Aircraft Performance: Takeoff Distance

Today we’re talking about takeoff distance. The majority of pilot-cause aircraft accidents occur during the takeoff and landing phase of flight. Therefore, a pilot must be familiar with all the variables that can influence aircraft performance during these critical phases. This post is excerpted from the Pilot’s Handbook of Aeronautical Knowledge.

The minimum takeoff distance is of primary interest in the operation of any aircraft because it defines the runway requirements. The minimum takeoff distance is obtained by taking off at some minimum safe speed that allows sufficient margin above stall and provides satisfactory control and initial rate of climb. Generally, the lift-off speed is some fixed percentage of the stall speed or minimum control speed for the aircraft in the takeoff configuration. As such, the lift-off will be accomplished at some particular value of lift coefficient and AOA. Depending on the aircraft characteristics, the liftoff speed will be anywhere from 1.05 to 1.25 times the stall speed or minimum control speed.

To obtain minimum takeoff distance at the specific lift-off speed, the forces that act on the aircraft must provide the maximum acceleration during the takeoff roll. The various forces acting on the aircraft may or may not be under the control of the pilot, and various procedures may be necessary in certain aircraft to maintain takeoff acceleration at the highest value.

The powerplant thrust is the principal force to provide the acceleration and, for minimum takeoff distance, the output thrust should be at a maximum. Lift and drag are produced as soon as the aircraft has speed, and the values of lift and drag depend on the AOA and dynamic pressure.

In addition to the important factors of proper procedures, many other variables affect the takeoff performance of an aircraft. Any item that alters the takeoff speed or acceleration rate during the takeoff roll will affect the takeoff distance.

For example, the effect of gross weight on takeoff distance is significant and proper consideration of this item must be made in predicting the aircraft’s takeoff distance. Increased gross weight can be considered to produce a threefold effect on takeoff performance:

  1. Higher lift-off speed
  2. Greater mass to accelerate
  3. Increased retarding force (drag and ground friction)

If the gross weight increases, a greater speed is necessary to produce the greater lift necessary to get the aircraft airborne at the takeoff lift coeffi cient. As an example of the effect of a change in gross weight, a 21 percent increase in takeoff weight will require a 10 percent increase in lift-off speed to support the greater weight.

A change in gross weight will change the net accelerating force and change the mass that is being accelerated. If the aircraft has a relatively high thrust-to-weight ratio, the change in the net accelerating force is slight and the principal effect on acceleration is due to the change in mass.

For example, a 10 percent increase in takeoff gross weight would cause:

  • A 5 percent increase in takeoff velocity.
  • At least a 9 percent decrease in rate of acceleration.
  • At least a 21 percent increase in takeoff distance.

With ISA conditions, increasing the takeoff weight of the average Cessna 182 from 2,400 pounds to 2,700 pounds (11 percent increase) results in an increased takeoff distance from 440 feet to 575 feet (23 percent increase).

For the aircraft with a high thrust-to-weight ratio, the increase in takeoff distance might be approximately 21 to 22 percent, but for the aircraft with a relatively low thrust-to-weight ratio, the increase in takeoff distance would be approximately 25 to 30 percent. Such a powerful effect requires proper consideration of gross weight in predicting takeoff distance.

The effect of wind on takeoff distance is large, and proper consideration also must be provided when predicting takeoff distance. The effect of a headwind is to allow the aircraft to reach the lift-off speed at a lower groundspeed while the effect of a tailwind is to require the aircraft to achieve a greater groundspeed to attain the lift-off speed.

A headwind that is 10 percent of the takeoff airspeed will reduce the takeoff distance approximately 19 percent. However, a tailwind that is 10 percent of the takeoff airspeed will increase the takeoff distance approximately 21 percent. In the case where the headwind speed is 50 percent of the takeoff speed, the takeoff distance would be approximately 25 percent of the zero wind takeoff distance (75 percent reduction).

The effect of wind on landing distance is identical to its effect on takeoff distance. The figure below illustrates the general effect of wind by the percent change in takeoff or landing distance as a function of the ratio of wind velocity to takeoff or landing speed.

Effect of wind on takeoff and landing.

Effect of wind on takeoff and landing.

