Friday, December 21, 2012

What Notion is about as Healthy as that a Rattlesnake makes a Pleasant Pet?

How about the idea that the purpose of the rudder is to steer the airplane around the corner? No way.

The rudder gives the pilot the means to combat the adverse yaw effect of the ailerons. This is what a coordinated turn is all about. That is why we use rudder on going into a turn and why we use rudder when coming out of a turn. If the ailerons had no adverse yaw a plane wouldn't need a rudder.

It would be great if a student pilot had a early and clear concept of what an airplane had a rudder for. Think of all the skidding and slipping it would eliminate. Think of the fatalities it would save.

Remember your steep turn training. It was easy to enter with slight rudder involvement. Recovering was another thing. 

Banking out of fast, low angle of attack flight into a steep turn there is not much adverse aileron yaw and the need for rudder is less. Unbanking out of slow, high angle of attack flight, there is much adverse aileron yaw and much need for rudder. Your correct response will prevent a "broken neck" so to speak.

There is only one way to get out of a steep turn quickly and safely. This is especially important if the recovery from the steep turn has begun to sour.

First, to reduce the angle of attack, let the stick or wheel come forward to unstall the wings and giving the ailerons less adverse yaw. This enables the wing to lift itself.

Second, now apply a lot of top rudder (left rudder in a right turn and vice-versa).

Third, begin to apply high aileron to roll the airplane out of the steep bank.

Lesson today, "Stick Forward" to reduce angle of attack.

Here's to flying safely!


Monday, October 1, 2012

Torque or Slipstream? - Left Turning tendency

The Real Reason

The left turning tendency occurs when the propeller pushes back a stream of air mass which spirals as it streams to the rear.

With its spiraling motion the air mass hits the vertical fin at a slight angle. This pushes the tail to the right and yaws the nose to the left. Heres where the fun begins.

The propeller hits a small particle of air mass at the right -hand side of the planes nose. The impact of the propeller sends it backwards  and downward along the right side of the fuselage where it crosses underneath the pilots seat to the left side of the fuselage where it flows upward (cork-screw) and backward along the left side of the tail. It is then ready to cross over the top of the tail back to the right side; but, it finds its path blocked by the tail fin. The air mass particle impacts the fin with a force and shoves the tail fin to the right.

At the same time, in the beginning, another air mass particle is caught by the propeller on the left side of the planes nose. The impact sends the air mass particle speeding backward along the left side of the fuselage  and slightly upward. It crosses over the top of the cockpit and flows downward and backward along the right side of the tail. It is then ready to cross underneath the tail back to the left side. But, it runs into a problem. There is no tail fin to block the air mass particle. It exerts no force on anything and flows away behind the plane.

The net result of these two circulating air mass particles is a resultant shove of the tail fin to the right and a yaw of the plane to the left.

In aircraft design the tail fin is set at a slight angle so to line it up with the actual line of direction of the air flow at the tail in cruising, level flight.  The true reason for off setting the tail fin is not to make a force but, rather, to keep a force from being made.

In slower flight, as the tightness of the spiral of the air mass particle increases, the sideways shove of force on the tail fin increases. If the design angle offset is not sufficient, the left turning tendency continues and you must hold right rudder.

In gliding flight this tendency doesn't appear because the propeller is not creating a slipstream. The offset built into the tail fin is not necessary and, in fact, yaws the nose of the aircraft to the right. The pilot, in a glide, now holds slight left rudder.

You could abolish the left turning tendency by putting as much tail fin underneath the tail as there is atop the tail. The problem is the tail fin underneath would interfere with the conventional landing gear of a tail dragger. New plane design, with tricycle landing gear, have allowed the tail fin arrangement mentioned above to appear in modern planes.

The H-tail is here and slanted engines have eliminated left turn tendencies that plagued older aircraft.

Friday, September 28, 2012

Power Control and Stabilty

Plane Stability - Plane Performance and Throttle Settings

What is your plane stability after you trim for a particular speed? A plane, with perfect stability, will maintain that speed whether the power if off or the power is increased. Right? 

Try this in actual flight at cruising speed in straight and level flight and you will discover what actually happens when you change the power setting. Cut the power and the typical plane will descend in a glide at a speed well above your cruising speed. The glide will steepen into a dive. Push the throttle wide open and the plane will settle on a different, slower speed as it climbs.

Just why does a plane speed up when you close the throttle and slow down when you open up the throttle? Seems contradictory to most pilots. 

Plane design and propeller blast is one reason. The tail surfaces ride in a place, on a plane, where the propeller blast hits them. In cruise mode, at a specific speed, the tail surfaces receive an extra wind in power on flight causing an extra down force on the tail surfaces. With power off that wind and extra force disappear. 

