Altimeter settings when in Combat?

[Glamdring]

Just curious really. How do combat pilots set their altimeter when in combat? I'm assuming they don't always constantly change to and fro between QNH and STD when diving in on targets and climbing away from an engagement? Or do they?

[SASless]

Why Dear Boy....would they not want to use QFE so they would know how high above the target they are when they drop their bombs?:E

They sure don't want to get below about 15,000 feet or anything....as there's folks down there that would shoot at them if they did!

[Lima Juliet]

AWACS or ASACS normally gives out a mission QNH of some sort. Most jets have a RADALT and/or GPWS with a terrain database.

I hope that answers your question?

LJ

[newt]

Biggest altimeter in the world! The ground!:ok:

[ORAC]

Playing "hard floor", huh Newt?

[Trim Stab]

GPWS with a terrain database.


Where do the terrain databases come from?

Clearly accurate topographic data is available in the UK training areas - but there are lots of places around the world which have not been ground-surveyed accurately - e.g. where does the Afghan data come from? I would guestimate satellite imagery can only produce topographical maps to about 20m vertical accuracy - is that good enough?

[ORAC]

Barometric is no more accurate in regional QNH, Radalt can be confused by snow and trees/brush. Even the Mk1 eyeball can be fooled flying into rising ground. I knew a Jag pilot who just about did something in his flying suit when flying at what he thought was about 100ft over a snow covered pine planation. Something clicked and he realised he was at about 10-20ft over newly planted saplings....

[Sandy Parts]

1013 was always my preferred option - especially during our overland sorties!! :)

[newt]

The only way ORAC old chap! 1013 very useful for low level abort!:ok:

[SASless]

ORAC......were Jag Pilots as slow as the aircraft?:uhoh:

[Bob Viking]

Sasless.
You are misinformed old chap. The Jag didn't have too many problems with speed once you got her up and running. Turning on the other hand...
As for the mental agility of the pilots? Well that's not for me to say.
BV

[pontifex]

Re ORAC's post. One of my ex students was killed flying a Harrier in Norway many years ago. He'd had been accustomed to the size of the trees in Scotland but the smaller Norwegian ones caught him out.

[Glamdring]

Thanks chaps. So generally they use a single setting throughout a mission?

[Sandy Parts]

errr - just to clarify - my (flippant) remark re SPS (1013) was due to the fact that using that meant we were (usually well) above transition alt and therefore nice and safe! Unlike the steely-eyed fighter/bomber types who would use whatever appropriate while they were working below us, we multi-types were happiest up above all threat ceilings (hopefully...)! Maybe you could re-phrase the question to indicate exactly which type of aircraft and what type of combat you meant? The answers will be different depending on the type and role. Thought I'd better explain in case there is a serious reason for the query (in which case, why ask on here ;)?)

[Glamdring]

Maybe you could re-phrase the question to indicate exactly which type of aircraft and what type of combat you meant? The answers will be different depending on the type and role. Thought I'd better explain in case there is a serious reason for the query (in which case, why ask on here ?)

Nothing serious in the query just a curiosity. Take for example an A10 providing CAS. Would it set the QNH before takeoff and keep that set until landing? Or would they use STD while above the TA en-route to the combat area and then switch to QNH?

[xray one]

"Hard deck my arse...we nailed that sucker"

[Lima Juliet]

Trim Stab

I would have thought your TA time would have told you about DTED? DTED - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/DTED) There are other formats available military applications. The exact fidelity of the terrain sample is obviously classified.

LJ

[Lima Juliet]

Glamdring

Usually there would be a force QNH that you set as you go 'sausage side' and that would allow friendlies to try and stop bumping into each other (part of the battle!). Outside of the fighting area then we go into the peacetime zone and its procedures - SPS above TA, regional QNH and QNH/QFE at the air base.

