Why does Lochini show as 1500m on map, yet 2500m on altimeter?

As title. Lochini shows as 2500m on ground on altimeter, yet map says it is at 1500m.

The pressure is stronk XD

Sorry, I have no idea what that means!

I think he's saying the altimeter determines altitude by air pressure but air pressure is broken or not set properly?

Thanks, but I'm no clearer.

If I land at Lochini, the altimeter shows 2500m but it should be 1500m. So, on approach, how am I supposed to know the correct height I'm at?

What do you mean by 'not set properly' or 'broken'?

Altimeters work by 'measuring' the air pressure local to the aircraft and comparing it to a reference point - generally the average ambient air pressure at sea level, that reference point being marked as the zero on your altimeter. Given that air density decreases at a known rate as we increase in altitude, the graduations on your altimeter have been precisely worked out and the instrument calibrated to indicate what this air pressure difference means in terms of your height above that sea level average. This is what is generally termed QNH reading.

But the average is just that - a mathematical approximation to the most common air pressures recorded and therefore have large error factors, as air pressure changes with various climatic conditions. You will rarely fly on a day when the air pressure is exactly the same as the datum.

Secondly, how many airfields do you know are located sea level? ;)

This is one of the reasons you can zero the altimeter manually. It gives you the opportunity to provide yourself with a quick reference to your altitude relative to something more relevant; like the airfield you are flying out of!

Lets's look at it this way;

a) You're practising your circuits at your local field; you're not going to venture far or into other airlanes so your only altitude concern is about what your height is above the airfield, yes? In this case you zero the altimeter on the runway just prior to takeoff. At this point you have just set QFE on your altimeter.

b) You want to fly from your airfield to another farther way but there are 1000ft hills in the way and some low cloud; you know the above mean sea level pressure height of these hills thanks to your map; you takeoff under QFE (Field Elevation) but once you reach a set altitude you then have to reset the altimeter to read QNH (Nautical Height - that above the mean sea level) using figures you've got from the Met Dept or tower prior to takeoff. Now if you fly at 1200ft you're sure to clear the hills even if you run into cloud.

Why is then your Spitty is reading 1000ft out? It could be local ambient air temp, it could be it's set to QNH or it could be both!

I understand all that, but my question is why is the altimeter 40% out? To my small brain, that seems wrong and makes the guage somewhat limited in practical use.

If I am flying over Lochini, and I know that it is (according to the map data) 1500m above sea level, then I would expect my altitude above ground to be the altimeter reading minus 1500.

Obviously, if I started on the ground, I could zero the altimeter, but I'm starting in the air.

Have you set you altimeter to the QNH of the airfield ?

Anyway, when I was using DCS and the Spitfire, I did notice some weird stuff with the altimeter settings, not allowing to turn the knob to properly set the reference pressure in the Kolllsman window.

Check the mission reported pressure and see if you can regulate the altimeter to go with it. You would then be able to read 1500

To my small brain, that seems wrong and makes the guage somewhat limited in practical use.

Your brain is not that small since you ask the right question :)

OK, after starting this thread, I am now swamped with more questions on using the altimeter on the Spitfire.

From another thread here, I watched this video

However, this has made my observations in DCS Spitfire even more confusing.

Let me just put some figures here:

In the various Instant Action scenarios, we have the following:

Landing - Lochini Map 1500m elevation, altimeter 2500m on ground

Free Flight - Seneki 34m and 500m

Cold Start - Beslan 1772m and 2350m

I understand the concept of QNH and QFE, but just don't understand how the above heights are supposed to be interpreted or understood.

I guess I have 2 points:

1) why are the values on the ground not either the QFE or QNH?

2) if adjustments have to be made to the altimeter on the Spit, how on earth is this done? I mean, the pressure values are so small, that it is impossible to read them without zooming in on the cockpit, and how this is supposed to be executed when in flight, I don't know!

Also, when given a QFE by ATC, how is that input to the altimeter when the gauge is in millibars and the ATC gives it in some other unit, e.g. 29.92.

I understand all that, but my question is why is the altimeter 40% out? To my small brain, that seems wrong and makes the guage somewhat limited in practical use.

If I am flying over Lochini, and I know that it is (according to the map data) 1500m above sea level, then I would expect my altitude above ground to be the altimeter reading minus 1500.

Obviously, if I started on the ground, I could zero the altimeter, but I'm starting in the air.

Set the kollsman window in the altimeter to the correct QNH. It is shown in the briefing (left Alt B) in mmHg and inchesHg. You will need to convert to hPa, which is the unit used in the altimeter.

Lochini elevation is about 1600 ft, not meters. The Spit altimeter also displays ft.

Set the kollsman window in the altimeter to the correct QNH. It is shown in the briefing (left Alt B) in mmHg and inchesHg. You will need to convert to hPa, which is the unit used in the altimeter.

 

Lochini elevation is about 1600 ft, not meters. The Spit altimeter also displays ft.

Thanks for that.

