Welcome to the first in a series of videos entitled... Don't Pull Back - Avoiding Stall and Spin Accidents. Today we will be using the X-Plane flight simulator... to illustrate how a skidding turn.. can trick a pilot into pulling back on the control yoke... to cause a stall and spin accident. Now a skidding turn can lead to a... stall and spin, but it is never the final cause. An airplane can't spin unless it's stalled... and with the exceptions of wind shear and icing... there is one thing and one thing only... that can cause and airplane to stall - pulling back on the yoke. Be it the pilot, be it the autopilot, or be it the trim tab, it is nearly impossible to stall and then spin an ariplane... unless one of these three is pulling back on the control yoke. Usually, it's the pilot. Now, licensed pilots are a very smart group of people, and every licensed pilot knows... that pulling back on the yoke... is about the only way to stall... and then spin an airplane. So how do so many pilots year after year... get tricked into killing themselves... by pulling back on the yoke? Well, there are a lot of ways, and throughout this series of video presentations, We're going to try and uncover them all. I want you to be able to recognize... situations and conditions that might... make you pull back on the yoke... against your better judgement. One of these is the skidding turn. So let's get started. Contrary to what you see in the movies, The elevator should not be used to control the altitude of your airplane. Let's see what happens when a typical... Hollywood aviation sequence... is played out in accordance with the laws of physics. Let's see what really happens when pilots... think that pulling back on the yoke... will increase their altitude. Secret agent 770... This is mission control. The safe zone is just a few miles ahead of you. James, why are we flying so low? Dr. Nasty has stolen some stinger missiles. We need to stay underneath his radar. James, are we going to make it over that ridge? Yes Darling, I'll just pull back on the yoke to make the plane go up. But James, we are no longer going up... we seem to be slowing down instead. That's strange... I guess I need to pull back on the yoke some more. What's happening James; The plane is falling! Every stall and spin accident... is caused by pulling back on the yoke. You just witnessed this accident... in it's simplest form; the pilot actually believed... that pulling back on the yoke... would make his airplane go up. Most people in the general population... believe this to be true. This misconception has killed thousands of pilots... over the years. As we proceed, we shall see... that the yoke elevator combination actually controls airspeed, that increasing power is... is what makes and airplane go up, and that... when you can no longer increase power, you can no longer increase the rate... at which an airplane can maintain a sustained climb. pulling back on the yoke... might make the airplane climb for a moment, but without extra power... this climb comes at the expense of airspeed. And if airspeed is allowed... to fall below stall speed... the airplane will no longer fly Let's watch this same seen again, but this time without the drama. Instead we will watch it simultaneously... from four different points of view. We will look at the airspeed indicator in the first view. Keep an eye on the green arc. When the needle moves past the low speed end; (50 Knots for this airplane) stall will occur. Let's mark the current airspeed (95 Knots) with a green line. We are using the color green, because green... because green indicates... a safe margin above stall speed. A second view will show us the control yoke. We're going to mark the yoke column... with a green line also... to show that extending the column to this... particular length will cause... the airplane to fly at exactly 95 Knots... by virtue of the fact that... the yoke is holding the elevator in this... particular position... as shown in the next two views... which we will also mark with green lines. Let's call this the 95 knot elevator position. The third view show us the elevator from close up... and from the side. The fourth view shows us the elevator from behind, and also allows us to see what's... happening to the airplane. In this scene, I want you to observe... that the yoke controls the elevator position... that the elevator position controls the airspeed, and that when airspeed falls below 50 knots... the airplane will stall. Here we go. The pilot wants to climb over the ridge, but he is already at full power... so a greater sustained rate of climb is impossible. He thinks that pulling back on the yoke will give... him the altitude he needs, so he starts to haul back. The airplane is starting to climb as we can see on the altimeter, so he thinks he is doing the right thing. He doesn't understand... that without extra power from the engine... he is paying for his greater rate of climb with airspeed. The elevator is now in the 50 Knot position. If the pilot knew how airplanes worked... he would stop pulling back, but his plan seems to be working... so he is encouraged to pull back some more, and it's the last thing he ever does. Stall and spin occurs as his airspeed falls below 50. If all we ever did was fly strait with wings level... then airspeed would be a very good... predictor of an on coming stall. All we would need to do... is keep the needle of the airspeed indicator... away from the low speed end of the green arc Here the plane is flying quite nicely... with wings level at 60 knots. But in turning flight... your stall speed increases as your bank angle increases, so the end of the green arc on your airspeed indicator... will no longer tell you... when you are approaching stall speed. At a bank angle of 45 degrees for instance... we see this airplane stall and spin at 65 Knots, which is a perfectly safe speed in wings level flight... and well within the green arc. I can't bear to watch... so