The effect of proper takeoff speed is especially important when runway lengths and takeoff distances are critical. The takeoff speeds specified in the AFM/POH are generally the minimum safe speeds at which the aircraft can become airborne. Any attempt to take off below the recommended speed means that the aircraft could stall, be difficult to control, or have a very low initial rate of climb. In some cases, an excessive AOA may not allow the aircraft to climb out of ground effect. On the other hand, an excessive airspeed at takeoff may improve the initial rate of climb and “feel” of the aircraft, but will produce an undesirable increase in takeoff distance. Assuming that the acceleration is essentially unaffected, the takeoff distance varies with the square of the takeoff velocity.

Thus, ten percent excess airspeed would increase the takeoff distance 21 percent. In most critical takeoff conditions, such an increase in takeoff distance would be prohibitive, and the pilot must adhere to the recommended takeoff speeds. The effect of pressure altitude and ambient temperature is to define the density altitude and its effect on takeoff performance. While subsequent corrections are appropriate for the effect of temperature on certain items of powerplant performance, density altitude defines specific effects on takeoff performance. An increase in density altitude can produce a twofold effect on takeoff performance:

  1. Greater takeoff speed
  2. Decreased thrust and reduced net accelerating force

If an aircraft of given weight and configuration is operated at greater heights above standard sea level, the aircraft requires the same dynamic pressure to become airborne at the takeoff lift coefficient. Thus, the aircraft at altitude will take off at the same indicated airspeed (IAS) as at sea level, but because of the reduced air density, the TAS will be greater.

The effect of density altitude on powerplant thrust depends much on the type of powerplant. An increase in altitude above standard sea level will bring an immediate decrease in power output for the unsupercharged reciprocating engine. However, an increase in altitude above standard sea level will not cause a decrease in power output for the supercharged reciprocating engine until the altitude exceeds the critical operating altitude. For those powerplants that experience a decay in thrust with an increase in altitude, the effect on the net accelerating force and acceleration rate can be approximated by assuming a direct variation with density. Actually, this assumed variation would closely approximate the effect on aircraft with high thrust-to-weight ratios.

Proper accounting of pressure altitude and temperature is mandatory for accurate prediction of takeoff roll distance. The most critical conditions of takeoff performance are the result of some combination of high gross weight, altitude, temperature, and unfavorable wind. In all cases, the pilot must make an accurate prediction of takeoff distance from the performance data of the AFM/POH, regardless of the runway available, and strive for a polished, professional takeoff procedure.

In the prediction of takeoff distance from the AFM/POH data, the following primary considerations must be given:

  • Pressure altitude and temperature—to define the effect of density altitude on distance
  • Gross weight—a large effect on distance
  • Wind—a large effect due to the wind or wind component along the runway
  • Runway slope and condition—the effect of an incline and retarding effect of factors such as snow or ice

More on Thursday from our CFI.

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CFI Brief: Logging Instrument Approaches

Federal Aviation Regulations and rules can get confusing, particularly those pertaining to instrument flight rules (IFR). One in particular I always found confusing, and at times up to interpretation, deals with when a pilot may log an IAP. As you know, logging instrument approaches is an important aspect in abiding by 14 CFR 61.57(c) which requires a pilot to log a minimum 6 IAP’s every 6 months to maintain IFR currency. To help clarify those conditions under which a pilot may log an IAP, the FAA has issued an Information for Operators (InFo 15012) on September 8th 2015.

InFo_15012 Logo

InFo 15012: Logging IAP

Whether you are already an instrument rated pilot or are in training to become one, I recommend you take some time to read through both 61.57(c) and the above InFo. Then, test your new insight and knowledge by answering the three questions below.

1. What minimum conditions are necessary for the instrument approaches required for IFR currency?
A—The approaches may be made in an aircraft, flight simulator, or flight training device.
B—At least three approaches must be made in the same category of aircraft to be flown.
C—At least three approaches must be made in the same category and class of aircraft to be flown.

2. Enroute weather conditions are IMC. However, during the descent to your destination for an ILS approach, you encounter VMC weather conditions prior to reaching the initial approach fix. You know that to log the ILS approach toward instrument currency requirements,
A—the flight must remain on an IFR flight plan throughout the approach and landing.
B—the ILS approach can be credited only if you use a view-limiting device.
C—the ILS approach can be credited regardless of actual weather if you are issued an IFR clearance.