In designing a plane there is something called a thrust-line location involved in a planes development. It concerns the location of the propeller in relation to the rest of the airplanes design. Consider a Cessna, with a high wing, with its engine mounted low to provide good vision for a pilot. This design arrangement will cause a nosing up tendency when the pull of the propeller coupled with the backward pull of the high wings drag with power on. This effect disappears when the power is off.

A change in relative wind created by the wings at cruise speed with the power on and how it changes with power off. Remember that the tail surfaces reside in the downwash created by the surfaces of the wing while in flight. With power on, the propeller blast hits certain parts of the wing. These parts work in an extra sharp relative wind that sends an extra sharp downwash to the tail surfaces. This produces an extra down force on the tail surfaces. When the power is off this effect disappears too.

The effect becomes more pronounced the heavier and more powerful the plane. To a pilot the effect is important because under some conditions an airplane may want to stall it self. 

From a safety point of view this may occur during a go-around as you attempt to land when a plane attempting to take off the runway suddenly appears in front of your plane. 

If your plane, that cruises at 100 mph in straight and level flight, stalls at 45 mph and your approach speed is 70 mph after trimming properly you could stall the aircraft in a go-around. You open the throttle wide to climb away and re-enter the airport flight pattern. If you don't simultaneously re-trim or apply strong forward pressure on the stick the plane wants to climb like mad. It will climb into a power stall because you think the plane will climb at 70 mph. (no change in airspeed).  Instead, the plane will want to fly at 45 mph or less to quickly gain altitude. 

You must respond by applying strong forward pressure on the stick and/or re-trimming to lower the nose of your plane to a safe climbing attitude and the speed up to a safe 70 mph.

Each plane, in review, has a built in tendency to keep its own   angle of attack constant and to keep its speed constant regardless of how the the amount of power delivered by the plane may change. This is basic. This basic tendency is overcome by the effects of power on and off discussed. You, the pilot must be aware of these contrary tendencies and act accordingly.

Wednesday, September 26, 2012

Deer Season - A Tendency to "Hunt!"

A "Hunting" Tendency

Stability - static and/or dynamic. In the real world most planes have a tendency to hunt. If you let go of your planes controls it won't fly at a constant speed.

Instead, it oscillates up and down. Why?

The up and down flight path of an oscillating plane is an complicated interaction of speed changes, flight paths, directions of the relative wind, angles of attack, changing drags, changing propeller efficiencies, horsepower outputs, changing lifts and slight downward and upward g-loads.

All the above means the plane is trying to get back to its proper cruising speed and proper angle of attack. The plane "over controls" itself and doesn't quite succeed in steadying itself down after you released the controls.

Since your plane is trying to return to a proper cruising speed and angle of attack, the apparent unstable "hunting" doesn't mean the airplane itself is unstable.

If the airplane was actually unstable, in a dive it would continue to dive or it would stay in a climb until it stalled.

The plane is primarily stable. If an airplane can't steady itself it is dynamically unstable. The airplanes oscillations continue to increase in violence until the plane disintegrates. 

The majority of airplanes are dynamically stable where the oscillations become weaker and weaker. The presence of unstable air or other disturbances may prevent the dampening of the oscillations. 

Knowing the technical theory on "hunting" is not very important to a pilot. Stability is important to a pilot because of the way it affects the feel and behavior of the plane while he controls the plane. 

If the pilot is controlling the plane it will not oscillate. 

Tuesday, September 25, 2012

Tail of an Airplane - Misunderstood

Tail of an Airplane

The tail of an airplane is arranged to resist the diving tendency of a plane. It is not meant to hold the lighter end of an airplane up in the air while in flight.

The purpose of the horizontal fin of the tail is to hold it down. It is like a wing but set at a negative angle of attack so the air flow against the horizontal tail fin produces, in normal flight, a downward force.

The reason for this downward force is the tail operates in the downwash of air that flows off the upper surface of the wing.

You recall an airplane creates "lift" by pushing air mass downward that creates a force upward that equals the weight of the plane in level, cruising flight. The downwash flows down on the horizontal fin of the tail and pushes it down more than you realize.

You know, from just looking at a plane, the nose is heavier than the tail. The nose-heavy plane tends to "nose the plane down" while the horizontal tail stabilizer tends to "nose it up."

When you trim a plane for level flight at cruising speed the two forces exactly balance each other. That is exactly what we do when we trim a plane for a certain speed. We adjust the angle of the horizontal tail fin so, at the particular speed we want to achieve, the downward air mass force on the tail will exactly balance the downward pull of the force of gravity on the nose.

Wednesday, September 19, 2012

Navigation, Speed and Wind Drift

Navigation - Which is Better -Slow Plane or Fast Plane 

Remember, a large plane and a slow both drift with the wind in straight and level flight. 

Speed does make a difference in navigation. Weight, size and horsepower do not make a difference.

