Ingo Noka

Crosswinds

In Flight Log on February 27, 2011 at 9:37 pm

Malaysian Flag flapping in 15 Kts wind

This Sunday I was finally able to do some crosswind landings. During the PPL period we did a few of those, but I always thought I hadn’t done enough to feel really comfortable.  As usual the wind around this time of the year is picking up and this weekend at noon we had a 15 to 20 kts blowing from the north (10). The tower made runway 34 the active, which is the first time that happens while I was flying.  Charlie Foxtrot was not available so I took AT-4 9M-EYM instead, which made the strong wind even more interesting (the airplane flight manual says that the AT-4 can handle up to 11.7 kts crosswind velocity).

On final I choose to bank into the wind rather than crab, but I had to deflect the left ruder almost to the maximum to stay aligned with the center line. I ended up adding a bit crabbing as well.   Everything worked better than expected.  In fact I was rather pleased with myself and I am happy to report that out of six landings the stall warning went off in two just before touch down.   Of course that should be the standard but I admit that doesn’t happen that often in my landings.

Since I was wondering how to calculate the cross-wind component, I did a bit of research.  Obviously the methods that comes to mind first is to use the E6B flight computer, but mine only has wind velocities in increments of 10 and everything in between becomes a bit of a guessing game.  Wikipedia informs me that the crosswind component is calculated by multiplying the sine of the runway heading (or direction of travel) with the wind speed.  With runway heading of 340º, wind blowing from 10º (i.e. difference is 30º) and an estimated wind speed of 17 kts, that makes a crosswind component of 8.5 kts. (Be careful to distinguish between radians and degree modes when you use computer or pocket calculator to calculate the sine.  In Google the default is radians, so you need to enter “sin(30 degrees)” to get the correct answer.)

That is easily calculated sitting at home, but inflight figuring out the sine will be a challenge.  (Good to remember that the sine of 30º is exactly 0.5, though.)  Googling, I found a couple of rules of thumb for estimating the cross-wind component quickly:

First one:

  • if angle = 10 deg then crosswind component = 1/6 wind strength
  • if angle = 20 deg then crosswind component = 1/3 wind strength
  • if angle = 30 deg then crosswind component = 1/2 wind strength
  • if angle = 40 deg then crosswind component = 2/3 wind strength
  • if angle = 50 deg then crosswind component = 5/6 wind strength
  • if angle = 60+ deg then crosswind componnet = wind strength

Another one:

  • 10 = 1 = 1/6
  • 20 = 2 = 2/6
  • 30 = 3 = 3/6
  • 40 = 4 = 4/6
  • 50 = 5 = 5/6
  • 60 = 6 = 6/6

And one more:

Angle + 20º = % of wind (in my real life example that would give me an accurate 30º+20º = 50%)

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