Knots -v- MPH

[poadeleted20]

I might try Yards per Hour. It will make me feel better flying west bound.

How about furlongs per fortnight?

 

[Pilawt]

Not really, the ASI isn't all that bloody critical to flying that it be calibrated to any particular speed. As far as the flying part goes it could just as easily be marked with V speeds: Vso, Vx, Vy, L/Dmax, Va, Cruise, Vno, Max Cruise, Vne.

Where it makes a difference is in navigation and your airspeed isn't particularly useful in those regards where as ground speed measured in knots gives you slight advantage over statute mile or kilometer measurements

Agreed. My Cub's ASI is in mph only; it would be just about as useful with only the colored arcs.

Regardless what is used on your ASI, you'll have to use knots and nautical miles when dealing with ATC.

For that reason I keep the Garmin 496 set to nautical miles.

 

[fgcason]

That's true, however if you are using airways... flying an instrument approach.. all of those distances and information are provided in nautical miles

Again: Don't mix units beyond what is essential. Pick the primary units that is obvious and standard for what you're doing. Convert other units to that standard as needed to have a single unit standard you're working from. It would be silly to work in statute when all but one thing is nautical.

There are always little variations in rules. Fine with that but don't necessarily nitpick every remote possible different scenario to pieces. Fly IFR and ATC and DME as nautical because that's the standard and how everything is supplied. Then when you are on final with a statute airspeed indicator that you've been using constantly for 800 hours and you don't even know best glide in knots much less glide range in meters of altitude, fly statute on the airspeed indicator and feet AGL...that way you don't have to do annoying long division math in your head when the engine quits.

It's about simplifying easily mixed up stuff and adapting when needed.

 

[TMetzinger]

Most of the planes I fly show knots, or both, and I use knots for everything.

 

[zaitcev]

Knots, and the dual MPH/KTS ASI in the Arrow I fly drives me up the freakin' wall.

You can always replace it, you know? BTW, our Arrow has an Aspen that indicates mph, and one of those ASIs that have a little TAS scroller. Once the speed gets high enough to hit the scroller, it's too difficult to read. Fortunately, it's only for backup these days.

 

[Bob Noel]

Both.

The ASI on my 140 is mph, but I use knots for all calculations

 

[Sac Arrow]

You can always replace it, you know? BTW, our Arrow has an Aspen that indicates mph, and one of those ASIs that have a little TAS scroller. Once the speed gets high enough to hit the scroller, it's too difficult to read. Fortunately, it's only for backup these days.

Yes, yes.

 

[Geico266]

MPH for me since that's the predominant marking on my airspeed indicator and what the references are in the POH. It is also easier to speak MPH to young eagles I'm flying since they can relate to it.

+1

How many time have you been talking to non flyers and you have to explain what a knot is? What a waste of time. We need to bring more people into the sport not make it more "elite" by using an antiquated using of measure.

Pilots use knots
Aviators use MPH

 

[Henning]

+1

How many time have you been talking to non flyers and you have to explain what a knot is? What a waste of time. We need to bring more people into the sport not make it more "elite" by using an antiquated using of measure.

Pilots use knots
Aviators use MPH

Seriously? You are defending Statute Miles Per Hour as the LESS antiquated unit of measure? Nautical Miles are based in the spherical trigonometry of the earth, what about the Statute Mile? Wikipedia has this to say:

The statute mile was so-named because it was defined by an English Act of Parliament in 1593, during the reign of Queen Elizabeth I. The statute states: "A Mile ſhall contain eight Furlongs, every Furlong forty Poles, and every Pole ſixteen Foot and a half." (35 Eliz. cap. 6.)[39] It was thus 1760 yards (5280 feet, about 1609 metres).[12] For surveying, the statute mile is divided into eight furlongs; each furlong into ten chains; each chain into four rods (also known as poles or perches); and each rod into 25 links. This makes the rod equal to 5½ yards or 16½ feet in both Imperial and US usage.

As for Nautical Miles this:

The nautical mile was originally defined as one minute of arc along a meridian of the Earth.[50] Navigators use dividers to step off the distance between two points on the navigational chart, then place the open dividers against the minutes-of-latitude scale at the edge of the chart, and read off the distance in nautical miles

The only thing I can conclude from your analysis of the situation is that you are a Republican.

 

[Geico266]

As for Nautical Miles this:


The only thing I can conclude from your analysis of the situation is that you are a Republican.

Now that was funny!

Okay, why do we use statute miles to describe visibility? And altitude in feet? Satellites are measured with statute miles above the earth.

 

[JeffDG]

Now that was funny!

