Radar vs barometric altimeter

Hi guys,

I realized that i almost never use, observe barometric altimeter gauges in my huey flights. I only use radio altimeter, unless i am not higher than 1500 feet.

Because i don't trust it since it only shows the altitute against sea level, or source level. Especially during night or low visibility flights and when i fly over mountains, i really need radio alt

how can you benefit from barometric alt?

I'm not a huge Huey pilot.....

Barometric is arguably more just as important, especially in high terrain or low visibility as it will tell you your actual height/elevation (altimeter setting dependant). Allowing you to use it to work with safety heights within the area you are flying. principly you would fly a set height above the highest terrain avoidance within a particular area, unless you are going low level.

Also your rad alt only tells you how high you are above the ground that is immediately below your aircraft at the time that sample is read (granted this is x times a second but you get this idea).

The flip side of this is, if you know where you are and how height you are above MSL you have a higher chance of avoiding terrain, given the map you are working with gives you an accurate terrain elevation and you have the correct pressure setting.

Hope that helps.

(source, working with real world pilots)

Instrument flight lowest safe altitudes are based on AMSL.

IRL ATC instructions are usually based on AMSL. Though they can use AGL, it is uncommon in my experience.

In undulating terrain it is usually easier to use AMSL to deconflict with other aircraft such as fast CAS or Strike aircraft.

- Bear

how can i know what the safe lowest altitude is? a few days ago, i was fliying over the mountains in a very foggy weather. my rad alt read 200ft . my barometric alt read 13000 ft.

if my rad alt had been disabled at that flight, what could i have done with my barometric alt? i was flying 13000 feets above the sea level or airport level but actually i was fliying a few meters above the surface. i just can't understand why i need a barometric alt gauge in a huey. can you give some tips?

how can i know what the safe lowest altitude is? a few days ago, i was fliying over the mountains in a very foggy weather. my rad alt read 200ft . my barometric alt read 13000 ft.

if my rad alt had been disabled at that flight, what could i have done with my barometric alt? i was flying 13000 feets above the sea level or airport level but actually i was fliying a few meters above the surface. i just can't understand why i need a barometric alt gauge in a huey. can you give some tips?

You know the safe lowest altitude by looking at the map. That's what every pilot does before the flight to get familiar with the route and make notes and restrictions such as lowest safe altitude. In DCS you can bring up your F10 map inflight to check the altitude of the sourrounding terrain.

Barometric altitude is also very important for the flight performance, because the performance of the helicopter changes with altitude. That's especially important when operating in hot and high conditions.

how can you benefit from barometric alt?

The most basic benefit is to be able to fly straight and level!

how can i know what the safe lowest altitude is? a few days ago, i was fliying over the mountains in a very foggy weather. my rad alt read 200ft . my barometric alt read 13000 ft.

if my rad alt had been disabled at that flight, what could i have done with my barometric alt? i was flying 13000 feets above the sea level or airport level but actually i was fliying a few meters above the surface. i just can't understand why i need a barometric alt gauge in a huey. can you give some tips?

Just in case you haven't familiarized with QNH and QFE yet, QNH will give you pressure altitude above mean sea level, while QFE will give you pressure height above the ground for which the QFE is valid, usually takeoff or landing airdrome, and it varies from location to location.

To be precise, QNH gives as I said PREASURE altitude, and it's not exactly the same as your real altitude. There are methods how to calculate between them in real life, but I'm not sure the atmosphere is modeled in that detail in DCS. I believe you don't need to consider it.

- Barometric gives [Altitude] = Height above the set pressure for mean sea level/QNH, or flight level, or height above runway, QFE.

- Radar alt gives [Height] = Actual height between helo and ground at present position.

Barometric is very good for separation between aircrafts. Set the same QNH or QFE or use 1013,25hpa /29.92 in the Hg and you can avoid each other by selecting different altitude.

Barometric is very good for separation to ground. Plan your flight and calculate the altitude needed to clear obstacles with sufficient margin.

Radar alt is a very good complement, and for certain procedures its good.

But it only tell you the vertical measurement, meaning you have no clue for the margin that's ahead. You cannot use it to avoid a high steep mountain with higher vertical size then the radalt max value.

Thanks for the replies guys. So I should use them both for level flights.

During the low level flights or some special tasks like sling ops or Cas etc I need radio alt more.

So how can I find these qnh values whenever I want ? I use mission editor a lot so I cannot use briefing. And also I guess these values change depending on the location so don't I have to update it periodically? Can I see specific qnh values on F10 map also ?

I believe both QNH and QFE is given on that briefing window that always appear before start, regardless if you go from ME or not. It's part of the auto generated information. QNH is in the weather info while QFE is with the airdrome/FARP info together with frequencies.

I'm not sure, but I believe QNH doesn't change over distance and time in DCS? Maybe if you have dynamic weather on? QFE is only given for your starting point, need to be calculated using elevation for other locations. Unless you ask ATC at an airdrome, they unfortunately give you QFE in DCS (I would prefer QNH myself). I don't have the procedure how to do the calculation in my head, but I'm sure you'll find it elsewhere on this forum.

Keep it simple...

Most people use RADAR ALT for the majority of the time...

For BARO ALT, short distance local flights QFE is good, i.e. the way it is when you jump into the cockpit.

For longer stuff depending on :-

• your interest
  
• the weather
  
• the time (day / night}
  
• the terrain
  
• Flying with true pilotage i.e. F10 set map only i.e. F10 does not show your location or others or threats etc..
  
• Congested airspace / Flying with others operationally on MP. i.e. Gunship Teams & Slicks need know or to set immediate deconflict heights... unless the ground is flat everywhere QNE is not effective.
  

...CONSIDER setting QNH. You can find your QNH settings at any time, anywhere, at the start, in flight, whenever :). Just look at your briefing page. LALT + B will bring it up at any time....

Most people use RADAR ALT for the majority of the time...

They do? I barely use it. I keep it deactivated most of the time, unless I'm flying in really bad visual conditions (night, fog). I don't really have any use for radar altitude in the Huey (except IFR), as I can see the ground with my eyes just fine. :dunno:

Radar altitude is more important to me in fixed wing aircraft where it is important for things like SAM threat safe altitude or weapon release heights.

They do? I barely use it. I keep it deactivated most of the time, unless I'm flying in really bad visual conditions (night, fog). I don't really have any use for radar altitude in the Huey (except IFR), as I can see the ground with my eyes just fine. :dunno:

Radar altitude is more important to me in fixed wing aircraft where it is important for things like SAM threat safe altitude or weapon release heights.

You should not be using the radar altimeter for IFR because the radar altimeter drops out at 1500 feet which you should be flying above. Also all of the IFR procedures are in MSL.

Also a lot of threat weapon systems have an engagement altitude greater that 1500 ft so it won’t help you there either.

The radar altimeter is very useful though under NVGs when you don’t have binocular vision (ie. Depth perception). Also gagging the exact height above the ground during the day is not easy. For example we have a company policy that requires us to stay above 500 ft agl so the radar altimeter is very useful for that.

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