CFI Brief: Mach Number

As you progress through a career in aviation you will hopefully one day start flying high speed jet aircraft, a fun and challenging learning experience. However there are many differences when moving from low-speed flight to high-speed flight. Today we will briefly touch on some of the required knowledge associated with high speed flight beginning with mach numbers.

Mach number is the ratio of the true airspeed to the speed of sound (TAS ÷ Speed of Sound). For example, an aircraft cruising at Mach .80 is flying at 80% of the speed of sound. The speed of sound is Mach 1.0. When in high-speed flight we refer to our airspeed in mach rather than true airspeeds or indicated airspeeds. At any airspeeds above Mach 1 you would be breaking the sound barrier.

A large increase in drag occurs when the air flow around the aircraft exceeds the speed of sound (Mach 1.0). Because lift is generated by accelerating air across the upper surface of the wing, local air flow velocities will reach sonic speeds while the aircraft Mach number is still considerably below the speed of sound. With respect to Mach cruise control, flight speeds can be divided into three regimes—subsonic, transonic and supersonic. The subsonic regime can be considered to occur at aircraft Mach numbers where all the local air flow is less than the speed of sound. The transonic range is where some but not all the local air flow velocities are Mach 1.0 or above. In supersonic flight, all the air flow around the aircraft exceeds Mach 1.0. The exact Mach numbers will vary with each aircraft type but as a very rough rule of thumb the subsonic regime occurs below Mach .75, the transonic regime between Mach .75 and Mach 1.20, and the supersonic regime over Mach 1.20.

A limiting speed for a subsonic transport aircraft is its critical Mach number (MCRIT). That is the speed at which airflow over the wing first reaches, but does not exceed, the speed of sound. At MCRIT there may be sonic but no supersonic flow.

When an airplane exceeds its critical Mach number, a shock wave forms on the wing surface that can cause a phenomenon known as shock stall. If this shock stall occurs symmetrically at the wing roots, the loss of lift and loss of downwash on the tail will cause the aircraft to pitch down or “tuck under.” This tendency is further aggravated in sweptwing aircraft because the center of pressure moves aft as the wing roots shock stall. If the wing tips of a sweptwing airplane shock stall first, the wing’s center of pressure would move inward and forward causing a pitch up motion. See the Figure below.

The less airflow is accelerated across the wing, the higher the critical Mach number (i.e., the maximum flow velocity is closer to the aircraft’s Mach number). Two ways of increasing MCRIT in jet transport designs are to give the wing a lower camber and increase wing sweep. A thin airfoil section (lower camber) causes less airflow acceleration. The sweptwing design has the effect of creating a thin airfoil section by inducing a spanwise flow, thus increasing the effective chord length. See the Figure below.

Although a sweptwing design gives an airplane a higher critical Mach number (and therefore a higher maximum cruise speed), it results in some undesirable flight characteristics. One of these is a reduced maximum coefficient of lift. This requires that sweptwing airplanes extensively employ high lift devices, such as slats and slotted flaps, to get acceptably low takeoff and landing speeds. The purpose of high lift devices such as flaps, slats and slots is to increase lift at low airspeeds and to delay stall to a higher angle of attack.

Another disadvantage of the sweptwing design is the tendency, at low airspeeds, for the wing tips to stall first. This results in loss of aileron control early in the stall, and in very little aerodynamic buffet on the tail surfaces.


[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about CFI...

Aerodynamics: Shock Waves

Today we’re taking a look at a concept related to high speed flight, shock waves, with an excerpt from the Pilot’s Handbook of Aeronautical Knowledge (FAA-H-8083-25B). During flight, a wing produces lift by accelerating the airflow over the upper surface. This accelerated air can, and does, reach sonic speeds even though the aircraft itself may be flying subsonic. At some extreme angles of attack (AOA), in some aircraft, the speed of the air over the top surface of the wing may be double the aircraft’s speed. It is therefore entirely possible to have both supersonic and subsonic airflow on an aircraft at the same time. When flow velocities reach sonic speeds at some location on an aircraft (such as the area of maximum camber on the wing), further acceleration results in the onset of compressibility effects, such as shock wave formation, drag increase, buffeting, stability, and control difficulties. Subsonic flow principles are invalid at all speeds above this point.