we will stop the action here. But before we leave this scene... take a look at the elevator. It's obvious that this pilot was pulling back on the yoke... more than he should have been... when flying at that particular bank angle. Or to say it another way, he was flying slower than he should have been when turning the airplane at a 45 degree angle of bank. There is one predictor of stall however... that never changes no matter how much... you bank your wings. and that is Angle of Attack. Your wings will always stall at the same... Critical Angle of Attack no matter... how much your wings are banked. Notice the elevator position in the plane below. The pilot is holding the control yoke forward. The plane is flying fast... at a small angle of attack. There is no danger of stall. Now look at the plane above. You can see from the elevator position... That the pilot is pulling the control yoke back. The airplane is flying slowly... at a large angle of attack. This airplane is in danger of stall. So if you understand what the Angle of Attack is... then you will be well prepared... to avoid stall and spin accidents. In turning flight as well as straight flight with wings level. Let's get aquainted with the angle of attack... in a familiar setting. We will watch the secret agent stall and spin scenario again, but this time we will make the flight path visible... and we will make the air visible as well. The purple line is our flight path, and the green lines are showing the air... as it moves past the wings. This air shown in green is called the relative wind. It's the wind that the airplane seems to feel... as the propeller pulls it through the air. It's not the propwash - It's not the air being thrown back by the propeller... but rather the wind that the wings feel... as they rush against the still air. You know this wind - it's the wind you feel when you... stick your hand out the window of a moving car. The air isn't moving, the car is moving, but if feels like wind just the same. Well, this relative wind... which seems to move against your wings... is what makes the airplane fly. But in order for the wings to work... the airplane needs to be pointed into the wind. To say it another way, the airplane must be pointed along it's flight path... to within about 18 degrees in order to avoid a stall. This is what the elevator and the rudder are for. They are used to keep the airplane... the airplane pointed along the flight path... so the wings can receive the air they need... from a direction that will allow the wings to work. Well if you are going to point your airplane along it's flight path... so as to align your wings with the relative wind, Then you will need to know where the flight path is... and it's not always easy to find. If it were, then no one would ever stall. In X-Plane, we can see the flight path - it's the purple line. but what about flying in the real world... where there is no purple line to guide you? How then can you tell if the airplane... is aligned with it's flight path? Well, the ball inclinometer tells you... if you need to yaw the nose of your airplane right or left by use of rudder. This is called coordinating your flight path. And your airspeed tells you if you need to... increase or decrease your Angle of Attack... by use of the elevator. This pilot can't see his Angle of Attack directly, but he knows from his airspeed... that his wings are just about to stall, and that he needs to get the control yoke forward... right away so as to reduce his Angle of Attack. The ailerons are the control surfaces... which allow you to chose the shape of your flight path. Wings level makes a strait flight path, and wings banked makes a circular flight path. in other words, the ailerons allow you to change direction. Please take note, that the rudder... does absolutely nothing to turn the airplane. banking the wings makes the airplane turn. The only thing the rudder is used for... in turning flight is to keep the airplane coordinated. Which means to keep the nose and tail... aligned with the circular flight path... as the need is indicated by the ball inclinometer. This is a very important job, however, and key to preventing stall and spin accidents... as we shall see shortly. Any pilot who tries to turn an airplane... by use of rudder alone, or any pilot who tries to help the ailerons in a turn.. by using more rudder than is necessary... to maintain coordination... is forcing the nose and tail... out of alignment with the flight path. This is called uncoordinated flight, and it is a very dangerous condition when flying at low airspeeds, or to say it more accurately, Uncoordinated flight, is a very dangerous condition... when flying near the Critical angle of Attack; because if the Critical Angle of Attack is exceeded... and the airplane stalls, then the airplane will also spin... if it is uncoordinated at the time of stall. What you have just seen is the skidded turn. During a skid, the nose is on the inside of a turn, and the tail is on the outside It's a killer. It's a killer once because it will cause your airplane... to spin in the event that your wings are stalled, this is what we have just seen, and it's a killer twice... because a skidded turn can trick a pilot... into pulling back on the control yoke, which will cause a stall and then spin... if the critical Angle of Attack is exceeded. We are going to take a look at how this happens, but before we can have that conversation... we need to see how descending flight... increases the angle of attack. Here our airplane is flying in a wings level position... at 84 knots, with a power setting of 2250 RPM. We have chosen this particular airspeed and power combination... because it is the only one that allows us to maintain... a constant altitude - see here... on the altimeter and the vertical speed indicator. while holding a pitch attitude of zero degrees... with respect to the horizon, as seen on the attitude indicator, and as shown from outside the