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Aircraft Systems: Carburetor Ice

Today we’re taking a look at carburetor ice with the Pilot’s Handbook of Aeronautical Knowledge.

As mentioned earlier, one disadvantage of the float-type carburetor is its icing tendency. Carburetor ice occurs due to the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburetor. If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve. [Figure 1]

Figure 1. The formation of carburetor ice may reduce or block fuel/air flow to the engine.

Figure 1. The formation of carburetor ice may reduce or block fuel/air flow to the engine.

The reduced air pressure, as well as the vaporization of fuel, contributes to the temperature decrease in the carburetor. Ice generally forms in the vicinity of the throttle valve and in the venturi throat. This restricts the flow of the fuel/air mixture and reduces power. If enough ice builds up, the engine may cease to operate. Carburetor ice is most likely to occur when temperatures are below 70°F or 21°C and the relative humidity is above 80 percent. Due to the sudden cooling that takes place in the carburetor, icing can occur even with temperatures as high as 100°F (38°C) and humidity as low as 50 percent. This temperature drop can be as much as 60 to 70°F (15 to 21°C). Therefore, at an outside air temperature of 100°F (37°C), a temperature drop of 70°F (21°C) results in an air temperature in the carburetor of 30°F (-1°C). [Figure 2]

Figure 2. Although carburetor ice is most likely to form when the temperature and humidity are in ranges indicated by this chart, carburetor ice is possible under conditions not depicted.

Figure 2. Although carburetor ice is most likely to form when the temperature and humidity are in ranges indicated by this chart, carburetor ice is possible under conditions not depicted.


The first indication of carburetor icing in an aircraft with a fixed-pitch propeller is a decrease in engine rpm, which may be followed by engine roughness. In an aircraft with a constant-speed propeller, carburetor icing is usually indicated by a decrease in manifold pressure, but no reduction in rpm. Propeller pitch is automatically adjusted to compensate for loss of power. Thus, a constant rpm is maintained. Although carburetor ice can occur during any phase of flight, it is particularly dangerous when using reduced power during a descent. Under certain conditions, carburetor ice could build unnoticed until power is added. To combat the effects of carburetor ice, engines with float-type carburetors employ a carburetor heat system.

We’ll see you Thursday for more from our CFI. Thanks for following the Learn to Fly Blog!

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CFI Brief: Knowledge Test Questions, Stalls & Spins

As the angle of attack is increased (to increase lift), air will no longer flow smoothly over the upper wing surface but instead will become turbulent or “burble” near the trailing edge. A further increase in the angle of attack will cause the turbulent area to expand forward. At an angle of attack of approximately 18° to 20° (for most wings), turbulence over the upper wing surface decreases lift so drastically that flight can not be sustained and the wing stalls. See the figure below.

Angle of Attack

Angle of Attack

The angle at which a stall occurs is called the critical angle of attack. An airplane can stall at any airspeed or any attitude, but will always stall at the same critical angle of attack. The indicated airspeed at which a given airplane will stall in a particular configuration, however, will remain the same regardless of altitude. Because air density decreases with an increase in altitude, the airplane has to be flown faster at higher altitudes to cause the same pressure difference between pitot impact pressure and static pressure.

An aircraft will spin only after it has stalled, and will continue to spin as long as the outside wing continues to provide more lift than the inside wing and the aircraft remains stalled.

Here are some sample private pilot knowledge test questions. You can find answers with explanations below, no scrolling down and cheating!

1. The angle of attack at which an airfoil stalls will
A—change with an increase in gross weight.
B—increase if the CG is moved forward.
C—remain the same regardless of gross weight.

2. During an approach to a stall, an increased load factor will cause the airplane to
A—stall at a higher airspeed.
B—have a tendency to spin.
C—be more difficult to control.

3. During a spin to the left, which wing(s) is/are stalled?
A—Neither wing is stalled.
B—Both wings are stalled.
C—Only the left wing is stalled.

4. As altitude increases, the indicated airspeed at which a given airplane stalls in a particular configuration will
A—decrease as the true airspeed increases.
B—remain the same regardless of altitude.
C—decrease as the true airspeed decreases.

