Quote:
Originally Posted by vivekiny2k just curious. Up in the air, surrounded by clouds, do pilots have any sense of what speed they are traveling at, so they can override the autothrottle? |
To answer your question, there is no sense of speed other than what is indicated by instruments.
Instruments
Four instruments in the basic "T"
- Airspeed Indicator,
- Artificial Horizon,
- Altimeter and
- Gyro-Compass;
and additionally - the Turn-and-Bank indicator and
- Vertical speed Indicator.
The
1958-1979 Boeing 707 was the world's first commercially successful jet airliner. Air-India had eleven of them. Six with the Rolls-Royce Conway engines and five with Pratt & Whitney JT3D turbofans.
Boeing 707 basic flight panel Boeing 707 cockpit Boeing 707 cockpit with my annotations
Overhead panel contains ignition and engine start switches, fire extinguisher switches, HF radios, alternate flap control, emergency exit lights, rain repellent, and exterior lights, compass and vertical gyro transfer functions, Mach Trim test, Fuel filter heaters, Winshield wipers, engine de-icing, hydraulic pumps, Heating switches for pitots and alpha vanes and Airconditioning & Gasper fan switches for Gyro motor and caging for gyrocompass and vertical gyro for bank angle and pitch attitude.
The
1974-2007 Airbus A300 and 1983-2007 A310, had
CRT monitors for altitude and navigation info display.
However they still used traditional mechanical gauges with needles and painted graduations,
for airspeed, altitude and vertical speed.
Cockpit of Airbus A300
With the
1988-onwards Airbus A320, and following that the
1993-onwards Airbus 340,
1994-onwards 330 and
2007-onwards 380 they all have full "glass cockpits".
Full glass cockpit of Airbus A330.
Note sidesticks and absence of control yokes.
All mechanical gauges and warning lights are replaced by interchangeable
general purpose CRT/LCD computer screens that display whatever the EFIS (Electronic Flight Instrument System computer) wants to display via a graphics card.
Autothrottle
Autothrottle on the Airbus is a feedback control system that can be in fixed SPEED mode or fixed THRUST mode.
In SPEED mode, the computer tries to maintain the speed to the pilot-ordered or autopilot-ordered speed, but still within the safety envelope of the aircraft.
In THRUST mode, Autothrottle maintains a fixed power setting
(what we car people call BHP, for a jet engine it's static thrust measured in kiloNewtons or pounds).
The throttles have six detent positions specified according to flight phase:
- TOGA (Take-Off/Go Around) power,
- FLX/MCT (Max. Continuous Thrust) power,
- CLB (Climb) power,
- IDLE power,[for flaring when landing]
- REV IDLE (reverse idle) power,
- MAX REV (max. reverse thrust) power
While the throttle is in the CLB detent and Auto thrust is active, the Airbus's FADEC (Full Authority Digital Engine Ctrl) can control the thrust from FLX/MCT to IDLE. The throttles are linked to the FADEC by electronic signals, not by cables unlike in Boeings.
This reduces weight (similar to fly-by-wire controls). Airbus also has brake by wire.
You order the CLB airspeed, and the autothrottle adjusts to maintain it.
Pilot workload greatly decreases, while fuel efficiency and performance improve because of the computerized precision power management.
However to work, Autothrottle needs
precise speed measurement.
If the pressure pitots are choked and send questionable speed info, everything can quickly go awry.
Ram