What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Why degrees Celsius?

So I drove 30 km to the airport today at an average speed of 60 km/h. I bought 60 l of gasoline for my car and 25 US gallons of gasoline for my airplane.

I flew at 150 knots to Victoria over the water at 4500 ft. The pressure was high (30.15 inHg) and the OAT was 10 degrees C. Best climb rate to clear a fog bank was 1400 fpm. My loaded weight was 1700 lb (f). Victoria tower was on 119.10 MHz. Wind was from 260 degrees, 15 Kn

Pop was a loonie ($1), coffee was a toonie ($2). Welcome to Canada, home of the loonie-toons!

I'm sure glad metric has simplified everything!

Vern
 
When I fly my glider speed is in knots, altitude is in feet and cross country distance is in km (and cross country speed km/h), water ballast is in kg (=liters) or lbs (or cans - one can is 25 lit or 50lb). Pressure settings are in mbar (in fact I don't care what it is I just set the number on the radio on the dial :))

When I fly my aeroplane speed is in kt (or mph on the outer scale!!), altitude is in feet, and cross country distance is in nm, fuel is bought in litres (to make the price sound reasonable) but gauged in US gallons.

If I ever get temps in C and want F I just double it and add 30.

Money should never have changed from £sd as base 12 better, but most can't do the mental arithmetic in anything other than base 10.

The one saving grace of the metric system is for anything to do with Newton's 2nd law. F=ma works in metric and fundamentally doesn't imperial. I can never remember what a slug is, or how to frig with lbf to get it to work. In the metric system it just works better (OK I know mass has to be in Newtons). If I ever have to work the lift equation I will always do it in metric (or SI) units and convert back to stall speeds in knots - I don't even know what the density of air is in imperial (1.225 kg/m^3).

Pete
in Blighty

PS For Rick, I did my apprenticeship at BAe Kingston (nee Hawkers) as the Hawk production was winding up. It was designed from the ground up as a metric aeroplane as the UK was just changing over in the 70s. We had several training exercises that weer dimensioned as 25.4mm x 50.8mm to get us sued to it (so we turned the ruler over). But then there were the Harriers across the isle that were (are still are) imperial aeroplanes. I would still rather work a lathe in thou than whatevers of a mm.
 
Last edited:
Being pedantic

penguin said:
When I fly my glider speed is in knots, altitude is in feet and cross country distance is in km (and cross country speed km/h), water ballast is in kg (=liters) or lbs (or cans - one can is 25 lit or 50lb). Pressure settings are in mbar (in fact I don't care what it is I just set the number on the radio on the dial :))

When I fly my aeroplane speed is in kt (or mph on the outer scale!!), altitude is in feet, and cross country distance is in nm, fuel is bought in litres (to make the price sound reasonable) but gauged in US gallons.

If I ever get temps in C and want F I just double it and add 30.

Money should never have changed from £sd as base 12 better, but most can't do the mental arithmetic in anything other than base 10.

The one saving grace of the metric system is for anything to do with Newton's 2nd law. F=ma works in metric and fundamentally doesn't imperial. I can never remember what a slug is, or how to frig with lbf to get it to work. In the metric system it just works better (OK I know mass has to be in Newtons). If I ever have to work the lift equation I will always do it in metric (or SI) units and convert back to stall speeds in knots - I don't even know what the density of air is in imperial (1.225 kg/m^3).

Pete
in Blighty

PS For Rick, I did my apprenticeship at BAe Kingston (nee Hawkers) as the Hawk production was winding up. It was designed from the ground up as a metric aeroplane as the UK was just changing over in the 70s. We had several training exercises that weer dimensioned as 25.4mm x 50.8mm to get us sued to it (so we turned the ruler over). But then there were the Harriers across the isle that were (are still are) imperial aeroplanes. I would still rather work a lathe in thou than whatevers of a mm.
Click to expand...

Mass is in kilograms and force is Newtons - which does make calculating structural frequencies much less prone to error.