When an airplane flies at subsonic speeds, the air ahead is “warned” of the airplane’s coming by a pressure change transmitted ahead of the airplane at the speed of sound. Because of this warning, the air begins to move aside before the airplane arrives and is prepared to let it pass easily. When the airplane’s speed reaches the speed of sound, the pressure change can no longer warn the air ahead because the airplane is keeping up with its own pressure waves. Rather, the air particles pile up in front of the airplane causing a sharp decrease in the flow velocity directly in front of the airplane with a corresponding increase in air pressure and density.

As the airplane’s speed increases beyond the speed of sound, the pressure and density of the compressed air ahead of it increase, the area of compression extending some distance ahead of the airplane. At some point in the airstream, the air particles are completely undisturbed, having had no advanced warning of the airplane’s approach, and in the next instant the same air particles are forced to undergo sudden and drastic changes in temperature, pressure, density, and velocity. The boundary between the undisturbed air and the region of compressed air is called a shock or “compression” wave. This same type of wave is formed whenever a supersonic airstream is slowed to subsonic without a change in direction, such as when the airstream is accelerated to sonic speed over the cambered portion of a wing, and then decelerated to subsonic speed as the area of maximum camber is passed. A shock wave forms as a boundary between the supersonic and subsonic ranges.

Whenever a shock wave forms perpendicular to the airflow, it is termed a “normal” shock wave, and the flow immediately behind the wave is subsonic. A supersonic airstream passing through a normal shock wave experiences these changes:

  • The airstream is slowed to subsonic.
  • The airflow immediately behind the shock wave does not change direction.
  • The static pressure and density of the airstream behind the wave is greatly increased.
  • The energy of the airstream (indicated by total pressure—dynamic plus static) is greatly reduced.

Shock wave formation causes an increase in drag. One of the principal effects of a shock wave is the formation of a dense high pressure region immediately behind the wave. The instability of the high pressure region, and the fact that part of the velocity energy of the airstream is converted to heat as it flows through the wave, is a contributing factor in the drag increase, but the drag resulting from airflow separation is much greater. If the shock wave is strong, the boundary layer may not have sufficient kinetic energy to withstand airflow separation. The drag incurred in the transonic region due to shock wave formation and airflow separation is known as “wave drag.” When speed exceeds the critical Mach number by about 10 percent, wave drag increases sharply. A considerable increase in thrust (power) is required to increase flight speed beyond this point into the supersonic range where, depending on the airfoil shape and the AOA, the boundary layer may reattach.

Normal shock waves form on the wing’s upper surface and form an additional area of supersonic flow and a normal shock wave on the lower surface. As flight speed approaches the speed of sound, the areas of supersonic flow enlarge and the shock waves move nearer the trailing edge.

Shock waves

Associated with “drag rise” are buffet (known as Mach buffet), trim, and stability changes and a decrease in control force effectiveness. The loss of lift due to airflow separation results in a loss of downwash and a change in the position of the center pressure on the wing. Airflow separation produces a turbulent wake behind the wing, which causes the tail surfaces to buffet (vibrate). The nose-up and nose-down pitch control provided by the horizontal tail is dependent on the downwash behind the wing. Thus, an increase in downwash decreases the horizontal tail’s pitch control effectiveness since it effectively increases the AOA that the tail surface is seeing. Movement of the wing center of pressure (CP) affects the wing pitching moment. If the CP moves aft, a diving moment referred to as “Mach tuck” or “tuck under” is produced, and if it moves forward, a nose-up moment is produced. This is the primary reason for the development of the T-tail configuration on many turbine-powered aircraft, which places the horizontal stabilizer as far as practical from the turbulence of the wings.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

Aircraft Systems: Electrical System

Today, we’re featuring an excerpt from the Pilot’s Handbook of Aeronautical Knowledge (FAA-8083-25B).

Most aircraft are equipped with either a 14- or a 28-volt direct current (DC) electrical system. A basic aircraft electrical system consists of the following components:

  • Alternator/generator
  • Battery
  • Master/battery switch
  • Alternator/generator switch
  • Bus bar, fuses, and circuit breakers
  • Voltage regulator
  • Ammeter/loadmeter
  • Associated electrical wiring

Engine-driven alternators or generators supply electric current to the electrical system. They also maintain a sufficient electrical charge in the battery. Electrical energy stored in a battery provides a source of electrical power for starting the engine and a limited supply of electrical power for use in the event the alternator or generator fails. Most DC generators do not produce a sufficient amount of electrical current at low engine rpm to operate the entire electrical system. During operations at low engine rpm, the electrical needs must be drawn from the battery, which can quickly be depleted.

