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.