3. Which additional instrument experience is required for you to meet the recent flight experience requirements to act as pilot in command of an airplane under IFR?
Your present instrument experience within the preceding 6 calendar months is:
1. 3 hours with holding, intercepting and tracking courses in an approved airplane flight simulator.
2. two instrument approaches in an airplane.

A—Three hours of simulated or actual instrument flight time in a helicopter and two instrument approaches in an airplane or helicopter.
B—Three instrument approaches in an airplane.
C—Four instrument approaches in an airplane, or an approved airplane flight simulator or training device.

Answers will be posted Friday in the comments section.

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Reflections and Tips from Recent Practical Tests

Once again, we’re pleased to feature a guest post FAA DPE and CFI Jason Blair. Check out his post from last week on why you should be practicing the glide and his post onflying the traffic pattern from earlier this year. He writes his own blog at

I would like to share a few reflections and tips from recent practical tests I have given. In most cases, the tests I have given are proof of fantastic candidates who are dedicated to learning and progressing as pilots, but there are also moments that leave me wondering about some of the basic preparation things that an applicant could do to make their time with me so much easier. So here are a few things I would offer:

Yes you should bring a FAR/AIM with you (unless somehow you have memorized it all) and yes it should be a current one. Too many times applicants either don’t have a FAR/AIM with them or the one they have isn’t current. I’m not certain which is worse to be honest. Not having one is bad, having an old one just shows an applicant doesn’t care to have current information.

It is a really good idea to have a copy (digital PDF on your iPad is fine) of the Practical Test Standards for the test your are taking (and yes it should be current also). This is the menu the examiner will use on the practical test. Have one and know it.

You should probably look at the aircraft inspections at least some time more than 2 minutes before your scheduled time for the practical test with your instructor and really understand what the required inspections are and when they will expire. This is a required set of questions an examiner will ask on EVERY practical test. We have to know that we are getting into a “legal” airplane and you will have to show us that it meets all the requirements. There are no exceptions.

Know when the aircraft registration expires or where to find the information. No, you won’t find this in the typical FARs you have bought, it’s in section 43 of the FARs. More about aircraft registration requirements can be found at

It is perfectly fine to discontinue a practical test if you don’t think the weather is good enough. Just because you and the examiner are both there and the ground is done, it doesn’t mean you have to fly. Here is the best question you should yourself when deciding: “will today’s weather adversely affect my ability to complete the required maneuvers within practical test standards?” If the answer is yes, reschedule for the flight. Simple as that.

Be confident in your knowledge. An examiner’s job includes determining if you will question things. Just because the examiner asked the dreaded “are you sure?” question doesn’t mean you were wrong. If you know something, stick with your answers, don’t change them. If you don’t know something, don’t try to make up an answer. The examiner will let you dig a hole then bury you in it. Be honest and tell us if you don’t know something.

These all seem like pretty simplistic tips, but I can’t tell you how many times these things are a factor on practical tests. While they don’t always result in the issuance of a disapproval, they will always raise stress levels and create delays in the progress of the practical test. Think about these ahead of time and your next practical test will be easier. If you have already taken one, share this with a friend who has one coming up to make their experience easier.

Jason Blair is an active single and multi-engine instructor and FAA Designated Pilot Examiner with 4,800 hours total time and 2,700 hours instruction given. He has served on several FAA/Industry aviation committees and has and continues to work with aviation associations on flight training issues. He also consults on aviation training and regulatory efforts for the general aviation industry.

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CFI Brief: Engine Failure, Video Clip

In keeping with the theme of gliding, this week I am going to follow-up Jason’s post with a clip from our Virtual Test Prep™ Flight Maneuvers DVD on airborne engine failures. After reading Monday’s post and watching this short clip see if you can answer the two following questions.

1. When executing an emergency approach to land in a single-engine airplane, it is important to maintain a constant glide speed because variations in glide speed
A—increase the chances of shock cooling the engine.
B—assure the proper descent angle is maintained until entering the flare.
C—nullify all attempts at accuracy in judgment of gliding distance and landing spot.

