Saturday, May 19, 2012

Vision - Is it Reliable

Down here in sunny South Carolina there are many trails that folks walk to just relax and get away from it all. If you regularly hike these trails the odds are you actually stepped over a Copperhead. No warning from these creatures. Their coloration pattern allows them to blend perfectly with the leaves and debris along a wooded nature trail. Sometimes you step on them and their bites account for the majority of bites treated in local hospitals. Very shy and difficult to provoke a strike but, thankfully, the venom is not life threatening but very painful. Visual Illusions abound in nature.

Another is a spotted fawn and other animals. If they remain motionless they are very difficult to spot.

In flight, camouflage used during wartime, protected important targets from discovery. What you see is not what is actually there. Entire encampments were disguised as serene villages when seen from the air.

For you and I visual illusions, especially under stress, can happen while flying. This is especially true in night flights. The "familiar" suddenly becomes the "unfamiliar."

Your instructor can provide other examples in Ground School.
The Leans

There are several ways you can experience the “Leans”. Some may be perceptual, others may effect the vestibular apparatus which is part of your inner ear.

This is the most common illusion during flight, and is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot. The reason a pilot can be unaware of such a gradual turn is that after twenty seconds a standard rate turn of two degrees per second falls below the detection threshold level of the semicircular canals

When you level the wings of your plane after such a turn it may cause an illusion that the plane is banking in the opposite direction. In response, a pilot may lean in the direction of the original turn in a corrective attempt to regain the appearance of normal straight and level flight.

From a playground setting , after riding a merry-go-round slowly and then jump off, you attempt to lean in the opposite direction from the spin of the merry-go-round. Hey, whats the matter, you got a case “of the leans?”

In instrument conditions this may lead to the "death spiral" if the pilot does't have a instrument rating. It is extremely difficult to recover from this illusion if you don't believe your instruments or rely on flying by the "seat of your pants."

If you have regular instrument conditions for flying where you live, think about instruction leading to a instrument rating.

Spiral Turn Illusion

The spiral turn illusion occurs to a pilot who enters a turn to the left or right inadvertently while on instruments .

For example, a pilot who enters a turn to the left will initially have a sensation of turning in the same direction. Without a visual horizon to verify what is happening the pilot will have the sensation that the turn is progressively decreasing. At this point, if the pilot applies right rudder to stop the left turn, the pilot will suddenly sense a turn in the opposite direction (to the right).

If the pilot believes that the airplane is turning to the right, the response will be to apply left rudder to stop the sensation of a right turn. However, by applying left rudder the pilot will unknowingly re-enter the original left turn. If the pilot cross-checks the turn indicator, he would see the turn needle indicating a left turn while he senses a right turn. This creates a sensory conflict between what the pilot sees on the instruments and what the pilot feels.

The whole purpose of instrument flight instruction is to believe what your instruments tell you about the position of your plane with respect to the surface of the earth without seeing the horizon. 

If the pilot believes the body sensations instead of trusting the instruments, the left turn will continue and it may deepen into a tight spiral turn that will result in altitude loss and forces may build up that results in structural damage to the plane and/or the loss of wings from the plane. If enough altitude is lost before the pilot recognizes this illusion a crash with the ground will result.

Visual illusions can kill. Fly aware and safely,

Coriolis Effect - Introduction

This illusion occurs when you stimulate two semicircular canals simultaneously. If you remember, in instrument flight training, when you were flying “under the hood” straight and level, your instructor dropped a object at your feet. Distraction while flying can precipitate this sensation.

As you leaned down to pick it up the instructor took over the controls and put the plane into a steep climbing turn to the right. You all know what the experience was like. Immediate nausea and the illusion that you were tumbling out of control. It is a very dangerous condition for a human being when flying a plane.

My instructor gave the control of the plane back to me and told me to land. I didn’t think I could I was so sick. But, land I did! He let me have a few minutes to get my “bearings” and ordered me to take-off and experience it again. By the way, the airport was a small grass strip with no communication facilities. A great spot to torture instrument flight students.

Net effect this can produce an overpowering sensation that the plane is rolling, pitching, and yawing all at the same time, which compares with the sensation of rolling down a hillside. This illusion can make the pilot quickly become disoriented and lose control of the plane. This introductory article is teaching you what not to do while on instruments. Know the attitude of your plane at all times.

Friday, May 18, 2012

The Dangers of Landing Behind Large Aircraft

Heavy planes, like airliners, produce vortexes at their wingtips. These twin tornados can flip a small plane over if the pilot doesn’t understand the hidden danger on the runway.