I understand a bit more. I don't know why, but I assumed that the altimeter would have been set to the default, whereas it was on 1050! When I reset to 1013.25, then the altitude on the ground showed as around 1500.

That leaves me with a few more questions now.

1) you say that the elevation at Lochini is around 1500 ft not metres. That makes sense as according to the Spit altimeter, it is 1500 ft. However, the map states an elevation of 1500 metres. How does that stack up?

2) why is the QHN and QFE stated in mmHg and inchesHg when the altimeter needs hPa?

3) how is that conversion supposed to be done in flight?

4) as I asked in my previous post, how is one supposed to make adjustments to the pressure on the altimeter in flight, as the gauge is so small that a large amount of zoom is required. In flight, that would make for a very unstable aircraft flying with no sight for a few seconds!

1) you say that the elevation at Lochini is around 1500 ft not metres. That makes sense as according to the Spit altimeter, it is 1500 ft. However, the map states an elevation of 1500 metres. How does that stack up?

Just checked various other airports, and they are all the same. Map states metres, but value is the same as the Spit's altimeter feet reading.

1. It obviously is a bug. I reported it, but no acknowledge so far: https://forums.eagle.ru/showthread.php?t=181767

2. In the USA inches of Hg are used. I guess that in Russia maybe they use mm of Hg. The origin of this simulator included aircraft of those two countries. Now there are planes with hPa (which is currently used in most of the world), but it is not updated. Also I think that german WW2 planes might use Atmospheres, but not sure.

3. TBH, I think that when a mission starts in flight, it should be already set, because that is what a competent pilot would have done before. When it starts on the ground it could be more realistic to set to a semi-random value, which would be local QNH (or QFE) the last time that aircraft flew.

4. While flying you can go to a place with different QNH (for short range aircraft like these, maybe up to 5 hPa, specially when flying to/from low pressure areas). Besides, in real life, above the "Transition Altitude", QNE is set (1013 hPa) to fly Flight Levels as opposed to Altitudes. Then you go back to the destination airport QNH before landing. These things are done in real life, it should be the same in the sim. If you trim the aircraft (and although the Spit is not very stable), with a bit of practice it is not that hard. Anyway, in the sim it is enough to set the altimeter to the airport elevation before takeoff and leave it there. No need for unit conversion or in flight changes most of the time.

Thanks for that.

I understand a bit more. I don't know why, but I assumed that the altimeter would have been set to the default, whereas it was on 1050! When I reset to 1013.25, then the altitude on the ground showed as around 1500.

That leaves me with a few more questions now.

1) you say that the elevation at Lochini is around 1500 ft not metres. That makes sense as according to the Spit altimeter, it is 1500 ft. However, the map states an elevation of 1500 metres. How does that stack up?

2) why is the QHN and QFE stated in mmHg and inchesHg when the altimeter needs hPa?

3) how is that conversion supposed to be done in flight?

4) as I asked in my previous post, how is one supposed to make adjustments to the pressure on the altimeter in flight, as the gauge is so small that a large amount of zoom is required. In flight, that would make for a very unstable aircraft flying with no sight for a few seconds!

1. It obviously is a bug. I reported it, but no acknowledge so far: https://forums.eagle.ru/showthread.php?t=181767

 

2. In the USA inches of Hg are used. I guess that in Russia maybe they use mm of Hg. The origin of this simulator included aircraft of those two countries. Now there are planes with hPa (which is currently used in most of the world), but it is not updated. Also I think that german WW2 planes might use Atmospheres, but not sure.

 

3. TBH, I think that when a mission starts in flight, it should be already set, because that is what a competent pilot would have done before. When it starts on the ground it could be more realistic to set to a semi-random value, which would be local QNH (or QFE) the last time that aircraft flew.

 

4. While flying you can go to a place with different QNH (for short range aircraft like these, maybe up to 5 hPa, specially when flying to/from low pressure areas). Besides, in real life, above the "Transition Altitude", QNE is set (1013 hPa) to fly Flight Levels as opposed to Altitudes. Then you go back to the destination airport QNH before landing. These things are done in real life, it should be the same in the sim. If you trim the aircraft (and although the Spit is not very stable), with a bit of practice it is not that hard. Anyway, in the sim it is enough to set the altimeter to the airport elevation before takeoff and leave it there. No need for unit conversion or in flight changes most of the time.

1) I've added to your original post and posted in the 2.0.5 section as the same happens there.

2) Fair enough, but as the Spit uses hPa, it wold be useful for the briefing to state that as well.

3) it should be set, but certainly in the Instant Action and Training missions it is not.

4) changing from QNH to QFE when approaching a landing phase is really awkward to achieve in DCS, especially in the Spitfire, which as you say is pretty unstable even when reasonably well trimmed!

4) changing from QNH to QFE when approaching a landing phase is really awkward to achieve in DCS, especially in the Spitfire, which as you say is pretty unstable even when reasonably well trimmed!

Just discovered Active Pause (LShift+LeftWin+Pause), and that allows you to make adjustments while the sim is in pause!