2. An airplane is flown in a glide at an airspeed where the L/D ratio is 8:1. How many feet air distance will this airplane glide for each 1,000 feet lost?

Answers below!

1. Answer (C)
A constant gliding speed should be maintained because variations of gliding speed nullify all attempts at accuracy in judgment of gliding distance and the landing spot.

2. 8,000 feet. The aircraft will travel 8 times further than altitude lost at an 8:1 L/D ratio. For example, if the aircraft was 4,000 feet AGL and you lost an engine, the aircraft would travel 32,000 feet (8 x 4,000) or roughly just over 6 miles (5,280 feet in a mile) in a no-wind condition before coming in contact with the ground.

(8 x 4,000) = 32,000 / 5,280 = 6.06 miles

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Practice the Glide

This week, we’re pleased to feature guest posts from CFI and FAA DPE Jason Blair! We featured Jason’s excellent write up on flying the traffic pattern earlier this year. He writes his own blog at

Gliding is for gliders, right? Well, it’s not just for them. Something I notice in many checkrides I give (and I know is the case for many pilots) is that they don’t really know how to “glide” the aircraft that they are flying. Why on earth would you want to know how to glide when I have a powered aircraft you might ask? The obvious answer is in the event of an engine failure.

When an engine quits in an aircraft, it effectively becomes a large, heavy glider. Even in a twin-engine aircraft, our approach path is significantly affected. Typically in training, pilots are introduced to this possibility and then given a checklist to go through of potential solutions while they are expected to “pick a suitable landing area” and prepare for a potentially off-airport landing. Somewhere before reaching 500′ AGL, a recovery is typically executed. There is something missing in this practice scenario; what would happen if you couldn’t perform a “go-around?”

What I notice when many pilots demonstrate this is that they are often not able to judge the glide distance to their intended landing point very well. In some cases they are setting up a glide that will put them short of the landing area, and in other cases setting up a glide that carries too much speed and would overfly the intended landing field. In a few cases they get lucky and it works out. When setting up a glide, I would typically prefer a pilot be long than short (it is always better to end up running off the end of a field rolling slowly than ending up short of the field going fast), but what I often see is that they aren’t just a little long, but are completely overshooting their intended landing area.

There is a simple solution to this problem. Practice it more frequently, and do a full landing instead of a go-around. Obviously this isn’t something that you are going to want to do in the local farmer’s field in your local practice area, and certainly please don’t do this with Wings of Mercy flight recipients on board, but it is certainly something you can practice at an airport.

Typically, when I am teaching this procedure I put pilots 2500′ to 3000′ AGL about 2 miles from the approach end of the preferred runway at the airport, then I retard the throttle to idle. This puts them in a position where reaching the runway is well within reach, but if they don’t work to dissipate some altitude, they will run long. By working in some S-turns before the final approach, the pilot is able to maintain a position where they will never have to turn more than 90 degrees from the runway (I never recommend turning your back to the intended field of landing for an emergency landing) while at the same time dissipating some altitude in preparation for their final approach to the landing.

The entire effort of this is to get the feel for the glide of the aircraft and to learn to judge the vertical descent path. By correctly judging the vertical descent path, a pilot is able to set themselves up to hit a desired touchdown area. Part of this is intended to help develop the visual picture in the pilot’s mind to judge the approach to landing and judge the touch point.

The experience gained by practicing the glide to an actual landing will develop a better feel for the last portions of the glide to the ground in a simulated emergency situation. These last moments have a different feel than the first portions of the glide, as the aircraft is manipulated through dissipation of speed, ground effect, and a flare for landing. To just set up and conduct emergency simulations to a 500′ AGL glide recovery does not allow the student to get a full picture of how the entire situation will unfold.

The best way to practice this is on approach to your destination airport through reduction of throttle to simulate the loss of power in a single-engine aircraft or through the setting of a throttle to a “zero-thrust” configuration to simulate the loss of one engine in a multi-engine aircraft. During your non-passenger carrying legs, take the time to simulate this for greater proficiency in the event that you ever encounter such a situation. While your training may officially be over, and we all hope you never need these skills, maintaining proficiency in these emergency procedures can make a real life situation more manageable and potentially lead to a more successful handling of an emergency.

