gboulton
Posts: 1862
Joined: 5/28/2005
From: La Vergne,
TN, USA
Status: offline
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Mr67Stang,
What you're overlooking is the fact that YOU ARE HOLDING THE WING. As such, you are imparting a force acting as thrust.
Here's the deal, folks...
What so often gets confused, as stated above, is ground speed or ground track and air speed. The trick to understanding lift, and the (lack of) effect wind has upon it is to IGNORE THE GROUND. Remember, when the plane's in the air, it has NO contact with the ground.
Consider that air is a fluid (any basic HS physics textbook will tell you this). let's compare it to another fluid...water.
The airborne airplane exists within this fluid in EXACTLY the same way that a fish exists within a fish tank. Now. Put that fish at the center of the tank. There he sits...motionless. Now...carry the tank across the room. You are providing "wind" (perhaps "current" if you prefer). The fish's ground track is, indeed, greatly effected (and in fact solely determined in this case) by the "wind"...but HE has remained motionless. HIS SPEED THROUGH THE WATER HAS NOT CHANGED.
Consider the same fish....say he starts swimming at 1 foot per second, from one end to the other of a 10' tank. Again...move the tank. EVEN IF YOU MOVE IT IN OPPOSITION to his direction of travel (a head wind), his speed THROUGH THE WATER hasn't changed...he's still swimming at 1 foot per second. Now, to be sure, after 10 seconds, though he HAS traversed 10 feet of water, he will NOT have traveled 10 feet along the ground....rather, he will have gone 10 feet - whatever offset you gave him moving the tank. Say you moved it backwards at 1/2 foot per second...he will have covered 10' of water, but moved only 5' across the room.
The airplane works the same way. It's usually easier to think about it the same as we did the fish...let's consider, for a minute, a motionless aircraft (a balloon is always a wonderful example for this)
Here sits the balloon..motionless in still air. Ok...fine. Now...let's add a 10 kt wind from the south. Guess what...the balloon is, indeed, moving along THE GROUND heading North at 10 kts...but relative to the AIR AROUND IT, it's still motionless. The air moves along at 10 kts North, the balloon moves along at 10 kts North...there is no difference between the two. Thus, AERODYNAMICALLY, the balloon is still motionless.
Now...give this item some thrust...it becomes an airplane. Say this airplane moves along at 100' per second heading 270 (due west). Now...toss in a 10' per second wind from 090 (from the east, heading west).
Sure enough...the airplane is, for every second, now covering 110' of ground...but it's STILL ONLY MOVING THROUGH 100' OF AIR.
The velocity and amount of air over its wings HAS NOT CHANGED. It simply CAN'T. the airplane MUST be carried along within the air in which it finds itself. Thus...AIRSPEED hasn't changed, as a result, LIFT hasn't changed.
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Do we take off and land into the wind? Sure. Do carriers turn into the wind for launch and recovery? Absolutely. If you hold a wing in a 25 kt wing, will you feel lift? you bet.
ALL of these things are relative to a FIXED POINT, the ground. Remember...it's absolutely acknowledged and true that wind DOES effect GROUND SPEED. Well, guess what boys and girls...I dunno about you, but I'd like my GROUND SPEED...the speed relative to either that big honking airplane killing tree (in the case of a full scale plane), or relative to little old ME in the case of an RC plane...to be as LOW as possible. I'm getting old...I don't react as well as I once did. |
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My Lanier Giant Extra 330 crash - 