ANSWERS AND EXPLANATIONS

1. The angle of attack at which an airfoil stalls will remain the same regardless of gross weight.

When the angle of attack is increased to between 18° and 20° (critical angle of attack) on most airfoils, the airstream can no longer follow the upper curvature of the wing because of the excessive change in direction. The airplane will stall if the critical angle of attack is exceeded. The indicated airspeed at which stall occurs will be determined by weight and load factor, but the stall angle of attack is the same.

Answer (A) is incorrect because an airfoil will always stall at the same angle of attack, regardless of the CG position or gross weight. Answer (B) is incorrect because an airfoil will always stall at the same angle of attack, regardless of the CG position or gross weight.

2. During an approach to a stall, an increased load factor will cause the airplane to stall at a higher airspeed.

Stall speed increases in proportion to the square root of the load factor. Thus, with a load factor of 4, an aircraft will stall at a speed which is double the normal stall speed.

Answer (B) is incorrect because an airplane’s tendency to spin does not relate to an increase in load factors. Answer (C) is incorrect because an airplane’s stability determines its controllability.

3. During a spin to the left, which wing(s) is/are stalled? Both wings are stalled.

One wing is less stalled than the other, but both wings are stalled in a spin.

Answer (B) is incorrect because both wings must be stalled through the spin.  Answer (C) is incorrect because both wings are stalled; but the right wing is less fully stalled than the left.

4. As altitude increases, the indicated airspeed at which a given airplane stalls in a particular configuration will remain the same regardless of altitude.

An increase in altitude has no effect on the indicated airspeed at which an airplane stalls at altitudes normally used by general aviation aircraft. This means that the same indicated airspeed should be maintained during the landing approach regardless of the elevation or the density altitude at the airport of landing.

Answer (A) is incorrect because true airspeed does not decrease with increased altitude, and indicated airspeed at which an airplane stalls does not change. Answer (B) is incorrect because the indicated airspeed of the stall does not decrease with increased altitude.

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Aerodynamics: Stalls and Spins

Today, we’re going to look at some flight maneuvers from one of our favorite books, the Pilot’s Handbook of Aeronautical Knowledge. Critical load factors apply to all flight maneuvers except unaccelerated straight flight where a load factor of 1 G is always present. Certain maneuvers considered in this section are known to involve relatively high load factors.

Stalls
The normal stall entered from straight-and-level flight, or an unaccelerated straight climb, does not produce added load factors beyond the 1 G of straight-and-level flight. As the stall occurs, however, this load factor may be reduced toward zero, the factor at which nothing seems to have weight. The pilot experiences a sensation of “floating free in space.” If recovery is effected by snapping the elevator control forward, negative load factors (or those that impose a down load on the wings and raise the pilot from the seat) may be produced.

During the pull up following stall recovery, significant load factors are sometimes induced. These may be further increased inadvertently during excessive diving (and consequently high airspeed) and abrupt pull ups to level flight. One usually leads to the other, thus increasing the load factor. Abrupt pull ups at high diving speeds may impose critical loads on aircraft structures and may produce recurrent or secondary stalls by increasing the AOA to that of stalling.

As a generalization, a recovery from a stall made by diving only to cruising or design maneuvering airspeed, with a gradual pull up as soon as the airspeed is safely above stalling, can be effected with a load factor not to exceed 2 or 2.5 Gs. A higher load factor should never be necessary unless recovery has been effected with the aircraft’s nose near or beyond the vertical attitude, or at extremely low altitudes to avoid diving into the ground.

Spins
A stabilized spin is not different from a stall in any element other than rotation and the same load factor considerations apply to spin recovery as apply to stall recovery. Since spin recoveries are usually effected with the nose much lower than is common in stall recoveries, higher airspeeds and consequently higher load factors are to be expected. The load factor in a proper spin recovery usually is found to be about 2.5 Gs.

The load factor during a spin varies with the spin characteristics of each aircraft, but is usually found to be slightly above the 1 G of level flight. There are two reasons for this:

  1. Airspeed in a spin is very low, usually within 2 knots of the unaccelerated stalling speeds.
  2. Aircraft pivots, rather than turns, while it is in a spin.

High Speed Stalls
The average light plane is not built to withstand the repeated application of load factors common to high speed stalls. The load factor necessary for these maneuvers produces a stress on the wings and tail structure, which does not leave a reasonable margin of safety in most light aircraft.

