S

smbrown

Member
Wondering why Vans continues to use MPH instead of KTS in performance specifications? I get the Marketing angle (my 230mph airplane is faster than your 200kts airplane...) but other than that must be just legacy, or is there a reason? My 1964 Cherokee used mph but that was long before we knew better. Is it just me that finds it annoying to have to convert everything to kts for the outside world? flight planning for example.

And now for the other side... I also find it annoying when passenger asks how fast we're going and I have to convert kts to mph.

And if the above wasn't controversial enough... what's up with inches, pounds, slugs, etc when we have uniform metric system everywhere else in the world?? ;-)
 
Marketing.

But why do you care how they market? You make your aircraft use whatever unit make sense to you. MPH, KTS, Kilometers per second....

I use knots in my RV-4 and it flies fine.

I will say the ATC standard seems to be KTS but other than it doesn't matter whats used.
 
Why knots?

Be careful on your way to work - the speed limit goes to 36.9 knots on Main Street and the cops run radar.
 
I fly my -8 with knots, but my transition training was in MPH....that's just the way Van wants it....

My iPhone has an app called 'GPS Info!'. It displays Miles/hour, Meters/second, Kilometers/hour, and Knots. I keep it up during flight so no conversions needed when my passenger asks how fast we're going. :)
 
For Us Old Folks

My 1946 Taylorcraft (sold it after 18 years when my -6 was finished) used mph and I have been flying since the early 1970's when everything was in mph. I would bet Van's likes to use mph to keep us old timers in the loop.

Disclaimer: I do use knots occasionally when dealing with ATC.
 
Why Knots?

smbrown said:
. . . that was long before we knew better. . .
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Knew better about what?

Knots are for sea faring vessels! Throwing over a rope with a knot every 47'3" (current measurements use a different distance than this even) to measure how many knots pass by an 18" floating chip of wood in 30 seconds (current measurements use 28 seconds) is a doable practice on a ship. Why would this be a logical tool for measuring speed through the air in an aircraft though? Given the fact that all of the above measurements of KNOTS and NAUTICAL MILES has changed over time for various reasons and add on top of this the idea that nautical measurement of distance changes as you move away from the equator and one has to wonder with all of this variation; What exactly do we know better now than we did before we started using knots as a measurement of speed?

REFERENCES:
Nautical Mile

Knot

What is a Knot?

Google search for definition(s) of "Knot"
 
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The FAA standardized certified aircraft airspeed instruments to knots in the 1976 time frame.

It might actually be time to catch up...:)


If we changed to furlongs per hour (fph) we could make those advertising department speeds about eight times faster...:D
 
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Because the US wants to be different from the rest of the world in every unit it uses? ;)

Since 1nm is the distance subtended by one minute of longitude, it seems to make sense to use it for navigation in preference to some arbitary unit. Also the lucky co-incidence that 1nm is about 6000ft and 1 radian is about 60 degrees makes all sorts of useful calculations easy in your head. Surely you guys have heard of the 1:60 rule.......... :p
 
Guess I'm an old school pilot... been flying 44 yrs.... I was born and raised on mph... I hate knots... it's meaningless to me. Everything in the US is miles, not knots, why use it here? The only thing I use it for is to convert to mph!!
 
paul330 said:
Since 1nm is the distance subtended by one minute of longitude, it seems to make sense to use it for navigation in preference to some arbitary unit. Also the lucky co-incidence that 1nm is about 6000ft and 1 radian is about 60 degrees makes all sorts of useful calculations easy in your head. Surely you guys have heard of the 1:60 rule.......... :p
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Ah, but the truth is; that 1nm distance changes ever so slightly as you move away from the equator. So exactly how is it then that the use of KNOTS is not also an arbitrary measurement? Even your own explanation is using words such as "about" to define the 1nm distance. Is that not also contributing to an arbitrary calculation?
 
This kind of thread always makes it apparent those that fly and talk to ATC and those that don't.
 
Whatever.

I use MPH and started that way back in 1966.

Nowadays, just use what's needed...talking to approach or tower..knots...to my wife and friends...MPH:)

Easy,
 
pierre smith said:
I use MPH and started that way back in 1966.