Alternators have several advantages over generators. Alternators produce sufficient current to operate the entire electrical system, even at slower engine speeds, by producing alternating current (AC), which is converted to DC. The electrical output of an alternator is more constant throughout a wide range of engine speeds.

Some aircraft have receptacles to which an external ground power unit (GPU) may be connected to provide electrical energy for starting. These are very useful, especially during cold weather starting. Follow the manufacturer’s recommendations for engine starting using a GPU. The electrical system is turned on or off with a master switch. Turning the master switch to the ON position provides electrical energy to all the electrical equipment circuits except the ignition system. Equipment that commonly uses the electrical system for its source of energy includes:

  • Position lights
  • Anticollision lights
  • Landing lights
  • Taxi lights
  • Interior cabin lights
  • Instrument lights
  • Radio equipment
  • Turn indicator
  • Fuel gauges
  • Electric fuel pump
  • Stall warning system
  • Pitot heat
  • Starting motor

Many aircraft are equipped with a battery switch that controls the electrical power to the aircraft in a manner similar to the master switch. In addition, an alternator switch is installed that permits the pilot to exclude the alternator from the electrical system in the event of alternator failure.

On this master switch, the left half is for the alternator and the right half is for the battery.

With the alternator half of the switch in the OFF position, the entire electrical load is placed on the battery. All nonessential electrical equipment should be turned off to conserve battery power.

A bus bar is used as a terminal in the aircraft electrical system to connect the main electrical system to the equipment using electricity as a source of power. This simplifies the wiring system and provides a common point from which voltage can be distributed throughout the system.

Electrical system schematic.

Fuses or circuit breakers are used in the electrical system to protect the circuits and equipment from electrical overload. Spare fuses of the proper amperage limit should be carried in the aircraft to replace defective or blown fuses. Circuit breakers have the same function as a fuse but can be manually reset, rather than replaced, if an overload condition occurs in the electrical system. Placards at the fuse or circuit breaker panel identify the circuit by name and show the amperage limit. An ammeter is used to monitor the performance of the aircraft electrical system. The ammeter shows if the alternator/generator is producing an adequate supply of electrical power. It also indicates whether or not the battery is receiving an electrical charge.

Ammeters are designed with the zero point in the center of the face and a negative or positive indication on either side. When the pointer of the ammeter is on the plus side, it shows the charging rate of the battery. A minus indication means more current is being drawn from the battery than is being replaced. A full-scale minus deflection indicates a malfunction of the alternator/generator. A full-scale positive deflection indicates a malfunction of the regulator. In either case, consult the AFM/POH for appropriate action to be taken.

Ammeter and loadmeter

Not all aircraft are equipped with an ammeter. Some have a warning light that, when lighted, indicates a discharge in the system as a generator/alternator malfunction. Refer to the AFM/POH for appropriate action to be taken.

Another electrical monitoring indicator is a loadmeter. This type of gauge has a scale beginning with zero and shows the load being placed on the alternator/generator. The loadmeter reflects the total percentage of the load placed on the generating capacity of the electrical system by the electrical accessories and battery. When all electrical components are turned off, it reflects only the amount of charging current demanded by the battery.

A voltage regulator controls the rate of charge to the battery by stabilizing the generator or alternator electrical output. The generator/alternator voltage output should be higher than the battery voltage. For example, a 12-volt battery would be fed by a generator/alternator system of approximately 14 volts. The difference in voltage keeps the battery charged.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

CFI Brief: Complex Airplane, No Longer Required on Checkride

The Federal Aviation Administration has issued a Notice of Change to National Policy regarding use of complex airplanes during Commercial Pilot (Single-Engine Land) or Flight Instructor checkrides. A complex airplane is defined as an airplane with flaps, retractable landing gear, and a constant speed propeller. This change in policy will no longer require the use of a complex airplane on the above named practical tests. Notice 8900.463 reads in part:

This notice outlines a change in policy regarding testing applicants for a commercial pilot or flight instructor certificate, regardless whether the training was received under Title 14 of the Code of Federal Regulations (14 CFR) part 61 or 141. Specifically, it outlines the policy which no longer requires applicants for a commercial pilot certificate with an airplane single-engine rating to provide a complex or turbine-powered airplane for the associated practical test and no longer requires applicants for a flight instructor certificate with an airplane single-engine rating to provide a complex airplane for the practical test.