The only way this stall can be induced at an airspeed above normal stalling involves the imposition of an added load factor, which may be accomplished by a severe pull on the elevator control. A speed of 1.7 times stalling speed (about 102 knots in a light aircraft with a stalling speed of 60 knots) produces a load factor of 3 Gs. Only a very narrow margin for error can be allowed for acrobatics in light aircraft. To illustrate how rapidly the load factor increases with airspeed, a high-speed stall at 112 knots in the same aircraft would produce a load factor of 4 Gs.

We’ll be back on Thursday for our regularly scheduled CFI Brief!

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CFI Brief: IMPORTANT Changes to EFAS (Flight Watch)

Earlier this year, all questions relating to Enroute Flight Advisory Service (EFAS) were removed from the knowledge test banks. In addition, the FAA announced that due to user preferences and a shift towards automated services Flight Watch would be eliminated. This caused some immediate concern for those who rely on the services provided by Flight Watch to obtain the latest enroute weather and safety of flight information.  However rest assured, Flight Watch may be going away but the services provided are not.

WHAT YOU NEED TO KNOW

Previously, you were able to contact a Flight Service professional by calling Flight Watch on 122.0 along with other high level discrete frequencies to obtain EFAS information. Beginning September 24th, 2015 (UPDATED*), these frequencies will be phased out. As to not cause an abrupt end, Lockheed Martin Flight Service (LMFS) will still monitor current EFAS frequencies and provide a RCO frequency to use in order to receive EFAS and related advisories during a 6-month transition period. All inflight services including EFAS will now be consolidated and available by contacting Flight Service common frequency on 122.2 and all Remote Communications Outlets (RCO) frequencies.

WHAT IS FLIGHT SERVICE

Contacting Flight Service puts you in contact with someone who has immediate access to the latest weather information, including “live” weather radar. You can normally expect to receive actual weather and thunderstorm activity along your proposed route. To assist Flight Service and other pilots, you are encouraged to report good as well as bad weather, and to confirm expected conditions as well as unexpected conditions. Beyond weather, Flight Service facilities offer updates to NOTAMs/TFRs, critical safety of flight information, flight planning services, and the ability to open/close flight plans. You can refer to Flight Service by the facility name and radio followed by your call sign.

Here is an example: “Seattle Radio, November One Two Three Four Alpha, over.”

BENEFITS OF CHANGE

The FAA is making this change as part of the Flight Service National Airspace Initiative (FSNI) additional information on FSNI and frequently asked questions can be found here:

http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/systemops/fs/faq/

By discontinuing Flight Watch, the Flight Service program is in part eliminating redundancies and underutilized services. This will allow for a more cost effective and efficient operation without jeopardizing safety of flight. As a pilot, this should simplify your life; you will now have the added benefits of obtaining access to all flight services, critical safety of flight information and even flight planning services with one call. In addition, Flight Service professionals are available on frequency 24 hours a day.

So remember, on September 24th, 2015 (UPDATED*) obtain all your inflight services on 122.2!

*On August 31st the FAA updated the proposed change date from October 1st to September 24th, 2015.

 

Contact 122.2

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Communication Procedures: Radar Assistance to VFR Aircraft

In many instances, a pilot is required to have contact with ATC. But even when not required, a pilot finds it helpful to request their services. Today, we’re taking a look at radar assistance with words and pictures from the Pilot’s Handbook of Aeronautical Knowledge.

Primary Radar
Radar is a device which provides information on range, azimuth, and/or elevation of objects in the path of the transmitted pulses. It measures the time interval between transmission and reception of radio pulses and correlates the angular orientation of the radiated antenna beam or beams in azimuth and/or elevation. Range is determined by measuring the time it takes for the radio wave to go out to the object and then return to the receiving antenna. The direction of a detected object from a radar site is determined by the position of the rotating antenna when the reflected portion of the radio wave is received.

Modern radar is very reliable and there are seldom outages. This is due to reliable maintenance and improved equipment. There are, however, some limitations which may affect ATC services and prevent a controller from issuing advisories concerning aircraft which are not under his or her control and cannot be seen on radar.

The characteristics of radio waves are such that they normally travel in a continuous straight line unless they are “bent” by atmospheric phenomena such as temperature inversions, reflected or attenuated by dense objects such as heavy clouds and precipitation, or screened by high terrain features.