airplane. this condition is an excellent starting point... from which to observe how descent increases the Angle of Attack. an airplane which is flying at a constant altitude... is following a flight path that extends toward the horizon, And an airplane which is... maintaining a pitch attitude of zero degrees... is pointing at the horizon. So this airplane is both moving toward the horizon, and pointing at it as well. We see here that the relative wind, Which moves toward the airplane... from the opposite direction of our flight path.. is meeting the cord line of the wings nearly head on. so we have a very small Angle of Attack. Now we will see what happens to the Angle of Attack... if we continue to point the airplane at the horizon... but fly towards the ground. Let's reduce power while holding the... same pitch attitude of zero degrees. this is accomplished by pulling back on the... control yoke as power is reduced. With reduced power, The airplane can no longer hold altitude... So now we have a descending flight path The descending flight path... produces and ascending relative wind... so the relative wind is now... striking the wing from below... instead of nearly head on... as it was before we started the descent. The result is an increased Angle of Attack... as you can see here, and the airspeed has decreased to... mark this new Angle of Attack. If we were to pitch down to match the angle of descent... we would again have a smaller safer... Angle of Attack. There are three life saving facts... to remember from this demonstration Fact one Pitch attitude is in no way... a direct measure of your Angle of Attack. so don't think that you can look out the window, or look at your attitude indicator.. and know how close you are... to the Critical Angle of Attack. Fact two. In non-turning flight your airspeed... is a direct measure of your angle of attack regardless of your pitch attitude, and regardless of your angle of ascent or descent. This is really important so let me say this another way: As long as you are not banking the wings, jerking the controls, or flying through ice or wind shear, you can always look at your airspeed indicator, and know how close you are to the critical Angle of Attack. The airspeed indicator is an accurate measure... of your angle of attack regardless of your altitude, regardless of your pitch attitude regardless of your power setting, and it reads true when you're climbing, descending or holding altitude. And finally Fact three, which is key... to understanding why skidded turns are so dangerous: Entering a descent increases your angle of attack... if do not pitch down to match to match the changing angle of your flight path. Now we have enough background information... to understand why a skidded turn can cause... a pilot to pull himself into a stall. Typically a skidded turn happens... because a pilot needs to turn quickly... and he is operating under the erroneous and dangerous notion that adding... more rudder than is necessary to maintain... coordination will make a tighter turn. For instance, if there is a strong tail wind... on the base leg of the... base to final turn, the pilot may likely find himself... over shooting the runway. In this situation a go around... is always the best choice, but if you must make a tight turn... perhaps to avoid an obstacle... then increasing bank angle while using... just enough rudder to maintain coordination... is much better than skidding your turn. This is because the airplane is much less... likely to stall to begin with, and if it does stall, then in will not spin, so recovery can be effected immediately... with minimal loss of altitude simply by... getting the control yoke forward. Let’s dissect the skidded turn now. We will start out with a normal coordinated turn... at a 45 degree bank angle... with flaps retracted for cruising flight. The end of the green arc will no longer mark... your critical angle of attack... because of the bank angle. But is possible to figure out in advance... what higher airspeed marks the... critical angle of attack when banked at 45 degrees, and with that knowledge, you can maintain... a safe margin of airspeed above stall. Let’s do the math real quick. I will slow it down and explain the details... in another video. also you can freeze the video at any point... so that you can follow along. The important thing to remember... is that you must convert your indicated airspeed... to calibrated airspeed... before making the calculation, and then convert the result back... to indicated airspeed for use in your airplane. Lets start by making observations... about our condition in this normal turn. The bank angle is 45 degrees... and we are turning to the left. Power is set so that the... prop is turning a 2250 RPM. The ball is centered in the inclinometer. That’s how we know we are coordinated, which is to say, that our nose and tail... are lined up with our circular flight path. The airplane is holding altitude as seen... on the altimeter and the vertical speed indicator. Notice that the stall warning indicator is not on... so we know that we are not flying near the critical angle of attack. Airspeed is constant at 75 Knots. And when we expose the flight path... and pull back from the outside, we can see that we have entered the turn here, and are currently flying circles... at a relatively constant altitude up here. Notice that the nose is level with the horizon. Now lets start skidding the turn... and watch what happens to the nose of the airplane... as we continue to view it against the horizon. We apply pressure to the left rudder peddle... causing full defection of the rudder. Now look at what’s happening to the horizon, or more correctly, look at what’s happening... to the nose of the airplane. The airplane is now pointing at the ground. This is partially because the plane is pitched down, but because the airplane is banked... as the skid is initiated, the nose has also been yawed toward the ground. This