Knots -MPH how fast..?

[Jack]

Took this picture in the C47 - how fast were we flying? We were flying over the White Ciffs of Dover at the time.....

 

 

[Mark]

161.109 122 72 mile/hour (mph)

[radiomike7]

161.109 122 72 mile/hour (mph)

 

 

Mark, what is the significance of 122 72?:confused: Were you quoting to 8 decimal places?

 

The answer is 161mph or 260kph assuming the airspeed indicator is reading 140 knots on it's first time round.

 

Mike

[Jessie The Jeep]

I do all my converting here - http://www.onlineconversion.com/ It does everything to everything ( except water into wine! )

 

If you put 140Kts in here, it does bring it to 8 decimal places.

 

Steve

[antarmike]

Whta's that in Warp factor?

[Adrian Barrell]

Knots to mph is easy, just add 15%. For those who don't know, a knot is one nautical mile per hour. So there is no such thing as knots per hour as is sometimes written. A nautical mile being the length of one minute of longditude at the equator if I remember correctly.

[antarmike]

But what is it in warp speed?

[Mark]

Mark, what is the significance of 122 72?:confused: Were you quoting to 8 decimal places?

 

The answer is 161mph or 260kph assuming the airspeed indicator is reading 140 knots on it's first time round.

 

Mike

 

 

I hope it was the first time around, other wise that is a damn fast C47 :-D

[Tony B]

Knots to mph is easy, just add 15%. For those who don't know, a knot is one nautical mile per hour. So there is no such thing as knots per hour as is sometimes written. A nautical mile being the length of one minute of longditude at the equator if I remember correctly.

 

As Adrian says A nautical mile was about 1 minute of arc. Trouble is with a Mercator Projection the 'Mile' changes as to where you are on the chart (Hence the origin of the expression Plane Sailing) in 1929 at Monaco international aggremment was reached to make a Nautical Mile exactaly 1,852 meters. Roughly 2000 yards so 10 cables= 1 nautical mile.

[Mark]

How long is a cable ?

[Tony B]

Sorry it's a Naval measurement of 200yards. :red: Don't watch Hornblower then? The other one is Fathom = Six feet or one thousandth of an Admiralty Mile ie Nautical mile. Supposedly the length of outstretched arms, named after the Old English for the gesture of opening arms and embracing, as when the sailor comes home (Diidn't know I had a romantic streack did you?)

Edited September 14, 2008 by Tony B

[Guest catweazle (Banned Member)]

Took this picture in the C47 - how fast were we flying? We were flying over the White Ciffs of Dover at the time.....

 

 

Any speeds registered in air or water would have to be corrected to give you your true speed over the ground,wind speed and tidal flow would have to be calucated and added or subtracted .or forget that and use Gps.

[Tony B]

The whole picture is a blast from the past. Spinning wheel and cogs, the most glass in that cockpit is the windscreen. One delightful little gadget the Dak had was a drop down windmill. There is a wind driven emergency generator that drops from under the cockpit. Back in the early 1960's Cambrian Airways used to fly them from Jersey to Wales. Being packed off to relatives on my own, or even accompanied, as a young boy (SOOO long ago) there was always an invitation to see the cockpit, got you out of the steweradess way. Got very familiar with Dak cockpits.

[AlienFTM]

As Adrian says A nautical mile was about 1 minute of arc. Trouble is with a Mercator Projection the 'Mile' changes as to where you are on the chart (Hence the origin of the expression Plane Sailing) in 1929 at Monaco international aggremment was reached to make a Nautical Mile exactaly 1,852 meters. Roughly 2000 yards so 10 cables= 1 nautical mile.

 

Funny. My yacht training taught me that plane sailing was the phenomenon of getting the yacht to surf on the front of the wave.

 

A monohull yacht's theoretical maximum speed is a function of hull length, achievable where the waterline of the yacht describes a sine wave from bow to stern. The wave created by the boat's movement through the water takes the form of a sine wave. The faster you go, the longer the wave. When the yacht is travelling faster than this calculable "hull speed", the back of the yacht is out of the water in the negative part of the wave and handling becomes extremely difficult.

 

If the yacht is at or near hull speed and the speed of the waves underneath the yacht is close to this speed and in the same direction, the yacht rises out of the water (and you can hear a layer of air roaring and bubbling between yacht and water) and the yacht surfs the wave. This motion is exhilirating and extremly comfortable with no wave action slapping the boat about, hence the term Plane Sailing passing into non-nautical use to describe a comfortable ride. Bigger the boat, bigger the exhileration (because you are goingfaster). Best I ever experienced was on Sabre, the Army's entry in the 1980 Tall Ships Race, across the Bay of Biscay.