Nowadays, just use what's needed...talking to approach or tower..knots...to my wife and friends...MPH:)

Easy,
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Since the units I have to use are completely arbitray, I only want to use one set - and since ATC uses knots, that's the one I use - very simple. No converting.

MPH? Yup, the numbers are bigger, so that's what guys selling airplanes and racing like to use.... I actually like to think that most pilots are smart enough not to be fooled by gimics like that...but hey, it's hard to resist a tool that is only $9.99 instead of $10, isn't it? ;)
 
RVbySDI said:
Ah, but the truth is; that 1nm distance changes ever so slightly as you move away from the equator.
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How about 1 nm x cosine (latitude). (Hopefully it is not a spherical trig relationship)

Why use MPH?

Answer: Because we are Americans!
 
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rv9av8tr said:
Huh?? I talk to ATC all the time... I never use knots and they never challenge it.
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However, when ATC asks you your airspeed, or asks you to maintain a specific airspeed, they definitely expect you to use knots. At the speeds we are operating in these aircraft, it is probably not a big problem for ATC. But if ATC asks you to maintain 300 KIAS and you maintain 300 MPH, they will probably note right away that you are quite a bit slower than the other aircraft they have maintaining 300 KIAS.
I started out back in the 60's with mph, too. But, when I started flying in the military and then professionally as a civilian, I learned that the world runs on knots. :)
 
Ironflight said:
I actually like to think that most pilots are smart enough not to be fooled by gimics like that...but hey, it's hard to resist a tool that is only $9.99 instead of $10, isn't it? ;)
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... or gas that's $3.999 instead of $4.000.:rolleyes:

On the speed units thing, I'll propose what I propose every time this subject cycles through the forums: furlongs per fortnight (eighths of a mile per two weeks). The conversion is 2688 fpf/mph, or 2337 fpf/knot. Marketing could have a field day with a 540,000 fpf airplane!
 
longranger said:
... or gas that's $3.999 instead of $4.000.:rolleyes:

i use mph. but what sets me off is the military channel on cable! they talk about OUR mustang or our B25 or any AMERICAN made airplane. with a speed of xxxkph and caryy xxx kilos whats wrong with 500 pmh and 2000#'s of bombs!!
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Calculations

I got my start in the Air Force as a Navigator, and am now a professional pilot. In Nav school, there were quite a few calculations that were much easier with Knots. 1 NM = 6000'. The 1:60 rule is the most common... You're 30 miles from the VOR and need to miss a cell by 10 miles. How far right do you tell the pilot to turn, etc. With today's new fangled GPS units, onboard radar, etc, most of these are not quite as necessary.

Flying around today, I still use 6000 feet per NM often. Turning final on a visual approach, your lead point to final is about 1% of your ground speed. How far is that on the ground?? If the runway is 6000 feet long, that's a mile; you can then visualize where to start the turn. Most of us do this in our head from experience though, and it usually works out.

The answer to the original question though is marketing. It's sexier to sell a 200 MPH airplane than a 174 knot airplane.

David
 
LIKE

longranger said:
... or gas that's $3.999 instead of $4.000.:rolleyes:

On the speed units thing, I'll propose what I propose every time this subject cycles through the forums: furlongs per fortnight (eighths of a mile per two weeks). The conversion is 2688 fpf/mph, or 2337 fpf/knot. Marketing could have a field day with a 540,000 fpf airplane!
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I've just come off Facebook and after reading this post, I was looking for the LIKE link!

I've worked as an engineer over 40 years, and the metric system has been promised but hasn't taken hold yet. Young engineers go through school and learn to think with the metric system but soon find we old-timers still think and talk the "old" system.

Great Post.
 
Marketing, I disagree.

Some of you have said its marketing because it sounds so much better to say 200mph then 170 something knots, I disagree. I watch Formula 1 on TV, they use kilometers per hour, that sounds even faster but it means nothing to me, the nice guys on Speed Channel even convert it to MPH for us in the U.S. witch now sounds slower but it means something to us, in the U.S. everyone understands what a mile is and what 55mph or 100mph or 200mph is. It?s MPH because that?s what everyone in the U.S. knows and that?s where Van?s aircraft is located.
 
