Can you answer this ?

[nickyboy007]

I am trying to work through this question below,

Find the aircraft groundspeed and track given that the
aircraft’s true airspeed was 75 knots, its heading 130º and the wind velocity 225º/25. Can you solve this using Cosine or Sine rule ?
Any help would be greatly appreciated.

Nick



Correct answer is 76.96 knots and the track 111.1.

[rob_k31]

You can use the wizz wheel. Just wizz it around until the correct speed etc come up. You don't need to use sine etc.:ugh:

[nickyboy007]

No wizz wheel allowed.

[tigermagicjohn]

Why no wizz wheel allowed???

That's the only pre-historic you are allowed everywhere in JAA land, you are learning to fly a multimillion pound aircraft, and you have some old retired Navigatiors loving to set up stupid outdated wizz wheel question!!!

[MarcK]

I get a slightly different answer: 81 kts and 115º. The vector solution can be found as:

Aircraft: 130º at 75 kt. x1 = 75*sin(130) = 57.45, y1 = 75*cos(130) = -48.21
Wind vector is (225-180) = 45º at 25 kt. x2 = 25*sin(45) = 17.68, y2 = 25*cos(45) = 17.68

Resultant: x = x1+x2 = 75.13, y = y1+y2 = -30.56.
Speed = sqrt(x^2 + y^2) = 81.09
Direction = ASin(75.13/81.09), ACos(-30.56/81.09) = 115.6º

If you draw it out, you can get very close. 130 is near 135, and a wind from 225 makes a nice right triangle with hypotenuse (result speed) of sqrt(75^2 + 25^2) = 79 kt.

I'd rather use a wizz wheel.

[tigermagicjohn]

By the time you have done that calculation in flight, you will have :mad:

[The African Dude]

You can also use your head. 130 to 225 degrees = 95, so 5 degrees behind the beam. Below 15 degrees use about a quarter of the windspeed, but this is really only a couple of degrees so it's 3 or 4 kts tailwind. Wind is more than 60 degrees off the nose/tail so use max drift, which for 75kts will be an approximate 2-3rds of the windspeed of 25kts, around 16 degrees port drift.

Would take about 15 seconds in flight to come up with about 78kts and about 109 degrees track. Check and adjust at your midpoint fix.

Sorry nickyboy, I realise I haven't answered your question though.