ATC Radar Beacon System (ATCRBS)
The ATC radar beacon system (ATCRBS) is often referred to as “secondary surveillance radar.” This system consists of three components and helps in alleviating some of the limitations associated with primary radar. The three components are an interrogator, transponder, and radarscope. The advantages of ATCRBS are the reinforcement of radar targets, rapid target identification, and a unique display of selected codes.

Transponder
The transponder is the airborne portion of the secondary surveillance radar system and a system with which a pilot should be familiar. The ATCRBS cannot display the secondary information unless an aircraft is equipped with a transponder.

A transponder code consists of four numbers from 0 to 7 (4,096 possible codes). There are some standard codes, or ATC may issue a four-digit code to an aircraft. When a controller requests a code or function on the transponder, the word “squawk” may be used. Figure 1 lists some standard transponder phraseology. Additional information concerning transponder operation can be found in the AIM, chapter 4.

Figure 1. Transponder phraseology.

Figure 1. Transponder phraseology.

Radar Traffic Advisories
Radar equipped ATC facilities provide radar assistance to aircraft on instrument flight plans and VFR aircraft provided the aircraft can communicate with the facility and are within radar coverage. This basic service includes safety alerts, traffic advisories, limited vectoring when requested, and sequencing at locations where this procedure has been established. ATC issues traffic advisories based on observed radar targets. The traffic is referenced by azimuth from the aircraft in terms of the 12-hour clock. Also, distance in nautical miles, direction in which the target is moving, and type and altitude of the aircraft, if known, are given. An example would be: “Traffic 10 o’clock 5 miles east bound, Cessna 152, 3,000 feet.” The pilot should note that traffic position is based on the aircraft track, and that wind correction can affect the clock position at which a pilot locates traffic. This service is not intended to relieve the pilot of the responsibility to see and avoid other aircraft. (Figure 2.)

Figure 2. Traffic advisories.

Figure 2. Traffic advisories.

In addition to basic radar service, terminal radar service area (TRSA) has been implemented at certain terminal locations. TRSAs are depicted on sectional aeronautical charts and listed in the A/FD. The purpose of this service is to provide separation between all participating VFR aircraft and all IFR aircraft operating within the TRSA. Class C service provides approved separation between IFR and VFR aircraft, and sequencing of VFR aircraft to the primary airport. Class B service provides approved separation of aircraft based on IFR, VFR, and/or weight, and sequencing of VFR arrivals to the primary airport(s).

We’ll be back on Thursday with a CFI report!

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CFI Brief: Off-Course Correction

The fundamentals of visual navigation include two main methods as discussed in Monday’s post, pilotage and dead reckoning, each of which should be used in conjunction with the other. Whether flying by means of visual navigation or even by reference to instruments like a VOR it is possible to find yourself in an off-course situation. Remember atmospheric conditions change and the winds you use for your flight plan are only forecasted and not exact.

Considering the theory explained in Monday’s post on the wind triangle (vector analysis), let’s discuss a quick and easy way to get back on course using what’s called the off-course correction equation.

Off-Course Equation

Off-Course Equation

I like to think of the above equation as a two part problem. The first part Distance Off x 60 / Distance Flown will give you a degree of heading change to parallel your intended course. Part two Distance Off x 60 / Distance Remaining will give you an added heading change degree to converge on your course at whatever distance remaining you enter into the equation. By adding part one and two together you get your Degrees of Total Correction. This is the degree of heading change you will need to converge back on course at whatever distance remaining you enter. So for example, if you enter a distance remaining of 50 miles you will converge back on your intended course at the 50 mile mark. Let’s work through a problem together.

 

Problem:
Off Course = 4 miles
Distance Flown = 40 miles
Distance Remaining = 80 miles

Step 1: Take our distance off course of 4 miles and multiply by 60 (4 x 60 = 240).
Step 2: Divide 240 from step one by distance flown of 40 miles (240 / 40 =).

So at this point a 6° heading change would allow us to parallel our intended course. To find the distance to converge back on course we will need to complete the second part of the problem.

Step 3: Take our distance off course of 4 miles and multiply by 60 (4 x 60 = 240).
Step 4: Divide 240 from step one by distance remaining of 80 miles (240 / 80 = ).