Okay, why do we use statute miles to describe visibility? And altitude in feet? Satellites are measured with statute miles above the earth.

None of these measures are used in navigation.

 

[ARFlyer]

Ah the good old Rod measurement! That has brought me so much joy into my life, NOT!. They use rods to measure portage distances in Canada. Do NOT mistake 700 rods for 700' like I did once!. Carrying a 80 pound canoe on your back for 2.2 MILES is not what I call fun.

I mostly use knots unless I am in our old IFR trainer which uses MPH.

 

[dmccormack]

How about furlongs per fortnight?

I have three hours endurance, silly. That leaves me several days shy of a single fortnight.

 

[Henning]

Now that was funny!

Okay, why do we use statute miles to describe visibility? And altitude in feet? Satellites are measured with statute miles above the earth.

"Because Jesus died on the cross for your sins, now shut up and eat your broccoli..." Same reason we do everything here, otherwise we'd be using that heathen metric system that you need a full set of fingers to use.

 

[steingar]

Fraction of c. I'm a small guy, I fly a small airplane, and I like small numbers.

 

[ARFlyer]

"Because Jesus died on the cross for your sins, now shut up and eat your broccoli..." Same reason we do everything here, otherwise we'd be using that heathen metric system that you need a full set of fingers to use.

That is exactly what my grandmother has always said. "If God wanted us to use the metric system he wouldn't have givin us inches"

 

[Geico266]

"Because Jesus died on the cross for your sins, now shut up and eat your broccoli..." Same reason we do everything here, otherwise we'd be using that heathen metric system that you need a full set of fingers to use.

But, I like broccoli!

 

[JeffDG]

Fraction of c. I'm a small guy, I fly a small airplane, and I like small numbers.

100 knots = 0.0000174148% c

 

[JeffDG]

"Because Jesus died on the cross for your sins, now shut up and eat your broccoli..." Same reason we do everything here, otherwise we'd be using that heathen metric system that you need a full set of fingers to use.

I remember getting into a debate in high school with a teacher. He claimed the imperial system was all arbitrary while the metric system was scientific.

I asked him "What's the basis for the meter?"

He went on about how it was based on the wavelength of some excited state of Kr gas. And my response was "So, someone arbitrarily selected that gas, and arbitrarily selected that particular state. It's still arbitrary, someone just abstracted it to make it sound sciencey"

 

[Henning]

I remember getting into a debate in high school with a teacher. He claimed the imperial system was all arbitrary while the metric system was scientific.

I asked him "What's the basis for the meter?"

He went on about how it was based on the wavelength of some excited state of Kr gas. And my response was "So, someone arbitrarily selected that gas, and arbitrarily selected that particular state. It's still arbitrary, someone just abstracted it to make it sound sciencey"

Right, my issue is not with arbitrariness of the base as much as the ease of use. The imperial system is very wasteful in time and materials in industry as people waste more time making calculations and are more prone to error using the Imperial system. Although, a kilo gram being based on a liter of fresh water, we lose a considerable amount of your arbitrariness argument.

 

[gismo]

I use whatever the airplane is equipped with.

For airplane performance and limitation issues that's the right choice. For that matter the ASI doesn't indicate speed, it indicates dynamic pressure and ought to be marked in PSI, Bar, or HectoPascals. Or better yet one of those pressure units to the half power since that's more representative of aerodynamic performance and would make the computation of TAS easier.

But for flight planning and navigation I find knots to be a better choice, even in an airplane with mph on the ASI. Charts show nautical miles (as someone pointed out you can infer nm from latitude if you happen to be flying exactly north or south), ATC want's to know knots, DMEs readout in nm, etc.

 

[steingar]

100 knots = 0.0000174148% c

Or 17.4 micro C's. Like I said, small numbers, easier for a small mind.

 

[dmccormack]

Right, my issue is not with arbitrariness of the base as much as the ease of use. The imperial system is very wasteful in time and materials in industry as people waste more time making calculations and are more prone to error using the Imperial system. Although, a kilo gram being based on a liter of fresh water, we lose a considerable amount of your arbitrariness argument.

Oh Pshaw...

They built this stuff using old, decrepit measuring systems:

 

[N801BH]

^ What he said.

I know we don't use this in our everyday flying, but the way that knots, nautical miles and the lat/lon system interface is amazing.

I had it all explained to me a few years ago by an old man who was a NASA ballistics expert in the 70's and now circumnavigates by himself on his 30 foot sloop using celestial navigation and dead reckoning.

This must have been the same NASA rocket scientist that miscalculated the distance for the Martian lander and sent it into the surface of mars at 400+MPH because of a conversion error.....

That was only a 450 million dollar mistake.....

