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Pilot Math

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Anyone have any quick math equations they use in the cockpit like the ones below?

1) Degrees off nose + 20 = crosswing percentage

Example: 40kt wind 30deg off nose = 20kt crosswind component

2) Ground Speed / 2, add a zero = 3 degree descent rate

Example: 120kt / 2 = 600 fpm vsi

3) 50% of wind gust = Addition to final approach speed

Example: Winds gusting 20 = add 10kts to final speed

4) Add 2 subtract 2 rule for reciprocal headings and runways

Example: 327 recip = 147. If add 2 to first number, subtract 2 to second number. 1st number is always opposite 2nd number. Third number is unchanged.

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Altitude and distance for a 3* glide slope

distance x 300 + airport elevation

so if your 10 miles out on an ILS and the airport elevation is 500ft:

10nm x 300 + 500ft = 3500 MSL

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4) Add 2 subtract 2 rule for reciprocal headings and runways

Example: 327 recip = 147. If add 2 to first number, subtract 2 to second number. 1st number is always opposite 2nd number. Third number is unchanged.

I like it! Thanks!

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To figure out descent gradients for the visual learners:

On your ADI, put the distance you have to the point at which you need to be at the new altitude on the 10deg line, then put the altitude difference on whatever corresponding line (we usually use 5deg decent when able).

Ex: You get a call to descend at pilot's discretion from FL280 to 3000 ft and you're 100 NM out from the fix...when's the optimal decent point?

So I want to use a 5deg descent, so I imagine the 5 deg line of my ADI representing 25 (25K ft of altitude to lose), thus the 10deg line represents 50NM (10 is 2x of 5). So at 50NM I should begin a 5deg descent to arrive at the fix at 3000 ft. However, I usually add another 5-10NM over that just b/c you don't want to be getting to the fix right as you hit the altitude, and you have to allow slop for wind, etc.

If I wanted to use a 3deg decent, I'd imagine the 3 deg line representing 25, thus the 10 deg line would be approx 85NM (9 deg line would be 75NM out, so estimate about another 10NM to get the 10deg line equivalent)...so at 85NM (add another 5-10 as usual) I'd start a 3 deg descent.

Kind of hard to explain without a picture, but maybe someone will understand what I just said. I know this helped me...back in the day if I got a descend at pilot's discretion, I just WAG'd it and had no real idea of what would work. Using this method now gives you a concrete time at which you should begin your descent instead of just guessing.

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Revival....anybody know where it says to use the “full gust factor” for crosswinds?  ie if it’s 32G40 then u use 40 instead of the old wom of using half the gust factor?  I seem to remember a long time ago people would use 36 for the wind strength since that’s half the difference for 32-40kts. 

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On 4/16/2018 at 1:17 PM, isuguy1234 said:

Revival....anybody know where it says to use the “full gust factor” for crosswinds?  ie if it’s 32G40 then u use 40 instead of the old wom of using half the gust factor?  I seem to remember a long time ago people would use 36 for the wind strength since that’s half the difference for 32-40kts. 

Would it make any sense to not use the higher corsswind value?  If the high value was above your crosswind limit and it gusted while you were landing then you'd be trying to land above your crosswind limit 

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2 hours ago, spaceman said:

Would it make any sense to not use the higher corsswind value?  If the high value was above your crosswind limit and it gusted while you were landing then you'd be trying to land above your crosswind limit 

I like the technique of telling the controller what crosswind I need to takeoff/land..the gusts usually take care of themselves. 

 

Plus most regs are ‘demonstrated’ crosswind limits...

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3 hours ago, spaceman said:

Would it make any sense to not use the higher corsswind value?  If the high value was above your crosswind limit and it gusted while you were landing then you'd be trying to land above your crosswind limit 

If you mean because someone will burn you as a result? Maybe... but there is some margin built in for making corrections. If you drifted down wind you'll need enough control power margin to correct for that error... if you were downwind (porking  it), not correcting, and then got a gust then you might be hosed... depends on the width of the runway and how white the knuckles are on your ungloved IPs hands.

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I use the clock method to determine XW component.

Just picture a clock with tick-marks at the quarter hours... 15 min(1/4 of clock) 30 min (1/2 of clock), and 45 min (3/4 of clock).

If winds are 15* off runway hdg, you take 1/4 of the wind speed as your XW component.  30* off is 1/2 the wind speed as your XW component.  45* off is 3/4 the wind speed as your XW component.  Anything above 60*,  take the full wind speed as your XW component.

Interpolate as needed to get more exact.  For example if winds are right at 60 off, I take the full minus 2.  If winds are 70 off, I take the full minus 1.

Using this technique, I’ve never been more than 2 knots off estimating the XW component, and it takes about 2 seconds to calculate.

Edited by flyusaf83
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On 4/16/2018 at 9:45 PM, matmacwc said:

1/2 your mom = 300lbs

Still a 1...

  • Upvote 2

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On 4/20/2018 at 8:59 AM, HossHarris said:

Half your age plus seven. 

Don’t forget to subtract 10% for the military discount. 

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