I now work in the states and interestingly the US Army uses metric for its new vehicles - perhaps because the rest of the motor industry does - but the USAF still uses traditional units for its aircraft. Can't call them Imperial units otherwise there would be 2,240 lb in a ton and 20 oz in a pint. I had to explain to to a colleague what a cwt meant in the manual for his beloved Healey. It's 112 lb btw and there are 20 of them in an Imperial ton which makes it much closer to a metric tonne of 1,000kg than an American ton of a mere 2,000 lb.

Anyway - back to reality.
 
Last edited:
METAR?

We are being 'fundamentally transformed' in all things we have traditional.

The new think is that America got it all wrong.. all of it.
 
ChiefPilot said:
After thinking about this a bit, I've decided I don't want to have such arbitrary units forced upon me. Therefore...

1. My altimeter shall be marked in fathoms.
2. My airspeed shall be calibrated in furlongs per fortnight.
3. I shall expect pressure settings to be read to me in atmospheres.

Who's with me?
Click to expand...

Furlongs, fortnights and slugs. :) I'm there!

I never verified it, but my physics prof claimed that if you used the furlongs/fortnight/slug "system", all the fundamental physical constants ended up being something close to 1 x 10^some power. No more having to remember things like 6.62 x 10^-34 :)
 
Last edited:
I was doing some searching for info on steel braided hoses and fittings and such for brakes, and got distracted reading a site that talked about the hoses and fittings on a Jaguar. (Isn't that always the case with Internet searches? LOL!). So check this out:

The ports where the hard lines connect to the inboard rear calipers themselves are 3/8"-24. Hence the hard lines from the hose to the calipers are metric threads on one end and 3/8" threads on the other. Don't you just love the British? Whatever, this opens more possibilities: you can replace the hard lines from the hose to the calipers with lines that have 3/8"-24 threads on both ends and then use the #4-#3 AN bulkhead fitting shown in the photos above on that end of the hose. You'll still need a metric adapter on the other end, unless you replace those hard lines too.
...
The connections where the short hard jumper lines connect to the front calipers are metric. ... The bleed screws are the same way: metric at the front, Imperial at the rear.
Click to expand...

What the....? :)
 
GLPalinkas said:
Trying to find the 13/64ths wrench or the 37/64 socket makes me crazy....or crazy'er....
Click to expand...

Yup, the guy who thought a 13/64ths wrench or a slotted screw was a good idea should be (deleted so not as to advocate violence on a 'family friendly' board).

What were they thinking?
 
My wife was one of the few lady engineers at Jag in Coventry when Ford bought them. Shortly after the deal a senior Ford executive gathered all of the engineers together and told them that the place was one of the worst he'd seen on the western side of the iron curtain. Not the most inspirational of pep talks but I guess the reality of years of underinvestment and nationalization. Perhaps the Indians will have better luck :)
Jim Sharkey
 
I'll apologise in advance for writing this as I read through the thread!

N999BT said:
I am a mechanical engineer...

Oh. The one thing that does make some sense is nautical miles, since it actually relates to something on the ground, the distance between the equator and the pole, divided by 60 degrees, divided by 60 minutes, and actually appears on the vertical longitude lines on the maps we use. :cool:
Click to expand...

And I have a degree in geography not that it helps much with business software development. I'd just like to say that Nautical miles are a great idea until you realise that the basis for the measurement is actually a variable.
The earth is not a perfect sphere: it is slightly flattened at the poles (technically an ellipsoid revolution).
A nautical mile was originally measured off the latitude scale on a chart: 1 minute of latitude = 1 nautical mile.
This means that nautical miles as measured on a maritime chart are shorter towards the poles than at the equator (I think I've got that the right way round, but you get the idea...).

Oh man, I carry some useless information around in my head!

Anyway, if you want a really stupid example of inconsistency, in the UK in air law (and aviation weather forecasts etc) all the defined horizontal distances are in metres, but all the vertical ones are in feet. Now explain to me how that's logical!