In all seriousness... I would love to find an oldtimer show me how this celestial navagation process really works... In my mind there are too many moving targets..

Ben.

 

[gismo]

100 knots = 0.0000174148% c

That's 17414.8 nanoCs. Sounds like a lot to me.

 

[Henning]

This must have been the same NASA rocket scientist that miscalculated the distance for the Martian lander and sent it into the surface of mars at 400+MPH because of a conversion error.....

That was only a 450 million dollar mistake.....

In all seriousness... I would love to find an oldtimer show me how this celestial navagation process really works... In my mind there are too many moving targets..

Ben.

I ain't that damn old, but I still came up in a time when celestial was our primary nav across the ocean. Amazing what a quarter century can bring.

It's really not that difficult. You work every LOP ('line of position' in this instance) as an individual. Not until you finish there do you worry about it being a multi star (typically maximum of 3) running fix, and advancing an LOP for time is not difficult in the slightest.

For the practical end of it, the most difficult thing to get down is the swinging of your sextant arc timed with the top of the pitch of your deck on the top of the wave/swell. That is the key to getting a good fix. To add a bit of perspective to that, on a small boat, <120', once you get it down and accurate, your 'fix triangle' gets down to around 3 mile accuracy of your fix. Your first sight reduction will be a good effort if you get below 25 miles.

For the Coast Guard end of it there are 2 tricks to your Oceans endorsement. First one is that you have to make your sight reduction form from memory. No programmed calculators, no preprint forms, none of it. So the first thing you do is walk in and write out your sight reduction form. After that it's a breeze, just apply the different parts of the form as appropriate for the problem.
Trick two is bring the finest lead mechanical pencil you can find, IIRC I had a .2mm 2H. Plotting out a running fix problem, if I was working with a typical #2 pencil that was half worn down, the width of the line will encompass choices A&C and will be right next to B. You need to be able to place your LOPs on the plotting sheets extremely accurately.

 

[gismo]

Oh Pshaw...

They built this stuff using old, decrepit measuring systems:

This stuff too (Tacoma Narrows Bridge, Minneapolis I35W Bridge, Hyatt-Regency walkway):

 

[fgcason]

This must have been the same NASA rocket scientist that miscalculated the distance for the Martian lander and sent it into the surface of mars at 400+MPH because of a conversion error..

See what happens when people don't use a single standard measure of units when they should. Wile E Coyote skydiving. Whee, BLAM, pop, the parachute covers up the hole you landed in.

100 knots = 0.0000174148% c

Good grief.
Let's do the nonstandard units thing right.
Airspeed in mph except for engine out scenarios which use feet per 3/17ths of a minute. ifr/atc in knots. Altitude changes in fathoms. DME in %c. Compass in degrees, vor in radians. Altitude given in meters, altimeters in feet. Flight planning speeds in yards per second and put on the form as meters per second except for controlled airspace which uses ells. Fuel supplied in gallons, measured in liters and calculated in quarts. Engine RPM measured in piston cycles per decade, double that number for 2 stroke engines then measure in cycles per second.
Wheee...

 

[poadeleted20]

I remember getting into a debate in high school with a teacher. He claimed the imperial system was all arbitrary while the metric system was scientific.

I asked him "What's the basis for the meter?"

He went on about how it was based on the wavelength of some excited state of Kr gas. And my response was "So, someone arbitrarily selected that gas, and arbitrarily selected that particular state. It's still arbitrary, someone just abstracted it to make it sound sciencey"

This is a science teacher? Meters (or "metres," to more historically accurate) were around long before anyone could measure the wavelength of the excited state of Krypton gas. Dates back to the 18th century, when it was defined as one ten-millionth of the distance from the Earth's equator to the North Pole at sea level. In any event, it was not arbitrary -- they really were trying to come up with a physical basis.

 

[N801BH]

I ain't that damn old, but I still came up in a time when celestial was our primary nav across the ocean. Amazing what a quarter century can bring.

It's really not that difficult. .

Thanks Henning..... I get the concept and the geometry involved, it is the properly identifying the correct stars and doing it fast enough to make some sense of it all that has me worried.. Also.. I am assuming on a cloudly night you are screwed ?

 

[poadeleted20]

Thanks Henning..... I get the concept and the geometry involved, it is the properly identifying the correct stars and doing it fast enough to make some sense of it all that has me worried.. Also.. I am assuming on a cloudly night you are screwed ?

With a really solid overcast you can't top, more or less, if LORAN wasn't available. You got low enough to see the surface so you can use the driftmeter and revert to wind triangles to DR your way across. And yes, I did have the opportunity to navigate off a driftmenter in a T-29 almost 40 years ago. Dunno what the ship-drivers did in that case.

