Why does my altimeter change from radar to barometric when I bank left or right at around 900ft?

[Jidai]

Landing practice at Nellis. When I take off then level at 900 and bank left for my downwind leg my altimeter which is set to radar suddenly changes to barometric (in the HUD) and displays 2000ft then once I roll out of the turn it switches back to radar and displays 900.  Usually this switch doesnt happen until Im above 5000ft then the barometric altimeter is enabled.

[zildac]

Landing practice at Nellis. When I take off then level at 900 and bank left for my downwind leg my altimeter which is set to radar suddenly changes to barometric (in the HUD) and displays 2000ft then once I roll out of the turn it switches back to radar and displays 900.  Usually this switch doesnt happen until Im above 5000ft then the barometric altimeter is enabled.

It's a radar and it points at the ground. When you bank past a certain point it can't "see" the ground any more so falls back to barometric. I'm pretty sure there's a far better explanation somewhere but I can't recall where.

[MAXsenna]

Landing practice at Nellis. When I take off then level at 900 and bank left for my downwind leg my altimeter which is set to radar suddenly changes to barometric (in the HUD) and displays 2000ft then once I roll out of the turn it switches back to radar and displays 900.  Usually this switch doesnt happen until Im above 5000ft then the barometric altimeter is enabled.

Probably because the sensor points down, and when you bank, it will not, but point to the ground at an angle, and then the ground will be further away.

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[Bunny Clark]

The radar altimeter will not function beyond 45° of pitch or bank, as it looks downward from the bottom of the aircraft. If it can't see the ground, it can't give you altitude. 

[Frederf]

Radar altimeters do point down but down isn't a laser beam. It's a fan of signal. Since the system is certified 40 degrees bank at 5000 it would normally work at more bank at lower heights. However it has a blanker system that prevents emission beyond pitch/bank limits to prevent erroneous readings. It turns itself off when out of angle limits which is why you get good performance and then a hard on/off behavior crossing limits.

 

So even if you were in a 90 bank attitude with a cliff "below" (beside) you that the antenna would normally be able to lock on to the gauge would read off because it's inhibited.

[MAXsenna]

Radar altimeters do point down but down isn't a laser beam. It's a fan of signal. Since the system is certified 40 degrees bank at 5000 it would normally work at more bank at lower heights. However it has a blanker system that prevents emission beyond pitch/bank limits to prevent erroneous readings. It turns itself off when out of angle limits which is why you get good performance and then a hard on/off behavior crossing limits.
 
So even if you were in a 90 bank attitude with a cliff "below" (beside) you that the antenna would normally be able to lock on to the gauge would read off because it's inhibited.

Thanks!

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[zildac]

What @Frederfsaid, far more eloquently than me

[MAXsenna]

What @Frederfsaid, far more eloquently than me

Yeah, that always happens to me too!

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[G.J.S]

Get some height, up at 10000 or more, and get a wingman (real) to fly directly beneath you - radalt will ping, radalt in action.

As your wingy slides slowly beneath you from one side, you will get an approximation of the radalt limits as he/she will ping it from around 40*ish left and right of directly below you.

[Fri13]

Does DCS: hornet simulate the strongest/closest return, or does it just show the real terrain distance below the aircraft? As based to Harrier NATOPS trees, buildings, hills etc should give a return range from them and not the ground, even when they are away from under the craft but inside beam spread.

 

In Harrier that isn't simulated so flying above buildings or forests etc gives real terrain altitude. But how it is in Hornet (or overall DCS)?

[G.J.S]

39 minutes ago, Fri13 said:

Does DCS: hornet simulate the strongest/closest return, or does it just show the real terrain distance below the aircraft? As based to Harrier NATOPS trees, buildings, hills etc should give a return range from them and not the ground, even when they are away from under the craft but inside beam spread.

 

In Harrier that isn't simulated so flying above buildings or forests etc gives real terrain altitude. But how it is in Hornet (or overall DCS)?

That’s probably due to how those things are modelled, as in “eye candy” versus physical objects.

Only reason I can imagine for that would be it’s easier to display a tree etc as a visual ‘thing’ than a fully modelled ‘thing’ with substance, for reasons maybe due to computing power?

Just an assumption though.

[Harker]

Does DCS: hornet simulate the strongest/closest return, or does it just show the real terrain distance below the aircraft? As based to Harrier NATOPS trees, buildings, hills etc should give a return range from them and not the ground, even when they are away from under the craft but inside beam spread.
 
In Harrier that isn't simulated so flying above buildings or forests etc gives real terrain altitude. But how it is in Hornet (or overall DCS)?

In my experience, yes. Haven't tested that extensively though..

[MAXsenna]

Now that went OT quickly, or am I missing something?
Cheers!

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[Jidai]

Ahhhh ok that makes perfect sense! Thanx for all the excellent responses!   I also fly the T45C and it doesn't do this. I can only assume this function isn't modeled, at least not yet.