X wind and drift calculations.

[Keygrip]

Mental powers only!! No computers, calculators - nothing but brain cells.

Sat at the end of the runway, have been given a take-off clearance which included the latest, up to the second, surface wind report.

How do you calculate if the wind is within X wind limits?

Next question - whilst en-route (or holding at a beacon), you need to calculate the current drift - lets put the aircraft in IMC (so you have no ground features to look at). Remember - no machines (includes radio aids). All you have is wind velocity as given by ATC or the weatherman - and a track required).

Go for it.

[BEagle]

Use the 'clock' method:

15 deg off=1/4 W/V
20 deg off=1/3 W/V
30 deg off=1/2 W/V
45 deg off=3/4 W/V
60 or more, use all W/V


Max drift is equal to W/V divided by your TAS in mi/min. So if you're doing 180KTAS, that's 3 mi/min. If the W/V is 30kts, max possible drift is 30/3 = 10 deg. Now apply clock factor as above; if the W/V is 210/30 and you're holding on 240 deg inbound, use 1/2 max drift and steer 235 deg inbound. Outbound use 3 times that, i.e. 15 deg and make your heading 075 deg.

Now try it bouncing around in a single engine aeroplane at 90 kts without a gyro compass, no autopilot and no co-pilot. At night and in IMC!

You can use a similar method to recompute your GS using (90-angle off) and the clock factor. So if the track is 060, TAS is 180Kts and the W/V is 120/30, your heading should be approx 070 deg and GS 165Kts.

[rustle]

Not an answer from me, but if you're going to cross-post can you put the link to this on the other thread in PF please? http://cgi.millband.plus.com/slalombbs/smilies/eyes.gif

[Keygrip]

BEagle - nice one. Now I put on the "devils advocate" hat and say, "Ah, but what if the ACTUAL drift at altitude is only, say, three degrees - but the MAX drift at that altitude is as much as eight degrees."

You lay off 3 x 8° (24°) outbound in the hold - when it should only be 9°. What will that do to the inbound?

(rustle: darned good point, sir!! That's what comes of posting before your second cup of coffee in the morning. I've done it for you now).

[BEagle]

I write simple for American...

Max drift is the drift you would experience if the wind was at 90 deg to your track. It is calculated like what I done bin' sayin', y'all.

Actual drift is the component (sorry about the long word) of the maximum, sorry, max drift resulting from the actual wind direction compared to your track.

Have a nice day....;)

[drauk]

If BEagle's clock-code system isn't scientific enough for you, what you're doing to determine the crosswind component is multiplying the sine of the angle of the wind by its speed. To do this, you need the sine of that angle. The clock-code is plenty accurate enough for determining the sine of that angle and better still errs on the side of caution at the greater angles.

For the first question - the calculation at takeoff is pretty easy using that clock code. 15deg wind - a quarter of the wind speed is crosswind. 30deg wind - half the wind speed is crosswind. 45 its three quarters. Just these three alone are accurate enough for most purposes I would have thought.

For the second question, use BEagle's method again. In a training aircraft doing around 110 knots I'd call it 2 miles a minute, so halve the windspeed and apply the clock code.

As for how you get the windspeed (before you're even tracking a beacon) if you're at 2000' you can take the surface wind from ATC, double it and add 30deg (in the UK) for a rough estimate.

[Keygrip]

BEagle - apologies on two counts.

1st: I missed the line Now apply clock factor as above; from your paragraph about converting max drift to actual drift.

2nd: I misjudged you. I thought that as an educated and experienced pilot with examiner qualifications, you would be able to instruct without lowering your standards to sarcasm. I was obviously wrong.

The whole point of the thread was to try to educate some of those with lesser experience than yourself, who may not have heard the "rules of thumb" before. What a pity you had to be so smart a**e about it - I thought I could rely on people like you to give intelligent responses. Sorry.

[BEagle]

Sorry if it came over as sarcasm - 'twas supposed to be a cheeky hint to re-read what should have been an easily understood post!

Hence the ;) !

But sorry if you were offended.

Now - have a nice day!!


PS - I deliberately avoided using the sine of the wind angle as referred to by drauk in order to keep things simple.

[Keygrip]

OK - truce.

I've been taken the wrong way on occassions when it is impossible to put real emotions - the smileys are a good start, but rarely cut it.

I most certainly read it as a nasty and unhelpful response.

Glad it wasn't meant that way - as I do respect (most of :p ) the answers you give to these pages.

[BEagle]

Truce it is!

.........but no tongues when kissing to make up, OK? :p=:yuk:


Back to the original topic of 'max drift' and the 'clock factor'- this method was taught to all UK military students once they'd learned to grapple with the whizz-wheel first. It's so easy that some people think that it's somehow cheating. But it's accurate enough - and in any case, how accurate is the wind estimate?

The KISS principle works just fine in aviation - as does 'TLAR':

That Looks About Right!

[DFC]

If one finds it hard to remember the above angles and factors, remember the 6th sense;

10 deg - 1/6
20 deg - 2/6
30 deg - 3/6
40 deg - 4/6
50 deg - 5/6
60 deg (or more) - 6/6

It is the exact same as the above but I find it more instinctive and easier to remember.

Regards,

DFC

[moggie]

BEagle - TLAR is my favourite tool for flying and is amazingly accurate!!!

Applies to aeroplane design, too - Spitfire, Hunter, Victor, VC10, Vulcan, Concorde etc.

[Chuck Ellsworth]

Hmmmm....


Now try it bouncing around in a single engine airplane at 90 kts. without a gyro compass, no autopilot and no co-pilot. At night and in IMC!

This question about drift would then be a moot point because the pilot would not have enough brain cells to figure it out.. :O

Chuck E.

[Keygrip]

Now try it bouncing around in a single engine airplane at 90 kts. without a gyro compass, no autopilot and no co-pilot. At night and in IMC!
You mean a standard British flight, Chuck?

Yeah - they could hack that - and do the math. Usual scenario actually.

[Chuck Ellsworth]

Keygrip:

I was just giving BEagle a hard time. :O

[Keygrip]

Sorry, Chuck - need more beer (not doing well at spotting sarcasms on this one).

[BEagle]

Of course if you're lucky enough to be flying in the clear air of beautiful BC, I guess that you have no problem!

[Chuck Ellsworth]

Actually living here on Vancouver Island is just about the same as living in England weather wise.

And we are catching up to you in the tax and fee department.

By the way I should be back at North Weald in about ten days or so.

Chuck

[FlyingForFun]

Keygrip, not sure what part of Britain you fly in, but near me I can't find anywhere to fly at night, whether it's with or without gyro compass, auto-pilot, co-pilot and in IMC. :(

FFF
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[Cloud Chaser]

Understand most of that but could someone tell me what the KISS technique and TLAR are.:uhoh:
Thanks

[BEagle]

KISS= "Keep It Simple, Stupid"

TLAR= "That Looks About Right"