The Setup: 

Make a 100 mile flight to a destination with a 20 mph wind blowing across your course to your destination. You take off and point the nose of your plane directly toward your destination without an allowance for drift in your 100 mph cruise in your slow plane. You correctly determine it should take one hour to complete your flight. After an hour you look at the ground and your destination is nowhere in sight. In one hour of flying through the air your plane has drifted with the air 20 miles to the downwind side of your course. If it is a hazy day with visibility of 7 miles or less you will not see your destination.

If you attempt this same trip in, a 300 mph plane, point it directly toward your destination without compensating for drift and, after an hour, it too will drift exactly 20 miles.  But, at 300 mph your faster plane will arrive at the planned destination in 20 minutes. If the wind is 20 mph, then in 20 minutes your plane will drift in the wind a little less than 7 miles. Now, when you look out of your plane after 20 minutes you will see your destination off to one site easily visible. Your navigation is better when you can see your destination when you are supposed to see your destination. In a fast plane, even though it is drifting in the wind just as helplessly as your flight in a small plane, the drift is proportionately less important to the faster plane. The drift angle is less in the faster plane and that is why a faster plane is much easier to navigate. 

Tuesday, September 18, 2012

Training - The Figure of Eight

Illustration of Figure of Eight in Flight Training - Wind

In pilot training an instructor had you practice figures of eights over a conspicuous object on the ground. Some times this was incorporated into a steep turn exercise. For an illustration of wind effect a 20 to 30 degree bank was sufficient.

When you pass over an object you can identify from a distance start a 30 degree bank. Hold this 30 degree bank for 360 degrees. It is better to pick a direction to start the instruction heading, for instance , straight West, as you pass over the object, to begin the 30 degree bank for 360 degrees.

In calm air conditions, when you have completed 360 degrees of 30 degree bank, and are just beginning to head out on a due West course you would expect a complete circle was flown and the object you picked out to begin the turn was again right under your plane. You are correct.

In wind conditions it changes the flight path. If you hold the same 30 degree bank for 360 degrees you describe an exact circle through the air. The air in which you fly moves on with your plane in the "soup." Your path on the ground is not a perfect circle. It is more like the figure "6" at the moment you are again heading exactly due West. But, after starting your 30 degree constantly held bank and flying the bank for 360 degrees your position is not exactly over the object where you started your turn. Your plane is several hundred feet downwind form the object.

If you understand the concept of a turn in the wind above you understand the whole problem of drift in turns.

The drifting of the plane during the maneuver is not accompanied by any forces from any direction. It is accompanied, though, by confusing sensations for you, the pilot.

If you did not watch the ground you would not notice any wind effects. But, you can not help seeing the ground, while turning at a constant 30 degree bank for 360  degrees and noticing how the ground speeds up, now it slides sideways, now it slows up and now it slides to the other side.

How you react depends on where your attention is centered. If you are centered on your path over the ground you would notice how your path is pulled out of shape. The proper response to the changing path over the ground is to do nothing. Let the drift take place and make no effort to resist the illusions of what drift does and causes you to try to keep the plane in a perfect circle. 

You don't want to involuntarily try to keep the shape of the turn you started perfect. You may involuntarily try shallowing or steeping your turn or the danger of "holding rudder against the drift" and slipping or skidding during the parts of the turn  when you have the "wind" from your side.

If your attention is on flying a nice turn the slipping and skidding tendencies will be opposite. As you notice your planes apparent sideways sliding you will tend to skid as you turn from upwind to downwind and you will tend to slip while you turn downwind to upwind.

You have to learn to fly the plane by attitude and the feel in the seat of your pants. You have to disregard the strong impressions of sideways and improper motion the ground transmits to your eyes.

Monday, September 17, 2012

Downwind Landings - Wind Effects

Downwind Landings

Straight downwind landings by mistake. Pilot fatigue leads to flight errors. Misread wind indicators or tower instructions.
 (more serious)

Landing downwind, when you think you're landing upwind, leads to confusion. 

You approach the runway through the air at 75 mph and, at the same time drifting with the air at 20 mph. Since the two motions are both in the same direction the plane's speed, relative to the ground, is 95 mph.

You sense the altitude above the runway, when landing, from visual clues. The speed of the runway surface and/or the speed of runway lights in his field of vision provide that information. You think you're close to the runway from your experience when landing upwind. You don't think you're in any danger from stalling and begin to slow the plane up  preparing to touch down momentarily.

You just fell into a dangerous visual illusion. It is true the plane has plenty of speed and speed is what keeps a plane from stalling. What you forgot, because of the illusion, it is the speed of your plane through the air that is important. Thats the speed your plane's wing is pushing through the air. That speed is 75 mph. 

Of your 95 mph that you think you are going only 75 mph is actually going through the air.

The apparent relative speed of your plane to the ground, 95 mph, gives you illusion that your plane is closer to the runway. In fact, your plane is higher than the visual clues that you mistakenly used to determine the altitude of your plane.

