Jump to content

DAMN IT. I JUST DONT GET QFE 2 QNH SETTINGS in F-5E


DaveRindner

Recommended Posts

Ok so once again what does the following mean.

 

"QFE is given X'' Hg then X+55 hPa is X+0.162''Hg. (1 hectopascal = 0.029529... inch of mercury)."

What is .162" what is it? What do I with this. I think at this, I am not getting an acceptable explanation.

58 HPa * .029529 = 1.71

Link to comment
Share on other sites

tom_19d Thank you.

 

So, OK lets work this. I am flying into moderately high elevation field, with elevation of 1840'. My origin was, for sake of argument, 1000 miles away with different weather and visibility. I take off and climb. I enter initial transition altitude of 18,000 feet above MSL. At this point of mission, I set my altimeter to standard pressure 29.92. Then I climb to 30,000 feet and continue on to destination. At 50nm out I notify ATC as inbound. ATC gives me QFE of 28.50. As part of my prelanding checklist I calculate proper Altimeter setting. With destination field elevation of 1,840 feet above MSL. I calculate as following. (Field Elevation in feet / 1000)+QFE = Altimeter setting for destination field (aka QNH)

((1840) / 1000) + 28.50 = 30.34

I descend to 15,000 feet and set my altimeter setting to 30.34

When I land the altimeter height should read about 1840 feet.

 

So is this correct?


Edited by DaveRindner
Link to comment
Share on other sites

I am curious. In real world of 1970 and 1980's when F-5E was in service with Brazilian, Thailand Taiwan, Swiss, S.Korean and other US allied air forces. How did the pilots handle IMC approach and landing, without radar altimeter , inertial navigation,and ILS. Air patrolling is a 365 24.7 operation, in all sorts of weather.

I imagine those air forces ordered their F-5Es with all weather operation capability.

 

DCS: F-5E, as flight instruments go, it is no more complex then Cessna Skymaster. Basic 6-Pack.

Airspeed, Art.Horizon, altimeter(barometric), turn and slip indicator, horizontal situation , and air speed. Rest is engine, fuel, and stores management.

Link to comment
Share on other sites

Hi Dave, that math looks great to me. And correct, doing it that way, when you land your altimeter should indicate field elevation, 1840 feet MSL in this case.

 

You should be able to practice this in game by flying into the Russian fields where they give QDE and checking your work in good weather, I have tried it a few times myself since this thread started without issue, so if you have any problem in the sim let me know.

 

PS: at least in the US we transistion to QNH as we descend through 18,000, but I don't think anyone in the sim will complain if you switch over at 15k haha. Plus different countries have different rules anyway.

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

TM Warthog HOTAS - TM Cougar MFDs - CH Pedals - TrackIR 5 - Samsung RU8000 55”

Link to comment
Share on other sites

Yes, in USA+Canada transition altitude , is 18K feet.The purpose of transition altitude is so regional ATC can stack aircraft so there is at least 1,000 feet vertical separation , and everybody setting standard day 29.92 settings insures that every crew has precise calibrated altitude above MSL.

 

Still, if F-5E with instruments from DCS: F-5E finds itself in inclement weather on approach with low , less then 5 nm visibility, how are they supposed to land. Does the ATC guided them to starting point for final, and rest is up to the crew , working with Outer and Inner marker, but no ILS?

 

See I am hazy on IMC navigation in F-5E. Without using theater map view, and without cheating marker position on kneepad, and with overcast low visibility, exactly how does the pilot know where he is. As F-5E has no inertial, no moving map, no GPS. Would he use TACAN to align with runway?

Why do I bring this up. Two words John Kennedy Jr. and his foolish attempt to fly in IMC, when he was not yet qualified for instrument flight. He got lost, lost his SA, and spatial orientation. He would have eventually run out of fuel.

Link to comment
Share on other sites

You nailed it with TACAN in this instance. A published TACAN approach is essentially a civil VOR/DME approach and can be conducted without INS/GPS or any of the other avionics you mentioned. (Be careful with a radar altimeter by the way, outside of very specific cases (CAT II and III ILSs that some of the airline guys here could tell you about) radar altimeters are never relied upon in IFR. They are only a situational awareness tool. Also remember the military has the ability to conduct PAR (Precision Approach Radar) approaches in which a controller talks the airplane down laterally and vertically to basically ILS minimums.

 

Here are the 476th vFs airport pubs. If you open up either the Geogia or Vegas books you can find many TACAN approaches that are useful for the F5.

