General aviation and the metric system

[Spokes]

Hoping someone can help me out. I have a weight and balance app on the app store that is selling so-so. This app also incorporates some fuel use estimation routines. I have had some requests to incorporate the metric system into this app. right now its all pounds, gallons inches etc. My problem is that I really don't have any experience with aircraft that calibrate things in metric.

So, I am guessing kg, and cm are common for weight and station to datum measurements, as are litres and lt/hr for fuel. But for the fuel estimator, I have some questions. Are km and km/hr every used by our metric (I am assuming european) using pilots, or always knots and nm? What about meters for altitude, or is it feet and fpm for climb? meter/sec?

Any help would be appreciated. Thank you.

[lownslow]

If it were me I'd start with going to metric for all things fuel related, the sooner the better. After that, find out where the metric requests are coming from and find a community of pilots from that region to work with on any other necessary conversions.

LnS.

[AirFrame]

As someone who occasionally wants to mix metric and imperial units (fuel in liters, but weights in pounds), why not make every unit configurable? Apps that force me into all Metric, or all Imperial, are very annoying and usually get deleted after one or two uses.

[seasonaldriver]

generally, here in Canada fuel is sold/metered in litres, but in my experience, all weights are in pounds for fuel burn and weight and balance calculations.

[Heliian]

Datums are in mm, fuel in kg, wind speed in m/s, altitude in m, pressure in bars and milibars. Most of the world is using the metric system.

[wallypilot]

Altitude is only in meters in Russia, China and a few other places. Speed is always knots and distance is nm. Fuel is kg, aircraft weight is kg, and datum is mm. Wind speed is knots, but vis would be km. altimeter setting in hectopascals, and atmospheric pressure in mb.

It really does vary depending which area of the world you go to, so best to get specifics of where your client is using the app.

[Cessna driver]

I generally use:
Speed - knots or mph if in a piper
Altitude - feet
Fuel - when tellin rampies for fuel loads litres, burn rate pph or gallons
Distance - nm

[Spokes]

Thank you all for your help.

I know what you mean about mixing units. I have been in Kandahar the past 3 years, visibility here is always meters, but altitude is feet, and wind speed knots. Altimitry always both QNH and inches, although most controllers will drop the QNH if they are talking to an American call sign.

Regarding making everything configurable, yes this is a good idea and was my intention, Its good to not include units that are not generally used, and not to omit those that are. I wouldn't have thought that datum measurements would be in mm. clearly I was wrong.

I get that Knots and nm are used even in metric countries and why. I am still undecided if I should provide utility for km and km/h. I suppose if metric distances and speeds are not used in Europe where the bulk of my metric market is I probably will not, but not sure yet.

What about altimetry? Is there a metric standard for rate of climb? m/s m/min?

While I realize that the metric system is pretty much ubiquitous everywhere except in America, it also seem that most GA aircraft come from America. I am still not too sure how those two notions come together outside CAN/US.

Thanks again for the help,

Mike.

[BigglesNBella]

In China and North Korea they use metres for altitudes, Russia used to as well but recently switched over to flight levels in feet. Winds in Russian metars/ATIS are given in metres per second. Visibilities everywhere (except for North America it seems) are given in metres as well. Interestingly, Russian metars include altimeter setting (QNH) in hectopascals but they use a different setting called QFE that will read zero at field elevation. The Russians are weird like that!

Fuel is ordered in litres everywhere I fly except for the US.

[Panama Jack]

Not really sure what your app is or what it does, but here in my company, fuel is sold to us in either liters or gallons but we convert everything to kilograms. Fuel gauges and weight &balance is done in kilograms and, being a transport aircraft, %MAC.

Everything else is the traditional measures- even when operating to metric altimetry areas we have to calculate it over to feet.

A few places give wind speed in meters per second, but that is a simple conversion of multiplying by 2.

[Panama Jack]

In China and North Korea they use metres for altitudes, Russia used to as well but recently switched over to flight levels in feet. Winds in Russian metars/ATIS are given in metres per second. Visibilities everywhere (except for North America it seems) are given in metres as well. Interestingly, Russian metars include altimeter setting (QNH) in hectopascals but they use a different setting called QFE that will read zero at field elevation. The Russians are weird like that!

Was that way in Eastern Bloc countries. It's a commie thing.

[complexintentions]

In China and North Korea they use metres for altitudes, Russia used to as well but recently switched over to flight levels in feet. Winds in Russian metars/ATIS are given in metres per second. Visibilities everywhere (except for North America it seems) are given in metres as well. Interestingly, Russian metars include altimeter setting (QNH) in hectopascals but they use a different setting called QFE that will read zero at field elevation. The Russians are weird like that!

Fuel is ordered in litres everywhere I fly except for the US.

Actually I believe the use of QFE is more of an RAF throwback. Using it would screw up most modern E-GPWS systems but since they don't have anything modern enough for it to matter, well... Same could be said of the Russian hardware.

I think what Panama meant was that he orders fuel by weight, not volume. Then the actual amount of liquid delivered depends on specific gravity but I agree that the only place in the world that that amount is described in gallons is the US. But then...

Map of Countries Not Officially Using the Metric System



The use of metric for altitude is no big deal, any relatively modern airliner/bizjet has the capability to show both at the push of a button. If they're going to standardize anything, my vote for the most important one safety-wise would be the bloody transition level!

[Panama Jack]

I think what Panama meant was that he orders fuel by weight, not volume. Then the actual amount of liquid delivered depends on specific gravity but I agree that the only place in the world that that amount is described in gallons is the US. !

Thanks for clarifying what I was trying to say. Yes, USA in gallons and, strangely enough, Bahrain too.