Jason Blair is an active single and multi-engine instructor and FAA Designated Pilot Examiner with 4,800 hours total time and 2,700 hours instruction given. He has served on several FAA/Industry aviation committees and has and continues to work with aviation associations on flight training issues. He also consults on aviation training and regulatory efforts for the general aviation industry.

For visualizing emergency procedures, as well as just about everything else you’ll do in your airplane, we recommend our Visualized Flight Maneuvers Handbook (also available for low-wing aircraft and in eBook format). This is a great resource for student pilots, pilots preparing for their practical, and experienced pilots maintaining proficiency. We’ll have more from DPE Jason Blair on Thursday! Thanks for following the Learn to Fly Blog!

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CFI Brief: Airplane Flight Manual (AFM)

In today’s post, we are going to discuss the Airplane Flight Manual (AFM). The AFM is a document that is developed by your airplane’s manufacturer containing specific information in regards to operating instructions of the aircraft. These manuals are specific to an aircraft’s serial number and are approved by the FAA. This manual must be carried on board the aircraft to maintain compliance with federal regulations outlined in FAR Part 91. Within the manual is where you can find specific operating limitations, weight and balance information, and equipment list all of which are required documents to have on board (we learned this in Monday’s post on MAROW).

Information contained within the AFM is presented in a standardized format as seen in the table below:


  1. General—you’ll find basic descriptive information on the airframe and powerplant. Serves as a quick reference to become familiar with the aircraft.
  2. Limitations—contains regulatory limitations or those necessary for the safe operation of the aircraft and all of its components.
  3. Emergency Procedures—here you’ll find checklists with recommended procedures for dealing with an emergency. You may also see an additional section of checklists dealing with abnormal procedures.
  4. Normal Procedures—a complete listing of airspeeds for normal operations will be listed at the beginning of this section. Following airspeeds will be a series of checklists also for normal operations like preflight inspection, before-takeoff check, climb, cruise, descent, etc.
  5. Performance—contains all regulatory and compliance information in relation to aircraft performance as required by the aircraft’s certification. You’ll find performance charts and tables depicting things like takeoff distance, landing distance, cruise performance, and stall speeds in various configurations to name just a few.
  6. W&B and Equipment List—contains all information deemed necessary to calculate aircraft weight and balance. Also in this section you’ll find a complete list of the equipment installed in the aircraft.
  7. System Description—an outline and description of each system on the aircraft.
  8. Handling, Service, and Maintenance—a description of maintenance and inspections as recommended by the manufacturer. You will also find information on preventative maintenance that may be accomplished by certificated pilots.
  9. Supplements—within this section you’ll find a listing of optional equipment installed that was not provided with the standard aircraft. You will also find information necessary to safely operate the aircraft with any optional equipment or systems installed.

It’s important to not get the AFM confused with an aircraft owner manual or information manual which may look  very similar in appearance to the AFM. Those documents, however, contains general information about the make and model of the aircraft and are not specific to the aircraft’s serial number and, furthermore, not approved by the FAA. You can best use these manuals to glean overall information about the make and model of aircraft you will be flying.

Next time you’re in the aircraft, pull out the AFM and take a look through. See if any additional equipment has been installed, or try to find information that’s unique to your specific aircraft.

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Regulations: Required Documents

The success of a flight depends largely on thorough preparation. In the course of your training, a pattern of regular preflight actions should be developed to ensure that this is the case. This includes planning a flight, and checking the airplane. These preflight actions must be based on the checks found in the pilot’s operation handbook (POH), manufacturer’s information manual, or the FAA-approved airplane flight manual (AFM) for your airplane. Today we’ll go over the documentation you’ll complete as part of your preflight and what’s required to be with you and in the airplane. This post is excerpted from The Pilot’s Manual: Flight School, the first textbook in our core-curriculum series for student pilots.

Typical information manuals.

Typical information manuals.