It is important to note this policy change does not affect the training and experience requirements as outlined in 14 CFR Parts 61 or 141. Applicants working towards a Commercial or Flight Instructor Certificate will still be required to obtain flight time and training in a complex airplane.

Part of the reasoning behind this change is that training providers have noted a concern regarding the availability of complex airplanes, adding to the complexity of scheduling checkrides. In addition, many of these aircraft are older models and require much higher maintenance cost to meet airworthiness standards. The FAA recognizes these flight school concerns and understands it might be cost-prohibitive and difficult to schedule applicant testing in a complex airplane.

Removing the requirements for a complex airplane to be used during the practical test will in turn reduce the overall cost of the practical test and allow applicants to utilize more cost effective and readily available aircraft.

Please note the corresponding changes to the Commercial Pilot ACS (FAA-S-ACS-7) and Flight Instructor PTS (FAA-S-8081-6D) as outlined below.

Change 3

  • Revised the “Equipment Requirements & Limitations” section in Appendix 7: Aircraft, Equipment, and Operational Requirements & Limitations.

Note: This change will also affect the wording in some of the Task, Skill elements. To see all change 3 revisions please refer to the complete document by following the link below. 

Change 6

  • Removed the complex airplane requirement from practical tests for an airplane single-engine instructor rating and made corresponding changes to Task elements and the following sections in the Introduction:
  • “Aircraft and Equipment Required for the Practical Test”
  • “Renewal or Reinstatement of a Flight Instructor Certificate”

An update will be available shortly for the ASA Commercial Pilot ACS and Flight Instructor PTS publications. To stay informed of all updates please follow the link below.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about CFI...

CFI Brief: sUAS Maintenance & Inspection

In addition to preflight and postflight considerations for small unmanned aircraft systems (sUAS) which was disused in Monday’s post, special attention should be placed on maintenance and inspection procedures. Unlike an airplane or helicopter, a sUAS does not require an airworthiness certificate nor is it required to have maintenance inspections done at certain intervals. It is the responsibility of the pilot in command to determine that the sUAS has been maintained in a condition for safe operation.

Maintenance for sUAS includes scheduled and unscheduled overhaul, repair, inspection, modification, replacement, and system software upgrades for the unmanned aircraft itself and all components necessary for flight.

Manufacturers may recommend a maintenance or replacement schedule for the unmanned aircraft and system components based on time-in-service limits and other factors. Follow all manufacturer maintenance recommendations to achieve the longest and safest service life of the sUAS. If the sUAS or component manufacturer does not provide scheduled maintenance instructions, it is recommended that you establish your own scheduled maintenance protocol. For example:

  • Document any repair, modification, overhaul, or replacement of a system component resulting from normal flight operations.
  • Record the time-in-service for that component at the time of the maintenance procedure.
  • Assess these records over time to establish a reliable maintenance schedule for the sUAS and its components.

During the course of a preflight inspection, you may discover that an sUAS component requires some form of maintenance outside of the scheduled maintenance period. For example, an sUAS component may require servicing (such as lubrication), repair, modification, overhaul, or replacement as a result of normal or abnormal flight operations. Or, the sUAS manufacturer or component manufacturer may require an unscheduled system software update to correct a problem. In the event such a condition is found, do not conduct flight operations until the discrepancy is corrected.

In some instances, the sUAS or component manufacturer may require certain maintenance tasks be performed by the manufacturer or by a person or facility specified by the manufacturer; maintenance should be performed in accordance with the manufacturer’s instructions. However, if you decide not to use the manufacturer or the personnel recommended by the manufacturer and you are unable to perform the required maintenance yourself, you should:

  • Solicit the expertise of maintenance personnel familiar with the specific sUAS and its components.
  • Consider using certificated maintenance providers, such as repair stations, holders of mechanic and repairman certificates, and persons working under the supervision of a mechanic or repairman.

If you or the maintenance personnel are unable to repair, modify, or overhaul an sUAS or component back to its safe operational specification, then it is advisable to replace the sUAS or component with one that is in a condition for safe operation. Complete all required maintenance before each flight—preferably in accordance with the manufacturer’s instructions or, in lieu of that, within known industry best practices.