And don't get me started on Pints and Gallons. The US has it just plain wrong at 16 fluid ounces! A pint is 20 fluid ounces, same as a proper sized beer (even in the US). OK the US gallon is still 8 pints, but the damage has already been done by then!
I've never worked out why in the US, where everything is BIGGER, that the pint is smaller!:confused:

But then again, what do I know? My ASI main scale is in MPH but my GPS gives me ground speed in Knots. And yes, I installed the ASI, and I do know how to change the scales on the GPS - I just choose not to!

As for the Jag having different threads each end of a hose, sounds like the global multi-national Ford has been at work sourcing bits from it's cheapest subsidiaries. The British Morris Motor company used to do the same in the 1930's - the small engines were French so had metric threads but the nut and bolt heads were British Standard sizes as that's the sizes of the spanners all the garages that would have to repair them had. Flippin' confusing to work on until it's explained to you.
 
There is a certain elegance

to a system that is where it is all base ten based. So to speak. I also find elegance in the fact that the volume, weight and length units are all based on a cc of water... 1 gm H20=1 cc volume. I have never been able to remember the whole cups, ounces, pints, gallons thing.

Hans
 
mixed units

I have never seen such a mixed up set of units until I entered this aviation thing.

Tradition over logic is my best explanation.

Its just a matter of getting used to it I guess.

I learned to love the metric (MKS) system of units in engineering school.

Always hated to get problems in other units: what the heck is "KIP" or a why
the same unit (LBS) for weight and mass, etc.,?

Dave
-9A finish kit
N514R reserved
 
There was a comedian on BBC TV here in the UK the other evening joking about how the British use degrees F when talking about hot summer's days ("It will be in the 90's tomorrow!", doesn't happen very often here by the way) but use degrees C when talking about cold weather ("It was chilly today, -1 C").

Funny thing is that it's exactly what we do here, biggest numbers for hot, smallest for cold (though not on the TAFs/METARS!).
 
Metre not meter.

What a fabulous post.
Good bits of humour, lots of sarcasm and some seriously useful information. And so far no brawls; even though someone mention ?taildraggers.?

Let me get my ?units beef? out of the way first, because this will be a long post and nobody will bother to read to the end.
Choose! Metric or Imperial? But don?t ever have a rivet that is 3.5 of 3/32 long. How dumb to mix decimals and fractions in the one mouthful.
OK! Got that out of the way.

Now let?s get this straight. The USA has officially been Metric for over one hundred years since Grover was the boss.
In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metric Convention.
Don?t believe me. Google ?Metrication in the United States wiki?.
I was bought up in Australia in the late 16th century when we used Imperial bits.
Whilst I was at college, Australia change to Metric.
So I?m ambidextrous and I know most Americans would give their right arm to be ambidextrous. Particularly if they were working on the Mars Orbiter.

And the use of 60 seconds is no more arbitrary (as someone suggested) than 16oz in a pint of US beer. (Poms feel cheated. They want 20oz of warm, flat, liquid amber). There are 60 seconds in an hour because the Babylonians used a sexagesimal (Base 60) system. And they invented the Rolex; or something similar. So they have a patent time.

There are a lot of comments in this post stating that some unit is arbitrary. No units are arbitrary. They relate to the ?Kings? Foot?, the ?Pharaoh's Arm? or something. They might seem antiquated, but they were chosen for a reason.

Sure, the metric System has some drawbacks, (it was invented by Man) most notably because we have ten digits on our hands. Eight would have made for a much better system. Dividing by two would be easy.

Certainly, conversion between Fahrenheit and Celcius would be easier if they had the same zero point, (ie. Zero at the freezing point of water) so that a simple rule of thumb could be used without having to account for the 32? offset. This is because Daniel Gabriel Fahrenheit did not use the same zero datum point as the Celsius scale uses, that is freezing water, instead using a frigorific Brine mixture which occurs at 32?F below the freezing point of water.

As someone pointed out knots, come from sailors who through a log overboard with a knotted rope attached and counted the knots paying out to estimate their speed. They wrote the result in a ?Logbook?. So if you don?t use knots you should be using an accountants ledger or a scrap of paper. But not a logbook.