 

[Henning]

Oh Pshaw...

They built this stuff using old, decrepit measuring systems:

What does that have to do with what I said? I said it was more wasteful, not impossible. How does showing multiple boondoggle projects discredit that?

 

[Henning]

Thanks Henning..... I get the concept and the geometry involved, it is the properly identifying the correct stars and doing it fast enough to make some sense of it all that has me worried.. Also.. I am assuming on a cloudly night you are screwed ?

You have three times of day when you take sights, dawn, local noon and dusk. If you cannot see your celestial bodies at those times, you are screwed. We got in a hurricane on the way back from Hawaii once, we had no clue of where we were outside 1000nm for a week, no sights, just kept the wind off the port quarter and drove the waves.

Identifying stars is easy, get a 'Starfinder' wheel (or 'app' these days) and you find it's really easy to recognize the 5 you'll use.

When the Nav Star system and Magnavox 4102 receiver came out, it was 'wow' you could get a solid fix or two a day on most days even if the clouds were there..unless they had lightning in them then eeeeeeehhhh, maybe. It even had a DR function that you could program to run between fixes.

I used the first public GPS unit Furuno released. On the way from LA to SF it was all over the hemisphere. I thought 'damn, if this is the latest greatest, it sucks'. Furuno came aboard in SF though and swapped out a bad board. For the rest of the trip it was very accurate even on the georef to the 'lollypop' on the new radar. THAT was better than sliced freakin bread, had never seen anything like it before.

 

[denverpilot]

To answer the original question... Knots.

My ASI is labeled in both. MPH on the outer ring, knots on the inner via a Kollsman window.

Why?

Because the aircraft POH is in knots and the Robertson STOL Addendum to the POH is in MPH.

The joys of the FAA STC system. The ASI must show MPH if you have a Robbie kit on my model year 182.

Seen birds where they did away with it, but technically as far as I can tell, unless you have the Robbie addendum in knots for that aircraft, it's not legal.

Or... someone will set me straight on that.

But that's the best I've come up with in my research...

 

[N801BH]

You have three times of day when you take sights, dawn, local noon and dusk. If you cannot see your celestial bodies at those times, you are screwed. We got in a hurricane on the way back from Hawaii once, we had no clue of where we were outside 1000nm for a week, no sights, just kept the wind off the port quarter and drove the waves.

Identifying stars is easy, get a 'Starfinder' wheel (or 'app' these days) and you find it's really easy to recognize the 5 you'll use.

When the Nav Star system and Magnavox 4102 receiver came out, it was 'wow' you could get a solid fix or two a day on most days even if the clouds were there..unless they had lightning in them then eeeeeeehhhh, maybe. It even had a DR function that you could program to run between fixes.

I used the first public GPS unit Furuno released. On the way from LA to SF it was all over the hemisphere. I thought 'damn, if this is the latest greatest, it sucks'. Furuno came aboard in SF though and swapped out a bad board. For the rest of the trip it was very accurate even on the georef to the 'lollypop' on the new radar. THAT was better than sliced freakin bread, had never seen anything like it before.

Thanks again for taking your time to explain things... As for the sliced bread moment..... Back when I had my first plane, a Warrior I bought a King 8001 Loran with the 01 option from Tropic Aero Marine in Ft Liquordale and the very first time I flew with it and was able to get to my tie down @ X04 within 25 feet I just about had an orgasm... The WAAS GPS'S of today are downright magical.

Ben.

 

[ejensen]

With a really solid overcast you can't top, more or less, if LORAN wasn't available. You got low enough to see the surface so you can use the driftmeter and revert to wind triangles to DR your way across. And yes, I did have the opportunity to navigate off a driftmenter in a T-29 almost 40 years ago. Dunno what the ship-drivers did in that case.

Reminds me of listening to my cousin (A6 BN) talk about night DR off the carrier in the middle of the Pacific. They actually did find their way back to the ship.

 

[skidoo]

Although my instruments are calibrated in kts. I find that the nautical mile per hour thing takes too long (one hour sample time) for a practical speed measurement. So, I describe my speed in feet per second. Therefore, my T182T will cruise at 240. Looks faster too!

 

[Dan Thomas]

My Jodel cruises at .000000144 lightspeed.

Dan

 

[dmccormack]

What does that have to do with what I said? I said it was more wasteful, not impossible. How does showing multiple boondoggle projects discredit that?

Notre Dame and the Empire State Building were boondogles?

 

[Everskyward]

Notre Dame and the Empire State Building were boondogles?

I am too. Wasn't that the Canadian Parliament building?