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3 Answers

LAST QUESTION…downwind

Asked by: 7910 views Flight Instructor, General Aviation

If the wind is blowing from the Northwest, would I still be downwind if I was heading Northeast?

I am thinking in terms of ground reference maneuvers and having to enter on the downwind and left hand turns (rectangular pattern).

If the wind was blowing FROM the Northwest, I think I'd have to enter on the Northeast side of the field in order to make left hand turns.  This confuses me b/c you don't have much of a tailwind in that sense, and I usually attribute tailwind with downwind.  I GUESS my question is, as long as I am heading North...I am on a downwind, correct?  I may not have much tailwind...but I am still downwind b/c I am flying DOWN THE WIND.

Also, if my wind speed is at 10 knots...and my electirc flight computer tells me that I have a headwind of 5kts and a left crosswind at 9kts...well, 9+5 = 14kts and that exceeds the total windspeed of 10kts.  I guess it's not factoring in the tailwind which could reduce and balance the 5kt headwind and the 9kt crosswind to the total windspeed of 14kts.

 

 

 

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3 Answers

  1. Best Answer


    Kent Shook on Oct 30, 2010

    Chapter 6 of the Airplane Flying Handbook (http://www.faa.gov/library/manuals/aircraft/airplane_handbook/media/faa-h-8083-3a-3of7.pdf) says that the rectangular pattern ground reference maneuver should be entered ad a 45-degree angle to the downwind. That is very much like a standard pattern entry.

    If the wind is blowing from the northwest, you’ll be heading southeast when you’re on the downwind. We enter the pattern from the outside of the rectangle, so our first turn will be a 45-degree turn to the right, ending on a southeast heading. So, you should start the maneuver by flying east, making a 45-degree turn to the southeast, and then flying around the rectangular pattern using left-hand turns.

    However, since this is a ground reference maneuver, and most rectangular references on the ground are oriented N/S/E/W (at least they are here in the Midwest), either a South or an East heading would work as your downwind, so you’d enter from a Southeast or Northeast heading. This sounds like maybe what your question really was – The “Downwind” should be the first leg of the rectangle, *not* the 45º entry heading.

    So, two things might be causing your confusion here: First, which leg should be downwind, and how the maneuver should be started. Hopefully I have answered both satisfactorily above.

    One thing I’m not understanding is how you determined that you want to start from the northeast side of the field, unless you meant starting at the north, heading southwest, and making your first left-hand 90º turn to the downwind heading (southeast). That’s not how the AFH says to start the maneuver.

    Also, if the wind is from the northwest and you’re looking for a course/ground track of northeast, you’ll have a crosswind from the left and you’ll have to compensate by pointing the nose of the airplane to the left, making your heading slightly more north than east and giving you a slight headwind component, not a tailwind.

    For your final question, your electronic flight computer is correct, and you do not have a tailwind at all. The reason that the two components don’t directly add up is that we’re talking about vectors – Sides of a triangle. It sounds like you put a 60-degree crosswind in. If you draw a triangle on a piece of graph paper, starting at the nose of the airplane and going straight ahead 5 squares (your headwind component – Draw an arrow pointing back at the nose of the airplane) and then going to the side 9 squares (again, draw an arrow back at the plane) you’ll find that if you measure the hypotenuse of the triangle, it will be about 10 squares long (9.5 to 10.5, since your flight computer probably only has a resolution of 1 full knot in its calculation/display).

    So, the only time the crosswind and headwind components will add up to the actual wind magnitude is when you either have a direct headwind, a direct crosswind, or a direct tailwind. If you have both a crosswind component and a headwind or tailwind component, they’ll add up to more than the wind magnitude.

    Aside from using a manual or electronic E6B, you can also find the headwind and crosswind components using a regular scientific calculator – The crosswind component is the sine of the wind angle off the nose times the wind magnitude, and the headwind/tailwind component is the cosine of the wind angle off the nose times the wind magnitude.

    Sorry this answer is so long – It would be a lot easier to show you this stuff graphically rather than textually!

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  2. Jason Schappert on Oct 30, 2010

    Lindsay,
     
    Cutting through all the fluff the short answer is yes
     
    Jason

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  3. Lindsay Atkins on Oct 30, 2010

    Kent and Jason…once again…THANK your for your help and for putting up with me.  I think I mistyped a heading in my original question, so sorry for the confusion.  I confused you guys AND me.
    Thanks again for everything!

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