Careful recordkeeping can be highly beneficial for sUAS owners and operators. For example, recordkeeping provides essential safety support for commercial operators who may experience rapidly accumulated flight operational hours/cycles. Consider maintaining a hardcopy and/or electronic logbook of all periodic inspections, maintenance, preventative maintenance, repairs, and alterations performed on the sUAS. See the figure below. Such records should include all components of the sUAS, including the:

  • Small unmanned aircraft itself;
  • Control station;
  • Launch and recovery equipment;
  • Data link equipment;
  • Payload; and
  • Any other components required to safely operate the sUAS.

You can find a UAS Operators Log here.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about CFI...

sUAS: Preflight Inspections

Today we’re pleased to feature an excerpt from our latest remote pilot textbook, The Complete Remote Pilot, by Bob Gardner and David Ison. Built on the foundation of Bob Gardner’s popular The Complete Private Pilot series, this textbook is tailored for anyone interested in pursuing and obtaining a Remote Pilot Certificate, which is required in order to operate drones for commercial use. The Complete Remote Pilot is designed to not only prepare you for the exam but to teach you about how UAS fly, their components and systems, and the aeronautical knowledge required to fly these systems in the same airspace as large commercial jets. This book covers specifics on the language of drones, regulations, airspace and navigation, airport and off-airport operations, radio communication procedures, weather, aerodynamics and aircraft performance, emergency procedures, human factors, maintenance, and preflight inspection procedures.

Since an sUAS potentially operates in proximity to and within the same airspace as manned aircraft, a high level of care is required to ensure that the aircraft is safe to operate and will not do anything to jeopardize the ability of the remote PIC to maintain positive control of the system while in use. The FAA explicitly spells this out in 14 CFR §107.15, stating that prior to each flight, “the remote pilot in command must check the small unmanned aircraft system to determine whether it is in a condition for safe operation.” Further, if at any time it is determined that this condition is compromised, the operation must cease immediately. Unmanned aircraft pilots should mimic their manned counterparts who are very familiar with the preflight inspection process, which is (or should be) a very thorough evaluation of the aircraft before taking flight.

While manned aircraft manufacturers typically provide a comprehensive checklist to use for preflight inspections, not all sUAS manufacturers do so. It may be necessary to create your own checklist. However, you may not need to start from scratch—or worse, learn the “hard” way; instead, look online to find out what work has been done on your individual system. Some great resources are available on various websites, especially for systems with minimal documentation provided by the manufacturer. In short, if the aircraft comes with a checklist or procedure for ensuring safe operation, use it. Feel free to add to it if you find some additional things that you feel need to be checked prior to use. If no such guidance is provided, create your own. So what should you include? Let’s take a look.

While each sUAS will vary, here are some key areas to consider for careful inspection before flight or on a regular basis. Before every flight, it’s important to do a thorough visual examination of the aircraft. Are there any loose parts? Is anything hanging off that should not be? Does anything look abnormal? Is there any damage to the structure? Next, you should take a look at the propellers. Before putting them on the aircraft, flex the blades slightly to confirm their integrity. While you are doing this, look over the blades and run your finger along their edges and surfaces. If there are nicks or cracks, you should replace the propeller. Once they are installed on the aircraft, propellers should be secure (and locked if applicable), but don’t overtighten them, as that can damage the threads or connections.

While you are in the vicinity of the motors, check them for proper rotation and security. Do they spin freely? Is anything sticking? Are any motors too loose? The best way to know for sure is by comparing one motor to another (or if the sUAS only has one motor, comparing it to how it appeared the last time). If anything is abnormal, it is advisable to remove and replace the item in question. (More experienced users may want to do some bench tests prior to replacing or flying.)

Next, check all peripheral items, such as the camera gimbal or other payloads. Are they properly connected and secured? How about the camera or other sensors? These typically are expensive pieces of equipment; you do not want to accidentally damage or lose them because you were in a hurry to fly.

You will also want to inspect the battery prior to installation. Note: be sure you know the correct power-on procedures for your sUAS. Some will be powered once the battery is installed, so if that is the case, you will want to be ready for that change in status. Typically, the controller is turned on first and then the sUAS is turned on, to reduce the chances of something unexpected happening (and if it does, by following this procedure, you should have control).