Another post wondered why to the ?one-in-sixty rule? ,1:60 (60:1?) rule works.
It works because the Tan of a small angle is equal to 1/60th of the angle.

The problem is not so much that the Metric system or the Imperial system is superior, but rather that the Metric System has been adopted in the US by the Army, university and countless other organisations and not by the country as a whole.

Finally here is a map showing all the other developed countries in the World that DON?T use the Metric system.

Pete.

http://img69.imageshack.us/img69/994/metricmap.gif
 
It's is only units

First, lots of great posts in this thread.

With the world market place we have now and the mix of unit we have (as have been pointed out in this thread) it is a wonder we have not read about any incidents/accidents/screw-ups/emergencies due to mis-calculation of number conversion. The only one I know of was a Mars landers (built by Lockheed) that crashed into the planet due to the people working the hardware and those doing the flight software where using different units.

(How do they do it in Star Trek when the Romulains give Jean-Luc 24 hours to leave the neutral zone, what planet's rotational cycle is that hour based on?)
 
plehrke said:
the world market place we have now and the mix of unit we have (as have been pointed out in this thread) it is a wonder we have not read about any incidents/accidents/screw-ups/emergencies due to mis-calculation of number conversion. The only one I know of was a Mars landers (built by Lockheed) that crashed into the planet due to the people working the hardware and those doing the flight software where using different units.
Click to expand...
The Air Canada 767 "Gimli Glider" accident was triggered by a metric conversion screwup when refueling an aircraft with an unserviceable fuel indication system. The details of exactly how they screwed it up are in the "Refueling" of the wikipedia article.
 
People-centric units of measurement

I didn't read every post, so this may already have been mentioned. I do a lot of long distance walking, so I find it nice that a mile is a nice power of ten. If I count paces (every time I step with my left foot), I count to 1000, and I've walked a mile. After all, that's where the word for mile comes from, the latin for 1000.

Many statute measurements are based on people sized units (feet, miles, furlongs, degrees fahrenheit, etc). Metric units are not quite so people-centric, being based on concepts like the size of the earth, or some decimal fraction of that size, or a weight or volume of a standard substance related to a fraction of that size. I suppose nautical miles are similar to metric units, in being related to the size of the earth.

The point is, different measurement systems make more or less sense depending on whether they are used in the context in which they were originally defined, or in some context that is farther afield. For walking, miles makes sense to me.
 
So how about this..I am an Engineer transplanted from UK where I learned everything in Metric...Cool, I have never really learnedthe English system, just made the occasional conversion. Well the economy has dictated I really need my PE license.So it's back to the books...so the fundamentals exam was made a lot less painful as it's all done in SI units..sat the exam in October...so assuing I passed I turned my attention to the next course of study. I.e the PE exam itself...guess what units that uses?...yes the English system.....Aaaaargh!

Guess I'll find out what a kip is!!!
Frank
 
What's the big deal?

Back to the original question...

My question is why when you listen to the current weather they give everything in imperial units (Feet, miles, etc.) except the temperature, which they give in degress Celsius. Why is that?
Click to expand...

What's the big deal? Here in Minnesota -40F = -40C:rolleyes:
 
What about Mach?

I've been doing this all wrong. Flight planning at mach 0.27

What was I thinking?
 
Grandpa Simpson had it right!

"The metric system is the tool of the devil. My car gets fourty rods to the hogs head and that's the way I likes it" - Grandpa Simpson
 
I might be slightly wrong on this observation, but, I can't help wondering why everybody is reading and replying to this thread when time would be better spent turning good pieces of alum into scrap. All the engineering aside, if equal effort was on building RV's , they would be like the hoard of box elder bugs flying around in my shop on a warm (global) day ! Yea, I'm a grump 'cause I'm math challanged and still call an inch and an eighth (a inch and one of them :D little things):p-----nevermind-- I hear the UPS truck in the drive--more parts for 'da plane. Christmas every day!
 
You must log in or register to reply here.
Back
Top