FINS Flashcards
Errors of the Pressure Altimeter
Pressure Instrument Temperature Hysteresis Barometric Lag Orohraphic Transonic
Pre Flight Tutor Altimeter Checks.
- Check static vents clear
- Set Airfield QFE (on both)
- Check both altimeters read within +- 60ft of zero.
- OR if QFE not known. Set altimeters to read zero. Altimeters must be within 4hPa of each other.
Temperature error correction formula and when:
In UK when temp less than or equal to zero.
4 x (no of thousand feet) x (temp diff from ISA (15))
When should you level out because of lag?
Level out by 1/10 of the rate of descent.
Eg. You descent from 6k to 3k @ 2k per min.
2000/10=200. Level out @ 3200
Why are static vents located either side of fueslage?
- compensate for unbalanced flight / yaw
- unaffected by forwards motion of a/c
- unaffected by changes of configuration (flaps)
Why is pitot locate under port wing?
- always points to free stream air
- far enough from surface of wing to avoid boundary layer
- unaffected by changes of configuration
- as AoA changes, the direction of relative airflow changes
- pitot continues to point into oncoming airflow irrespective of attitude
VSI Errors
PLIT Pressure Instrument Transonic Lag
ASI Errors
PLID Pressure Instruments Density Lag
Why IAS is used, not TAS
- Aerodynamic forces and thus the IAS will be the same @ different heights / densities
- gives pilots just one set of limitations to work to
VSI Checks
- Check static vents are clear
- Check VSI glass unbroken
- Check VSI reads 0 (+/- 100ft)
TUTOR PITOT STATIC SYSTEM
PITOT > ASI only
STATIC to ASI, ALTx2, VSI, Height encoder
EMERGENCY STATIC VENT feeds all static too
Types of orographic error:
- Orographic lows. Air tends to sweep around High ground. Results in low pressure in lee of hill.
- Venturi effect. Air that rises and flows over high ground experiences constriction owing to the tropopause barrier that lies a few miles above. As a result there may be a drop in pressure due to Venturi effect, in the same way as an aircraft wing:
- Funnelling. Between adjacent hills or valleys may be a drop in pressure caused by Venturi effect:
- Adiabatic temperature error. Air that rises and flows over high ground will cool adiabatically at a rate that is higher or lower than ISA.
What is rigidity?
If a gyro has complete freedom, it’s spin axis will remain fixed in space, however much the frame is displaced. RHYME
Depends on:
- Mass (more = more stable)
- Distribution of mass (the further the mass is from gyro axis; the more stable)
- Speed of rotation (more = more stable)
What is precession?
If acted upon by a force, a gyro will move as if the the force had been applied 90• further round in the direction of rotation. It’s affected by size of force and rigidity.
Precession is used to later the orientation of the gyroscope
Types of gyro, degrees of freedom and what they’re used for?
- Displacement gyro. 2 degrees of freedom. Angular displacement between gyro spin axis and gyro frame display orientation. Can not measure displacement around spin axis. Used for artificial horizon and direction indicator.
- Rate gyro. 1 degree of freedom. Measures rate of movement from gimbal in the plane that it lacks freedom. Used in turn indicator.
DR / DOCTOR / 2,1