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

TM Warthog HOTAS - TM Cougar MFDs - CH Pedals - TrackIR 5 - Samsung RU8000 55”

Link to comment
Share on other sites

I live in LA. Somewhat close, but not too close to LAX. LAX is IMHO is 405 Rush hour of airports. Anyhow, the pattern for LAX is that departures go over the ocean, arrivals follow a flight path over land. The aircraft on final are so close together, it is mesmerizing to say the least. On a good night with little haze/smog you can see the dozens of airliners on final , like beads on a string. You can almost imagine and , in your mind's eye, draw the ILS beam that those aircraft are using. But sometimes , here in LA, we get really fierce low clouds and fog. Fog dense enough , to make driving hazardous. From cockpit, all you would see is grey, white, blush, vapor and with no visibility. No break in the clouds. Yet the LAX tower keeps em landing and departing. Southern Cali, IMHO is way to complicated of airspace to enjoy flight. Especcially along the coast between LA and San Diego. We got LAX, Burbank, Ontario, Anaheim, Santa Monica, Van Nyes, San Diego, Coronado NAS, Camp Pendelton, and Vandenburg AFB, China Lake, and Pt. Mugu. That is a lot of fields and air traffic crammed into one area. How all this works with in severe IMC without CFIT or inflight collisions, is beyond me.


Edited by DaveRindner
Link to comment
Share on other sites

Your 58 hPa to “ Hg was wrong.

I wasn't converting 58 hPa. In DCSTbilisi is not 58 hPa above sea level because Tbilisi is not elevation 1624', it is 1526'. Real life Tbilisi might be 1624' but in DCS it is not. The correct number is 55 hPa for DCS. You cannot use real life charts for DCS as DCS is not an accurate representation of Earth.

 

58 hPa is 1.71 inches of Mercury not .162.

Sorry, type I mean 1.62 inHg not 0.162. But 58 hPa is wrong as a starting point. 55 hPa x 0.029529"Hg/hPa = 1.62"Hg.

 

If you have difficulty converting p.s.i. to atmospheres to millibar to bar to Pascal to kiloPascal to hectoPascal to milometers mercury to inches mercury then that is something to practice. They are all just pressures in different units. I'm sorry that the chart was in hPa. I didn't write the chart!

 

55 hPa is:

0.7977075575 psi

0.0542807797 atm

55 millibar

41.253392549 torr

41.253506548 millimeter mercury

1.6241532256 inch mercury

Whatever pressure units you're using, add the pressure to the pressure. 25.23 + 1.62.

 

If this seems like an annoying problem then you understand correctly. No air force would do this to their pilots. The F-5 pilots will receive QNH from air traffic control as a rule. Even Soviet pilots with special altimeters that can adjust very low will be told something else than QFE if the situation calls for it. Real air forces do not make the lives of their pilots difficult on purpose.

 

It should be remembered that QFE-to-QNH is not a magic number to add to exactly convert in all weather.

SLT -40C QFF 29.92 QFE 27.93 QNH 29.525 Δ 1.595

SLT +40C QFF 29.92 QFE 28.43 QNH 30.05 Δ 1.620

The amount you add is less when the temperature is cold and more when the temperature is hot. In this case the error is very small and even an ILS flown to CAT I minimums it would not cause any safety issue.

Link to comment
Share on other sites

Prior to takeoff, or even en-route, just reference the F10 map and look at the airfield info for your destination. Whatever you see in the field elevation, that is the altitude you will see on your barometric altimeter upon touchdown. If you want a meaningful decision altitude on an instrument approach on when you should execute a missed approach if you don't see the runway, simply add 200 feet to the field elevation. When you see this value on your altimeter on the approach, execute a missed approach and try again, or proceed to your alternate airfield.

 

What I'm trying to explain to you is NOT to use the QFE. It's not a common practice in a lot of ICAO countries, and is never used (as far as I've experienced) in FAA airspace. I know DCS World uses it, but DCS has been using pretty much the same ATC system for almost 10 years. And it is not accurate at all to real-world ATC, it's at best a placeholder system.

 

 

 

Some aircraft aren't even designed to be used in this way. The reason the standard barometric altimeter used in the F-5 (and a lot of other western aircraft) can't go that low on the pressure setting knob is because they weren't DESIGNED to, because western flight procedures don't use it. But DCS started being based around Russian regions and Russian aircraft, which do use QFE. And unfortunately the ATC system has never been updated to account for western maps like Nevada or western flight procedures.

 

Ive never seen QFE used in North America.

 

When you get the altitude using F10, what is it, true, indicated, pressure, or denisty altitude?

 

Without ever paying attention, I was kind of thinking it must be true altitude. If this is the case, referencing it to set the altimeter is a bad idea at altitude, because it is not safe to assume standard temperature and you will get errors magnified down low where accuracy is even more critical.

 

Using normal settings on the altimeter, if it’s colder than standard, pressure levels are more tightly packed, so your true altitude will be less than indicated altitude. This is why approaches sometimes require cold weather correction.

