Why does aviation still use imperial system?

[RDavies]

I have only recently started in the aviation game and I had expected that if any industry would have switched over to metric, it would have been aviation. Currently only Myanmar, Liberia and USA are the only countries clinging to imperial (Even the USA military started using metric years ago). A few countries do use metric for aviation, do you think Australia (or other countries) will eventually switch to metric for aviation?

 

 

[Old Koreelah]

Sadly we seem to be going backwards. When Oz metricated it became an offence for businesses to advertise products in imperial measurements. Now, three decades later feet, inches and other medieval units are again commonly heard and seen on packaging. Try buying metric drills.

 

At Ausfly I almost get into a fight with an American who was promoting Wankel engines; his brochures and signs contained only imperial units, including Fl Oz (whatever the hell they are) and pounds. I am well aware what aviation standards are, but I saw it as incredible arrogance or ignorance that he was trying to sell his products in our country, but refused to use our weights and measures.

 

Why can't Americans adapt like the rest of us?

 

 

[red750]

including Fl Oz (whatever the hell they are)

I'm sure you really know what a Fl oz (abbreviation for fluid ounce) is, OK, but if not, it is 1/20th of an imperial pint, or 1/160th of an imperial gallon. Equivalent of 28.4 ml.

 

 

[Old Koreelah]

Thanks Red. You've just pointed out the abso-bloody-lute absurdity of persisting with these strange units.

 

 

[Mriya]

To answer the basic question. Aviation hardware standards were established a while back now and have USA military origins (AN = Army Navy, MS =Military Std, etc). Civil Aviation in the USA adopted these standards and seeing as the US have been such a large player in aviation, these standards became common worldwide.

 

Of course some British aircraft from yesteryear use Whitworth hardware and with the rise of European LSA's we now see much more metric hardware in use too, however the AN, MS, NAS standards are so well established and proven it is hard to see a need to discard them.

 

 

[Camel]

I have only recently started in the aviation game and I had expected that if any industry would have switched over to metric, it would have been aviation. Currently only Myanmar, Liberia and USA are the only countries clinging to imperial (Even the USA military started using metric years ago). A few countries do use metric for aviation, do you think Australia (or other countries) will eventually switch to metric for aviation?

The main reason is for navigation, one degree of Latitude or longitude equals sixty nautical miles ( at equator ) .

 

Height in feet is for international reasons for separation, distance from cloud, visibity, runway length etc is expressed in meters usually in Australia.

 

 

[spacesailor]

O.K

 

The only absurdity of the french metric system is. If you put people on a desert island the would naturally end up with the OLD system based on practical application,.

 

The names for part/size would be different but would be interchangeable with the thousand year old system.

 

Could have used the German DIN system or even the Japanese system, wait till you see the french metric time they dreamed up for us.

 

spacsailor

 

 

[Ultralights]

Sadly, the ICAO convention, the convention where all countries agreed to use the same standards in aviation in regards to everything from distances, radio terminology, and most importantly, aircraft certification rules, so that an aircraft designed and built in one country can safely fly in another, was signed in Chicago.. im sure if it was signed in Europe, then it would all be metric.

 

 

[kaz3g]

One minute of latitude is equal to one nautical mile at any point on Earth. One minute of longitude only equals a nautical mile at the equator.

 

Lines of latitude are parallel so the distance between them remains the same.

 

When you are navigating at sea, the common way to plot a course is with parallel rulers to get the direction of a rose printed on the chart, and with dividers to calculate the distance against the latitude scale on the side of the chart. You find out where you are by shooting a sight with a sextant and looking at a set of tables in an almanac.

 

In the early days of sailing, when the great square riggers were coming from England to Australia along the Great Circle Route in the Roaring Forties, and in not much more than a month, they met the southern coastline with almost monotonous regularity because they could tell pretty accurately from sun shots what longitude they were at but had to rely on their chronometer's time keeping and log to calculate the latitude. That's why the south-west coast of Victoria is known as the Shipwreck Coast.

 

Kaz

 

I'm glad it stayed imperial because it would be too confusing to change at my age.

 

 

[facthunter]

Some countries use metric on the altimeters. Russia, Indonesia to name a couple. Vertical separation is usually 1,000 feet but you need more at higher levels. To use metrics you would be using some pretty odd numbers for similar separation. I've been operating planes where the fuel is loaded in Litres, the weight of which is the shown in Pounds (Lbs) on the load sheet and the flow rate and fuel quantity in US gallons. How's that for a set up to fail? Nev

 

 

[old man emu]

One good reason for using the American measurement system for hardware is that the American manufacturers are able to provide records of the source materials for each batch of metal used to make hardware. I've seen records which can be used to trace a batch of split pins right back to the pig of metal they wer made from, and I am confident that the pig can be traced back to the furnace.

