Thus he must learn three things all at once, all of them brand new—first, that the airplane can fly in this fashion at all—second, how it responds to the controls in this kind of flight—third, how to judge its flight path so that contact with the ground will be smooth. He has to get acquainted with flight at high Angle of Attack under the most difficult condition, that is, near the ground.
And he has to get acquainted with the ground under the most difficult condition, that is, while flying at high Angle of Attack.
True, the instructor usually prepares the student by giving him some power-off stalls at altitude before giving him landings. This is no doubt better than no preparation at all; but it still does not give the student much chance to become really at home in slow, nose- high flight. For in stall practice, too, the ship goes through the whole range of Angles of Attack rather fast. Sometimes such practice may even reinforce the idea that, whenever the nose is high, a stall will inevitably result within a few seconds.
For what you observe there is the very heart of the matter. Suppose now you continue your flight experiment. Open your throttle a bit wider and then do whatever is necessary to maintain a strictly level flight path. Can it be done? Obviously it can. Dean R. Flight now. Because the wings now meet the air at higher speed, they need not turn it downward quite so sharply and hence need no longer meet it at quite so large an Angle of Attack.
But of course they still have an Angle of Attack, and they still wash the air down. It is still trtte that the airplane keeps itself up by pushing the air down. Angle of Attack is almost inv isibly small, downwash slight. This is normal cruising condition. CRl'ISING Now, as a third step in your experiment, suppose you advance your throttle to regular cruising power, assumed in this instance to be 2. Again, in order to hold level flight and keep from climbing, you will have to hold the nose down farther. And there you are. Now this condition, cruising flight: is it essentially at all different from that nose-high "mushing " sort of flight that you had earlier?
It may seem so. For now, when the airplane is flying level it also points level; in other words the airplane points where it is going; or, in still other words, the airplane now actually goes in the up and down sense where its nose is pointing. But there is no other principle. There is an Angle of Attack. There must be. If there were not. It has no way to keep itself up except by continually beating the air down. The difference is again only one of degree, not of kind.
It is only that now. Only difference: wing section, used upside down, is inefficient as a down deflector.
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Hence a large Angle of Attack is needed to produce enough downwash and thus enough lift. The fuselage points level in cruising flight—simply because the designer joined it to the wings at such an angle the angle of incidence that, with the wings in level flight at cruising Angle of Attack, it would point level! WIDE OPEN Next, suppose you pursue your experiment one further step: you open your throttle all the way and still do whatever is necessary to maintain a level flight path.
Again, of course, you have to put your nose down farther to keep from climbing, and you will have to hold it down by continual forward pressure on the stick. Again this results in an increase in speed. Presently you find yourself hurrying along with the nose pointing definitely down, as if you were in a shallow dive, and yet holding your altitude! Apparently the Angle of Attack is now negative!
Doesn't this prove that there is something else to a wing's lift—some principle other than Angle of Attack and the downwashing of air? The whole problem, however, is merely one of vocabulary. It is customary to reckon Angle of Attack as the angle that the chord of the wing makes with the oncoming air. Chord, in other words, is the reference line.
But the chord is not what really counts in a wing. It is used by the practical engineers only for the sake of convenience because it is easily measured. Say that the wing is basically simply a plane, set at a slight inclination the Angle of Attack so as to wash the air down. This inclined plane is shown on page And this basic inclined plane, which is in an imaginary fashion contained of every wing, is the no-lift line when you look at the wing in cross section.
The curved streamlining is arranged around this plane, as shown on page 17; that is, it is set around it in an unsymmetrical fashion. But it only looks that way; essentially, it still meets the air at an Angle of Attack; and it still makes lift simply by washing the air down. In basic idea, a wing is an inclined plane, set into a wind so as to deflect the air downward.get link
Aviation History Book Review: Stick and Rudder
For greater efficiency, this basic inclined plane is enclosed by a curved outer shape. In aviation practice, Angle of Attack is reckoned as the angle between the chord and the Relative Wind. In that sense, it is true that a wing can develop lift at zero or even at negative Angle of Attack. And in that sense, it is true that a wing cannot develop lift unless it has an Angle of Attack.
For every speed, there is one Angle of Attack that will produce just enough lift to hold your ship up. The more speed you have, the less Angle of Attack you need; the less speed you have, the more Angle of Attack you need. Suppose now you make a final experiment at a safe altitude.
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Set your throttle for about r. In the attempt to maintain altitude, you will pull the stick back; the airplane will slow up; you will have to pull the stick back still farther, and the nose still higher—and eventually, you will stall. What too many pilots do not understand is just why the stall really occurs and how it is tied up with this whole matter of Angle of Attack.
For the fact is that Angle of Attack, w'hich is the key to so many things in flying, is the key also to the puzzle of the stall. A stall is not directly caused by lack of speed.
It is possible to stall an airplane at speeds very much higher than usual by loading the airplane up excessively with centrifugal force. In a degree banked turn, for instance, your stalling speed will be nearly one and a half times as high as it is in normal straight flight. Somewhat the same will be true during a sharp pull-out from a dive.
It is possible to stall your airplane at any speed, even at top speed, simply by pulling the stick back far enough abruptly enough! In this condition, its wings will develop considerable lift. In short, lack of speed is not the direct cause of a stall. Plenty of speed is not necessarily a protection from the stall. This is true, too. Under other conditions an airplane can stall with its nose well below the horizon; for example, during a steep turn with power off.
The lift may not be enough to maintain the airplane in flight, but the wing will not be stalled. But whenever a wing meets the air at too large an Angle of Attack, and tries to wash it down too sharply, the air fails to take the downward curve.
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In causing this commotion, the wing therefore experiences much drag but very little lift. That's what a stall is: the failure of the air to take the downward curve. And that's how a stall is caused: the excessive demands made on the air by a wing which meets it at too large an Angle of Attack. But it is not the only cause. Thus, simply by pulling the stick back far enough, the pilot can stall his airplane at any speed. The classic example of this is the snap roll.
At twice his ordinary stalling speed, the pilot pulls the stick back rather sharply and far. Thus the wings meet the air at an excessively large Angle of Attack, and they stall—even though the speed is high. This kind of stall is sometimes called a snap stall and can occur, regardless of speed, whenever the stick is brought back too abruptly and too far.
This is described here not in order to explain the snap roll, much less to give a recipe for how to do one. Now that this is clearly understood, we can go back to our flight experiment—the last phase of it, when the pilot is trying to maintain altitude on about r. He does this by holding the stick farther back. The slower his flight the larger is the Angle of Attack he needs. Then, suppose the pilot slows the ship up still a little more; in his attempt to keep the ship flying, he then increases his Angle of Attack still a little more, and he thereby exceeds the critical angle beyond which his wing cannot work; the wing stalls.
But now for a more realistic picture of what really goes on when we maneuver. That first flight experiment was carefully set up so it would not be confusing. Hence the air flows at the airplane not necessarily horizontally from straight ahead. It may, for instance, flow at the airplane upward, from ahead and below.
Hence the Angle of Attack cannot be seen simply by looking out the window; in fact, it cannot be seen at all! For remember, Angle of Attack is the angle at which the wing meets the air —and we can't see air. That is perhaps largely why flying is so much of an art.
Aviation History Book Review: Stick and Rudder
In baseball the batter keeps his eye on the ball that he is going to hit. If there were, flying would be much simpler. If you want to understand flight, you have to understand the Angle of Attack. This is a rather fancy word for a quite simple thing.