Our total heading correction to converge would be 6° + 3° = 9°.

Some additional tips and tricks: by properly using a navigation log associated with my flight plan, I will have known approximately how far I have flown and my distance remaining to either my destination or next check point. You may also use an E6-B or CX-2 Flight Computer to determine off-course corrections.

Try one on your own.

Off Course = 2 miles
Distance Flown = 15 miles
Distance Remaining = 22 miles
(Answer posted in the comments section)

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Navigation: Vector Analysis

Today, we’ll put together a few things we’ve learned on the Learn To Fly Blog to introduce a skill every beginning student should develop: thinking in terms of a wind triangle. Check out last week’s posts on magnetic variation and using your E6B Flight Computer to determine magnetic heading, as well as early posts on navigation. Today’s post features excerpted content from the Pilot’s Handbook of Aeronautical Knowledge.

Dead reckoning is navigation solely by means of computations based on time, airspeed, distance, and direction. The products derived from these variables, when adjusted by wind speed and velocity, are heading and GS. The predicted heading takes the aircraft along the intended path and the GS establishes the time to arrive at each checkpoint and the destination. Except for flights over water, dead reckoning is usually used with pilotage for cross-country flying. The heading and GS as calculated is constantly monitored and corrected by pilotage as observed from checkpoints.

If there is no wind, the aircraft’s ground track is the same as the heading and the GS is the same as the true airspeed. This condition rarely exists. A wind triangle, the pilot’s version of vector analysis, is the basis of dead reckoning. The wind triangle is a graphic explanation of the effect of wind upon flight. GS, heading, and time for any flight can be determined by using the wind triangle. It can be applied to the simplest kind of cross-country flight as well as the most complicated instrument flight. The experienced pilot becomes so familiar with the fundamental principles that estimates can be made which are adequate for visual flight without actually drawing the diagrams.

If flight is to be made on a course to the east, with a wind blowing from the northeast, the aircraft must be headed somewhat to the north of east to counteract drift. This can be represented by a diagram as shown in Figure 1. Each line represents direction and speed. The long blue and white hashed line shows the direction the aircraft is heading, and its length represents the distance the airspeed for 1 hour. The short blue arrow at the right shows the wind direction, and its length represents the wind velocity for 1 hour. The solid yellow line shows the direction of the track or the path of the aircraft as measured over the earth, and its length represents the distance traveled in 1 hour, or the GS.

Figure 1. Principle of the wind triangle.

Figure 1. Principle of the wind triangle.

In actual practice, the triangle illustrated in Figure 1 is not drawn; instead, construct a similar triangle as shown by the blue, yellow, and black lines in Figure 2, which is explained in the following example.

Figure 2. The wind triangle as is drawn in navigation practice.

Figure 2. The wind triangle as is drawn in navigation practice.

Suppose a flight is to be flown from E to P. Draw a line on the aeronautical chart connecting these two points; measure its direction with a protractor, or plotter, in reference to a meridian. This is the true course, which in this example is assumed to be 090° (east). From the NWS, it is learned that the wind at the altitude of the intended flight is 40 knots from the northeast (045°). Since the NWS reports the wind speed in knots, if the true airspeed of the aircraft is 120 knots, there is no need to convert speeds from knots to mph or vice versa.

Now, on a plain sheet of paper draw a vertical line representing north to south. (The various steps are shown in Figure 3.)

Figure 3. Steps in drawing the wind triangle.

Figure 3. Steps in drawing the wind triangle.

Step 1
Place the protractor with the base resting on the vertical line and the curved edge facing east. At the center point of the base, make a dot labeled “E” (point of departure), and at the curved edge, make a dot at 90° (indicating the direction of the true course) and another at 45° (indicating wind direction).

Step 2
With the ruler, draw the true course line from E, extending it somewhat beyond the dot by 90°, and labeling it “TC 090°.”

Step 3
Next, align the ruler with E and the dot at 45°, and draw the wind arrow from E, not toward 045°, but downwind in the direction the wind is blowing, making it 40 units long, to correspond with the wind velocity of 40 knots. Identify this line as the wind line by placing the letter “W” at the end to show the wind direction.

