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KTS or SMPH?

Hartstoc

Well Known Member
I?ve been flying for almost 40 years but have never gotten completely comfortable with the prospect of mentally jumping back and forth between knots and miles per hour. My preference has been to configure everthing in my homebuilts in statute miles per hour. Intrinsically simpler, direct crossover from driving, ego boost of bigger numbers, and so on.

Now I?m installing an all-Garmin IFR panel in my 7A- 10? G3X Touch, G5 backup, GTN 750, 507 autopilot with Garmin servos, GTX345, GNS245 panel mount, and assorted remote devices. I plan on regaining currency of my long held but little used IFR rating and getting very comfortable with all the precision GPS proceedures coming available.

With this fresh start, I have to decide between configuring this whole package in KTS or MPH. Any thoughts or opinions from seasoned IFR RV flyers out there would be appreciated. I appreciate that ATC speaks KTS, so pretty much anticipate a lot of sentiment toward that choice, but still curious what others have to say. Thanks in advance- Otis
 
Real airplanes use knots.

Which is more useful, one minute of latitude (nautical mile) or a thousand paces of the average Roman soldier (later defined by queen Mary)?
 
On my RV-3B project, I'm trying to keep as much as possible common with my C180. Besides manual flaps and the flap speed, I'm using mph, to match. So for that reason alone I'm using that unit.

Besides, knots are nautical miles per hour, and these things ain't boats.

Dave
 
Real airplanes use knots.

Which is more useful, one minute of latitude (nautical mile) or a thousand paces of the average Roman soldier (later defined by queen Mary)?
Hmmmm, given this concept, what is more useful?

1 Kilometer = 1000 meters
1 Meter = one/ten-millionth of the distance from the equator to the north pole along a meridian through Paris, France
OR
1 Mile = 5280 feet
1 Foot = the average size of that above mentioned Roman soldier's foot!
 
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I?ve been flying for almost 40 years but have never gotten completely comfortable with the prospect of mentally jumping back and forth between knots and miles per hour. My preference has been to configure everthing in my homebuilts in statute miles per hour. Intrinsically simpler, direct crossover from driving, ego boost of bigger numbers, and so on.

Thanks in advance- Otis

Yep, for those of us who started flying back in the dark ages, and never went beyond the basic private ticket, MPH is pretty common.

The new S 21 will be in MPH
 
I started flying in MPH, then transitioned to KTS when I got my instrument ticket. After 20+ years thinking in knots, it's become second nature. A plane marked solely in MPH is a VFR-only bird for me.
 
Real airplanes use knots.

Which is more useful, one minute of latitude (nautical mile) or a thousand paces of the average Roman soldier (later defined by queen Mary)?
Neither?

Having said that, I use knots in the airplane. I do rough conversions for passengers if needed, otherwise I don't worry about it. If I need the exact numbers for some reason or other, it's easy enough to do the math even if I don't have a calculator handy (which is really, really rare).
 
Actually, in the days of sectionals (remember those?), the latitude minute ticks could be used as a reference for nautical miles.
 
Cant comment on the utility in the IFR environment, but with an integrated glass package you are installing, most of the mental gymnatics are done for you. Once all the time/speed/distance stuff is displayed for you, constantly updated, then the origin of a speed display is reduced to a simple unit of measure. If you are looking for "XX" on approach, do you really care if its Knots, MPH, or meters per second as long as the value is appropriate for your airplane?

I flew for a long time with Statute numbers but made the switch to knots when I started flying glass. No trouble at all making the switch.
 
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My RV-8 has an EFIS set for MPH and had an MPH steam gauge airspeed indicator, and the Garmin 496 was set in knots.

So I had to decide to normalize to one scale. I selected knots because of sectionals.

So I replaced the ASI with a knotmeter. I'm calibrating that and when I'm done I'll change the EFIS to knots.
 
I fly from the left seat and Ann flies from the right. The EFIS and instruments on the left side are set up in knots and GPS and instruments on the right side are set up in mph. Her side goes faster, but has farther to go. So we usually get there about the same time.

When talking with pilots, I use knots. When talking with non-pilots I talk in mph, because 200 mph sounds much faster than 175 knots.

Now my plans are to add a machmeter to the Cub.
 
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Given that my iPad will be bluetoothing airspeed, attitude, wass gps, etc, off G3X, it is a simple matter to display TAS in mph in one corner to satisfy my ego(I just love seeing the number 200 in cruise!) I guess the writing is on the wall- all the Garmin goddies in KTS.

Someone remind me why visibility is expressed in statute miles?
 
Someone remind me why visibility is expressed in statute miles?

The government agencies that produce aviation weather reports actually have many other users besides aviators, and statute miles serve best for the user community as a whole. For the same reason, wind directions are reported as true rather than magnetic.
 
I appreciate that ATC speaks KTS, so pretty much anticipate a lot of sentiment toward that choice,
I think you answered your own question. Aviation pretty much is standarized on KTS.

If you are looking for "XX" on approach, do you really care if its Knots, MPH, or meters per second as long as the value is appropriate for your airplane?

Exactly, which units you use are not as important is being consistent and using the correct values.