Since you are tired and you think you are landing upwind, you may instead be close to a stall as you slow your plane down for a landing while still high above the runway.

If you discover your mistake in time you may, depending on actual altitude above the runway, lower your plane's nose, give immediate power application, recover from the stall and think things through before you attempt another approach.

Too many pilots don't get a second chance. 

Saturday, September 15, 2012

Wind Drift and Crabbing

Wind Drift and Crabbing

Crabbing in straight and level flight for the initiated. Good example to use, with ground reference, is a N-S highway. The wind is out of the West at 20 MPH. Remember, this is a mass of air moving which is defined as "wind." You fly at a speed of 100 miles per hour, straight ( nose of the aircraft in a N-S direction) and level for 15 minutes. 

Question is, where will you be? You will be exactly 25 miles North of where you started due to your flying through the air and exactly 5 miles East of the N-S highway due to your flying with the air.

Since the airplane is completely immersed in the air it must, simultaneously, move with the air eastward, as well as through the air, northward. This is exactly what happens. To the uninitiated it looks wrong.

To a person familiar to ground-associated eye reference they think the airplane is sliding sideways. This just doesn't seem possible when compared to the ground oriented travel.

Like a visual illusion, the inexperienced pilot has a strong urge to apply left rudder to stop the planes movement to the right. The mistake is the left rudder just makes the nose of the aircraft swing to the left and does nothing to prevent the aircraft from continuing to the right. Continued left rudder pressure will swing the nose further and further to the left and the plane will still exhibit its rightward slide. If this left rudder pressure still continues, as he tries to counteract the drift, the plane will turn completely off its heading and begin to circle. It will still slide to the right.

Now the danger. Cross-controlling. Extreme cross controlling will increase the angle of attack to precipitate a stall. The uninitiated uses right aileron against his left rudder, flying with his right wing low. The two controls cancel each other and the airplane will fly inefficiently in a slight sideslip. The airplane still slides eastward.

Some pilots think the air is blowing at the planes left side and shoving the nose of the plane to the left.(weather-cocking) The pilot then applies right rudder to counteract the imagined tendency to weather-cock.

In reality, the planes sideways movement to the right is pure drift. It is motion with the air mass or wind. It doesn't need any compensating control movement. The plane is behaving as in calm flight.

The experienced pilot knows the eastward flow of the air mass from the west cannot be stopped. He just gently turns the entire plane slightly to the west of north. The longitudinal axis of the plane is changed. The pilot is hoping the eastward movement of the plane in the air mass plus the slight northwest flight of the plane through the air mass will result in a actual flight path over the ground of true north.

You keep adjusting for the drift until it stops. The student flyer must understand clearly that a normal turn is always made to compensate for drift. These compensating turns allow the track of the plane over the ground to follow a true north direction.

Friday, September 14, 2012

Wind Drift - What Does it Do

Wind Drift

The three keys of understanding "drift" from a pilots point of view are:
  • Air is a soup
  • Motion is relative
  • You are "in" the air
Air is a soup.

In physics there exist three states of matter. A solid, a liquid and a gas. Air is a gas. It is composed of a number of different molecules that have mass and take up space. It is like an invisible fluid that flows. Wind is air in motion.

Motion is relative.

A moving stream is like moving air or ''wind." If you are floating downstream in an enclosed boat without windows you don't have a sensation of actually moving. You can move about in the boat easily. If you ignore all the noise outside the boat you don't have any sensation that you are moving. You really are in a moving mass of soup. Steady flow of air is wind. As long as the flow of water is steady you feel like there is no motion at all. If you walk to one end of the boat and return to where you started you are, in fact, moving in the boat while the boat has continued to float downstream.The fact that motion downstream is taking place is real. Frame of reference is important. Which side of facts you choose to disregard. Do you judge your position by reference to the boat or by the boats position to the shore outside? Try climbing a down escalator in a store. Its a matter of relativity of motion. On the ground you don't have trouble with the "familiar." In flying it suddenly matters.

Your "in" the air.

An airplane that flies in moving air is like, in the example above, when you walked back and forth in a boat. Your plane is "contained" ,once in flight, by the surrounding air. The difference, when we fly, is the air is invisible as it surrounds the plane and the boat surrounds you in the stream.

The airplane, like the boat, has two motions both at the same time. It has motion through the air mass, like walking in the boat, and it has motion with the air called "drift." In the boat you were "drifting" downstream (one motion) and walking in the boat. (the other motion)

You, as the pilot, can fix your attention on one type of motion or on the other as you choose. After you feel comfortable in the air, you can watch both motions at the same time and not become confused.

Thursday, September 13, 2012

Thunderstorms - Are They Good for Something

Thunderstorms - The Good - The Bad - The Evil

Thunderstorms can damage or destroy planes flying into or under them. As long as pilots use common sense in preflight weather briefings and practice techniques to exit a thunderstorm or avoid one while flying they do have a few good points.