 

I’m with you on most of this, and Especially on your recomendation not to use QFE. My preference would be to stick with the western convention for local altimeter and pressure altitude afte climbing above the transition level.

6700K@4.6 48Gb - 1080Ti Hybrid - Warthog - RIFT

Link to comment
Share on other sites

When flying into Moscow ATC always issues the QFE. After receiving the QFE during the descend you ask for the QNH. After that you set the QNH as usual and use the conversion table that's provided.

 

Temperature correction is only applied for low temp.

 

Thanks for that... So, when you say ATC, are you talking the tower, approach, or what? Just curious because if you have two airfields at different elevation nearby, and aircraft all using QFE going into each are talking to the same controller, this could be a great source of confusion and could lead to worse. If we’re just talking about traffic for one airport, fine, but otherwise it’s a bad idea all around.

 

It’s also confusing to think some airplanes will be using QNH and others QFE. More potential for misunderstandings.

6700K@4.6 48Gb - 1080Ti Hybrid - Warthog - RIFT

Link to comment
Share on other sites

Thanks for that... So, when you say ATC, are you talking the tower, approach, or what? Just curious because if you have two airfields at different elevation nearby, and aircraft all using QFE going into each are talking to the same controller, this could be a great source of confusion and could lead to worse. If we’re just talking about traffic for one airport, fine, but otherwise it’s a bad idea all around.

 

It’s also confusing to think some airplanes will be using QNH and others QFE. More potential for misunderstandings.

 

This situation is not unique. SoCal approach works dozens of airports and local altimeter settings can vary by quite a bit despite the relatively close proximity. As an example, it would not be uncommon for one aircraft to be given a QNH of 29.78 at say, Victorville, while another aircraft on the same frequency might be given a QNH of 29.99 for their approach into Ontario. The ATC in DCS is not really set up for something like this which is why I don’t use the dynamic weather option and just set the QNH given in the briefing.

Link to comment
Share on other sites

This situation is not unique. SoCal approach works dozens of airports and local altimeter settings can vary by quite a bit despite the relatively close proximity. As an example, it would not be uncommon for one aircraft to be given a QNH of 29.78 at say, Victorville, while another aircraft on the same frequency might be given a QNH of 29.99 for their approach into Ontario. The ATC in DCS is not really set up for something like this which is why I don’t use the dynamic weather option and just set the QNH given in the briefing.

 

I get where you are going with this Midnight but I think this is apples to oranges. I won't disagree that there can be differences between the altimeter settings at the fields SoCal TRACON covers (even for a single controller). But lets do some math. 29.78 (1008.5mb) to 29.99 (1015.6). Granted, I admit this is a large discrepancy (basically 200 feet) between indicated altitudes of airplanes that might only be 34.2 nm (ONT to VCV, 63 km) apart.

 

However, consider that according to Ahrens' "Meteorology Today" 8th edition a storm in 1998 flipped over trucks and ripped the roofs off houses with a pressure gradient of only 32 mb per 500 km (1 mb per 16 km). Google pressure gradient force and you will find a set of slides from the University of California Irvine that associates tornadoes and hurricanes with pressure gradients of 1 mb per 6 km. Your example has a pressure gradient of 7.1 mb per 63 km, or 1 mb per 9 km. So your example requires something WELL beyond a normal Santa Ana wind and closer to a hurricane to be valid. (1/16 for 90+ knot winds, 1/9 for your example, 1/6 for a hurricane).

 

Conversely, take Centennial airport in Denver and Denver International. They are 19 nm apart and have a field elevation difference of 451 feet. If Denver approach used QFE, aircraft taking off 19 nm apart would have a difference of 451 feet between their indicated altitudes at the moment of takeoff, every single time. Then mix in all the VFR traffic in the area (just like in SoCal) and imagine trying to deconflict that as a controller. Of course, if it is like Bbrz says and a single controller rarely works multiple fields, this isn't a problem, but in your example this isn't the case.

 

Maybe I am missing something here or I have some math or meteorology wrong (please point it out if I do!) but I think Cake has it correct here. Sure there can be some slight variations with QNH across a sector but NOTHING like QFE would create.

Multiplayer as Variable

 

Asus Z97-A - I7 4790K - 32 GB HyperX - EVGA GTX 1080 Ti - Corsair 750i PSU

 

TM Warthog HOTAS - TM Cougar MFDs - CH Pedals - TrackIR 5 - Samsung RU8000 55”

Link to comment
Share on other sites

Maybe I am missing something here or I have some math or meteorology wrong (please point it out if I do!) but I think Cake has it correct here. Sure there can be some slight variations with QNH across a sector but NOTHING like QFE would create.

 

Yes, thanks. This is exactly my point. Not a problem below the flight levels using QNH, but QFE is a problem, and I'm sure that's why they don't do it in the states.

