Mainly a question for the SMEs: Why the blend of units?

[frostycab]

I'm curious as to why the Apache using metric units for range and speed measurements but still uses imperial for altitude and fuel flow. AFAIK all the other modern Western aircraft (except  maybe the Gazelle if my memory isn't totally awful?) use nautical miles and knots.

Please enlighten me so that I may become worthy. 

[Raptor9]

Because the Apache was designed to operate as an Army "maneuver" unit, just as other ground forces like tanks. These ground forces use MGRS, which is a metric based system.

This is why it has a blend of nautical mile/feet based measurements for speed, altitude and distance, but performs targeting in metric, with the option to also toggle distance calculations for navigation to metric as well.

The flexibility to integrate with multiple types of air and ground forces is also apparent with its integrated use of Lat/Long in its point file system.

As for fuel, I imagine it just makes it easier to manage munitions and fuel loads when they are all in a mass based measurement of pounds, versus having the fuel measured in volume in gallons.

Edited March 26, 2022 by Raptor9

[frostycab]

Cool! Yeah, sorry about the knots thing. I was thinking about the other helis and I think I got the Russian birds stuck in my mind.

I hadn't considered the integration with ground units, which I expect can be a major part in the daily life of an Apache pilot. having though about it now I wonder why there wasn't some concession made with the A-10 in that respect.

Altitude I have no problem with. Years of flying airliners in sims makes feet second-nature for me, and I struggle a bit with the DCS birds that use metres. Same for speed in knots. 

[frostycab]

20 minutes ago, kgillers3 said:

nah nah give it to @Raptor9 he answered first @frostycab

Apologies to Raptor9. I actually meant to click on Quote. (It's coming up on 4am here.) Corrected it now.

Huge respect to both of you for your insights throughout the forum though.

Edited March 26, 2022 by frostycab

[kgillers3]

 

[frostycab]

Can I ask another question on a bit of a tangent?

Does the Apache have any way of making offsets? For example, you get a call from a ground unit, saying something like "Enemy units entrenched 800m north of the water tower." Do you need to eyeball it, or can you mark the water tower and then plot a position relative to that mark?

[Frederf]

2 hours ago, frostycab said:

Cool! Yeah, sorry about the knots thing. I was thinking about the other helis and I think I got the Russian birds stuck in my mind.

I hadn't considered the integration with ground units, which I expect can be a major part in the daily life of an Apache pilot. having though about it now I wonder why there wasn't some concession made with the A-10 in that respect.

Altitude I have no problem with. Years of flying airliners in sims makes feet second-nature for me, and I struggle a bit with the DCS birds that use metres. Same for speed in knots. 

There was. The A-10 can be set to kilometers too.

[MAXsenna]

17 hours ago, Raptor9 said:

As for fuel, I imagine it just makes it easier to manage munitions and fuel loads when they are all in a mass based measurement of pounds, versus having the fuel measured in volume in gallons.

 

AFAIK fuel is always measured in weight, because weight doesn't change with altitude, (pressure). Volume does for liquids and gases. 

Think I heard this on the Fighter Pilot Podcast . 

Cheers! 

Edited March 26, 2022 by MAXsenna
Missing text

[frostycab]

Usually, yes. There are a few caveats to that if you expand it beyond DCS. I believe most light GA aircraft have fuel gauges in volume. It can get a little bit confusing when you come to commercial aviation too. Fuel is bought and paid for by volume, but for obvious reasons the crew and flight management computers reference weight. This means that any time they uplift fuel they need to do a set of calculations based on things such as the tested specific density of the fuel being supplied at that airport on that day.

[MAXsenna]

29 minutes ago, frostycab said:

Usually, yes. There are a few caveats to that if you expand it beyond DCS. I believe most light GA aircraft have fuel gauges in volume. It can get a little bit confusing when you come to commercial aviation too. Fuel is bought and paid for by volume, but for obvious reasons the crew and flight management computers reference weight. This means that any time they uplift fuel they need to do a set of calculations based on things such as the tested specific density of the fuel being supplied at that airport on that day.

That's what happened to that Canadian Air that sideslipped "into" a drag race, on an abandoned airfield IIRC.

Incorrect calculations by the ground crew or something.  

[frostycab]

27 minutes ago, MAXsenna said:

That's what happened to that Canadian Air that sideslipped "into" a drag race, on an abandoned airfield IIRC.

Incorrect calculations by the ground crew or something.  

Yeah. I believe what happened there was confusion regarding units. They'd worked out figures in kg, but the actual fuel was loaded according to lbs. I'd need to look up the incident to go into detail about it (or see the pretty good "made for tv" film again.) I do remember the PIC being hailed in the same way that Sully was.

[Rick50]

 

The Canadian Army, US Army and many other units use metric like KM (Kilometre, literally 1000 meters), meters and so on, largely because of the early days of the NATO treaty in the 1949.  We had to be able to work directly alongside, cooperatively, with dozens of European armies, seamlessly upon landing.

We'd be needing their maps too. The radio comms to call in artillery strikes, or to report enemy tank formations accurately that everyone could be certain of, SUPER important. The MLRS rocket systems are often referred to as "grid square removers"... a grid square is basically a square kilometre. 

So North American armies learned the Metric system and adopted the whole thing. Except that flying is still kinda mostly Imperial units! 

...

So MAX and Frosty mentioned the airliner... Back in 1983, an Air Canada airliner, Boeing 767, was on one of it's early flights, and the fuel unit measurements were in Kilograms instead of the North American common use of pounds of fuel. There was one or a few mistakes in converting the numbers, as the fuel provider could only read pounds, and also a system failure on the Boeing. 

The result? only 45% of the fuel needed for the flight. Ran out of fuel. Fly a loaded 767 with no engines... glide to land!  Read about it in the link below.

https://en.wikipedia.org/wiki/Gimli_Glider

Funny part is, the plane was later fixed, and spent a very long career until it houred-out for retirement! 

Edited March 26, 2022 by Rick50

[cordite]

3 hours ago, MAXsenna said:

That's what happened to that Canadian Air that sideslipped "into" a drag race, on an abandoned airfield IIRC.

Incorrect calculations by the ground crew or something.  

The airfield they chose was and is still in use, just not the runway they picked.

[MAXsenna]

The airfield they chose was and is still in use, just not the runway they picked.

Right! Long time since I saw the episode of Mayday/Aircraft Investigations.
Thanks!

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