You must ask the control tower to lengthen your approach to give the ground turbulence time to dissipate before you touch down. If a slight cross-wind is present you should check the wind sock to see direction and possible velocity of the cross-wind.

The cross-wind may place one of the vortexes right on the runway just as you land. It is your responsibility to avoid that from happening.

You can ask for a go-around if you are unsure. That may save you from experiencing a bad day.

Ask your flight instructor at you local fixed-base operation to detail, for you, other precautions involved in mixed aircraft landings and takeoffs.

Pilot Signs of Fear and Loss of Control

World events can, in the commercial arena of flying can produce aberrant behavior when a pilot of an airliner suffered a breakdown. He felt the airline would explode in mid-air.

This is a carryover from headlines he read about an increase in terroristic attacks on commercial aviation. When a person is bombarded with negative input he/she will act out to warn passengers of an impending disaster.

This psychological background factors can manifest itself when a private pilot is thrust into a situation that he never experienced before. An example, flying into bad weather. In some cases training is forgotten and the pilot may put himself and the plane into great danger.

His proper training can return if he recognizes the signs of losing control of what he already knows to do in an emergency.

Here is a partial list:

Stop rapping your fingers.
Slow down your breathing.
Stop unnecessary chatter.
Concentrate on your instrument scan.
Fly the plane.
Radio to a controller that you are having difficulty.

There are more you and your instructor can discuss. The idea is to calm yourself down to bring back the training you already know to gain control.

In the case of the airline pilot the actions were beyond his control and force was used to prevent an accident.

It is always good to have a plan of action ready on any trip or flight where weather may occur.

Climbing and Level Flight Illusions

If you climb rapidly in a plane and then suddenly level off, the otoliths in your inner ear send amessage to your brain of tumbling backwards.

Your first impulse, if you are on instruments, is to push the plane into a nose down attitude. That reaction can intensify the illusion.

If you don’t recognize and ignore the illusion you may enter an outside loop with serious consequences to both plane and pilot. 

If you are not controlling the attitude of your plane, because of distraction, and you enter a climb, the plane attitude may set you up for the illusion when you discover your error and attempt to return to straight and level flight.

This illusion may occur when entering and exiting a series of cloud layers while you are climbing.

Your Instrument Instructor is a good source of a person who experienced some of the illusions and can aid the uninitiated 

Wednesday, May 16, 2012

Archimedes Principle - Bounancy - Balloons

The ground work story is an atom has mass and since molecules are made of atoms a molecule has mass. Liquids and gases contain molecules that are displaced, under certain conditions.

Liquids are first, since we swim in liquids, float things in liquids get the point. When an object, you or a boat, is immersed in a liquid the liquid exerts an upward force which is known as buoyant force and it is proportional to the weight of displaced liquid.

For instance, you float better in salt water than fresh water since salt water's density is greater than fresh water. 

If you have a constant size object that weighs, let say, twenty five pounds, and it  is a toy boat with high sides, it will ride higher in salt water than fresh water. Why? The toy boat will have to displace more fresh water (lower density) with a buoyant (upward force) of twenty five pounds to match the twenty five pound weight, hence it rides lower in the fresh water. The boat will displace less salt water to equal the buoyant upward force of twenty five pounds.  The sum force acting on the boat, then, is proportional to the difference between the weight of the boat('down' force of twenty five pounds) and the weight of displaced liquid ('up' force of twenty five pounds), hence equilibrium buoyancy is achieved when these two weights (and thus forces) are equal. Wow!

Isn't that neat! Same thing happens to you when you first swim in fresh water and then go on a vacation by the sea. You discover it is easier to swim in the ocean.

Density (mass per unit volume in liquids) is important. Salt water is more dense than fresh water.

Lets turn to air. It is a gas rather than a liquid. Same rules hold for objects immersed in air as they are in a liquid. Now we get into balloons immersed in air. 

Why do they float? If a balloon doesn't displace its weight in air molecules the upward buoyant forces exerted by the air molecules isn't as great as the weight of the balloon and it sinks. Think of a Birthday Balloon that, at first, rises to the top of a room but, after a few days air leaks out and the balloon displaces less and less air. It sinks! (Another story is when the balloon is filled with helium!)

The Hot Air Balloons make for a wonderful scenic ride. They are a perfect example of a controlled displacement volume aircraft.

Since air has a relatively constant density, the balloon, as it fills, will swell and displace more and more air. When the balloon fills and finally displaces more upward buoyant force exerted by the air than the downward force of the weight of the balloon, its basket and passengers - it float and begin to rise.