On a humorous note, if you are inside a thunderstorm your aircraft traffic usually falls to zero.

They provide water for many continents during the summer months world-wide. Without water many continents would become dry. Plants, which use carbon dioxide ( do you really want to limit carbon dioxide emissions ) and release oxygen as a by-product, receive water in large amounts from the rain produced by thunderstorms. Without water fish would die, crops fail from extreme droughts and animals would perish.

Environmentalists need to create thunderstorms to prevent global warming. Thunderstorms are natural air conditioners. Hot air from the earths surface is rises up into the high atmosphere from the formation of a thunderstorm. The cloud formation from thunderstorms give humans and lower animals shade and eventually cooling rain on a hot day.

This is interesting. The earth, without thunderstorms, would have it's temperature rise as much as 20 degrees F.

The summer dust, haze ( impediment to VFR flying conditions and safety ) and other pollutants come together in the lower atmosphere to create smog. When thunderstorms are created by rising air and moisture that trap pollutants the air spreads the pollutants higher up into the atmosphere clearing the air below. Once the cumulus clouds build into the actual thunderstorm, with resulting rain, the air is washed and the pollutants are returned to the earths soil. Breathing becomes easier and less harmful.

Lightning produced by thunderstorms helps keep the electrical balance between the earth and the atmosphere under control. Friction of the gases ( air ) creates static electricity that is released by the formation of lightning. This can be observed by dry lightning that many pilots view periodically at night.

Lightning is also a fertilizer. It changes nitrogen gas in the air to nitrogen compounds that fall to the ground by gravity or through the rain produced by thunderstorms. Nitrogen is one of the main ingredients of fertilizer needed for farming to produce the crops eaten world-wide. Ten percent of the nitrogen fertilizer needed for farming, world-wide, is made by lightening.

Finally, what beautiful rainbows a thunderstorm can produce along with the inspiration for song and dance.

Sunday, September 9, 2012

Taxiway Lighting Systems

Taxiways - Lost and Found

First, a taxiway is a communication path on an airport connecting runways with ramps, hangers, terminals and repair facilities. Larger airports the taxiways are hard surfaced to support heavy aircraft.

The Blue Lights mark Taxiway Edge lights and emit blue light. They make finding your way around easier. Jeppeson Charts have taxiways well marked for the pilots benefit.

Jet Ports have high-speed exits off the Main Runways to facilitate moving large planes. Once off they use the taxiways.

The center of the taxiways have a single yellow line to help you center your plane for taxiing.

The taxiway edge markings have two different purposes. If they have two solid yellow strips it marks an edge of the taxiway that separates the taxiway from a surface that doesn't, for instance, support a plane straying into that area.

The second is two broken double yellow strips that separate a surface that does support a plane crossing over onto it's surface but is not the actual taxiway.

Taxiways have Yellow Information Blocks as they approach a runway. The blocks contain black lettering and numbers that provide taxiway information when erected signs are not possible.

The lighting and informational choices expand as the complexity of the airport increases. Night increases the possibility of confusion. 

If  you fly into busy airports the following link is complete and will help you in the identification possibilities before you actually take off and, of course, is a part of your pre-planning. Airport Lighting Systems.

Monday, August 27, 2012

Garmin Pilot for I-Phone and I Pad - Possible Problems

Garmin Pilot

As a backup, in private aircraft flying, the I-Phone screen is quite small. In turbulent conditions, during IFR approaches, controlling and reading the device is nearly impossible.

As a flight planning device it has exceptional features. Use a  Search Engine to find test results and/or detailed information on the Standard or Pro versions of the Garmin App and the many features the Garmin device offers.

The I-Pad has a larger screen. Easy to read screens, in flight, are a blessing. Information is available and good.

There are still some disadvantages that interfere with the I-Pad.

A common one is glare. Ever try and read a modern gas pump screen if sunlight is hitting the screen? You get the point. Glare on the I-Pad screen makes use almost impossible. Later models of the I-Pad have brighter screens that make use possible. Changing the position of the I-Pad screen helps. Ton of kneeboards and mounts that alleviate some of the glare drawbacks.

Electrical discharge in the latest and greatest I-Pads, controlled by fast processors, adds up to heat. Heat will cause an I-Pad to shut down when you need it the most. Aircraft cockpits in direct sunlight and dark surfaces allow heat to build quickly inside the plane. Couple this with any heat producing electrical device and shutdown can occur. 

When an application uses more power than what is supplied from a charger, the time of operation is compromised. The power required to operate all the bells and whistles is greater in the latest models. Cutting the power to some features will eliminate the discrepancy between power out (device) and power in (charger).

