How to get height above ground when over 5,000ft barometric?

[bbrz]

Precise enough because imacken assumed that the precision of RA is required.

[imacken]

Precise enough because imacken assumed that the precision of RA is required.

 

Don't know where that came from.

[Eviscerador]

You can set QFE on your altimeter in NEVADA and work with Nellis altitude as zero to ease your calculations.

 

Once the TGP comes, you will be able to read the GPS altitude of the designated point on there, like on the A10C.

 

Other than that, use the F10 map and do the math.

[bbrz]

You can set QFE on your altimeter in NEVADA and work with Nellis altitude as zero to ease your calculations.

? How would you do that since the altimeter setting range is only from 28.10 - 31.00.

[bbrz]

Don't know where that came from.

https://forums.eagle.ru/showpost.php?p=3988136&postcount=15

[imacken]

https://forums.eagle.ru/showpost.php?p=3988136&postcount=15

https://forums.eagle.ru/showpost.php?p=3988122&postcount=11

We're talking at complete cross purposes here!

[imacken]

? How would you do that since the altimeter setting range is only from 28.10 - 31.00.

This begs the question I've always wondered, what is the reason for this restriction?

[Ramsay]

You can set QFE on your altimeter in NEVADA and work with Nellis altitude as zero to ease your calculations.

AFAIK the weapons computer uses MSL (QNH) or the GPS reference ellipsoid for the aircraft's altitude and waypoint data or DTED for the target's elevation i.e.

 

• if you are are 25,000 ft MSL Baro and the terrain below at 5,000 ft MSL - you are assumed to be 20,000 ft above the target's elevation.

 

• if you set QFE so the baro reads 20,000 ft (at 25,000 ft MSL) and the terrian below is at 5,000 ft MSL - the weapons computer will assume you are 15,000 ft above the target's elevation.

 

You can set QFE for circuits if it's within the mechanical range of the instrument and QNE (29.92 inHg) for ferry flights/while enroute but AFAIK, you should/must set QNH when fencing in.

Edited July 25, 2019 by Ramsay

[Eviscerador]

? How would you do that since the altimeter setting range is only from 28.10 - 31.00.

 

IIRC nellis airbase is at around 1800 ft. That is around 28.20 on a sunny day. Of course if you have a low pressure front that's another story.

[bbrz]

IIRC nellis airbase is at around 1800 ft. That is around 28.20 on a sunny day. Of course if you have a low pressure front that's another story.

You don't need a low pressure front to make QFE unusable. KLSV 1870ft, KLAS 2181ft.

 

@imacken, mechanical precision/complexity? Furthermore since QFE usually isn't used, this adjustment range for QNH ops is sufficient.

[Fri13]

In the Harrier it’s the DMT/ARBS, in the Hornet/Viper the A/G radar should be used (this can be used to range the ground at altitudes much higher than your RADALT). I’m curious if this is currently reflected in the Hornets CCIP accuracy as it should substitute the need to know an exact target elevation.

 

 

 

According to Raytheon's fact sheet for the Paveway 2, 99 deliveries of guided munitions will yield a circular error probable (CEP) of only 3.6 feet (1.1 metres), versus a CEP of 310 feet (94.49 metres) for 99 unguided bombs dropped under similar conditions.

https://en.m.wikipedia.org/wiki/GBU-12_Paveway_II

 

It would be interesting to know what is that "similar conditions".

 

 

The targeting pods etc should be there to perform same capability as ARBS does, but A-G should be less accurate anyways, and if DCS would model then as well worse as ground units would detect the A-G radar emission.

 

And someone here mentioned that real pilots he has been talking to, said that the hornet A-G radar was mainly used against ships, instead on ground targets.

[Harker]

There are several ways to get a target's MSL elevation, like marking a point on the ground or using the TGP. Most of these ways require that your aircraft is equipped with DTED, so it knows the elevation of that point on the ground. In my understanding, these methods are 2D, so the DTED database is required.

 

Another way is to use A/G radar ranging, which can be most useful if the target is on a different elevation than the terrain under you. In DCS ou can see the effect of using radar ranging versus just the radar altimeter in the Mirage. It uses radar ranging when you activate TAS, in the A/G menu.

[Browny]

May be a silly question, but I've often wondered, how do you get height above ground when altimeters only show barometric over 5,000ft?

Hey mate the actual operational limits of the Hornet RADALT is 0 to 5000ft. therefore the RADALT won't operate above 5000ft.

[Fri13]

Hey mate the actual operational limits of the Hornet RADALT is 0 to 5000ft. therefore the RADALT won't operate above 5000ft.

 

I believe that the altitude radar would operate, but it would become too unreliable at the higher altitudes like 6000-7000ft so it is limited to be used at 5000ft. And that would give a high reliability and accuracy.

 

It is not that the altitude radars are binary by functionality, that it either can range distance or it can't. It is just that at some point the accuracy suffers too much and then it is not possible get the ranging each time, when the distance (altitude) gets longer.

 

So sure it can be said "RADALT won't operate above 5000ft" as it is the last height system uses and then it switches to barometric altitude, but it keeps continually ranging with radar if the terrain happen to come at range below 5000ft.