Step 4
Finally, measure 120 units on the ruler to represent the airspeed, making a dot on the ruler at this point. The units used may be of any convenient scale or value (such as ¼ inch = 10 knots), but once selected, the same scale must be used for each of the linear movements involved. Then place the ruler so that the end is on the arrowhead (W) and the 120-knot dot intercepts the true course line. Draw the line and label it “AS 120.” The point “P” placed at the intersection represents the position of the aircraft at the end of 1 hour. The diagram is now complete.

The distance flown in 1 hour (GS) is measured as the numbers of units on the true course line (88 NMPH, or 88 knots). The true heading necessary to offset drift is indicated by the direction of the airspeed line, which can be determined in one of two ways:

  • By placing the straight side of the protractor along the north-south line, with its center point at the intersection of the airspeed line and north-south line, read the true heading directly in degrees (076°). (Figure 4)
  • By placing the straight side of the protractor along the true course line, with its center at P, read the angle between the true course and the airspeed line. This is the WCA, which must be applied to the true course to obtain the true heading. If the wind blows from the right of true course, the angle is added; if from the left, it is subtracted. In the example given, the WCA is 14° and the wind is from the left; therefore, subtract 14° from true course of 090°, making the true heading 076°. (Figure 5)
Figure 4. Finding true heading by the wind correction angle.

Figure 4. Finding true heading by the wind correction angle.

Figure 5. Finding true heading by direct measurement.

Figure 5. Finding true heading by direct measurement.

After obtaining the true heading, apply the correction for magnetic variation to obtain magnetic heading, and the correction for compass deviation to obtain a compass
heading. The compass heading can be used to fly to the destination by dead reckoning.

To determine the time and fuel required for the flight, first find the distance to destination by measuring the length of the course line drawn on the aeronautical chart (using the appropriate scale at the bottom of the chart). If the distance measures 220 NM, divide by the GS of 88 knots, which gives 2.5 hours, or 2:30, as the time required. If fuel consumption is 8 gallons an hour, 8 x 2.5 or about 20 gallons is used. Briefly summarized, the steps in obtaining flight information are as follows:

  • TC—direction of the line connecting two desired points, drawn on the chart and measured clockwise in degrees from true north on the mid-meridian.
  • WCA—determined from the wind triangle. (Added to TC if the wind is from the right; subtracted if wind is from the left).
  • TH—direction measured in degrees clockwise from true north, in which the nose of the plane should point to make good the desired course.
  • Variation—obtained from the isogonic line on the chart (added to TH if west; subtracted if east).
  • MH—an intermediate step in the conversion (obtained by applying variation to true heading).
  • Deviation—obtained from the deviation card on the aircraft (added to MH or subtracted from, as indicated).
  • Compass heading—reading on the compass (found by applying deviation to MH) which is followed to make good the desired course.
  • Total distance—obtained by measuring the length of the TC line on the chart (using the scale at the bottom of the chart).
  • GS—obtained by measuring the length of the TC line on the wind triangle (using the scale employed for drawing the diagram).
  • Estimated time en route (ETE)—total distance divided by GS.
  • Fuel rate—predetermined gallons per hour used at cruising speed.

NOTE: Additional fuel for adequate reserve should be added as a safety measure.

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CFI Brief: Enroute questions using the E6B Flight Computer

This week we are going to look at a few questions as they relate to enroute flight, specifically questions that require the use of an E6B. Enroute flight is a popular topic on the FAA knowledge exam and these questions may be very similar to the ones you encounter on your knowledge test. The first question involves determining a magnetic heading using our E6B Flight Computer.

(Refer to Figure 26.) Determine the magnetic heading for a flight from Fort Worth Meacham (area 4) to Denton Muni (area 1). The wind is from 330° at 25 knots, the true airspeed is 110 knots, and the magnetic variation is 7° east.

Figure 26

Figure 26

Let’s break this question down into four simple steps.

  1. Plot a course from Meacham to Denton, and determine the course heading using a plotter. I get 021°.
  2. Next, using the wind given in the question (330 @ 25) , calculate a correction angle using the E6B. This angle will be the difference between the course bearing and the heading required to maintain that course. I’ve computed a correction angle of 10° to the left.
  3. Remember a left correction angle is subtracted from the course to obtain a true heading. 021° (course from step 1) – 010° (wind correction from step 2) = 011° (true heading)
  1. Lastly find the magnetic heading by adding or subtracting the variation given in the question (7° east) to the true heading. Remember subtract east and add west. 011 – 7 = 004° (magnetic heading)

Your answer to the question would be 004°. Next.