I was standing beside Van once at OSH, someone asked him why he uses mph instead of knots. His reply was "I can't see a knot on the ground, but I can see a mile section line."
 
RV10Man said:
I was standing beside Van once at OSH, someone asked him why he uses mph instead of knots. His reply was "I can't see a knot on the ground, but I can see a mile section line."
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Yet an other reason that is not marketing and has nothing to do with how fast it sounds.
 
longranger said:
... or gas that's $3.999 instead of $4.000.:rolleyes:

On the speed units thing, I'll propose what I propose every time this subject cycles through the forums: furlongs per fortnight (eighths of a mile per two weeks). The conversion is 2688 fpf/mph, or 2337 fpf/knot. Marketing could have a field day with a 540,000 fpf airplane!
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Let's not forget to use slugs as a measure of mass, too. :)

Virtually every system we use has some arbitrary basis. The only that *isn't* arbitrary, but has some actual mathematical soundness to it, is radians.

Hours? Arbitrarily dividing the day into 24 of them, because of who knows why. Minutes and seconds? Arbitrary.

Statute miles? Arbitrary, AND not "American" in the first place, but rather defined by the British formally in the 1500s. And based on yards, which are again, arbitrary. I always laugh when someone says we use miles because it's "American".

Meters come the closest to being not entirely arbitrary, since 1m is equal to 1/10,000,000th of the distance from the pole to the equator at sea level (which is not level at all, thus introducing the concepts of the geoid, etc.).

And nautical miles? Well, maybe in olden days the legend of using a rope to measure "knots" was true (or not, no pun intended), but the actual measurement today is 1 nm = 1' arc of longitude at the equator, or 1' of arc of latitude.

Want some more arbitrary units? We've talked about these...pounds (force) per square inch. Rotations per minute. Degrees Fahrenheit (talk about a dumb system...make the scale *first*, then figure out where your reference points, the freezing and boiling points of water, are on the scale, thus giving you two completely oddball numbers). Degrees (of arc)...360 of them in a circle? Who came up with *that*, instead of using radians? Gallons (at least a liter is equal to 1,000 cubic centimeters of water, which, ta da, is the equal to 1 kilogram).

ETA: I nearly forgot my favorite (stupid) unit...inches of mercury as a measurement of pressure. LOL!

The list goes on... :)

ATC uses knots. That's why I use it.

Manufacturers use mph because a) it sounds faster, and b) in the 60s and 70s, they were trying to appeal to the automobile-buying public, by making planes "as easy as a car". In other words, marketing.
 
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Why not use both?

My -6 is set up to solo from either seat. I fly from the left and Ann flies from the right.
She has her side of the airplane set up in mph. My side of the airplane is set up in kts.
She goes faster than I do, but she has farther to go.
We generally get there about the same time.
(We both use hours and minutes for time!)
 
longranger said:
On the speed units thing, I'll propose what I propose every time this subject cycles through the forums: furlongs per fortnight (eighths of a mile per two weeks).
Click to expand...

Gents, we settled all this years ago. The official VAF Unit of Speed is the Mock. 100 MPH is Mock 1. All RV owners get to claim Mock 2 at beer call, unless they own an RV-12, or a slug with no fairings and the wrong propeller.
 
I'm sure glad the British still use mph. It makes watching Top Gear more enjoyable! :D

I use mph but knots is right there along side on my steam AS indicator. My GPS is in statute miles but my AP shows NM to waypoint and knots. All the planes that I've ever flown were in mph, so is my car, and the signs along the highway. My brain is just calibrated in mph, right or wrong.
 
YIKES!!!!

Man.....all the discussion in this thread is tying my brain up in knots:D Maybe we should rename the site "Knots Landing"....or maybe knot?:D How about talking about wood props...you may be able to get a couple more knots in the aircraft?:) I suppose I could continue....but DR may banish me from VAF! :(
 
aviation weather is still reported in Statute Miles visibility, winds in kts, approach minimum in SM, but DME in nm...so much for the STANDARD.