It’s a pilot’s responsibility to check certain documents prior to flight to ensure the airplane is airworthy. You should know the significance of each document, and know where to locate them in the cockpit or at the flight school. The documents important to the individual pilot are:

  • maintenance records (check every flight);
  • the POH with aircraft limitations and placards (should always be in the airplane);
  • aircraft weight and balance data, and equipment list (check the POH or flight manual);
  • the Certificate of Airworthiness (must always be in the airplane), which shows that the airplane has met certain FAA safety requirements, and remains in effect in required inspections and maintenance has been performed; and
  • the Certificate of Registration (must be in the airplane), containing airplane and owner information—a new owner requires a new Certificate of Registration.

An easy way to remember the required documents is with the mnemonic MAROW:

M Maintenance records.
A Airworthiness certificate.
R Registration certificate.
O Operating limiations (shown in the POH, color-coding on instruments, and cockpit decals).
W Weight and balance. This is included in the POH or FAA-approved AFM, and sometimes found folded and stapled in the glove box or a seat pocket; weight and balance paperwork needs to be available on board the aircraft, but on many flights need not be filled in. An equipment list should always be on board, and this is often found with the weight and balance information.

The maintenance records should be checked prior to each flight, and any maintenance that you think is required should be specified after flight. Sometimes there will be no formal written maintenance release; however, do not accept responsibility for the airplane if it has defects that may make it unacceptable for flight.

If in any doubt, discuss the matter with your flight instructor or with an aircraft mechanic. There are some simple maintenance actions that may be performed by a qualified pilot, such as topping the oil, but certainly not anything that might affect the airworthiness of the airplane, such as the flight controls. Aircraft and engine logbooks should be available, but are not required to be on board.

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CFI Brief: Gyroscopic Flight Instrument Questions

Monday’s post gave us an introduction into the world of gyroscopic flight instruments and as we learned these include the attitude indicator, turn coordinator, and heading indicator also referred to as the directional gyro. Each one of these gyroscopic flight instruments functions based off the principle of rigidity in space. To put it more simply gyroscopes are rapidly spinning wheels or disks which resist any attempt to move them from their plane of rotation. Let’s take a moment to expand just a bit on each of the three instruments.

Attitude Indicator
The rigidity in space principle makes the gyroscope an excellent “artificial horizon” around which the attitude indicator (and the airplane) pivot.

When viewing the attitude indicator, the direction of bank is determined by the relationship of the miniature airplane to the horizon bar. The miniature airplane may be moved up or down from the horizon with an adjustment knob. Normally, the miniature airplane will be adjusted so that the wings overlap the horizon bar whenever the airplane is in straight-and-level flight.

Turn Coordinator
The turn coordinator (also using the principle of the gyroscope) uses a miniature airplane to provide information concerning rate of roll and rate of turn. As the airplane enters a turn, movement of the miniature aircraft indicates rate of roll. When the bank is held constant, rate of turn is indicated. Simultaneously, the quality of turn, or movement about the yaw axis, is indicated by the ball of the inclinometer.

Heading Indicator
The heading indicator is a gyroscopic instrument designed to avoid many of the errors inherent in a magnetic compass. However, the heading indicator does suffer from precession, caused mainly by bearing friction. Because of this precessional error, the heading indicator must periodically be realigned with the magnetic compass during straight-and-level, unaccelerated flight.

Below I have included some questions as they relate to gyroscopic flight instruments, these are very similar to what you can expect to see on your private pilot knowledge exam as well as your instrument rating knowledge exam. I will go ahead and post the answers in the comments section Monday.

1. One characteristic that a properly functioning gyro depends upon for operation is the
A—ability to resist precession 90° to any applied force.
B—resistance to deflection of the spinning wheel or disc.
C—deflecting force developed from the angular velocity of the spinning wheel.




2. (Refer to Figure 5.) A turn coordinator provides an indication of the
A—movement of the aircraft about the yaw and roll axis.
B—angle of bank up to but not exceeding 30°.
C—attitude of the aircraft with reference to the longitudinal axis.

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Flight Instruments: Gyroscopic Instruments

This week we’re looking again at flight instruments. More specifically, gyroscopic instruments. Take a look at what we’ve posted so far on flight instruments, including our CFI’s series on pitot-static systems. This post is excerpted from Bob Gardner’s The Complete Private Pilot.