When talking with pilots, I use kts. When talking with non-pilots I talk in mph,
Same here. When you are talking to pilots (and ATC or anyone else in aviation) you want/need to be accurate. When talking to non-pilots you can afford to use a very quick conversion in your head as they do not use the number for anything but comparison with their car. If i want to do mental math I would rather do it for someone that it matters little then the guy that needs the data to provide me real inputs.
 
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The government agencies that produce aviation weather reports actually have many other users besides aviators, and statute miles serve best for the user community as a whole. For the same reason, wind directions are reported as true rather than magnetic.

I believe that vis is reported in miles as it used to be based upon human observations of a known feature/structure and all recorded distances, other than sectionals and marine charts are in feet or miles (pre-GPS days). The tower would have identified landmarks at 1 mile, 2 miles, etc. and vis was established based upon the furthest one they could see.

Before the electronic sensors became available, Vis was reported only by aviation stations (very specific to the terminal area) and not really used by or offered to other consumers. Visibility at an airport is of no use to a mariner, as it is often quite different where the land meets the sea. Their vis data came from light houses and harbors, albeit less precise.

Larry
 
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When talking with pilots, I use kts. When talking with non-pilots I talk in mph, because 200 mph sounds much faster than 175 kts.

In Australia for aviation we use kts. Otherwise we use the metric system so when talking with non-pilots I use km/h because 324 km/h sounds much faster than 175 kts.

Fin.
9A
 
Some trivia points, since all the salient points have already been covered:
* The appropriate abbreviation is KT, not KTS;
* One definition of a foot according to wiki is the average length of 16 left feet of men coming out of church, and I seem to recall it also being the average to 12 men, but I didn't find the reference;
* A pace in the Roman army was the distance from one foot leaving the ground to it touching the ground again, about five feet. Mille was the Roman word for thousand, so a thousand paces was about a mile. Our word mile then came from mille...
* Glider pilots think in knots. One knot vertically is pretty close to 100 feet per minute (6076 feet per hour is one knot), so doing everything in knots makes glide ratios easy to compute.

Somebody obviously has too much time on his hands and trivia in his head...
 
Real pilots use nautical (Knot). 20 years ago I argued for SM, but somewhere along the way found that NM works out better for everything aeronautiocal. BTW, if you give Real pilots your cruise speed in SM, they will just chuckle. :D
 
For a REAL ego boost, give furlongs per fortnight a try. 1 statute mph = 2,688 fpf.

On cross country flying, I seem to pay more attention to ETE than to speed in either set of units. Time is one set of units the whole world pretty much seems to agree on (even though there?s absolutely nothing ?metric? when converting between seconds, minutes, hours, etc. ;)) Along that same line I tend to interpret fuel gauge readings in hours instead of gallons. It?s a pretty simple matter to compare ETE on the GPS to hours of fuel remaining.
 
KTS

With all the Electronics we have in our planes today why not use both Kt and MPH?I set up my EFIS in MPH for true airspeed readings and because I have Vansaircraft numbers in my head and Vans used MPH.Set up my GPS in Knots because controllers use knots and its handy to have both.On my boat there is no reason not to use knots.
Bob
 
KIAS.... ATC speaks in knots, not MPH.

+1 What ever yields the least confusion. Kt works for the "system" . :D


I just hate the mixed units though. Like an ASOS report; C, kts, statute visibility. If it changes, do it all at once, don't suddenly sneak C in there for F.

Cars (thanks Jimmy) have mixed fasteners, metric and SAE. You don't know what you will find. At least with airplanes it is ALL SAE, oh, except for the nasty metric threads on the starter. Arrg.

At least we don't have Whitworth mixed in there too. :eek:
 
Personal Preference

Well since we build/own experimental aircrafts, I would say it's a personal preference since this could be a never ending debate. I personally use KTS, even when I flew an older C310 that I had miles per hour, I always crossed checked my Garmin 496 that I set up for knots to check my ground speed. However, now I'm exactly opposite... I have my primary instruments set up in KTS and have a back up GPS in Miles for ground speed :D . It comes down to what you are comfortable with correct? Heck, why not in Mach?
 
I've flown Certificated airplanes that have had mph only airspeed indicators and its fine for VFR only, but I wouldn't much care for it in an IFR environment.

ATC speaks Knots
Approach plate times are based on groundspeed in Knots.
Longitude tic marks are in Knots.
Even the flight plan form has you reference your airspeed in Knots.

Obviously you can do whatever you want, but it seems to me that trying to get an IFR airplane to speak MPH causes a lot of conversion hassles needlessly.
 
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I go forth and back on this.

My analog ASI is marked with MPH on the outer ring and KTS in the inner ring.

It's the standby ASI. My D-100 is the PFD.

I set up the D-100 for MPH so that if it fails I don't have to convert or look at the inner ring. Heck, if it fails I've got other things to focus on, right?

I do like that 190 MPH sounds more impressive than 165 KTS to the non-aviation (what's a knot?) types. :)
 
Use the units you're most comfortable with and have an intuitive feel for. If you know all your key airspeeds and other performance parameters in "mph" and "SM", then its safer to stick with that system.