Check the battery connection pins/slots to verify that they are not damaged or dirty. Check the body of the battery. Is there any “puffiness” or bulging of the outer coating or sides? If the answer is yes, your battery is failing. Never use a puffy or bulging battery. Is the battery warm or hot? If so, let it cool before using. Do you know the charging status? If not, it is best to know this before flight for quality assurance and performance tracking. Once you are happy with the battery’s status, install it (or position it for installation).

The ground control station and any other equipment also should be inspected. Are the antennae properly installed and attached? Are there any missing or loose parts? What is the battery status of the components? Will the capacity be enough to complete the mission with an additional time cushion?

Is your crew briefed and ready to go? If yes, power on the sUAS (after completing necessary checklists) to check lights and other markings. Do a control check (if possible) and gimbal check. Does everything move freely without abnormal resistance or noises? Next, you will want to do an idle check with motors on (again, only when ready and post-checklists). Check for any unusual noises or vibrations. If any are detected, shut down and investigate further before departing. The final check prior to initiating the mission is an airborne control check. For example, if you’re using a quadcopter, lift the aircraft off to a hover just above the ground. Input left/right, forward/back, yaw, and power inputs to ensure the system reacts as expected. Additionally, confirm that there are no weird noises or “ticks” experienced during this operational check.

Upon completing a flight, the sUAS should be inspected again. Essentially you will want to check the same items as in the preflight inspection, noting any changes in aircraft status. Batteries will generally be warm because of discharging, but they should not be hot. Use caution if the battery condition changes between the pre- and post-flight inspections (e.g., it begins to bulge). Note any issues in your maintenance log (explained later) and replace any parts that are damaged or at the end of their service life.

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

CFI Brief: Pop Quiz—Clouds

If you are reading today’s blog then you have already committed yourself to this mandatory 5-question pop quiz. Too late, you can’t leave now! Plus, who doesn’t love a good pop quiz to test your level of aviation meteorology knowledge. Meteorology you say? That’s right todays pop quiz is on clouds, so I hope you read Monday’s blog post, if not go back and give it a quick read thru by following the below link.

Blog Post – Weather: Clouds

Before you jump right into the quiz let’s highlight some knowledge pertaining to clouds you should know.

  • Stability determines which of two types of clouds will be formed: cumuliform or stratiform.
  • Cumuliform clouds are the billowy-type clouds having considerable vertical development, which enhances the growth rate of precipitation. They are formed in unstable conditions, and they produce showery precipitation made up of large water droplets.
  • Stratiform clouds are the flat, more evenly based clouds formed in stable conditions. They produce steady, continuous light rain and drizzle made up of much smaller raindrops.
  • Steady precipitation (in contrast to showery) preceding a front is an indication of stratiform clouds with little or no turbulence.
  • Clouds are divided into four families according to their height range: low, middle, high, and clouds with extensive vertical development.
  • The first three families—low, middle, and high—are further classified according to the way they are formed. Clouds formed by vertical currents (unstable) are cumulus (heap) and are billowy in appearance. Clouds formed by the cooling of a stable layer are stratus (layered) and are flat and sheet-like in appearance. A further classification is the prefix “nimbo-” or suffix “-nimbus,” which means raincloud.
  • High clouds, called cirrus, are composed mainly of ice crystals; therefore, they are least likely to contribute to structural icing (since it requires water droplets).

Ready, set, pop quiz!

Pop Quiz – Weather, Clouds

1. Clouds, fog, or dew will always form when
A—water vapor condenses.
B—water vapor is present.
C—relative humidity reaches 100 percent.

2. If an unstable air mass is forced upward, what type clouds can be expected?
A—Stratus clouds with little vertical development.
B—Stratus clouds with considerable associated turbulence.
C—Clouds with considerable vertical development and associated turbulence.

3. The suffix ‘nimbus,’ used in naming clouds, means
A—a cloud with extensive vertical development.
B—a rain cloud.
C—a middle cloud containing ice pellets.

4. Clouds are divided into four families according to their
A—outward shape.
B—height range.

5. What clouds have the greatest turbulence?
A—Towering cumulus.

So, how do you think you did? Check out the Answers & Explanations.

Note, the question above are sample questions representative to what you might see on your FAA Private Pilot Knowledge Exam. 

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about CFI...

Very first thing, though is you should create the book.

