QFE (Question For Experts)

[flo57100]

Hi there,

 

With the Viggen now in the air, QFE is now a very important information to know for weapons delivery.

 

So here is my question for experts: if during a flight I contact a JTAC who gives me coordinates and target elevation, is it possible to know or determine the qfe information for the target location ?

[SnorreSelmer]

Yes, if you take the difference in altitude from a known reference with QFE (like the starting airfield), then you should be able to add/subtract the number of mB needed to get the target QFE. There will be inaccuracies, but they should be manageable. This ofcourse has the prerequisite that you don't run Dynamic Weather

 

Remember, the swedish doctrine was to use the Viggen for pre-planned attacks against Russian forces on swedish soil, so they would have detailed knowledge of terrain, and could get barometric info from nearby weather stations. The AJS 37 wasn't really designed for CAS and loitering for targets. ;)

 

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[Essah]

Hi there,

 

With the Viggen now in the air, QFE is now a very important information to know for weapons delivery.

 

So here is my question for experts: if during a flight I contact a JTAC who gives me coordinates and target elevation, is it possible to know or determine the qfe information for the target location ?

 

Yes, We can figure out the right QFE for any given ground altitude with a little trick.

You have 2 altimeters with independent QFE settings, the Main altimeter (left of the radar scope) and the reserve altimeter (smaller and to the right of the radar scope), of which the main one is the one the computer derives information from. This will come in handy. Before take off we want to set the reserve altimeter to reflect sea level. simply check the field elevation for your starting base, and set the reserve altimeter to that. for example if homeplate is at 100 meters and we set the altimeter to 100 meters. 0 would be sealevel right?

great. now we have a permanent reference to sea level in our pit.

now when you receive target elevation from JTAC. lets say 250 meters ASL, what we have to do is level out, check our reserve altimeter reading and set our main altimeter to indicate an altitude 250 meters LOWER than the reserve altimeter. If the target was located below sea level like it can be in Nevada we would have to set the main altimeter HIGHER than the

reserve altimeter and voila we have the target QFE setting.

An example

Take off at 100 meters ASL: Secondary altimeter set to indicate 100 meters

In the air levelled off circling IP at 1000 meters ASL as indicated by secondary altimeter.

Target altitude 250 meters. We set our main altimeter to indicate 750 meters

(1000-750=750)

[Xxx]

An example

Take off at 100 meters ASL: Secondary altimeter set to indicate 100 meters

In the air levelled off circling IP at 1000 meters ASL as indicated by secondary altimeter.

Target altitude 250 meters. We set our main altimeter to indicate 750 meters

(1000-750=750)

 

(1000-250=750) I think a typo?

 

I really like this idea, can't wait to try it out since I like using JTAC! Although its outside the intended Sweedish mission methodology for the Viggen, which was to attack known Soviet targets, from a pre planned route. Nice quick method though.:)

 

The only question is what if the barometric pressure is different over the target, than the pressure at your take off airfield? Would this not affect the altitude?

 

I havn't checked, but if the pressure is constant over the DCS World map, then this should be ok.

 

Regards,

 

David.

Edited February 11, 2017 by Accipiter
my typo

[grunf]

 

The only question is what if the barometric pressure is different over the target, than the pressure at your take off airfield? Would this not affect the altitude?

 

I havn't checked, but if the pressure is constant over the DCS World map, then this should be ok.

The pressure doesn't matter, you're changing the altitude, and the difference in altitude is always the same, regardless of pressure :D. You just have to be in level flight when adjusting the altitude.

[JanTelefon]

I do like this solution until we can get a better way to extract QFE data from DCS via the F10 menu or otherwise. Great help. Rep incoming.

[flo57100]

Thanks for your answers, reaaly helpful :thumbup:

 

I will experiment asap :thumbup:

[alfredo_laredo]

The pressure doesn't matter, you're changing the altitude, and the difference in altitude is always the same, regardless of pressure :D. You just have to be in level flight when adjusting the altitude.

 

great trick, just a remainder, this only works as long as Pressure stays the same on all DCS Map (static weather), if using Dynamic Weather, Pressure changes and what was your ASL at airfield may not be the same 50 miles out.

 

JTAC should be improved by giving you the pressure at the target.

[Xxx]

great trick, just a remainder, this only works as long as Pressure stays the same on all DCS Map (static weather), if using Dynamic Weather, Pressure changes and what was your ASL at airfield may not be the same 50 miles out.

 

JTAC should be improved by giving you the pressure at the target.

 

Yes that's what I thought. Just leave dynamic weather off. Keep barometric pressure even, like a typical Anticyclonic weather system.

 

I would like to see the JTAC including pressure at target, I really enjoy using JTAC in the Hog and Ka50. With the Viggens Lola system, its ideal for quickly setting up targets from JTAC/AFAC. I can see some hours spent in the mission planner!:smilewink:

 

Regards

 

David

[grunf]

great trick, just a remainder, this only works as long as Pressure stays the same on all DCS Map (static weather), if using Dynamic Weather, Pressure changes and what was your ASL at airfield may not be the same 50 miles out.

