ASE & SAS, What's the difference?

[Flag Track]

Just terminology? Replies gratefully received!

[212man]

ASE is Automatic Stabilisation Equipment, and would typically include attitude retention along with rate damping.

SAS is Stability Augmentation System and is typically just short term rate damping.

[nodrama]

Alot of the terminology for these systems gets generalised by different manufacturers and operators, and sometimes it can even depend on what part of the world you come from.

SAS provides enhanced stability and gust dampening. The system detects a rate of change in angular displacement in an axis (using a rate gyro) and commands a series actuator to produce a proportional and opposing control input to counter the disturbance and reduce the detected rate of change to zero. This doesn't necessarily mean the aircraft will return to it's exact original attitude before the disturbance, because the SAS has no actual attitude reference data.

ASE (sometimes also called attitude stabilisation equipment) is a progression from SAS that detects actual attitude displacement also. This can be done by integrating the rate gyro data or by introducing a vertical gyro per axis to the system.
Now the system will not only provide gust dampening but will also provide attitude hold. The accuracy of this attitude hold depends on the system used and whether it uses integrated rate data or raw attitude data.

[Shawn Coyle]

As with all communications, words get in the way of understanding.
The terms are very loosely used, and it is essential to know exactly what those terms mean. SAS as described in the early CH-47 series operated differently than the SAS fitted to the UK RAF / RN Gazelle.
Bascially nodrama has a good overall differentiation.

[nodrama]

OK, maybe someone can help me with this one then....

What's SCAS? (never worked on a helicopter that had it fitted, but have heard of it).

Is it just a term used by Bell for ASE with maybe a HDG hold and/ or ALT hold capability?

[419]

SCAS is indeed the Bell terminology for a SAS system.

It stands for Stabilisation Control and Augmentation System.

The other mode used on Bell helicopters is ATT (Attitude mode), and is the same as an ASE system in that it is for long term attitude retention.


There is no rate input into the ATT system as this is handled by the SCAS computers, and these must be operative before the ATT mode can be engaged.

[nodrama]

Thanks 419 :ok:

.....another person who has experienced the delights of the land of wahalla-o?

[419]

Yes'o.

I did my stint there. (and I'm still not back to normal)

[SilsoeSid]

I'd rather have someone from the SAS with me in a firefight, than someone from the Army School of Education.
(No diss to the ASE)


Sorry, Ok I'm off to check the dinners not burning ;)

[Shawn Coyle]

Bell did indeed misuse the term SCAS for many years. They are now more educated.
The CA for control augmentation indicated that the pilot's control inputs were fed forward to the actuators to make them move further in the desired direction of motion, as the system was going to be sensing the motion of the helicopter and trying to stop it in a few milli-seconds. And quite rightly, not all systems did this, but Bell still referred to everything as a SCAS.