The more you increase the size of the balloon the more it will rise. If you let air out of the balloon and the size of the balloon decreases it will begin to sink. That is where the phrase, controlled displacement volume aircraft originated.

Tuesday, May 15, 2012

Prevention of a Secondary Stall

In instrument conditions recovery from a spin or inadvertent stall this technique may save your life or prevent unusual attitude motion sickness.

If you are in a recovery situation from a primary stall, and you have it under control, you want to return to straight and level flight. The vertical speed indicator is important to recovery.

When you recover from a primary stall I was taught to back off on power and apply forward pressure on the yoke. You are trying to reach a level wing flight attitude while keeping a continual scan of the vertical speed indicator.

As the airplane recovers you will see a decrease in the rate of losing altitude on the vertical speed indicator and corroborated by the altimeter. Your airspeed is higher, at this point, than your normal cruise speed.

Once the vertical speed indication indicates no rate of loss you will still experience resistance to keeping the nose of the aircraft from rising. 

This is important: When the vertical speed indicator stops moving upward or downward your airplane attitude is in level flight with greater airspeed that cruising airspeed. Keep forward pressure on the stick or wheel until the airspeed slows to your aircraft cruising speed. At this point the pressure on the yoke (wheel or stick) will abate to normal if you were properly trimmed before the stall ever began.

It is at this point you can slowly increase power to maintain altitude and cruising speed.

Note: while you were doing this the vertical speed indicator has remained at its neutral position that shows no rate of gain or loss. You are flying level.

You must return, even though the seat of your pants may disagree, to normal flight according to your instrument training. Your sensory input from your body may take a few minutes to agree with what your instruments are telling you about the correct attitude of the airplane - straight and level with respect to the earths surface at normal cruise speed.

Monday, May 14, 2012

Do Aircraft Plane - Yes

Newton's Laws; Bernoulli Effect or Both? Air is a gas made up of atoms linked together to form molecules of the different components of air. Atoms have mass, even though we can't see them with the naked eye.

For comparison think of a pair of skis planing over the surface of packed snow; a water board planing over the surface of a lake. Now you get the idea for a airplane!

Yes, airplanes do plane through the air and both Newton's Third Law and the  Bernoulli's  Effect are operating to produce the concept of Lift together. In special cases only Newton;s Law is responsible for the force that pushes a aircraft upward into the sky.

Wow. It isn't that difficult.  First, Newton's Laws are all about Force. Bernoulli's Principle is about creating a Negative Pressure area that allows nature to do its thing - namely to reduce that Negative Pressure. Remember, nature hates a vacuum. It has nothing to do with Force.

Lets talk Newton: His 3rd Law states that for every action there is a equal and opposite reaction. Think of "action" as a "force", like a pressure of air molecules measured in pounds per square inch. As the airplane skims across the air it pushes the mass of air molecules downward with a force that reacts upward on the bottom surface of the airplanes wings. If the sum total of all the reacting forces on the wings reaches or exceeds the weight of the airplane, in pounds, the airplane is flying.

Lets talk Bernoulli: His effect states that air flows, in this instance, faster on the upper surface of the wing than it does on the bottom surface of the wing and it creates a "negative pressure" region on the upper surface of the wings. It would seem the airplane is "sucked up" into the air. One additional example is a chimney  from a home. air passing over the top of the chimney creates a low pressure (or negative pressure) area above the opening of the chimney. The air pressure of the atmosphere is higher than the pressure just above the chimney. Net result pushes air(which is smoke)  up the chimney. We make use of pressure differentials when breathing. Beware, this is a very simplistic example and the mathematics is too complicated for this Blog.

Lets talk Newton and Bernoulli together: What Bernoulli accomplishes is making it possible for a airplane to move slower at a slightly increased "angle of attack" to create a reaction force to push the airplane into the air. Example, a small private airplane will takeoff and land at slower velocities that a similar more aerodynamically designed airplane. Another example is a interceptor jet airplane that performs best by reducing the overall drag on the airplane by using symmetrical wings. There isn't a "camber" that produces the Bernoulli Effect. Without that help the jet airplane must move much faster to achieve the upward force that equals its weight in pounds before becoming airborne. Lift, thrust, weight and drag are all involved in the design of a airplane and its ultimate purpose.

Lift is not just Bernoulli Effect alone or, except as noted, just as Newton's 3rd Law can't operate in lowered power airplanes without the Bernoulli Effect.