 

When I was working for QED Hardware, I tried and tried to get this sort of information for metric hardware - for those of you who wanted it for your planes - but never could. Therefore, I never trusted metric hardware.

 

As for using a length measuring system based on a length we call a "foot", which is first divided into 12 equal lengths called and "inch", then (for aviation purposes) the inch is divided into eight equal parts. For really short distances, the one-eighth part can be further divided by 2 or 4.

 

In practice, the size of an item of hardware can often be estimated with a fair degree of accuracy through experience gained over the years.

 

AW sh!t. I can't carry on writing on this topic knowing that Maj is not here to read and comment on it.

 

OME

 

 

[DWF]

In the early days of sailing, when the great square riggers were coming from England to Australia along the Great Circle Route in the Roaring Forties, and in not much more than a month, they met the southern coastline with almost monotonous regularity because they could tell pretty accurately from sun shots what longitude they were at but had to rely on their chronometer's time keeping and log to calculate the latitude. That's why the south-west coast of Victoria is known as the Shipwreck Coast.

Kaz, I think that should be sun (or star) shots for latitude and the chronomoter for longitude.

Until accurate chronometers became available sailors were never sure of their exact longitude and so often bumped into Australia before they expected to.

 

DWF

 

 

[Soleair]

Why does aviation still use the Imperial system? For the same reason English is used as the lingua franca of the air - uniformity.

 

And it has to be accepted that America does account for a sizeable proportion of aeroplanes in the sky - even if they can't spell the word properly.

 

Bruce

 

 

[Neil_S]

....I'm glad it stayed imperial because it would be too confusing to change at my age.....

LOL - I feel pretty much the same, Kaz! However, I wish countries would either convert to metric, or not - rather than what they did in my home land of the UK where they have a half-arsed mix of the two. It is stupid going into a woodstore and buying 2 metres of 4 by 2 (as in 4 inches by 2 inches), and buying fuel from the servo in litres while car speedometers and road signs are still in miles per hour...

 

Cheers,

 

Neil

 

 

[facthunter]

The metric system is far easier. I do a lot of machining and fitting and work in both, which is an extra imposition. and workload Imperial threads are a nightmare but they do cover the situation. AN is a great system with reliable quality control

 

Weights and measures are weird. in imperial

 

Aviation as far as altimetry is concerned stick with 1,000s of feet rather than 1,000's of metres because ONE is too big but it's used for distance (Vis etc)

 

Oh Mr HART .What a MESS. Nev

 

 

[kaz3g]

Kaz, I think that should be sun (or star) shots for latitude and the chronomoter for longitude.Until accurate chronometers became available sailors were never sure of their exact longitude and so often bumped into Australia before they expected to.

DWF

Hi DWF. I'm glad you guys are ok after those devastating fires.

 

Yes, you are right...I had it back the front which was really stupid having talked about the uniform distances between degrees of latitude. Age!

 

As I'm sure you know, sun shots (yes, the stars can be used too but I'm a mug) were taken at midday and the difference in latitude made by a few of minutes of time was not of great consequence. The chronometer is much more important for getting longitudinal position because the calculation relies on the fact that the Earth's speed of rotation on its longitudinal axis is pretty much constant and, as it rotates through 360 degrees in 24 hours it will move through 15 degrees in just one hour. Knowing the local time (midday) and an accurate GMT allowed a calculation of the time difference and hence the longitude.

 

The other reason they bumped into the coast was sheer pigheadedness! Their egos were stroked when they made fast times and they hated to have to reduce sail at night even when they knew they didn't have far to go. The southern coastline was a bit of a trap being crescent shaped and with Tassie hanging there in the way as well if they were going on to Sydney Town.

 

The obstinacy of sea captains in those times is legendary. It was a fairly calm clear day in Port Phillip on 19 November 1865 when the City of Launceston departed Melbourne for the Heads via the West Channel. She was a steam-sail vessel under the command of Captain William Thom. She was destined for Launceston with a cargo of sundries, incl. brandy, port, rum, cigars, tea and boots and carrying sail as well as using her engines.