How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?

To find the distance flown in a given time, multiply ground speed by time. The distance flown in 2-1/2 minutes (convert to hours by dividing by 60) at a ground speed of 98 knots is .04 x 98 = 4.08 NM.

Or…

Using our E6B we would take our rate indicator of 60 on the inner scale and line it up with 98 on the outer scale. The inner scale shows time, so we would locate 25 (2.5 minutes) and on the outer scale read 40.8 interpreting that as 4.08 NM.

This next question requires us to sort of work in a backwards direction to find the correct answer.

If a true heading of 135° results in a ground track of 130° and a true airspeed of 135 knots results in a groundspeed of 140 knots, the wind would be from?

So a 135° means we are flying in a southeast direction and if this true heading is resulting in a ground tack of 130° the wind would have to be coming from somewhere off our right wing pushing the aircraft to the left. In addition, we know that the wind is also resulting in an increase of groundspeed so the wind is somewhere behind us. Using these two key pieces of information we can determine the wind must be from the southwest.

Using the wind side of the E6B we will line our true Index up with our true course of 135° with the grommet located at 135 on the center vertical line to account for the true airspeed. From there we have determined that the wind is coming from southwest so looking between the S and W find on the vertical line the 5° and count vertically down 5 to account for the 5 knot increase in speed. Draw a line from that point back to the grommet and rotate the circle until the line appears under the true index. On the inner circle read your wind direction of 246° and counting up from the grommet to the end of the line your wind speed of 13. Your wind is coming from 246 @ 13 knots.

See, its really not all that hard if you break the questions down into smaller chunks. Try one on your own and leave the answer in the comments section below, I will let you know if the answer is correct.

(Refer to Figure 26.) Determine the magnetic heading for a flight from Dallas Executive (area 3) to Fort Worth Meacham (area 4). The wind is from 030° at 10 knots, the true airspeed is 135 knots, and the magnetic variation is 7° east.

 

 

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Enroute Flight: Magnetic Variation

Plotting a course? Today we’re learning about magnetic variation, with help from Bob Gardner’s The Complete Private Pilot textbook.

For flight planning purposes you must recognize that although the lines of latitude and longitude on charts are neatly perpendicular and relate to the True North Pole there is nothing in your airplane that relates to True North. The magnetic compass indicates the direction to the magnetic North Pole, which is in northern Canada (Figure 1).

Figure 1. Magnetic and true north poles.

Figure 1. Magnetic and true north poles.

You must take the variation between true north and magnetic north into account when flight planning.

Figure 2 shows isogonic lines, or lines of equal magnetic variation, across the continent. Along the line which passes through Chicago and Key West, a pilot looking toward the North Star or the True North Pole will also be looking toward the magnetic North Pole, and there will be no variation. The line of zero variation is called the agonic line. East or West of that line, the angle between true and magnetic north increases. A pilot in Los Angeles who measures a course line on an aeronautical chart in relation to the longitude lines (or true north) must subtract 14° from that true course to get a magnetic course (“East is least“), while a pilot in Philadelphia will add 10° (“West is best“). You will determine the true course by using your navigation plotter.

Figure 2. Isogonic lines.

Figure 2. Isogonic lines.

The variation on your sectional chart is almost certainly out-of-date. The isogonic lines on current sectionals were last updated in 2005 and will not be updated until 2011. Variations for navaids and airports are “assigned” and do not reflect the actual variation; variation for a VOR or airport can be up to three degrees different from actual variation is a current Airport/Facility Directory. You can get current variation information for airports along your route by going to http://www.ngdc.gov/geomagmodels/Declination.jsp.

Using the Navigation Plotter
A navigation plotter combines a protractor with mileage scales, and they are available in many forms. You use the protractor to measure the angle between a line of latitude or longitude and your course line. Refer to the Seattle sectional chart excerpt at the back of the book. Draw a line from the center of the airport symbol at Easton (A) to the center of the airport symbol at Wenatchee (H). Align the straight edge of your plotter with this course line and slide the plotter until the hole is over a vertical line of longitude; the angle should be approximately 78 degrees, indicating that the true course from Easton to Wenatchee is 078° and that the course for the return trip is 258°.

