Knots on Airspeed indicator - when started?

[ubadger]

US AF planes used MPH speed indicators in WW2, and went to knots after the war. Do you know the year when transition started?

RAF used MPH and went to knost after the war  or in the end of war. My guess that transition started in 1944.


US Navy used knots on air speed indicators, but when it started?
Did they always used it, or it too used MPH in the start?

What unit used US Marine Corps planes during WWII?

[GScholz]

The British have always used knots since Imperial miles and nautical miles are identical.

[ubadger]

Originally posted by GScholz
The British have always used knots since Imperial miles and nautical miles are identical.

Imperial mile =  1609.34 meters
imperial nautical mile = 1853.18 meters

They are hardly identical to me.

[GScholz]

Ok, technically that's correct, but when the Brits talk about miles they mean nautical miles for distance and speed even in cars IIRC. The British used knots for aircraft instrumentation even before WWII, but still they called it mph.

[ubadger]

Originally posted by GScholz
Ok, technically that's correct, but when the Brits talk about miles they mean nautical miles for distance and speed even in cars IIRC. The British used knots for aircraft instrumentation even before WWII, but still they called it mph.

U can look brits manuals here, Spit XIV manual for example - they clearly call MPH - MPH, and knots- knots.

I don't know why you decided that they called knots MPH and used them before the war.


Take a look at well known Spitfire Testing site - if MPH there is KNOTS really then Spits were a way better planes than anything else

[stantond]

If there is a set of units that works well but seems to have no reasoning behind it whatsoever, its British.   Unfortunately, the United States has embellished and modified the system even more!  However, in US pilots manuals, a knot is a US nautical mile.  Which, of course, is not to be confused with a british nautical mile.  Fortunately, there are conversions and with a little math things become clear(er).  


The US Navy and Marines used knots for airpeed and the Air Force used mph.  I believe it was just to be different.  Of course the Air Force first used metric, because all the WW1 planes were French.  

Converting everything to metric is often helpful.

[Angus]

The RAF referred to miles as the English mile, not the nautical mile.
This once caused a catastrophy, when they launced Spitfires of a carrier, heading to Malta (emm,,,maybe it was Hurricanes)
The RAF guys gave the ships captain the estimated range in miles, he took it for nautical miles and the aircraft were launched very much to far away.
Only 3 or 4 made it, on the fumes.

[GScholz]

... metric rules ...

[rshubert]

Originally posted by GScholz
... metric rules ...

Metric is for the math challenged.  All that simple divide-by-ten stuff.  Not a manly system at all, with converting fractions to thousandths and ounces to gallons and grains to pounds...



shubie

[rshubert]

my 1967 Cessna 172 was in MPH, not knots.  The 1972 Cessna 172 I trained on was in knots, not MPH.

[HoHun]

Hi shubie,

>Not a manly system at all, with converting fractions to thousandths and ounces to gallons and grains to pounds...

You know the official definition of the inch, which is the most basic unit of the Imperial system?

Regards,

Henning (HoHun)

[Angus]

What they taught me in Farm School was 2.54 centimetres for the inch, 30.5 cm for the foot, 1609 metres for the imperial mile and I think 1852 metres for the nautical mile.
And importantly a Pound is 0.45 Kg's, and a pint is LESS than 0,5 litre, which is important when you go pubcrawling


All from memory though...

[Schutt]

I think british traffic signs list the speed in imperial miles, not nautical.

At least they did last time i was there.

[artik]

Originally posted by Angus
What they taught me in Farm School was 2.54 centimetres for the inch, 30.5 cm for the foot, 1609 metres for the imperial mile and I think 1852 metres for the nautical mile.
And importantly a Pound is 0.45 Kg's, and a pint is LESS than 0,5 litre, which is important when you go pubcrawling


All from memory though...

Most interesting in nautical mile - the reason it is used very much is that 1mile = 1' of earth that makes it so usefull - the length of equator is 40,000KM thus 40,000/(360*60)=1,852Km - it makes the nautical mile so usefull - and it was allways used in Navy.

By the way the reason that nautical mile per hour is called knot came from the Navy.

Metrical units are much more usefull for any kind of calculations - for example if I want to calculate how much altitude had changed from bomb drop in 5 seconds I can calculate it easily in metric units: H=(g*t^2)/2 where g=9.81 M/c^2 and t is time in seconds.

What is value of constant "g" in feets/c^2 ? Anybody knows
I don't.

Edit: I hate to work with Inches and other kind of non metric measurements - but sometimes you have to.........

[HoHun]

Hi Artik,

>Most interesting in nautical mile - the reason it is used very much is that 1mile = 1' of earth that makes it so usefull - the length of equator is 40,000KM thus 40,000/(360*60)=1,852Km - it makes the nautical mile so usefull - and it was allways used in Navy.

Well, that's the reason for the "new" angular measurement Gon. 400 Gon = 360°, so 1 km = 0,01 Gon on a great circle.

Gon is a legal unit in SI countries and has been used for geodetic calculations for long. French IGN maps provide Gon coordinates exclusively, which can be something of a problem when you travel with an American GPS. (Don't ask me how I found out!)

If you check your pocket calculator, you'll probably find it has a GRAD mode, which is just "Gon" under a different name, even if that calculator is some 20 years old.

Regards,

Henning (HoHun)