 

Another example of two nearby airports is Boise (KBOI) and McCall ID (KMYL). It's just a short 80 nm hop between Boise (2871.4 ft. / 875.2 m) and MCall (5024.2 ft. / 1531 m). Salt Lake City Center handles MYL and BOI, but BOI is also handled by Big Sky Approach. Using QNH, the setting betwwen the two will most likely differ, but not usually enough to cause a problem

 

Let's say we use QFE. If two jets are flying between the two airports in opposite directions they are likely less than 10 minutes apart. Say the aircraft leaving BOI is using BOI QFE and indicating 10,000 ft. Assuming ISA, true altitude would be about 12,900 ft. An aircraft leaving MYL using QFE and indicating 8,000 ft would be at approximately the same true altitude. See the problem?

 

Also, MSA is probably something like 11,000ft MSL in between them.

 

Talk about confusing. Now imagine a lost comms situation, aircraft to aircraft communication, or inexperienced pilots using the wrong settings for an approach, or a diversion after a missed approach. I think the QFE system is WAY less safe. I understand it is used in places, but just to have the field indicate zero?????

 

As far as DCS is concerned, I think we should be getting the way it is done in the local we are flying. I also think think there should be options to:

 

Respond to the radio checkin with

(a) the altimeter given or

(b) a QNH request if appropriate.

 

Furthermore, I think the act of responding through the DCS comms menu should also set the aircraft altimeter(s) accordingly.

  • Like 1

6700K@4.6 48Gb - 1080Ti Hybrid - Warthog - RIFT

Link to comment
Share on other sites

I get where you are going with this Midnight but I think this is apples to oranges. I won't disagree that there can be differences between the altimeter settings at the fields SoCal TRACON covers (even for a single controller). But lets do some math. 29.78 (1008.5mb) to 29.99 (1015.6). Granted, I admit this is a large discrepancy (basically 200 feet) between indicated altitudes of airplanes that might only be 34.2 nm (ONT to VCV, 63 km) apart.

 

However, consider that according to Ahrens' "Meteorology Today" 8th edition a storm in 1998 flipped over trucks and ripped the roofs off houses with a pressure gradient of only 32 mb per 500 km (1 mb per 16 km). Google pressure gradient force and you will find a set of slides from the University of California Irvine that associates tornadoes and hurricanes with pressure gradients of 1 mb per 6 km. Your example has a pressure gradient of 7.1 mb per 63 km, or 1 mb per 9 km. So your example requires something WELL beyond a normal Santa Ana wind and closer to a hurricane to be valid. (1/16 for 90+ knot winds, 1/9 for your example, 1/6 for a hurricane).

 

Conversely, take Centennial airport in Denver and Denver International. They are 19 nm apart and have a field elevation difference of 451 feet. If Denver approach used QFE, aircraft taking off 19 nm apart would have a difference of 451 feet between their indicated altitudes at the moment of takeoff, every single time. Then mix in all the VFR traffic in the area (just like in SoCal) and imagine trying to deconflict that as a controller. Of course, if it is like Bbrz says and a single controller rarely works multiple fields, this isn't a problem, but in your example this isn't the case.

 

Maybe I am missing something here or I have some math or meteorology wrong (please point it out if I do!) but I think Cake has it correct here. Sure there can be some slight variations with QNH across a sector but NOTHING like QFE would create.

 

Holy cow that's some detailed analysis! :) My only point was that the ATC system in DCS is wholly unsuited to detailed (or even realistic) altimetry, especially for "Western" style flying. I will admit, my example might be a bit excessive, but remember there is a mountain range between ONT and VCV, so some pretty significant differences can, and do often exist. I really wish ED would make the sim ATC capable of reporting QNH, but this is a combat oriented sim and the nuances of altimetry are not what its really about. Setting the weather as static and using the briefing QNH works fine for my purposes.

Link to comment
Share on other sites

Not a personal attack on you MidnightZulu... but I really dislike people making the excuse that this is an combat sim so its okay.

 

Everyone sets their altimeter (well I can't really say it happens everywhere; grass strips in the boonies where a guy might not care, but in the major areas like LA where I learned) Its so basic its taken for granted... that is until you come to DCS. Its not a good excuse... its within the very fabric of flying in the real world and it should be in this sim.

 

On my very first flight lesson I was introduced to dealing with the radios and setting the altimeter. I learned out of KLGB so had to do the full listen in on ATIS (set altimeter), then contact clearance delivery, ground, and finally tower to get airborne... all on my first flight.

 

I can't say my experience is universal but I bet its close.

 

ETA: I mean having to contact ATIS and then set altimeter, and use radios in some fashion when starting.


Edited by aileron
Link to comment
Share on other sites

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...