Deviation
A course, whether identified as true or magnetic, is only a line on a chart linking departure point and destination. For flight planning purposes, you must allow for magnetic influences in the airplane itself and for the effect of wind drift. Because your airplane has some iron and steel components which are affected by the earth’s magnetic field, and because it contains wiring which creates a magnetic field within the airplane itself, the airplane’s magnetic compass develops an error called deviation which varies with aircraft heading. Looking back at Figure 2, it is apparent that the heading of the airplane has nothing to do with magnetic variation — a pilot in Seattle must apply a 20° easterly variation regardless of the direction of flight. Because magnetic deviation is unique to each airplane and is dependent on heading, a compass correction card (Figure 3) must be prepared by accurately lining up the airplane on known magnetic headings, checking the magnetic compass reading, and recording the deviation error for each heading. Small adjustment magnets are provided so that the error can be minimized.

Figure 3. Compass correction card.

Figure 3. Compass correction card.

This compass correction table is originally made at the factory but should be re-checked by a mechanic whenever cockpit equipment installations are made. When a pilot has applied variation and deviation to a measured true course, the result is the compass course:

True ± Variation = Magnetic ± Deviation = Compass

Variation is shown on navigational charts to the nearest one-half degree. You will find that rounding off to the nearest whole degree will speed up your calculations without affecting accuracy. If you make long flights over water or featureless terrain, deviation and compass course will be very important to you, and an accurate compass correction card may be a lifesaver. Pilots who fly by reference to the surface (pilotage) will make little use of compass heading except to adjust their gyroscopic heading indicators.

Any difference between an airplane’s planned course and its track over the ground is caused by wind drift. Always compute the wind correction angle first, and then apply variation and deviation, as National Weather Service winds aloft forecasts are always referenced to True North.

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CFI Brief: Effects of Weight on Performance

So over the last two weeks while away at EAA AirVenture in Oshkosh, Wisconsin, I may have overindulged a bit too much in deep fried cheese curds. This has unfortunately resulted in a slight weight increase around my waistline and has more than likely affected my athletic performance. Not to compare myself to an airplane, but the same can be said with regards to how an increase in weight will affect the performance of an aircraft. When weight, whether it is in the form of fuel, passengers, or cargo is added to an aircraft you will start to notice a performance decrease.

To help understand this concept think back to aerodynamics and the four forces, two in particular, lift and weight. In order to climb, lift needs to exceed weight and to remain in level flight, lift will need to equal weight. So essentially, the heavier the airplane is, the more lift the wings will need to produce, resulting in a greater angle of attack, increased airspeed, or a combination of both. A maximum weight is specified for each aircraft as determined by the manufacturer. Any increase in weight exceeding this will severely diminish aircraft performance resulting in unsafe aircraft characteristics.

Lift vs Weight

Lift = Weight

The Pilots Manual Ground School text outlines several performance characteristics caused by a heavier airplane these include:

  • a higher stall speed;
  • a higher takeoff speed and a longer takeoff run;
  • poorer climb performance (poorer climb angle and climb rate);
  • a lower cruising level;
  • less maneuverability;
  • higher fuel consumption, and less range and endurance;
  • reduced cruise speed for a given power setting;
  • a higher landing speed and a longer landing distance; and
  • greater braking requirements when stopping.

For example, a higher takeoff speed will be required to generate additional lift to counteract an increase in weight and drag resulting in a longer takeoff run. As discussed briefly above the airplane will require a greater angle of attack as weight is increased. Increasing the angle of attack will increase drag resulting in higher fuel consumption and less range and endurance. With increases in drag due to the greater angle of attack you will see reduced cruise speeds for a given power setting. This may correlate to increasing power settings to maintain specified cruising speeds contributing to higher fuel burns.

Image from The Pilots Manual Groundschool text book.

Image from The Pilots Manual Groundschool text book.

With that said, you can see how a simple change in weight will effect a myriad of other performance factors. It’s ok and perfectly safe to operate at maximum weight but as a pilot you should understand the effects and changes that weight will have on performance. You should also fully comprehend the dangers of flying above maximum gross weight.

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