combination of pitch and yaw towards the ground... combined with the vertical descent... creates an almost irresistible and deadly urge... in a surprised pilot to pull back on the yoke. This of course causes a stall and spin. But we were expecting this... so we will leave the yoke forward... and maintain our airspeed... and along with it, a sufficiently small angle of attack to avoid stall. Good thing we are leaving the control yoke in place... because the skid is causing serious loss of altitude, which has increased our angle of attack so much... that the stall warning light is now on. We are already very close to the... critical angle of attack... and the only change we made... was to apply significantly more rudder... than was needed to maintain coordination. Now remember, we went to a lot of trouble... to calculate that 75 knots was a safe margin... above stall speed when banked at 45 degrees. Well we are flying at 75 Knots now... with a bank angle of 45 degrees, but the stall warning light is on - so we must conclude that our stall speed calculations... are only valid when coordinated, and when skidding our turns, the calculations grossly underestimate... the airspeed required to maintain flight. Let’s see what this all looks like... from outside the aircraft. We apply bottom rudder right here to start the skid, and immediately, find ourselves in a nose low attitude... as we start to lose altitude. We haven’t stalled yet because we understood our situation... and resisted the urge to pull back on the control yoke. So we can still stop this simply by applying... enough right rudder to coordinate the airplane. This would give us the same... stable turn we had before. We’re not in any real trouble yet... and we can stay out of trouble... until we get near the ground as long as... we maintain our airspeed and angle of attack, which is the same thing as saying as long as saying... we don’t pull back on the control yoke. By the way this is definitely not the correct way... to perform an emergency descent. Your FAA certified flight instructor can teach you... the safest way to do that procedure... in your particular airplane. We are starting to get close to the ground, and now I would say: We are officially in trouble. We can’t lose any more altitude... or we will hit the ground... so we had better stop skidding this turn... and fly coordinated right now. If we did only this by applying right rudder... until the ball inclinometer was centered, then the airplane would immediately... hold its altitude as a before, and we could simply continue the turn... until we were pointing at the lake... at which time we would fly away from the terrain. But we got into this trouble in the first place... because we thought that a skidded turn... would be tighter than a normal turn... and that would seem to be true... if we looked at our flight path from the top. But when seen from the side... or from inside the airplane... we understand immediately that this is a very... dangerous way to achieve a tight turn. So in order to demonstrate how to safely... fly the tightest possible turn, and without losing any altitude, we will create another emergency by reversing the direction of the turn, which will bring us near rising terrain. As we start to reverse the direction of the turn... we will apply just enough right rudder.. to maintain coordination as seen... on the ball inclinometer. This alone should stop our descent. We will also add full power. This won’t make us go any faster... as it would in a car, but rather it will increase our altitude, or at least slow our descent. Any altitude that we can get right now... will be extra helpful because the terrain ahead of us is rising. We need to turn hard immediately... to avoid hitting the mountainside ahead. The tightest possible turn is achieved by banking... at the maximum bank angle we can have without stalling. Remember that stall speed increases... as bank angle increases, and a good pilot has calculated in advance.. and committed to memory... the stalls speeds for the various bank angles. Right now our airspeed is 79 Knots, and we can’t get any more airspeed... without lowering the nose to reduce our angle of attack, and pitching down won’t be an option... until the airplane starts to climb. So we are stuck with our current airspeed. The greatest bank angle we can have in this airplane... at an airspeed of 79 Knots... without stalling is 60 degrees. We are simultaneously coordinating... our flight path with right rudder, banking the wings to 60 degrees with right aileron, and adding full power. This high power maneuver is drawing more power... than our engine can produce... and we can’t make up the difference... by spending altitude energy so... our airspeed energy reserve... will diminish as we continue the turn. Remembering that our airplane will stall when airspeed... drops below 78 Knots at 60 degrees of bank, we gradually reduce angle of bank so as to ensure... our stall speed remains below our diminishing airspeed. Look at the turn we just made. It’s every bit as tight as the skidding turn... but we didn’t lose an inch of altitude... and we didn’t expose ourselves to the danger of spinning... in the event that stall occurs. So while it’s best to avoid, at all cost, situations where tight turns are required, if you must turn hard, and you cannot accept a loss of altitude, then stay coordinated, add power, increase bank angle... until your rising stall speed... starts to approach your airspeed, and then reduce bank angle again... if airspeed decays so as to ensure... that your stall speed always remains lower... than your current airspeed; but please don’t under any circumstances... skid your turns. Let’s review the lifesaving facts... that were covered in this video presention:
I watched the whole thing and now I'm ready for my pilots test.
Dr. Nasty sounds like someone I want to meet.
He sounds like Kripke from Big bang.
That was awesome. This is the original audio?