The trade off between size of the I-Pad and placement in the plane may present problems. If the device covers instruments that is a no-no. Yoke mounting can eliminate the instrument problem. A neat idea is mounting the device on the co-pilot yoke. Aiming the device at you makes reading the information provided easy. Placing the I-Pad on the floor and bringing it up to view charts is another solution. Be careful, if unsecured by a retaining structure, the I-Pad slips behind the seats. Moving your head about to find the I-Pad can result in disorientation.

Finally, trying to use any device in turbulence is very difficult when your holding the I-Pad with one hand and inputing information with the other hand. A dash or yoke mounted I-Pad is safer to operate.

Modern gadgetry is great but a few problems exist. Keep in mind, though, the many great features that exist to make the purchase of the App a wonderful addition to flight safety.

Friday, August 24, 2012

Pussy Footing Around - Detecting a Cushion

Sensing Float (Buoyancy)

In landing an airplane sensations you receive from the plane to you are very important. Short fields require sensitivity to the subtle clues that affect lift. Floating is not nice as you run out of runway.

You want a slight cushion, when you land, to flare out, check the descent of your plane and contact the ground. This is the very slight touch of your wheels in a perfect landing. The "Ahh, what a landing" reaction from pilot and passengers. 

This is "flying the edge" to some folks. To arrive at the edge and not drop off the cliff is the goal in every landing.

We talked about lift reserve before. The perfect landing results from a cushion of reserve lift that allows the plane to touchdown quickly with as little float when you pull back on the stick or wheel and stall.

When you pull back on the stick you don't want to feel a surge of lift that requires a checking of the descent from you!

At altitude you can test the effect by flying a slow glide at the very edge of a stall. When you pull the stick back a few inches the flight path of the plane does not go up. Instead the plane begins to stall and settle. The flight path goes down. In a fast glide, with lots of reserve lift, when you pull back on the stick a few inches, the plane balloons with a firm push into your bottom. Net result is an upward flight path and a much longer movement forward before the plane settles down to land.

At altitude you can't  really see the deflection of the aircraft upward. You feel it. In an actual landing flare, near the ground, the slightest ballooning or settling of the plane is very apparent to the eye. You feel the changes you make in the stick position by sensing the slight weight changes (lightness or heaviness) that occur from stick handling.

If a pull back on the stick makes you feel slightly heavier you are gliding too fast and the plane "floats" until the glide slows.

If you pull back on the stick and you feel lighter, like going down in a fast elevator, your reserve of lift is limited and you descend.

Your perception of weight change is very sensitive. You make a conscious effort to pay attention to that "sense" and act accordingly. If you are a passenger in the right seat of a small plane during the final stages of a landing you will see the pilot make small changes in the stick position (both back and forward) as he "senses" the planes descent to a perfect landing.

This gives credence to the term "flying by the seat of your pants" when landing an airplane.

In conclusion, sensing the cushion effect is important to a good approach and landing. Your senses become very sensitive as you glide lower to the ground and control movements are limited to prevent major changes in flight attitude (up and down).

Thursday, August 16, 2012

The Breakdown of a Spiral Turn Before the Breakup

The Breakdown:

Something disturbs the plane in straight and level flight at cruising speed. The right wing drops slightly. The plane enters a gentle sideslip to the right. In a slip a crossflow of air initiates a dihedral response to pick up the right wing.

The vertical tail fin responds, simultaneously, by yawing the plane slightly to the right. If the plane is spirally unstable the rudder (tail fin) forces the plane around before the dihedral had time to pick the right wing up.

The rudder produces a yaw which introduces an over-banking tendency while the plane turns. In a turn to the right the left wing is moving, at the moment, faster through the air and generates more lift. At the same time the right wing is slowed a bit and generates less lift. The net result is the left wing goes up slightly and the right wing drops. The over-banking tendency cancels out the attempt of the dihedral to the right wing to return the plane to level flight. Net result the right wing stays down.

The slight sideslip to the right continues and the dihedral tries again to right the right wing to stop the sideslip. The vertical tail again over-rides the dihedral and the plane enters a new over-banking effect. This process will repeat itself unless stopped.

If this isn't stopped the plane enters a steeper bank and a tighter turn. This continues if you don't interfere. 

The g-load increases due to the centrifugal force build-up. The increase in load forces the plane to drop its nose and pick up speed. The plane has a built-in tendency to keep itself at a constant Angle of Attack. The extra load, created by the centrifugal force build-up, creates a situation where the plane can only maintain a constant Angle of Attack by picking up additional speed. The dive combines with the spiral turn to create a spiral dive.

When an increase in the bank reaches a certain point another effect forces the nose of the plane downward toward the earth. In this deep bank the earth is on the right side and the sky is on the left side. The rudder (vertical fin) continues to push the plane around to the right. It now is pushing the plane into a dive toward the earth.

In summary, this is what a plane "wants to do" once it is in a turn. The plane wants to do this even when the pilot is on the controls. 

