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    abera's Avatar
    abera Posts: 1, Reputation: 1
    New Member
     
    #1

    Jan 3, 2007, 06:17 AM
    Air Craft Instrument
    Helow Dear

    1.my First Question What Is The Difference Between Turn And Bank Also Skid And Slip
    2.the Difference Bettwen Ground Speed ,relative Speed,dynamic Speed
    dflak's Avatar
    dflak Posts: 18, Reputation: 3
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    #2

    Mar 14, 2007, 11:18 AM
    Quote Originally Posted by abera
    Helow Dear

    1.my First Question What Is The Difference Betwen Turn And Bank Also Skid And Slip
    2.the Difference Bettwen Ground Speed ,relative Speed,dynamic Speed
    In answer to the first question:

    Bank is what causes turn.

    Lift always works perpendicular to the wings. If you are flying straight and level, the force is straight up and it equals the weight of the aircraft. When you bank the airplane, part of the lift is directed horizontally in the direction of the lower wing causing the airplane to turn that way.

    By redirecting the direction of the lift, you also lose part of the lift that was pointing away from the earth (counteracting gravity), so to make up for it, you have to pull back on the yoke or stick and pull some G forces if you want to stay level in the turn. It's basically a high school geometry exercise.

    For example, at 60 degrees of bank, you have to pull back hard enough so you have twice the lift needed for level flight (2G's). At this force, the component of lift still pointing earthwards and counteracting gravity is again equal to the weight of the airplane.

    As for skid and slip. It's a related issue. The above description of turn is based on coordinated flight, that is, the tail of the airplane stays in line with the turn (or at least on the part of the turn you are in). Normally when you bank the airplane, you also press in on the rudder on the same side a little to push the tail in line with the turn.

    If you push too much or too little for the amount of turn, the airplane will "fishtail;" that is the tail of the airplane wants to move out in the front of the airplane. Like its automotive counterpart this is called a skid.

    For a coordinated turn, you press in on the rudder on the side to which you are making the turn. If you press on the opposite rudder (this is called cross-controling), you fight the turn. The wings are trying to make you turn, but the fuselage is pointed outside of the turn and the forward motion of the aircraft is trying to fly straight.

    So you wind up with a combination of things. The plane is not turning, but it is moving towards the lower wing. You stay pointed in the same direction, but you are moving horizontally. This is slip. Slip comes in handy when you have a cross wind. You want the airplane pointed in the direction of the runway, but the wind is trying to blow you off the centerline. If you slip into the wind at just the right amount, you will stay lined up with the runway, and stay on the centerline.

    As for the airspeed question, I have no idea what relative speed and dynamic speed are. Basically you deal with three airspeeds in an airplane: indicated airspeed, true airspeed, and groundspeed.

    Indicated airspeed is simply a measure of how many air molecules you collide with each second. It is measured by a pitot tube which measures air pressure caused by the airplane colliding with the air particles.

    Now as you go up in altitude, the air molecules get farther apart. At around 18,000 feet, they are about twice as far apart as they are at sea level. So in order to collide with them at the same pressure, you have to be moving twice as fast. This is true airspeed. True airspeed is indicated airspeed compensated for altitude (and a few other minor factors).

    Finally there is ground speed. This is simply true airspeed corrected for the wind. Again it's high school geometry. Headwinds and tailwinds are easy to figure out; you just add or subtract them. Cross winds are different; you have to aim the airplane into the wind a little to keep you on course. This aiming takes a little bit away from your forward progress on the ground.
    Flying Blue Eagle's Avatar
    Flying Blue Eagle Posts: 2,056, Reputation: 225
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    #3

    Sep 30, 2007, 11:08 PM
    Hey dflak - YOU answered that question prety good . AS for cross control I always used that for cross wind landings it's a lot easer, you just have to be quick at just the right moment just before touchdown. I was taught to do this in USAF. GO to the problem that (Cellistjames ),Put on for some answers, about two different airplanes leaveing from the same airport, one heading north & one heading East,
    Mylittlesunshyne's Avatar
    Mylittlesunshyne Posts: 60, Reputation: 5
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    #4

    Nov 13, 2007, 05:39 PM
    Comment on dflak's post
    Extremely! He spent a lot of time on that one!

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