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-   -   Knots are for boats! (https://www.pprune.org/tech-log/490129-knots-boats.html)

rsiano 9th Jul 2012 23:49

Knots are for boats!
 
I have been bothered by the change from miles per hour to knots for speed values for aircraft for more than 35 years. Lets bring back miles per hour for aircraft. For example, since most people reference speed using miles per hour, advertising a speed in knots for new aircraft is penalizing their perceived capability. For example, the listed maximum cruise speed for the Cessna Citation Ten is 527 knots or it is 605 miles per hour. Which sounds more impressive? To me it is 605 mph. What do you think?
Thanks!

EpsilonVaz 9th Jul 2012 23:54

......which sounds even better as 974kph (which is more commonly used worldwide than mph).

svhar 10th Jul 2012 00:06

The metric system is the only way. The Russians are way ahead of us. Miles and knots are from the past. As are gallons, stones, yards, feet and inches.

Capt Claret 10th Jul 2012 00:14

Haven't used mph for 40 years. Knots or kph for me please. A few hundred million Americans might be happy with mph but hundreds of millions more non Americans won't.

27/09 10th Jul 2012 00:45

For me it comes down to using the graticule scale on a chart for measuring distance. One minute of one degree of latitude equals one nautical mile, therefore the use of knots makes perfect sense.

P.S. I can't agree that the metric system is the only way to go.

galaxy flyer 10th Jul 2012 01:36

The metric system is a scurvy French idea brought to us by a Corsican defeated by Lord Wellington. Unfortunately, Napolean is getting his revenge.

zerozero 10th Jul 2012 02:20

Totally agree with 27/09.

As long as we're navigating with nautical miles it makes more sense to use knots.

The metric system is useful in other applications (lab work for one).

But whatever the case, we should ALL be using the same measurements (China, I'm looking at YOU).

:hmm:

sevenstrokeroll 10th Jul 2012 03:12

27/09...agree

and folks, DME is in knots

also, descent tables for ILS glideslopes can be approximated by using ground speed IN KNOTS time 5 for descent rate in FPM.

I remember the changeover...hated it then...happy about it now.

also, wasn't it "the high and the mighty" where the navigator makes a mistake in converting miles to knots and screws up things?

Mach E Avelli 10th Jul 2012 04:03

Until they rejigger the whole system of positioning away from latitude and divide the points of the compass and bearings into something like 100 or 1000 units, the knot will stay. And rightly so, otherwise I would have to buy new charts, a new gps and a new compass for my boat and my bugsmasher.
Statute miles are up there with leagues and cubits as an outdated measure of distance. Like gallons and lbs.
Km is alright for cars, but is pretty useless in the middle of an ocean.
When the USA was the leading builder of aircraft they could get away with mph, but if they went back to that now, they would lose even more sales to those pesky foreigners.

ImbracableCrunk 10th Jul 2012 04:50

"The metric system is the tool of the devil! My car gets forty rods to the hogshead and that's the way I likes it."

InSoMnIaC 10th Jul 2012 05:40

a bit off topic but since someone mentioned the metric system. It seems pretty stupid why metric using countries like China issue altitudes in Metres but Rate of descent or Climb instructions in feet per minute. yeah i know the VSI if in fpm in most aircarft but so is the Altimeter. Make up your mind. Either metres or feet

Loose rivets 10th Jul 2012 05:49

In Pillars of the Earth, Ken Follett had his man keeping the rod locked in a stone shed. Careful with it, they were. Trouble was, it wasn't quite the same length as the rod in the next town. Then there's time and the railway.


The world will have to be divided up metrically one day. Charts will all be on iPad type things, and correct for curvature as one sweeps the locations. Coming from the days of ink pens and curved localizer tracks, I welcome the technology.

Mind you, Miles per Gallon should be absolved from all requirements governing change.

Tu.114 10th Jul 2012 06:46

With all the inability to agree on one of the already present units of measurement, maybe it would be better to find something new for widespread use?

There are so many possibilities ranging from Angström/week via Stadions/Olympiad to A. U./Indiction, there is surely one to be found that no-one in the world has ever used and consequently is not ideologically burdened and may be introduced worldwide?

Firestorm 10th Jul 2012 07:04

Knots are a perfectly acceptable and sensible method of expressing speeds for aviation. Before changing that perhaps it would make more sense for the Yanqis to adopt metric measures and weights for fuel rather than using the US gallon measurement which is easily confused with the proper gallon which even us Brits have largely given up on (as it would cause us a severe brain haemorrhage and fit o rage) when buying petrol for our cars as it currently cost about £6.50 per gallon.

fireflybob 10th Jul 2012 07:12


For me it comes down to using the graticule scale on a chart for measuring distance. One minute of one degree of latitude equals one nautical mile, therefore the use of knots makes perfect sense.
27/09 I think you will find that's the geographic nautical mile (which as I am sure we know varies in distance over the earth since the latter is an oblate spheroid).

The International Nautical Mile, last time I checked, is defined as 1852 metres (no doubt the eurokrats got their hands on this definition!).

That said I agree with your reasoning for sticking with nautical miles and knots - "miles per hour" was an awful American invention.

Saint Jack 10th Jul 2012 07:36

Knots are for boats!
 
rsiano: Not a particularly accurate statement, '27/09'. 'zerozero', 'sevenstrokeroll' (eh!) and 'mach E avelli' are correct, knots are for NAVIGATION.

Al Murdoch 10th Jul 2012 07:48

It actually makes sense to have a variety of systems of measurement in use for different things... For example, RVR and visibility are expressed in meters, speed in knots, altitudes in feet.
If you hear someone say 10,000 Feet, you know they must be talking about altitude (generally speaking). If you hear 100m, its likely to be RVR etc etc.

Check Airman 10th Jul 2012 07:57


If you hear someone say 10,000 Feet, you know they must be talking about altitude (generally speaking). If you hear 100m, its likely to be RVR etc etc.
You could also hear 300ft in the US. Now is that cloud base, or RVR?:}

nitpicker330 10th Jul 2012 09:11

RVR 300' ( 91 m ) wow that's way below CAT3B territory and I think you'd be told "RVR 300 feet". Couldn't even takeoff with 300' RVR :eek:

darkroomsource 10th Jul 2012 09:15


If you hear someone say 10,000 Feet, you know they must be talking about altitude (generally speaking). If you hear 100m, its likely to be RVR etc etc.
You could also hear 300ft in the US. Now is that cloud base, or RVR?
Wasn't that his point?
use knots for speed, miles (nautical miles preferably) for distance, feet for altitude, meters for RVR, feet per minute for climb/descent.
Then, you know what's being talked about based on the unit of measure.
Of course, if you grew up in the US, it's hard to judge distance by meters, because they're aren't exactly yards... and if you grew up elsewhere it's hard to judge height by feet, because you have to divide by 3 (approximately).


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