 

The ss Penola, a steel-hulled steamship somewhat larger than the CoL, had like wise departed Geelong and was steaming down channel to the intersection with the West Channel which both vessels approached at the same time. Their respective captains had a heated exchange regarding who had right of way, the Penola being on the right and the CoL having sails hoisted (but also steaming) (bit like the who's runway argument, isn't it?). The invective and intransigence of the two captains was only exceeded by their joint stupidity and the Penola neatly removed the first 20 feet or so of the CoL's bows causing the latter to sink.

 

Fortunately, the calm conditions and proximity to help ensured that no hands or passengers were lost. The CoL settled upright with the tops of her masts showing a couple of miles off Port Arlington. But that's not the end of the saga.

 

The CoL was carrying mail and quite a few valuables and attempts were put in train to have them recovered by putting salvage out to tender. McKay of Sunshine Harvester fame develope and patented his special lifting apparatus comprising a number of large leather bags attached to cables with each containing a rudimentary Kipp's apparatus....a container of hydrochloride acid and Zinc filings. He chartered the tender, Eleutheria and took her out to the wreck site. His divers went down and attached the various cables and tipped the canisters so that the acid and zinc filings were mixed. Large volumes of hydrogen gas were evolved, the leather bags filled, and with a quiet gurgle as the suction with the mud was broken, the CoL rose rather majestically to the surface.

 

The Eleutheria was brought hard alongside and her lines shortened.

 

Then one by one the leather bags tipped over, spilling their contents and the CoL returned to the bottom taking the tender with her!

 

I was working in the Maritime Heritage Unit when the site of the CoL was rediscovered in the mid 1990's and some quite amazing artefacts recovered for conservation.

 

Kaz

 

 

[sain]

Off topic a bit, but the Halifax incident makes some fascinating reading (and listening/viewing) on the subject of Captains and obstinence.

 

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

 

 

[Deskpilot]

What's the easiest to remember, 8ft X 4ft, or 2.4384meters X 1.2192meters. I seem to work with anything over an inch is imperial and anything less is millimeters. Comes from being a pom for half my life and an Aussie for the rest.

 

 

[Dieselten]

You may as well ask why aviation, shipping and the scientific and business worlds still use English - because no-one's come up with anything that works better and which people are prepared to adopt. It works, that's why.

 

The Germans persisted with units of angular measure called "grads" in which there were 100 grad in a right-angle and four hundred grads in a circle. Try buying a sextant, or a set-square, or a protractor, or a goniometer calibrated in grads these days (if you can still find a sextant for sale, that is.)

 

 

[kasper]

What's the easiest to remember, 8ft X 4ft, or 2.4384meters X 1.2192meters. I seem to work with anything over an inch is imperial and anything less is millimeters. Comes from being a pom for half my life and an Aussie for the rest.

But that's false logic:

My wing is 11m span with 15m^2 area ... nice round numbers because it was designed with metric in mind (in the 1980's in the UK!!)

 

But I turn it around and it's suddenly 36.09ft span and 161.4ft^2 area

 

It only easiest to remember when its whole numbers - regardless of unit of measure.

 

 

[facthunter]

Yes whatever it started out in will be whole numbers They round out to achieve it when you convert it gets messed up with awkward fractions. 360 divides by a lot of numbers.

 

The islamics invented "0" (zero) and must have been hard to sell at first.

 

What's the funny symbol you have there, Akmed?.

 

Oh it's nothing,. It's like a hole but not a whole, but when you put it near a one, it's ten. One more than nine..

 

You been drinking again, Akmed? ........... Nev

 

 

[Kamloops]

Here in Canada we are sort of on the Metric system.

 

But I and many others still use inches, feet, pounds etc.

 

Temperature is about all i like to see in metric.

 

 

[dazza 38]

When I was an Airframe fitter / aircraft technician on the General Dynamics F111 for eight and a half years I had the imperial system down pat.

 

Then I worked on the Tornado which was metric.

 

I have pretty much forgotten most of the imperial sizes. By that I mean. I could look at a ring spanner and tell what size it was without reading it. I can't do that now.

 

 

[Nightmare]

It's all a bit blended isn't it? Look at the VFR rules on keeping clear of cloud, 1500 metres horizontally and 1000 feet vertically, then you have nautical miles for distance over ground. Can't say aviation isn't a thinking persons activity, keeps the grey matter busy.

 

 

[Birdseye]

From the latest version of ICAO's Annex 5 is the following:

 

Table 4-1. Termination dates for non-SI alternative units

 

a) No termination date has yet been established for use of nautical mile and knot.

 

b) No termination date has yet been established for use of the foot.