ATC may REQUEST an airspeed but they will never be able to verify it so it really doesn't matter as long as the net result occurs... separation from traffic. The don't know the winds, your pitot/static errors, your heading calibrations, etc..

MPH cause I can.
 
Quite entertaining

Flying Scotsman said:
SNIP Degrees Fahrenheit (talk about a dumb system...make the scale *first*, then figure out where your reference points, the freezing and boiling points of water, are on the scale, thus giving you two completely oddball numbers). SNIP
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You are correct, all units are arbitrary. However, for clarity, the Fahrenheit scale was set up with body temperature as 100 and ice/salt solution as 0. Obviously some errors on both ends (as with 0 and 100C), but many of us who drive in the northern areas in winter are aware that salt on the roadways is not effective when the road is below zero F.

Celsius simply picked two other points, one of which is very dependent on altitude (no doubt in furlongs...)!

Kilograms - good luck with that one. Kilogram force, kilogram mass, lots of sporting reading on those. Force in the SI system is truly only measured in Newtons - quick, how many Newtons do you exert on a scale (at least at one specific place on one specific planet)?
 
Like button pushed

Mel said:
My -6 is set up to solo from either seat. I fly from the left and Ann flies from the right.
She has her side of the airplane set up in mph. My side of the airplane is set up in kts.
She goes faster than I do, but she has farther to go.
We generally get there about the same time.
(We both use hours and minutes for time!)
Click to expand...

Best post so far.
 
AlexPeterson said:
You are correct, all units are arbitrary. However, for clarity, the Fahrenheit scale was set up with body temperature as 100 and ice/salt solution as 0. Obviously some errors on both ends (as with 0 and 100C), but many of us who drive in the northern areas in winter are aware that salt on the roadways is not effective when the road is below zero F.

Celsius simply picked two other points, one of which is very dependent on altitude (no doubt in furlongs...)!

Kilograms - good luck with that one. Kilogram force, kilogram mass, lots of sporting reading on those. Force in the SI system is truly only measured in Newtons - quick, how many Newtons do you exert on a scale (at least at one specific place on one specific planet)?
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Without looking it up, it's ~4.4 lbf/N so I weigh <redacted, too scary> N on earth.

I'm an engineer and I like to use English units (inches, psi (pressure and stress), seconds, lbf, lbm -or- slugs, depending) for design, stress analysis, and fluids stuff but SI units for dynamics problems (particle motion, projectiles, etc).
 
Dual indications

I have an A/S indicator that has both MPH & Knots, this way I can report my top speed in MPH while stating stall speed in Knots. Isn't this the best of both worlds? :D:D.
 
Yikes! I hadn't intended to start a units jihad... it was an honest (as in not knowing the answer or being a loaded) question. I guess I thought more of us were on the knots train... but perhaps NOT ;-)

It's knots for me, just like all physics problems are SI, then converted to local preference if needed, but then that's what got Mars orbiter in trouble... Now I know
 
nautical mile

I thought Napoleon developed the nautical mile so he could invade Russia and use the stars to determine distance. A lot of good that did him. He should have just told the troops, "its just another furlong, but don't freeze". Those Russians were smart and devastated his troops. JMHO
 
Top Gear UK uses MPH

If my buddies at Top Gear UK can use MPH, I feel safe doing the same. I loved the comment about the 1-60 rule being 1 in 60 pilots don't have an opinion about this or anything! (Using knots does make you sound more interesting)
 
If you're really interested in all this measurement stuff, pick up a copy of "Measuring America" by Andro Linklater, which explains a lot about various measurements and how/why they came to be used. Great read.

The original speeds reported for aircraft (in the US anyway) were in MPH, not knots.

Greg
 
It's simple. Van can use MPH if he wants to .. and it appears he does. That's it.

I use knots to non aviation types since it gives me a chance to educate.

I use MPH to the "certified aviation" type pilots and if they ague I ask them why a Mooney 231 is named as such.

I always use Knots with ATC .. Well just because you can't completely argue the man, it looks bad after awhile.
 
"all physics problems are SI"

Actually, most professional physicists dislike SI and prefer "rationalized Gaussian - cgs" units, for philosophical reasons having to do with electricity and magnetism. Sorry for the thread drift.
 
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