Terrain avoidance is engaged automatically??

[Snacko]

How does the Su-25 Terrain Avoidance work?

 

For the Su-25t Autopilot, the FC2 Manual says this on the bottom of pg 61:

"Terrain avoidance" is engaged automatically from the "radar altitude hold", "barometric altitude hold", or "attitude hold" ACS modes, and also in "ENROUTE" and "LANDING" navigation avionics operational modes with any attitude or altitude hold ACS mode (e.g. "radar altitude hold," "barometrical altitude hold") engaged.

1) I don't understand this sentence. :cry: What is this sentence trying to say?

 

-- and --

 

In another place in the manual it says:

 

The "terrain avoidance" submode is engaged whenever:

 

• The current altitude AGL as measured by the radio altimeter is half or less than its initial value in the "barometric altitude hold" ACS mode, or
  
• The rate of descent measured by the radio altimeter exceeds –50 m/s.
  

2) How can it be half, it if first becomes less than the original value?

 

-- and --

 

Above this in the manual, it refers to the Radar Altitude hold mode as the only mode with with Terrain Avoidance. So, I am very confused.

 

Radar altitude hold with automatic terrain avoidance

3) How can it be engaged from the other modes in the first quote above, if it is only on the Radar Altitude Hold mode?

 

-- also --

 

4) What exactly is Terrain avoidance? I assume it uses Radar to avoid the ground. What are the limits? Just keeping you above of some set value?

 

Thanks for trying to answer my dumb questions.. :thumbup:

 

Snacko :smartass:

[Nate--IRL--]

There isn't really Terrain Avoidance in the normal sense of the phrase, in that the Radar altimeter only points straight down. It cannot read the Terrain in front of the aircraft, with the obvious pitfall this presents.

 

Nate

 

Edit:- 1) sounds like a bad translation

2) It seems to say if your Barometric hold is at, say 500m, and the Radar alt reads 250m, the Autopilot will engage the Terrain Avoidance mode.

3) I think if you happen to be in any of those mode mentioned in 1 then 2 will apply.

 

Edit 2:- As a general rule, just don't trust it and keep your wits about you when using it.

Edited May 25, 2010 by Nate--IRL--

[TAIPAN_]

When flying low, it will follow slight contours (because there is time to catchup).

 

But when a hill comes, give the stick a pull and then let it come back to a steady level ride along the new terrain level.

 

The best time to use altitude hold is along the ocean, no hills :) You can fly at 15m and alot of high aircraft won't take notice of you.

 

Works well against ships as well, fly at one to block the guns of the others, so only one can shoot at your missiles.