Gain Programming

[graziani]

What Is The Autopilot Gain Programming ?

[Engineer]

Gain Scheduling

The shaping or programming of certain gains to compensate for varying conditions, such as airspeed, beam convergence, etc.

As an example in the autopilot when you capture the glideslope and move closer to the centre of the beam gain scheduling is automatically provided by radio altitude input to compensate for glideslope radio beam convergence. i.e. When the aircraft is further away from the beam centre it needs a larger signal to reposition towards the centre of the beam. However when close to the beam centre smaller responses are needed and this is acheived by reducing the gain of the signal or to dampen the effect of the signal variation.

An analogy would be taking a shower when you first turn it on you will need to adjust the temperature control with large movements to get the approximate temperature(otherwise you will be burnt or very cold :) ). Then only small adjustments are needed to obtain the required temperature. Your body senses the change and your hand movement provides the automatic gain programming

[graziani]

thanks very much...I appreciate

[Engineer]

If we are talking about roll input:

then during the descent along the glide slope beam, as the ILS transmitter is neared, since the beam-error radio signal is a function of angular beam errors, a significant increase results in the sensitivity of the input beam-error radio signal to movement of the airplane relative to the beam centre.

That is, because the radio measures angular beam errors rather than actual linear distances, as the transmitter is neared, a small airplane movement off the beam centre results in a proportionately large angular beam error.
A correspondingly large radio beam-error signal would result, causing overcontrol. To correct for this condition, a desensitiser network is included.

This network receives an input from the radio altimeter which is applied to a function generator. When the altitude of the airplane drops below 1000 feet, the output of the function generator changes the gain of the desensitiser circuit, which provides initial amplification of the beam-error signal for initial very tight control.

The descent of the airplane down the glide slope beam towards the transmitter is directly proportional to the radio altitude as the airplane approaches the localizer transmitter. Therefore, the function generator controls the desensitiser circuit to reduce the gain of the beam-error signal in proportion to the increase in sensitivity of this signal, thus preventing overcontrol to small linear beam displacements.

Another function generator is included in the final bank-angle limiter. This function generator goes into operation at an altitude of approximately 1000 feet and reduces the bank-angle limit as the airplane approaches touchdown. The bank-angle limit is reduced to a maximum of 5 degrees, as touchdown is neared. This prevents excessive bank angles as touchdown is approached.

[mutley320]

I believe it's also the reason you cant do an auto land AND auto touchdown on some runways due to undulating terrain on short final that confuses the "gain programing" from the Rad Alt reference to glideslope & pitch.
I believe a certain runway in Jo'burg is mentioned in the limits section.

[mutley320]

Sorry, Talking about Airbus 320 limits/ OEB. But otherwise relevant i believe.

[graziani]

IN SUPPLEMENTARY CHAPTER BOEING 737 .........


note.DO NOT USE VOR/LOC AFDS mode when conducting VOR approaches if the VOR/DME statin elevation is more than 5000 ft MSL , if there is no co-located DME trasmitter available at the VOR station to be used or when the DME is invalid for any other reason.........


WHY ???
SOMEONE CAN EXPLAIN TO ME
PLEASE
THANKS:ugh: