times and speed in my head tricky when asked and also flying and navigating a diversion. If one person says "thats quite helpful" then I will have fulfilled the purpose of this post!

[jonkil]

Very Simple one, I use for WB on the microlight:

Mogas Weight:

Weight of Mogas = 3/4 the volume.
Example
40 Litres Mogas = 30 KGS in weight
60 Litres Mogas = 45 KGS in weight

[whitehorse]

If this is your thing a "rule of thumb book" is produced by Flight Time Publications www.flight-time.com Itīs a pocket sized book of about 20 pages if I remember correctly. The latest price on the site is $7.95. Gives all the usual rules and some which are quite exotic, how you are supposed to work these out in your head I donīt know.

The rule of thumb methods are good, just to confirm that what you are doing is reasonable, itīs a question of finding out which ones suit you.

For those of you who only use the GPS, the new 1 in 60 rule is -
1 time in 60 the GPS will fail, due to batteries, not updated software, incorrect data put in etc etc etc.
PS I love my GPS

WH

[Blues&twos]

Robbo0885 - that's quite helpful.

I'm a newby to flying - all of these are great.

Provided I remember them when the chips are down......hmmm.

[IFollowRailways]

For diversions - Finding a rough heading.

Think of your present position as the centre of a clock face. Draw a mental line to where you want to go and think of it as a clock hand - Mentally give that hand a 'time' (Where it would be pointing on the clock face)

Multiply the 'time' x 3 and stick a 0 on the result and you get the heading. For example -

Imaginary line is in the '8' position, 8 x 3 = 24. Add 0 = 240 degrees

Line in '5' position. 5 x 3 = 15. Add 0 = 150 degrees

[wbryce]

Another one for working out time taken when doing diversions...

GS - 140kts per hour so:
140/60, take it down to basic fractions - 7/3.

35nm leg, divide the top number into the distance to fly (7 into 35 = 5 then times it by the bottom number 3 * 5 = 15 mins). Its easy once you have some yardsticks stored in your head if your not good at working the fractions out...once you realise estimates are good enough then you end up just using simple rules like 120 = 2 miles a minute, if your slightly over or under then it doesnt matter much, the estimate will still be good enough, just use common sense and add/subtract a minute if necessary. 90kts is 1.5 miles a min or 3/2 in fractions, 100kts - 5/3.

[Final 3 Greens]

A useful approximation is ground speed divided by 2 x 10 = descent rate in fpm for 3 degree glidepath.

e.g. 90 divided by 2 = 45 * 10 = 450 fpm

[Fg Off Max Stout]

...as stated in post #3!

[MIKECR]

Descent planning:-

height to lose x 3 = distance to top of descent, then add 5nm to slow a/c and configure.
Rate of descent = 5 x groundspeed

Example - 20,000ft descent to 3000ft at 200knots =

20 - 3 = 17, x3 = 51nm, add 5nm to slow a/c = 56nm

5 x 200 = 1000ft per minute

Oh and for Final 3 greens post - perhaps easier just to work out 5 x groundspeed = rate of descent for 3 degree ILS glidepath

[al446]

Sticky please

I'm with Henry Hallam and G-EMMA on this. The learning curve for us aspiring PPLs can be quite steep and having all this in one place is VERY useful. I know there are archaic things knocking around called "books", I have been known to use one or two, and I dont for a minute think this is any kind of replacement but, when experiencing severe brain fade, a thread such as this is useful, it also informs us as to what peeps actually use in real world flying.

Cheers

[Rattus]

Converting the Beaufort Scale to knots - the Corlett Scale

If you're planning a sea crossing, the Coastguard can be a useful source of met information, though wind speeds in maritime forecasts are always given with reference to the Beaufort Scale. These can easily be converted to knots, though not being round numbers, some of these are not easy to remember. The Corlett Scale simply involves rounding up or down by 1 or 2 knots, so that with the exception of Force 1, which is unlikely to bother most aviators anyway, all are multiples of 5:
Force 1 = 02 kts call it CALM
Force 2 = 05 kts call it 05
Force 3 = 09 kts call it 10
Force 4 = 13 kts call it 15
Force 5 = 19 kts call it 20
Force 6 = 24 kts call it 25

Very few recreational pilots are likely to be flying in much over force 6, but the scale can be extended right up to Hurricane Force. For completeness, here's the rest:
Force 7 = 30 kts call it 30
Force 8 = 37 kts call it 35
Force 9 = 44 kts call it 45
Force 10 = 52 kts call it 50
Force 11 = 60 kts call it 60
Force 12 = 64 kts call it 65

Regards
Rattus