The attitude indicator, the turn indicator, and the directional gyro or heading indicator operate on the principle of gyroscopic rigidity in space. A spinning body, such as a bicycle wheel, will maintain its position in space as long as a rotational force is applied—riding your bike “no hands” is an example of this. Precession, or turning, occurs when any external force is applied to the spinning body, which will react as though the force has been applied at a point 90° away in the direction of rotation. If you lean your bicycle to the right, the turning force is as though pressure has been applied to the left front of the wheel—90° in the direction of rotation. Actually turning the wheel to the right may cause the bicycle to topple over to the right, again the result of gyroscopic precession.

Precession of a gyroscope resulting from an applied deflective force. (Figure 7-19 from FAA-H-8083-25)

Precession of a gyroscope resulting from an applied deflective force. (Figure 7-19 from FAA-H-8083-25)

For the foreseeable future, questions about the gyroscopic instruments on your knowledge exam will be based on mechanical gyros—those that have an actual metal disk being driven by either air passing over vanes or an electric motor. The bicycle example is easy to visualize and demonstrate in the classroom.

Gyroscopic “instruments” in this modern age are displayed on a screen, and their inputs come from solid-state devices that deal in forms of mass that it is hard to get our brains around. The most accurate (and expensive) of these is the laser-ring gyro that makes use of interference between multiple lasers; less expensive but least accurate are devices using MEMs (micro-electro-mechanical). A MEM might be as simple as a vibrating crystal…try to visualize the mass being detected in that situation. The whole package, consisting of MEM gyroscopes, accelerometers, and magnetometers, is called an Attitude and Heading Reference System (AHRS). An Air Data Computer can be added, providing airspeed, outside air temperature, actual winds aloft, etc.

The errors inherent in mechanical gyroscopes still exist in solid-state devices, but they are small, constantly monitored internally, and easily corrected without any action on the pilot’s part. If the system detects an anomaly it simply blacks out the display screen or displays a big red X.

As always, our CFI will return on Thursday.

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CFI Brief: Carb Heat

Let’s recap some of the important information we learned from Monday’s post on carburetor ice.

As air flows through a carburetor, it expands rapidly. At the same time, fuel entering the airstream is vaporized. Expansion of the air and vaporization of the fuel causes a sudden cooling of the mixture which may cause ice to form inside the carburetor. The possibility of icing should always be considered when operating in conditions where the outside air temperature is between 20°F and 70°F and the relative humidity is high.

Carburetor heat preheats the air before it enters the carburetor and either prevents carburetor ice from forming or melts any ice which may have formed. When heat is applied, unfiltered air enters directly through the ram air inlet. This induction air passes through part of the exhaust system acting as the heating mechanism and continues onto the carburetor. By manipulating the carburetor heat control in the cockpit, you are simply opening or closing an air valve allowing unfiltered heated air in while dumping filtered cold air overboard, and vice versa. You can see this in the figures below.

When carburetor heat is applied, the heated air that enters the carburetor is less dense. This causes the air/fuel mixture to become enriched, and this in turn decreases engine output (less engine horsepower) and increases engine operating temperatures.

Some things to take note of:

  • During engine run-up, prior to departure from a high-altitude airport, the pilot may notice a slight engine roughness which is not affected by the magneto check but grows worse during the carburetor heat check. In this case, the air/fuel mixture may be too rich due to the lower air density at the high altitude and applying carburetor heat will decrease the air density even more. A leaner setting of the mixture control may correct this problem.
  • In an airplane with a fixed-pitch propeller, the first indication of carburetor ice will likely be a decrease in RPM as the air supply is choked off. Application of carburetor heat will decrease air density, causing the RPM to drop even lower. Then, as the carburetor ice melts, the RPM will rise gradually.
  • Fuel injection systems, which do not utilize a carburetor, are generally considered to be less susceptible to icing than carburetor systems are.

Which statement is true concerning the effect of the application of carburetor heat?
A—It enriches the fuel/air mixture.
B—It leans the fuel/air mixture.
C—It has no effect on the fuel/air mixture.

Can you expand on this question and explain to us why? Let us know in the comments section and if you’re correct well give you mad props! (get it?)

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