Neither system is "better" than the other.
 
Remember Hubble?

How about instead of using what you're comfortable with, using what everyone else has agreed is the standard?

I'm from Europe, so I'm comfortable with metric, but I live in the US now, so I use miles, Fahrenheit and fractions of an inch. That way, I'm speaking the same language as the people I work with.

Just because you're comfortable with mph when driving your car, doesn't make it OK to use mph in an environment where the standard and internationally agreed measure is knots.

The only time it's OK to use mph is if you don't have a radio in your plane :p
 
I've flown Certificated airplanes that have had mph only airspeed indicators and its fine for VFR only, but I wouldn't much care for it in an IFR environment.

.....

Then the certified planes you flew are now considered antiques and are so old they qualify for less registration fees in AZ....:)

IIRC the FAA requirements for certified planes standardized on Knots in 1977.
 
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Then the certified planes you flew are now considered antiques and are so old they qualify for less registration fees in AZ....:)

IIRC the FAA requirements for certified planes standardized on Knots in 1977.


Up until Cessna started building new singles in the late 90's, pretty much everything I'd ever flown would fall into that category!
 
ATC

It does not matter to me flying the airplane if it reads MPH or KTS.

Everytime I talk to Air Traffic Control, they are talking in KTS so I like new airplanes to have everything displayed in KTS so that I do not need to convert in my head for ATC. I do not like a few second pause to convert from MPH to KTS in my head to tell ATC. Talking to friends on the ground, it does not bother me to take a few seconds to convert in my head to MPH for them to understand.
 
By happy coincidence:

1nm is approx 6000'
1 radian is approx 60 degrees
There are 60 seconds in a minute and 60 minutes in an hour

This makes so many mental calculations easy if you use KT. For instance, the required RoD for a 3 degree slope is 5 times your GS in KT.....

As for being "used to" speeds in mph, it's just a number. It's going to be different in your Cub as against your Lancair. Just fly the numbers......
 
With all the Electronics we have in our planes today why not use both Kt and MPH?I set up my EFIS in MPH for true airspeed readings and because I have Vansaircraft numbers in my head and Vans used MPH.Set up my GPS in Knots because controllers use knots and its handy to have both.On my boat there is no reason not to use knots.
Bob

Van and other certified aircraft manufacturers have used MPH because it sounds faster and sells airplanes. Mooney even named one model the "201" since it boasted a cruse speed of 201 MPH. Sounds better than the Mooney 174.664. I echo Terry Shortt's comment:

ATC speaks Knots
Approach plate times are based on ground speed in Knots.
Longitude tic marks are in Knots.
Even the flight plan form has you reference your airspeed in Knots.


Of course, if you are a VFR pilot and never plan on talking to ATC (or me) then do whatever you please. It's your airplane.
 
Ultimately it makes the most sense to use what you are comfortable with. For me, making life easier in some ways by using knots makes it more comfortable. Also I just don't feel like a pilot unless it is in knots. I'm also a math teacher and like making my kids do the math when they ask how fast my plane is going to go. :D
 
I stick with knots for all the above reasons, plus...

Knots accommodate the 60-to-1 rule.
http://aviationknowledge.wikidot.com/aviation:60-to-1-rule

For simplicity sake, let one nautical mile equal 6000 feet (it doesn't, but close enough).

Take two lines (rays?) originating from a common point, but diverging by 1 degree.

At 60 nautical miles from the point of origin, those two lines are separated by 1 nautical mile, AKA 6000 feet, AKA 60 hundred feet.

Therefore, if the lines are 60 hundred feet apart at 60 miles, they are 1 hundred feet apart at one mile.

So what? Think aviation.

If the lines (rays?) diverge by 3 degrees, then they are 300 feet apart at one mile. Therefore, a 3 degree glideslope places the airplane 300' above the threshold for every nautical mile away from the ILS antenna. At 5 DME I should be at 1500' (300 x 5). BTW, the DME is in NM, so my speed is in knots.

If my standard rate turn radius is 1 nm (for simplicity), then 20 miles from the station I need to start my turn 3 degrees short of the target VOR radial to roll out on the radial. (1 degree at 20NM equals 20 hundred feet, so I need 3 degrees for a 60 hundred foot turn radius).

This certainly is not exact, but it sure works great for me: I can do that math.

This rule does not work for statute miles. 60 SM equals about 52.2 NM: Therefore, at 60 SM the two diverging lines (rays?) are about 5220 feet apart.

BTW, this sorta feels like the Fop vs Dapper Dan debate from 'Oh Brother Where Art Though'. They both work, for their particular users.
Me? I'm a Dapper Dan Man. (Note: That's 100 Nautical mL at the bottom of the can. :cool:)
hr_465-210-00_dapper-dan-deluxe-pomade_1.jpg
 
Excellent post there councillor -:)
It brings back memories (or nightmares) from eons ago, now mostly defunct knowledge. We only use Kts down under as it's more universal world wide at commercial level which I fly in as well as Pvt Ops -:) I still convert (1.85) to KPH for non aviators out there -:)
 
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