This, in previous posts, is the anatomy of the "death spiral" that causes many lost lives where instrument flight skills are lacking and/or the pilot tries to fly an airplane so it makes him "feel good or more 'natural'."

Flight Controllers have testified about their inability to talk an untrained pilot out of a "death spiral." They try to put the aircraft into a flight attitude where their sensations are "more natural." In effect, they don't believe what the plane's instruments are telling the pilot about the actual attitude of the plane (a deep spiral dive).

This is a safety lesson on proper instrument pilot training. Knowing the normal tendency of a plane, in a turn, can set you up for a vestibular illusion that may end your and your passengers lives in a needless spiral dive accident.

Wednesday, August 15, 2012

No Controls Touched - Will a Plane Fly Straight?

Will a plane fly straight or turn away from it's cruising straight ahead attitude of flight , if you release the controls?

What does an airplane really want to do concerning the direction of its flight? 

Unfortunately, aircraft built to American specifications don't have the stability to remain straight and level with the controls released.

A pilot knows this if he experiments at a safe altitude. Release the controls and the plane will enter a turn. Pilots say the reason a plane enters a turn is because of:

  • Torque
  • Stiff controls
  • Wing heaviness
Planes will enter a turn. Once into the turn they will keep increasing the angle of bank, the rate of turn, the speed and the rate of descent. This results in a true spiral which is an ever tightening turn combined with an ever steepening dive.

The end result, if the plane is left to its own fate, is the plane will break up in this tight corkscrew because of excessive g forces that exceed the aircrafts maximum load limits.

The spiral looks like a spin except the plane's controls will function in a normal manner and no stall is involved. You can recover from a spiral dive any time you elect to use the controls.

The entrance into a spiral begins when something disturbs the plane's right-left sense. The aircraft will respond to the disturbance in two different ways simultaneously. One is a planes vertical tail will yaw the plane around to point itself into the direction it was actually moving. At the same time its tendency to refuse to sideslip, due to the dihedral angle of its wings, will cause the plane to lift one wing and drop the other to regain its lateral balance. Both events occur together

The turn causes the relative wind, to blow slightly crosswise at the plane to affect both the vertical tail and the wings dihedral at the same time. A plane will respond to a disturbance depending on weather the yaw effect or the wing-righting response is quicker and more forceful.

Think about a plane that has a very small tail and a pronounced dihedral. If a gust throws the ship into a slight sideslip the right wing will pick itself up before the small tail has a chance to yaw the plane around to the right. After the disturbance the plane will resume its flight in the origiinal direction.

Now think of a plane with no dihedral and a large vertical tail fin. The gust above will cause the plane to turn entirely from the yawing. If it does recover, it will head in a different direction. 

Students think the vertical tail fin is there to keep the plane flying straight. Instead, it actually makes the plane turn.

All of the above also depends on tail length and wing span. The density of the air plays a role in the dampening effect. A gust may cause a quick response but the air density will damp the quickness. A short tail and short wings will react quickly. Slower for a long tail-long wingspan aircraft.

Designing a stable non-spiraling plane is not worth the time for aircraft designers. They design a plane to actually help a pilot in controlling the aircraft. They contend that a spirally stable airplane is hard to fly in rough air. It will tire the pilot out over a long period of time.

To a pilot, in a steep spiral turn, is that tendencies that exist in a plane with controls released will be noticeable when the pilot flies the turn.

Plane design should make stability a priority. 

Friday, August 10, 2012

For Pilot Training Which is Better - High Wing or Low Wing?

High Wing versus Low Wing Trainers

I learned in a Cessna 120 tail-dragger. With experience, the Angle of Attack is controlled by the elevator. Keep in mind the Angle of Attack is the angle the attitude of your wings makes to the relative wind.

Lift is nothing but lowness of the Angle of Attack. When the stick is in a certain position the well balanced plane will assume a certain Angle of Attack. Put the stick further back the higher the Angle of Attack.

Whether the plane goes up, stays level or goes down at that Angle of Attack does not on stick position but entirely on the throttle position.

A good visible indication of this is a commercial jet aircraft descending on a landing flight path. The attitude of the airplane doesn't change due to its Angle of Attack but it is descending. If the pilot needs to maintain a flight altitude he applies power to maintain altitude. The stick  remains in the same position. If he needs to resume the original downward flight path he reduces power. The speed of the approach remains constant.

This confirms what a pilot wants to know about lift, that is how far he is from a stall.

Students need to appreciate and experience the pressures that increase  while he approaches a stall Angle of Attack. In a high-wing trainer stick movement to achieve this is much greater than in a low-wing airplane. The increased pressure you feel is  very noticeable and important. 

It is easier, in a glide, to let the stick creep backwards while in the glide. The pilot does this without realizing the slow change in position of the stick that results in a gradual increase in angle of attack. This is a drawback to high-wing trainers. An inexperienced new private pilot could approach a stall without adequate notice.

