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Thread: Your Plane is a Ship

  1. #1
    Senior Member RanRan's Avatar
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    Default Your Plane is a Ship

    A reminder after Vinton's death...



    It's about the difference in mentality between sail-boaters and power-boaters. Most of you are power-boaters plowing through the blue. And why not? You got a throttle and controls that will get you through just about anything. Just about. You need to go back to the elements.


    Sailboats are not pushed, they are sucked along – especially, on a reach where they obtain they fastest speeds. Sails are air-foils just like your wings. Pressure is reduced in front of the sails in the same way it's reduced on top of your wings – the only difference is one is vertical and the other horizontal – the sailboat is propelled and you are lifted. Physics. It's the same wind.


    On a run (with the wind behind you) both airplanes and sailboats are least efficient (in terms of air-foils) – and are both subject to deception. The sailor will feel a decrease in wind (he's running with it), while the pilot will see an increase in ground speed – all will be fine until either wishes to turn.


    And then what? The sailor may broach and the pilot may stall as both see their air-foils changed dramatically in a moment.


    Why? Because the power of the wind is much greater than a 10 ton sailboat or a 900 pound aircraft wanting desperately to overcome it. It will treat you like a bobber or a leaf – the only difference will be the amount of time you can complain about it or react. It's moments in time in either case – with no bragging rights. Silly, paltry bravado in the face of the great what is.


    “My 3 ton keel will overcome you.” says the sailor.


    “My 180 prancing horses will overcome you.” says the pilot.


    “Isn't it nice to think so.” says the wind.

    Your plane is a ship. A SAILING ship.
    Last edited by RanRan; 05-01-2011 at 09:15 PM.

  2. #2
    Senior Member couleeone's Avatar
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    Default Re: Your Plane is a Ship

    Interesting parallel! However doesn't the pilot have a 180HP fan pulling him through the turn with out loss of airspeed? Whereas the sailboat loses all momentum when broaching in the wind.

    I still have difficulties visualizing the physics of turning downwind and losing airspeed.
    Geo
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  3. #3
    Senior Member RanRan's Avatar
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    Default Re: Your Plane is a Ship

    Quote Originally Posted by couleeone View Post
    Interesting parallel! However doesn't the pilot have a 180HP fan pulling him through the turn with out loss of airspeed? Whereas the sailboat loses all momentum when broaching in the wind.

    I still have difficulties visualizing the physics of turning downwind and losing airspeed.
    If you had a tailwind of 30 knots and showing a ground speed of 70 knots, you are actually near a stall - the air speed under the wings is only 40 knots. Anytime you turn downwind you are going to lose airspeed but pick up ground speed. So it's very possible to stall at 70 - 80 knots ground speed in a strong tailwind. You're moving right along, but that movement is deceptive. So in a downwind leg in high winds watch your AIR speed not the ground going by. With any tailwind your stall speeds will go up relative to the ground.

    When practicing stalls - watch your ground speed at stall and see how much it varies with wind direction and intensity.
    Last edited by RanRan; 05-02-2011 at 08:31 AM.

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    Default Re: Your Plane is a Ship

    Quote Originally Posted by RanRan View Post
    If you had a tailwind of 30 knots and showing a ground speed of 70 knots, you are actually near a stall - the air speed under the wings is only 40 knots. Anytime you turn downwind you are going to lose airspeed but pick up ground speed. So it's very possible to stall at 70 - 80 knots ground speed in a strong tailwind. You're moving right along, but that movement is deceptive. So in a downwind leg in high winds watch your AIR speed not the ground going by. With any tailwind your stall speeds will go up relative to the ground.

    When practicing stalls - watch your ground speed at stall and see how much it varies with wind direction and intensity.
    Hi RanRan,

    Okay, you got me to bite on the old "downwind turn" myth. I believe that if an aircraft is flying upwind at 40 kts and then turns downwind that the airspeed is still..... 40 kts! YOU may notice a change in groundspeed but the aircraft doesn't know that. The aircraft is flying a constant 40 kts within an airmass that is moving across the ground.

    I agree that we must have awareness of the effect of the moving airmass has on our reference to the ground. Especially when doing ground based manuevers such as traffic patterns. It also is good information for endurance calculations and crosswind limits when landing or taking off. Which brings up a good point. If a constant airspeed is effected in the air by a turn from a headwind to tailwind why don't we ever exceed our crosswind limitation in the turn?

    Windshear is a different animal as that is a change in the velocity or direction of the airmass itself and would have the negative effects you mention. If that is what you were discussing, well, then I just wasted space and ink.

  5. #5
    Senior Member RanRan's Avatar
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    Default Re: Your Plane is a Ship

    Quote Originally Posted by WillM View Post
    Hi RanRan,

    Okay, you got me to bite on the old "downwind turn" myth. I believe that if an aircraft is flying upwind at 40 kts and then turns downwind that the airspeed is still..... 40 kts! YOU may notice a change in groundspeed but the aircraft doesn't know that. The aircraft is flying a constant 40 kts within an airmass that is moving across the ground.
    You're right, Will. I haven't been thinking about this correctly. We fly in a fluid - whether it's moving (relative to the ground) or not - makes little difference in actual air speed. I got it now and thanks for the correction!

    I feel like an idiot for missing the obvious.
    Last edited by RanRan; 05-02-2011 at 09:44 PM.

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    Default Re: Your Plane is a Ship

    Don't give it a second thought. I have someone here who almost daily helps remind me when my thinking is off track

  7. #7
    Senior Member RanRan's Avatar
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    Default Re: Your Plane is a Ship

    Quote Originally Posted by WillM View Post
    Don't give it a second thought. I have someone here who almost daily helps remind me when my thinking is off track
    That was a good move on your part to marry a physicist. I keep going for cocktail waitresses. ;-)

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