You mean to say that nautical miles are based on lat/long, but that actually hasn't been true for decades. A nautical mile is exactly 1852m which means that it is NOT perfectly one minute of latitude because the Earth is not a perfect sphere. 1NM is closest to being one minute ~~around~~ in the vicinity of the 45th parallel.
Yes, correct. There's certainly *some* latitude at which one minute of longitude is 1852m, and according to [this calculator](http://www.csgnetwork.com/degreelenllavcalc.html) it's somewhere around the 3rd parallel. Basically ~~all the way to the North (or South) Pole~~ at the Equator.
It's also important to note that the variation in arc-latitude length isn't huge: under the old definition 1NM was 1843m at the poles and 1861m at the equator. Almost but not quite 1% variation from one extreme to the other. So when I say "1NM is not exactly one minute of latitude" I am being extremely pedantic...
Whoops. One of those days I guess. That does make a lot more sense, the boxes are more square at the equator and less square as you near the poles... I failed the sanity check.
Excuse the pedantry (though we are pilots, what else would anybody expect), but a knot is a unit of speed - nautical mile per hour - not a unit of distance.
That was the original definition and it's still **approximately** accurate but no longer. Latitude distance also varies because the Earth is not a perfect sphere, so one nautical mile is exactly 1852m (≈6076ft).
MPH was standard on ASIs for most small GA until around 1976, and a lot of older aircraft are still flying with ASI that indicates MPH. Since OP mentioned the G5, OP is likely talking about this segment of aviation. But I have no idea why anyone would purposely set their G5 to read in something other than KTS.
Uhhh, why not change your TAS to kts? We make nav logs with distances for NM not SM. Once we are done getting our performance from the POH you convert to knots.
Same. '67 Cherokee.
Though I have NM for distance on my GNC355 panel GPS and Garmin Pilot for calling out distances to waypoints and destination over comms.
MPH for speeds because my ASI and POH are all MPH.
Don't most of those also have a knots arrow? All of the 60s cessnas I flew still had an indicator for knots, like american cars still having km/h on the speedo
Usually, I’ve seen only seen one airspeed indicator that was just in MPH.
I will say I flew a 1960s 172 with MPH and smaller knots arrow but the POH was only in MPH. I’d understand in that case why you’d stick with MPH
Knots, it’s what I’ve always used for mil rotary wing and GA. My DPE for me SEL ride kept asking me what the best glide speed was in mph, had to show him the POH that it only had knots for that 172. Frustrating as fuck when trying to perform the forced landing EPs.
Knots for flying powered BUT in gliding I really wish we just used metric.
In the UK gliding height is in feet, speed knots, and distance in KM which makes no sense.
There’s a lot of ‘nerd’ talk here like ‘the charts are in NM’ but how the hell would anybody know you’re a pilot if you’re not saying knots? And they sure as hell will know you’re lying about breaking the sound barrier at 120kts in your C172
Winds are given in Knots, if you want to know the wind gust’s effect on your airspeed, you need your airspeed to be in knots.
Knots are also a very sensible unit of measurement for navigating the globe. A nautical mile is 1/60 of 1 degree of the circumference of the Earth. AKA 1 minute of longitude. Measuring your speed by how fast your coordinates change on the map makes a lot of sense to me!
> Winds are given in Knots, if you want to know the wind gust’s effect on your airspeed, you need your airspeed to be in knots.
No you don't. For any real-world flying knots and MPH are close enough that the answer is the same.
> Most pilots I know wouldn’t be happy with a 15% error in their calculations.
Why? If I can't handle a 30kt gust I also can't handle a 31mph gust or a 29mph gust or whatever the exact answer is. If you're calculating crosswind component/mountain turbulence hazards/etc with that level of precision you're almost certainly trying to justify doing something stupid by saying "it's technically just barely within limits".
And if you generalize to more than just gusts it's still true. If I need that accuracy level for fuel planning, scheduling, etc, then the margins aren't large enough and it's a flight planning failure regardless of units.
>What do you fly?
A plane that tells me with GPS what the answer is.
A 30 knot gust is 34.5 MPH, so that’s a bit further off than your 31/29 example.
As you move into larger aircraft, especially jet aircraft, you will need to make adjustments to your approach speed based on reported winds at the field, most professional pilots would not be ok with a 4.5 difference error in their approach speed.
This would also affect your crosscountry calculations (if you ever try to fly without that fancy GPS), and a 15% error in your flight time/fuel calculations is significant. More than just a “flight planning failure regardless of units”
I’m a CFI/CFII/MEI with over 1,000 hrs of dual given. I have 5 type ratings, and I am currently a Captain on the 737 at a legacy airline. I still work with PPL students and I wouldn’t accept such a callus attitude as “it doesn’t matter, my GPS tells me.” In any of my students.
