Flight instruments
Lesson plan revised 30 January 2007; instrument theory..
Objective
The student should gain a working knowledge of the pitot-static and gyroscopic flight instruments, in order to better understand the operation and limitations.
Elements
•• Pitot Static
oo Altimeter
oo Airspeed indicator
oo Vertical speed indicator
•• Gyroscopic
oo Horizontal situation indicator
oo Turn-and-slip indicator / turn coordinator and inclinometer
•• Magnetic compass
•• Clock
Schedule
Introduction 0505 MMaaiin bbooddyy 2255 Applplicicatatioionn 0505 CCoonncclluussiioonn 0055 TToottaall 440 mmiinnuutteess
Equipment
•• model aircraft •• whiteboard and markers
•• ASA’s Instrument Flying , chapter 2
•• laptop with: o Flight simulator
o Warrior systems trainer
Online resources
• Pitot-Static System and Instruments • Gyroscopic instruments
• Air Safety Foundation – pneumatic systems
• Magnetism and the Magnetic Compass
• Attitude indicator
Instructor’s Actions
• Discuss the lesson objective • Introduce by discussing earlier private-level instrument experience
• Describe and introduce the basic flight instruments
• With illustrations from ASA’s Instrument Flying , describe instrument construction
• Describe operation using the Warrior systems trainer
• Explain and review flight instrument use, using flight simulator to show relationships
• Evaluate student’s learning by posing review questions throughout and correcting to 100%
Student’s Actions
• Prepare for the briefing by reading Instrument Flying chapter 2 or Jeppesen chapter • Participate with discussion, taking notes throughout
• Answer questions and leave with a general understanding
Completion Standards
The lesson is complete when the student can demonstrate an adequate level of understanding of the flight instruments, their construction, and their operation. A private pilot level of knowledge is expected in the interpretation of flight instrument indications. Throughout the lesson they should be able to correctly answer a majority of the questions without significant instructor prompting.
Teaching outline Throughout, the Warrior systems trainer should be used to illustrate the construction and operation of the flight instruments and their systems.
Pitot-static system
• Components o pitot tube
o static port(s) – multiple ports can balance or act as backup
o alternate static port
o drains
o altitude encoder – transponder component
• Airspeed, altimeter, and VSI
• Static port(s) provide ‘ambient’ air to the system
o alternate air is available in some systems, causing a rise in airspeed, altitude, and vertical trend (windows and vents closed, heater+defroster on)
o if alternate air is unavailable, breaking the glass of the VSI will create one
• Pitot tube provides ‘ram’ air to the airspeed indicator
o heated to prevent blockage
o drain hole to allow impacted rain or other potential blockages to leave the lines
Airspeed indicator, IF 36
• Displays indicated airspeed only; Kollsmann window allows for correction to true airspeed with density altitude • Limitations and markings:
o White arc – flap range
o Green arc – normal operation
o Yellow arc – caution range
o Red line – never exceed
• Operated by ram air moving a diaphragm which is linked to the airspeed needle
o Sealed case receives static air o Measures dynamic air pressure – the difference between static and ram
Altimeter, IF 46
• What is a sensitive altimeter? • Displays indicated altitude
o Types of altitudes
• Operated by static system pressure entering the sealed case
o Sealed aneroid disks expand with higher altitudes and contract with lower
o Mechanical linkage to altitude needles
o Kollsmann window allows sea level pressure input using the calibration knob
• SLP must be adjusted as flight proceeds and pressure changes
o If the flight encounters lower pressure unadjusted, the altitude will indicate lower than true; the opposite holds for higher pressure
o High to low, look out below (temp and pressure).
• Servicing requirements
Vertical speed indicator, IF 52
• Displays ascent and descent rate, or vertical speed • Not a required IFR instrument, but commonly found in the six pack of instruments
• Configured like the altimeter, but with a calibrated leak in the case
o The static system is connected directly to the diaphragm, causing pressure changes to indicate a trend
System malfunctions and errors (review questions)
• Errors stem from blockages o pitot blocked, drain open: IAS reads zero
o pitot and drain blocked: acts like an altimeter, and airspeed increases with altitude o static blocked: altimeter, VSI frozen, airspeed functions but incorrect
Gyroscopic systems
• Vacuum or electric
o Motor spins the gyro if electric
o Engine-operated vacuum pump, often with electric backup pump
• Suction gauge indicates system pressure – know the safe range
Principles of gyroscope operation
• Precession causes errors in the heading and attitude indicators, and is used by the turn coordinator • Rigidity in space is used by the heading and attitude indicators
Attitude indicator or artificial horizon, IF 31
• As the name suggests, it’s a replacement for the real, outside horizon • Fixed airplane or wings on the face of the instrument
• Gimballed, moving horizon reference in the back
• Shows changes in pitch and bank
• Self-erecting gyroscope, spinning around a vertical axis
o double-gimballed
o rigidity in space – the airplane moves around the gyroscope
• Precession (when rolling out of a steep 180° turn) and acceleration errors
o self-corrects with pendulous vanes – when not upright, vanes open due to forces and air corrects the spin
• During the after-start checklist and taxi it should stabilize after 5 minutes and bank less than 5° during level taxi turns
Turn-and-slip indicator / turn coordinator, IF 53, and inclinometer, IF 55
• Simplified way to maintain a 3°/second turn rate • Electrically driven gyroscope, set at a 30° angle o senses roll and rate
• Inclinometer displays the aircraft’s coordination – the quality of the turn
o much like a carpenter’s bubble level
• During the instrument check, there should be no flag, the aircraft should bank into the turn, and the ball should go outside, indicating a skid
Heading indicator, IF 40
• Shows a top-down representation of the aircraft, with a compass card rotating around the outside • Uses rigidity in space; the aircraft pivots around the gyro, indicating the turn
• Must be regularly reset to the magnetic compass, due to gyroscopic precession and mechanical inaccuracies
o 15 minutes is the general rule
Horizontal situation indicator, IF 45
• Gets data from a remote sensing flux gate compass o updates the compass card with the slaving motor
Magnetic compass, IF 56
• Points to magnetic north, subject to a variety of turn and acceleration errors • ANDS – accelerate north, decelerate south (east-west headings)
o when accelerating, the compass turns towards the north
o when decelerating, the compass turns towards the south
• UNOS – undershoot north, overshoot south
o starting a turn from the north, the compass lags – we have to undershoot our heading
o starting a turn from the south, the compass leads, and we have to overshoot our heading
Clock, IF 57
• Needs to be physically installed in the aircraft, set, and turning • It’s a clock. It tells time. Question bank
1. How does the principle of rigidity in space apply to the heading indicator? The attitude indicator? 2. The attitude indicator is self-erecting. What does this mean?
3. How does the airspeed indicator determine the current airspeed?
4. What will happen if the pitot tube is blocked? The static port?
5. Why do we need to input the correct sea level pressure into our altimeter? What is the window called?
6. Why do we need to regularly check our heading indicator? What should we compare it to, and under what conditions?
7. If the static ports are blocked, how can we regain static pressure in the system?
8. Why is the VSI the instrument to break? recently added lesson plans
Notes: Top 5 Mistakes Pilots Make (AOPA seminar Feb 21 2008)
Revised 24 February 2008
Takeoff and landing
Revised 29 January 2008; maneuver.
FAA resource guide
Revised 1 September 2007
Steep spirals
Revised 12 August 2007; maneuver.
Air traffic control clearances
Revised 27 July 2007; theory.
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