In low-wing aircraft, like the American Yankee, the range of stick movement is very small in comparison to a Cessna 120. I found out first hand when I pushed the stick forward just a couple of inches forward and I was in a fast power dive than in level flight. Same situation in a very steep climb. The Yankee, close to a stall, required only a couple of inches of back stick movement to reach that state.

A student tends to over-control. This is not good to use a quick reaction trainer if you want a student to recognize how a plane reaches a stall. It will enter a stall too quickly. This is frightening to a new learner.

You really have to "fly" a Yankee. I think this analogy pertains to the majority of low-wing aircraft.

In conclusion, a training airplane should require a wide, highly noticeable changes of stick position for small changes in Angle of Attack. The high-winged trainer would be my choice.

Wednesday, August 8, 2012

Sensing Angle of Attack

If Angle of Attack is associated with lift can we sense the angle of Attack?

Yes, No and Sometimes. The question should be " How reliable are our Senses to sense Angle of Attack?"


Low Angle of Attack and speed are almost the same thing in fast flight. High Angle of Attack and its relation to Load were discussed in an earlier post.


Ever play Blind Mans Bluff? There is way too many variables to trust your "reasoning" when it involves Angle of Attack. Here are several rationales,
  • You "reason" since your power is on full and your planes attitude is slightly up you have good air speed.
  • My power is very reduced and my nose (aircraft attitude) is down therefore I have good but not super fast air speed.
  • Taking off from a high altitude airport the engine does not perform as well in the thrust department and a pilot trusting his throttle will rotate to his usual takeoff angle and the plane will stall.
If you are using your "reasoning" to judge "speed" it is wise to make sure your "reasoning" is correct and you are aware of all the factors involved.

Be aware of our old friend "g-load" where, in a tight turn, the airplane flying at a certain speed loads itself up with centrifugal force (load). This causes the plane to assume a larger Angle of Attack and gets itself closer to a stall. (Remember lift reserve?) 

The plane, at a larger Angle of Attack, the wings have more drag and slows the plane. To prevent the plane from slowing you must apply more power. This, if you think back, creates an even higher Angle of Attack and the plane edges ever closer to a stall.

You must realize and understand how dangerous this effect is. A small plane fully loaded and with the throttle set to maintain a level cruising speed will not maintain indefinitely any turn with bank at  45 degrees or more. The plane will slow down gradually as it circles as the pilots stick comes further and further back. If everything remains constant the plane will complete more turns until it stalls. This happened out of level flight at cruising speed.

An example may be a pilot taking his family out for a "spin", so to speak, to enter a tight turn to show them several things above their town that requires many turns to view completely. Things happen fast and you may suddenly see them as you hurdle down in a stall-spin accident.


Airplanes make all sorts of big and little sounds that tells a pilot, by their pitch (high pitch=faster and low pitch=slower) that relates to speed and to the changing sound that indicates whether the plane is increasing or decreasing in speed. The problem is all planes are unique. The sounds one plane makes in different attitudes, speeds, etc. are all different. The beginning pilot hears the sounds but ignores them. The greatest danger of all is nothing at all - silence.

With experience, a pilot get away from just using the sense of sight and use his other senses to provide a "sense" of attitude that vision alone cannot.

Unfortunately the sounds of flight are not a good clue to provide the flight condition out of which a stall-spin accident develops.

Flight safety is learning from the good experience of others. Talk frequently to your instructor. Ask him how he can recognize dangerous flight situations in the air.

Tuesday, August 7, 2012

In Flying - How Far are You from a Stall?

Speed - Load and a Stall

The lowest of the Angle of Attack means the same thing to many of us as "Speed." Slow flight, as covered before, means high Angle of Attack.

Another factor to consider about the Angle of Attack when you fly a plane depends on its load. If you load your plane up and need to maintain the same speed you need more Angle of Attack.

When you increase the Angle of Attack to compensate for the increased load to maintain the same speed you achieved at a lighter load you lose your reserve of lift. 

A stall occurs when your plane reaches the limit of its reserve of lift. Your load can increase only to that point where the maximum reserve lift limit is reached. At that point the plane will stall at the straight and level flight and speed.

Now, how does this apply to practical flying? The centrifugal force experienced in a turn or pulling up after a dive (g-forces) act like real weight or load that brings you and your plane closer to the maximum limit of your reserve of lift

Now you understand that, in a turn or pull out from a dive, the increase in weight does several things:
  • Angle of Attack increases.
  • Reserve Lift decreases.
  • It approaches a stall even though the speed remains the same.
In straight flight speed and a sense of "lift" are the same thing. If a pilot can sense his speed he can also sense his lift. This is a definition of buoyancy. 

The tight turn centrifugal forces and g-forces in recovery from a dive can quickly turn into a stall. You must think ahead if you anticipate what can happen if you suddenly increase your load your plane carries.