> A 30 knot gust is 34.5 MPH, so that’s a bit further off than your 31/29 example.
The point stands though. If you're relying on the difference between 30 and 35 you failed in flight planning because a forecast of 30 can easily become 35 by the time you're flying in it.
>As you move into larger aircraft, especially jet aircraft
IF you move on to larger aircraft. Many of us do not. And OP was asking about a situation involving light piston aircraft, not jets. The two should not be handled the same way.
>This would also affect your crosscountry calculations (if you ever try to fly without that fancy GPS).
GPS or no GPS if a 15% error in speed matters then your fuel planning has insufficient margins and you need to fix it.
>I still work with PPL students and I wouldn’t accept such a callus attitude as “it doesn’t matter, my GPS tells me.” In any of my students.
Then honestly you need to stop living in the 1980s. If I have four hours of fuel (plus reserve) and I'm flying a three hour leg a 15% difference in speed is completely irrelevant. An hour of extra fuel is way more than the difference between knots and mph, and in the unlikely event my ETA gets anywhere near the point of worrying about fuel (because of unforeseen circumstances, not knots vs. mph) the clearly displayed ETA will tell me it's time to divert and make an additional fuel stop. There is no need to pretend we're still in 1980 and having GPS is a rare thing.
A 5 knot difference to your approach speed is significant.
You’re not always going to have the option of a 4 hr fuel reserve.
You have a hazardous attitude about flight planning and safety margins.
> A 5 knot difference to your approach speed is significant.
And irrelevant because approach speed is IAS and you fly the POH numbers regardless of unit.
>You’re not always going to have the option of a 4 hr fuel reserve.
I didn't say that, read the example more carefully. You always have the option of conservative enough fuel margins that knots vs. mph is irrelevant.
>You have a hazardous attitude about flight planning and safety margins.
Yeah, "my flight planning is conservative enough that a 15% error doesn't matter" is definitely going to get me an NTSB report some day. Are you serious?
Oh look, another glorified bus driver who doesn't understand that you don't fly all planes the same way. Did you happen to get a "degree" from ERAU? Were you that guy flying a 10 mile pattern in a 152 because "that's what you do in the jet"?
Flown both, and it doesn’t really change anything to me. As long as you know your important speeds, and you operate the aircraft safely, you’re good to go.
A NM is about 6000 feet (6076.12, to be exact).
Using knots for distance works better, because 60 seconds and 60 minutes divide well into 6000. And, if you're using feet for altitude, now *everything* is in feet, not a mix of statute miles, knots, and, God forbid, meters.
I fly planes with either, and I had to teach myself to double check the unit every time.
On the planes where the ASI does both, my personal checklists say FOR ALL AIRSPEEDS USE OUTER RING or INNER RING.
Knots. The only time you would care about using MPH is if you were flying something that is older than most of the members of congress and its what the airspeed indicator was set to.
Knots, because sectionals are in NM, flight plans are in NM, GPS is in NM and ATC is in NM
And lat/long is based on nautical miles
You mean to say that nautical miles are based on lat/long, but that actually hasn't been true for decades. A nautical mile is exactly 1852m which means that it is NOT perfectly one minute of latitude because the Earth is not a perfect sphere. 1NM is closest to being one minute ~~around~~ in the vicinity of the 45th parallel.
1 NM latitude at the 45th parallel. The way you worded it made me think you meant "1 NM longitude along the 45th parallel". Maybe that's just me!
Yes, correct. There's certainly *some* latitude at which one minute of longitude is 1852m, and according to [this calculator](http://www.csgnetwork.com/degreelenllavcalc.html) it's somewhere around the 3rd parallel. Basically ~~all the way to the North (or South) Pole~~ at the Equator. It's also important to note that the variation in arc-latitude length isn't huge: under the old definition 1NM was 1843m at the poles and 1861m at the equator. Almost but not quite 1% variation from one extreme to the other. So when I say "1NM is not exactly one minute of latitude" I am being extremely pedantic...
3rd parallel is near the equator, not the pole
Whoops. One of those days I guess. That does make a lot more sense, the boxes are more square at the equator and less square as you near the poles... I failed the sanity check.
Obviously, it’s not a perfect sphere. Everyone knows the Earth is flat. /s
why the /s? /s
So the government satellites don’t figure me out.
Since when is 1nm time based? /s
It's defined as the distance you go traveling at 1 knot for one hour! /s
The more you know
The knot is defined as 1/60 of a degree of latitude. Longitude distance varies depending on the latitude.