 

I see no way of deriving this expression from navigation using a Mercator projection. But I am sure you'll show me. Lol

Edited September 15, 2008 by AlienFTM

[AlienFTM]

Sorry it's a Naval measurement of 200yards. :red: Don't watch Hornblower then? The other one is Fathom = Six feet or one thousandth of an Admiralty Mile ie Nautical mile. Supposedly the length of outstretched arms, named after the Old English for the gesture of opening arms and embracing, as when the sailor comes home (Diidn't know I had a romantic streack did you?)

 

That was my understanding too. (Though I have this nagging question whether the figure was exactly 2000 yards or not. Cannot be bothered to go away and Google it.)

[Tony B]

I was told as a kid that plane sailing was when you were using a small scale chart and didn't have to remeber to use the scale adjacent to the course. I see what you lot mean with a boat on the plane.

[AlienFTM]

I was told as a kid that plane sailing was when you were using a small scale chart and didn't have to remeber to use the scale adjacent to the course. I see what you lot mean with a boat on the plane.

 

On a nautical chart ISTR you don't need a scale because in the latitudinal axis, one second of arc = one nautical mile, so there is a ready-made scale down the side of the chart already.

[Adrian Barrell]

Any speeds registered in air or water would have to be corrected to give you your true speed over the ground,wind speed and tidal flow would have to be calucated and added or subtracted .or forget that and use Gps.

 

In flying, ground speed is not normally much of an issue except when calculating descent paths. Airspeed is always used. Indicated airspeed is just that and needs to be corrected for position error to obtain calibrated airspeed and then the altitude or more correctly pressure level factored in to find true airspeed which is nearly always higher than indicated.

[Tony B]

In all this the funny thing the Nautical mile Admiralty mile, knots etc are not reconised as ISO units. A good old throwback to when things were measuered by people not science.

[Guest catweazle (Banned Member)]

In flying, ground speed is not normally much of an issue except when calculating descent paths. Airspeed is always used. Indicated airspeed is just that and needs to be corrected for position error to obtain calibrated airspeed and then the altitude or more correctly pressure level factored in to find true airspeed which is nearly always higher than indicated.

Thanks for that Adrian.for us water babys speed over the ground is more inportant,fast motor boats that is,as wind and tide dont have a large effect as on sailing boats.one of the few modern inventions i like is the chartplotter,i can see exactly where i am and how fast direction etc all at a glance,i once came back from Brighton in a F7 on the nose ,to Portsmouth by just following the track line on the chart,there was allmost no visibility and the people with me thought i was wonderfull ,knowing the way back without landmarks.They couldnt see the Chart plotter :rofl:conventional navigation in these circumstances would of been very difficult.i suspect aircraft must have something similar nowadays.CW.

[Tony B]

:-DClock compass and fingers crossed! :shocked:

[Guest catweazle (Banned Member)]

:-DClock compass and fingers crossed! :shocked:

Now you know why we need the RNLI.

[Tony B]

Now you know why we need the RNLI.

Thankfully there are the brave competent skilled crews of the RNLI. Any of us who love the sea and boats, hope we won't need them, and are very thankful they are there. There work is often done far from the media, in places, abd conditions the standard emergency srvices wouldn't dare to go. There is also a military involvment in SOLAS Saftey Of Life At Sea. a RAF Nimrod will often take control of a large operation and of course the RAF Air Sea Rescue aircraft. All of them deserve praise and respect.

[Adrian Barrell]

Thanks for that Adrian.for us water babys speed over the ground is more inportant,fast motor boats that is,as wind and tide dont have a large effect as on sailing boats.one of the few modern inventions i like is the chartplotter,i can see exactly where i am and how fast direction etc all at a glance,i once came back from Brighton in a F7 on the nose ,to Portsmouth by just following the track line on the chart,there was allmost no visibility and the people with me thought i was wonderfull ,knowing the way back without landmarks.They couldnt see the Chart plotter :rofl:conventional navigation in these circumstances would of been very difficult.i suspect aircraft must have something similar nowadays.CW.

 

The nearest in flying would be the moving map GPS. Very good and nice to use but not sanctioned as a primary means of navigation. The military often conduct jamming trials and it renders it unreliable!

[Guest catweazle (Banned Member)]

The nearest in flying would be the moving map GPS. Very good and nice to use but not sanctioned as a primary means of navigation. The military often conduct jamming trials and it renders it unreliable!

Thanks for info :tup::