Your personal essay is an important part of the college application procedure and you must make certain which you are writing it in a manner that reveals your maturity and in a style that is professional. If you’re caught in the major period of doing research and don’t have any time for genuine creating, you will need to think about putting a purchase on the net to locate individual essay for school. Read More »

[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

Weather: Clouds

Today we’ll review one of the fundamental concepts in aviation weather, understanding clouds. This post feature’s an excerpt from the Pilot’s Handbook of Aeronautical Knowledge (8083-25B).

Clouds are visible indicators and are often indicative of future weather. For clouds to form, there must be adequate water vapor and condensation nuclei, as well as a method by which the air can be cooled. When the air cools and reaches its saturation point, the invisible water vapor changes into a visible state. Through the processes of deposition (also referred to as sublimation) and condensation, moisture condenses or sublimates onto miniscule particles of matter like dust, salt, and smoke known as condensation nuclei. The nuclei are important because they provide a means for the moisture to change from one state to another.

Cloud type is determined by its height, shape, and characteristics. They are classified according to the height of their bases as low, middle, or high clouds, as well as clouds with vertical development.

Basic cloud types

Low clouds are those that form near the Earth’s surface and extend up to about 6,500 feet AGL. They are made primarily of water droplets but can include supercooled water droplets that induce hazardous aircraft icing. Typical low clouds are stratus, stratocumulus, and nimbostratus. Fog is also classified as a type of low cloud formation. Clouds in this family create low ceilings, hamper visibility, and can change rapidly. Because of this, they influence flight planning and can make visual flight rules (VFR) flight impossible.

Middle clouds form around 6,500 feet AGL and extend up to 20,000 feet AGL. They are composed of water, ice crystals, and supercooled water droplets. Typical middle-level clouds include altostratus and altocumulus. These types of clouds may be encountered on cross-country flights at higher altitudes. Altostratus clouds can produce turbulence and may contain moderate icing. Altocumulus clouds, which usually form when altostratus clouds are breaking apart, also may contain light turbulence and icing.

High clouds form above 20,000 feet AGL and usually form only in stable air. They are made up of ice crystals and pose no real threat of turbulence or aircraft icing. Typical high level clouds are cirrus, cirrostratus, and cirrocumulus.

Clouds with extensive vertical development are cumulus clouds that build vertically into towering cumulus or cumulonimbus clouds. The bases of these clouds form in the low to middle cloud base region but can extend into high altitude cloud levels. Towering cumulus clouds indicate areas of instability in the atmosphere, and the air around and inside them is turbulent. These types of clouds often develop into cumulonimbus clouds or thunderstorms. Cumulonimbus clouds contain large amounts of moisture and unstable air and usually produce hazardous weather phenomena, such as lightning, hail, tornadoes, gusty winds, and wind shear. These extensive vertical clouds can be obscured by other cloud formations and are not always visible from the ground or while in flight. When this happens, these clouds are said to be embedded, hence the term, embedded thunderstorms.

To pilots, the cumulonimbus cloud is perhaps the most dangerous cloud type. It appears individually or in groups and is known as either an air mass or orographic thunderstorm. Heating of the air near the Earth’s surface creates an air mass thunderstorm; the upslope motion of air in the mountainous regions causes orographic thunderstorms. Cumulonimbus clouds that form in a continuous line are nonfrontal bands of thunderstorms or squall lines.

Since rising air currents cause cumulonimbus clouds, they are extremely turbulent and pose a significant hazard to flight safety. For example, if an aircraft enters a thunderstorm, the aircraft could experience updrafts and downdrafts that exceed 3,000 fpm. In addition, thunderstorms can produce large hailstones, damaging lightning, tornadoes, and large quantities of water, all of which are potentially hazardous to aircraft.

Cloud classification can be further broken down into specific cloud types according to the outward appearance and cloud composition. Knowing these terms can help a pilot identify visible clouds.

The following is a list of cloud classifications:

  • Cumulus—heaped or piled clouds
  • Stratus—formed in layers
  • Cirrus—ringlets, fibrous clouds, also high level clouds above 20,000 feet
  • Castellanus—common base with separate vertical development, castle-like
  • Lenticularus—lens-shaped, formed over mountains in strong winds
  • Nimbus—rain-bearing clouds
  • Fracto—ragged or broken
  • Alto—middle level clouds existing at 5,000 to 20,000 feet
[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

Ground Reference Maneuvers: Turns Around a Point

Today we’re featuring a follow-up to our recent post on the rectangular course with an excerpt from the Airplane Flying Handbook (FAA-H-8083-3B).