 

JTAC should be improved by giving you the pressure at the target.

You're right, if the pressure over the target is different than over the starting point (dynamic weather), it will not work. I was wrong earlier. :music_whistling:

[unipus]

I do like this solution until we can get a better way to extract QFE data from DCS via the F10 menu or otherwise. Great help. Rep incoming.

 

You can do this now. The kneeboard has pages with data on all of your waypoints, including QFE. If you need to set a waypoint using new information, such as provided by JTAC, you can get LON/LAT from the JTAC/F10 map, input it into the computer, and save new waypoints. xxJohnxx just released a very good video tutorial on how to do this. I believe at that point your kneeboard should update accordingly... of course I could be wrong, and haven't tried it.

[Justin Case]

1 millibar is also about 8 meters of elevation. If QNH is 1000 and your target is at an elevation of 80 meters, target QFE is then 990.

 

You could also start from airfield QFE and work it out that way.

[SnorreSelmer]

You can do this now. The kneeboard has pages with data on all of your waypoints, including QFE. If you need to set a waypoint using new information, such as provided by JTAC, you can get LON/LAT from the JTAC/F10 map, input it into the computer, and save new waypoints. xxJohnxx just released a very good video tutorial on how to do this. I believe at that point your kneeboard should update accordingly... of course I could be wrong, and haven't tried it.

 

Tried it the other day, didn't work. But that was before the latest update I think, maybe they added that functionality now?

 

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[JanTelefon]

You can do this now. The kneeboard has pages with data on all of your waypoints, including QFE. If you need to set a waypoint using new information, such as provided by JTAC, you can get LON/LAT from the JTAC/F10 map, input it into the computer, and save new waypoints. xxJohnxx just released a very good video tutorial on how to do this. I believe at that point your kneeboard should update accordingly... of course I could be wrong, and haven't tried it.

 

The pre planned flights from the mission editor is no trouble at all, and punching in waypoints manually isn't the issue. Getting the proper QFE readout is. As of last night the kneeboard doesn't update when you punch in coordinates. If we could get barometric data from the F10 map that issue could be tackled. As is, we need to compare altitude differences between sea level and target, and that won't work with dynamic weather.

[grunf]

We should have a synoptic chart of the area, just as the mission planers IRL would have. :)

[Xxx]

We should have a synoptic chart of the area, just as the mission planers IRL would have. :)

 

The synoptic charts would provide QFF.

 

QFF = the actual pressure at a measuring station, reduced to mean sea level. It in essence is the opposite to QFE where QFE is the MSL pressure adjusted for the height of the staion. QFF is what is used on meteorological synoptics charts with isobars.

 

Given the mission objectives the Viggen was designed for, the current target derived QFE target setting, in the mission map and printed in the kneeboard, would seem fit for purpose.

 

However we always want our missions to do more! I would guess that in a more fluid battle zone, a JTAC would be equipped to provide an extra line of information, the QFE at the target.

 

So its down to some clever programmer with the ability to add a pressure reading to the JTAC target coordinates:book:

 

 

Great food for thought!:D

 

Regards

 

David.

[unipus]

Here's a bigger question: why can't we access the mission planner in multiplayer???

[xxJohnxx]

1 millibar is also about 8 meters of elevation. If QNH is 1000 and your target is at an elevation of 80 meters, target QFE is then 990.

 

While this is true in the real world in standard conditions (1 hPa = 8.3m) I found that there seems to be a diffrent pressure per meter change in DCS. Some testing I did showed that for a point at 2000m above sea level, the ratio seems to be more like: 1hPa =9.3m.

Wondering why that is the case. Maybe a DCS quirk?

Edited February 14, 2017 by xxJohnxx

[grunf]

I think the best solution would be to obtain the QFE from the F10 map, by hovering over a spot,just like the coordinates and altitude. But this should probably be asked in DCS whishlist.

[Fishbreath]

I think the best solution would be to obtain the QFE from the F10 map, by hovering over a spot,just like the coordinates and altitude. But this should probably be asked in DCS whishlist.

 

While we're at it, it would be nice if the atmosphere scripting environment object had a getQFE(Vec2 point) function.

[Justin Case]

While this is true in the real world in standard conditions (1 hPa = 8.3m) I found that there seems to be a diffrent pressure per meter change in DCS. Some testing I did showed that for a point at 2000m above sea level, the ratio seems to be more like: 1hPa =9.6m.

Wondering why that is the case. Maybe a DCS quirk?

 

The generalisation is only valid close to sea level, each unit of pressure represents a larger height deviation the higher you go. I don't know how accurate DCS is in this regard.

It wasn't a problem in the Swedish archipelago were it was intended to be used...so all we need is a Swedish map!

[SnorreSelmer]

...so all we need is a Swedish map!

When it was revealed on the Viggen live stream that a new map was in the early stages of planning or something, I was really excited. I'm hoping for a Baltic Sea area scenario as it would be perfect for a 70s/80s cold war scenario with the AJS-37, MiG-21, Mi-8 and the F-5...

 

 

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[Justin Case]

If we all remain good boys maybe Cobra Claus will bring us something nice!