LJ

[Trim Stab]

Leon - yes I do know this in considerable detail! I fly as a survey pilot, so my current job entails building topographical maps in remote parts of the world. But even flying low and slow, with large format vertical cameras and the best available civilian IMUs, and then sending out ground surveyors to get GCPs (in order to pin the 3D map to a datum such as WGS84 or DTED, or any of the other standards), we cannot get much better than a metre vertical accuracy. So I would question the accuracy of topo maps in some remote areas of the world if they have only been satellite surveyed and are too hostile/remote to obtain accurate GCP data.

[Lima Juliet]

Trim

The Space Shuttle using a RADAR surveyed about 90% of the globe with a 10m accuracy (about 30ft or 1hPa) about 10 years ago. There are other more advanced satellites that can map terrain to far higher tolerances.

I'll take a 30ft accurate terrain database, linked to a RADALT, any day over a barometric instrument.

LJ

[Trim Stab]

I have no direct knowledge of latest military satellite capability but the onboard processing capability and downlink bandwidth must be pretty mind-bogglingly expensive if they compete with aircraft systems with onboard storage that can be downloaded on the ground. Probably not a problem for US DoD I suppose.

Out of interest, I've recently been doing some trial flying of a high-resolution 3D oblique camera (UltraCamOsprey (http://www.microsoft.com/ultracam/en-us/UltraCamOsprey.aspx)) that uses cloud point technology to make 3D images of ground features to within few cm accuracy - definitely has some useful military recon utility. Certainly a lot better than the crappy old 2D Leica images we used to have to plan from!

[Lima Juliet]

Trim

Even in the commercial satellite world you can get over 300 mega bits per second (mbps) down a single transponder. So downloading data at that rate wouldn't take long.

LJ

[unmanned_droid]

TS,

What's the ball park costs of one of those Osprey Cams?

[Trim Stab]

Leon - yes, I agree you can get high bit rate - but the amount of bits is very large - much higher than even HD video. All the raw images are huge bit-map files, and each image has to have 60-80% forward overlap with its neighbour, and about 30% side lap to get sufficient trigonometric accuracy. Transmitting raw imagery to the ground would be inefficient - presumably there is some automated onboard processing - but without some sort of human control in the loop there must be some degrading of the image quality. As I said, it must all add up to some ferociously expensive data. Also military satellite imagery is usually only something like 40cm/pixel resolution - we fly down to 3cm/pixel, which is approx 1000ft AGL and just a few knots above stall speed to give the camera time to write the image file between shots.

[Trim Stab]

TS,

What's the ball park costs of one of those Osprey Cams?

About €1m. The 3D images they produce are astonishing. Another unintended benefit of the oblique lens is that you no longer have to fly directly over your target.

[AutoBit]

STD is used in areas where a Force QNH is not available. If the pressure is above 1013, no problems as you'll always be on the high side. Below 1013 you apply a correction (usually the job of the wingman to work out while you get yourself sorted).

Interestingly in some areas tgt deconfliction is a higher safety concern then enemy action, hence everyone needs to be on the same setting.

[FanstopFlameout]

Bastion QNH. At all times.

[just another jocky]

The same as everyone else around you when actual height above the ground was relatively unimportant and not hitting anyone else was very important.

When IMC, day or night, GPS height would give you a good idea, especially in mountainous terrain. Ally that to TFR, Rad Alt and GPWS and you were pretty well covered.

I guess it's all theatre dependant.

[polomint]

In the UK, if the FJ are being controlled by GCI, they will be passed the lowest QNH for the region they are working. If they are above FL245 in deconflicted airspace, it doesn't matter, they stick to the QNH.

The main reason for not switching to SAS (and I'm sure I will be corrected if I'm wrong), is that obviously everyone needs to be on the same setting, so, in the heat of a fight, you cannot guarantee that all players will switch between QNH/SAS.

In terms of separation against other traffic, GCI will pass the restriction in flight levels above FL245 and let the crews work out the difference. GCI will have also worked out the difference for below 245, but, can advise the crews if it particularly quirky.