Turns around a point are a logical extension of both the rectangular course and S-turns across a road. The maneuver is a 360° constant radius turn around a single ground-based reference point. The principles are the same in any turning ground reference maneuver—higher groundspeeds require steeper banks and slower ground speeds require shallower banks. The objectives of turns around a point are as follows:

  • Maintaining a specific relationship between the airplane and the ground.
  • Dividing attention between the flightpath, groundbased references, manipulating of the flight controls, and scanning for outside hazards and instrument indications.
  • Adjusting the bank angle during turns to correct for groundspeed changes in order to maintain a constant radius turn; steeper bank angles for higher ground speeds, shallow bank angles for slower groundspeeds.
  • Improving competency in managing the quickly changing bank angles.
  • Establishing and adjusting the wind correction angle in order to maintain the track over the ground.
  • Developing the ability to compensate for drift in quickly changing orientations.
  • Developing further awareness that the radius of a turn is correlated to the bank angle.

Turns around a point.

To perform a turn around a point, the pilot must complete at least one 360° turn; however, to properly assess wind direction, velocity, bank required, and other factors related to turns in wind, the pilot should complete two or more turns. As in other ground reference maneuvers, when wind is present, the pilot must a constantly adjust the airplane’s bank and wind correction angle to maintain a constant radius turn around a point. In contrast to the ground reference maneuvers discussed previously in which turns were approximately limited to either 90° or 180°, turns around a point are consecutive 360° turns where, throughout the maneuver, the pilot must constantly adjust the bank angle and the resulting rate of turn in proportion to the groundspeed as the airplane sequences through the various wind directions. The pilot should make these adjustments by applying coordinated aileron and rudder pressure throughout the turn.

When performing a turn around a point, the pilot should select a prominent, ground-based reference that is easily distinguishable yet small enough to present a precise reference. The pilot should enter the maneuver downwind, where the groundspeed is at its fastest, at the appropriate radius of turn and distance from the selected ground-based reference point. In a high-wing airplane, the lowered wing may block the view of the ground reference point, especially in airplanes with side-by-side seating during a left turn (assuming that the pilot is flying from the left seat). To prevent this, the pilot may need to change the maneuvering altitude or the desired turn radius. The pilot should ensure that the reference point is visible at all times throughout the maneuver, even with the wing lowered in a bank.

Upon entering the maneuver, depending on the wind’s speed, it may be necessary to roll into the initial bank at a rapid rate so that the steepest bank is set quickly to prevent the airplane from drifting outside of the desired turn radius. This is best accomplished by repeated practice and assessing the required roll in rate. Thereafter, the pilot should gradually decrease the angle of bank until the airplane is headed directly upwind. As the upwind becomes a crosswind and then a downwind, the pilot should gradually steepen the bank to the steepest angle upon reaching the initial point of entry.

During the downwind half of the turn, the pilot should progressively adjust the airplane’s heading toward the inside of the turn. During the upwind half, the pilot should progressively adjust the airplane’s heading toward the outside of the turn. Recall from the previous discussion on wind correction angle that the airplane’s heading should be ahead of its position over the ground during the downwind half of the turn behind its position during the upwind half. Remember that the goal is to make a constant radius turn over the ground and, because the airplane is flying through a moving air mass, the pilot must constantly adjust the bank angle to achieve this goal.

The following are the most common errors in the performance of turns around a point:

  • Failure to adequately clear the area above, below, and on either side of the airplane for safety hazards, initially and throughout the maneuver.
  • Failure to establish a constant, level altitude prior to entering the maneuver.
  • Failure to maintain altitude during the maneuver.
  • Failure to properly assess wind direction.
  • Failure to properly execute constant radius turns.
  • Failure to manipulate the flight controls in a smooth and continuous manner.
  • Failure to establish the appropriate wind correction angle.
  • Failure to apply coordinated aileron and rudder pressure, resulting in slips or skids.
[] [Digg] [Facebook] [Furl] [Google] [Reddit] [StumbleUpon] [Twitter] [Email]

Read more about ASA...

You may want to put some text here



Get this Wordpress newsletter widget
for newsletter software