Altimeter Kollsman window

[scotth6]

Hi,

 

First off thanks for the F-5, it is an awesome rendition of an awesome aircraft.

 

I have just noticed something while flying the F-5 around Vegas for the first time. I actually haven't flown in V2 alpha for a while, and haven't noticed this before.

 

When getting takeoff clearance or inbound info from ATC they give me a QFE setting for the altimeter. I often get the info from ATC in DCS 1.5 also, but I can't recall if they give QFE or QNH (I have just done some reading so I don't mix the two up - QFE to set an airport elevation as zero and QNH for altitude above sea level). As far as I've read previously the UK uses QFE but the US does not.

 

I'm not sure if it is a DCS World issue or an F-5 issue. Actually I suppose there are two issues. First one I assume would be a DCS World issue; which is ATC giving QFE settings instead of QNH. The second issue is that regardless of the setting I receive from ATC, the minimum setting in the Kollsman window in the F-5E is 28.10. In two missions in Vegas I was given QFE settings of 27.87 and 27.70.

 

Not a big deal of course, just thought I would report what I found.

 

I am loving flying the F-5E!:thumbup:

 

Cheers,

[scotth6]

Good to know. Thanks for the informative reply.

 

Cheers,

[Andrew-76]

How can I get QNH when I'm on ground? To set altimeter while start-up procedure? In tutorial they say look at mission briefing into weather section. But there is only info about wind, turbulence, clouds and temperature. No barometric pressure.

[Pocket Sized]

How can I get QNH when I'm on ground? To set altimeter while start-up procedure? In tutorial they say look at mission briefing into weather section. But there is only info about wind, turbulence, clouds and temperature. No barometric pressure.

 

For the time being I'd just set the altimeter to airport elevation. This can be found with F2 or by going to the F10 map and clicking your aircraft.

[rrohde]

QNH is fine and dandy when you have auto-landing and/or radar altimeter equipped, but the F5 does not. When doing touch-and-goes at the same airfield that you took off from, QFE is preferred, especially in an VFR aircraft like the F5. How else would you determine your zero altitude for landing? :)

 

Airport elevation works, but then you have to remember that this value is now your "new zero altitude" when you approach for landing. QNH would mean you have to do some math on the fly to determine your zero altitude equivalent, subtracting airport elevation from the QNH value, which in the heat of the moment might not be the best thing to do...

 

And when the wx condition is such that you cannot dial in the airport elevation into your altimeter, because it's out of reach (happens on NTTR a lot), then you'll have to do a lot more math on the fly. :)

 

Quick write-up from a RL pilot friend of mine:

 

Altimeter:

 

If local altitude settings are lower than settings shown in the Kollsman window, you’re actually flying lower than you think (or are displaying on your altimeter).

 

 

Example:

 

Kollsman window shows 29.00, however, local alt is 28.00, you are 1,000ft lower than altimeter indicates.

 

- For each 0.10 of a difference in the Kollsman window, subtract 100ft from indicated altitude

- For each 1.00 of a difference, subtract 1,000ft from indicated altitude

 

 

“From High to Low, look out below” (air pressure, that is)

Edited August 31, 2016 by rrohde

[Andrew-76]

Well that is the problem. I mean no radar altitude. Real barometric altitute can come in handy because lot of stuff is marked in this way. Like mountains height. So you want to know your "above sea leavel" altitude. Bud also "above ground". Especially when landing, right? So I'd somehow expect to change this settings depending if I'm in "fly" or "landing" mode. Before start I'd like to set "above sea level" zero altitude because I don't need airfield-zero for take off. When going to land I'd expect that airfield tells me their barometric pressure for zero altitude on runway so I can set my barometric altmetr to 0 on runway I'm going to land to. This may vary for same runway weather depended so you should recieve this information before landing (probably useless to write it into papers as it can vary). I'd expect to be able to ask ATC for this information but can't see it in radio option nor in papers (I looked into them just in case) to current airfield. So I'm confused. It is just my common logic, don't know how it work IRL.

[rrohde]

Points well made! Would be nice of ED improves the ATC system to such a realistic extent. Not sure if military airfields use ATIS, but McCarran sure does.

[rrohde]

Good points, bbrz. Didn't consider A/C performance in my statement.

 

Edit: Of course you could find that airfield elevation on the respective approach plate.

Edited August 31, 2016 by rrohde

[emko]

I'd also like the ATC to give me QNH. Civ air traffic usually use that - in EU when you ask for a flight clearance you have to tell them "I have info (some letter designating a time the weather information was issued, you get it by listening to ATIS) and QNH (e.g. 1013)". Flying even in IMC with just QNH and no radar altimeter is OK because you have to see the runway anyway (unless you are equipped for CAT-III ILS which allows for 0/0 visibility ... but how do you plan to taxi in these conditions?).

 

Imagine a very well equipped Champ or Cub flying to a local airport in Czech Republic (this is an official real world chart).

 

http://lis.rlp.cz/ais_data/aip/data/valid/a2-mt-ils22.pdf

 

You are Cat A aircraft (i.e. slow approach speed) and equipped (and certified) to do Cat-II ILS approach. You need to see the runway from 867ft MSL/ 58 ft AGL.

 

And on the top of the paper you see that the official airport elevation is 844 ft, but the runway threshold is 808 ft MSL.

 

Military aircraft and procedures are of course different. But if you know the QNH and runway threshold elevation, it's no problem. You just need to remember that the wheels will hit ground when the altimeter shows 808ft. No law requires airliners or private aircraft equipped for instrument flying to have a radar altimeter. Boeing and Airbus put it there for pilots' convenience.

Edited September 1, 2016 by emko

[Andrew-76]

Of course you could find that airfield elevation on the respective approach plate.

 

Airfield elevation is in papers (just be careful if value is in meters or feet, you may need to recalculate value to units you need), you can find it there ingame (also in F-10 map you can find it). But you need to flight perfectly straight (no altitude change) and then make change on your altimeter. I can imagine this approach is very open to inaccuracy. Set barometric value is just way better.

Edited September 1, 2016 by Andrew-76