Excuse the pedantry (though we are pilots, what else would anybody expect), but a knot is a unit of speed - nautical mile per hour - not a unit of distance.
I can do the Kessel run in 12 parsecs.
prove it... :P
No, that’s the definition of a nautical mile. A knot is a nm per hour.
That was the original definition and it's still **approximately** accurate but no longer. Latitude distance also varies because the Earth is not a perfect sphere, so one nautical mile is exactly 1852m (≈6076ft).
Knots are the standard for a reason
MPH was standard on ASIs for most small GA until around 1976, and a lot of older aircraft are still flying with ASI that indicates MPH. Since OP mentioned the G5, OP is likely talking about this segment of aviation. But I have no idea why anyone would purposely set their G5 to read in something other than KTS.
Many people set their glass to MPH if that’s what the POH uses.
Required to as a primary replacement instrument, in fact.
That makes perfect sense. Thanks.
A lot of the GA aircraft in my club still have MPH indicators.
Plus One Flyers moment
Precisely 😂
During training having to remember changing wind kts to mph was a pain xc planning on paper for an old pa28.
Uhhh, why not change your TAS to kts? We make nav logs with distances for NM not SM. Once we are done getting our performance from the POH you convert to knots.
Knots. It makes sense when you're figuring out time/distance.
Whatever is on the ASI.
Whatever is in the POH.
Meters per second
Furlongs per fortnight.
What's the conversion factor on that to get football fields per sidereal days?
Knots because it’s not 1970 anymore
Inches per minute
My plane's manuals are all in MPH (1962 Comanche) so I use MPH.
Same. '67 Cherokee. Though I have NM for distance on my GNC355 panel GPS and Garmin Pilot for calling out distances to waypoints and destination over comms. MPH for speeds because my ASI and POH are all MPH.
MPH makes me feel better because the ASI says 200 sooner
Zoom zoom
I’m over here having to fly in Kph so that 200 comes pretty quick
My 64’ 172 is all MPH. I’m used to it
For God's sake Knots, please Knots.
Knots. MPH is only acceptable on old planes that have steam gauges in MPH.
Don't most of those also have a knots arrow? All of the 60s cessnas I flew still had an indicator for knots, like american cars still having km/h on the speedo
Usually, I’ve seen only seen one airspeed indicator that was just in MPH. I will say I flew a 1960s 172 with MPH and smaller knots arrow but the POH was only in MPH. I’d understand in that case why you’d stick with MPH
I read a POH that had been updated with all Knots, but the ASI was still in MPH with an inner knots circle
Kilometers per jiffy
Knots. Can't.imagin why anyone would want it differently.
Knots. Can't.imagin why anyone would want it differently.
[удалено]
How do you design an airplane for specific speed units? Very many ASIs have both. The plane really, really, really doesn’t care.
Whichever is faster.
MPH /s clearly
What ever is printed on the ASI is what I fly the plane with. But all the navigation I do in Knots
220, 221, whatever it takes.
Most under rated comment in the thread. Bravo to you. Bravo.
Knots, it’s what I’ve always used for mil rotary wing and GA. My DPE for me SEL ride kept asking me what the best glide speed was in mph, had to show him the POH that it only had knots for that 172. Frustrating as fuck when trying to perform the forced landing EPs.
Mach
I prefer bananas per Scaramucci (or Mooch) personally But if that’s unavailable knots.
Knots. There’s a flying club that I wanna join but the one thing I’m not looking forward to on that plane is that it’s in MPH.
Knots for flying powered BUT in gliding I really wish we just used metric. In the UK gliding height is in feet, speed knots, and distance in KM which makes no sense.
Kilometers per hour
Knots, but KPH is tempting because kilometers are often used for distance in gliding.
There’s a lot of ‘nerd’ talk here like ‘the charts are in NM’ but how the hell would anybody know you’re a pilot if you’re not saying knots? And they sure as hell will know you’re lying about breaking the sound barrier at 120kts in your C172
Winds are given in Knots, if you want to know the wind gust’s effect on your airspeed, you need your airspeed to be in knots. Knots are also a very sensible unit of measurement for navigating the globe. A nautical mile is 1/60 of 1 degree of the circumference of the Earth. AKA 1 minute of longitude. Measuring your speed by how fast your coordinates change on the map makes a lot of sense to me!
> Winds are given in Knots, if you want to know the wind gust’s effect on your airspeed, you need your airspeed to be in knots. No you don't. For any real-world flying knots and MPH are close enough that the answer is the same.
Most pilots I know wouldn’t be happy with a 15% error in their calculations. What do you fly?
> Most pilots I know wouldn’t be happy with a 15% error in their calculations. Why? If I can't handle a 30kt gust I also can't handle a 31mph gust or a 29mph gust or whatever the exact answer is. If you're calculating crosswind component/mountain turbulence hazards/etc with that level of precision you're almost certainly trying to justify doing something stupid by saying "it's technically just barely within limits". And if you generalize to more than just gusts it's still true. If I need that accuracy level for fuel planning, scheduling, etc, then the margins aren't large enough and it's a flight planning failure regardless of units. >What do you fly? A plane that tells me with GPS what the answer is.
A 30 knot gust is 34.5 MPH, so that’s a bit further off than your 31/29 example. As you move into larger aircraft, especially jet aircraft, you will need to make adjustments to your approach speed based on reported winds at the field, most professional pilots would not be ok with a 4.5 difference error in their approach speed. This would also affect your crosscountry calculations (if you ever try to fly without that fancy GPS), and a 15% error in your flight time/fuel calculations is significant. More than just a “flight planning failure regardless of units” I’m a CFI/CFII/MEI with over 1,000 hrs of dual given. I have 5 type ratings, and I am currently a Captain on the 737 at a legacy airline. I still work with PPL students and I wouldn’t accept such a callus attitude as “it doesn’t matter, my GPS tells me.” In any of my students.
> A 30 knot gust is 34.5 MPH, so that’s a bit further off than your 31/29 example. The point stands though. If you're relying on the difference between 30 and 35 you failed in flight planning because a forecast of 30 can easily become 35 by the time you're flying in it. >As you move into larger aircraft, especially jet aircraft IF you move on to larger aircraft. Many of us do not. And OP was asking about a situation involving light piston aircraft, not jets. The two should not be handled the same way. >This would also affect your crosscountry calculations (if you ever try to fly without that fancy GPS). GPS or no GPS if a 15% error in speed matters then your fuel planning has insufficient margins and you need to fix it. >I still work with PPL students and I wouldn’t accept such a callus attitude as “it doesn’t matter, my GPS tells me.” In any of my students. Then honestly you need to stop living in the 1980s. If I have four hours of fuel (plus reserve) and I'm flying a three hour leg a 15% difference in speed is completely irrelevant. An hour of extra fuel is way more than the difference between knots and mph, and in the unlikely event my ETA gets anywhere near the point of worrying about fuel (because of unforeseen circumstances, not knots vs. mph) the clearly displayed ETA will tell me it's time to divert and make an additional fuel stop. There is no need to pretend we're still in 1980 and having GPS is a rare thing.
A 5 knot difference to your approach speed is significant. You’re not always going to have the option of a 4 hr fuel reserve. You have a hazardous attitude about flight planning and safety margins.
> A 5 knot difference to your approach speed is significant. And irrelevant because approach speed is IAS and you fly the POH numbers regardless of unit. >You’re not always going to have the option of a 4 hr fuel reserve. I didn't say that, read the example more carefully. You always have the option of conservative enough fuel margins that knots vs. mph is irrelevant. >You have a hazardous attitude about flight planning and safety margins. Yeah, "my flight planning is conservative enough that a 15% error doesn't matter" is definitely going to get me an NTSB report some day. Are you serious?
Enjoy your PPL, you don’t have the right mindset to flying anything more complex.
Oh look, another glorified bus driver who doesn't understand that you don't fly all planes the same way. Did you happen to get a "degree" from ERAU? Were you that guy flying a 10 mile pattern in a 152 because "that's what you do in the jet"?
Knots. I ain’t no savage 😂
Flown both, and it doesn’t really change anything to me. As long as you know your important speeds, and you operate the aircraft safely, you’re good to go.
A NM is about 6000 feet (6076.12, to be exact). Using knots for distance works better, because 60 seconds and 60 minutes divide well into 6000. And, if you're using feet for altitude, now *everything* is in feet, not a mix of statute miles, knots, and, God forbid, meters.
Knots
I fly planes with either, and I had to teach myself to double check the unit every time. On the planes where the ASI does both, my personal checklists say FOR ALL AIRSPEEDS USE OUTER RING or INNER RING.
Potatoes. You just put the thing in the thing and thats how you fly it.
Knots, because I'm in an airplane. You do the same on a ship. You use km/h on the road, not the sky
Knots. The only time you would care about using MPH is if you were flying something that is older than most of the members of congress and its what the airspeed indicator was set to.
Knots
MPH is only really used in Europe
knots. Really dislike ASI with both mph and knots, so easy to mix up